Radiance and polarization in the diffusion region with an arbitrary scattering phase matrix

NASA Astrophysics Data System (ADS)

Sun, Bingqiang; Kattawar, George W.; Yang, Ping

2016-11-01

Radiance and polarization patterns in an optically deep region, the so-called diffusion region or asymptotic region, of a homogeneous atmosphere or ocean, depend mainly on the scattering phase matrix and the single-scattering albedo of the medium. The radiance and polarization properties in the diffusion region for an arbitrary scattering phase matrix can be obtained in terms of a series of the generalized spherical functions. The number of terms is closely related to the single-scattering albedo of the medium. If the medium is conservative, the radiance is isotropic in conjunction with no polarization. If the single-scattering albedo is close to 1, several terms are sufficient to obtain the patterns, in which the degree of polarization feature is less than 1%. If the medium is highly absorptive, more expansion terms are required to obtain the diffusion patterns. The examples of simulated radiance and polarization patterns for Rayleigh scattering, Henyey-Greenstein-Rayleigh scattering, and haze L and cloud C1 scattering, defined by Deirmendjian, are calculated.

Temporal and spatial mapping of atmospheric dust opacity and surface albedo on Mars

NASA Technical Reports Server (NTRS)

Lee, S. W.; Clancy, R. T.; Gladstone, G. R.; Martin, T. Z.

1993-01-01

The Mariner 9 and Viking missions provided abundant evidence that eolian processes are active over much of the surface of Mars. Past studies have demonstrated that variations in regional albedo and wind streak patterns are indicative of sediment transport through a region, while thermal inertia data (derived from the Viking Infrared Thermal Mapper (IRTM) datasets) are indicative of the degree of surface mantling by dust deposits. We are making use of the method developed by T. Z. Martin to determine dust opacity from IRTM thermal observations. We have developed a radiative transfer model that allows corrections for the effects of atmospheric dust loading on observations of surface albedo to be made. This approach to determining 'dust-corrected surface albedo' incorporates the atmospheric dust opacity, the single-scattering albedo and particle phase function of atmospheric dust, the bidirectional reflectance of the surface, and accounts for variable lighting and viewing geometry.

Mars dust and cloud opacities and scattering properties

NASA Technical Reports Server (NTRS)

Clancy, R. T.; Lee, S. W.

1992-01-01

We have recently completed an analysis of the visible emission-phase function (EPF) sequences obtained with the solar-band channel of the Infrared Thermal Mapping (IRTM) instrument onboard the two Viking Orbiters. Roughly 100 of these EPF sequences were gathered during the 1977-1980 period, in which the total broadband (.3-3.0 microns) reflectances of the atmosphere/surface above specific locations on Mars were measured versus emission angle as the spacecraft passed overhead. A multiple scattering radiative transfer program was employed to model the EPF observations in terms of the optical depths of dust/clouds, their single scattering albedos and phase functions, and the Lambert albedos and phase coefficient of the underlying surfaces. Due to the predominance of atmospheric scattering at large atmospheric pathlengths and/or large dust opacities, we were able to obtain strong constraints on the scattering properties of dust/clouds and their opacities for a wide range of latitudes, longitudes, and seasons on Mars.

Solid hydrogen coated graphite particles in the interstellar medium. I.

NASA Technical Reports Server (NTRS)

Swamy, K. S. K.; Wickramasinghe, N. C.

1969-01-01

Solid para hydrogen coated graphite particles expulsion into interstellar medium from star formation regions, considering mantles stability and particles extinction efficiency, albedo and phase function

The surface brightness of reflection nebulae. Ph.D. Thesis, Dec. 1972

NASA Technical Reports Server (NTRS)

Rush, W. F.

1974-01-01

Hubble's equation relating the maximum apparent angular extent of a reflection nebula to the apparent magnitude of the illuminating star has been reconsidered under a set of less restrictive assumptions. A computational technique is developed which permits the use of fits to observed m, log a values to determine the albedo of the particles composing reflection nebulae, providing only that one assumes a particular phase function. Despite the fact that all orders of scattering, anisotropic phase functions, and illumination by the general stellar field are considered, the albedo which is determined for reflection nebulae by this method appears larger than that for interstellar particles in general. The possibility that the higher surface brightness might be due to a continuous fluorescence mechanism is considered both theoretically and observationally.

Phase-Angle Dependence of Determinations of Diameter, Albedo, and Taxonomy: A Case Study of NEO 3691 Bede

NASA Technical Reports Server (NTRS)

Wooden, Diane H.; Lederer, Susan M.; Jehin, Emmanuel; Howell, Ellen S.; Fernandez, Yan; Harker, David E.; Ryan, Erin; Lovell, Amy; Woodward, Charles E.; Benner, Lance A.

2015-01-01

Parameters important for NEO risk assessment and mitigation include Near-Earth Object diameter and taxonomic classification, which translates to surface composition. Diameters of NEOs are derived from the thermal fluxes measured by WISE, NEOWISE, Spitzer Warm Mission and ground-based telescopes including the IRTF and UKIRT. Diameter and its coupled parameters Albedo and IR beaming parameter (a proxy for thermal inertia and/or surface roughness) are dependent upon the phase angle, which is the Sun-target-observer angle. Orbit geometries of NEOs, however, typically provide for observations at phase angles greater than 20 degrees. At higher phase angles, the observed thermal emission is sampling both the day and night sides of the NEO. We compare thermal models for NEOs that exclude (NEATM) and include (NESTM) night-side emission. We present a case study of NEO 3691 Bede, which is a higher albedo object, X (Ec) or Cgh taxonomy, to highlight the range of H magnitudes for this object (depending on the albedo and phase function slope parameter G), and to examine at different phase angles the taxonomy and thermal model fits for this NEO. Observations of 3691 Bede include our observations with IRTF+SpeX and with the 10 micrometer UKIRT+Michelle instrument, as well as WISE and Spitzer Warm mission data. By examining 3691 Bede as a case study, we highlight the interplay between the derivation of basic physical parameters and observing geometry, and we discuss the uncertainties in H magnitude, taxonomy assignment amongst the X-class (P, M, E), and diameter determinations. Systematic dependencies in the derivation of basic characterization parameters of H-magnitude, diameter, albedo and taxonomy with observing geometry are important to understand. These basic characterization parameters affect the statistical assessments of the NEO population, which in turn, affects the assignment of statistically-assessed basic parameters to discovered but yet-to-be-fully-characterized NEOs.

Albedo of Carbon Dioxide Ice in Mars' Residual South Polar Cap

NASA Astrophysics Data System (ADS)

James, P. B.; Wolff, M. J.; Bonev, B.

2015-12-01

The albedo of surface CO2 deposits in the Residual South Polar Cap (RSPC) of Mars controls their net condensation / sublimation over a martian year and is therefore a crucial parameter in determining RSPC stability. The albedo used in previous analyses is obtained by dividing I/F, determined from radiometrically calibrated imaging data, by the cosine of the incidence angle. Because of atmospheric aerosols, the albedo calculated from I/F above the atmosphere is not the surface albedo that enters into stability considerations. In order to determine the surface albedo, we interpolate optical depths determined from CRISM EPF measurements to provide estimates of the dust and ice opacities over the RSPC (Wolff et al., 2009) and use these to determine the actual surface albedos from MARCI images using the radiative transport program DISORT (Stamnes et al., 1988). Assuming that dust is the only contributor to atmospheric opacity, the retrieved surface albedos for the longer wavelength MARCI filters in MY 28 and 29 are found to be consistent despite very different dust opacities in the two years (James et al., 2014). However, this model fails to reproduce the short wavelength behavior in early summer and suggests either an additional opacity source or modification of the CRISM dust opacity or the dust phase function. The consequences of these changes will be discussed.

Inferring heat recirculation and albedo for exoplanetary atmospheres: Comparing optical phase curves and secondary eclipse data

NASA Astrophysics Data System (ADS)

von Paris, P.; Gratier, P.; Bordé, P.; Selsis, F.

2016-03-01

Context. Basic atmospheric properties, such as albedo and heat redistribution between day- and nightsides, have been inferred for a number of planets using observations of secondary eclipses and thermal phase curves. Optical phase curves have not yet been used to constrain these atmospheric properties consistently. Aims: We model previously published phase curves of CoRoT-1b, TrES-2b, and HAT-P-7b, and infer albedos and recirculation efficiencies. These are then compared to previous estimates based on secondary eclipse data. Methods: We use a physically consistent model to construct optical phase curves. This model takes Lambertian reflection, thermal emission, ellipsoidal variations, and Doppler boosting, into account. Results: CoRoT-1b shows a non-negligible scattering albedo (0.11 < AS < 0.3 at 95% confidence) as well as small day-night temperature contrasts, which are indicative of moderate to high re-distribution of energy between dayside and nightside. These values are contrary to previous secondary eclipse and phase curve analyses. In the case of HAT-P-7b, model results suggest a relatively high scattering albedo (AS ≈ 0.3). This confirms previous phase curve analysis; however, it is in slight contradiction to values inferred from secondary eclipse data. For TrES-2b, both approaches yield very similar estimates of albedo and heat recirculation. Discrepancies between recirculation and albedo values as inferred from secondary eclipse and optical phase curve analyses might be interpreted as a hint that optical and IR observations probe different atmospheric layers, hence temperatures.

Interior radiances in optically deep absorbing media. 3: Scattering from Haze L

NASA Technical Reports Server (NTRS)

Kattawar, G. W.; Plass, G. N.

1974-01-01

The interior radiances are calculated within an optically deep absorbing medium scattering according to the Haze L phase function. The dependence on the solar zenith angle, the single scattering albedo, and the optical depth within the medium is calculated by the matrix operator method. The development of the asymptotic angular distribution of the radiance in the diffusion region is illustrated through a number of examples; it depends only on the single scattering albedo and on the phase function for single scattering. The exact values of the radiance in the diffusion region are compared with values calculated from the approximate equations proposed by Van de Hulst. The variation of the radiance near the lower boundary of an optically thick medium is illustrated with examples. The attenuation length is calculated for various single scattering albedos and compared with the corresponding values for Rayleigh scattering. The ratio of the upward to the downward flux is found to be remarkably constant within the medium. The heating rate is calculated and found to have a maximum value at an optical depth of two within a Haze L layer when the sun is at the zenith.

The Albedo of Kepler's Small Worlds

NASA Astrophysics Data System (ADS)

Jansen, Tiffany; Kipping, David

2018-01-01

The study of exoplanet phase curves has been established as a powerful tool for measuring the atmospheric properties of other worlds. To first order, phase curves have the same amplitude as occultations, yet far greater temporal baselines enabling substantial improvements in sensitivity. Even so, only a relatively small fraction of Kepler planets have detectable phase curves, leading to a population dominated by hot-Jupiters. One way to boost sensitivity further is to stack different planets of similar types together, giving rise to an average phase curve for a specific ensemble. In this work, we measure the average albedo, thermal redistribution efficiency, and greenhouse boosting factor from the average phase curves of 115 Neptunian and 50 Terran (solid) worlds. We construct ensemble phase curve models for both samples accounting for the reflection and thermal components and regress our models assuming a global albedo, redistribution factor and greenhouse factor in a Bayesian framework. We find modest evidence for a detected phase curve in the Neptunian sample, although the albedo and thermal properties are somewhat degenerate meaning we can only place an upper limit on the albedo of Ag < 0.23 and greenhouse factor of f < 1.40 to 95% confidence. As predicted theoretically, this confirms hot-Neptunes are darker than Neptune and Uranus. Additionally, we place a constraint on the albedo of solid, Terran worlds of Ag < 0.42 and f < 1.60 to 95% confidence, compatible with a dark Lunar-like surface.

Implications of the Small Spin Changes Measured for Large Jupiter-Family Comet Nuclei

NASA Astrophysics Data System (ADS)

Kokotanekova, R.; Snodgrass, C.; Lacerda, P.; Green, S. F.; Nikolov, P.; Bonev, T.

2018-06-01

Rotational spin-up due to outgassing of comet nuclei has been identified as a possible mechanism for considerable mass-loss and splitting. We report a search for spin changes for three large Jupiter-family comets (JFCs): 14P/Wolf, 143P/Kowal-Mrkos, and 162P/Siding Spring. None of the three comets has detectable period changes, and we set conservative upper limits of 4.2 (14P), 6.6 (143P) and 25 (162P) minutes per orbit. Comparing these results with all eight other JFCs with measured rotational changes, we deduce that none of the observed large JFCs experiences significant spin changes. This suggests that large comet nuclei are less likely to undergo rotationally-driven splitting, and therefore more likely to survive more perihelion passages than smaller nuclei. We find supporting evidence for this hypothesis in the cumulative size distributions of JFCs and dormant comets, as well as in recent numerical studies of cometary orbital dynamics. We added 143P to the sample of 13 other JFCs with known albedos and phase-function slopes. This sample shows a possible correlation of increasing phase-function slopes for larger geometric albedos. Partly based on findings from recent space missions to JFCs, we hypothesise that this correlation corresponds to an evolutionary trend for JFCs. We propose that newly activated JFCs have larger albedos and steeper phase functions, which gradually decrease due to sublimation-driven erosion. If confirmed, this could be used to analyse surface erosion from ground and to distinguish between dormant comets and asteroids.

Galileo Photometry of Asteroid 951 Gaspra

USGS Publications Warehouse

Helfenstein, P.; Veverka, J.; Thomas, P.C.; Simonelli, D.P.; Lee, P.; Klaasen, K.; Johnson, T.V.; Breneman, H.; Head, J.W.; Murchie, S.; Fanale, F.; Robinson, M.; Clark, B.; Granahan, J.; Garbeil, H.; McEwen, A.S.; Kirk, R.L.; Davies, M.; Neukum, G.; Mottola, S.; Wagner, R.; Belton, M.; Chapman, C.; Pilcher, C.

1994-01-01

Galileo images of Gaspra make it possible for the first time to determine a main-belt asteroid's photometric properties accurately by providing surface-resolved coverage over a wide range of incidence and emission angles and by extending the phase angle coverage to phases not observable from Earth. We combine Earth-based telescopic photometry over phase angles 2?? ??? ?? ??? 25?? with Galileo whole-disk and disk-resolved data at 33?? ??? ?? ??? 51?? to derive average global photometric properties in terms of Hapke's photometric model. The microscopic texture and particle phase-function behavior of Gaspra's surface are remarkably like those of other airless rocky bodies such as the Moon. The macroscopic surface roughness parameter, ??̄ = 29??, is slightly larger than that reported for typical lunar materials. The particle single scattering albedo, ??́0 = 0.36 ?? 0.07, is significantly larger than for lunar materials, and the opposition surge amplitude, B0 = 1.63 ?? 0.07, is correspondingly smaller. We determine a visual geometric albedo pv = 0.22 ?? 0.06 for Gaspra, in close agreement with pv = 0.22 ?? 0.03 estimated from Earth-based observations. Gaspra's phase integral is 0.47, and the bolometric Bond albedo is estimated to be 0.12 ?? 0.03. An albedo map derived by correcting Galileo images with our average global photometric function reveals subdued albedo contrasts of ??10% or less over Gaspra's northern hemisphere. Several independent classification algorithms confirm the subtle spectral heterogeneity reported earlier (S. Mottola, M. DiMartino, M. Gonano-Beurer, H. Hoffman, and G. Neukum, 1993, Asteroids, Comets, Meteors, pp. 421-424; M. J. S. Belton et al., 1992, Science 257, 1647-1652). Whole-disk colors (0.41 ??? ?? ??? 0.99 ??m) vary systematically with longitude by about ??5%, but color differences as large as 30% occur locally. Colors vary continuously between end-member materials whose areal distribution correlates with regional topography. Infrared: violet (0.99:0.41-??m) color ratios on Gaspra are strongly correlated with local elevation, being largest at lower elevations and smaller at higher elevations. No correlation was detected between elevation and the green:violet (0.56:0.41-??m) color ratio. Bright materials with a strong 1-??m absorption occur primarily in association with craters along ridges, while darker materials with 30% weaker 1-??m signatures occur downslope. The variations of color and albedo cannot be easily explained by grain-size effects alone or by differences in photometric geometry. The trends observed are consistent with those revealed by laboratory studies of the effects of comminution, glass formation, and segregation of metal from silicate components in chondritic meteorites and also in some silicate mixtures. The relative importance of these various processes on Gaspra remains to be determined. ?? 1994 Academic Press. All rights reserved.

Physical properties of Jupiter-family comets and KBOs from ground-based lightcurve observations

NASA Astrophysics Data System (ADS)

Kokotanekova, Rosita; Snodgrass, Colin; Lacerda, Pedro; Green, Simon F.

2017-10-01

Rotational lightcurves are among the most powerful tools to study the physical characteristics of small bodies in the Solar system. They can be used to constrain their spin rates, shapes, densities and compositions. We have developed a method to derive precise lightcurves and phase functions from sparsely sampled data, calibrated using Pan-STARRS stellar magnitudes. We employ this technique to characterize the physical properties of Jupiter Family Comets (JFCs) and Kuiper Belt Objects (KBOs).We provide an updated study of the collective properties of JFCs by increasing the sample of comets with well-studied rotational and surface characteristics. To collect the sample, we reviewed the properties of 35 previously-studied JFCs and added new lightcurves and phase functions for nine JFCs observed between 2004 and 2015.The new extended sample confirms the known cut-off in bulk density at ˜0.6 g cm-3 if JFCs are strengthless. For typical density and elongations, we determined that JFCs require tensile strength of 10-25 Pa to remain stable against rotational instabilities. To provide further constraints on the physical characteristics of JFCs we combine these findings with a study of the activity-induced spin changes of JFCs. Using the newly derived albedos and phase functions, we found that the median linear phase function coefficient for JFCs is 0.046 mag/deg and the median albedo is 4.2 per cent. We found evidence for an increasing linear phase function coefficient with increasing albedo.In an attempt to relate JFCs to their source populations, we compare them to KBOs. We performed a magnitude-limited survey of 40 KBOs, observed with the 3.6-m ESO New Technology Telescope between 2014 and 2017. This is the first survey with a 4m-class telescope conducted in an entirely homogeneous manner (using the same telescope, observing strategy, and data analysis). This program allows us to relate the rotation rates, physical properties and surface characteristics of JFCs and KBOs in order to test the different hypotheses for their formation and subsequent evolution.

The albedo, effective temperature, and energy balance of Uranus, as determined from Voyager IRIS data

NASA Technical Reports Server (NTRS)

Pearl, J. C.; Conrath, B. J.; Hanel, R. A.; Pirraglia, J. A.; Coustenis, A.

1990-01-01

The albedo, T(eff), and energy balance of Uranus are presently derived from Voyager IR Spectrometer and Radiometer data. By obtaining the absolute phase curve of Uranus, it has become possible to evaluate the Bond albedo without making separate determinations of the geometric albedo and phase integral. An orbital mean value for the bolometric Bond albedo of 0.3 + or - 0.049 yields an equilibrium temperature of 58.2 + or - 1.0 K. Thermal spectra from pole-to-pole latitude coverage establish a T(eff) of 59.1 + or - 0.3 K, leading to an energy balance of 1.06 + or - 0.08 for Uranus.

Apollo 11 and 16 Soil Bi-directional Solar Reflectance Measurements, Models and LRO Diviner Observations

NASA Astrophysics Data System (ADS)

Foote, E. J.; Paige, D. A.; Shepard, M. K.; Johnson, J. R.; Biggar, S. F.; Greenhagen, B. T.; Allen, C.

2010-12-01

We have compared laboratory solar reflectance measurements of Apollo 11 and 16 soil samples to Lunar Reconnaissance Orbiter (LRO) Diviner orbital albedo measurements at the Apollo landing sites. The soil samples are two representative end member samples from the moon, low albedo lunar maria (sample 10084) and high albedo lunar highlands (sample 68810). Bidirectional reflectance distribution function (BRDF) measurements of the soil samples were conducted at Bloomsburg University (BUG) and at the University of Arizona [1,2]. We collected two different types of BUG datasets: a standard set of BRDF measurements at incidence angles of 0-60°, emission angles of 0-80°, and phase angles of 3-140°, and a high-incidence angle set of measurements along and perpendicular to the principal plane at incidence angles of 0-75° and phase angles of 3-155°. The BUG measurements generated a total of 765 data points in four different filters 450, 550, 750 and 950 nm. The Blacklab measurements were acquired at incidence angles of 60-88°, emission angles 60-82°, and phase angles of 17-93° at wavelengths of 455, 554, 699, 949nm. The BUG data were fit to two BRDF models: Hapke’s model [3] as described by Johnson et al, 2010 [4], and a simplified empirical function. The fact that both approaches can satisfactorily fit the BUG data is not unexpected, given the similarities between the functions and their input parameters, and the fact that the BRDF for dark lunar soil is dominated by the single scattering phase functions of the individual soil particles. To compare our lunar sample measurements with LRO Diviner data [5], we selected all daytime observations acquired during the first year of operation within 3 km square boxes centered at the landing sites. We compared Diviner Channel 1 (0.3 - 3 µm) Lambert albedos with model calculated Lambert albedos of the lunar samples at the same photometric angles. In general, we found good agreement between the laboratory and Diviner measurements, particularly at intermediate incidence angles. We are currently reconciling any differences observed between our two datasets to provide mutual validation, and to better understand the Diviner solar reflectance measurements in terms of lunar regolith properties. [1] Shepard, M.K., Solar System Remote Sensing Symposium, #4004, LPI, 2002; [2] Biggar, S.F. et al, Proc. Soc. Photo-Opt. Instrum. Eng. 924:232-240, 1988; [3] Hapke, B. Theory of Reflectance and Emittance Spectroscopy, Cambridge University Press, 1993; [4] Johnson J.R. et al, Fall AGU 2010; [5] Paige, D.A. et al, Space Science Reviews, 150:125-160, 2010;

Process-model Simulations of Cloud Albedo Enhancement by Aerosols in the Arctic

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kravitz, Benjamin S.; Wang, Hailong; Rasch, Philip J.

2014-11-17

A cloud-resolving model is used to simulate the effectiveness of Arctic marine cloud brightening via injection of cloud condensation nuclei (CCN). An updated cloud microphysical scheme is employed, with prognostic CCN and cloud particle numbers in both liquid and mixed-phase marine low clouds. Injection of CCN into the marine boundary layer can delay the collapse of the boundary layer and increase low-cloud albedo. Because nearly all of the albedo effects are in the liquid phase due to the removal of ice water by snowfall when ice processes are involved, albedo increases are stronger for pure liquid clouds than mixed-phase clouds.more » Liquid precipitation can be suppressed by CCN injection, whereas ice precipitation (snow) is affected less; thus the effectiveness of brightening mixed-phase clouds is lower than for liquid-only clouds. CCN injection into a clean regime results in a greater albedo increase than injection into a polluted regime, consistent with current knowledge about aerosol-cloud interactions. Unlike previous studies investigating warm clouds, dynamical changes in circulation due to precipitation changes are small.« less

Asteroid (21) Lutetia: Disk-resolved photometric analysis of Baetica region

NASA Astrophysics Data System (ADS)

Hasselmann, P. H.; Barucci, M. A.; Fornasier, S.; Leyrat, C.; Carvano, J. M.; Lazzaro, D.; Sierks, H.

2016-03-01

(21) Lutetia has been visited by Rosetta mission on July 2010 and observed with a phase angle ranging from 0.15° to 156.8°. The Baetica region, located at the north pole has been extensively observed by OSIRIS cameras system. Baetica encompass a region called North Pole Crater Cluster (NPCC), shows a cluster of superposed craters which presents signs of variegation at the small phase angle images. For studying the location, we used 187 images distributed throughout 14 filter recorded by the NAC (Narrow Angle Camera) and WAC (Wide Angle Camera) of the OSIRIS system on-board Rosetta taken during the fly-by. Then, we photometrically modeled the region using Minnaert disk-function and Akimov phase function to obtain a resolved spectral slope map at phase angles of 5 ° and 20 ° . We observed a dichotomy between Gallicum and Danuvius-Sarnus Labes in the NPCC, but no significant phase reddening (- 0.04 ± 0.045 % μm-1deg-1). In the next step, we applied the Hapke (Hapke, B. [2008]. Icarus 195, 918-926; Hapke, B. [2012]. Theory of Reflectance and Emittance Spectroscopy, second ed. Cambridge University Press) model for the NAC F82+F22 (649.2 nm), WAC F13 (375 nm) and WAC F17 (631.6 nm) and we obtained normal albedo maps and Hapke parameter maps for NAC F82+F22. On Baetica, at 649.2 nm, the geometric albedo is 0.205 ± 0.005 , the average single-scattering albedo is 0.181 ± 0.005 , the average asymmetric factor is - 0.342 ± 0.003 , the average shadow-hiding opposition effect amplitude and width are 0.824 ± 0.002 and 0.040 ± 0.0007 , the average roughness slope is 11.45 ° ± 3 ° and the average porosity is 0.85 ± 0.002 . We are unable to confirm the presence of coherent-backscattering mechanism. In the NPCC, the normal albedo variegation among the craters walls reach 8% brighter for Gallicum Labes and 2% fainter for Danuvius Labes. The Hapke parameter maps also show a dichotomy at the opposition effect coefficients, single-scattering albedo and asymmetric factor, that may be attributed to the maturation degree of the regolith or to compositonal variation. In addition, we compared the Hapke (Hapke, B. [2008]. Icarus 195, 918-926; Hapke, B. [2012]. Theory of Reflectance and Emittance Spectroscopy, second ed. Cambridge University Press) and Hapke (Hapke, B. [1993]. Theory of Reflectance and Emittance Spectroscopy) parameters with laboratory samples and other small Solar System bodies visited by space missions.

The extreme ultraviolet albedos of the planet Mercury and of the moon

NASA Technical Reports Server (NTRS)

Wu, H. H.; Broadfoot, A. L.

1977-01-01

The albedo of the moon in the far UV was measured by Mariner 10 at a solar phase angle of 74 deg, and the geometric albedo of Mercury was measured in same wavelength range (584-1657 A) at solar phase angles ranging from 50 to 120 deg. For both the moon and Mercury there is a general increase in albedo for wavelengths decreasing from 1657 to 584 A. The ratio of the albedos of Mercury and the moon increases from about 0.6 to 0.8 in the range 600-1600 A. This merely points to a difference in the surfaces of the moon and Mercury, there being insufficient data to make any conclusions regarding the nature of the difference.

15-digit accuracy calculations of Ambartsumian-Chandrasekhar's H-functions for four-term phase functions with the double-exponential formula

NASA Astrophysics Data System (ADS)

Kawabata, Kiyoshi

2018-01-01

We have established an iterative scheme to calculate with 15-digit accuracy the numerical values of Ambartsumian-Chandrasekhar's H-functions for anisotropic scattering characterized by the four-term phase function: the method incorporates some advantageous features of the iterative procedure of Kawabata (Astrophys. Space Sci. 358:32, 2015) and the double-exponential integration formula (DE-formula) of Takahashi and Mori (Publ. Res. Inst. Math. Sci. Kyoto Univ. 9:721, 1974), which proved highly effective in Kawabata (Astrophys. Space Sci. 361:373, 2016). Actual calculations of the H-functions have been carried out employing 27 selected cases of the phase function, 56 values of the single scattering albedo π0, and 36 values of an angular variable μ(= cosθ), with θ being the zenith angle specifying the direction of incidence and/or emergence of radiation. Partial results obtained for conservative isotropic scattering, Rayleigh scattering, and anisotropic scattering due to a full four-term phase function are presented. They indicate that it is important to simultaneously verify accuracy of the numerical values of the H-functions for μ<0.05, the domain often neglected in tabulation. As a sample application of the isotropic scattering H-function, an attempt is made in Appendix to simulate by iteratively solving the Ambartsumian equation the values of the plane and spherical albedos of a semi-infinite, homogeneous atmosphere calculated by Rogovtsov and Borovik (J. Quant. Spectrosc. Radiat. Transf. 183:128, 2016), who employed their analytical representations for these quantities and the single-term and two-term Henyey-Greenstein phase functions of appreciably high degrees of anisotropy. While our results are in satisfactory agreement with theirs, our procedure is in need of a faster algorithm to routinely deal with problems involving highly anisotropic phase functions giving rise to near-conservative scattering.

Parameterization of single-scattering properties of snow

NASA Astrophysics Data System (ADS)

Räisänen, P.; Kokhanovsky, A.; Guyot, G.; Jourdan, O.; Nousiainen, T.

2015-02-01

Snow consists of non-spherical grains of various shapes and sizes. Still, in many radiative transfer applications, single-scattering properties of snow have been based on the assumption of spherical grains. More recently, second-generation Koch fractals have been employed. While they produce a relatively flat phase function typical of deformed non-spherical particles, this is still a rather ad-hoc choice. Here, angular scattering measurements for blowing snow conducted during the CLimate IMpacts of Short-Lived pollutants In the Polar region (CLIMSLIP) campaign at Ny Ålesund, Svalbard, are used to construct a reference phase function for snow. Based on this phase function, an optimized habit combination (OHC) consisting of severely rough (SR) droxtals, aggregates of SR plates and strongly distorted Koch fractals is selected. The single-scattering properties of snow are then computed for the OHC as a function of wavelength λ and snow grain volume-to-projected area equivalent radius rvp. Parameterization equations are developed for λ = 0.199-2.7 μm and rvp = 10-2000 μm, which express the single-scattering co-albedo β, the asymmetry parameter g and the phase function P11 as functions of the size parameter and the real and imaginary parts of the refractive index. The parameterizations are analytic and simple to use in radiative transfer models. Compared to the reference values computed for the OHC, the accuracy of the parameterization is very high for β and g. This is also true for the phase function parameterization, except for strongly absorbing cases (β > 0.3). Finally, we consider snow albedo and reflected radiances for the suggested snow optics parameterization, making comparisons to spheres and distorted Koch fractals.

Parameterization of single-scattering properties of snow

NASA Astrophysics Data System (ADS)

Räisänen, P.; Kokhanovsky, A.; Guyot, G.; Jourdan, O.; Nousiainen, T.

2015-06-01

Snow consists of non-spherical grains of various shapes and sizes. Still, in many radiative transfer applications, single-scattering properties of snow have been based on the assumption of spherical grains. More recently, second-generation Koch fractals have been employed. While they produce a relatively flat phase function typical of deformed non-spherical particles, this is still a rather ad hoc choice. Here, angular scattering measurements for blowing snow conducted during the CLimate IMpacts of Short-Lived pollutants In the Polar region (CLIMSLIP) campaign at Ny Ålesund, Svalbard, are used to construct a reference phase function for snow. Based on this phase function, an optimized habit combination (OHC) consisting of severely rough (SR) droxtals, aggregates of SR plates and strongly distorted Koch fractals is selected. The single-scattering properties of snow are then computed for the OHC as a function of wavelength λ and snow grain volume-to-projected area equivalent radius rvp. Parameterization equations are developed for λ = 0.199-2.7 μm and rvp = 10-2000 μm, which express the single-scattering co-albedo β, the asymmetry parameter g and the phase function P11 as functions of the size parameter and the real and imaginary parts of the refractive index. The parameterizations are analytic and simple to use in radiative transfer models. Compared to the reference values computed for the OHC, the accuracy of the parameterization is very high for β and g. This is also true for the phase function parameterization, except for strongly absorbing cases (β > 0.3). Finally, we consider snow albedo and reflected radiances for the suggested snow optics parameterization, making comparisons to spheres and distorted Koch fractals.

A photometric study of Enceladus

NASA Technical Reports Server (NTRS)

Verbiscer, Anne J.; Veverka, Joseph

1994-01-01

We have supplemented Voyager imaging data from Enceladus (limited to phase angles of 13 deg-43 deg) with recent Earth-based CCD observations to obtain an improved determination of the Bond albedo, to construct an albedo map of the satellite, and to constrain parameters in Hapke's (1986) photometric equation. A major result is evidence of regional variations in the physical properties of Enceladus' surface. The average global photometric properties are described by single scattering albedo omega(sub 0) average = 0.998 +/- 0.001, macroscopic roughness parameter theta average = 6 +/- 1 deg, and Henyey-Greenstein asymmetry parameter g = -0.399 +/- 0.005. The value of theta average is smaller than the 14 deg found by fitting whole-disk data, which include all terrains on Enceladus. The opposition surge amplitude B(sub 0) = 0.21 +/- 0.07 and regolith compaction parameter h = 0.014 +/- 0.02 are loosely constrained by the scarcity of and uncertainty in near-opposition observations. From the solar phase curve we determine the geometric albedo of Enceladus p(sub v) = 0.99 +/- 0.06 and phase integral q = 0.92 +/- 0.05, which corresponds to a spherical albedo A = p(sub v)q = 0.91 +/- 0.1. Since the spectrum of Enceladus is fairly flat, we can approximate the Bond albedo A(sub B) with the spherical albedo. Our photometric analysis is summarized in terms of an albedo map which generally reproduces the satellite's observed lightcurve and indicates that normal reflectances range from 0.9 on the leading hemisphere to 1.4 on the trailing one. The albedo map also revels an albedo variation of 15% from longitudes 170 deg to 200 deg, corresponding to the boundary between the leading and trailing hemispheres.

Complex refractive index of Martian dust - Wavelength dependence and composition

NASA Technical Reports Server (NTRS)

Pang, K.; Ajello, J. M.

1977-01-01

The size distribution and complex refractive index of Martian dust-cloud particles observed in 1971 with the Mariner 9 UV spectrometer are determined by matching the observed single-scattering albedo and phase function with Mie-scattering calculations for size distributions of spheres. Values of phase function times single-scattering albedo are presented for 12 wavelength intervals in the range from 190 to 350 nm, and best-fit values are obtained for the absorption index. It is found that the absorption index of the dust particles increases with decreasing wavelength from 350 to about 210 nm and then drops off shortward of 210 nm, with a structural shoulder occurring in the absorption spectrum between 240 and 250 nm. A search for a candidate material that can explain the strong UV absorption yields TiO2, whose anatase polymorph has an absorption spectrum matching that of the Martian dust. The TiO2 content of the dust particles is estimated to be a few percent or less.

Phase Offsets and the Energy Budgets of Hot Jupiters

NASA Astrophysics Data System (ADS)

Schwartz, Joel C.; Kashner, Zane; Jovmir, Diana; Cowan, Nicolas B.

2017-12-01

Thermal phase curves of short-period planets on circular orbits provide joint constraints on the fraction of incoming energy that is reflected (Bond albedo) and the fraction of absorbed energy radiated by the night hemisphere (heat recirculation efficiency). Many empirical studies of hot Jupiters have implicitly assumed that the dayside is the hottest hemisphere and the nightside is the coldest hemisphere. For a given eclipse depth and phase amplitude, an orbital lag between a planet’s peak brightness and its eclipse—a phase offset—implies that planet’s nightside emits greater flux. To quantify how phase offsets impact the energy budgets of short-period planets, we compile all infrared observations of the nine planets with multi-band eclipse depths and phase curves. Accounting for phase offsets shifts planets to lower Bond albedo and greater day-night heat transport, usually by ≲1σ. For WASP-12b, the published phase variations have been analyzed in two different ways, and the inferred energy budget depends sensitively on which analysis one adopts. Our fiducial scenario supports a Bond albedo of {0.27}-0.13+0.12, significantly higher than the published optical geometric albedo, and a recirculation efficiency of {0.03}-0.02+0.07, following the trend of larger day-night temperature contrast with greater stellar irradiation. If instead we adopt the alternative analysis, then WASP-12b has a Bond albedo consistent with zero and a much higher recirculation efficiency. To definitively determine the energy budget of WASP-12b, new observational analyses will be necessary.

Atmospheric Modeling of the Martian Polar Regions: One Mars Year of CRISM EPF Observations of the South Pole

NASA Astrophysics Data System (ADS)

Brown, A. J.; Wolff, M. J.

2009-03-01

We have used CRISM Emission Phase Function gimballed observations to investigate atmospheric dust/ice opacity and surface albedo in the south polar region for the first Mars year of MRO operations. This covers the MY28 "dust event" and cap recession.

EXOPLANET ALBEDO SPECTRA AND COLORS AS A FUNCTION OF PLANET PHASE, SEPARATION, AND METALLICITY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cahoy, Kerri L.; Marley, Mark S.; Fortney, Jonathan J., E-mail: kerri.l.cahoy@nasa.go

2010-11-20

First generation space-based optical coronagraphic telescopes will obtain images of cool gas- and ice-giant exoplanets around nearby stars. Exoplanets lying at planet-star separations larger than about 1 AU-where an exoplanet can be resolved from its parent star-have spectra that are dominated by reflected light to beyond 1 {mu}m and punctuated by molecular absorption features. Here, we consider how exoplanet albedo spectra and colors vary as a function of planet-star separation, metallicity, mass, and observed phase for Jupiter and Neptune analogs from 0.35 to 1 {mu}m. We model Jupiter analogs with 1x and 3x the solar abundance of heavy elements, andmore » Neptune analogs with 10x and 30x the solar abundance of heavy elements. Our model planets orbit a solar analog parent star at separations of 0.8 AU, 2 AU, 5 AU, and 10 AU. We use a radiative-convective model to compute temperature-pressure profiles. The giant exoplanets are found to be cloud-free at 0.8 AU, possess H{sub 2}O clouds at 2 AU, and have both NH{sub 3} and H{sub 2}O clouds at 5 AU and 10 AU. For each model planet we compute moderate resolution (R = {lambda}/{Delta}{lambda} {approx} 800) albedo spectra as a function of phase. We also consider low-resolution spectra and colors that are more consistent with the capabilities of early direct imaging capabilities. As expected, the presence and vertical structure of clouds strongly influence the albedo spectra since cloud particles not only affect optical depth but also have highly directional scattering properties. Observations at different phases also probe different volumes of atmosphere as the source-observer geometry changes. Because the images of the planets themselves will be unresolved, their phase will not necessarily be immediately obvious, and multiple observations will be needed to discriminate between the effects of planet-star separation, metallicity, and phase on the observed albedo spectra. We consider the range of these combined effects on spectra and colors. For example, we find that the spectral influence of clouds depends more on planet-star separation and hence atmospheric temperature than metallicity, and it is easier to discriminate between cloudy 1x and 3x Jupiters than between 10x and 30x Neptunes. In addition to alkalis and methane, our Jupiter models show H{sub 2}O absorption features near 0.94 {mu}m. While solar system giant planets are well separated by their broadband colors, we find that arbitrary giant exoplanets can have a large range of possible colors and that color alone cannot be relied upon to characterize planet types. We also predict that giant exoplanets receiving greater insolation than Jupiter will exhibit higher equator-to-pole temperature gradients than are found on Jupiter and thus may exhibit differing atmospheric dynamics. These results are useful for future interpretation of direct imaging exoplanet observations as well as for deriving requirements and designing filters for optical direct imaging instrumentation.« less

EFFECT OF LONGITUDE-DEPENDENT CLOUD COVERAGE ON EXOPLANET VISIBLE WAVELENGTH REFLECTED-LIGHT PHASE CURVES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Webber, Matthew W.; Lewis, Nikole K.; Cahoy, Kerri

2015-05-10

We use a planetary albedo model to investigate variations in visible wavelength phase curves of exoplanets. Thermal and cloud properties for these exoplanets are derived using one-dimensional radiative-convective and cloud simulations. The presence of clouds on these exoplanets significantly alters their planetary albedo spectra. We confirm that non-uniform cloud coverage on the dayside of tidally locked exoplanets will manifest as changes to the magnitude and shift of the phase curve. In this work, we first investigate a test case of our model using a Jupiter-like planet, at temperatures consistent to 2.0 AU insolation from a solar type star, to considermore » the effect of H{sub 2}O clouds. We then extend our application of the model to the exoplanet Kepler-7b and consider the effect of varying cloud species, sedimentation efficiency, particle size, and cloud altitude. We show that, depending on the observational filter, the largest possible shift of the phase curve maximum will be ∼2°–10° for a Jupiter-like planet, and up to ∼30° (∼0.08 in fractional orbital phase) for hot-Jupiter exoplanets at visible wavelengths as a function of dayside cloud distribution with a uniformly averaged thermal profile. The models presented in this work can be adapted for a variety of planetary cases at visible wavelengths to include variations in planet–star separation, gravity, metallicity, and source-observer geometry. Finally, we tailor our model for comparison with, and confirmation of, the recent optical phase-curve observations of Kepler-7b with the Kepler space telescope. The average planetary albedo can vary between 0.1 and 0.6 for the 1300 cloud scenarios that were compared to the observations. Many of these cases cannot produce a high enough albedo to match the observations. We observe that smaller particle size and increasing cloud altitude have a strong effect on increasing albedo. In particular, we show that a set of models where Kepler-7b has roughly half of its dayside covered in small-particle clouds high in the atmosphere, made of bright minerals like MgSiO{sub 3} and Mg{sub 2}SiO{sub 4,} provide the best fits to the observed offset and magnitude of the phase-curve, whereas Fe clouds are found to be too dark to fit the observations.« less

A FALSE POSITIVE FOR OCEAN GLINT ON EXOPLANETS: THE LATITUDE-ALBEDO EFFECT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cowan, Nicolas B.; Abbot, Dorian S.; Voigt, Aiko

2012-06-10

Identifying liquid water on the surface of planets is a high priority, as this traditionally defines habitability. One proposed signature of oceans is specular reflection ('glint'), which increases the apparent albedo of a planet at crescent phases. We post-process a global climate model of an Earth-like planet to simulate reflected light curves. Significantly, we obtain glint-like phase variations even though we do not include specular reflection in our model. This false positive is the product of two generic properties: (1) for modest obliquities, a planet's poles receive less orbit-averaged stellar flux than its equator, so the poles are more likelymore » to be covered in highly reflective snow and ice; and (2) we show that reflected light from a modest-obliquity planet at crescent phases probes higher latitudes than at gibbous phases, therefore a planet's apparent albedo will naturally increase at crescent phase. We suggest that this 'latitude-albedo effect' will operate even for large obliquities: in that case the equator receives less orbit-averaged flux than the poles, and the equator is preferentially sampled at crescent phase. Using rotational and orbital color variations to map the surfaces of directly imaged planets and estimate their obliquity will therefore be a necessary pre-condition for properly interpreting their reflected phase variations. The latitude-albedo effect is a particularly convincing glint false positive for zero-obliquity planets, and such worlds are not amenable to latitudinal mapping. This effect severely limits the utility of specular reflection for detecting oceans on exoplanets.« less

Sensitivity of aerosol optical depth, single scattering albedo, and phase function calculations to assumptions on physical and chemical properties of aerosol

EPA Science Inventory

In coupled chemistry-meteorology simulations, the calculation of aerosol optical properties is an important task for the inclusion of the aerosol effects on the atmospheric radiative budget. However, the calculation of these properties from an aerosol profile is not uniquely defi...

A radar survey of M- and X-class asteroids II. Summary and synthesis

NASA Astrophysics Data System (ADS)

Shepard, Michael K.; Clark, Beth Ellen; Ockert-Bell, Maureen; Nolan, Michael C.; Howell, Ellen S.; Magri, Christopher; Giorgini, Jon D.; Benner, Lance A. M.; Ostro, Steven J.; Harris, Alan W.; Warner, Brian D.; Stephens, Robert D.; Mueller, Michael

2010-07-01

Using the S-band radar at Arecibo Observatory, we observed six new M-class main-belt asteroids (MBAs), and re-observed one, bringing the total number of Tholen M-class asteroids observed with radar to 19. The mean radar albedo for all our targets is σ=0.28±0.13, significantly higher than the mean radar albedo of every other class (Magri, C., Nolan, M.C., Ostro, S.J., Giorgini, J.D. [2007]. Icarus 186, 126-151). Seven of these objects (Asteroids 16 Psyche, 129 Antigone, 216 Kleopatra, 347 Pariana, 758 Mancunia, 779 Nina, 785 Zwetana) have radar albedos indicative of a very high metal content (meanσ=0.41±0.13), and consistent with a remnant iron/nickel core interpretation (irons) or exotic high metal meteorite types such as CB. We propose designating these high radar albedo objects as Mm. Two asteroids, 110 Lydia and 678 Fredegundis, have more moderate radar albedos (meanσ=0.22), but exhibit high values (σ˜0.35) at some rotation phases suggesting a significant metal content. The remaining 10 objects have moderate radar albedos (σ=0.20±0.06) at all rotation phases. Most of our targets have visible/near-infrared spectra (Hardersen, P.S., Gaffey, M.J., Abell, P.A. [2005]. Icarus 175, 141-158; Fornasier, S., Clark, B.E., Dotto, E., Migliorini, A., Ockert-Bell, M., Barucci, M.A. [2009]. Icarus, submitted for publication) that indicate the presence of at least some silicate phases. All of the non-Mm asteroids show a positive correlation between visual and radar albedo but the reasons for this are not clear. All of the higher radar albedo targets (the 7 Mm asteroids, Lydia, and Fredegundis) show moderate to large variations in radar albedo with rotation phase. We suggest that their high radar reflectivity exaggerates irregularities in the asteroid shape to cause this behavior. One-third of our targets show evidence for asteroid-scale concavities or bifurcation. Based on all the evidence available, we suggest that most Tholen M-class asteroids are not remnant iron cores or enstatite chondrites, but rather collisional composites of silicates and irons with compositions more analogous to stony-iron meteorites and high-iron carbonaceous chondrites.

Photometric analysis of Asteroid (21) Lutetia from Rosetta-OSIRIS images

NASA Astrophysics Data System (ADS)

Masoumzadeh, N.; Boehnhardt, H.; Li, Jian-Yang; Vincent, J.-B.

2015-09-01

We analyzed the photometric properties of Asteroid (21) Lutetia based on images captured by Rosetta during its flyby. We utilized the images recorded in the F17 filter (λ = 631.6 nm) of the Wide Angle Camera (WAC) and in the F82 & F22 filters (λ = 649.2 nm) of the Narrow Angle Camera (NAC) of the OSIRIS imaging system onboard the spacecraft. We present the results of Hapke and Minnaert modeling using disk-integrated and disk-resolved data derived from the surface of the asteroid. At 631.6 nm and 649.2 nm, the geometric albedo of Lutetia is 0.194 ± 0.002. The Bond albedo is 0.076 ± 0.002 at 649.2 nm, and 0.079 ± 0.002 at 631.6 nm. The roughness parameter is 28 ° ± 1 ° , the opposition surge parameters B0 and h are 1.79 ± 0.08 and 0.041 ± 0.003, respectively, and the asymmetry factor of the phase function is -0.28 ± 0.01. The single-scattering albedo is 0.226 ± 0.002 at 631.6 and 649.2 nm. The modeled Hapke parameters of Asteroid Lutetia are close to those of typical S-type asteroids. The Minnaert k parameter of Lutetia at opposition (0.526 ± 0.002) is comparable with other asteroids and comets. Albedo ratio images indicate no significant variation across the surface of Lutetia, apart from the so called NPCC region on Lutetia where a pronounced variation is seen at large phase angle. The small width of the albedo distribution of the surface (∼7% at half maximum) and the similarity between phase ratio maps derived from the measurements and from the modeling suggests that the light scattering property over the whole visible and illuminated surface of the asteroid is widely uniform. The comparison between the reflectance measurement of Lutetia and the available laboratory samples suggests that the regolith on Lutetia is concrete with possible grain size distribution of150 μm or larger.

The Bidirectional Reflectance Distribution Function and Albedo Analysis for Various Land-Cover Types in the Midwestern United States for the Tempo Satellite

NASA Astrophysics Data System (ADS)

Marshall, Bethany

The Tropospheric Emissions: Monitoring of Pollution (TEMPO) satellite, scheduled to be launched around the year 2020, is the first phase of NASA's next generation of missions that will study the composition of the Earth's atmosphere. TEMPO provides a new set of high-resolution ( 0.4 nm) spectral data in the ultraviolet and visible portion of the electromagnetic spectrum that can be used to measure atmospheric pollutants. Due to its high spectral resolution and hourly temporal resolution covering entire North America, TEMPO data can also be used along with the calculation of spectral indices using the bidirectional reflection distribution functions (BRDF) or albedo to improve crop growth and yield monitoring for regional food security. The objectives of this thesis research were to 1) characterize BRDF/albedo of various land-cover types in Midwestern United States that can be used to remove land surface competent from at-sensor TEMPO radiances for accurate estimation of atmospheric chemistry and 2) evaluation of TEMPO data for regional agro-ecosystem studies. To this end, we: (1) collected 461 upwelling and downwelling solar irradiances and spectral albedo of various land-cover types (e.g., grapevine, maize, soybean, tomato, rock, asphalt road and concrete pave way, clean and turbid waters) at 110 sites in the States of Missouri, Illinois, Indiana, and Colorado using a PSR-3500 hand-held Spectroradiometer; (2) conducted a field and manned aircraft data collection campaign in Maryland Heights, Missouri using the Geo-TASO flight instrument flown onboard the NASA HU-25C Falcon aircraft on August 13, 2014; and (3) utilized Ross-Li Kernel BRDF model and MODTRAN radiative transfer simulations to characterize BRDF/albedo of various land-cover types. TEMPO retrieval of atmospheric gases must account for the effects of surface BRDF/albedo. Since BRDF is an inherent optical properties of surface, this research will contribute to the TEMPO mission by providing high-resolution spectral BRDF/albedo database, which may also promote the use of the TEMPO data for agricultural and ecosystem monitoring.

Matrix operator theory of radiative transfer. 2: scattering from maritime haze.

PubMed

Kattawar, G W; Plass, G N; Catchings, F E

1973-05-01

Matrix operator theory is used to calculate the reflected and transmitted radiance of photons that have interacted with plane-parallel maritime haze layers. The results are presented for three solar zenith angles, three values of the surface albedo, and a range of optical thicknesses from very thin to very thick. The diffuse flux at the lower boundary and the cloud albedo are tabulated. The forward peak and other features in the single scattered phase function cause the radiance in many cases to be very different from that for Rayleigh scattering. In particular the variation of the radiance with both the zenith or nadir angle and the azimuthal angle is more marked and the relative limb darkening under very thick layers is greater for haze M than for Rayleigh scattering. The downward diffuse flux at the lower boundary for A = 0 is always greater and the cloud albedo is always less for haze M than for Rayleigh layers.

Triton's surface properties - A preliminary analysis from ground-based, Voyager photopolarimeter subsystem, and laboratory measurements

NASA Technical Reports Server (NTRS)

Buratti, B. J.; Lane, A. L.; Gibson, J.; Burrows, H.; Nelson, R. M.; Bliss, D.; Smythe, W.; Garkanian, V.; Wallis, B.

1991-01-01

The surface properties of Triton were investigated using data from the ground-based and Voyager photopolarimeter subsystem (PPS) observations of Triton's phase curve. The results indicate that Triton has a high single-scattering albedo (0.96 +/-0.01 at 0.75 micron) and an unusually compacted surface, possibly similar to that of Europa. Results also suggest that Triton's single-particle phase function and the macroscopically rough character of its surface are similar to those of most other icy satellites.

Large quasi-circular features beneath frost on Triton

NASA Technical Reports Server (NTRS)

Helfenstein, Paul; Veverka, Joseph; Mccarthy, Derek; Lee, Pascal; Hillier, John

1992-01-01

Specially processed Voyager 2 images of Neptune's largest moon, Triton, reveal three large quasi-circular features ranging in diameter from 280 to 935 km within Triton's equatorial region. The largest of these features contains a central irregularly shaped area of comparatively low albedo about 380 km in diameter, surrounded by crudely concentric annuli of higher albedo materials. None of the features exhibit significant topographic expression, and all appear to be primarily albedo markings. The features are located within a broad equatorial band of anomalously transparent frost that renders them nearly invisible at the large phase angles (alpha greater than 90 deg) at which Voyager obtained its highest resolution coverage of Triton. The features can be discerned at smaller phase angles (alpha = 66 deg) at which the frost only partially masks underlying albedo contrasts. The origin of the features is uncertain but may have involved regional cryovolcanic activity.

On Spectral Invariance of Single Scattering Albedo for Water Droplets and Ice Crystals at Weakly Absorbing Wavelengths

NASA Technical Reports Server (NTRS)

Marshak, Alexander; Knyazikhin, Yuri; Chiu, J. Christine; Wiscombe, Warren J.

2012-01-01

The single scattering albedo omega(sub O lambda) in atmospheric radiative transfer is the ratio of the scattering coefficient to the extinction coefficient. For cloud water droplets both the scattering and absorption coefficients, thus the single scattering albedo, are functions of wavelength lambda and droplet size r. This note shows that for water droplets at weakly absorbing wavelengths, the ratio omega(sub O lambda)(r)/omega(sub O lambda)(r (sub O)) of two single scattering albedo spectra is a linear function of omega(sub O lambda)(r). The slope and intercept of the linear function are wavelength independent and sum to unity. This relationship allows for a representation of any single scattering albedo spectrum omega(sub O lambda)(r) via one known spectrum omega(sub O lambda)(r (sub O)). We provide a simple physical explanation of the discovered relationship. Similar linear relationships were found for the single scattering albedo spectra of non-spherical ice crystals.

Asymptotic Solutions for Optical Properties of Large Particles with Strong Absorption

NASA Technical Reports Server (NTRS)

Yang, Ping; Gao, Bo-Cai; Baum, Bryan A.; Hu, Yong X.; Wiscombe, Warren J.; Mishchenko, Michael I.; Winker, Dave M.; Nasiri, Shaima L.; Einaudi, Franco (Technical Monitor)

2000-01-01

For scattering calculations involving nonspherical particles such as ice crystals, we show that the transverse wave condition is not applicable to the refracted electromagnetic wave in the context of geometric optics when absorption is involved. Either the TM wave condition (i.e., where the magnetic field of the refracted wave is transverse with respect to the wave direction) or the TE wave condition (i.e., where the electric field is transverse with respect to the propagating direction of the wave) may be assumed for the refracted wave in an absorbing medium to locally satisfy the electromagnetic boundary condition in the ray tracing calculation. The wave mode assumed for the refracted wave affects both the reflection and refraction coefficients. As a result, a nonunique solution for these coefficients is derived from the electromagnetic boundary condition. In this study we have identified the appropriate solution for the Fresnel reflection/refraction coefficients in light scattering calculation based on the ray tracing technique. We present the 3 x 2 refraction or transmission matrix that completely accounts for the inhomogeneity of the refracted wave in an absorbing medium. Using the Fresnel coefficients for an absorbing medium, we derive an asymptotic solution in an analytical format for the scattering properties of a general polyhedral particle. Numerical results are presented for hexagonal plates and columns with both preferred and random orientations. The asymptotic theory can produce reasonable accuracy in the phase function calculations in the infrared window region (wavelengths near 10 micron) if the particle size (in diameter) is on the order of 40 micron or larger. However, since strong absorption is assumed in the computation of the single-scattering albedo in the asymptotic theory, the single scattering albedo does not change with variation of the particle size. As a result, the asymptotic theory can lead to substantial errors in the computation of single-scattering albedo for small and moderate particle sizes. However, from comparison of the asymptotic results with the FDTD solution, it is expected that a convergence between the FDTD results and the asymptotic theory results can be reached when the particle size approaches 200 micron. We show that the phase function at side-scattering and backscattering angles is insensitive to particle shape if the random orientation condition is assumed. However, if preferred orientations are assumed for particles, the phase function has a strong dependence on scattering azimuthal angle. The single-scattering albedo also shows very strong dependence on the inclination angle of incident radiation with respect to the rotating axis for the preferred particle orientations.

Surface photometric properties and albedo changes in the central equatorial region of Mars

NASA Technical Reports Server (NTRS)

Strickland, Edwin L., III

1992-01-01

Comparison of the Viking Orbiter 2 Approach mosaic taken 11 Mars months later provides qualitative information on the photometric properties of the martian albedo features, and the distribution of dust and sand deposits responsible for the atmosphere near the northern summer solstice. The approach mosaic was taken at L (sub s) 106 degrees (early N. summer), phase angle 106 degrees; and airmasses varying from 4.6 at 30 degrees N to 3.3 near 10 degrees S. The apoapsis mosaic was taken in four sequences between L (sub s) 72 degrees and 76 degrees (late N. spring), near phase angles of 47 degrees, and at airmasses near 2.5. Systematic differences in the photometric decalibrations used to generate these mosaics may induce multiplicative errors of 5-10 percent of the observed albedos in comparisons of the mosaics, but they are probably nearer 3 percent of the albedos. In the study area (30 degrees N to 20 degrees S, 57 degrees E to 75 degrees W), scene-average approach Minnaert albedos were about 10 percent greater than apoapsis albedos and slightly less 'red'. The preferred explanation for the observed approach-apoapsis albedo difference is that both Arabia and Meridiani materials are smoother on millimeter and larger scales than other units in the study area. This is in good agreement with preliminary conclusions of Thorpe and (for dark intracrater Meridiani splotches) Regner et al. This is also consistent with reasonable models of these surfaces. 'Dark Blue' Meridiani surfaces are interpreted as consisting of sand dunes and sand sheets, which would be expected to have macroscopically smooth, nonshadowing surfaces. Viking Lander images of the surfaces at both landing sites show that smooth drift area's brightnesses are close to those of adjacent rough soil areas at low phase angles, but drifts become much brighter than rough soils when looking up-sun at high phase angles. Smooth patches of duricrust at both landing sites, interpreted by Strickland as eolian deposits (regardless of how they became salt enriched and cemented), also show this behavior.

Surface photometric properties and albedo changes in the central equatorial region of Mars

NASA Astrophysics Data System (ADS)

Strickland, Edwin L., III

1992-12-01

Comparison of the Viking Orbiter 2 Approach mosaic taken 11 Mars months later provides qualitative information on the photometric properties of the martian albedo features, and the distribution of dust and sand deposits responsible for the atmosphere near the northern summer solstice. The approach mosaic was taken at L s 106 degrees (early N. summer), phase angle 106 degrees; and airmasses varying from 4.6 at 30 degrees N to 3.3 near 10 degrees S. The apoapsis mosaic was taken in four sequences between L s 72 degrees and 76 degrees (late N. spring), near phase angles of 47 degrees, and at airmasses near 2.5. Systematic differences in the photometric decalibrations used to generate these mosaics may induce multiplicative errors of 5-10 percent of the observed albedos in comparisons of the mosaics, but they are probably nearer 3 percent of the albedos. In the study area (30 degrees N to 20 degrees S, 57 degrees E to 75 degrees W), scene-average approach Minnaert albedos were about 10 percent greater than apoapsis albedos and slightly less 'red'. The preferred explanation for the observed approach-apoapsis albedo difference is that both Arabia and Meridiani materials are smoother on millimeter and larger scales than other units in the study area. This is in good agreement with preliminary conclusions of Thorpe and (for dark intracrater Meridiani splotches) Regner et al. This is also consistent with reasonable models of these surfaces. 'Dark Blue' Meridiani surfaces are interpreted as consisting of sand dunes and sand sheets, which would be expected to have macroscopically smooth, nonshadowing surfaces. Viking Lander images of the surfaces at both landing sites show that smooth drift area's brightnesses are close to those of adjacent rough soil areas at low phase angles, but drifts become much brighter than rough soils when looking up-sun at high phase angles. Smooth patches of duricrust at both landing sites, interpreted by Strickland as eolian deposits (regardless of how they became salt enriched and cemented), also show this behavior.

REFLECTED LIGHT CURVES, SPHERICAL AND BOND ALBEDOS OF JUPITER- AND SATURN-LIKE EXOPLANETS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dyudina, Ulyana; Kopparla, Pushkar; Ingersoll, Andrew P.

Reflected light curves observed for exoplanets indicate that a few of them host bright clouds. We estimate how the light curve and total stellar heating of a planet depends on forward and backward scattering in the clouds based on Pioneer and Cassini spacecraft images of Jupiter and Saturn. We fit analytical functions to the local reflected brightnesses of Jupiter and Saturn depending on the planet’s phase. These observations cover broadbands at 0.59–0.72 and 0.39–0.5 μ m, and narrowbands at 0.938 (atmospheric window), 0.889 (CH4 absorption band), and 0.24–0.28 μ m. We simulate the images of the planets with a ray-tracingmore » model, and disk-integrate them to produce the full-orbit light curves. For Jupiter, we also fit the modeled light curves to the observed full-disk brightness. We derive spherical albedos for Jupiter and Saturn, and for planets with Lambertian and Rayleigh-scattering atmospheres. Jupiter-like atmospheres can produce light curves that are a factor of two fainter at half-phase than the Lambertian planet, given the same geometric albedo at transit. The spherical albedo is typically lower than for a Lambertian planet by up to a factor of ∼1.5. The Lambertian assumption will underestimate the absorption of the stellar light and the equilibrium temperature of the planetary atmosphere. We also compare our light curves with the light curves of solid bodies: the moons Enceladus and Callisto. Their strong backscattering peak within a few degrees of opposition (secondary eclipse) can lead to an even stronger underestimate of the stellar heating.« less

Improving Estimated Optical Constants With MSTM and DDSCAT Modeling

NASA Astrophysics Data System (ADS)

Pitman, K. M.; Wolff, M. J.

2015-12-01

We present numerical experiments to determine quantitatively the effects of mineral particle clustering on Mars spacecraft spectral signatures and to improve upon the values of refractive indices (optical constants n, k) derived from Mars dust laboratory analog spectra such as those from RELAB and MRO CRISM libraries. Whereas spectral properties for Mars analog minerals and actual Mars soil are dominated by aggregates of particles smaller than the size of martian atmospheric dust, the analytic radiative transfer (RT) solutions used to interpret planetary surfaces assume that individual, well-separated particles dominate the spectral signature. Both in RT models and in the refractive index derivation methods that include analytic RT approximations, spheres are also over-used to represent nonspherical particles. Part of the motivation is that the integrated effect over randomly oriented particles on quantities such as single scattering albedo and phase function are relatively less than for single particles. However, we have seen in previous numerical experiments that when varying the shape and size of individual grains within a cluster, the phase function changes in both magnitude and slope, thus the "relatively less" effect is more significant than one might think. Here we examine the wavelength dependence of the forward scattering parameter with multisphere T-matrix (MSTM) and discrete dipole approximation (DDSCAT) codes that compute light scattering by layers of particles on planetary surfaces to see how albedo is affected and integrate our model results into refractive index calculations to remove uncertainties in approximations and parameters that can lower the accuracy of optical constants. By correcting the single scattering albedo and phase function terms in the refractive index determinations, our data will help to improve the understanding of Mars in identifying, mapping the distributions, and quantifying abundances for these minerals and will address long-standing questions on fundamental physics in the martian surface (e.g., what is the fundamental scattering unit for closely packed dust or regolith grains?). This work was supported by NASA's Mars Fundamental Research Program and performed with the Pleiades cluster courtesy of NASA's Advanced Supercomputing Division.

Titan: Preliminary results on surface properties and photometry from VIMS observations of the early flybys

USGS Publications Warehouse

Buratti, B.J.; Sotin, Christophe; Brown, R.H.; Hicks, M.D.; Clark, R.N.; Mosher, J.A.; McCord, T.B.; Jaumann, R.; Baines, K.H.; Nicholson, P.D.; Momary, T.; Simonelli, D.P.; Sicardy, B.

2006-01-01

Cassini observations of the surface of Titan offer unprecedented views of its surface through atmospheric windows in the 1-5 ??m region. Images obtained in windows for which the haze opacity is low can be used to derive quantitative photometric parameters such as albedo and albedo distribution, and physical properties such as roughness and particle characteristics. Images from the early Titan flybys, particularly T0, Ta, and T5 have been analyzed to create albedo maps in the 2.01 and 2.73 ??m windows. We find the average normal reflectance at these two wavelengths to be 0.15??0.02 and 0.035??0.003, respectively. Titan's surface is bifurcated into two albedo regimes, particularly at 2.01 ??m. Analysis of these two regimes to understand the physical character of the surface was accomplished with a macroscopic roughness model. We find that the two types of surface have substantially different roughness, with the low-albedo surface exhibiting mean slope angles of ???18??, and the high-albedo terrain having a much more substantial roughness with a mean slope angle of ???34??. A single-scattering phase function approximated by a one-term Henyey-Greenstein equation was also fit to each unit. Titan's surface is back-scattering (g???0.3-0.4), and does not exhibit substantially different backscattering behavior between the two terrains. Our results suggest that two distinct geophysical domains exist on Titan: a bright region cut by deep drainage channels and a relatively smooth surface. The two terrains are covered by a film or a coating of particles perhaps precipitated from the satellite's haze layer and transported by eolian processes. Our results are preliminary: more accurate values for the surface albedo and physical parameters will be derived as more data is gathered by the Cassini spacecraft and as a more complete radiative transfer model is developed from both Cassini orbiter and Huygens Lander measurements. ?? 2006 Elsevier Ltd. All rights reserved.

Modeling the bidirectional reflectance distribution function of mixed finite plant canopies and soil

NASA Technical Reports Server (NTRS)

Schluessel, G.; Dickinson, R. E.; Privette, J. L.; Emery, W. J.; Kokaly, R.

1994-01-01

An analytical model of the bidirectional reflectance for optically semi-infinite plant canopies has been extended to describe the reflectance of finite depth canopies contributions from the underlying soil. The model depends on 10 independent parameters describing vegetation and soil optical and structural properties. The model is inverted with a nonlinear minimization routine using directional reflectance data for lawn (leaf area index (LAI) is equal to 9.9), soybeans (LAI, 2.9) and simulated reflectance data (LAI, 1.0) from a numerical bidirectional reflectance distribution function (BRDF) model (Myneni et al., 1988). While the ten-parameter model results in relatively low rms differences for the BRDF, most of the retrieved parameters exhibit poor stability. The most stable parameter was the single-scattering albedo of the vegetation. Canopy albedo could be derived with an accuracy of less than 5% relative error in the visible and less than 1% in the near-infrared. Sensitivity were performed to determine which of the 10 parameters were most important and to assess the effects of Gaussian noise on the parameter retrievals. Out of the 10 parameters, three were identified which described most of the BRDF variability. At low LAI values the most influential parameters were the single-scattering albedos (both soil and vegetation) and LAI, while at higher LAI values (greater than 2.5) these shifted to the two scattering phase function parameters for vegetation and the single-scattering albedo of the vegetation. The three-parameter model, formed by fixing the seven least significant parameters, gave higher rms values but was less sensitive to noise in the BRDF than the full ten-parameter model. A full hemispherical reflectance data set for lawn was then interpolated to yield BRDF values corresponding to advanced very high resolution radiometer (AVHRR) scan geometries collected over a period of nine days. The resulting parameters and BRDFs are similar to those for the full sampling geometry, suggesting that the limited geometry of AVHRR measurements might be used to reliably retrieve BRDF and canopy albedo with this model.

Phase function, backscatter, extinction, and absorption for standard radiation atmosphere and El Chichon aerosol models at visible and near-infrared wavelengths

NASA Technical Reports Server (NTRS)

Whitlock, C. H.; Suttles, J. T.; Lecroy, S. R.

1985-01-01

Tabular values of phase function, Legendre polynominal coefficients, 180 deg backscatter, and extinction cross section are given for eight wavelengths in the atmospheric windows between 0.4 and 2.2 microns. Also included are single scattering albedo, asymmetry factor, and refractive indices. These values are based on Mie theory calculations for the standard rediation atmospheres (continental, maritime, urban, unperturbed stratospheric, volcanic, upper atmospheric, soot, oceanic, dust, and water-soluble) assest measured volcanic aerosols at several time intervals following the El Chichon eruption. Comparisons of extinction to 180 deg backscatter for different aerosol models are presented and related to lidar data.

Multiple scattered radiation emerging from continental haze layers. 1: Radiance, polarization, and neutral points

NASA Technical Reports Server (NTRS)

Kattawar, G. W.; Plass, G. N.; Hitzfelder, S. J.

1975-01-01

The complete radiation field is calculated for scattering layers of various optical thicknesses. Results obtained for Rayleigh and haze scattering are compared. Calculated radiances show differences as large as 23% compared to the approximate scalar theory of radiative transfer, while the same differences are approximately 0.1% for a continental haze phase function. The polarization of reflected and transmitted radiation is given for various optical thicknesses, solar zenith angles, and surface albedos. Two types of neutral points occur for aerosol phase functions. Rayleigh-like neutral points arise from zero polarization that occurs at scattering angles of 0 deg and 180 deg. For Rayleigh phase functions, the position of these points varies with the optical thickness of the scattering layer. Non-Rayleigh neutral points are associated with the zeros of polarization which occur between the end points of the single scattering curve, and are found over a wide range of azimuthal angles.

A new description of Titan's aerosol optical properties from the analysis of VIMS Emission Phase Function observations

NASA Astrophysics Data System (ADS)

Maltagliati, Luca; Rodriguez, Sebastien; Sotin, Christophe; Rannou, Pascal; Bezard, Bruno; Cornet, Thomas

2016-06-01

The Huygens probe gave unprecedented information on the properties of Titan's aerosols (vertical distribution, opacity as a function of wavelength, phase function, single scattering albedo) by in-situ measurements (Tomasko et al. 2008). Being the only existing in-situ atmospheric probing for Titan, this aerosol model currently is the reference for many Titan studies (e.g. by being applied as physical input in radiative transfer models of the atmosphere). Recently a reanalysis of the DISR dataset, corroborated by data from the Downward-Looking Visible Spectrometer (DLVS), was carried out by the same group (Doose et al. 2016), leading to significant changes to the indications given by Tomasko et al. (2008). Here we present the analysis of the Emission Phase Function observation (EPF) performed by VIMS during the Cassini flyby T88 (November 2012). An EPF observes the same spot on the surface (and thus the same atmosphere) with the same emergence angle but with different incidence angles. In this way, our EPF allows, for the first time, to have direct information on the phase function of Titan's aerosols, as well as on other important physical parameters of the aerosols as the behavior of their extinction as a function of wavelength and the single scattering albedo (also as a function of wavelength) for the whole VIMS range (0.8-5.2 µm). The T88 EPF is composed of 25 VIMS datacubes spanning a scattering angle range approximately from 0°to 70°. We used the radiative transfer model described in Hirtzig et al. (2013) as baseline, updated with improved methane (+ related isotopes) spectroscopy. By changing the aerosol description in the model, we found the combination of aerosol optical parameters that fits best a constant aerosol column density over the whole set of the VIMS datacubes. We confirmed that the new results from Doose et al. (2016) do improve the fit for what concerns the vertical profile and the extinction as a function of wavelength. However, a different phase function with respect to what they propose must be employed, especially in the trend towards the backscattering peak. We also find that darker aerosols are needed in order to reproduce the value of the column opacity measured in-situ by Huygens.

A new description of Titan's aerosol optical properties from the analysis of VIMS Emission Phase Function observations

NASA Astrophysics Data System (ADS)

Rodriguez, Sebastien; Maltagliati, Luca; Sotin, Christophe; Rannou, Pascal; Bézard, Bruno; Cornet, Thomas

2016-10-01

The Huygens probe gave unprecedented information on the properties of Titan's aerosols (vertical distribution, opacity as a function of wavelength, phase function, single scattering albedo) by in-situ measurements (Tomasko et al. 2008). Being the only existing in-situ atmospheric probing for Titan, this aerosol model currently is the reference for many Titan studies (e.g. by being applied as physical input in radiative transfer models of the atmosphere). Recently a reanalysis of the DISR dataset, corroborated by data from the Downward-Looking Visible Spectrometer (DLVS), was carried out by the same group (Doose et al. 2016), leading to significant changes to the indications given by Tomasko et al. (2008).Here we present the analysis of the Emission Phase Function observation (EPF) performed by VIMS during the Cassini flyby T88 (November 2012). An EPF observes the same spot on the surface (and thus the same atmosphere) with the same emergence angle but with different incidence angles. In this way, our EPF allows, for the first time, to have direct information on the phase function of Titan's aerosols, as well as on other important physical parameters of the aerosols as the behavior of their extinction as a function of wavelength and the single scattering albedo (also as a function of wavelength) for the whole VIMS range (0.8-5.2 μm). The T88 EPF is composed of 25 VIMS datacubes spanning a scattering angle range approximately from 0°to 70°.We used the radiative transfer model described in Hirtzig et al. (2013) as baseline, updated with improved methane (+ related isotopes) spectroscopy. By changing the aerosol description in the model, we found the combination of aerosol optical parameters that fits best a constant aerosol column density over the whole set of the VIMS datacubes. We confirmed that the new results from Doose et al. (2016) do improve the fit for what concerns the vertical profile and the extinction as a function of wavelength. However, a different phase function with respect to what they propose must be employed, especially in the trend towards the backscattering peak. We also find that darker aerosols are needed in order to reproduce the value of the column opacity measured in-situ by Huygens.

Assessing the measurement of aerosol single scattering albedo by Cavity Attenuated Phase-Shift Single Scattering Monitor (CAPS PMssa)

NASA Astrophysics Data System (ADS)

Perim de Faria, Julia; Bundke, Ulrich; Onasch, Timothy B.; Freedman, Andrew; Petzold, Andreas

2016-04-01

The necessity to quantify the direct impact of aerosol particles on climate forcing is already well known; assessing this impact requires continuous and systematic measurements of the aerosol optical properties. Two of the main parameters that need to be accurately measured are the aerosol optical depth and single scattering albedo (SSA, defined as the ratio of particulate scattering to extinction). The measurement of single scattering albedo commonly involves the measurement of two optical parameters, the scattering and the absorption coefficients. Although there are well established technologies to measure both of these parameters, the use of two separate instruments with different principles and uncertainties represents potential sources of significant errors and biases. Based on the recently developed cavity attenuated phase shift particle extinction monitor (CAPS PM_{ex) instrument, the CAPS PM_{ssa instrument combines the CAPS technology to measure particle extinction with an integrating sphere capable of simultaneously measuring the scattering coefficient of the same sample. The scattering channel is calibrated to the extinction channel, such that the accuracy of the single scattering albedo measurement is only a function of the accuracy of the extinction measurement and the nephelometer truncation losses. This gives the instrument an accurate and direct measurement of the single scattering albedo. In this study, we assess the measurements of both the extinction and scattering channels of the CAPS PM_{ssa through intercomparisons with Mie theory, as a fundamental comparison, and with proven technologies, such as integrating nephelometers and filter-based absorption monitors. For comparison, we use two nephelometers, a TSI 3563 and an Aurora 4000, and two measurements of the absorption coefficient, using a Particulate Soot Absorption Photometer (PSAP) and a Multi Angle Absorption Photometer (MAAP). We also assess the indirect absorption coefficient measurement from the CAPS PM_{ssa (calculated as the difference from the measured extinction and scattering). The study was carried out in the laboratory with controlled particle generation systems. We used both light absorbing aerosols (Regal 400R pigment black from Cabot Corp. and colloidal graphite - Aquadag - from Agar Scientific) and purely scattering aerosols (ammonium sulphate and polystyrene latex spheres), covering single scattering albedo values from approximately 0.4 to 1.0. A new truncation angle correction for the CAPS PM_{ssa integrated sphere is proposed.

Continuous versus discontinuous albedo representations in a simple diffusive climate model

NASA Astrophysics Data System (ADS)

Simmons, P. A.; Griffel, D. H.

1988-07-01

A one-dimensional annually and zonally averaged energy-balance model, with diffusive meridional heat transport and including icealbedo feedback, is considered. This type of model is found to be very sensitive to the form of albedo used. The solutions for a discontinuous step-function albedo are compared to those for a more realistic smoothly varying albedo. The smooth albedo gives a closer fit to present conditions, but the discontinuous form gives a better representation of climates in earlier epochs.

Use of Moderate-Resolution Imaging Spectroradiometer bidirectional reflectance distribution function products to enhance simulated surface albedos

NASA Astrophysics Data System (ADS)

Roesch, Andreas; Schaaf, Crystal; Gao, Feng

2004-06-01

Moderate-Resolution Imaging Spectroradiometer (MODIS) surface albedo at high spatial and spectral resolution is compared with other remotely sensed climatologies, ground-based data, and albedos simulated with the European Center/Hamburg 4 (ECHAM4) global climate model at T42 resolution. The study demonstrates the importance of MODIS data in assessing and improving albedo parameterizations in weather forecast and climate models. The remotely sensed PINKER surface albedo climatology follows the MODIS estimates fairly well in both the visible and near-infrared spectra, whereas ECHAM4 simulates high positive albedo biases over snow-covered boreal forests and the Himalayas. In contrast, the ECHAM4 albedo is probably too low over the Sahara sand desert and adjacent steppes. The study clearly indicates that neglecting albedo variations within T42 grid boxes leads to significant errors in the simulated regional climate and horizontal fluxes, mainly in mountainous and/or snow-covered regions. MODIS surface albedo at 0.05 resolution agrees quite well with in situ field measurements collected at Baseline Surface Radiation Network (BSRN) sites during snow-free periods, while significant positive biases are found under snow-covered conditions, mainly due to differences in the vegetation cover at the BSRN site (short grass) and the vegetation within the larger MODIS grid box. Black sky (direct beam) albedo from the MODIS bidirectional reflectance distribution function model captures the diurnal albedo cycle at BSRN sites with sufficient accuracy. The greatest negative biases are generally found when the Sun is low. A realistic approach for relating albedo and zenith angle has been proposed. Detailed evaluations have demonstrated that ignoring the zenith angle dependence may lead to significant errors in the surface energy balance.

Process-model simulations of cloud albedo enhancement by aerosols in the Arctic.

PubMed

Kravitz, Ben; Wang, Hailong; Rasch, Philip J; Morrison, Hugh; Solomon, Amy B

2014-12-28

A cloud-resolving model is used to simulate the effectiveness of Arctic marine cloud brightening via injection of cloud condensation nuclei (CCN), either through geoengineering or other increased sources of Arctic aerosols. An updated cloud microphysical scheme is employed, with prognostic CCN and cloud particle numbers in both liquid and mixed-phase marine low clouds. Injection of CCN into the marine boundary layer can delay the collapse of the boundary layer and increase low-cloud albedo. Albedo increases are stronger for pure liquid clouds than mixed-phase clouds. Liquid precipitation can be suppressed by CCN injection, whereas ice precipitation (snow) is affected less; thus, the effectiveness of brightening mixed-phase clouds is lower than for liquid-only clouds. CCN injection into a clean regime results in a greater albedo increase than injection into a polluted regime, consistent with current knowledge about aerosol-cloud interactions. Unlike previous studies investigating warm clouds, dynamical changes in circulation owing to precipitation changes are small. According to these results, which are dependent upon the representation of ice nucleation processes in the employed microphysical scheme, Arctic geoengineering is unlikely to be effective as the sole means of altering the global radiation budget but could have substantial local radiative effects. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

Process-model simulations of cloud albedo enhancement by aerosols in the Arctic

PubMed Central

Kravitz, Ben; Wang, Hailong; Rasch, Philip J.; Morrison, Hugh; Solomon, Amy B.

2014-01-01

A cloud-resolving model is used to simulate the effectiveness of Arctic marine cloud brightening via injection of cloud condensation nuclei (CCN), either through geoengineering or other increased sources of Arctic aerosols. An updated cloud microphysical scheme is employed, with prognostic CCN and cloud particle numbers in both liquid and mixed-phase marine low clouds. Injection of CCN into the marine boundary layer can delay the collapse of the boundary layer and increase low-cloud albedo. Albedo increases are stronger for pure liquid clouds than mixed-phase clouds. Liquid precipitation can be suppressed by CCN injection, whereas ice precipitation (snow) is affected less; thus, the effectiveness of brightening mixed-phase clouds is lower than for liquid-only clouds. CCN injection into a clean regime results in a greater albedo increase than injection into a polluted regime, consistent with current knowledge about aerosol–cloud interactions. Unlike previous studies investigating warm clouds, dynamical changes in circulation owing to precipitation changes are small. According to these results, which are dependent upon the representation of ice nucleation processes in the employed microphysical scheme, Arctic geoengineering is unlikely to be effective as the sole means of altering the global radiation budget but could have substantial local radiative effects. PMID:25404677

Precise calculations in simulations of the interaction of low energy neutrons with nano-dispersed media

NASA Astrophysics Data System (ADS)

Artem'ev, V. A.; Nezvanov, A. Yu.; Nesvizhevsky, V. V.

2016-01-01

We discuss properties of the interaction of slow neutrons with nano-dispersed media and their application for neutron reflectors. In order to increase the accuracy of model simulation of the interaction of neutrons with nanopowders, we perform precise quantum mechanical calculation of potential scattering of neutrons on single nanoparticles using the method of phase functions. We compare results of precise calculations with those performed within first Born approximation for nanodiamonds with the radius of 2-5 nm and for neutron energies 3 × 10-7-10-3 eV. Born approximation overestimates the probability of scattering to large angles, while the accuracy of evaluation of integral characteristics (cross sections, albedo) is acceptable. Using Monte-Carlo method, we calculate albedo of neutrons from different layers of piled up diamond nanopowder.

Significantly high polarization degree of the very low-albedo asteroid (152679) 1998 KU2

NASA Astrophysics Data System (ADS)

Kuroda, Daisuke; Ishiguro, Masateru; Watanabe, Makoto; Hasegawa, Sunao; Sekiguchi, Tomohiko; Naito, Hiroyuki; Usui, Fumihiko; Imai, Masataka; Sato, Mitsuteru; Kuramoto, Kiyoshi

2018-03-01

We present a unique and significant polarimetric result regarding the near-Earth asteroid (152679) 1998 KU2, which has a very low geometric albedo. From our observations, we find that the linear polarization degrees of 1998 KU2 are 44.6 ± 0.5% in the RC band and 44.0 ± 0.6% in the V band at a solar phase angle of 81.0°. These values are the highest of any known airless body in the solar system (i.e., high-polarization comets, asteroids, and planetary satellites) at similar phase angles. This polarimetric observation is not only the first for primitive asteroids at large phase angles, but also for low-albedo (<0.1) airless bodies. Based on spectroscopic similarities and polarimetric measurements of materials that have been sorted by size in previous studies, we conjecture that 1998 KU2 has a highly microporous regolith structure comprising nano-sized carbon grains on the surface.

Ganymede and Callisto - Surface textural dichotomies and photometric analysis

NASA Technical Reports Server (NTRS)

Buratti, Bonnie J.

1991-01-01

Complete solar phase curves of the Ganymede and Callisto leading and trailing hemispheres, which have been obtained by reducing Voyager imaging observations and combining them with ground-based telescopic data, are presently fit to scattering models in order to derive hemispherical values of the single scattering albedo, the single particle phase function (SPPF), the compaction state (CS) of the optically active portion of the regolith, and the mean slope angle of macroscopic features. While Callisto's leading side is composed of particles that are more strongly backscattering than the trailing side, no hemispheric differences are found in the CS, surface roughness, or SPPF.

Parameterization of single-scattering properties of snow

NASA Astrophysics Data System (ADS)

Räisänen, Petri; Kokhanovsky, Alexander; Guyot, Gwennole; Jourdan, Olivier; Nousiainen, Timo

2015-04-01

Snow consists of non-spherical ice grains of various shapes and sizes, which are surrounded by air and sometimes covered by films of liquid water. Still, in many studies, homogeneous spherical snow grains have been assumed in radiative transfer calculations, due to the convenience of using Mie theory. More recently, second-generation Koch fractals have been employed. While they produce a relatively flat scattering phase function typical of deformed non-spherical particles, this is still a rather ad-hoc choice. Here, angular scattering measurements for blowing snow conducted during the CLimate IMpacts of Short-Lived pollutants In the Polar region (CLIMSLIP) campaign at Ny Ålesund, Svalbard, are used to construct a reference phase function for snow. Based on this phase function, an optimized habit combination (OHC) consisting of severely rough (SR) droxtals, aggregates of SR plates and strongly distorted Koch fractals is selected. The single-scattering properties of snow are then computed for the OHC as a function of wavelength λ and snow grain volume-to-projected area equivalent radius rvp. Parameterization equations are developed for λ=0.199-2.7 μm and rvp = 10-2000 μm, which express the single-scattering co-albedo β, the asymmetry parameter g and the phase function as functions of the size parameter and the real and imaginary parts of the refractive index. Compared to the reference values computed for the OHC, the accuracy of the parameterization is very high for β and g. This is also true for the phase function parameterization, except for strongly absorbing cases (β > 0.3). Finally, we consider snow albedo and reflected radiances for the suggested snow optics parameterization, making comparisons with spheres and distorted Koch fractals. Further evaluation and validation of the proposed approach against (e.g.) bidirectional reflectance and polarization measurements for snow is planned. At any rate, it seems safe to assume that the OHC selected here provides a substantially better basis for representing the single-scattering properties of snow than spheres do. Moreover, the parameterizations developed here are analytic and simple to use, and they can also be applied to the treatment of dirty snow following (e.g.) the approach of Kokhanovsky (The Cryosphere, 7, 1325-1331, doi:10.5194/tc-7-1325-2013, 2013). This should make them an attractive option for use in radiative transfer applications involving snow.

Preliminary results of aerosols' optical properties studied with EPF measurements from the SPICAM/UV instrument

NASA Astrophysics Data System (ADS)

Willame, Y.; Vandaele, A.-C.; Depiesse, C.; Gillotay, D.; Kochenova, S.; Montmessin, F.

2011-10-01

Aerosols on Mars have an important impact on the radiative transfer properties of its atmosphere. Today their spectral properties and therefore their interaction with UV radiation are only poorly known. Improving the radiative transfer modeling requires a better knowledge of their characteristics, in particular of their phase function, single scattering albedo and opacity. We will show that such information can be accessed by using EPF observations.

Retrieval of the scattering and microphysical properties of aerosols from ground-based optical measurements including polarization. I. Method.

PubMed

Vermeulen, A; Devaux, C; Herman, M

2000-11-20

A method has been developed for retrieving the scattering and microphysical properties of atmospheric aerosol from measurements of solar transmission, aureole, and angular distribution of the scattered and polarized sky light in the solar principal plane. Numerical simulations of measurements have been used to investigate the feasibility of the method and to test the algorithm's performance. It is shown that the absorption and scattering properties of an aerosol, i.e., the single-scattering albedo, the phase function, and the polarization for single scattering of incident unpolarized light, can be obtained by use of radiative transfer calculations to correct the values of scattered radiance and polarized radiance for multiple scattering, Rayleigh scattering, and the influence of ground. The method requires only measurement of the aerosol's optical thickness and an estimate of the ground's reflectance and does not need any specific assumption about properties of the aerosol. The accuracy of the retrieved phase function and polarization of the aerosols is examined at near-infrared wavelengths (e.g., 0.870 mum). The aerosol's microphysical properties (size distribution and complex refractive index) are derived in a second step. The real part of the refractive index is a strong function of the polarization, whereas the imaginary part is strongly dependent on the sky's radiance and the retrieved single-scattering albedo. It is demonstrated that inclusion of polarization data yields the real part of the refractive index.

Distinguishing the albedo of exoplanets from stellar activity

NASA Astrophysics Data System (ADS)

Serrano, L. M.; Barros, S. C. C.; Oshagh, M.; Santos, N. C.; Faria, J. P.; Demangeon, O.; Sousa, S. G.; Lendl, M.

2018-03-01

Context. Light curves show the flux variation from the target star and its orbiting planets as a function of time. In addition to the transit features created by the planets, the flux also includes the reflected light component of each planet, which depends on the planetary albedo. This signal is typically referred to as phase curve and could be easily identified if there were no additional noise. As well as instrumental noise, stellar activity, such as spots, can create a modulation in the data, which may be very difficult to distinguish from the planetary signal. Aims: We analyze the limitations imposed by the stellar activity on the detection of the planetary albedo, considering the limitations imposed by the predicted level of instrumental noise and the short duration of the obervations planned in the context of the CHEOPS mission. Methods: As initial condition, we have assumed that each star is characterized by just one orbiting planet. We built mock light curves that included a realistic stellar activity pattern, the reflected light component of the planet and an instrumental noise level, which we have chosen to be at the same level as predicted for CHEOPS. We then fit these light curves to try to recover the reflected light component, assuming the activity patterns can be modeled with a Gaussian process. Results: We estimate that at least one full stellar rotation is necessary to obtain a reliable detection of the planetary albedo. This result is independent of the level of noise, but it depends on the limitation of the Gaussian process to describe the stellar activity when the light curve time-span is shorter than the stellar rotation. As an additional result, we found that with a 6.5 magnitude star and the noise level of CHEOPS, it is possible to detect the planetary albedo up to a lower limit of Rp = 0.03 R*. Finally, in presence of typical CHEOPS gaps in the simulations, we confirm that it is still possible to obtain a reliable albedo.

Vertical profile of cloud optical parameters derived from airborne measurements above, inside and below clouds

NASA Astrophysics Data System (ADS)

Melnikova, Irina; Gatebe, Charles K.

2018-07-01

Past strategies for retrieving cloud optical properties from remote sensing assumed significant limits for desired parameters such as semi-infinite optical thickness, single scattering albedo equaling unity (non-absorbing scattering), absence of spectral dependence of the optical thickness, etc., and only one optical parameter could be retrieved (either optical thickness or single scattering albedo). Here, we demonstrate a new method based on asymptotic theory for thick atmospheres, and the presence of a diffusion domain within the clouds that does not put restrictions and makes it possible to get two or even three optical parameters (optical thickness, single scattering albedo and phase function asymmetry parameter) for every wavelength independently. We applied this method to measurements of angular distribution of solar radiation above, inside and below clouds, obtained with NASA's Cloud Absorption Radiometer (CAR) over two cases of marine stratocumulus clouds; first case, offshore of Namibia and the second case, offshore of California. The observational and retrieval errors are accounted for by regularization, which allows stable and smooth solutions. Results show good potential for parameterization of the shortwave radiative properties (reflection, transmission, radiative divergence and heating rate) of water clouds.

Spectral and diurnal variations in clear sky planetary albedo

NASA Technical Reports Server (NTRS)

Briegleb, B.; Ramanathan, V.

1982-01-01

Spectral and diurnal variations in the clear sky planetary albedo of the earth are calculated using a radiative transfer model to obtain January and July values for a 5 deg x 5 deg global grid. The model employs observed climatological values of temperatures, humidities, snow and sea-ice cover. The diurnal cycle of clear sky albedo is calculated in the following intervals: 0.2-0.5, 0.5-0.7, and 0.7-4 microns. Observed ozone distribution is specified as a function of latitude and season. The 0.2-0.5 micron spectral albedo is 10-20% higher than the total albedo for all latitudes because of Rayleigh scattering; the 0.5-0.7 micron albedo differs from the total albedo by 1-2% for most latitudes, while the 0.7-4 micron albedo is 5-10% lower than the total because of strong atmospheric absorption. Planetary albedo decreases from morning to local noon, with diurnal variations being particularly strong over water.

The Surface of Deimos: Contribution of Materials and Processes to Its Unique Appearance

NASA Astrophysics Data System (ADS)

Thomas, P. C.; Adinolfi, D.; Helfenstein, P.; Simonelli, D.; Veverka, J.

1996-10-01

Among the well-imaged small satellites and asteroids, Deimos displays a unique surface: very smooth with global-scale albedo features. We have examined the disk-resolved photometry of Deimos using Viking Orbiter images for clues to its distinctive appearance. Hapke parameters were fit to characterize the phase behavior and to compute normal reflectance. The opposition surge amplitude (B0) is smaller for Deimos than for Phobos. Outside the range of the opposition effect the two martian satellites have similarly shaped phase curves, but Deimos is about 20-30% brighter than Phobos from 10°-80° phase. The calculated mean normal reflectance of Deimos (λeff= 0.54 μm) is 0.068 ± 0.007. The brighter and darker areas on Deimos exhibit constant contrast between 0.6° and 81° phase; this characteristic allows a calculation of the range of normal reflectances over most of its surface, nearly all of which values are between 0.06 and 0.09. The trailing side of Deimos has a larger relative distribution of the brighter material, and is on average about 10% brighter than the leading side. The mean normal reflectance cannot be formally distinguished from that of Phobos (0.071 ± 0.012; Simonelli, D. P., M. Wisz, A. Switala, D. Adinolfi, J. Veverka, P. C. Thomas, and P. Helfenstein 1996. Submitted toIcarus). Although the statistical distribution of normal reflectances on the two satellites is similar, the geography of the albedo variations is very different. Deimos has gradational changes in albedo downslope from ridge crests, primarily manifested in long albedo “streamers.” On Phobos there is a more patchy global distribution of albedos, apparently related to ejecta from the large crater Stickney. Because of the similarity of mean density, spectral properties, mean normal reflectance, the range of normal reflectance, and phase function outside the opposition effect, Deimos appears to be made of materials with compositions very similar to those on Phobos, although the apparent wider distribution of ejecta on Deimos has been cited as indicating a greater role for strength scaling in cratering on Deimos (Lee, S. W., P. Thomas, and J. Veverka 1986.Icarus68, 77-86). Simple modeling of the formation of the albedo patterns by gardening, creep, and “weathering” of bright material from crater rims suggests that impact gardening contributes very little to the motion of the material downslope, and that vertical mixing and/or “weathering” must be important in addition to an unspecified creep process. The distinction of Deimos is primarily in the smooth surface that allows a particularly large scale of downslope movement of regolith on very gentle slopes. This smoothness is most easily explained by the effects from impact formation of a 10-km concavity at high southern latitudes in the latter half of Deimos' surface history. This impact scar is relatively much larger than is the crater Stickney on Phobos. The effects of this large impact probably include blanketing by an average of nearly 200 m of ejecta, but also may include seismic erasing of craters similar to that proposed for Ida by Asphauget al. (Asphaug, E., J. M. Moore, D. Morrison, W. Benz, and R. A. Sullivan 1996.Icarus120, 158-184).

Hungaria Asteroid Region Telescopic Spectral Survey (HARTSS) II: Spectral Homogeneity Among Hungaria Family Asteroids

NASA Astrophysics Data System (ADS)

Lucas, Michael P.; Emery, Joshua; Pinilla-Alonso, Noemi; Lindsay, Sean S.; MacLennan, Eric M.; Cartwright, Richard; Reddy, Vishnu; Sanchez, Juan A.; Thomas, Cristina A.; Lorenzi, Vania

2017-10-01

Spectral observations of asteroid family members provide valuable information regarding parent body interiors, the source regions of near-Earth asteroids, and the link between meteorites and their parent bodies. Hungaria family asteroids constitute the closest samples to the Earth from a collisional family (~1.94 AU), permitting observations of smaller fragments than accessible for Main Belt families. We have carried out a ground-based observational campaign - Hungaria Asteroid Region Telescopic Spectral Survey (HARTSS) - to record reflectance spectra of these preserved samples from the inner-most primordial asteroid belt. During HARTSS phase one (Lucas et al. [2017]. Icarus 291, 268-287) we found that ~80% of the background population is comprised of stony S-complex asteroids that exhibit considerable spectral and mineralogical diversity. In HARTSS phase two, we turn our attention to family members and hypothesize that the Hungaria collisional family is homogeneous. We test this hypothesis through taxonomic classification, albedo estimates, and spectral properties.During phase two of HARTSS we acquired near-infrared (NIR) spectra of 50 new Hungarias (19 family; 31 background) with SpeX/IRTF and NICS/TNG. We analyzed X-type family spectra for NIR color indices (0.85-J J-K), and a subtle ~0.9 µm absorption feature that may be attributed to Fe-poor orthopyroxene. Surviving fragments of an asteroid collisional family typically exhibit similar taxonomies, albedos, and spectral properties. Spectral analysis of X-type Hungaria family members and independently calculated WISE albedo determinations for 428 Hungaria asteroids is consistent with this scenario. Furthermore, ~1/4 of the background population exhibit similar spectral properties and albedos to family X-types.Spectral observations of 92 Hungaria region asteroids acquired during both phases of HARTSS uncover a compositionally heterogeneous background and spectral homogeneity down to ~2 km for collisional family members. Taxonomy, albedos, and spectral properties reveal that the Hungaria family progenitor was an igneous body that formed under reduced conditions, and was compositionally consistent with the enstatite achondrite (i.e., aubrite) meteorite group.

First Retrieval of Surface Lambert Albedos From Mars Reconnaissance Orbiter CRISM Data

NASA Astrophysics Data System (ADS)

McGuire, P. C.; Arvidson, R. E.; Murchie, S. L.; Wolff, M. J.; Smith, M. D.; Martin, T. Z.; Milliken, R. E.; Mustard, J. F.; Pelkey, S. M.; Lichtenberg, K. A.; Cavender, P. J.; Humm, D. C.; Titus, T. N.; Malaret, E. R.

2006-12-01

We have developed a pipeline-processing software system to convert radiance-on-sensor for each of 72 out of 544 CRISM spectral bands used in global mapping to the corresponding surface Lambert albedo, accounting for atmospheric, thermal, and photoclinometric effects. We will present and interpret first results from this software system for the retrieval of Lambert albedos from CRISM data. For the multispectral mapping modes, these pipeline-processed 72 spectral bands constitute all of the available bands, for wavelengths from 0.362-3.920 μm, at 100-200 m/pixel spatial resolution, and ~ 0.006\\spaceμm spectral resolution. For the hyperspectral targeted modes, these pipeline-processed 72 spectral bands are only a selection of all of the 544 spectral bands, but at a resolution of 15-38 m/pixel. The pipeline processing for both types of observing modes (multispectral and hyperspectral) will use climatology, based on data from MGS/TES, in order to estimate ice- and dust-aerosol optical depths, prior to the atmospheric correction with lookup tables based upon radiative-transport calculations via DISORT. There is one DISORT atmospheric-correction lookup table for converting radiance-on-sensor to Lambert albedo for each of the 72 spectral bands. The measurements of the Emission Phase Function (EPF) during targeting will not be employed in this pipeline processing system. We are developing a separate system for extracting more accurate aerosol optical depths and surface scattering properties. This separate system will use direct calls (instead of lookup tables) to the DISORT code for all 544 bands, and it will use the EPF data directly, bootstrapping from the climatology data for the aerosol optical depths. The pipeline processing will thermally correct the albedos for the spectral bands above ~ 2.6 μm, by a choice between 4 different techniques for determining surface temperature: 1) climatology, 2) empirical estimation of the albedo at 3.9 μm from the measured albedo at 2.5 μm, 3) a physical thermal model (PTM) based upon maps of thermal inertia from TES and coarse-resolution surface slopes (SS) from MOLA, and 4) a photoclinometric extension to the PTM that uses CRISM albedos at 0.41 μm to compute the SS at CRISM spatial resolution. For the thermal correction, we expect that each of these 4 different techniques will be valuable for some fraction of the observations.

The neuron net method for processing the clear pixels and method of the analytical formulas for processing the cloudy pixels of POLDER instrument images

NASA Astrophysics Data System (ADS)

Melnikova, I.; Mukai, S.; Vasilyev, A.

Data of remote measurements of reflected radiance with the POLDER instrument on board of ADEOS satellite are used for retrieval of the optical thickness, single scattering albedo and phase function parameter of cloudy and clear atmosphere. The method of perceptron neural network that from input values of multiangle radiance and Solar incident angle allows to obtain surface albedo, the optical thickness, single scattering albedo and phase function parameter in case of clear sky. Two last parameters are determined as optical average for atmospheric column. The calculation of solar radiance with using the MODTRAN-3 code with taking into account multiple scattering is accomplished for neural network learning. All mentioned parameters were randomly varied on the base of statistical models of possible measured parameters variation. Results of processing one frame of remote observation that consists from 150,000 pixels are presented. The methodology elaborated allows operative determining optical characteristics as cloudy as clear atmosphere. Further interpretation of these results gives the possibility to extract the information about total contents of atmospheric aerosols and absorbing gases in the atmosphere and create models of the real cloudiness An analytical method of interpretation that based on asymptotic formulas of multiple scattering theory is applied to remote observations of reflected radiance in case of cloudy pixel. Details of the methodology and error analysis were published and discussed earlier. Here we present results of data processing of pixel size 6x6 km In many studies the optical thickness is evaluated earlier in the assumption of the conservative scattering. But in case of true absorption in clouds the large errors in parameter obtained are possible. The simultaneous retrieval of two parameters at every wavelength independently is the advantage comparing with earlier studies. The analytical methodology is based on the transfer theory asymptotic formula inversion for optically thick stratus clouds. The model of horizontally infinite layer is considered. The slight horizontal heterogeneity is approximately taken into account. Formulas containing only the measured values of two-direction radiance and functions of solar and view angles were derived earlier. The 6 azimuth harmonics of reflection function are taken into account. The simple approximation of the cloud top boarder heterogeneity is used. The clouds, projecting upper the cloud top plane causes the increase of diffuse radiation in the incident flux. It is essential for calculation of radiative characteristics, which depends on lighting conditions. Escape and reflection functions describe this dependence for reflected radiance and local albedo of semi-infinite medium - for irradiance. Thus the functions depending on solar incident angle is to replace by their modifications. Firstly optical thickness of every pixel is obtained with simple formula assuming conservative scattering for all available view directions. Deviations between obtained values may be taken as a measure of the cloud top deviation from the plane. The special parameter is obtained, which takes into account the shadowing effect. Then single scattering albedo and optical thickness (with the true absorption assuming) are obtained for pairs of view directions with equal optical thickness. After that the averaging of values obtained and relative error evaluation is accomplished for all viewing directions of every pixel. The procedure is repeated for all wavelengths and pixels independently.

Phase Function Determination in Support of Orbital Debris Size Estimation

NASA Technical Reports Server (NTRS)

Hejduk, M. D.; Cowardin, H. M.; Stansbery, Eugene G.

2012-01-01

To recover the size of a space debris object from photometric measurements, it is necessary to determine its albedo and basic shape: if the albedo is known, the reflective area can be calculated; and if the shape is known, the shape and area taken together can be used to estimate a characteristic dimension. Albedo is typically determined by inferring the object s material type from filter photometry or spectroscopy and is not the subject of the present study. Object shape, on the other hand, can be revealed from a time-history of the object s brightness response. The most data-rich presentation is a continuous light-curve that records the object s brightness for an entire sensor pass, which could last for tens of minutes to several hours: from this one can see both short-term periodic behavior as well as brightness variations with phase angle. Light-curve interpretation, however, is more art than science and does not lend itself easily to automation; and the collection method, which requires single-object telescope dedication for long periods of time, is not well suited to debris survey conditions. So one is led to investigate how easily an object s brightness phase function, which can be constructed from the more survey-friendly point photometry, can be used to recover object shape. Such a recovery is usually attempted by comparing a phase-function curve constructed from an object s empirical brightness measurements to analytically-derived curves for basic shapes or shape combinations. There are two ways to accomplish this: a simple averaged brightness-versus phase curve assembled from the empirical data, or a more elaborate approach in which one is essentially calculating a brightness PDF for each phase angle bin (a technique explored in unpublished AFRL/RV research and in Ojakangas 2011); in each case the empirical curve is compared to analytical results for shapes of interest. The latter technique promises more discrimination power but requires more data; the former can be assembled in its essentials from fewer measurements but will be less definitive in its assignments. The goal of the present study is to evaluate both techniques under debris survey conditions to determine their relative performance and, additionally, to learn precisely how a survey should be conducted in order to maximize their performance. Because the distendedness of objects has more of an effect than their precise shape in calculating a characteristic dimension, one is interested in the techniques discrimination ability to distinguish between an elongated rectangular prism and a short rectangular prism or cube, or an elongated cylinder from a squat cylinder or sphere. Sensitivity studies using simulated data will be conducted to determine discrimination power for both techniques as a function of amount of data collected and range (and specific region) of phase angles sampled. Empirical GEODSS photometry data for distended objects (dead payloads with solar panels, rocket bodies) and compact objects (cubesats, calibration spheres, squat payloads) will also be used to test this discrimination ability. The result will be a recommended technique and data collection paradigm for debris surveys in order to maximize this type of discrimination.

Inferring planetary obliquity using rotational and orbital photometry

NASA Astrophysics Data System (ADS)

Schwartz, J. C.; Sekowski, C.; Haggard, H. M.; Pallé, E.; Cowan, N. B.

2016-03-01

The obliquity of a terrestrial planet is an important clue about its formation and critical to its climate. Previous studies using simulated photometry of Earth show that continuous observations over most of a planet's orbit can be inverted to infer obliquity. However, few studies of more general planets with arbitrary albedo markings have been made and, in particular, a simple theoretical understanding of why it is possible to extract obliquity from light curves is missing. Reflected light seen by a distant observer is the product of a planet's albedo map, its host star's illumination, and the visibility of different regions. It is useful to treat the product of illumination and visibility as the kernel of a convolution. Time-resolved photometry constrains both the albedo map and the kernel, the latter of which sweeps over the planet due to rotational and orbital motion. The kernel's movement distinguishes prograde from retrograde rotation for planets with non-zero obliquity on inclined orbits. We demonstrate that the kernel's longitudinal width and mean latitude are distinct functions of obliquity and axial orientation. Notably, we find that a planet's spin axis affects the kernel - and hence time-resolved photometry - even if this planet is east-west uniform or spinning rapidly, or if it is north-south uniform. We find that perfect knowledge of the kernel at 2-4 orbital phases is usually sufficient to uniquely determine a planet's spin axis. Surprisingly, we predict that east-west albedo contrast is more useful for constraining obliquity than north-south contrast.

Mapping Global Ocean Surface Albedo from Satellite Observations: Models, Algorithms, and Datasets

NASA Astrophysics Data System (ADS)

Li, X.; Fan, X.; Yan, H.; Li, A.; Wang, M.; Qu, Y.

2018-04-01

Ocean surface albedo (OSA) is one of the important parameters in surface radiation budget (SRB). It is usually considered as a controlling factor of the heat exchange among the atmosphere and ocean. The temporal and spatial dynamics of OSA determine the energy absorption of upper level ocean water, and have influences on the oceanic currents, atmospheric circulations, and transportation of material and energy of hydrosphere. Therefore, various parameterizations and models have been developed for describing the dynamics of OSA. However, it has been demonstrated that the currently available OSA datasets cannot full fill the requirement of global climate change studies. In this study, we present a literature review on mapping global OSA from satellite observations. The models (parameterizations, the coupled ocean-atmosphere radiative transfer (COART), and the three component ocean water albedo (TCOWA)), algorithms (the estimation method based on reanalysis data, and the direct-estimation algorithm), and datasets (the cloud, albedo and radiation (CLARA) surface albedo product, dataset derived by the TCOWA model, and the global land surface satellite (GLASS) phase-2 surface broadband albedo product) of OSA have been discussed, separately.

Near-opposition martian limb-darkening: Quantification and implication for visible-near-infrared bidirectional reflectance studies.

NASA Astrophysics Data System (ADS)

de Grenier, Muriel; Pinet, Patrick C.

1995-06-01

A nearly global coverage of the martian eastern hemisphere, acquired under small phase angles and varying observational geometries conditions, has been produced from 1988 opposition by spectral (0.5-1 μm) imaging data obtained at the Pic du Midi Observatory in France. From this data set, the methodology presented here permits a systematic analysis of martian photometric behavior at a regional scale of 100-300 km in the visible and near-infrared. The quantification of limb-darkening as a function of wavelength and surface albedo gives access in martian regional properties as a function of wavelength and surface albedo and results in the production of visible and near-infrared geometric albedo maps. A linear relation between the limb darkening parameter k and geometric albedo exists in the near infrared. Based on laboratory studies, it suggests a spectral response of particulate type for the martian soil. Conversely, in the visible, the value of k parameter is 0.6 independent of albedo and is consistent with a single scattering photometric behavior in the surface layer. However, the observed change in the martian photometry from single to multiple scattering may be partially due to a large contribution of atmospheric scattering above 0.7 μm. In the absence of a multitemporal dataset analysis, it must be emphasized that the present results are a priori only pertinent to the atmospheric and surface conditions existing on Mars at the time of observation. However, this analysis may contribute to characterize some physical properties, such as surface roughness. In the near-infrared, for bright terrains, k tends to 0.8 and agrees with the presence of very fine particulate materials. Photometry of dark areas is more irregular (0.48 < k < 0.64) and might result from surface roughness heterogeneities. However, a few dark areas reveal that k anomalous values in the range 0.7-0.8 may be caused by the presence of a coating of very fine materials or duricrust. Finally, we evaluate the influence of reflectance geometrical effects on the multispectral and spectroscopic data of the martian surface.

NEAs: Phase Angle Dependence of Asteroid Class and Diameter from Observational Studies

NASA Astrophysics Data System (ADS)

Wooden, Diane H.; Lederer, Susan M.; Bus, Schelte; Tokunaga, Alan; Jehin, Emmanuel; Howell, Ellen S.; Nolan, Michael C.; Ryan, Erin; Fernandez, Yan; Harker, David; Reddy, Vishnu; Benner, Lance AM; Lovell, Amy; Moskovitz, Nicholas; Kerr, Tom; Woodward, Charles

2015-08-01

We will discuss the results of a planned observation campaign of Near Earth Asteroids (NEAs), 1999 CU3, 2002 GM2, 2002 FG7, and 3691 Bede with instruments on the United Kingdom Infrared Telescope (UKIRT) from 15-Mar-2015 to 28-April 2015 UT. We will study the phase-angle dependence of the reflectance and thermal emission spectra. Recent publications reveal that the assignment of the asteroid class from visible and near-IR spectroscopy can change with phase angle for NEAs with silicate-bearing minerals on their surfaces (S-class asteroids) (Thomas et al. 2014, Icarus 228, 217; Sanchez et al. 2012 Icarus 220, 36). Only three of the larger NEAs have been measured at a dozen phase angles and the trends are not all the same, so there is not yet enough information to create a phase-angle correction. Also, the phase angle effect is not characterized well for the thermal emission including determination of the albedo and the thermal emission. The few NEAs were selected for our study amongst many possible targets based on being able to observe them through a wide range of phase angles, ranging from less than about 10 degrees to greater than 45 degrees over the constrained date range. The orbits of NEAs often generate short observing windows at phase angles higher than 45 deg (i.e., whizzing by Earth and/or close to dawn or dusk). Ultimately, lowering the uncertainty of the translation of asteroid class to meteorite analog and of albedo and size determinations are amongst our science goals. On a few specific nights, we plan to observe the 0.75-2.5 micron spectra with IRTF+SpeX for comparison with UKIRT data including 5-20 micron with UKIRT+UIST/Michelle to determine as best as possible the albedos. To ensure correct phasing of spectroscopic data, we augment with TRAPPIST-telescope light curves and R-band guider image data. Our observations will contribute to understanding single epoch mid-IR and near-IR measurements to obtain albedo, size and IR beaming parameters (the outcomes of thermal models) and asteroid spectral class.

NEAs: Phase Angle Dependence of Asteroid Class and Diameter from Observational Studies

NASA Technical Reports Server (NTRS)

Wooden, Diane H.; Lederer, Susan M.; Bus, Schlete; Tokunaga, Alan; Jehin, Emmanuel; Howell, Ellen S.; Nolan, Michael C.; Ryan, Erin; Fernandez, Yan; Harker, David;

Coarse Scale In Situ Albedo Observations over Heterogeneous Land Surfaces and Validation Strategy

NASA Astrophysics Data System (ADS)

Xiao, Q.; Wu, X.; Wen, J.; BAI, J., Sr.

2017-12-01

To evaluate and improve the quality of coarse-pixel land surface albedo products, validation with ground measurements of albedo is crucial over the spatially and temporally heterogeneous land surface. The performance of albedo validation depends on the quality of ground-based albedo measurements at a corresponding coarse-pixel scale, which can be conceptualized as the "truth" value of albedo at coarse-pixel scale. The wireless sensor network (WSN) technology provides access to continuously observe on the large pixel scale. Taking the albedo products as an example, this paper was dedicated to the validation of coarse-scale albedo products over heterogeneous surfaces based on the WSN observed data, which is aiming at narrowing down the uncertainty of results caused by the spatial scaling mismatch between satellite and ground measurements over heterogeneous surfaces. The reference value of albedo at coarse-pixel scale can be obtained through an upscaling transform function based on all of the observations for that pixel. We will devote to further improve and develop new method that that are better able to account for the spatio-temporal characteristic of surface albedo in the future. Additionally, how to use the widely distributed single site measurements over the heterogeneous surfaces is also a question to be answered. Keywords: Remote sensing; Albedo; Validation; Wireless sensor network (WSN); Upscaling; Heterogeneous land surface; Albedo truth at coarse-pixel scale

On Spectral Invariance of Single Scattering Albedo for Weakly Absorbing Wavelengths

NASA Technical Reports Server (NTRS)

Marshak, Alexander; Knyazikhin, Yuri; Chiu, J. Christine; Wiscombe, Warren J.

2011-01-01

This note shows that for water droplets at weakly absorbing wavelengths, the ratio omega(sub O lambda(r))/omega(sub O lambda(r(sub O)) of two single scattering albedo spectra, omega(sub O lambda(r) and omega(sub O lambda(r (sub O)), is a linear function of omega(sub O lambda(r). The slope and intercept of the linear function are wavelength independent and sum to unity. This relationship allows for a representation of any single scattering albedo omega(sub O lambda(r) via one known spectrum omega(sub O lambda(r(sub O)). The note provides a simple physical explanation of the discovered relationship. In addition to water droplets, similar linear relationships were found for the single scattering albedo of non-spherical ice crystals.

Dust scattering from the Taurus Molecular Cloud

NASA Astrophysics Data System (ADS)

Narayan, Sathya; Murthy, Jayant; Karuppath, Narayanankutty

2017-04-01

We present an analysis of the diffuse ultraviolet emission near the Taurus Molecular Cloud based on observations made by the Galaxy Evolution Explorer. We used a Monte Carlo dust scattering model to show that about half of the scattered flux originates in the molecular cloud with 25 per cent arising in the foreground and 25 per cent behind the cloud. The best-fitting albedo of the dust grains is 0.3, but the geometry is such that we could not constrain the phase function asymmetry factor (g).

Migration of Frosts from High-Albedo Regions of Pluto: what New Horizons Reveals

NASA Astrophysics Data System (ADS)

Buratti, Bonnie J.; Stern, S. A.; Weaver, Hal A.; Young, Leslie A.; Olkin, Cathy B.; Ennico, Kimberly; Binzel, Richard P.; Zangari, Amanda; Earle, Alissa M.

2015-11-01

With its high eccentricity and obliquity, Pluto should exhibit seasonal volatile transport on its surface. Several lines of evidence support this transport: doubling of Pluto’s atmospheric pressure over the past two decades (Young et al., 2013, Ap. J. 766, L22; Olkin et al., 2015, Icarus 246, 230); changes in its historical rotational light curve, once all variations due to viewing geometry have been modelled (Buratti et al., 2015; Ap. J. 804, L6); and changes in HST albedo maps (Buie et al., 2010, Astron. J. 139, 1128). New Horizons LORRI images reveal that the region of greatest albedo change is not the polar cap(s) of Pluto, but the feature informally named Tombaugh Regio (TR). This feature has a normal reflectance as high as ~0.8 in some places, and it is superposed on older, lower-albedo pre-existing terrain with an albedo of only ~0.10. This contrast is larger than any other body in the Solar System, except for Iapetus. This albedo dichotomy leads to a complicated system of cold-trapping and thermal segregation, beyond the simple picture of seasonal volatile transport. Whatever the origin of TR, it initially acted as a cold trap, as the temperature differential between the high and low albedo regions could be enormous, possibly approaching 20K, based on their albedo differences and assuming their normalized phase curves are similar. This latter assumption will be refined as the full New Horizons data set is returned.Over six decades of ground-based photometry suggest that TR has been decreasing in albedo over the last 25 years. Possible causes include changing insolation angles, or sublimation from the edges where the high-albedo material impinges on a much warmer substrate.Funding by the NASA New Horizons Project acknowledged.

Global albedos of Pluto and Charon from LORRI New Horizons observations

NASA Astrophysics Data System (ADS)

Buratti, B. J.; Hofgartner, J. D.; Hicks, M. D.; Weaver, H. A.; Stern, S. A.; Momary, T.; Mosher, J. A.; Beyer, R. A.; Verbiscer, A. J.; Zangari, A. M.; Young, L. A.; Lisse, C. M.; Singer, K.; Cheng, A.; Grundy, W.; Ennico, K.; Olkin, C. B.

2017-05-01

The exploration of the Pluto-Charon system by the New Horizons spacecraft represents the first opportunity to understand the distribution of albedo and other photometric properties of the surfaces of objects in the Solar System's ;Third Zone; of distant ice-rich bodies. Images of the entire illuminated surface of Pluto and Charon obtained by the Long Range Reconnaissance Imager (LORRI) camera provide a global map of Pluto that reveals surface albedo variegations larger than any other Solar System world except for Saturn's moon Iapetus. Normal reflectances on Pluto range from 0.08-1.0, and the low-albedo areas of Pluto are darker than any region of Charon. Charon exhibits a much blander surface with normal reflectances ranging from 0.20-0.73. Pluto's albedo features are well-correlated with geologic features, although some exogenous low-albedo dust may be responsible for features seen to the west of the area informally named Tombaugh Regio. The albedo patterns of both Pluto and Charon are latitudinally organized, with the exception of Tombaugh Regio, with darker regions concentrated at the Pluto's equator and Charon's northern pole. The phase curve of Pluto is similar to that of Triton, the large moon of Neptune believed to be a captured Kuiper Belt Object (KBO), while Charon's is similar to that of the Moon. Preliminary Bond albedos are 0.25 ± 0.03 for Charon and 0.72 ± 0.07 for Pluto. Maps of an approximation to the Bond albedo for both Pluto and Charon are presented for the first time. Our work shows a connection between very high albedo (near unity) and planetary activity, a result that suggests the KBO Eris may be currently active.

Variation in foliar nitrogen and albedo in response to nitrogen fertilization and elevated CO2

Treesearch

Haley F. Wicklein; Scott V. Ollinger; Mary E. Martin; David Y. Hollinger; Lucie C. Lepine; Michelle C. Day; Megan K. Bartlett; Andrew D. Richardson; Richard J. Norby

2012-01-01

Foliar nitrogen has been shown to be positively correlated with midsummer canopy albedo and canopy near infrared (NIR) reflectance over a broad range of plant functional types (e.g., forests, grasslands, and agricultural lands). To date, the mechanism(s) driving the nitrogen-albedo relationship have not been established, and it is unknown whether factors affecting...

Colorimetry and magnitudes of asteroids

NASA Technical Reports Server (NTRS)

Bowell, E.; Lumme, K.

1979-01-01

In the present paper, 1500 UBV observations are analyzed by a new rather general multiple scattering theory which provided clear insight into previously poorly-recognized optical nature of asteroid surfaces. Thus, phase curves are shown to consist of a surface-texture controlled component, due to singly scattered light, and a component due to multiple scattering. Phase curve shapes can be characterized by a single parameter, the multiple scattering factor, Q. As Q increases, the relative importance of the opposition effect diminishes. Asteroid surfaces are particulate and strikingly similar to texture, being moderately porous and moderately rough on a scale greater than the wavelength of light. In concequence, Q (and also the phase coefficient) correlate well with geometric albedo, and there exists a purely photometric means of determining albedos and diameters.

The seasonal cycle of snow cover, sea ice and surface albedo

NASA Technical Reports Server (NTRS)

Robock, A.

1980-01-01

The paper examines satellite data used to construct mean snow cover caps for the Northern Hemisphere. The zonally averaged snow cover from these maps is used to calculate the seasonal cycle of zonally averaged surface albedo. The effects of meltwater on the surface, solar zenith angle, and cloudiness are parameterized and included in the calculations of snow and ice albedo. The data allows a calculation of surface albedo for any land or ocean 10 deg latitude band as a function of surface temperature ice and snow cover; the correct determination of the ice boundary is more important than the snow boundary for accurately simulating the ice and snow albedo feedback.

Solution of the radiative transfer equation for Rayleigh scattering using the infinite medium Green's function

NASA Astrophysics Data System (ADS)

Biçer, M.; Kaşkaş, A.

2018-03-01

The infinite medium Green's function is used to solve the half-space albedo, slab albedo and Milne problems for the unpolarized Rayleigh scattering case; these problems are the most classical problems of radiative transfer theory. The numerical results are obtained and are compared with previous ones.

Phase Curves of WASP-33b and HD 149026b and a New Correlation between Phase Curve Offset and Irradiation Temperature

NASA Astrophysics Data System (ADS)

Zhang, Michael; Knutson, Heather A.; Kataria, Tiffany; Schwartz, Joel C.; Cowan, Nicolas B.; Showman, Adam P.; Burrows, Adam; Fortney, Jonathan J.; Todorov, Kamen; Desert, Jean-Michel; Agol, Eric; Deming, Drake

2018-02-01

We present new 3.6 and 4.5 μm Spitzer phase curves for the highly irradiated hot Jupiter WASP-33b and the unusually dense Saturn-mass planet HD 149026b. As part of this analysis, we develop a new variant of pixel-level decorrelation that is effective at removing intrapixel sensitivity variations for long observations (>10 hr) where the position of the star can vary by a significant fraction of a pixel. Using this algorithm, we measure eclipse depths, phase amplitudes, and phase offsets for both planets at 3.6 and 4.5 μm. We use a simple toy model to show that WASP-33b’s phase offset, albedo, and heat recirculation efficiency are largely similar to those of other hot Jupiters despite its very high irradiation. On the other hand, our fits for HD 149026b prefer a very high albedo. We also compare our results to predictions from general circulation models, and we find that while neither planet matches the models well, the discrepancies for HD 149026b are especially large. We speculate that this may be related to its high bulk metallicity, which could lead to enhanced atmospheric opacities and the formation of reflective cloud layers in localized regions of the atmosphere. We then place these two planets in a broader context by exploring relationships between the temperatures, albedos, heat transport efficiencies, and phase offsets of all planets with published thermal phase curves. We find a striking relationship between phase offset and irradiation temperature: the former drops with increasing temperature until around 3400 K and rises thereafter. Although some aspects of this trend are mirrored in the circulation models, there are notable differences that provide important clues for future modeling efforts.

Nimbus 7 earth radiation budget wide field of view climate data set improvement. I - The earth albedo from deconvolution of shortwave measurements

NASA Technical Reports Server (NTRS)

Hucek, Richard R.; Ardanuy, Philip E.; Kyle, H. Lee

1987-01-01

A deconvolution method for extracting the top of the atmosphere (TOA) mean, daily albedo field from a set of wide-FOV (WFOV) shortwave radiometer measurements is proposed. The method is based on constructing a synthetic measurement for each satellite observation. The albedo field is represented as a truncated series of spherical harmonic functions, and these linear equations are presented. Simulation studies were conducted to determine the sensitivity of the method. It is observed that a maximum of about 289 pieces of data can be extracted from a set of Nimbus 7 WFOV satellite measurements. The albedos derived using the deconvolution method are compared with albedos derived using the WFOV archival method; the developed albedo field achieved a 20 percent reduction in the global rms regional reflected flux density errors. The deconvolution method is applied to estimate the mean, daily average TOA albedo field for January 1983. A strong and extensive albedo maximum (0.42), which corresponds to the El Nino/Southern Oscillation event of 1982-1983, is detected over the south central Pacific Ocean.

Combining NLCD and MODIS to create a land cover-albedo database for the continental United States

USGS Publications Warehouse

Wickham, J.; Barnes, Christopher A.; Nash, M.S.; Wade, T.G.

2015-01-01

Land surface albedo is an essential climate variable that is tightly linked to land cover, such that specific land cover classes (e.g., deciduous broadleaf forest, cropland) have characteristic albedos. Despite the normative of land-cover class specific albedos, there is considerable variability in albedo within a land cover class. The National Land Cover Database (NLCD) and the Moderate Resolution Imaging Spectroradiometer (MODIS) albedo product were combined to produce a long-term (14 years) integrated land cover-albedo database for the continental United States that can be used to examine the temporal behavior of albedo as a function of land cover. The integration identifies areas of homogeneous land cover at the nominal spatial resolution of the MODIS (MCD43A) albedo product (500 m × 500 m) from the NLCD product (30 m × 30 m), and provides an albedo data record per 500 m × 500 m pixel for 14 of the 16 NLCD land cover classes. Individual homogeneous land cover pixels have up to 605 albedo observations, and 75% of the pixels have at least 319 MODIS albedo observations (≥ 50% of the maximum possible number of observations) for the study period (2000–2013). We demonstrated the utility of the database by conducting a multivariate analysis of variance of albedo for each NLCD land cover class, showing that locational (pixel-to-pixel) and inter-annual variability were significant factors in addition to expected seasonal (intra-annual) and geographic (latitudinal) effects.

Development of a high spectral resolution surface albedo product for the ARM Southern Great Plains central facility

NASA Astrophysics Data System (ADS)

McFarlane, S. A.; Gaustad, K. L.; Mlawer, E. J.; Long, C. N.; Delamere, J.

2011-09-01

We present a method for identifying dominant surface type and estimating high spectral resolution surface albedo at the Atmospheric Radiation Measurement (ARM) facility at the Southern Great Plains (SGP) site in Oklahoma for use in radiative transfer calculations. Given a set of 6-channel narrowband visible and near-infrared irradiance measurements from upward and downward looking multi-filter radiometers (MFRs), four different surface types (snow-covered, green vegetation, partial vegetation, non-vegetated) can be identified. A normalized difference vegetation index (NDVI) is used to distinguish between vegetated and non-vegetated surfaces, and a scaled NDVI index is used to estimate the percentage of green vegetation in partially vegetated surfaces. Based on libraries of spectral albedo measurements, a piecewise continuous function is developed to estimate the high spectral resolution surface albedo for each surface type given the MFR albedo values as input. For partially vegetated surfaces, the albedo is estimated as a linear combination of the green vegetation and non-vegetated surface albedo values. The estimated albedo values are evaluated through comparison to high spectral resolution albedo measurements taken during several Intensive Observational Periods (IOPs) and through comparison of the integrated spectral albedo values to observed broadband albedo measurements. The estimated spectral albedo values agree well with observations for the visible wavelengths constrained by the MFR measurements, but have larger biases and variability at longer wavelengths. Additional MFR channels at 1100 nm and/or 1600 nm would help constrain the high resolution spectral albedo in the near infrared region.

Development of a high spectral resolution surface albedo product for the ARM Southern Great Plains central facility

NASA Astrophysics Data System (ADS)

McFarlane, S. A.; Gaustad, K. L.; Mlawer, E. J.; Long, C. N.; Delamere, J.

2011-05-01

We present a method for identifying dominant surface type and estimating high spectral resolution surface albedo at the Atmospheric Radiation Measurement (ARM) facility at the Southern Great Plains (SGP) site in Oklahoma for use in radiative transfer calculations. Given a set of 6-channel narrowband visible and near-infrared irradiance measurements from upward and downward looking multi-filter radiometers (MFRs), four different surface types (snow-covered, green vegetation, partial vegetation, non-vegetated) can be identified. A normalized difference vegetation index (NDVI) is used to distinguish between vegetated and non-vegetated surfaces, and a scaled NDVI index is used to estimate the percentage of green vegetation in partially vegetated surfaces. Based on libraries of spectral albedo measurements, a piecewise continuous function is developed to estimate the high spectral resolution surface albedo for each surface type given the MFR albedo values as input. For partially vegetated surfaces, the albedo is estimated as a linear combination of the green vegetation and non-vegetated surface albedo values. The estimated albedo values are evaluated through comparison to high spectral resolution albedo measurements taken during several Intensive Observational Periods (IOPs) and through comparison of the integrated spectral albedo values to observed broadband albedo measurements. The estimated spectral albedo values agree well with observations for the visible wavelengths constrained by the MFR measurements, but have larger biases and variability at longer wavelengths. Additional MFR channels at 1100 nm and/or 1600 nm would help constrain the high resolution spectral albedo in the near infrared region.

Poster 13: Large-scale simultaneous mapping of Titan's aerosol opacity and surface albedo by a new massive inversion method of Cassini/VIMS data

NASA Astrophysics Data System (ADS)

Maltagliati, Luca; Rodriguez, Sebastien; Sotin, Christophe; Rannou, Pascal; Bezard, Bruno; Solomonidou, Anezina; Coustenis, Athena; Appere, Thomas; Cornet, Thomas; Le Mouelic, Stephane

2016-06-01

We have still limited information on Titan's surface albedo in the near-infrared. Only few spectral windows exist in between the intense methane bands, and even those windows are strongly affected by atmospheric contributions (absorption, scattering). Yet, this part of the spectrum is important to determine the surface composition thanks to the wealth of absorption bands by minerals and ices present there. A radiative transfer model is an effective tool to take the atmospheric effects into consideration in the analysis (e.g. Rannou et al. 2010, Griffith et al 2012, Solomonidou et al. 2016,...), but it is too time-consuming to process the whole VIMS hyperspectral dataset (millions of spectra) and create large-scale maps of the surface albedo. To overcome this problem, we developed an inversion method of VIMS data that employs lookup tables of synthetic spectra produced by a state-of-the-art radiative transfer model (described in its original form in Hirtzig et al. 2013). The heavy computational part (calling the radiative transfer model) is thus done only once for all during the creation of the modeled spectra. We updated the model with new methane spectroscopy and the new aerosol parameters we found in our analysis of the VIMS Emission Phase Function (see the other Maltagliati et al. abstract in this workshop). We analyzed in detail the behavior of the spectra as a function of the free parameters of the model (three inputs, the incidence, emergence and azimuth angles; and two products: the aerosol opacity and the surface albedo) in order to create an optimized grid for the lookup table. The lookup tables were then grafted onto an ad-hoc inversion model. Our method can process a whole 64x64 VIMS datacube in few minutes, with a gain in computational time of a factor of more than one thousand with respect to the standard method. This will consent for the first time a truly massive inversion of VIMS data and large-scale acquisition of Titan's surface albedo, paving the way for global maps of mineralogical composition (and related temporal variations). Results of simultaneous maps of aerosol opacity and surface albedo for the various surface windows are shown for some selected flybys observing the same area with different geometries, to highlight the robustness of the method to correct seamlessly the atmospheric effects.

UV/visible albedos from airborne measurements

NASA Astrophysics Data System (ADS)

Webb, A.; Kylling, A.; Stromberg, I.

2003-04-01

During the INSPECTRO campaign effective surface albedo was measured at UV and visible wavelengths from two airborne platforms, a Cessna light aircraft and a hot air balloon. On board the Cessna was a scanning spectroradiometer measuring from 300 - 500nm at 10nm intervals. The NILU cube, with 6 faces and two UV channels at 312 and 340nm, was suspended beneath the hot air balloon. Flights took place over East Anglia during September, 2002. Balloon flights were made below cloud layers, while the Cessna flew both above and below cloud. The Cessna also flew over Barton Bendish, where surface albedos have been measured for ground truthing of satellite data, and measured the effective albedo at four visible wave- lengths in the centres of the satellite bandpass functions. Results of measurements from the different platforms are compared, and model simulations used to deduce the surface albedo from the effective albedo at altitude, giving, for example, an albedo of 0.02 ± 0.01 at 340nm.

Physical Characterization of Warm Spitzer-observed Near-Earth Objects

NASA Technical Reports Server (NTRS)

Thomas, Cristina A.; Emery, Joshua P.; Trilling, David E.; Delbo, Marco; Hora, Joseph L.; Mueller, Michael

2014-01-01

Near-infrared spectroscopy of Near-Earth Objects (NEOs) connects diagnostic spectral features to specific surface mineralogies. The combination of spectroscopy with albedos and diameters derived from thermal infrared observations can increase the scientific return beyond that of the individual datasets. For instance, some taxonomic classes can be separated into distinct compositional groupings with albedo and different mineralogies with similar albedos can be distinguished with spectroscopy. To that end, we have completed a spectroscopic observing campaign to complement the ExploreNEOs Warm Spitzer program that obtained albedos and diameters of nearly 600 NEOs (Trilling et al., 2010). The spectroscopy campaign included visible and near-infrared observations of ExploreNEOs targets from various observatories. Here we present the results of observations using the low-resolution prism mode (approx. 0.7-2.5 microns) of the SpeX instrument on the NASA Infrared Telescope Facility (IRTF). We also include near-infrared observations of Explore-NEOs targets from the MIT-UH-IRTF Joint Campaign for Spectral Reconnaissance. Our dataset includes near-infrared spectra of 187 ExploreNEOs targets (125 observations of 92 objects from our survey and 213 observations of 154 objects from the MIT survey). We identify a taxonomic class for each spectrum and use band parameter analysis to investigate the mineralogies for the S-, Q-, and V-complex objects. Our analysis suggests that for spectra that contain near-infrared data but lack the visible wavelength region, the Bus-DeMeo system misidentifies some S-types as Q-types. We find no correlation between spectral band parameters and ExploreNEOs albedos and diameters. We investigate the correlations of phase angle with band area ratio and near-infrared spectral slope. We find slightly negative Band Area Ratio (BAR) correlations with phase angle for Eros and Ivar, but a positive BAR correlation with phase angle for Ganymed.The results of our phase angle study are consistent with those of (Sanchez et al., 2012). We find evidence for spectral phase reddening for Eros, Ganymed, and Ivar. We identify the likely ordinary chondrite type analog for an appropriate subset of our sample. Our resulting proportions of H, L, and LL ordinary chondrites differ from those calculated for meteorite falls and in previous studies of ordinary chondrite-like NEOs.

kepler's dark worlds: A low albedo for an ensemble of Neptunian and Terran exoplanets

NASA Astrophysics Data System (ADS)

Jansen, Tiffany; Kipping, David

2018-05-01

Photometric phase curves provide an important window onto exoplanetary atmospheres and potentially even their surfaces. With similar amplitudes to occultations but far longer baselines, they have a higher sensitivity to planetary photons at the expense of a more challenging data reduction in terms of long-term stability. In this work, we introduce a novel non-parametric algorithm dubbed phasma to produce clean, robust exoplanet phase curves and apply it to 115 Neptunian and 50 Terran exoplanets observed by kepler. We stack the signals to further improve signal-to-noise, and measure an average Neptunian albedo of Ag < 0.23 to 95% confidence, indicating a lack of bright clouds consistent with theoretical models. Our Terran sample provides the first constraint on the ensemble albedo of exoplanets which are most likely solid, constraining Ag < 0.42 to 95% confidence. In agreement with our constraint on the greenhouse effect, our work implies that kepler's solid planets are unlikely to resemble cloudy Venusian analogs, but rather dark Mercurian rocks.

Weak localization of electromagnetic waves and opposition phenomena exhibited by high-albedo atmosphereless solar system objects.

PubMed

Mishchenko, Michael I; Rosenbush, Vera K; Kiselev, Nikolai N

2006-06-20

The totality of new and previous optical observations of a class of high-albedo solar system objects at small phase angles reveals a unique combination of extremely narrow brightness and polarization features centered at exactly the opposition. The specific morphological parameters of these features provide an almost unequivocal evidence that they are caused by the renowned effect of coherent backscattering.

VIS and NIR land surface albedo sensitivity of the Ent Terrestrial Biosphere Model to forcing leaf area index

NASA Astrophysics Data System (ADS)

Montes, C.; Kiang, N. Y.; Ni-Meister, W.; Yang, W.; Schaaf, C.; Aleinov, I. D.; Jonas, J.; Zhao, F. A.; Yao, T.; Wang, Z.; Sun, Q.; Carrer, D.

2016-12-01

Land surface albedo is a major controlling factor in vegetation-atmosphere transfers, modifying the components of the energy budget, the ecosystem productivity and patterns of regional and global climate. General Circulation Models (GCMs) are coupled to Dynamic Global Vegetation Models (DGVMs) to solve vegetation albedo by using simple schemes prescribing albedo based on vegetation classification, and approximations of canopy radiation transport for multiple plant functional types (PFTs). In this work, we aim at evaluating the sensitivity of the NASA Ent Terrestrial Biosphere Model (TBM), a demographic DGVM coupled to the NASA Goddard Institute for Space Studies (GISS) GCM, in estimating VIS and NIR surface albedo by using variable forcing leaf area index (LAI). The Ent TBM utilizes a new Global Vegetation Structure Dataset (GVSD) to account for geographically varying vegetation tree heights and densities, as boundary conditions to the gap-probability based Analytical Clumped Two-Stream (ACTS) canopy radiative transfer scheme (Ni-Meister et al., 2010). Land surface and vegetation characteristics for the Ent GVSD are obtained from a number of earth observation platforms and algorithms, including the Moderate Resolution Imaging Spectroradiometer (MODIS) land cover and plant functional types (PFTs) (Friedl et al., 2010), soil albedo derived from MODIS (Carrer et al., 2014), and vegetation height from the Geoscience Laser Altimeter System (GLAS) on board ICESat (Ice, Cloud, and land Elevation Satellite) (Simard et al., 2011; Tang et al., 2014). Three LAI products are used as input to ACTS/Ent TBM: MODIS MOD15A2H product (Yang et al., 2006), Beijing Normal University LAI (Yuan et al., 2011), and Global Data Sets of Vegetation (LAI3g) (Zhu et al. 2013). The sensitivity of the Ent TBM VIS and NIR albedo to the three LAI products is assessed, compared against the previous GISS GCM vegetation classification and prescribed Lambertian albedoes (Matthews, 1984), and against MODIS snow-free black-sky and white-sky albedo estimates. In addition, we test the sensitivity of the Ent/ACTS albedo to different sets of leaf spectral albedos derived from the literature.

Are the circular, dark features on Comet Borrelly's surface albedo variations or pits?

USGS Publications Warehouse

Nelson, R.M.; Soderblom, L.A.; Hapke, B.W.

2004-01-01

The highest resolution images of Comet 19P/Borrelly show many dark features which, upon casual inspection, appear to be low albedo markings, but which may also be shadows or other photometric variations caused by a depression in the local topography. In order to distinguish between these two possible interpretations we conducted a photometric analysis of three of the most prominent of these features using six of the highest quality images from the September 22, 2001 Deep Space 1 (DS1) flyby. We find that: 1. The radiance in the darkest parts of each feature increases as phase angle decreases, similarly to the radiance behavior of the higher albedo surrounding terrain. The dark features could be either fully illuminated low albedo spots or, alternatively, they could be depressions. No part of any of the three regions was in full shadow. 2. One of the regions has a radiance profile consistent with a rimmed depression, the second, with a simple depression with no rim, and the third with a low albedo spot. 3. The regolith particles are backscattering and carbon black is one of the few candidate regolith materials that might explain this low albedo. We conclude that Borrelly's surface is geologically complex to the limit of resolution of the images with a combination complex topography, pits, troughs, peaks and ridges, and some very dark albedo markings, perhaps a factor of two to three darker than the average 3-4% albedo of the surrounding terrains. Our technique utilizing measured radiance profiles through the dark regions is able to discriminate between rimmed depressions, rimless depressions and simple albedo changes not associated with topography. ?? 2003 Elsevier Inc. All rights reserved.

Resolved spectrophotometric properties of the Ceres surface from Dawn Framing Camera images

NASA Astrophysics Data System (ADS)

Schröder, S. E.; Mottola, S.; Carsenty, U.; Ciarniello, M.; Jaumann, R.; Li, J.-Y.; Longobardo, A.; Palmer, E.; Pieters, C.; Preusker, F.; Raymond, C. A.; Russell, C. T.

2017-05-01

We present a global spectrophotometric characterization of the Ceres surface using Dawn Framing Camera (FC) images. We identify the photometric model that yields the best results for photometrically correcting images. Corrected FC images acquired on approach to Ceres were assembled into global maps of albedo and color. Generally, albedo and color variations on Ceres are muted. The albedo map is dominated by a large, circular feature in Vendimia Planitia, known from HST images (Li et al., 2006), and dotted by smaller bright features mostly associated with fresh-looking craters. The dominant color variation over the surface is represented by the presence of "blue" material in and around such craters, which has a negative spectral slope over the visible wavelength range when compared to average terrain. We also mapped variations of the phase curve by employing an exponential photometric model, a technique previously applied to asteroid Vesta (Schröder et al., 2013b). The surface of Ceres scatters light differently from Vesta in the sense that the ejecta of several fresh-looking craters may be physically smooth rather than rough. High albedo, blue color, and physical smoothness all appear to be indicators of youth. The blue color may result from the desiccation of ejected material that is similar to the phyllosilicates/water ice mixtures in the experiments of Poch et al. (2016). The physical smoothness of some blue terrains would be consistent with an initially liquid condition, perhaps as a consequence of impact melting of subsurface water ice. We find red terrain (positive spectral slope) near Ernutet crater, where De Sanctis et al. (2017) detected organic material. The spectrophotometric properties of the large Vendimia Planitia feature suggest it is a palimpsest, consistent with the Marchi et al. (2016) impact basin hypothesis. The central bright area in Occator crater, Cerealia Facula, is the brightest on Ceres with an average visual normal albedo of about 0.6 at a resolution of 1.3 km per pixel (six times Ceres average). The albedo of fresh, bright material seen inside this area in the highest resolution images (35 m per pixel) is probably around unity. Cerealia Facula has an unusually steep phase function, which may be due to unresolved topography, high surface roughness, or large average particle size. It has a strongly red spectrum whereas the neighboring, less-bright, Vinalia Faculae are neutral in color. We find no evidence for a diurnal ground fog-type haze in Occator as described by Nathues et al. (2015). We can neither reproduce their findings using the same images, nor confirm them using higher resolution images. FC images have not yet offered direct evidence for present sublimation in Occator.

Albedo, Land Cover, and Daytime Surface Temperature Variation Across an Urbanized Landscape

NASA Astrophysics Data System (ADS)

Trlica, A.; Hutyra, L. R.; Schaaf, C. L.; Erb, A.; Wang, J. A.

2017-11-01

Land surface albedo is a key parameter controlling the local energy budget, and altering the albedo of built surfaces has been proposed as a tool to mitigate high near-surface temperatures in the urban heat island. However, most research on albedo in urban landscapes has used coarse-resolution data, and few studies have attempted to relate albedo to other urban land cover characteristics. This study provides an empirical description of urban summertime albedo using 30 m remote sensing measurements in the metropolitan area around Boston, Massachusetts, relating albedo to metrics of impervious cover fraction, tree canopy coverage, population density, and land surface temperature (LST). At 30 m spatial resolution, median albedo over the study area (excluding open water) was 0.152 (0.112-0.187). Trends of lower albedo with increasing urbanization metrics and temperature emerged only after aggregating data to 500 m or the boundaries of individual towns, at which scale a -0.01 change in albedo was associated with a 29 (25-35)% decrease in canopy cover, a 27 (24-30)% increase in impervious cover, and an increase in population from 11 to 386 km-2. The most intensively urbanized towns in the region showed albedo up to 0.035 lower than the least urbanized towns, and mean mid-morning LST 12.6°C higher. Trends in albedo derived from 500 m Moderate Resolution Imaging Spectroradiometer (MODIS) measurements were comparable, but indicated a strong contribution of open water at this coarser resolution. These results reveal linkages between albedo and urban land cover character, and offer empirical context for climate resilient planning and future landscape functional changes with urbanization.

Re-analysis of previous laboratory phase curves: 1. Variations of the opposition effect morphology with the textural properties, and an application to planetary surfaces

NASA Astrophysics Data System (ADS)

Déau, Estelle; Flandes, Alberto; Spilker, Linda J.; Petazzoni, Jérôme

2013-11-01

Typical variations in the opposition effect morphology of laboratory samples at optical wavelengths are investigated to probe the role of the textural properties of the surface (roughness, porosity and grain size). A previously published dataset of 34 laboratory phase curves is re-analyzed and fit with several morphological models. The retrieved morphological parameters that characterize the opposition surge, amplitude, width and slope (A, HWHM and S respectively) are correlated to the single scattering albedo, the roughness, the porosity and the grain size of the samples. To test the universality of the laboratory samples’ trends, we use previously published phase curves of planetary surfaces, including the Moon, satellites and rings of the giant planets. The morphological parameters of the surge (A and HWHM) for planetary surfaces are found to have a non-monotonic variation with the single scattering albedo, similar to that observed in asteroids (Belskaya, I.N., Shevchenko, V.G. [2000]. Icarus 147, 94-105), which is unexplained so far. The morphological parameters of the surge (A and HWHM) for laboratory samples seem to exhibit the same non-monotonic variation with single scattering albedo. While the non-monotonic variation with albedo was already observed by Nelson et al. (Nelson, R.M., Hapke, B.W., Smythe, W.D., Hale, A.S., Piatek, J.L. [2004]. Planetary regolith microstructure: An unexpected opposition effect result. In: Mackwell, S., Stansbery, E. (Eds.), Proc. Lunar Sci. Conf. 35, p. 1089), we report here the same variation for the angular width.

Tables of asymptotic directions, cutoff rigidities, and reentrant albedo calculations for Palestine, Dallas, and Midland, Texas. Special repts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shea, M.A.; Smart, D.F.

1974-03-26

Using the trajectory-tracing technique, the asymptotic directions and cut-off rigidities for Palestine, Dallas, amd Midland,Texas were calculated as a function of various zenith and azimuth angles. Continuation of the trajectory-tracing process below the Stormer cutoff allows an evaluation of the reentrant albedo; the invariant latitude of the guiding center of the trajectory at the albedo origin is seen to be the same as the invariant latitude of the guiding center of the particle trajectory at the specified zenith and azimuth angle of the detection point. Tables of asymptotic directions, cutoff rigidities, and the location of the reentrant albedo for eachmore » of these locations are given. Summaries of cutoff rigidity calculations as a function of zenith and azimuth directions for some miscellaneous locations are also included. (GRA)« less

A new look at photometry of the Moon

USGS Publications Warehouse

Goguen, J.D.; Stone, T.C.; Kieffer, H.H.; Buratti, B.J.

2010-01-01

We use ROLO photometry (Kieffer, H.H., Stone, T.C. [2005]. Astron. J. 129, 2887-2901) to characterize the before and after full Moon radiance variation for a typical highlands site and a typical mare site. Focusing on the phase angle range 45??. ) to calculate the scattering matrix and solve the radiative transfer equation for I/. F. The mean single scattering albedo is ??=0.808, the asymmetry parameter is ???cos. ?????=0.77 and the phase function is very strongly peaked in both the forward and backward scattering directions. The fit to the observations for the highland site is excellent and multiply scattered photons contribute 80% of I/. F. We conclude that either model, roughness or multiple scattering, can match the observations, but that the strongly anisotropic phase functions of realistic particles require rigorous calculation of many orders of scattering or spurious photometric roughness estimates are guaranteed. Our multiple scattering calculation is the first to combine: (1) a regolith model matched to the measured particle size distribution and index of refraction of the lunar soil, (2) a rigorous calculation of the particle phase function and solution of the radiative transfer equation, and (3) application to lunar photometry with absolute radiance calibration. ?? 2010 Elsevier Inc.

Multi-color, rotationally resolved photometry of asteroid 21 Lutetia from OSIRIS/Rosetta observations

NASA Astrophysics Data System (ADS)

Lamy, P. L.; Faury, G.; Jorda, L.; Kaasalainen, M.; Hviid, S. F.

2010-10-01

Context. Asteroid 21 Lutetia is the second target of the Rosetta space mission. Extensive pre-encounter, space-, and ground-based observations are being performed to prepare for the flyby in July 2010. Aims: The aim of this article is to accurately characterize the photometric properties of this asteroid over a broad spectral range from the ultraviolet to the near-infrared and to search for evidence of surface inhomogeneities. Methods: The asteroid was imaged on 2 and 3 January 2007 with the Narrow Angle Camera (NAC) of the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) during the cruise phase of the Rosetta spacecraft. The geometric conditions were such that the aspect angle was 44^circ (i.e., mid-northern latitudes) and the phase angle 22.4^circ. Lutetia was continuously monitored over 14.3 h, thus exceeding one rotational period and a half, with twelve filters whose spectral coverage extended from 271 to 986 nm. An accurate photometric calibration was obtained from the observations of a solar analog star, 16 Cyg B. Results: High-quality light curves in the U, B, V, R and I photometric bands were obtained. Once they were merged with previous light curves from over some 45 years, the sidereal period is accurately determined: Prot = 8.168271 ± 0.000002 h. Color variations with rotational phase are marginally detected with the ultraviolet filter centered at 368 nm but are absent in the other visible and near-infrared filters. The albedo is directly determined from the observed maximum cross-section obtained from an elaborated shape model that results from a combination of adaptive-optics imaging and light curve inversion. Using current solutions for the phase function, we find geometric albedos pV = 0.130 ± 0.014 when using the linear phase function and pV(H-G) = 0.180 ± 0.018 when using the (H-G) phase function, which incorporates the opposition effect. The spectral variation of the reflectance indicates a steady decrease with decreasing wavelength rather than a sharp fall-off. Photometric tables (Tables 4 to 8) are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/521/A19

On the definition of albedo and application to irregular particles

NASA Technical Reports Server (NTRS)

Hanner, M. S.; Giese, R. H.; Weiss, K.; Zerull, R.

1981-01-01

The various definitions of albedo used in planetary astronomy are reviewed. In particular, the Bond albedo, which refers only to the reflected and refracted components, is not applicable to small particles or highly irregular particles, where diffraction is not restricted to a well-defined lobe at small scattering angles. Measured scattering functions for irregular particles are presented in a normalized form and are applied to the case of zodiacal light.

Erratum: Voyager Color Photometry of Saturn's Main Rings

NASA Technical Reports Server (NTRS)

Estrada, Paul R.; Cuzzi, Jeffrey N.; Showalter, Mark R.; DeVincenzi, Donald (Technical Monitor)

2002-01-01

We correct a calibration error in our earlier analysis of Voyager color observations of Saturn's main rings at 14 deg phase angle and present thoroughly revised and reanalyzed radial profiles of the brightness of the main rings in Voyager G, V, and UV filters, and ratios of these brightnesses. These results are consistent with more recent HST results at 6 deg phase angle, once allowance is made for plausible phase reddening of the rings. Unfortunately, the Voyager camera calibration factors are simply not sufficiently well known for a combination of the Voyager and HST data to be used to constrain the phase reddening quantitatively. However, some interesting radial variations in reddening between 6-14 deg phase angles are hinted at. We update a ring-and-satellite color vs. albedo plot from Cuzzi and Estrada in several ways. The A and B rings are still found to be in a significantly redder part of color-albedo space than Saturn's icy satellites.

Discrete Angle Radiative Transfer in Uniform and Extremely Variable Clouds.

NASA Astrophysics Data System (ADS)

Gabriel, Philip Mitri

The transfer of radiant energy in highly inhomogeneous media is a difficult problem that is encountered in many geophysical applications. It is the purpose of this thesis to study some problems connected with the scattering of solar radiation in natural clouds. Extreme variability in the optical density of these clouds is often believed to occur regularly. In order to facilitate study of very inhomogeneous optical media such as clouds, the difficult angular part of radiative transfer calculations is simplified by considering a series of models in which conservative scattering only occurs in discrete directions. Analytic and numerical results for the radiative properties of these Discrete Angle Radiative Transfer (DART) systems are obtained in the limits of both optically thin and thick media. Specific results include: (a) In thick homogeneous media, the albedo (reflection coefficient), unlike the transmission, cannot be obtained by a diffusion equation. (b) With the aid of an exact analogy with an early model of conductor/superconductor mixtures, it is argued that inhomogeneous media with embedded holes, neither the transmission, nor the albedo can be described by diffusive random walks. (c) Using renormalization methods, it is shown that thin cloud behaviour is sensitive to the scattering phase functions since it is associated with a repelling fixed point, whereas, the thick cloud limit is universal in that it is phase function independent, and associated with an attracting fixed point. (d) In fractal media, the optical thickness required for a given albedo or transmission can differ by large factors from that required in the corresponding plane parallel geometry. The relevant scaling exponents have been calculated in a very simple example. (e) Important global meteorological and climatological implications of the above are discussed when applied to the scattering of visible light in clouds. In the remote sensing context, an analysis of satellite data reveals that augmenting a satellite's resolution reveals increasingly detailed structures that are found to occupy a decreasing fraction of the image, while simultaneously brightening to compensate. By systematically degrading the resolution of visible and infra red satellite cloud and surface data as well as radar rain data, resolution -independent co-dimension functions were defined which were useful in describing the spatial distribution of image features as well as the resolution dependence of the intensities themselves. The scale invariant functions so obtained fit into theoretically predicted functional forms. These multifractal techniques have implications for our ability to meaningfully estimate cloud brightness fraction, total cloud amount, as well as other remotely sensed quantities.

Weird planets and odd relations: Atmospheric Circulation on Hot Jupiters

NASA Astrophysics Data System (ADS)

Zhang, Michael; Knutson, Heather; Kataria, Tiffany; Burrows, Adam; Fortney, Jonathan

2018-01-01

We extract phase curves from Spitzer photometry for the highly irradiated hot Jupiter WASP-33b and the unusually dense Saturn-mass planet HD 149026b. To do so, we develop a new variant of Pixel Level Decorrelation that is effective at removing intrapixel sensitivity variations for long observations (> 10 hours) where the position of the star can vary by a significant fraction of a pixel. Using this algorithm, we derive eclipse depths, phase amplitudes, and phase offsets for both planets at 3.6 um and 4.5 um. We use a simple toy model to show that WASP-33b's phase offset, albedo, and heat recirculation efficiency are largely similar to those of other hot Jupiters despite its very high irradiation. On the other hand, our fits for HD 149026b prefer a very high albedo and an unusually high recirculation efficiency. We also compare our results to predictions from GCM models, and find that while neither provide a good match to the data, the discrepancies for HD 149026b are unusually large. We speculate that this may be related to its high bulk metallicity, which could lead to enhanced atmospheric opacities and the formation of reflective cloud layers in localized regions of the atmosphere. We then place these two planets in a broader context by exploring relationships between the temperatures, albedos, efficiencies, and phase offsets of all planets with published thermal phase curves. We find a striking relationship between phase offset and irradiation temperature--the former dips with temperature until around 3300 K, and rises thereafter. Although some aspects of this trend are mirrored in GCM models, there are notable differences that provide important clues for future modeling efforts.

New Horizons High-Phase Observations of Distant Kuiper Belt Objects

NASA Astrophysics Data System (ADS)

Verbiscer, A.; Porter, S.; Spencer, J. R.; Buie, M. W.; Benecchi, S.; Weaver, H. A., Jr.; Buratti, B. J.; Ennico Smith, K.; Olkin, C.; Stern, S. A.; Young, L. A.; Cheng, A. F.

2017-12-01

From its unique vantage point far from the Sun, NASA's New Horizons spacecraft has observed Kuiper Belt Objects at separations ranging from 0.1 to 70 AU, and at solar phase angles far larger than those attainable from Earth. We have constructed the first KBO solar phase curves with substantial phase angle coverage for targets including Haumea, Makemake, Quaoar, Arawn (Porter et al. 2016, Astrophys. J. Lett. 828, L15), and 2002 MS4. We compare the phase functions of these KBOs with those of objects in the Pluto system and other Solar System bodies such as comets, asteroids, and icy satellites. For KBOs with known geometric albedos, these measurements enable calculation of the phase integral, an important photometric property that characterizes the energy balance on a distant KBO surface. During its approach to 2014 MU69, and following its close encounter on 1 January 2019, New Horizons will continue to exploit its capabilities as NASA's only observatory within the Kuiper Belt itself.

Analytic expressions for the black-sky and white-sky albedos of the cosine lobe model.

PubMed

Goodin, Christopher

2013-05-01

The cosine lobe model is a bidirectional reflectance distribution function (BRDF) that is commonly used in computer graphics to model specular reflections. The model is both simple and physically plausible, but physical quantities such as albedo have not been related to the parameterization of the model. In this paper, analytic expressions for calculating the black-sky and white-sky albedos from the cosine lobe BRDF model with integer exponents will be derived, to the author's knowledge for the first time. These expressions for albedo can be used to place constraints on physics-based simulations of radiative transfer such as high-fidelity ray-tracing simulations.

Asymmetry of reflective properties of the hemispheres of Jupiter satellite Europa

NASA Astrophysics Data System (ADS)

Vidmachenko, Anatoliy; Morozhenko, A.; Klyanchin, A.; Shavlovskiy, V.; Ivanov, Yu.; Kostogryz, N.

2011-12-01

Rotation around the central planet of Europa is synchronous. Leading hemisphere - is much brighter and less polluted by "no ice" material than the trailing one. The high albedo of the satellite may indicates that the ice on the surface is clean enough and is formed recently: 1,5-30 million years ago. Comparison of surface images of spacecrafts "Voyager" and "Galileo" with a low spatial resolution did not detect any significant changes during 20 years. But a detailed analysis of observational data with high resolution points to a number of features on the surface, which may indicate a change in the geological structures during this time. Spectral geometric albedo in the wavelength range 346-750 nm of leading and trailing hemispheres of Galilean satellites were defined using of our spectral observations in 2009 and 2010 and the observations of the other authors at different values of orbital and solar phase angles. The high geometric albedo in the red region of Io and Europa spectrum are confirmed; albedo of Io decreases sharply with decreasing of wavelength for ? < 500 nm; albedo of Ganymede and Callisto - reduced smoothly; albedo of Europa - have an intermediate gradient of reduction. Such behavior of the spectral variation of Europa surface albedo can be explained by deposition of sulfur from Io. Moreover, the sulfur absorption is more strongly on the trailing hemisphere. This indicates that the sulfur on the leading hemisphere is "processed" by meteoritic bombardment much faster and is gone to the the sub-surface regolith layer.

Columnar aerosol properties over oceans by combining surface and aircraft measurements: sensitivity analysis.

PubMed

Zhang, T; Gordon, H R

1997-04-20

We report a sensitivity analysis for the algorithm presented by Gordon and Zhang [Appl. Opt. 34, 5552 (1995)] for inverting the radiance exiting the top and bottom of the atmosphere to yield the aerosol-scattering phase function [P(?)] and single-scattering albedo (omega(0)). The study of the algorithm's sensitivity to radiometric calibration errors, mean-zero instrument noise, sea-surface roughness, the curvature of the Earth's atmosphere, the polarization of the light field, and incorrect assumptions regarding the vertical structure of the atmosphere, indicates that the retrieved omega(0) has excellent stability even for very large values (~2) of the aerosol optical thickness; however, the error in the retrieved P(?) strongly depends on the measurement error and on the assumptions made in the retrieval algorithm. The retrieved phase functions in the blue are usually poor compared with those in the near infrared.

Derivation and Application of a Global Albedo yielding an Optical Brightness To Physical Size Transformation Free of Systematic Errors

NASA Technical Reports Server (NTRS)

Mulrooney, Dr. Mark K.; Matney, Dr. Mark J.

2007-01-01

Orbital object data acquired via optical telescopes can play a crucial role in accurately defining the space environment. Radar systems probe the characteristics of small debris by measuring the reflected electromagnetic energy from an object of the same order of size as the wavelength of the radiation. This signal is affected by electrical conductivity of the bulk of the debris object, as well as its shape and orientation. Optical measurements use reflected solar radiation with wavelengths much smaller than the size of the objects. Just as with radar, the shape and orientation of an object are important, but we only need to consider the surface electrical properties of the debris material (i.e., the surface albedo), not the bulk electromagnetic properties. As a result, these two methods are complementary in that they measure somewhat independent physical properties to estimate the same thing, debris size. Short arc optical observations such as are typical of NASA's Liquid Mirror Telescope (LMT) give enough information to estimate an Assumed Circular Orbit (ACO) and an associated range. This information, combined with the apparent magnitude, can be used to estimate an "absolute" brightness (scaled to a fixed range and phase angle). This absolute magnitude is what is used to estimate debris size. However, the shape and surface albedo effects make the size estimates subject to systematic and random errors, such that it is impossible to ascertain the size of an individual object with any certainty. However, as has been shown with radar debris measurements, that does not preclude the ability to estimate the size distribution of a number of objects statistically. After systematic errors have been eliminated (range errors, phase function assumptions, photometry) there remains a random geometric albedo distribution that relates object size to absolute magnitude. Measurements by the LMT of a subset of tracked debris objects with sizes estimated from their radar cross sections indicate that the random variations in the albedo follow a log-normal distribution quite well. In addition, this distribution appears to be independent of object size over a considerable range in size. Note that this relation appears to hold for debris only, where the shapes and other properties are not primarily the result of human manufacture, but of random processes. With this information in hand, it now becomes possible to estimate the actual size distribution we are sampling from. We have identified two characteristics of the space debris population that make this process tractable and by extension have developed a methodology for performing the transformation.

Analysis of Snow Bidirectional Reflectance from ARCTAS Spring-2008 Campaign

NASA Technical Reports Server (NTRS)

Lyapustin, A.; Gatebe, C. K.; Redemann, J.; Kahn, R.; Brandt, R.; Russell, P.; King, M. D.; Pedersen, C. A.; Gerland, S.; Poudyal, R.;

Improving ROLO lunar albedo model using PLEIADES-HR satellites extra-terrestrial observations

NASA Astrophysics Data System (ADS)

Meygret, Aimé; Blanchet, Gwendoline; Colzy, Stéphane; Gross-Colzy, Lydwine

2017-09-01

The accurate on orbit radiometric calibration of optical sensors has become a challenge for space agencies which have developed different technics involving on-board calibration systems, ground targets or extra-terrestrial targets. The combination of different approaches and targets is recommended whenever possible and necessary to reach or demonstrate a high accuracy. Among these calibration targets, the moon is widely used through the well-known ROLO (RObotic Lunar Observatory) model developed by USGS. A great and worldwide recognized work was done to characterize the moon albedo which is very stable. However the more and more demanding needs for calibration accuracy have reached the limitations of the model. This paper deals with two mains limitations: the residual error when modelling the phase angle dependency and the absolute accuracy of the model which is no more acceptable for the on orbit calibration of radiometers. Thanks to PLEIADES high resolution satellites agility, a significant data base of moon and stars images was acquired, allowing to show the limitations of ROLO model and to characterize the errors. The phase angle residual dependency is modelled using PLEIADES 1B images acquired for different quasi-complete moon cycles with a phase angle varying by less than 1°. The absolute albedo residual error is modelled using PLEIADES 1A images taken over stars and the moon. The accurate knowledge of the stars spectral irradiance is transferred to the moon spectral albedo using the satellite as a transfer radiometer. This paper describes the data set used, the ROLO model residual errors and their modelling, the quality of the proposed correction and show some calibration results using this improved model.

Physical characterization of Warm Spitzer-observed near-Earth objects

NASA Astrophysics Data System (ADS)

Thomas, Cristina A.; Emery, Joshua P.; Trilling, David E.; Delbó, Marco; Hora, Joseph L.; Mueller, Michael

2014-01-01

Near-infrared spectroscopy of Near-Earth Objects (NEOs) connects diagnostic spectral features to specific surface mineralogies. The combination of spectroscopy with albedos and diameters derived from thermal infrared observations can increase the scientific return beyond that of the individual datasets. For instance, some taxonomic classes can be separated into distinct compositional groupings with albedo and different mineralogies with similar albedos can be distinguished with spectroscopy. To that end, we have completed a spectroscopic observing campaign to complement the ExploreNEOs Warm Spitzer program that obtained albedos and diameters of nearly 600 NEOs (Trilling, D.E. et al. [2010]. Astron. J. 140, 770-784. http://dx.doi.org/10.1088/0004-6256/140/3/770). The spectroscopy campaign included visible and near-infrared observations of ExploreNEOs targets from various observatories. Here we present the results of observations using the low-resolution prism mode (˜0.7-2.5 μm) of the SpeX instrument on the NASA Infrared Telescope Facility (IRTF). We also include near-infrared observations of ExploreNEOs targets from the MIT-UH-IRTF Joint Campaign for Spectral Reconnaissance. Our dataset includes near-infrared spectra of 187 ExploreNEOs targets (125 observations of 92 objects from our survey and 213 observations of 154 objects from the MIT survey). We identify a taxonomic class for each spectrum and use band parameter analysis to investigate the mineralogies for the S-, Q-, and V-complex objects. Our analysis suggests that for spectra that contain near-infrared data but lack the visible wavelength region, the Bus-DeMeo system misidentifies some S-types as Q-types. We find no correlation between spectral band parameters and ExploreNEOs albedos and diameters. We investigate the correlations of phase angle with Band Area Ratio and near-infrared spectral slope. We find slightly negative Band Area Ratio (BAR) correlations with phase angle for Eros and Ivar, but a positive BAR correlation with phase angle for Ganymed. The results of our phase angle study are consistent with those of (Sanchez, J.A., Reddy, V., Nathues, A., Cloutis, E.A., Mann, P., Hiesinger, H. [2012]. Icarus 220, 36-50. http://dx.doi.org/10.1016/j.icarus.2012.04.008, arXiv:1205.0248). We find evidence for spectral phase reddening for Eros, Ganymed, and Ivar. We identify the likely ordinary chondrite type analog for an appropriate subset of our sample. Our resulting proportions of H, L, and LL ordinary chondrites differ from those calculated for meteorite falls and in previous studies of ordinary chondrite-like NEOs.

Enhancement of the MODIS Daily Snow Albedo Product

NASA Technical Reports Server (NTRS)

Hall, Dorothy K.; Schaaf, Crystal B.; Wang, Zhuosen; Riggs, George A.

2009-01-01

The MODIS daily snow albedo product is a data layer in the MOD10A1 snow-cover product that includes snow-covered area and fractional snow cover as well as quality information and other metadata. It was developed to augment the MODIS BRDF/Albedo algorithm (MCD43) that provides 16-day maps of albedo globally at 500-m resolution. But many modelers require daily snow albedo, especially during the snowmelt season when the snow albedo is changing rapidly. Many models have an unrealistic snow albedo feedback in both estimated albedo and change in albedo over the seasonal cycle context, Rapid changes in snow cover extent or brightness challenge the MCD43 algorithm; over a 16-day period, MCD43 determines whether the majority of clear observations was snow-covered or snow-free then only calculates albedo for the majority condition. Thus changes in snow albedo and snow cover are not portrayed accurately during times of rapid change, therefore the current MCD43 product is not ideal for snow work. The MODIS daily snow albedo from the MOD10 product provides more frequent, though less robust maps for pixels defined as "snow" by the MODIS snow-cover algorithm. Though useful, the daily snow albedo product can be improved using a daily version of the MCD43 product as described in this paper. There are important limitations to the MOD10A1 daily snow albedo product, some of which can be mitigated. Utilizing the appropriate per-pixel Bidirectional Reflectance Distribution Functions (BRDFs) can be problematic, and correction for anisotropic scattering must be included. The BRDF describes how the reflectance varies with view and illumination geometry. Also, narrow-to-broadband conversion specific for snow on different surfaces must be calculated and this can be difficult. In consideration of these limitations of MOD10A1, we are planning to improve the daily snow albedo algorithm by coupling the periodic per-pixel snow albedo from MCD43, with daily surface ref|outanoom, In this paper, we compare a daily version of MCD43B3 with the daily albedo from MOD10A1. and MCD43B3 with a 16-day average of MOD10A1, over Greenland. We also discuss some near-future planned enhancements to MOD10A1.

Albedo of an irradiated plane-parallel atmosphere with finite optical depth

NASA Astrophysics Data System (ADS)

Fukue, Jun

2018-03-01

We analytically derive albedo for a plane-parallel atmosphere with finite optical depth, irradiated by an external source, under the local thermodynamic equilibrium approximation. Albedo is expressed as a function of the photon destruction probability ɛ and optical depth τ, with several parameters such as dilution factors of the external source. In the particular case of the infinite optical depth, albedo A is expressed as A=[1 + (1-W_J/W_H)√{3ɛ}/3]/(1+√{3ɛ}), where WJ and WH are the dilution factors for the mean intensity and Eddington flux, respectively. An example of a model atmosphere is also presented under a gray approximation.

Investigation of Titan's surface and atmosphere photometric functions using the Cassini/VIMS instrument

NASA Astrophysics Data System (ADS)

Cornet, Thomas; Altobelli, Nicolas; Rodriguez, Sébastien; Maltagliati, Luca; Le Mouélic, Stéphane; Sotin, Christophe; Brown, Robert; Barnes, Jason; Buratti, Bonnie; Baines, Kevin; Clark, Roger; Nicholson, Phillip

2015-04-01

After 106 flybys spread over 10 years, the Cassini Visual and Infrared Mapping Spectrometer (VIMS) instrument acquired 33151 hyperspectral cubes pointing at the surface of Titan on the dayside. Despite this huge amount of data available for surface studies, and due to the strong influence of the atmosphere (methane absorption and haze scattering), Titan's surface is only visible with VIMS in 7 spectral atmospheric windows centred at 0.93, 1.08, 1.27, 1.59, 2.01, 2.7-2.8 and 5 microns. Atmospheric scattering and absorption effects dominate Titan's spectrum at wavelengths shorter than 3 microns, while the 5 micron window, almost insensitive to the haze scattering, only presents a reduced atmospheric absorption contribution to the signal recorded by VIMS. In all cases, the recorded I/F represents an apparent albedo, which depends on the atmospheric contributions and the surface photometry at each wavelength. We therefore aim to determine real albedo values for Titan's surface by finding photometric functions for the surface and the atmosphere that could be used as a basis for empirical corrections or Radiative Transfer calculations. After updating the navigation of the VIMS archive, we decomposed the entire VIMS data set into a MySQL relational database gathering the viewing geometry, location, time (season) and I/F (for pure atmosphere and surface-atmosphere images) for each pixel of the 33151 individual VIMS cubes. We then isolated all the VIMS pixels where Titan's surface has been repeatedly imaged at low phase angles (< 20 degrees) in order to characterize phase curves for the surface at 5 microns and for the atmosphere. Among these, the T88 flyby appears noteworthy, with a "Emergence-Phase Function (EPF)"-type observation: 25 cubes acquired during the same flyby, over the same area (close to Tortola Facula, in relatively dark terrains), at a constant incidence and with varying emergence and phase (from 0 to 60 degrees) angles. The data clearly exhibit an increase of I/F at 5 microns at very low phase angles, which is indicative of an opposition effect for the surface, and kinks in the I/F at low and high emergence/phase angles, increasing with decreasing wavelength (and thus with increasing atmospheric scattering). The latter dependency is present in both pure atmosphere and surface-atmosphere images, which clearly indicates that it is of atmospheric origin. We are currently investigating these dependencies with angles and try to determine best fit models that would describe the phase curves for the surface at 5 microns and for the atmosphere at lower wavelengths in this particular area.

Albedo climatology for European land surfaces retrieved from AVHRR data (1990-2014) and its spatial and temporal analysis from green-up to vegetation senescence

NASA Astrophysics Data System (ADS)

Sütterlin, M.; Stöckli, R.; Schaaf, C. B.; Wunderle, S.

2016-07-01

Satellite-based, long-term records of surface albedo characterization that accurately capture spatial and temporal patterns are essential to develop climate models and to monitor the impact of land use changes on the terrestrial energy and water balance. This study presents the first Bidirectional Reflectance Distribution Function (BRDF) and albedo data set derived from the Advanced Very High Resolution Radiometer (AVHRR) Local Area Coverage reflectance data acquired on board National Oceanic and Atmospheric Administration and Meteorological Operational platforms from 1990 to 2014 over Europe. The objectives of this paper are to describe the data set's surface albedo climatology and anomalies in the visible, near-infrared, and shortwave broadbands for the growing season months of May to September in order to facilitate utilization of the data by the climate modeling communities. The results demonstrate that the AVHRR BRDF and albedo data have temporal and spatial patterns that are appropriate for the underlying predominant land cover type and accurately reflect the associated climate variation. Visible and near-infrared broadband albedo anomalies are found to be contrasting in most years, and their spatial distributions depict responses of vegetation to climate events (e.g., heat waves). Visible albedo of crops and near-infrared albedo of pastures show a higher interannual variation than respective albedos of other snow-free land covers, while the interannual standard deviations are found to be lower than 0.015. Our findings indicate the importance of taking into account the spectrally distinct variability of surface albedo when analyzing its complex spatiotemporal dynamics in climate-related research.

Revised albedos of Trojan asteroids (911) Agamemnon and (4709) Ennomos

NASA Astrophysics Data System (ADS)

Shevchenko, V. G.; Slyusarev, I. G.; Belskaya, I. N.

2014-01-01

CCD-photometry was performed for two Jupiter Trojan asteroids (911) Agamemnon and (4709) Ennomos for which the diameters were obtained from occultation events. New data on rotation periods, lightcurve amplitudes, color indices, magnitude-phase slopes, and absolute magnitudes were obtained for these asteroids. We have used the diameters from occultations (166 and 99 km) and new data on absolute magnitudes at the instant occultation (7.95 and 8.85 mag) to revise their albedos to 0.042 (911 Agamemnon) and 0.052 (4709 Ennomos).

Photometric normalization of LROC WAC images

NASA Astrophysics Data System (ADS)

Sato, H.; Denevi, B.; Robinson, M. S.; Hapke, B. W.; McEwen, A. S.; LROC Science Team

2010-12-01

The Lunar Reconnaissance Orbiter Camera (LROC) Wide Angle Camera (WAC) acquires near global coverage on a monthly basis. The WAC is a push frame sensor with a 90° field of view (FOV) in BW mode and 60° FOV in 7-color mode (320 nm to 689 nm). WAC images are acquired during each orbit in 10° latitude segments with cross track coverage of ~50 km. Before mosaicking, WAC images are radiometrically calibrated to remove instrumental artifacts and to convert at sensor radiance to I/F. Images are also photometrically normalized to common viewing and illumination angles (30° phase), a challenge due to the wide angle nature of the WAC where large differences in phase angle are observed in a single image line (±30°). During a single month the equatorial incidence angle drifts about 28° and over the course of ~1 year the lighting completes a 360° cycle. The light scattering properties of the lunar surface depend on incidence(i), emission(e), and phase(p) angles as well as soil properties such as single-scattering albedo and roughness that vary with terrain type and state of maturity [1]. We first tested a Lommel-Seeliger Correction (LSC) [cos(i)/(cos(i) + cos(e))] [2] with a phase function defined by an exponential decay plus 4th order polynomial term [3] which did not provide an adequate solution. Next we employed a LSC with an exponential 2nd order decay phase correction that was an improvement, but still exhibited unacceptable frame-to-frame residuals. In both cases we fitted the LSC I/F vs. phase angle to derive the phase corrections. To date, the best results are with a lunar-lambert function [4] with exponential 2nd order decay phase correction (LLEXP2) [(A1exp(B1p)+A2exp(B2p)+A3) * cos(i)/(cos(e) + cos(i)) + B3cos(i)]. We derived the parameters for the LLEXP2 from repeat imaging of a small region and then corrected that region with excellent results. When this correction was applied to the whole Moon the results were less than optimal - no surprise given the variability of the regolith from region to region. As the fitting area increases, the accuracy of curve fitting decreases due to the larger variety of albedo, topography, and composition. Thus we have adopted an albedo-dependent photometric normalization routine. Phase curves are derived for discreet bins of preliminary normalized reflectance calculated from Clementine global mosaic in a fitting area that is composed of predominantly mare in Oceanus Procellarum. The global WAC mosaic was then corrected pixel-by-pixel according to its preliminary reflectance map with satisfactory results. We observed that the phase curves per normalized-reflectance bins become steeper as the reflectance value increases. Further filtering by using FeO, TiO2, or optical maturity [5] for parameter calculations may help elucidate the effects of surface composition and maturity on photometric properties of the surface. [1] Hapke, B.W. (1993) Theory of Reflectance and Emittance Spectroscopy, Cambridge Univ. Press. [2] Schoenberg (1925) Ada. Soc. Febb., vol. 50. [3] Hillier et al. (1999) Icarus 141, 205-225. [4] McEwen (1991) Icarus 92, 298-311. [5] Lucey et al. (2000) JGR, v105, no E8, p20377-20386.

LUCHS - an approach to introduce Land Use Changes in a regional climate models by using EO data

NASA Astrophysics Data System (ADS)

Preuschmann, S.; Jacob, D.

2012-04-01

Changes in the albedo are influencing climate simulations, which is shown by the results of e.g.: Pongratz et al. (2009), Preuschmann and Jacob (2008), Rechid and Jacob (2006), Vamborg et al. (2011). To investigate the land atmosphere interaction for regional aspects, the lower boundary description for climate models should be able to represent a realistic seasonal cycle of the physical attributed parameters, as albedo, Leaf Area Index and vegetation ratio. The description of the lower boundary for the REgional MOdel REMO has discrepancies for the albedo seasonal cycle. In comparison to satellite observation data, the amplitude and phase of the albedo climatology are showing a too homogeneous pattern. Additionally in case of land use change studies, the parametrization scheme is mixing different constant data sets. Changes in one of them can lead to unexpected values. These aspects are demanding a new approach instead of an adaptation of representing the lower boundary for REMO. A new approach called Land Use CHaracter Shifts (LUCHS), combines techniques of remote sensing techniques and climate modelling techniques. Land cover maps derived from satellite data, are used to get information for each land cover type. Therefore a characteristic albedo climatology gets extracted for every land cover type, which reflects exactly the regional dependent amplitude, phase and level of the seasonal albedo cycle. The extracted information is used as a master information. It is transferalbe onto areas, which are defined as extension areas. To keep regional specific conditions, an autochthonous information is integrated within the character shifting method. It results in a albedo distribution, which reflects characteristics of the transferred land cover type, and accounts implicitly to regional floral, soil and cultural specifications. LUCHS is not free of assumptions and uncertainties, but by using observations, it is reflects a realistic albedo. The observed information on characteristics is regionally specific but persistent in time. Therefore it is transferable through space and at least for ±50 years in time. Pongratz, J., T. Raddatz, C. H. Reick, M. Esch and M. Claussen (2009). Radiative forcing from anthropogenic land cover change since AD 800. Geophysical Research Letters, 36, L02709. Vamborg, F. S. E., V. Brovkin and M. Claussen (2011). The effect of a dynamic background albedo scheme on Sahel/Sahara precipitation during the mid-Holocene. Climate Of The Past, 7(1), 117-131. Preuschmann, S. and D. Jacob (2008). Sensitivity study for parameterization of woods in the regional climate model REMO. In Geophysical Research Abstracts, Vol. 10, EGU2008-A-08618, 2008 SRef-ID: 1607-7962/gra/EGU2008-A-08618 EGU General Assembly 2008.

Growing season carries stronger contributions to albedo dynamics on the Tibetan plateau

PubMed Central

2017-01-01

The Tibetan Plateau has experienced higher-than-global-average climate warming in recent decades, resulting in many significant changes in ecosystem structure and function. Among them is albedo, which bridges the causes and consequences of land surface processes and climate. The plateau is covered by snow/ice and vegetation in the non-growing season (nGS) and growing season (GS), respectively. Based on the MODIS products, we investigated snow/ice cover and vegetation greenness in relation to the spatiotemporal changes of albedo on the Tibetan Plateau from 2000 through 2013. A synchronous relationship was found between the change in GSNDVI and GSalbedo over time and across the Tibetan landscapes. We found that the annual average albedo had a decreasing trend, but that the albedo had slightly increased during the nGS and decreased during the GS. Across the landscapes, the nGSalbedo fluctuated in a synchronous pattern with snow/ice cover. Temporally, monthly snow/ice coverage also had a high correspondence with albedo, except in April and October. We detected clear dependencies of albedo on elevation. With the rise in altitude, the nGSalbedo decreased below 4000 m, but increased for elevations of 4500–5500 m. Above 5500 m, the nGSalbedo decreased, which was in accordance with the decreased amount of snow/ice coverage and the increased soil moisture on the plateau. More importantly, the decreasing albedo in the most recent decade appeared to be caused primarily by lowered growing season albedo. PMID:28886037

Growing season carries stronger contributions to albedo dynamics on the Tibetan plateau.

PubMed

Tian, Li; Chen, Jiquan; Zhang, Yangjian

2017-01-01

The Tibetan Plateau has experienced higher-than-global-average climate warming in recent decades, resulting in many significant changes in ecosystem structure and function. Among them is albedo, which bridges the causes and consequences of land surface processes and climate. The plateau is covered by snow/ice and vegetation in the non-growing season (nGS) and growing season (GS), respectively. Based on the MODIS products, we investigated snow/ice cover and vegetation greenness in relation to the spatiotemporal changes of albedo on the Tibetan Plateau from 2000 through 2013. A synchronous relationship was found between the change in GSNDVI and GSalbedo over time and across the Tibetan landscapes. We found that the annual average albedo had a decreasing trend, but that the albedo had slightly increased during the nGS and decreased during the GS. Across the landscapes, the nGSalbedo fluctuated in a synchronous pattern with snow/ice cover. Temporally, monthly snow/ice coverage also had a high correspondence with albedo, except in April and October. We detected clear dependencies of albedo on elevation. With the rise in altitude, the nGSalbedo decreased below 4000 m, but increased for elevations of 4500-5500 m. Above 5500 m, the nGSalbedo decreased, which was in accordance with the decreased amount of snow/ice coverage and the increased soil moisture on the plateau. More importantly, the decreasing albedo in the most recent decade appeared to be caused primarily by lowered growing season albedo.

Assessment of VIIRS daily BRDF/Albedo product using in situ measurement of SURFRAD sites and MODIS V006 daily BRDF/Albedo product

NASA Astrophysics Data System (ADS)

Liu, Y.; Wang, Z.; Sun, Q.; Schaaf, C.; Roman, M. O.

2014-12-01

Surface albedo is defined as the ratio of upwelling to downwelling radiative flux. It's important for understanding the global energy budget. Remote sensing albedo products provide global time continuous coverage to help capture global energy variability and change. The Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi-NPP satellite, launched on October 28, 2011, is aiming to provide continues data record with the MODerate resolution Imaging Spectroradiometer (MODIS), which has been providing Bidirectional Reflectance Distribution Function (BRDF)/Albedo product since 2000. By utilizing the same approach that was used for the most recently V006 daily MODIS BRDF/Albedo product, VIIRS has the ability to keep providing products for research and operational users. Validating albedo product of VIIRS using in situmeasured albedo can assure the quality for land surface climate and biosphere models, and comparing with MODIS product can assure time continues of BRDF/albedo product. The daily BRDF/Albedo product still uses 16-day period multispectral, cloud-cleared, atmospherically-corrected surface reflectances to fit the Ross-Thick/Li-Sparse-Reciprocal semi-empirical BRDF model. But the multiday observations are also weighted based on proximity to the production date in order to emphasis on that individual day. Surface Radiation Budget Network (SURFRAD) was established in 1993 through the support of NOAA's Office of Global Programs. In situ albedo was driven from downwelling and upwelling radiative flux measured from the towers. Fraction of diffuse sky light was calculated using the direct and diffuse solar recorded in the data. It was further used to translate VIIRS, MODIS black sky and white sky albedos into actual albedo at local solar noon. Results show that VIIRS, MODIS and in situ albedo agree well at SURFARD spatially representative sites. While the VIIRS surface reflectance, snow, and cloud algorithms are still undergoing revision, the result shows that VIIRS can provide comparable albedo products with MODIS. The accuracy of both products can meet the requirement for climate and biosphere models. In situ albedo also can be gained from Baseline Surface Radiation Network (BSRN), FLUXNET and Long Term Ecological Research network (LTER) etc., which will be used in future validation work.

Quantifying the missing link between forest albedo and productivity in the boreal zone

NASA Astrophysics Data System (ADS)

Hovi, Aarne; Liang, Jingjing; Korhonen, Lauri; Kobayashi, Hideki; Rautiainen, Miina

2016-11-01

Albedo and fraction of absorbed photosynthetically active radiation (FAPAR) determine the shortwave radiation balance and productivity of forests. Currently, the physical link between forest albedo and productivity is poorly understood, yet it is crucial for designing optimal forest management strategies for mitigating climate change. We investigated the relationships between boreal forest structure, albedo and FAPAR using a radiative transfer model called Forest Reflectance and Transmittance model FRT and extensive forest inventory data sets ranging from southern boreal forests to the northern tree line in Finland and Alaska (N = 1086 plots). The forests in the study areas vary widely in structure, species composition, and human interference, from intensively managed in Finland to natural growth in Alaska. We show that FAPAR of tree canopies (FAPARCAN) and albedo are tightly linked in boreal coniferous forests, but the relationship is weaker if the forest has broadleaved admixture, or if canopies have low leaf area and the composition of forest floor varies. Furthermore, the functional shape of the relationship between albedo and FAPARCAN depends on the angular distribution of incoming solar irradiance. We also show that forest floor can contribute to over 50 % of albedo or total ecosystem FAPAR. Based on our simulations, forest albedos can vary notably across the biome. Because of larger proportions of broadleaved trees, the studied plots in Alaska had higher albedo (0.141-0.184) than those in Finland (0.136-0.171) even though the albedo of pure coniferous forests was lower in Alaska. Our results reveal that variation in solar angle will need to be accounted for when evaluating climate effects of forest management in different latitudes. Furthermore, increasing the proportion of broadleaved trees in coniferous forests is the most important means of maximizing albedo without compromising productivity: based on our findings the potential of controlling forest density (i.e., basal area) to increase albedo may be limited compared to the effect of favoring broadleaved species.

The global blue-sky albedo change between 2000 - 2015 seen from MODIS

NASA Astrophysics Data System (ADS)

Chrysoulakis, N.; Mitraka, Z.; Gorelick, N.

2016-12-01

The land surface albedo is a critical physical variable, which influences the Earth's climate by affecting the energy budget and distribution in the Earth-atmosphere system. Blue-sky albedo estimates provide a quantitative means for better constraining global and regional scale climate models. The Moderate Resolution Imaging Spectroradiometer (MODIS) albedo product includes parameters for the estimation of both the directional-hemispherical surface reflectance (black-sky albedo) and the bi-hemispherical surface reflectance (white-sky albedo). This dataset was used here for the blue-sky albedo estimation over the globe on an 8-day basis at 0.5 km spatial resolution for the whole time period covered by MODIS acquisitions (i.e. 2000 until today). To estimate the blue-sky albedo, the fraction of the diffused radiation is needed, a function of the Aerosol Optical Thickness (AOT). Required AOT information was acquired from the MODIS AOT product at 1̊ × 1̊ spatial resolution. Since the blue-sky albedo depends on the solar zenith angle (SZA), the 8-day mean blue-sky albedo values were computed as averages of the corresponding values for the representative SZAs covering the 24-hour day. The estimated blue-sky albedo time series was analyzed to capture changes during the 15 period. All computation were performed using the Google Earth Engine (GEE). The GEE provided access to all the MODIS products needed for the analysis without the need of searching or downloading. Moreover, the combination of MODIS products in both temporal and spatial terms was fast and effecting using the GEE API (Application Program Interface). All the products covering the globe and for the time period of 15 years were processed via a single collection. Most importantly, GEE allowed for including the calculation of SZAs covering the 24-hour day which improves the quality of the overall product. The 8-day global products of land surface albedo are available through http://www.rslab.gr/downloads.html

Bimodal albedo distributions in the ablation zone of the southwestern Greenland Ice Sheet

NASA Astrophysics Data System (ADS)

Moustafa, S. E.; Rennermalm, A. K.; Smith, L. C.; Miller, M. A.; Mioduszewski, J. R.

2014-09-01

Surface albedo is a key variable controlling solar radiation absorbed at the Greenland Ice Sheet (GrIS) surface, and thus, meltwater production. Recent decline in surface albedo over the GrIS has been linked to enhanced snow grain metamorphic rates and amplified ice-albedo feedback from atmospheric warming. However, the importance of distinct surface types on ablation zone albedo and meltwater production is still relatively unknown, and excluded in surface mass balance models. In this study, we analyze albedo and ablation rates using in situ and remotely-sensed data. Observations include: (1) a new high-quality in situ spectral albedo dataset collected with an Analytical Spectral Devices (ASD) spectroradiometer measuring at 325-1075 nm, along a 1.25 km transect during three days in June 2013; (2) broadband albedo at two automatic weather stations; and (3) daily MODerate Resolution Imaging Spectroradiometer (MODIS) albedo (MOD10A1) between 31 May and 30 August. We find that seasonal ablation zone albedos have a bimodal distribution, with two alternate states. This suggests that an abrupt switch from high to low albedo can be triggered by a modest melt event, resulting in amplified surface ablation rates. Our results show that such a shift corresponds to an observed melt rate percent difference increase of 51.6% during peak melt season (between 10-14 and 20-24 July 2013). Furthermore, our findings demonstrate that seasonal changes in GrIS ablation zone albedo are not exclusively a function of a darkening surface from ice crystal growth, but rather are controlled by changes in the fractional coverage of snow, bare ice, and impurity-rich surface types. As the climate continues to warm, regional climate models should consider the seasonal evolution of ice surface types in Greenland's ablation zone to improve projections of mass loss contributions to sea level rise.

Bimodal Albedo Distributions in the Ablation Zone of the Southwestern Greenland Ice Sheet

NASA Astrophysics Data System (ADS)

Moustafa, S.; Rennermalm, A. K.; Smith, L. C.; Miller, M. A.; Mioduszewski, J.; Koenig, L.

2014-12-01

Surface albedo is a key variable controlling solar radiation absorbed at the Greenland Ice Sheet (GrIS) surface, and thus meltwater production. Recent decline in surface albedo over the GrIS has been linked to enhanced snow grain metamorphic rates and amplified ice-albedo feedback from atmospheric warming. However, the importance of distinct surface types on ablation zone albedo and meltwater production is still relatively unknown, and excluded in surface mass balance models. In this study, we analyze albedo and ablation rates (m d-1) using in situ and remotely-sensed data. Observations include: 1) a new high-quality in situ spectral albedo dataset collected with an Analytical Spectral Devices (ASD) spectroradiometer measuring at 325-1075 nm, along a 1.25 km transect during three days in June 2013; 2) broadband albedo at two automatic weather stations; and 3) daily MODerate Resolution Imaging Spectroradiometer (MODIS) albedo (MOD10A1) between 31 May and 30 August. We find that seasonal ablation zone albedos have a bimodal distribution, with two alternate states. This suggests that an abrupt switch from high to low albedo can be triggered by a modest melt event, resulting in amplified ablation rates. Our results show that such a shift corresponds to an observed melt rate percent difference increase of 51.6% during peak melt season (between 10-14 July and 20-24 July, 2013). Furthermore, our findings demonstrate that seasonal changes in GrIS ablation zone albedo are not exclusively a function of a darkening surface from ice crystal growth, but rather are controlled by changes in the fractional coverage of snow, bare ice, and impurity-rich surface types. As the climate continues to warm, regional climate models should consider the seasonal evolution of ice surface types in Greenland's ablation zone to improve projections of mass loss contributions to sea level rise.

Evaluation of the VIIRS BRDF, Albedo and NBAR products suite and an assessment of continuity with the long term MODIS record

USDA-ARS?s Scientific Manuscript database

Bidirectional Reflectance Distribution Function (BRDF) model parameters, Albedo quantities, and Nadir BRDF Adjusted Reflectance (NBAR) products derived from the Visible Infrared Imaging Radiometer Suite (VIIRS), on the Suomi-NPP (National Polar-orbiting Partnership) satellite are evaluated through c...

Monitoring NEON terrestrial sites phenology with daily MODIS BRDF/albedo product and landsat data

USDA-ARS?s Scientific Manuscript database

The MODerate resolution Imaging Spectroradiometer (MODIS) Bidirectional Reflectance Distribution Function (BRDF) and albedo products (MCD43) have already been in production for more than a decade. The standard product makes use of a linear “kernel-driven” RossThick-LiSparse Reciprocal (RTLSR) BRDF m...

Evaluation of Moderate-Resolution Imaging Spectroradiometer (MODIS) Snow Albedo Product (MCD43A) over Tundra

NASA Technical Reports Server (NTRS)

Wang, Zhuosen; Schaaf, Crystal B.; Chopping, Mark J.; Strahler, Alan H.; Wang, Jindi; Roman, Miguel O.; Rocha, Adrian V.; Woodcock, Curtis E.; Shuai, Yanmin

2012-01-01

This study assesses the MODIS standard Bidirectional Reflectance Distribution Function (BRDF)/Albedo product, and the daily Direct Broadcast BRDF/Albedo algorithm at tundra locations under large solar zenith angles and high anisotropic diffuse illumination and multiple scattering conditions. These products generally agree with ground-based albedo measurements during the snow cover period when the Solar Zenith Angle (SZA) is less than 70deg. An integrated validation strategy, including analysis of the representativeness of the surface heterogeneity, is performed to decide whether direct comparisons between field measurements and 500- m satellite products were appropriate or if the scaling of finer spatial resolution airborne or spaceborne data was necessary. Results indicate that the Root Mean Square Errors (RMSEs) are less than 0.047 during the snow covered periods for all MCD43 albedo products at several Alaskan tundra areas. The MCD43 1- day daily albedo product is particularly well suited to capture the rapidly changing surface conditions during the spring snow melt. Results also show that a full expression of the blue sky albedo is necessary at these large SZA snow covered areas because of the effects of anisotropic diffuse illumination and multiple scattering. In tundra locations with dark residue as a result of fire, the MODIS albedo values are lower than those at the unburned site from the start of snowmelt.

Inversion Schemes to Retrieve Atmospheric and Oceanic Parameters from SeaWiFS Data

NASA Technical Reports Server (NTRS)

Frouin, Robert; Deschamps, Pierre-Yves

1997-01-01

Firstly, we have analyzed atmospheric transmittance and sky radiance data connected at the Scripps Institution of Oceanography pier, La Jolla during the winters of 1993 and 1994. Aerosol optical thickness at 870 nm was generally low in La Jolla, with most values below 0.1 after correction for stratospheric aerosols. For such low optical thickness, variability in aerosol scattering properties cannot be determined, and a mean background model, specified regionally under stable stratospheric component, may be sufficient for ocean color remote sensing, from space. For optical thicknesses above 0. 1, two modes of variability characterized by Angstrom exponents of 1.2 and 0.5 and corresponding, to Tropospheric and Maritime models, respectively, were identified in the measurements. The aerosol models selected for ocean color remote sensing, allowed one to fit, within measurement inaccuracies, the derived values of Angstrom exponent and 'pseudo' phase function (the product of single scattering albedo and phase function), key atmospheric correction parameters. Importantly, the 'pseudo' phase function can be derived from measurements of the Angstrom exponent. Shipborne sun photometer measurements at the time of satellite overpass are usually sufficient to verify atmospheric correction for ocean color.

Multi-modal albedo distributions in the ablation area of the southwestern Greenland Ice Sheet

NASA Astrophysics Data System (ADS)

Moustafa, S. E.; Rennermalm, A. K.; Smith, L. C.; Miller, M. A.; Mioduszewski, J. R.; Koenig, L. S.; Hom, M. G.; Shuman, C. A.

2015-05-01

Surface albedo is a key variable controlling solar radiation absorbed at the Greenland Ice Sheet (GrIS) surface and, thus, meltwater production. Recent decline in surface albedo over the GrIS has been linked to enhanced snow grain metamorphic rates, earlier snowmelt, and amplified melt-albedo feedback from atmospheric warming. However, the importance of distinct surface types on ablation area albedo and meltwater production is still relatively unknown. In this study, we analyze albedo and ablation rates using in situ and remotely sensed data. Observations include (1) a new high-quality in situ spectral albedo data set collected with an Analytical Spectral Devices Inc. spectroradiometer measuring at 325-1075 nm along a 1.25 km transect during 3 days in June 2013; (2) broadband albedo at two automatic weather stations; and (3) daily MODerate Resolution Imaging Spectroradiometer (MODIS) albedo (MOD10A1) between 31 May and 30 August 2012 and 2013. We find that seasonal ablation area albedos in 2013 have a bimodal distribution, with snow and ice facies characterizing the two peaks. Our results show that a shift from a distribution dominated by high to low albedos corresponds to an observed melt rate increase of 51.5% (between 10-14 July and 20-24 July 2013). In contrast, melt rate variability caused by albedo changes before and after this shift was much lower and varied between ~10 and 30% in the melting season. Ablation area albedos in 2012 exhibited a more complex multimodal distribution, reflecting a transition from light to dark-dominated surface, as well as sensitivity to the so called "dark-band" region in southwest Greenland. In addition to a darkening surface from ice crystal growth, our findings demonstrate that seasonal changes in GrIS ablation area albedos are controlled by changes in the fractional coverage of snow, bare ice, and impurity-rich surface types. Thus, seasonal variability in ablation area albedos appears to be regulated primarily as a function of bare ice expansion at the expense of snow, surface meltwater ponding, and melting of outcropped ice layers enriched with mineral materials, enabling dust and impurities to accumulate. As climate change continues in the Arctic region, understanding the seasonal evolution of ice sheet surface types in Greenland's ablation area is critical to improve projections of mass loss contributions to sea level rise.

Sun and aureole spectrometer for airborne measurements to derive aerosol optical properties.

PubMed

Asseng, Hagen; Ruhtz, Thomas; Fischer, Jürgen

2004-04-01

We have designed an airborne spectrometer system for the simultaneous measurement of the direct Sun irradiance and aureole radiance. The instrument is based on diffraction grating spectrometers with linear image sensors. It is robust, lightweight, compact, and reliable, characteristics that are important for airborne applications. The multispectral radiation measurements are used to derive optical properties of tropospheric aerosols. We extract the altitude dependence of the aerosol volume scattering function and of the aerosol optical depth by using flight patterns with descents and ascents ranging from the surface level to the top of the boundary layer. The extinction coefficient and the product of single scattering albedo and phase function of separate layers can be derived from the airborne measurements.

Recent impact on (4709) Ennomos?

NASA Astrophysics Data System (ADS)

Rozehnal, Jakub; Broz, Miroslav

2017-10-01

In this work, we try to associate the albedo variations of the Trojan L5 asteroid (4709) Ennomos (Emery et al., 2016) with a relatively recent impact structure on its surface. Although the mean visual albedo of Trojans is generally very low (pV~0.07, Grav et al., 2012), especially for asteroids with diameter D > 50 km, Fernández et al. (2003) reported unusually high albedo of (4709) Ennomos (pV~0.12 to 0.18), which diameter is D ~ 80 km. However, the albedo of (4709) Ennomos determined from the WISE data by Grav et al. (2012) is only pV ~ 0.09 and the same albedo derived from AKARI is about pV ~ 0.08 (Usui et al., 2011). One possible explanation for these discrepancies is that the albedo of (4709) Ennomos is strongly dependent on its rotational phase. Emery et al. (2016) reported a clear evidence of spectral slope variations of (4709) Ennomos with its rotation, what may also suggest an existence of a bright spot on its surface, caused e.g. by impact. As we reported the asteroid family associated with (4709) Ennomos in our previous works (eg. Broz and Rozehnal, 2011, Rozehnal et al., 2016), we try to simulate the family origin by SPH simulations (Benz and Aspaugh, 1994).Because the albedo variations could be in principle used to estimate an approximate size of the impact structure (in the case of cratering event, what means MLR/MPB > 0.5) on the family parent body an hence an approximate size of the impactor, this is a uniqe chance to compare it with the results of the SPH simulations. In our work we also try to determine the age of the Ennomos family by simulating the dynamical evolution of our synthetic families in different impact geometries (with different f and ω).

Satellite Material Type and Phase Function Determination in Support of Orbital Debris Size Estimation

NASA Technical Reports Server (NTRS)

Hejduk, M. D.; Cowardin, H. M.; Stansbery, Eugene G.

2012-01-01

In performing debris surveys of deep-space orbital regions, the considerable volume of the area to be surveyed and the increased orbital altitude suggest optical telescopes as the most efficient survey instruments; but to proceed this way, methodologies for debris object size estimation using only optical tracking and photometric information are needed. Basic photometry theory indicates that size estimation should be possible if satellite albedo and shape are known. One method for estimating albedo is to try to determine the object's material type photometrically, as one can determine the albedos of common satellite materials in the laboratory. Examination of laboratory filter photometry (using Johnson BVRI filters) on a set of satellite material samples indicates that most material types can be separated at the 1-sigma level via B-R versus R-I color differences with a relatively small amount of required resampling, and objects that remain ambiguous can be resolved by B-R versus B-V color differences and solar radiation pressure differences. To estimate shape, a technique advanced by Hall et al. [1], based on phase-brightness density curves and not requiring any a priori knowledge of attitude, has been modified slightly to try to make it more resistant to the specular characteristics of different materials and to reduce the number of samples necessary to make robust shape determinations. Working from a gallery of idealized debris shapes, the modified technique identifies most shapes within this gallery correctly, also with a relatively small amount of resampling. These results are, of course, based on relatively small laboratory investigations and simulated data, and expanded laboratory experimentation and further investigation with in situ survey measurements will be required in order to assess their actual efficacy under survey conditions; but these techniques show sufficient promise to justify this next level of analysis.

Early Spring Post-Fire Snow Albedo Dynamics in High Latitude Boreal Forests Using Landsat-8 OLI Data

NASA Technical Reports Server (NTRS)

Wang, Zhuosen; Erb, Angela M.; Schaaf, Crystal B.; Sun, Qingsong; Liu, Yan; Yang, Yun; Shuai, Yanmin; Casey, Kimberly A.; Roman, Miguel O.

2016-01-01

Taking advantage of the improved radiometric resolution of Landsat-8 OLI which, unlike previous Landsat sensors, does not saturate over snow, the progress of fire recovery progress at the landscape scale (less than 100 m) is examined. High quality Landsat-8 albedo retrievals can now capture the true reflective and layered character of snow cover over a full range of land surface conditions and vegetation densities. This new capability particularly improves the assessment of post-fire vegetation dynamics across low- to high-burn severity gradients in Arctic and boreal regions in the early spring, when the albedos during recovery show the greatest variation. We use 30 m resolution Landsat-8 surface reflectances with concurrent coarser resolution (500 m) MODIS high quality full inversion surface Bidirectional Reflectance Distribution Functions (BRDF) products to produce higher resolution values of surface albedo. The high resolution full expression shortwave blue sky albedo product performs well with an overall RMSE of 0.0267 between tower and satellite measures under both snow-free and snow-covered conditions. While the importance of post-fire albedo recovery can be discerned from the MODIS albedo product at regional and global scales, our study addresses the particular importance of early spring post-fire albedo recovery at the landscape scale by considering the significant spatial heterogeneity of burn severity, and the impact of snow on the early spring albedo of various vegetation recovery types. We found that variations in early spring albedo within a single MODIS gridded pixel can be larger than 0.6. Since the frequency and severity of wildfires in Arctic and boreal systems is expected to increase in the coming decades, the dynamics of albedo in response to these rapid surface changes will increasingly impact the energy balance and contribute to other climate processes and physical feedback mechanisms. Surface radiation products derived from Landsat-8 data will thus play an important role in characterizing the carbon cycle and ecosystem processes of high latitude systems.

Early spring post-fire snow albedo dynamics in high latitude boreal forests using Landsat-8 OLI data

PubMed Central

Wang, Zhuosen; Erb, Angela M.; Schaaf, Crystal B.; Sun, Qingsong; Liu, Yan; Yang, Yun; Shuai, Yanmin; Casey, Kimberly A.; Román, Miguel O.

2018-01-01

Taking advantage of the improved radiometric resolution of Landsat-8 OLI which, unlike previous Landsat sensors, does not saturate over snow, the progress of fire recovery progress at the landscape scale (< 100m) is examined. High quality Landsat-8 albedo retrievals can now capture the true reflective and layered character of snow cover over a full range of land surface conditions and vegetation densities. This new capability particularly improves the assessment of post-fire vegetation dynamics across low- to high- burn severity gradients in Arctic and boreal regions in the early spring, when the albedos during recovery show the greatest variation. We use 30 m resolution Landsat-8 surface reflectances with concurrent coarser resolution (500m) MODIS high quality full inversion surface Bidirectional Reflectance Distribution Functions (BRDF) products to produce higher resolution values of surface albedo. The high resolution full expression shortwave blue sky albedo product performs well with an overall RMSE of 0.0267 between tower and satellite measures under both snow-free and snow-covered conditions. While the importance of post-fire albedo recovery can be discerned from the MODIS albedo product at regional and global scales, our study addresses the particular importance of early spring post-fire albedo recovery at the landscape scale by considering the significant spatial heterogeneity of burn severity, and the impact of snow on the early spring albedo of various vegetation recovery types. We found that variations in early spring albedo within a single MODIS gridded pixel can be larger than 0.6. Since the frequency and severity of wildfires in Arctic and boreal systems is expected to increase in the coming decades, the dynamics of albedo in response to these rapid surface changes will increasingly impact the energy balance and contribute to other climate processes and physical feedback mechanisms. Surface radiation products derived from Landsat-8 data will thus play an important role in characterizing the carbon cycle and ecosystem processes of high latitude systems. PMID:29769751

Early spring post-fire snow albedo dynamics in high latitude boreal forests using Landsat-8 OLI data.

PubMed

Wang, Zhuosen; Erb, Angela M; Schaaf, Crystal B; Sun, Qingsong; Liu, Yan; Yang, Yun; Shuai, Yanmin; Casey, Kimberly A; Román, Miguel O

2016-11-01

Taking advantage of the improved radiometric resolution of Landsat-8 OLI which, unlike previous Landsat sensors, does not saturate over snow, the progress of fire recovery progress at the landscape scale (< 100m) is examined. High quality Landsat-8 albedo retrievals can now capture the true reflective and layered character of snow cover over a full range of land surface conditions and vegetation densities. This new capability particularly improves the assessment of post-fire vegetation dynamics across low- to high- burn severity gradients in Arctic and boreal regions in the early spring, when the albedos during recovery show the greatest variation. We use 30 m resolution Landsat-8 surface reflectances with concurrent coarser resolution (500m) MODIS high quality full inversion surface Bidirectional Reflectance Distribution Functions (BRDF) products to produce higher resolution values of surface albedo. The high resolution full expression shortwave blue sky albedo product performs well with an overall RMSE of 0.0267 between tower and satellite measures under both snow-free and snow-covered conditions. While the importance of post-fire albedo recovery can be discerned from the MODIS albedo product at regional and global scales, our study addresses the particular importance of early spring post-fire albedo recovery at the landscape scale by considering the significant spatial heterogeneity of burn severity, and the impact of snow on the early spring albedo of various vegetation recovery types. We found that variations in early spring albedo within a single MODIS gridded pixel can be larger than 0.6. Since the frequency and severity of wildfires in Arctic and boreal systems is expected to increase in the coming decades, the dynamics of albedo in response to these rapid surface changes will increasingly impact the energy balance and contribute to other climate processes and physical feedback mechanisms. Surface radiation products derived from Landsat-8 data will thus play an important role in characterizing the carbon cycle and ecosystem processes of high latitude systems.

On the relationships among cloud cover, mixed-phase partitioning, and planetary albedo in GCMs

DOE PAGES

McCoy, Daniel T.; Tan, Ivy; Hartmann, Dennis L.; ...

2016-05-06

In this study, it is shown that CMIP5 global climate models (GCMs) that convert supercooled water to ice at relatively warm temperatures tend to have a greater mean-state cloud fraction and more negative cloud feedback in the middle and high latitude Southern Hemisphere. We investigate possible reasons for these relationships by analyzing the mixed-phase parameterizations in 26 GCMs. The atmospheric temperature where ice and liquid are equally prevalent (T5050) is used to characterize the mixed-phase parameterization in each GCM. Liquid clouds have a higher albedo than ice clouds, so, all else being equal, models with more supercooled liquid water wouldmore » also have a higher planetary albedo. The lower cloud fraction in these models compensates the higher cloud reflectivity and results in clouds that reflect shortwave radiation (SW) in reasonable agreement with observations, but gives clouds that are too bright and too few. The temperature at which supercooled liquid can remain unfrozen is strongly anti-correlated with cloud fraction in the climate mean state across the model ensemble, but we know of no robust physical mechanism to explain this behavior, especially because this anti-correlation extends through the subtropics. A set of perturbed physics simulations with the Community Atmospheric Model Version 4 (CAM4) shows that, if its temperature-dependent phase partitioning is varied and the critical relative humidity for cloud formation in each model run is also tuned to bring reflected SW into agreement with observations, then cloud fraction increases and liquid water path (LWP) decreases with T5050, as in the CMIP5 ensemble.« less

FLASH_TISA_Terra+Aqua_Version3C

Atmospheric Science Data Center

2018-04-04

... Cloud Particle Phase Cloud Infrared Emissivity Cloud Base Pressure Surface (Radiative) Flux TOA Flux Surface Types Albedo LW Flux Order Data:  Earthdata Search:  Order Data Guide Documents:  ...

CERES-MISR Info

Atmospheric Science Data Center

2013-05-20

... Surface Albedo Cloud Area Fraction Cloud Effective Pressure Cloud Effective Temperature Cloud Effective Height Cloud Top Pressure Cloud Base Pressure Cloud Particle Phase Liquid Water Path Ice Water Path Water Particle Radius Ice Particle ...

The Influence of Thermodynamic Phase on the Retrieval of Mixed-Phase Cloud Microphysical and Optical Properties in the Visible and Near Infrared Region

NASA Technical Reports Server (NTRS)

Lee, Joonsuk; Yang, Ping; Dessler, Andrew E.; Baum, Bryan A.; Platnick, Steven

2005-01-01

Cloud microphysical and optical properties are inferred from the bidirectional reflectances simulated for a single-layered cloud consisting of an external mixture of ice particles and liquid droplets. The reflectances are calculated with a rigorous discrete ordinates radiative transfer model and are functions of the cloud effective particle size, the cloud optical thickness, and the values of the ice fraction in the cloud (i.e., the ratio of ice water content to total water content). In the present light scattering and radiative transfer simulations, the ice fraction is assumed to be vertically homogeneous; the habit (shape) percentage as a function of ice particle size is consistent with that used for the Moderate Resolution Imaging Spectroradiometer (MODIS) operational (Collection 4 and earlier) cloud products; and the surface is assumed to be Lambertian with an albedo of 0.03. Furthermore, error analyses pertaining to the inference of the effective particle sizes and optical thicknesses of mixed-phase clouds are performed. Errors are calculated with respect to the assumption of a cloud containing solely liquid or ice phase particles. The analyses suggest that the effective particle size inferred for a mixed-phase cloud can be underestimated (or overestimated) if pure liquid phase (or pure ice phase) is assumed for the cloud, whereas the corresponding cloud optical thickness can be overestimated (or underestimated).

Preliminary assessment of the GOES-R ABI hourly land surface albedo and reflectance products prototyped with Himawari AHI data

NASA Astrophysics Data System (ADS)

He, T.; Liang, S.; Zhang, Y.; Yu, Y.

2016-12-01

Land surface albedo and reflectance are critical geophysical variables used in climate and environmental applications. The multispectral Advanced Baseline Imager (ABI) onboard the next generation geostationary satellites (GOES-R series, set to launch in late 2016) offers high temporal and medium spatial resolution observations, which can be used for monitoring diurnal variation of surface albedo and reflectance. In the GOES-R data processing chain there is no atmospheric correction to generate surface reflectance product, which is usually required for surface albedo estimation. We propose an optimization method to simultaneously retrieve surface bidirectional reflectance distribution function (BRDF) parameters and aerosol optical depth with GOES-R ABI data on a daily-basis, which are used for estimating surface albedo and reflectance. Before the launch of the GOES-R satellite, our algorithm was prototyped with data from the Advanced Himawari Imager (AHI) onboard the Japanese Himawari-8 satellite, which has spectral bands and spatial resolutions similar to GOES-R ABI. Cal/val activities were carried out against ground measurements at the OzFlux sites in Australia and satellite data including albedo/BRDF products from MODIS and Landsat. The preliminary accuracy assessment showed promising results for both the surface albedo and reflectance estimates. The GOES-R surface albedo and reflectance products will serve as critical inputs for downstream GOES-R satellite products and also help improve climate modeling and weather forecasting with a high temporal resolution.

Impact of Land Cover Characterization and Properties on Snow Albedo in Climate Models

NASA Astrophysics Data System (ADS)

Wang, L.; Bartlett, P. A.; Chan, E.; Montesano, P.

2017-12-01

The simulation of winter albedo in boreal and northern environments has been a particular challenge for land surface modellers. Assessments of output from CMIP3 and CMIP5 climate models have revealed that many simulations are characterized by overestimation of albedo in the boreal forest. Recent studies suggest that inaccurate representation of vegetation distribution, improper simulation of leaf area index, and poor treatment of canopy-snow processes are the primary causes of albedo errors. While several land cover datasets are commonly used to derive plant functional types (PFT) for use in climate models, new land cover and vegetation datasets with higher spatial resolution have become available in recent years. In this study, we compare the spatial distribution of the dominant PFTs and canopy cover fractions based on different land cover datasets, and present results from offline simulations of the latest version Canadian Land Surface Scheme (CLASS) over the northern Hemisphere land. We discuss the impact of land cover representation and surface properties on winter albedo simulations in climate models.

CERES SSF Current Info

Atmospheric Science Data Center

2013-05-17

... Surface Albedo Cloud Area Fraction Cloud Effective Pressure Cloud Effective Temperature Cloud Effective Height Cloud Top Pressure Cloud Base Pressure Cloud Particle Phase Liquid Water Path Ice Water Path Water Particle Radius Ice Particle ...

Re-analysis of previous laboratory phase curves: 2. Connections between opposition effect morphology and spectral features of stony meteorites

NASA Astrophysics Data System (ADS)

Déau, Estelle; Spilker, Linda J.; Flandes, Alberto

2016-07-01

We investigate connections between the opposition phase curves and the spectra from ultraviolet to near infrared wavelengths of stony meteorites. We use two datasets: the reflectance dataset of Capaccioni et al. ([1990] Icarus, 83, 325), which consists of optical phase curves (from 2° to 45°) of 17 stony meteorites (three carbonaceous chondrites, 11 ordinary chondrites, and three achondrites), and the spectral dataset from the RELAB database consisting of near-ultraviolet to near-infrared spectra of the same meteorites. We re-analyzed the first dataset and fit it with two morphological models to derive the amplitude A, the angular width HWHM of the surge and the slope S of the linear part. Our re-analysis confirms that stony meteorites have a non-monotonic behavior of the surge amplitude with albedo, which is also observed in planetary surfaces (Déau et al. [2013] Icarus, 226, 1465), laboratory samples (Nelson et al. [2004] Proc. Lunar Sci. Conf., 35, p. 1089) and asteroids (Belskaya and Shevchenko [2000] Icarus, 147, 94). We find a very strong correlation between the opposition effect morphological parameters and the slope of the spectra between 0.75 μm and 0.95 μm. In particular, we found that meteorites with a positive amplitude-albedo correlation have a positive spectral slope between 0.75 μm and 0.95 μm, while meteorites with a negative amplitude-albedo correlation have a negative spectral slope between 0.75 μm and 0.95 μm. We have ruled out the role of the meteorite samples' macro-properties (grain size, porosity and macroscopic roughness) in the correlations found because these properties were constant during the preparation of the samples. If this hypothesis is correct, this implies that other properties like the composition or the micro-properties (grain inclusions, grain shape or microscopic roughness) could have a preponderant role in the non-monotonic behavior of the surge morphology with albedo at small and moderate phase angles. Further accurate characterization of carbonaceous chondrites samples are necessary to draw conclusions about the role of the micro-properties.

CHANGING PHASES OF ALIEN WORLDS: PROBING ATMOSPHERES OF KEPLER PLANETS WITH HIGH-PRECISION PHOTOMETRY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Esteves, Lisa J.; Mooij, Ernst J. W. De; Jayawardhana, Ray, E-mail: esteves@astro.utoronto.ca, E-mail: demooij@astro.utoronto.ca, E-mail: rayjay@yorku.ca

We present a comprehensive analysis of planetary phase variations, including possible planetary light offsets, using eighteen quarters of data from the Kepler space telescope. Our analysis found fourteen systems with significant detections in each of the phase curve components: planet’s phase function, secondary eclipse, Doppler boosting, and ellipsoidal variations. We model the full phase curve simultaneously, including primary and secondary transits, and derive albedos, day- and night-side temperatures and planet masses. Most planets manifest low optical geometric albedos (< 0.25), with the exception of Kepler-10b, Kepler-91b, and KOI-13b. We find that KOI-13b, with a small eccentricity of 0.0006 ± 0.0001,more » is the only planet for which an eccentric orbit is favored. We detect a third harmonic for HAT-P-7b for the first time, and confirm the third harmonic for KOI-13b reported in Esteves et al.: both could be due to their spin–orbit misalignments. For six planets, we report a planetary brightness peak offset from the substellar point: of those, the hottest two (Kepler-76b and HAT-P-7b) exhibit pre-eclipse shifts or on the evening-side, while the cooler four (Kepler-7b, Kepler-8b, Kepler-12b, and Kepler-41b) peak post-eclipse or on the morning-side. Our findings dramatically increase the number of Kepler planets with detected planetary light offsets, and provide the first evidence in the Kepler data for a correlation between the peak offset direction and the planet’s temperature. Such a correlation could arise if thermal emission dominates light from hotter planets that harbor hot spots shifted toward the evening-side, as theoretically predicted, while reflected light dominates cooler planets with clouds on the planet’s morning-side.« less

Probing exoplanet clouds with optical phase curves.

PubMed

Muñoz, Antonio García; Isaak, Kate G

2015-11-03

Kepler-7b is to date the only exoplanet for which clouds have been inferred from the optical phase curve--from visible-wavelength whole-disk brightness measurements as a function of orbital phase. Added to this, the fact that the phase curve appears dominated by reflected starlight makes this close-in giant planet a unique study case. Here we investigate the information on coverage and optical properties of the planet clouds contained in the measured phase curve. We generate cloud maps of Kepler-7b and use a multiple-scattering approach to create synthetic phase curves, thus connecting postulated clouds with measurements. We show that optical phase curves can help constrain the composition and size of the cloud particles. Indeed, model fitting for Kepler-7b requires poorly absorbing particles that scatter with low-to-moderate anisotropic efficiency, conclusions consistent with condensates of silicates, perovskite, and silica of submicron radii. We also show that we are limited in our ability to pin down the extent and location of the clouds. These considerations are relevant to the interpretation of optical phase curves with general circulation models. Finally, we estimate that the spherical albedo of Kepler-7b over the Kepler passband is in the range 0.4-0.5.

Potential effects of forest management on surface albedo

NASA Astrophysics Data System (ADS)

Otto, J.; Bréon, F.-M.; Schelhaas, M.-J.; Pinty, B.; Luyssaert, S.

2012-04-01

Currently 70% of the world's forests are managed and this figure is likely to rise due to population growth and increasing demand for wood based products. Forest management has been put forward by the Kyoto-Protocol as one of the key instruments in mitigating climate change. For temperate and boreal forests, the effects of forest management on the stand-level carbon balance are reasonably well understood, but the biophysical effects, for example through changes in the albedo, remain elusive. Following a modeling approach, we aim to quantify the variability in albedo that can be attributed to forest management through changes in canopy structure and density. The modelling approach chains three separate models: (1) a forest gap model to describe stand dynamics, (2) a Monte-Carlo model to estimate the probability density function of the optical path length of photons through the canopy and (3) a physically-based canopy transfer model to estimate the interaction between photons and leaves. The forest gap model provides, on a monthly time step the position, height, diameter, crown size and leaf area index of individual trees. The Monte-Carlo model computes from this the probability density function of the distance a photon travels through crown volumes to determine the direct light reaching the forest floor. This information is needed by the canopy transfer model to calculate the effective leaf area index - a quantity that allows it to correctly represent a 3D process with a 1D model. Outgoing radiation is calculated as the result of multiple processes involving the scattering due to the canopy layer and the forest floor. Finally, surface albedo is computed as the ratio between incident solar radiation and calculated outgoing radiation. The study used two time series representing thinning from below of a beech and a Scots pine forest. The results show a strong temporal evolution in albedo during stand establishment followed by a relatively stable albedo once the canopy is closed. During this period, albedo is affected for a short time by forest operations. The modelling approach allowed us to estimate the importance of ground vegetation in the stand albedo. Given that ground vegetation depends on the light reaching the forest floor, ground vegetation could act as a natural buffer to dampen changes in albedo, allowing the stand to maintain optimal leaf temperature. Consequently, accounting for only the carbon balance component of forest management ignores albedo impacts and is thus likely to yield biased estimates of the climate benefits of forest ecosystems.

On Diffusive Climatological Models.

NASA Astrophysics Data System (ADS)

Griffel, D. H.; Drazin, P. G.

1981-11-01

A simple, zonally and annually averaged, energy-balance climatological model with diffusive heat transport and nonlinear albedo feedback is solved numerically. Some parameters of the model are varied, one by one, to find the resultant effects on the steady solution representing the climate. In particular, the outward radiation flux, the insulation distribution and the albedo parameterization are varied. We have found an accurate yet simple analytic expression for the mean annual insolation as a function of latitude and the obliquity of the Earth's rotation axis; this has enabled us to consider the effects of the oscillation of the obliquity. We have used a continuous albedo function which fits the observed values; it considerably reduces the sensitivity of the model. Climatic cycles, calculated by solving the time-dependent equation when parameters change slowly and periodically, are compared qualitatively with paleoclimatic records.

Assimilating MODIS-based albedo and snow cover fraction into the Common Land Model to improve snow depth simulation with direct insertion and deterministic ensemble Kalman filter methods

NASA Astrophysics Data System (ADS)

Xu, Jianhui; Shu, Hong

2014-09-01

This study assesses the analysis performance of assimilating the Moderate Resolution Imaging Spectroradiometer (MODIS)-based albedo and snow cover fraction (SCF) separately or jointly into the physically based Common Land Model (CoLM). A direct insertion method (DI) is proposed to assimilate the black and white-sky albedos into the CoLM. The MODIS-based albedo is calculated with the MODIS bidirectional reflectance distribution function (BRDF) model parameters product (MCD43B1) and the solar zenith angle as estimated in the CoLM for each time step. Meanwhile, the MODIS SCF (MOD10A1) is assimilated into the CoLM using the deterministic ensemble Kalman filter (DEnKF) method. A new DEnKF-albedo assimilation scheme for integrating the DI and DEnKF assimilation schemes is proposed. Our assimilation results are validated against in situ snow depth observations from November 2008 to March 2009 at five sites in the Altay region of China. The experimental results show that all three data assimilation schemes can improve snow depth simulations. But overall, the DEnKF-albedo assimilation shows the best analysis performance as it significantly reduces the bias and root-mean-square error (RMSE) during the snow accumulation and ablation periods at all sites except for the Fuyun site. The SCF assimilation via DEnKF produces better results than the albedo assimilation via DI, implying that the albedo assimilation that indirectly updates the snow depth state variable is less efficient than the direct SCF assimilation. For the Fuyun site, the DEnKF-albedo scheme tends to overestimate the snow depth accumulation with the maximum bias and RMSE values because of the large positive innovation (observation minus forecast).

Effects of bubbles, cracks, and volcanic tephra on the spectral albedo of bare ice near the Transantarctic Mountains: Implications for sea glaciers on Snowball Earth

NASA Astrophysics Data System (ADS)

Dadic, Ruzica; Mullen, Peter C.; Schneebeli, Martin; Brandt, Richard E.; Warren, Stephen G.

2013-09-01

Spectral albedo was measured along a 6 km transect near the Allan Hills in East Antarctica. The transect traversed the sequence from new snow through old snow, firn, and white ice, to blue ice, showing a systematic progression of decreasing albedo at all wavelengths, as well as decreasing specific surface area (SSA) and increasing density. Broadband albedos under clear-sky range from 0.80 for snow to 0.57 for blue ice, and from 0.87 to 0.65 under cloud. Both air bubbles and cracks scatter sunlight; their contributions to SSA were determined by microcomputed tomography on core samples of the ice. Although albedo is governed primarily by the SSA (and secondarily by the shape) of bubbles or snow grains, albedo also correlates highly with porosity, which, as a proxy variable, would be easier for ice sheet models to predict than bubble sizes. Albedo parameterizations are therefore developed as a function of density for three broad wavelength bands commonly used in general circulation models: visible, near-infrared, and total solar. Relevance to Snowball Earth events derives from the likelihood that sublimation of equatorward-flowing sea glaciers during those events progressively exposed the same sequence of surface materials that we measured at Allan Hills, with our short 6 km transect representing a transect across many degrees of latitude on the Snowball ocean. At the equator of Snowball Earth, climate models predict thick ice, or thin ice, or open water, depending largely on their albedo parameterizations; our measured albedos appear to be within the range that favors ice hundreds of meters thick.

Detecting tree-like multicellular life on extrasolar planets.

PubMed

Doughty, Christopher E; Wolf, Adam

2010-11-01

Over the next two decades, NASA and ESA are planning a series of space-based observatories to find Earth-like planets and determine whether life exists on these planets. Previous studies have assessed the likelihood of detecting life through signs of biogenic gases in the atmosphere or a red edge. Biogenic gases and the red edge could be signs of either single-celled or multicellular life. In this study, we propose a technique with which to determine whether tree-like multicellular life exists on extrasolar planets. For multicellular photosynthetic organisms on Earth, competition for light and the need to transport water and nutrients has led to a tree-like body plan characterized by hierarchical branching networks. This design results in a distinct bidirectional reflectance distribution function (BRDF) that causes differing reflectance at different sun/view geometries. BRDF arises from the changing visibility of the shadows cast by objects, and the presence of tree-like structures is clearly distinguishable from flat ground with the same reflectance spectrum. We examined whether the BRDF could detect the existence of tree-like structures on an extrasolar planet by using changes in planetary albedo as a planet orbits its star. We used a semi-empirical BRDF model to simulate vegetation reflectance at different planetary phase angles and both simulated and real cloud cover to calculate disk and rotation-averaged planetary albedo for a vegetated and non-vegetated planet with abundant liquid water. We found that even if the entire planetary albedo were rendered to a single pixel, the rate of increase of albedo as a planet approaches full illumination would be comparatively greater on a vegetated planet than on a non-vegetated planet. Depending on how accurately planetary cloud cover can be resolved and the capabilities of the coronagraph to resolve exoplanets, this technique could theoretically detect tree-like multicellular life on exoplanets in 50 stellar systems.

The moon in heiligenschein

USGS Publications Warehouse

Wildey, R.L.

1978-01-01

An analysis of 25 photometric digital images of the moon has been carried out to obtain a single image in a new mapping parameter, the Heiligenschein exponent. The data necessarily represent a range of lunar phases, but all are within 10 hours of full moon. The new parameter characterizes the rate at which lunar features brighten as their local phase angles approach zero. Although considerable contrast is present in this parameter, there is only a small correlation with normal albedo. In particular, the large albedo difference between maria and highlands is not simply reflected in Heiligenschein differences, which are larger within each category of terrain than the difference between the Heiligenschein averages of each. A correlation with age may be present in both the maria and the highlands, but its determination will require separation into distinct geochemical provinces. Copyright ?? 1978 AAAS.

The size distribution of interstellar grains

NASA Technical Reports Server (NTRS)

Witt, Adolf N.

1987-01-01

Three major areas involving interstellar grains were investigated. First, studies were performed of scattering in reflection nebulae with the goal of deriving scattering characteristics of dust grains such as the albedo and the phase function asymmetry throughout the visible and the ultraviolet. Secondly, studies were performed of the wavelength dependence of interstellar extinction designed to demonstrate the wide range of grain size distributions naturally occurring in individual clouds in different parts of the galaxy. And thirdly, studies were also performed of the ultraviolet powered emission of dust grains in the 0.5 to 1.0 micron wavelength range in reflection nebulae. Findings considered of major importance are highlighted.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Masiero, Joseph R.; Mainzer, A. K.; Bauer, J. M.

We present preliminary diameters and albedos for 13511 Main Belt asteroids (MBAs) that were observed during the 3-Band Cryo phase of the Wide-field Infrared Survey Explorer (WISE; after the outer cryogen tank was exhausted) and as part of the NEOWISE Post-Cryo Survey (after the inner cryogen tank was exhausted). With a reduced or complete loss of sensitivity in the two long wavelength channels of WISE, the uncertainty in our fitted diameters and albedos is increased to {approx}20% for diameter and {approx}40% for albedo. Diameter fits using only the 3.4 and 4.6 {mu}m channels are shown to be dependent on themore » literature optical H absolute magnitudes. These data allow us to increase the number of size estimates for large MBAs which have been identified as members of dynamical families. We present thermal fits for 14 asteroids previously identified as the parents of a dynamical family that were not observed during the fully cryogenic mission.« less

Photometric functions for photoclinometry and other applications

USGS Publications Warehouse

McEwen, A.S.

1991-01-01

Least-squared fits to the brightness profiles across a disk or "limb darkening" described by Hapke's photometric function are found for the simpler Minnaert and lunar-Lambert functions. The simpler functions are needed to reduce the number of unknown parameters in photoclinometry, especially to distinguish the brightness variations of the surface materials from that due to the resolved topography. The limb darkening varies with the Hapke parameters for macroscopic roughness (??), the single-scattering albedo (w), and the asymmetry factor of the particle phase function (g). Both of the simpler functions generally provide good matches to the limb darkening described by Hapke's function, but the lunar-Lambert function is superior when viewing angles are high and when (??) is less than 30??. Although a nonunique solution for the Minnaert function at high phase angles has been described for smooth surfaces, the discrepancy decreases with increasing (??) and virtually disappears when (??) reaches 30?? to 40??. The variation in limb darkening with w and g, pronounced for smooth surfaces, is reduced or eliminated when the Hapke parameters are in the range typical of most planetary surfaces; this result simplifies the problem of photoclinometry across terrains with variable surface materials. The Minnaert or lunar-Lambert fits to published Hapke models will give photoclinometric solutions that are very similar (>1?? slope discrepancy) to the Hapke-function solutions for nearly all of the bodies and terrains thus far modeled by Hapke's function. ?? 1991.

Photometric properties of comet 67P/Churyumov-Gerasimenko from VIRTIS-M onboard Rosetta

NASA Astrophysics Data System (ADS)

Ciarniello, M.; Capaccioni, F.; Filacchione, G.; Raponi, A.; Tosi, F.; De Sanctis, M. C.; Capria, M. T.; Erard, S.; Bockelee-Morvan, D.; Leyrat, C.; Arnold, G.; Barucci, A.; Beck, P.; Bellucci, G.; Fornasier, S.; Longobardo, A.; Mottola, S.; Palomba, E.; Quirico, E.; Schmitt, B.

2015-11-01

Aims: We investigate the nucleus photometric properties of the comet 67P/Churyumov-Gerasimenko as observed by the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) onboard the Rosetta spacecraft. Both full-disk and disk-resolved images of the comet have been analyzed, deriving light and phase curves as well as a photometric reduction of the radiance factor (I/F) to single scattering albedo (SSA) in the 0.4-3.5 μm range. Methods: Hyperspectral cubes from VIRTIS were calibrated and corrected for instrumental artifacts. We computed integrated fluxes from full-disk acquisitions to derive nucleus light curves and phase curves at low phase angles (1.2°<α < 14.9°). Disk-resolved observations in the phase angle range 27.2°<α< 111.5° were reduced to SSA by means of a simplified Hapke model, deriving average spectrophotometric properties of the surface and producing SSA maps at different wavelengths. Spectral phase reddening in the visible (VIS) and infrared (IR) ranges was measured. Finally, full-disk and disk-resolved data were used together to derive a phase curve of the nucleus in the 1.2°<α < 111.5° range. Results: We measure an asymmetric double-peaked light curve that is due to the elongated shape of the nucleus. The average SSA albedo shows a reddish spectrum with a strong absorption feature centered at 3.2 μm, while the surface exhibits a backscattering behavior. The derived geometric albedo is Ageo = 0.062 ± 0.002 at 0.55 μm, indicating a very dark surface. Phase reddening is significant both in the VIS and IR ranges, and we report spectral slopes of 0.20/kÅ and 0.033/kÅ, respectively, after applying photometric reduction. SSA maps indicate that Hapi and Imothep regions are the brightest in the VIS, with the former showing a bluer spectrum with respect to the rest of the surface. The phase curve of the nucleus shows a strong opposition effect, with β = 0.077 ± 0.002 for α < 15°.

Planetary Regolith Microstructure: An Unexpected Opposition Effect Result

NASA Technical Reports Server (NTRS)

Nelson, R. M.; Hapke, B. W.; Smythe, W. D.; Hale, A. S.; Piatek, J. L.

2004-01-01

The Opposition Effect (OE) is the non-linear increase in the intensity of light scattered from a surface as phase angle approaches 0 deg. It is seen in laboratory experiments and in remote sensing observations of planetary surfaces. Understanding the OE is a requirement to fitting photometric models which will produce meaningful results about regolith texture. Our previous laboratory studies are consistent with the hypothesis that the OE in particulate materials is due to two processes, Shadow Hiding (SHOE) and Coherent Backscattering (CBOE). SHOE arises because, as phase angle approaches zero, shadows cast by regolith grains on other grains become invisible to the observer. CBOE results from constructive interference between rays traveling the same path but in opposite directions. In this study we measured the angular scattering properties of 9 mixtures of Aluminum Oxide and Boron Carbide powders of the same particle diameter (25 microns). The reflectance of the materials ranged from 7% (pure B4C) to 91% (pure Al2O3). Along with the reflectance phase curve we measured the circular polarization ratio (CPR) - the ratio of the intensity of the light returned with the same helicity as the incident light to that with the opposite helicity. An increase in CPR with decreasing phase angle indicates increased multiple scattering and is consistent with CBOE (Hapke, 1993). Popular conceptions of CBOE (Belskaya et al, 2003) hold that materials of higher albedo would exhibit increased multiple scattering and that the contribution of CBOE to the OE would increase as albedo increases. Remarkably, we find the highest albedo samples did not have the strongest CBOE opposition peaks. Instead, the maximum CBOE contribution is observed in samples with reflectance between 15 and 40%.

Potential Long-Term Records of Surface Albedo at Fine Spatiotemporal Resolution from Landsat/Sentinle-2A Surface Reflectance and MODIS/VIIRS BRDF

NASA Astrophysics Data System (ADS)

Li, Z.; Schaaf, C.; Shuai, Y.; Liu, Y.; Sun, Q.; Erb, A.; Wang, Z.

2016-12-01

The land surface albedo products at fine spatial resolutions are generated by coupling surface reflectance (SR) from Landsat (30 m) or Sentinel-2A (20 m) with concurrent surface anisotropy information (the Bidirectional Reflectance Distribution Function - BRDF) at coarser spatial resolutions from sequential multi-angular observations by the Moderate Resolution Imaging Spectroradiometer (MODIS) or its successor, the Visible Infrared Imaging Radiometer Suite (VIIRS). We assess the comparability of four types of fine-resolution albedo products (black-sky and white-sky albedos over the shortwave broad band) generated by coupling, (1) Landsat-8 Optical Land Imager (OLI) SR with MODIS BRDF; (2) OLI SR with VIIRS BRDF; (3) Sentinel-2A MultiSpectral Instrument (MSI) SR with MODIS BRDF; and (4) MSI SR with VIIRS BRDF. We evaluate the accuracy of these four types of fine-resolution albedo products using ground tower measurements of surface albedo over six SURFace RADiation Network (SURFRAD) sites in the United States. For comparison with the ground measurements, we estimate the actual (blue-sky) albedo values at the six sites by using the satellite-based retrievals of black-sky and white-sky albedos and taking into account the proportion of direct and diffuse solar radiation from the ground measurements at the sites. The coupling of the OLI and MSI SR with MODIS BRDF has already been shown to provide accurate fine-resolution albedo values. With demonstration of a high agreement in BRDF products from MODIS and VIIRS, we expect to see consistency between all four types of fine-resolution albedo products. This assurance of consistency between the couplings of both OLI and MSI with both MODIS and VIIRS guarantees the production of long-term records of surface albedo at fine spatial resolutions and an increased temporal resolution. Such products will be critical in studying land surface changes and associated surface energy balance over the dynamic and heterogeneous landscapes most susceptible to climate change (such as arctic, coastal, and high-elevation zones).

Exogenic and endogenic albedo and color patterns on Europa

NASA Technical Reports Server (NTRS)

Mcewen, A. S.

1986-01-01

New global and high-resolution multispectral mosaics of Europa have been produced from the Voyager imaging data. Photometric normalizations are based on multiple-image techniques that explicitly account for intrinsic albedo variations through pixel-by-pixel solutions. The exogenic color and albedo pattern on Europa is described by a second-order function of the cosine of the angular distance from the apex of orbital motion. On the basis of this second-order function and of color trends that are different on the leading and trailing hemispheres, the exogenic pattern is interpreted as being due to equilibrium between two dominant processes: (1) impact gardening and (2) magnetospheric interactions, including sulfur-ion implantation and sputtering redistribution. Removal of the model exogenic pattern in the mosaics reveals the endogenic variations, consisting of only two major units: darker (redder) and bright materials. Therefore Europa's visual spectral reflectivity is simple, having one continuous exogenic pattern and two discrete endogenic units.

Attitude estimation from magnetometer and earth-albedo-corrected coarse sun sensor measurements

NASA Astrophysics Data System (ADS)

Appel, Pontus

2005-01-01

For full 3-axes attitude determination the magnetic field vector and the Sun vector can be used. A Coarse Sun Sensor consisting of six solar cells placed on each of the six outer surfaces of the satellite is used for Sun vector determination. This robust and low cost setup is sensitive to surrounding light sources as it sees the whole sky. To compensate for the largest error source, the Earth, an albedo model is developed. The total albedo light vector has contributions from the Earth surface which is illuminated by the Sun and visible from the satellite. Depending on the reflectivity of the Earth surface, the satellite's position and the Sun's position the albedo light changes. This cannot be calculated analytically and hence a numerical model is developed. For on-board computer use the Earth albedo model consisting of data tables is transferred into polynomial functions in order to save memory space. For an absolute worst case the attitude determination error can be held below 2∘. In a nominal case it is better than 1∘.

Physical characterization of Near Earth Objects with Spitzer

NASA Astrophysics Data System (ADS)

Trilling, David; Hora, Joseph; Mommert, Michael; Chesley, Steve; Emery, Joshua; Fazio, Giovanni; Harris, Alan; Mueller, Migo; Smith, Howard

2018-05-01

We propose here an efficient, flux-limited survey of 426 optically discovered NEOs in order to measure their diameters and albedos. We include only targets not previously detected by Spitzer or NEOWISE and includes all NEOs available to Spitzer in Cycle 14. This program will maintain the fraction of all known NEOs with measured diameters and albedos at around 20% even in the face of increasingly successful NEO discovery surveys. By the conclusion of this program nearly 3500 NEOs will have measured diameters and albedos, with nearly 3000 of those observations being made by Spitzer and our team. We will determine an independent size distribution of NEOs at 100 meters that is free from albedo assumptions, addressing a current controversy. We will also derive, through our albedo measurements, the compositional distribution of NEOs as a function of size. We will measure or constrain lightcurves for more than 400 NEOs, thus constraining their shapes in addition to sizes and compositions. This catalog will enable a number of other science cases to be pursued by us and other researchers. Our team has unmatched experience observing NEOs with Spitzer.

Multiple scattered radiation emerging from Rayleigh and continental haze layers. 1: Radiance, polarization, and neutral points.

PubMed

Kattawar, G W; Plass, G N; Hitzfelder, S J

1976-03-01

The complete radiation field including polarization is calculated by the matrix operator method for scattering layers of various optical thicknesses. Results obtained for Rayleigh scattering are compared with those for scattering from a continental haze. Radiances calculated using Stokes vectors show differences as large as 23% compared to the approximate scalar theory of radiative transfer, while the same differences are only of the order of 0.1% for a continental haze phase function. The polarization of the reflected and transmitted radiation is given for a wide range of optical thicknesses of the scattering layer, for various solar zenith angles, and various surface albedos. Two entirely different types of neutral points occur for aerosol phase functions. Rayleigh-like neutral points (RNP) arise from the zero polarization in single scattering that occurs for all phase functions at scattering angles of 0 degrees and 180 degrees . For Rayleigh phase functions, the position of the RNP varies appreciably with the optical thickness of the scattering layer. At low solar elevations there may be four RNP. For a continental haze phase function the position of the RNP in the reflected radiation shows only a small variation with the optical thickness, and the RNP exists in the transmitted radiation only for extremely small optical thicknesses. Another type of neutral point (NRNP) exists for aerosol phase functions. It is associated with the zeros of the single scattered polarization, which occur between the end points of the curve; these are called non-Rayleigh neutral points (NRNP). There may be from zero to four of these neutral points associated with each zero of the single scattering curve. They occur over a range of azimuthal angles, unlike the RNP that are in the principal plane only. The position of these neutral points is given as a function of solar angle and optical thickness.

Intercomparison of MODIS Albedo Retrievals and In Situ Measurements Across the Global FLUXNET Network

NASA Technical Reports Server (NTRS)

Cescatti, Alessandro; Marcolla, Barbara; Vannan, Suresh K. Santhana; Pan, Jerry Yun; Roman, Miguel O.; Yang, Xiaoyuan; Ciais, Philippe; Cook, Robert B.; Law, Beverly E.; Matteucci, Girogio;

An Approach for the Long-Term 30-m Land Surface Snow-Free Albedo Retrieval from Historic Landsat Surface Reflectance and MODIS-based A Priori Anisotropy Knowledge

NASA Technical Reports Server (NTRS)

Shuai, Yanmin; Masek, Jeffrey G.; Gao, Feng; Schaaf, Crystal B.; He, Tao

2014-01-01

Land surface albedo has been recognized by the Global Terrestrial Observing System (GTOS) as an essential climate variable crucial for accurate modeling and monitoring of the Earth's radiative budget. While global climate studies can leverage albedo datasets from MODIS, VIIRS, and other coarse-resolution sensors, many applications in heterogeneous environments can benefit from higher-resolution albedo products derived from Landsat. We previously developed a "MODIS-concurrent" approach for the 30-meter albedo estimation which relied on combining post-2000 Landsat data with MODIS Bidirectional Reflectance Distribution Function (BRDF) information. Here we present a "pre-MODIS era" approach to extend 30-m surface albedo generation in time back to the 1980s, through an a priori anisotropy Look-Up Table (LUT) built up from the high quality MCD43A BRDF estimates over representative homogenous regions. Each entry in the LUT reflects a unique combination of land cover, seasonality, terrain information, disturbance age and type, and Landsat optical spectral bands. An initial conceptual LUT was created for the Pacific Northwest (PNW) of the United States and provides BRDF shapes estimated from MODIS observations for undisturbed and disturbed surface types (including recovery trajectories of burned areas and non-fire disturbances). By accepting the assumption of a generally invariant BRDF shape for similar land surface structures as a priori information, spectral white-sky and black-sky albedos are derived through albedo-to-nadir reflectance ratios as a bridge between the Landsat and MODIS scale. A further narrow-to-broadband conversion based on radiative transfer simulations is adopted to produce broadband albedos at visible, near infrared, and shortwave regimes.We evaluate the accuracy of resultant Landsat albedo using available field measurements at forested AmeriFlux stations in the PNW region, and examine the consistency of the surface albedo generated by this approach respectively with that from the "concurrent" approach and the coincident MODIS operational surface albedo products. Using the tower measurements as reference, the derived Landsat 30-m snow-free shortwave broadband albedo yields an absolute accuracy of 0.02 with a root mean square error less than 0.016 and a bias of no more than 0.007. A further cross-comparison over individual scenes shows that the retrieved white sky shortwave albedo from the "pre-MODIS era" LUT approach is highly consistent (R(exp 2) = 0.988, the scene-averaged low RMSE = 0.009 and bias = -0.005) with that generated by the earlier "concurrent" approach. The Landsat albedo also exhibits more detailed landscape texture and a wider dynamic range of albedo values than the coincident 500-m MODIS operational products (MCD43A3), especially in the heterogeneous regions. Collectively, the "pre-MODIS" LUT and "concurrent" approaches provide a practical way to retrieve long-term Landsat albedo from the historic Landsat archives as far back as the 1980s, as well as the current Landsat-8 mission, and thus support investigations into the evolution of the albedo of terrestrial biomes at fine resolution.

The cloud radiation impact from optics simulation and airborne observation

NASA Astrophysics Data System (ADS)

Melnikova, Irina; Kuznetsov, Anatoly; Gatebe, Charles

2017-02-01

The analytical approach of inverse asymptotic formulas of the radiative transfer theory is used for solving inverse problems of cloud optics. The method has advantages because it does not impose strict constraints, but it is tied to the desired solution. Observations are accomplished in extended stratus cloudiness, above a homogeneous ocean surface. Data from NASA`s Cloud Absorption Radiometer (CAR) during two airborne experiments (SAFARI-2000 and ARCTAS-2008) were analyzed. The analytical method of inverse asymptotic formulas was used to retrieve cloud optical parameters (optical thickness, single scattering albedo and asymmetry parameter of the phase function) and ground albedo in all 8 spectral channels independently. The method is free from a priori restrictions and there is no links to parameters, and it has been applied to data set of different origin and geometry of observations. Results obtained from different airborne, satellite and ground radiative experiments appeared consistence and showed common features of values of cloud parameters and its spectral dependence (Vasiluev, Melnikova, 2004; Gatebe et al., 2014). Optical parameters, retrieved here, are used for calculation of radiative divergence, reflected and transmitted irradiance and heating rates in cloudy atmosphere, that agree with previous observational data.

Effect of ice-albedo feedback on global sensitivity in a one-dimensional radiative-convective climate model

NASA Technical Reports Server (NTRS)

Wang, W.-C.; Stone, P. H.

1980-01-01

The feedback between the ice albedo and temperature is included in a one-dimensional radiative-convective climate model. The effect of this feedback on global sensitivity to changes in solar constant is studied for the current climate conditions. This ice-albedo feedback amplifies global sensitivity by 26 and 39%, respectively, for assumptions of fixed cloud altitude and fixed cloud temperature. The global sensitivity is not affected significantly if the latitudinal variations of mean solar zenith angle and cloud cover are included in the global model. The differences in global sensitivity between one-dimensional radiative-convective models and energy balance models are examined. It is shown that the models are in close agreement when the same feedback mechanisms are included. The one-dimensional radiative-convective model with ice-albedo feedback included is used to compute the equilibrium ice line as a function of solar constant.

Joint DEnKF-albedo assimilation scheme that considers the common land model subgrid heterogeneity and a snow density-based observation operator for improving snow depth simulations

NASA Astrophysics Data System (ADS)

Xu, Jianhui; Zhang, Feifei; Zhao, Yi; Shu, Hong; Zhong, Kaiwen

2016-07-01

For the large-area snow depth (SD) data sets with high spatial resolution in the Altay region of Northern Xinjiang, China, we present a deterministic ensemble Kalman filter (DEnKF)-albedo assimilation scheme that considers the common land model (CoLM) subgrid heterogeneity. In the albedo assimilation of DEnKF-albedo, the assimilated albedos over each subgrid tile are estimated with the MCD43C1 bidirectional reflectance distribution function (BRDF) parameters product and CoLM calculated solar zenith angle. The BRDF parameters are hypothesized to be consistent over all subgrid tiles within a specified grid. In the SCF assimilation of DEnKF-albedo, a DEnKF combining a snow density-based observation operator considers the effects of the CoLM subgrid heterogeneity and is employed to assimilate MODIS SCF to update SD states over all subgrid tiles. The MODIS SCF over a grid is compared with the area-weighted sum of model predicted SCF over all the subgrid tiles within the grid. The results are validated with in situ SD measurements and AMSR-E product. Compared with the simulations, the DEnKF-albedo scheme can reduce errors of SD simulations and accurately simulate the seasonal variability of SD. Furthermore, it can improve simulations of SD spatiotemporal distribution in the Altay region, which is more accurate and shows more detail than the AMSR-E product.

Regional mapping of aerosol population and surface albedo of Titan by the massive inversion of the Cassini/VIMS dataset

NASA Astrophysics Data System (ADS)

Rodriguez, S.; Cornet, T.; Maltagliati, L.; Appéré, T.; Le Mouelic, S.; Sotin, C.; Barnes, J. W.; Brown, R. H.

2017-12-01

Mapping Titan's surface albedo is a necessary step to give reliable constraints on its composition. However, even after the end of the Cassini mission, surface albedo maps of Titan, especially over large regions, are still very rare, the surface windows being strongly affected by atmospheric contributions (absorption, scattering). A full radiative transfer model is an essential tool to remove these effects, but too time-consuming to treat systematically the 50000 hyperspectral images VIMS acquired since the beginning of the mission. We developed a massive inversion of VIMS data based on lookup tables computed from a state-of-the-art radiative transfer model in pseudo-spherical geometry, updated with new aerosol properties coming from our analysis of observations acquired recently by VIMS (solar occultations and emission phase curves). Once the physical properties of gases, aerosols and surface are fixed, the lookup tables are built for the remaining free parameters: the incidence, emergence and azimuth angles, given by navigation; and two products (the aerosol opacity and the surface albedo at all wavelengths). The lookup table grid was carefully selected after thorough testing. The data inversion on these pre-computed spectra (opportunely interpolated) is more than 1000 times faster than recalling the full radiative transfer at each minimization step. We present here the results from selected flybys. We invert mosaics composed by couples of flybys observing the same area at two different times. The composite albedo maps do not show significant discontinuities in any of the surface windows, suggesting a robust correction of the effects of the geometry (and thus the aerosols) on the observations. Maps of aerosol and albedo uncertainties are also provided, along with absolute errors. We are thus able to provide reliable surface albedo maps at pixel scale for entire regions of Titan and for the whole VIMS spectral range.

A New Bond Albedo for Performing Orbital Debris Brightness to Size Transformations

NASA Technical Reports Server (NTRS)

Mulrooney, Mark K.; Matney, Mark J.

2008-01-01

We have developed a technique for estimating the intrinsic size distribution of orbital debris objects via optical measurements alone. The process is predicated on the empirically observed power-law size distribution of debris (as indicated by radar RCS measurements) and the log-normal probability distribution of optical albedos as ascertained from phase (Lambertian) and range-corrected telescopic brightness measurements. Since the observed distribution of optical brightness is the product integral of the size distribution of the parent [debris] population with the albedo probability distribution, it is a straightforward matter to transform a given distribution of optical brightness back to a size distribution by the appropriate choice of a single albedo value. This is true because the integration of a powerlaw with a log-normal distribution (Fredholm Integral of the First Kind) yields a Gaussian-blurred power-law distribution with identical power-law exponent. Application of a single albedo to this distribution recovers a simple power-law [in size] which is linearly offset from the original distribution by a constant whose value depends on the choice of the albedo. Significantly, there exists a unique Bond albedo which, when applied to an observed brightness distribution, yields zero offset and therefore recovers the original size distribution. For physically realistic powerlaws of negative slope, the proper choice of albedo recovers the parent size distribution by compensating for the observational bias caused by the large number of small objects that appear anomalously large (bright) - and thereby skew the small population upward by rising above the detection threshold - and the lower number of large objects that appear anomalously small (dim). Based on this comprehensive analysis, a value of 0.13 should be applied to all orbital debris albedo-based brightness-to-size transformations regardless of data source. Its prima fascia genesis, derived and constructed from the current RCS to size conversion methodology (SiBAM Size-Based Estimation Model) and optical data reduction standards, assures consistency in application with the prior canonical value of 0.1. Herein we present the empirical and mathematical arguments for this approach and by example apply it to a comprehensive set of photometric data acquired via NASA's Liquid Mirror Telescopes during the 2000-2001 observing season.

Long-term archives of land surface albedo products through the EUMETSAT/LSA-SAF and ECMWF/C3S projects: status and project development plan

NASA Astrophysics Data System (ADS)

Carrer, D.; Pinault, F.; Ceamanos, X.; Meurey, C.; Moparthy, S.; Swinnen, E.; Trigo, I.

2017-12-01

The two space programs of EUMETSAT (project CDOP3, LSA-SAF) and ECMWF (the Copernicus Climate Change Service; C3S_312a Lot9) provide (or will provide) added-value satellite products for the meteorological and environmental science communities, especially in the fields of climate modeling, environmental management, natural hazards management, and climate change detection. The EUMETSAT/LSA-SAF project started in 1999 with research and development activities. The Third Continuous Development and Operations Phase (CDOP-3) starts in March 2017 and will end in 2022. This project uses instruments on board European satellites that were, or will be, launched between 2004 and 2022. Unlike the LSA-SAF, the COPERNICUS/C3S_312a project has no NRT constraint. Its first phase started in november 2016. One of the major objective of the COPERNICUS/C3S_312a project is to harmonize datasets from various sensors in order to provide consistent and continuous ECV products from the 80's until now.Presently, the delivered operational products comprise several surface albedo products using data from various space missions (METEOSAT, NOAA, METOP, …). We present here the portfolio of the surface albedo products that are disseminated with an operational status. Their characteristics and accuracy are detailed here after. Also we will present the development plan to produce long-term re-analysis and to prepare the arrival of the next generation of satellite (MTG, EPS-SG, ...). This work will lead in 2018 to 40 years of products characterizing the albedo properties of the surface. These programs provide a great opportunity to monitor and identify human-induced climate change since consistent production of data sets is guaranteed until at least 2022.

Radiative transfer in the surfaces of atmosphereless bodies. III - Interpretation of lunar photometry

NASA Technical Reports Server (NTRS)

Lumme, K.; Irvine, W. M.

1982-01-01

Narrowband and UBV photoelectric phase curves of the entire lunar disk and surface photometry of some craters have been interpreted using a newly developed generalized radiative transfer theory for planetary regoliths. The data are well fitted by the theory, yielding information on both macroscopic and microscopic lunar properties. Derived values for the integrated disk geometric albedo are considerably higher than quoted previously, because of the present inclusion of an accurately determined opposition effect. The mean surface roughness, defined as the ratio of the height to the radius of a typical irregularity, is found to be 0.9 + or - 0.1, or somewhat less than the mean value of 1.2 obtained for the asteroids. From the phase curves, wavelength-dependent values of the single scattering albedo and the Henyey-Greenstein asymmetry factor for the average surface particle are derived.

Monitoring Land Surface Albedo and Vegetation Dynamics Using High Spatial and Temporal Resolution Synthetic Time Series from Landsat and the MODIS BRDF/NBAR/Albedo Product

NASA Technical Reports Server (NTRS)

Wang, Zhuosen; Schaaf, Crystal B.; Sun, Quingsong; Kim, Jihyun; Erb, Angela M.; Gao, Feng; Roman, Miguel O.; Yang, Yun; Petroy, Shelley; Taylor, Jeffrey R.;

Lunar Phase Function at 1064 Nm from Lunar Orbiter Laser Altimeter Passive and Active Radiometry

NASA Technical Reports Server (NTRS)

Barker, M. K.; Sun, X.; Mazarico, E.; Neumann, G. A.; Zuber, M. T.; Smith, D. E.

2016-01-01

We present initial calibration and results of passive radiometry collected by the Lunar Orbiter Laser Altimeter onboard the Lunar Reconnaissance Orbiter over the course of 12 months. After correcting for time- and temperature-dependent dark noise and detector responsivity variations, the LOLA passive radiometry measurements are brought onto the absolute radiance scale of the SELENE Spectral Profiler. The resulting photometric precision is estimated to be 5%. We leverage the unique ability of LOLA to measure normal albedo to explore the 1064 nm phase function's dependence on various geologic parameters. On a global scale, we find that iron abundance and optical maturity (quantified by FeO and OMAT) are the dominant controlling parameters. Titanium abundance (TiO2), surface roughness on decimeter to decameter scales, and soil thermo- physical properties have a smaller effect, but the latter two are correlated with OMAT, indicating that exposure age is the driving force behind their effects in a globally-averaged sense. The phase function also exhibits a dependence on surface slope at approximately 300 m baselines, possibly the result of mass wasting exposing immature material and/or less space weathering due to reduced sky visibility. Modeling the photometric function in the Hapke framework, we find that, relative to the highlands, the maria exhibit decreased backscattering, a smaller opposition effect (OE) width, and a smaller OE amplitude. Immature highlands regolith has a higher backscattering fraction and a larger OE width compared to mature highlands regolith. Within the maria, the backscattering fraction and OE width show little dependence on TiO2 and OMAT. Variations in the phase function shape at large phase angles are observed in and around the Copernican-aged Jackson crater, including its dark halo, a putative impact melt deposit. Finally, the phase function of the Reiner Gamma Formation behaves more optically immature than is typical for its composition and OMAT, suggesting the visible-to-near-infrared spectrum and phase function respond differently to the unusual regolith evolution and properties at this location. The phase difference map revealed additional geologically-influenced variations in the phase function's shape. In particular, variations were observed associated with the dark halo around Jackson crater, the impact ejecta of Copernicus and Giordano Bruno, and the Reiner Gamma Formation. For the latter, we 915 found that the phase function behaves more optically immature than the global phase function for its composition and OMAT, suggesting a difference in how the visible-to-near-IR spectrum and phase function respond to the unusual regolith evolution and properties at this location.

Changes in blast zone albedo patterns around new martian impact craters

NASA Astrophysics Data System (ADS)

Daubar, I. J.; Dundas, C. M.; Byrne, S.; Geissler, P.; Bart, G. D.; McEwen, A. S.; Russell, P. S.; Chojnacki, M.; Golombek, M. P.

2016-03-01

"Blast zones" (BZs) around new martian craters comprise various albedo features caused by the initial impact, including diffuse halos, extended linear and arcuate rays, secondary craters, ejecta patterns, and dust avalanches. We examined these features for changes in repeat images separated by up to four Mars years. Here we present the first comprehensive survey of the qualitative and quantitative changes observed in impact blast zones over time. Such changes are most likely due to airfall of high-albedo dust restoring darkened areas to their original albedo, the albedo of adjacent non-impacted surfaces. Although some sites show drastic changes over short timescales, nearly half of the sites show no obvious changes over several Mars years. Albedo changes are more likely to occur at higher-latitude sites, lower-elevation sites, and at sites with smaller central craters. No correlation was seen between amount of change and Dust Cover Index, relative halo size, or historical regional albedo changes. Quantitative albedo measurements of the diffuse dark halos relative to their surroundings yielded estimates of fading lifetimes for these features. The average lifetime among sites with measurable fading is ∼15 Mars years; the median is ∼8 Mars years for a linear brightening. However, at approximately half of sites with three or more repeat images, a nonlinear function with rapid initial fading followed by a slow increase in albedo provides a better fit to the fading behavior; this would predict even longer lifetimes. The predicted lifetimes of BZs are comparable to those of slope streaks, and considered representative of fading by global atmospheric dust deposition; they last significantly longer than dust devil or rover tracks, albedo features that are erased by different processes. These relatively long lifetimes indicate that the measurement of the current impact rate by Daubar et al. (Daubar, I.J. et al. [2013]. Icarus 225, 506-516. http://dx.doi.org/10.1016/j.icarus.2013.04.009) does not suffer significantly from overall under-sampling due to blast zones fading before new impact sites can be initially discovered. However, the prevalence of changes seen around smaller craters may explain in part their shallower size frequency distribution.

Changes in blast zone albedo patterns around new martian impact craters

USGS Publications Warehouse

Daubar, Ingrid J.; Dundas, Colin; Byrne, Shane; Geissler, Paul; Bart, Gwen; McEwen, Alfred S.; Russell, Patrick; Chojnacki, Matthew; Golombek, M.P.

2016-01-01

“Blast zones” (BZs) around new martian craters comprise various albedo features caused by the initial impact, including diffuse halos, extended linear and arcuate rays, secondary craters, ejecta patterns, and dust avalanches. We examined these features for changes in repeat images separated by up to four Mars years. Here we present the first comprehensive survey of the qualitative and quantitative changes observed in impact blast zones over time. Such changes are most likely due to airfall of high-albedo dust restoring darkened areas to their original albedo, the albedo of adjacent non-impacted surfaces. Although some sites show drastic changes over short timescales, nearly half of the sites show no obvious changes over several Mars years. Albedo changes are more likely to occur at higher-latitude sites, lower-elevation sites, and at sites with smaller central craters. No correlation was seen between amount of change and Dust Cover Index, relative halo size, or historical regional albedo changes. Quantitative albedo measurements of the diffuse dark halos relative to their surroundings yielded estimates of fading lifetimes for these features. The average lifetime among sites with measurable fading is ∼15 Mars years; the median is ∼8 Mars years for a linear brightening. However, at approximately half of sites with three or more repeat images, a nonlinear function with rapid initial fading followed by a slow increase in albedo provides a better fit to the fading behavior; this would predict even longer lifetimes. The predicted lifetimes of BZs are comparable to those of slope streaks, and considered representative of fading by global atmospheric dust deposition; they last significantly longer than dust devil or rover tracks, albedo features that are erased by different processes. These relatively long lifetimes indicate that the measurement of the current impact rate by Daubar et al. (Daubar, I.J. et al. [2013]. Icarus 225, 506–516. http://dx.doi.org/10.1016/j.icarus.2013.04.009) does not suffer significantly from overall under-sampling due to blast zones fading before new impact sites can be initially discovered. However, the prevalence of changes seen around smaller craters may explain in part their shallower size frequency distribution.

Probing exoplanet clouds with optical phase curves

PubMed Central

Muñoz, Antonio García; Isaak, Kate G.

2015-01-01

Kepler-7b is to date the only exoplanet for which clouds have been inferred from the optical phase curve—from visible-wavelength whole-disk brightness measurements as a function of orbital phase. Added to this, the fact that the phase curve appears dominated by reflected starlight makes this close-in giant planet a unique study case. Here we investigate the information on coverage and optical properties of the planet clouds contained in the measured phase curve. We generate cloud maps of Kepler-7b and use a multiple-scattering approach to create synthetic phase curves, thus connecting postulated clouds with measurements. We show that optical phase curves can help constrain the composition and size of the cloud particles. Indeed, model fitting for Kepler-7b requires poorly absorbing particles that scatter with low-to-moderate anisotropic efficiency, conclusions consistent with condensates of silicates, perovskite, and silica of submicron radii. We also show that we are limited in our ability to pin down the extent and location of the clouds. These considerations are relevant to the interpretation of optical phase curves with general circulation models. Finally, we estimate that the spherical albedo of Kepler-7b over the Kepler passband is in the range 0.4–0.5. PMID:26489652

Photometric diversity of terrains on Triton

NASA Technical Reports Server (NTRS)

Hillier, J.; Veverka, J.; Helfenstein, P.; Lee, P.

1994-01-01

Voyager disk-resolved images of Triton in the violet (0.41 micrometers) and green (0.56 micrometer wavelengths have been analyzed to derive the photometric characteristics of terrains on Triton. Similar conclusions are found using two distinct but related definitions of photometric units, one based on color ratio and albedo properties (A. S. McEwen, 1990), the other on albedo and brightness ratios at different phase angles (P. Lee et al., 1992). A significant diversity of photometric behavior, much broader than that discovered so far on any other icy satellite, occurs among Triton's terrains. Remarkably, differences in photometric behavior do not correlate well with geologic terrain boundaries defined on the basis of surface morphology. This suggests that in most cases photometric properties on Triton are controlled by thin deposits superposed on underlying geologic units. Single scattering albedos are 0.98 or higher and asymmetry factors range from -0.35 to -0.45 for most units. The most distinct scattering behavior is exhibited by the reddish northern units already identified as the Anomalously Scattering Region (ASR), which scatters light almost isotropically with g = -0.04. In part due to the effects of Triton's clouds and haze, it is difficult to constrain the value of bar-theta, Hapke's macroscopic roughness parameter, precisely for Triton or to map differences in bar-theta among the different photometric terrains. However, our study shows that Triton must be relatively smooth, with bar-theta less than 15-20 degs and suggests that a value of 14 degs is appropriate. The differences in photometric characteristics lead to significantly different phase angle behavior for the various terrains. For example, a terrain (e.g., the ASR) that appears dark relative to another at low phase angles will reverse its contrast (become relatively brighter) at larger phase angles. The photometric parameters have been used to calculate hemispherical albedos for the units and to infer likely surface temperatures. Based on these results, we determine that all but the most southerly regions (i.e., mostly south of the equator) of the reddish northern terrains are likely to have been covered with deposits of nitrogen frost at the time of the Voyager flyby, in agreement with the suggestion from the photometry that these units are overlain by a thin veneer of material.

Effect of cadmium pollution of atmospheric origin on field-grown maize in two consecutive years with diverse weather conditions.

PubMed

Anda, Angéla; Illés, Bernadett; Soós, G

2013-12-01

The aim of the study was to analyse the effect of atmospheric cadmium (Cd) pollution of atmospheric origin in maize compared to a control without Cd pollution. The plant parameters investigated were the timing of phenological phases, leaf area index (LAI) and yield, while radiation and water regime parameters were represented by albedo (reflection grade) and evapotranspiration, respectively. In treatments with and without irrigation, Cd caused a significant reduction in LAI, accompanied by lower evapotranspiration. The mean annual albedo in the Cd-polluted treatment only rose to a moderate extent in 2011 (in 2010 there was hardly any change), but changes within the year were more pronounced in certain phases of development. Cd led to greater reflection of radiation by plants during the vegetative phase, so the radiation absorption of the canopy was reduced leading to a lower level of evapotranspiration. In the dry, hot year of 2011 maize plants in the non-irrigated treatments showed a substantial reduction in grain dry matter, but maize yield losses could be reduced by irrigation in areas exposed to Cd pollution.

Recovering the colour-dependent albedo of exoplanets with high-resolution spectroscopy: from ESPRESSO to the ELT.

NASA Astrophysics Data System (ADS)

Martins, J. H. C.; Figueira, P.; Santos, N. C.; Melo, C.; Garcia Muñoz, A.; Faria, J.; Pepe, F.; Lovis, C.

2018-05-01

The characterization of planetary atmospheres is a daunting task, pushing current observing facilities to their limits. The next generation of high-resolution spectrographs mounted on large telescopes - such as ESPRESSO@VLT and HIRES@ELT - will allow us to probe and characterize exoplanetary atmospheres in greater detail than possible to this point. We present a method that permits the recovery of the colour-dependent reflectivity of exoplanets from high-resolution spectroscopic observations. Determining the wavelength-dependent albedo will provide insight into the chemical properties and weather of the exoplanet atmospheres. For this work, we simulated ESPRESSO@VLT and HIRES@ELT high-resolution observations of known planetary systems with several albedo configurations. We demonstrate how the cross correlation technique applied to theses simulated observations can be used to successfully recover the geometric albedo of exoplanets over a range of wavelengths. In all cases, we were able to recover the wavelength dependent albedo of the simulated exoplanets and distinguish between several atmospheric models representing different atmospheric configurations. In brief, we demonstrate that the cross correlation technique allows for the recovery of exoplanetary albedo functions from optical observations with the next generation of high-resolution spectrographs that will be mounted on large telescopes with reasonable exposure times. Its recovery will permit the characterization of exoplanetary atmospheres in terms of composition and dynamics and consolidates the cross correlation technique as a powerful tool for exoplanet characterization.

Evaluation of the MODIS Albedo Product over a Heterogeneous Agricultural Area

NASA Technical Reports Server (NTRS)

Sobrino, Jose Antonio; Franch, B.; Oltra-Carrio, R.; Vermote, E. F.; Fedele, E.

2013-01-01

In this article, the Moderate Resolution Imaging Spectroradiometer (MODIS) Bidirectional Reflectance Distribution Function (BRDF)/Albedo product (MCD43) is evaluated over a heterogeneous agricultural area in the framework of the Earth Observation: Optical Data Calibration and Information Extraction (EODIX) project campaign, which was developed in Barrax (Spain) in June 2011. In this method, two models, the RossThick-LiSparse-Reciprocal (RTLSR) (which corresponds to the MODIS BRDF algorithm) and the RossThick-Maignan-LiSparse-Reciprocal (RTLSR-HS), were tested over airborne data by processing high-resolution images acquired with the Airborne Hyperspectral Scanner (AHS) sensor. During the campaign, airborne images were retrieved with different view zenith angles along the principal and orthogonal planes. Comparing the results of applying the models to the airborne data with ground measurements, we obtained a root mean square error (RMSE) of 0.018 with both RTLSR and RTLSR-HS models. The evaluation of the MODIS BRDF/Albedo product (MCD43) was performed by comparing satellite images with AHS estimations. The results reported an RMSE of 0.04 with both models. Additionally, taking advantage of a homogeneous barley pixel, we compared in situ albedo data to satellite albedo data. In this case, the MODIS albedo estimation was (0.210 +/- 0.003), while the in situ measurement was (0.204 +/- 0.003). This result shows good agreement in regard to a homogeneous pixel.

Mars hemispherical albedo map: absolute value and interannual variability inferred from OMEGA data.

NASA Astrophysics Data System (ADS)

Vincendon, M.; Audouard, J.; Langevin, Y.; Poulet, F.; Bellucci, G.; Bibring, J.-P.; Gondet, B.

2012-04-01

The surface reflectance integrated over all directions and solar wavelengths ("hemispherical albedo") controls the radiative budget at the surface of Mars, and hence its climate. Reference albedo maps are usually derived from nadir observation of surface reflectance through clear atmospheric conditions. However, the atmosphere of Mars is permanently loaded with a significant amount of aerosols (typical visible optical depths of 0.5 under clear atmospheric conditions), which impacts the evaluation of "aerosol free" surface reflectances from remote sensing data. Moreover, the Martian surface is usually assumed to be Lambertian, both for simplicity and due to the lack of robust constraints about its bidirectional properties. We used OMEGA visible and near-IR measurements, with an appropriate UV extrapolation, to calculate as a function of space and time the hemispherical surface albedo of Mars. The contribution of aerosols is removed using a radiative transfer model and recent aerosols properties. Uncertainties associated with this procedure are calculated. The aerosols correction increases the bright/dark surfaces contrast. Typical, mean bidirectional reflectance properties of the martian surface are estimated using MER surface measurements and CRISM remote "EPF" observations. From these constraints, we have derived a typical relationship that makes it possible to convert single nadir measurements of the reflectance into hemispherical albedo. Accounting for the BRDF of the martian surface typically modify by ± 15% the derived albedo, depending on solar zenith angles. We will present our methods and preliminary results regarding seasonal and interannual variations of the surface albedo of Mars during years 2004-2011.

Spectrally-Invariant Approximation Within Atmospheric Radiative Transfer

NASA Technical Reports Server (NTRS)

Marshak, A.; Knyazikhin, Y.; Chiu, J. C.; Wiscombe, W. J.

2011-01-01

Certain algebraic combinations of single scattering albedo and solar radiation reflected from, or transmitted through, vegetation canopies do not vary with wavelength. These "spectrally invariant relationships" are the consequence of wavelength independence of the extinction coefficient and scattering phase function in vegetation. In general, this wavelength independence does not hold in the atmosphere, but in clouddominated atmospheres the total extinction and total scattering phase function vary only weakly with wavelength. This paper identifies the atmospheric conditions under which the spectrally invariant approximation can accurately describe the extinction. and scattering properties of cloudy atmospheres. The validity of the assumptions and the accuracy of the approximation are tested with ID radiative transfer calculations using publicly available radiative transfer models: Discrete Ordinate Radiative Transfer (DISORT) and Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART). It is shown for cloudy atmospheres with cloud optical depth above 3, and for spectral intervals that exclude strong water vapor absorption, that the spectrally invariant relationships found in vegetation canopy radiative transfer are valid to better than 5%. The physics behind this phenomenon, its mathematical basis, and possible applications to remote sensing and climate are discussed.

Surface texture of Vesta from optical polarimetry

NASA Technical Reports Server (NTRS)

Le Bertre, T.; Zellner, B.

1980-01-01

Polarimetric, photometric, and reflective spectroscopic properties of asteroid 4 Vesta are simulated in the laboratory by a preparation of eucrite Bereba consisting of a broad mixture of particle sizes (mainly greater than 50-micron) mixed and partially coated with particles of size 10 microns and less. Coarse grains are necessary for producing the same albedo and a very fine dust coating is necessary for producing the same polarization inversion angle as observed for Vesta. There are less small grains and fine dust in this sample than in lunar soils. Photometrically, if coating a sphere, this sample shows a constant brightness on the sunward half of the observed hemisphere, the brightness being given on the other half by the Minnaert reciprocity principle. With such a photometric behavior, the global geometric albedo and the sub-earth point geometric albedo differ by no more than 5%. The microscopic phase coefficient is 0.021 magnitude per degree for the sample; the larger value, 0.025, observed telescopically for Vesta, indicates that large-scale roughness is present on this asteroid.

Positive effects of vegetation: urban heat island and green roofs.

PubMed

Susca, T; Gaffin, S R; Dell'osso, G R

2011-01-01

This paper attempts to evaluate the positive effects of vegetation with a multi-scale approach: an urban and a building scale. Monitoring the urban heat island in four areas of New York City, we have found an average of 2 °C difference of temperatures between the most and the least vegetated areas, ascribable to the substitution of vegetation with man-made building materials. At micro-scale, we have assessed the effect of surface albedo on climate through the use of a climatological model. Then, using the CO(2) equivalents as indicators of the impact on climate, we have compared the surface albedo, and the construction, replacement and use phase of a black, a white and a green roof. By our analyses, we found that both the white and the green roofs are less impactive than the black one; with the thermal resistance, the biological activity of plants and the surface albedo playing a crucial role. Copyright © 2011 Elsevier Ltd. All rights reserved.

The opposition effect in Saturn's main rings as seen by Cassini ISS: 4. Correlations of the surge morphology with surface albedos and VIMS spectral properties

NASA Astrophysics Data System (ADS)

Déau, Estelle; Dones, Luke; Mishchenko, Michael I.; West, Robert A.; Helfenstein, Paul; Hedman, Matt M.; Porco, Carolyn C.

2018-05-01

In this paper, we continue our analysis of the saturnian ring opposition effect seen by Cassini ISS. The ring opposition effect is a peak in the rings' reflectivity caused as the directions from a spot on the rings to the observer and to the light source, respectively, converge toward zero degrees. So far, the exact origin of the ring's opposition effect is still a matter of debate. In our previous work (Déau, et al., 2013, Icarus, 226, 591-603), we compared the opposition effect morphology with the rings' optical depth and found that only the slope of the linear part of the rings' phase curves was strongly correlated with the optical depth. We interpreted this as an indication of the predominant role of interparticle shadowing at moderate phase angles (α ∼ 10-40o). More recently (Déau, 2015, Icarus, 253, 311-345), we showed that interparticle shadowing cannot explain the behavior at low phase angles (α < 1o), indirectly confirming our 2013 result. These findings led to the idea that coherent backscattering is preponderant at the smallest phase angles. Coherent backscattering depends on the microscopic scale of the regolith, and there is a growing body of evidence that regolith grain size, porosity, roughness, and composition control the opposition surge behavior for α < 1o. To test this hypothesis, we compare the opposition surge morphology to the regolith albedo and other spectral properties related to the regolith, such as water ice band depths and spectral slopes derived from Cassini VIMS data (Hedman et al., 2013, Icarus, 223, 105-130). Indeed, it has been recently proven that coherent backscattering affects the water ice band depth variations with phase angle for icy saturnian regoliths (Kolokolova et al., 2010, The Astrophysical Journal Letters, 711, L71-L74). We find that the opposition surge morphology is strongly correlated with the water ice band depth and the regolith albedo. We interpret this finding as an indication that coherent backscattering plays a role in affecting both the water ice band depths and the opposition surge at low phase angles (α < 1o). As the regolith albedo and spectral properties are related to the grain size, porosity, roughness, and composition, we try to assess which of these regolith properties are preponderant in coherent backscattering. Our study is able to narrow down the parameter space of these properties, whose values allow a good match between the angular width predicted by models of coherent backscattering and the width of the observed peak.

High-resolution mapping and modelling of surface albedo in Norwegian boreal forests: from remotely sensed data to predictions

NASA Astrophysics Data System (ADS)

Cherubini, Francesco; Hu, Xiangping; Vezhapparambu, Sajith; Stromman, Anders

2017-04-01

Surface albedo, a key parameter of the Earth's climate system, has high variability in space, time, and land cover and its parameterization is among the most important variables in climate models. The lack of extensive estimates for model improvement is one of the main limitations for accurately quantifying the influence of surface albedo changes on the planetary radiation balance. We use multi-year satellite retrievals of MODIS surface albedo (MCD43A3), high resolution land cover maps, and meteorological records to characterize albedo variations in Norway across latitude, seasons, land cover type, and topography. We then use this dataset to elaborate semi-empirical models to predict albedo values as a function of tree species, age, volume and climate variables like temperature and snow water equivalents (SWE). Given the complexity of the dataset and model formulation, we apply an innovative non-linear programming approach simultaneously coupled with linear un-mixing. The MODIS albedo products are at a resolution of about 500 m and 8 days. The land cover maps provide vegetation structure information on relative abundance of tree species, age, and biomass volumes at 16 m resolution (for both deciduous and coniferous species). Daily observations of meteorological information on air temperature and SWE are produced at 1 km resolution from interpolation of meteorological weather stations in Norway. These datasets have different resolution and projection, and are harmonized by identifying, for each MODIS pixel, the intersecting land cover polygons and the percentage area of the MODIS pixel represented by each land cover type. We then filter the subplots according to the following criteria: i) at least 96% of the total pixel area is covered by a single land cover class (either forest or cropland); ii) if forest area, at least 98% of the forest area is covered by spruce, deciduous or pine. Forested pixels are then categorized as spruce, deciduous, or pine dominant if the fraction of the respective tree species is greater than 75%. Results show averages of albedo estimates for forests and cropland depicting spatial (along a latitudinal gradient) and temporal (daily, monthly, and seasonal) variations across Norway. As the case study region is a country with heterogeneous topography, we also study the sensitivity of the albedo estimates to the slope and aspect of the terrain. The mathematical programming approach uses a variety of functional forms, constraints and variables, leading to many different model outputs. There are several models with relatively high performances, allowing for a flexibility in the model selection, with different model variants suitable for different situations. This approach produces albedo predictions at the same resolution of the land cover dataset (16 m, notably higher than the MODIS estimates), can incorporate changes in climate conditions, and is robust to cross-validation between different locations. By integrating satellite measurements and high-resolution vegetation maps, we can thus produce semi-empirical models that can predict albedo values for boreal forests using a variety of input variables representing climate and/or vegetation structure. Further research can explore the possible advantages of its implementation in land surface schemes over existing approaches.

Galileo photometry of asteroid 243 Ida

USGS Publications Warehouse

Helfenstein, P.; Veverka, J.; Thomas, P.C.; Simonelli, D.P.; Klaasen, K.; Johnson, T.V.; Fanale, F.; Granahan, J.; McEwen, A.S.; Belton, M.; Chapman, C.

1996-01-01

Galileo imaging observations over phase angles 19.5?? to 109.8?? are combined with near-opposition Earth-based data to derive the photometric properties of Ida. To first order these properties are uniform over the surface and well modeled at ?? = 0.55 ??m by Hapke parameters ????0 = 0.22, h = 0.020, B0 = 1.5, g = -0.33, and ?? = 18?? with corresponding geometric albedo p = 0.21??0.030.01 and Bond albedo AB = 0.081??0.0170.008. Ida's photometric properties are more similar to those of "average S-asteroids" (P. Helfenstein and J. Veverka 1989, Asteroids II, Univ. of Arizona Press, Tucson) than are those of 951 Gaspra. Two primary color units are identified on Ida: Terrain A exhibits a spectrum with relatively shallower 1-??m absorption and a relatively steeper red spectral slope than average Ida, while Terrain B has a deeper 1-??m absorption and a less steep red slope. The average photometric properties of Ida and Terrain A are similar while those of Terrain B differ mostly in having a slightly higher value of ????0 (0.22 versus 0.21), suggesting that Terrain B consists of slightly brighter, more transparent regolith particles. Galileo observations of Ida's satellite Dactyl over phase angles 19.5?? to 47.6?? suggest photometric characteristics similar to those of Ida, the major difference being Dactyl's slightly lower albedo (0.20 compared to 0.21). ?? 1990 Academic Press, Inc.

Lunar phase function at 1064 nm from Lunar Orbiter Laser Altimeter passive and active radiometry

NASA Astrophysics Data System (ADS)

Barker, M. K.; Sun, X.; Mazarico, E.; Neumann, G. A.; Zuber, M. T.; Smith, D. E.

2016-07-01

We present initial calibration and results of passive radiometry collected by the Lunar Orbiter Laser Altimeter onboard the Lunar Reconnaissance Orbiter over the course of 12 months. After correcting for time- and temperature-dependent dark noise and detector responsivity variations, the LOLA passive radiometry measurements are brought onto the absolute radiance scale of the SELENE Spectral Profiler. The resulting photometric precision is estimated to be ∼5%. We leverage the unique ability of LOLA to measure normal albedo to explore the 1064 nm phase function's dependence on various geologic parameters. On a global scale, we find that iron abundance and optical maturity (quantified by FeO and OMAT) are the dominant controlling parameters. Titanium abundance (TiO2), surface roughness on decimeter to decameter scales, and soil thermophysical properties have a smaller effect, but the latter two are correlated with OMAT, indicating that exposure age is the driving force behind their effects in a globally-averaged sense. The phase function also exhibits a dependence on surface slope at ∼300 m baselines, possibly the result of mass wasting exposing immature material and/or less space weathering due to reduced sky visibility. Modeling the photometric function in the Hapke framework, we find that, relative to the highlands, the maria exhibit decreased backscattering, a smaller opposition effect (OE) width, and a smaller OE amplitude. Immature highlands regolith has a higher backscattering fraction and a larger OE width compared to mature highlands regolith. Within the maria, the backscattering fraction and OE width show little dependence on TiO2 and OMAT. Variations in the phase function shape at large phase angles are observed in and around the Copernican-aged Jackson crater, including its dark halo, a putative impact melt deposit. Finally, the phase function of the Reiner Gamma Formation behaves more optically immature than is typical for its composition and OMAT, suggesting the visible-to-near-infrared spectrum and phase function respond differently to the unusual regolith evolution and properties at this location.

Lunar Phase Function at 1064 Nm from Lunar Orbiter Laser Altimeter Passive and Active Radiometry

NASA Technical Reports Server (NTRS)

Barker, M. K.; Sun, X.; Mazarico, E.; Neumann, G. A.; Zuber, M. T.; Smith, D. E.

2016-01-01

We present initial calibration and results of passive radiometry collected by the Lunar Orbiter Laser Al- timeter onboard the Lunar Reconnaissance Orbiter over the course of 12 months. After correcting for time- and temperature-dependent dark noise and detector responsivity variations, the LOLA passive radiometry measurements are brought onto the absolute radiance scale of the SELENE Spectral Profiler. The resulting photometric precision is estimated to be approximately 5%. We leverage the unique ability of LOLA to measure normal albedo to explore the 1064 nm phase function's dependence on various geologic parameters. On a global scale, we find that iron abundance and optical maturity (quantified by FeO and OMAT) are the dominant controlling parameters. Titanium abundance (TiO2 ), surface roughness on decimeter to decameter scales, and soil thermophysical properties have a smaller effect, but the latter two are correlated with OMAT, indicating that exposure age is the driving force behind their effects in a globally-averaged sense. The phase function also exhibits a dependence on surface slope at approximately 300 m baselines, possibly the result of mass wasting exposing immature material and/or less space weathering due to reduced sky visibility. Modeling the photometric function in the Hapke framework, we find that, relative to the highlands, the maria exhibit decreased backscattering, a smaller opposition effect (OE) width, and a smaller OE amplitude. Immature highlands regolith has a higher backscattering fraction and a larger OE width compared to mature highlands regolith. Within the maria, the backscattering fraction and OE width show little dependence on TiO2 and OMAT. Variations in the phase function shape at large phase angles are observed in and around the Copernican-aged Jackson crater, including its dark halo, a putative impact melt deposit. Finally, the phase function of the Reiner Gamma Formation behaves more optically immature than is typical for its composition and OMAT, suggesting the visible-to-near-infrared spectrum and phase function respond differently to the unusual regolith evolution and properties at this location.

Radiative transfer modeling of dust-coated Pancam calibration target materials: Laboratory visible/near-infrared spectrogoniometry

USGS Publications Warehouse

Johnson, J. R.; Sohl-Dickstein, J.; Grundy, W.M.; Arvidson, R. E.; Bell, J.F.; Christensen, P.R.; Graff, T.; Guinness, E.A.; Kinch, K.; Morris, Robert; Shepard, M.K.

2006-01-01

Laboratory visible/near-infrared multispectral observations of Mars Exploration Rover Pancam calibration target materials coated with different thicknesses of Mars spectral analog dust were acquired under variable illumination geometries using the Bloomsburg University Goniometer. The data were fit with a two-layer radiative transfer model that combines a Hapke formulation for the dust with measured values of the substrate interpolated using a He-Torrance approach. We first determined the single-scattering albedo, phase function, opposition effect width, and amplitude for the dust using the entire data set (six coating thicknesses, three substrates, four wavelengths, and phase angles 3??-117??). The dust exhibited single-scattering albedo values similar to other Mars analog soils and to Mars Pathfinder dust and a dominantly forward scattering behavior whose scattering lobe became narrower at longer wavelengths. Opacity values for each dust thickness corresponded well to those predicted from the particles sizes of the Mars analog dust. We then restricted the number of substrates, dust thicknesses, and incidence angles input to the model. The results suggest that the dust properties are best characterized when using substrates whose reflectances are brighter and darker than those of the deposited dust and data that span a wide range of dust thicknesses. The model also determined the dust photometric properties relatively well despite limitations placed on the range of incidence angles. The model presented here will help determine the photometric properties of dust deposited on the MER rovers and to track the multiple episodes of dust deposition and erosion that have occurred at both landing sites. Copyright 2006 by the American Geophysical Union.

Cellulose nanocrystal from pomelo (C. Grandis osbeck) albedo: Chemical, morphology and crystallinity evaluation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zain, Nor Fazelin Mat; Yusop, Salma Mohamad; Ahmad, Ishak

Citrus peel is one of the under-utilized waste materials that have potential in producing a valuable fibre, which are cellulose and cellulose nanocrystal. Cellulose was first isolated from pomelo (C. Grandis Osbeck) albedo by combination of alkali treatment and bleaching process, followed by acid hydrolysis (65% H{sub 2}SO{sub 4}, 45 °C, 45min) to produce cellulose nanocrystal. The crystalline, structural, morphological and chemical properties of both materials were studied. Result reveals the crystallinity index obtained from X-ray diffraction for cellulose nanocrystal was found higher than extracted cellulose with the value of 60.27% and 57.47%, respectively. Fourier transform infrared showed that themore » chemical treatments removed most of the hemicellulose and lignin from the pomelo albedo fibre. This has been confirmed further by SEM and TEM for their morphological studies. These results showed that cellulose and cellulose nanocrystal were successfully obtained from pomelo albedo and might be potentially used in producing functional fibres for food application.« less

Quantifying the influence of deep soil moisture on ecosystem albedo: the role of vegetation Zulia M. Sánchez-Mejía 1 and Shirley A. Papuga1 1School of Natural Resources and the Environment, University of Arizona, Tucson, AZ

NASA Astrophysics Data System (ADS)

Sanchez-Mejia, Z. M.; Papuga, S. A.

2012-12-01

Water limited ecosystems in arid and semiarid regions are characterized by sparse vegetation and a relatively large fraction of bare soil. Importantly, the land surface in these dryland regions is highly sensitive to pulses of moisture that affect the vegetation canopy in density and color, as well as the soil color. Changes in surface conditions due to these pulses have been shown to affect the surface energy fluxes and atmospheric processes in these regions. For instance, previous studies have shown that shallow soil moisture ( < 20 cm below the surface) significantly changes surface albedo (a= SWup/ SWin). Recent studies have highlighted the importance of deep soil moisture ( > 20 cm below the surface) for vegetation dynamics in these regions. We hypothesize that deep soil moisture will change vegetation canopy density and color enough that changes in albedo will be observable at the surface, therefore linking deep soil moisture and albedo. We adopt a conceptual framework to address this hypothesis, where at any point in time the soil profile falls into one of four cases: (1) dry shallow soil and dry deep soil; (2) wet shallow soil and dry deep soil; (3) wet shallow soil and wet deep soil; and (4) dry shallow soil and wet deep soil. At a creosotebush dominated ecosystem of the Santa Rita Experimental Range, southern Arizona during summers of 2011 and 2012, we took albedo measurements during these cases at multiple bare and vegetated patches within the footprint of an eddy covariance tower. We found that when the soil is completely dry (Case 1) albedo is highest in both bare and vegetated patches. Likewise, when the soil is wet in both the shallow and deep regions (Case 3), albedo is lowest in both bare and vegetated patches. Interestingly, we also found that albedo is significantly lower for vegetated patches when the deep soil is wet and shallow soil is dry (Case 4). These results imply that deep soil moisture can be important in altering ecosystem level albedo. We note that ecosystems with higher percent vegetative cover are likely to be more sensitive to deep soil moisture driven changes in albedo. To quantify the influence of percent cover on ecosystem albedo, we populate a 100 x 100 cell grid randomly with bare and vegetated cells. For each case, we assign an albedo value to each cell based on probability distribution functions (PDFs) of soil moisture and albedo created from our field campaign data. Using this technique we can identify for each soil moisture case at which point the percent vegetative cover will significantly influence ecosystem albedo. Quantitative analyses of these ecosystem interactions help identify the unique role of deep soil moisture in land surface - atmosphere interactions.

The Global Albedo of the Moon at 1064 nm from LOLA

NASA Technical Reports Server (NTRS)

Lucey, P. G.; Neumann, G. A.; Riner, M. A.; Mazarico, E.; Smith, D. E.; Zuber, M. T.; Paige, D. A.; Bussey, D. B.; Cahill, J. T.; McGovern, A.;

Average Albedos of Close-in Super-Earths and Super-Neptunes from Statistical Analysis of Long-cadence Kepler Secondary Eclipse Data

NASA Astrophysics Data System (ADS)

Sheets, Holly A.; Deming, Drake

2017-10-01

We present the results of our work to determine the average albedo for small, close-in planets in the Kepler candidate catalog. We have adapted our method of averaging short-cadence light curves of multiple Kepler planet candidates to long-cadence data, in order to detect an average albedo for the group of candidates. Long-cadence data exist for many more candidates than the short-cadence data, and so we separate the candidates into smaller radius bins than in our previous work: 1-2 {R}\\oplus , 2-4 {R}\\oplus , and 4-6 {R}\\oplus . We find that, on average, all three groups appear darker than suggested by the short-cadence results, but not as dark as many hot Jupiters. The average geometric albedos for the three groups are 0.11 ± 0.06, 0.05 ± 0.04, and 0.23 ± 0.11, respectively, for the case where heat is uniformly distributed about the planet. If heat redistribution is inefficient, the albedos are even lower, since there will be a greater thermal contribution to the total light from the planet. We confirm that newly identified false-positive Kepler Object of Interest (KOI) 1662.01 is indeed an eclipsing binary at twice the period listed in the planet candidate catalog. We also newly identify planet candidate KOI 4351.01 as an eclipsing binary, and we report a secondary eclipse measurement for Kepler-4b (KOI 7.01) of ˜7.50 ppm at a phase of ˜0.7, indicating that the planet is on an eccentric orbit.

Preliminary results of aerosols' properties studied with EPF measurements from the SPICAM/UV instrument

NASA Astrophysics Data System (ADS)

Willame, Yannick; Carine Vandaele, Ann; Depiesse, Cedric; Gillotay, Didier; Kochenova, Svetlana; Montmessin, Franck

2013-04-01

Aerosols on Mars have an important impact on the radiative transfer properties of its atmosphere. Today their spectral properties and therefore their interaction with UV radiation are only poorly known. Improving the radiative transfer modeling requires a better knowledge of their characteristics, in particular of their opacity, phase function and single scattering albedo. Part of such information can be accessed by using EPF observations. The SPICAM instrument on board of the Mars-Express satellite is a 2 channel spectrometer. One channel operates in the ultraviolet (118-320 nm) and the second one in the infrared (1.0-1.7μm). SPICAM has been orbiting around the red planet since 2003 and has thus provided a large set of data. The instrument is capable of measuring under different geometries (nadir, limb, occultation) and one of them, called EPF (Emission Phase Function), can be a tool to study aerosols' properties. We have developed a new retrieval algorithm for nadir measurements based on the radiative transfer model LIDORT. This new code performs simulations of spectra taking into account gas absorption, surface reflection and scattering by aerosols and gases. The retrieval method, based on the optimal estimation, allows us up to now to deduce the ozone column density, the aerosols' optical depth and the surface albedo (with fixed wavelength dependencies). We are developing our model further in order to better study the aerosols' characteristics using EPF observations, which consist in looking at the same point on the planet while the satellite moves along the orbit. As the attempt to study all the aerosols' properties simultaneously was not convincing, we started studying their opacity and the influence of its altitude distribution with the other characteristics fixed. We will present preliminary results of our study on aerosols' properties using EPF data from SPICAM.

Preliminary results of aerosols' properties studied with EPF measurements from the SPICAM/UV instrument

NASA Astrophysics Data System (ADS)

Willame, Y.; Vandaele, A.-C.; Depiesse, C.; Gillotay, D.; Kochenova, S.; Montmessin, F.

2012-04-01

Aerosols on Mars have an important impact on the radiative transfer properties of its atmosphere. Today their spectral properties and therefore their interaction with UV radiation are only poorly known. Improving the radiative transfer modeling requires a better knowledge of their characteristics, in particular of their opacity, phase function and single scattering albedo. We will show that such information can be accessed by using EPF observations. The SPICAM instrument on board of the Mars-Express satellite is a 2 channel spectrometer. One channel operates in the ultraviolet (118-320 nm) and the second one in the infrared (1.0-1.7μm). SPICAM has been orbiting around the red planet since 2003 and has thus provided a large set of data. The instrument is capable of measuring under different geometries (nadir, limb, occultation) and one of them, called EPF (Emission Phase Function), is a practical tool to study aerosols' properties. We have developed a new retrieval algorithm for nadir measurements based on the radiative transfer model LIDORT. This new code performs simulations of spectra taking into account gas absorption, surface reflection and scattering by aerosols and gases. The retrieval method, based on the optimal estimation, allows us up to now to deduce the ozone column density, the aerosols' optical depth and the surface albedo (with fixed wavelength dependencies). We are developing our model further in order to better study the aerosols' characteristics using EPF observations, which consist in looking at the same point on the planet while the satellite moves along the orbit. As the attempt to study all the aerosols' properties simultaneously was not convincing, we will start with studying their opacity and its altitude distribution with the other characteristics fixed. We will present preliminary results of our study on aerosols' properties and their wavelength dependencies, using EPF data. The method will be illustrated by investigating SPICAM observations obtained in EPF mode.

PHOTOMETRIC ORBITS OF EXTRASOLAR PLANETS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brown, Robert A.

We define and analyze the photometric orbit (PhO) of an extrasolar planet observed in reflected light. In our definition, the PhO is a Keplerian entity with six parameters: semimajor axis, eccentricity, mean anomaly at some particular time, argument of periastron, inclination angle, and effective radius, which is the square root of the geometric albedo times the planetary radius. Preliminarily, we assume a Lambertian phase function. We study in detail the case of short-period giant planets (SPGPs) and observational parameters relevant to the Kepler mission: 20 ppm photometry with normal errors, 6.5 hr cadence, and three-year duration. We define a relevantmore » 'planetary population of interest' in terms of probability distributions of the PhO parameters. We perform Monte Carlo experiments to estimate the ability to detect planets and to recover PhO parameters from light curves. We calibrate the completeness of a periodogram search technique, and find structure caused by degeneracy. We recover full orbital solutions from synthetic Kepler data sets and estimate the median errors in recovered PhO parameters. We treat in depth a case of a Jupiter body-double. For the stated assumptions, we find that Kepler should obtain orbital solutions for many of the 100-760 SPGP that Jenkins and Doyle estimate Kepler will discover. Because most or all of these discoveries will be followed up by ground-based radial velocity observations, the estimates of inclination angle from the PhO may enable the calculation of true companion masses: Kepler photometry may break the 'msin i' degeneracy. PhO observations may be difficult. There is uncertainty about how low the albedos of SPGPs actually are, about their phase functions, and about a possible noise floor due to systematic errors from instrumental and stellar sources. Nevertheless, simple detection of SPGPs in reflected light should be robust in the regime of Kepler photometry, and estimates of all six orbital parameters may be feasible in at least a subset of cases.« less

THEMIS high-resolution digital terrain: Topographic and thermophysical mapping of Gusev Crater, Mars

USGS Publications Warehouse

Cushing, G.E.; Titus, T.N.; Soderblom, L.A.; Kirk, R.L.

2009-01-01

We discuss a new technique to generate high-resolution digital terrain models (DTMs) and to quantitatively derive and map slope-corrected thermophysical properties such as albedo, thermal inertia, and surface temperatures. This investigation is a continuation of work started by Kirk et al. (2005), who empirically deconvolved Thermal Emission Imaging System (THEMIS) visible and thermal infrared data of this area, isolating topographic information that produced an accurate DTM. Surface temperatures change as a function of many variables such as slope, albedo, thermal inertia, time, season, and atmospheric opacity. We constrain each of these variables to construct a DTM and maps of slope-corrected albedo, slope- and albedo-corrected thermal inertia, and surface temperatures across the scene for any time of day or year and at any atmospheric opacity. DTMs greatly facilitate analyses of the Martian surface, and the MOLA global data set is not finely scaled enough (128 pixels per degree, ???0.5 km per pixel near the equator) to be combined with newer data sets (e.g., High Resolution Imaging Science Experiment, Context Camera, and Compact Reconnaissance Imaging Spectrometer for Mars at ???0.25, ???6, and ???20 m per pixel, respectively), so new techniques to derive high-resolution DTMs are always being explored. This paper discusses our technique of combining a set of THEMIS visible and thermal infrared observations such that albedo and thermal inertia variations within the scene are eliminated and only topographic variations remain. This enables us to produce a high-resolution DTM via photoclinometry techniques that are largely free of albedo-induced errors. With this DTM, THEMIS observations, and a subsurface thermal diffusion model, we generate slope-corrected maps of albedo, thermal inertia, and surface temperatures. In addition to greater accuracy, these products allow thermophysical properties to be directly compared with topography.

Lightcurve, Color and Phase Function Photometry of the OSIRIS-REx Target Asteroid (101955) Bennu

NASA Astrophysics Data System (ADS)

Hergenrother, Carl W.; Nolan, Michael C.; Binzel, Richard P.; Cloutis, Edward A.; Barucci, Maria Antonietta; Michel, Patrick; Scheeres, Daniel J.; d'Aubigny, Christian Drouet; Lazzaro, Daniela; Pinilla-Alonso, Noemi; Campins, Humberto; Licandro, Javier; Clark, Beth E.; Rizk, Bashar; Beshore, Edward C.; Lauretta, Dante S.

2013-09-01

The NASA OSIRIS-REx mission will retrieve a sample of the carbonaceous near-Earth Asteroid (101955) Bennu and return it to Earth in 2023. Photometry in the Eight Color Asteroid Survey (ECAS) filter system and Johnson-Cousins V and R filters were conducted during the two most recent apparitions in 2005/2006 and 2011/2012. Lightcurve observations over the nights of September 14-17, 2005 yielded a synodic rotation period of 4.2905 ± 0.0065 h, which is consistent with the results of Nolan et al. (2013). ECAS color measurements made during the same nights confirm the B-type classification of Clark et al. (Clark, B.E., Binzel, R.P., Howell, E.S., Cloutis, E.A., Ockert-Bell, M., Christensen, P., Barucci, M.A., DeMeo, F., Lauretta, D.S., Connolly, H., Soderberg, A., Hergenrother, C., Lim, L., Emery, J., Mueller, M. [2011]. Icarus 216, 462-475). A search for the 0.7 μm hydration feature using the method of Vilas (Vilas, F. [1994]. Icarus 111, 456-467) did not reveal its presence. Photometry was obtained over a range of phase angles from 15° to 96° between 2005 and 2012. The resulting phase function slope of 0.040 magnitudes per degree is consistent with the phase slopes of other low albedo near-Earth asteroids (Belskaya, I.N., Shevchenko, V.G. [2000]. Icarus 147, 94-105).

Visible-NIR Spectroscopic Evidence for the Composition of Low-Albedo Altered Soils on Mars

NASA Astrophysics Data System (ADS)

Murchie, S.; Merenyi, E.; Singer, R.; Kirkland, L.

1996-03-01

Spectroscopic studies of altered Martian soils at visible and at NIR wavelengths have generally supported the canonical model of the surface layer as consisting mostly of 2 components, bright red hematite-containing dust and dark gray pyroxene-containing sand. However several of the studies have also provided tantalizing evidence for distinct 1 micrometer Fe absorptions in discrete areas, particularly dark red soils which are hypothesized to consist of duricrust. These distinct absorptions have been proposed to originate from one or more non-hematitic ferric phases. We have tested this hypothesis by merging high spatial resolution visible- and NIR-wavelength data to synthesize composite 0.44-3.14 1lm spectra for regions of western Arabia and Margaritifer Terra. The extended wavelength coverage allows more complete assessment of ferric, ferrous, and H2O absorptions in both wavelength ranges. The composite data show that, compared to nearby bright red soil in Arabia, dark red soil in Oxia has a lower albedo, a more negative continuum slope, and a stronger 3 micrometer H2O absorption . However Fe absorptions are closely similar in position and depth. These results suggest that at least some dark red soils may differ from "normal" dust and mafic sand more in texture than in Fe mineralogy, although there appears to be enrichment in a water-containing phase and/or a dark, spectrally neutral phase. In contrast, there is clear evidence for enrichment of a low-albedo ferric mineral in dark gray soils composing Sinus Meridiani. These have visible- and NIR-wavelength absorptions consistent with crystalline hematite with relatively little pyroxene, plus a very weak 3 micrometer H2O absorption. These properties suggest a Ethology richer in crystalline hematite and less hydrated than both dust and mafic-rich sand.

MALIBU: A High Spatial Resolution Multi-Angle Imaging Unmanned Airborne System to Validate Satellite-derived BRDF/Albedo Products

NASA Astrophysics Data System (ADS)

Wang, Z.; Roman, M. O.; Pahlevan, N.; Stachura, M.; McCorkel, J.; Bland, G.; Schaaf, C.

2016-12-01

Albedo is a key climate forcing variable that governs the absorption of incoming solar radiation and its ultimate transfer to the atmosphere. Albedo contributes significant uncertainties in the simulation of climate changes; and as such, it is defined by the Global Climate Observing System (GCOS) as a terrestrial essential climate variable (ECV) required by global and regional climate and biogeochemical models. NASA's Goddard Space Flight Center's Multi AngLe Imaging Bidirectional Reflectance Distribution Function small-UAS (MALIBU) is part of a series of pathfinder missions to develop enhanced multi-angular remote sensing techniques using small Unmanned Aircraft Systems (sUAS). The MALIBU instrument package includes two multispectral imagers oriented at two different viewing geometries (i.e., port and starboard sides) capture vegetation optical properties and structural characteristics. This is achieved by analyzing the surface reflectance anisotropy signal (i.e., BRDF shape) obtained from the combination of surface reflectance from different view-illumination angles and spectral channels. Satellite measures of surface albedo from MODIS, VIIRS, and Landsat have been evaluated by comparison with spatially representative albedometer data from sparsely distributed flux towers at fixed heights. However, the mismatch between the footprint of ground measurements and the satellite footprint challenges efforts at validation, especially for heterogeneous landscapes. The BRDF (Bidirectional Reflectance Distribution Function) models of surface anisotropy have only been evaluated with airborne BRDF data over a very few locations. The MALIBU platform that acquires extremely high resolution sub-meter measures of surface anisotropy and surface albedo, can thus serve as an important source of reference data to enable global land product validation efforts, and resolve the errors and uncertainties in the various existing products generated by NASA and its national and international partners.

Evaluation of coarse scale land surface remote sensing albedo product over rugged terrain

NASA Astrophysics Data System (ADS)

Wen, J.; Xinwen, L.; You, D.; Dou, B.

2017-12-01

Satellite derived Land surface albedo is an essential climate variable which controls the earth energy budget and it can be used in applications such as climate change, hydrology, and numerical weather prediction. The accuracy and uncertainty of surface albedo products should be evaluated with a reliable reference truth data prior to applications. And more literatures investigated the validation methods about the albedo validation in a flat or homogenous surface. However, the albedo performance over rugged terrain is still unknow due to the validation method limited. A multi-validation strategy is implemented to give a comprehensive albedo validation, which will involve the high resolution albedo processing, high resolution albedo validation based on in situ albedo, and the method to upscale the high resolution albedo to a coarse scale albedo. Among them, the high resolution albedo generation and the upscale method is the core step for the coarse scale albedo validation. In this paper, the high resolution albedo is generated by Angular Bin algorithm. And a albedo upscale method over rugged terrain is developed to obtain the coarse scale albedo truth. The in situ albedo located 40 sites in mountain area are selected globally to validate the high resolution albedo, and then upscaled to the coarse scale albedo by the upscale method. This paper takes MODIS and GLASS albedo product as a example, and the prelimarily results show the RMSE of MODIS and GLASS albedo product over rugged terrain are 0.047 and 0.057, respectively under the RMSE with 0.036 of high resolution albedo.

The Relationship Between Arctic Sea Ice Albedo and the Geophysical Parameters of the Ice Cover

NASA Astrophysics Data System (ADS)

Riihelä, A.

2015-12-01

The Arctic sea ice cover is thinning and retreating. Remote sensing observations have also shown that the mean albedo of the remaining ice cover is decreasing on decadal time scales, albeit with significant annual variability (Riihelä et al., 2013, Pistone et al., 2014). Attribution of the albedo decrease between its different drivers, such as decreasing ice concentration and enhanced surface melt of the ice, remains an important research question for the forecasting of future conditions of the ice cover. A necessary step towards this goal is understanding the relationships between Arctic sea ice albedo and the geophysical parameters of the ice cover. Particularly the question of the relationship between sea ice albedo and ice age is both interesting and not widely studied. The recent changes in the Arctic sea ice zone have led to a substantial decrease of its multi-year sea ice, as old ice melts and is replaced by first-year ice during the next freezing season. It is generally known that younger sea ice tends to have a lower albedo than older ice because of several reasons, such as wetter snow cover and enhanced melt ponding. However, the quantitative correlation between sea ice age and sea ice albedo has not been extensively studied to date, excepting in-situ measurement based studies which are, by necessity, focused on a limited area of the Arctic Ocean (Perovich and Polashenski, 2012).In this study, I analyze the dependencies of Arctic sea ice albedo relative to the geophysical parameters of the ice field. I use remote sensing datasets such as the CM SAF CLARA-A1 (Karlsson et al., 2013) and the NASA MeaSUREs (Anderson et al., 2014) as data sources for the analysis. The studied period is 1982-2009. The datasets are spatiotemporally collocated and analysed. The changes in sea ice albedo as a function of sea ice age are presented for the whole Arctic Ocean and for potentially interesting marginal sea cases. This allows us to see if the the albedo of the older sea ice in the central parts of the Arctic Ocean is resistant to the decreasing overall trend.A similar analysis is also extended to ice concentration, melt season length and other appropriate parameters describing the surface conditions. The results of the analyses are summed up to provide an assessment of the relative impact strengths of the ice field parameters on the albedo.

Albedo feedbacks to future climate via climate change impacts on dryland biocrusts.

PubMed

Rutherford, William A; Painter, Thomas H; Ferrenberg, Scott; Belnap, Jayne; Okin, Gregory S; Flagg, Cody; Reed, Sasha C

2017-03-10

Drylands represent the planet's largest terrestrial biome and evidence suggests these landscapes have large potential for creating feedbacks to future climate. Recent studies also indicate that dryland ecosystems are responding markedly to climate change. Biological soil crusts (biocrusts) ‒ soil surface communities of lichens, mosses, and/or cyanobacteria ‒ comprise up to 70% of dryland cover and help govern fundamental ecosystem functions, including soil stabilization and carbon uptake. Drylands are expected to experience significant changes in temperature and precipitation regimes, and such alterations may impact biocrust communities by promoting rapid mortality of foundational species. In turn, biocrust community shifts affect land surface cover and roughness-changes that can dramatically alter albedo. We tested this hypothesis in a full-factorial warming (+4 °C above ambient) and altered precipitation (increased frequency of 1.2 mm monsoon-type watering events) experiment on the Colorado Plateau, USA. We quantified changes in shortwave albedo via multi-angle, solar-reflectance measurements. Warming and watering treatments each led to large increases in albedo (>30%). This increase was driven by biophysical factors related to treatment effects on cyanobacteria cover and soil surface roughness following treatment-induced moss and lichen mortality. A rise in dryland surface albedo may represent a previously unidentified feedback to future climate.

Albedo feedbacks to future climate via climate change impacts on dryland biocrusts

NASA Astrophysics Data System (ADS)

Rutherford, William A.; Painter, Thomas H.; Ferrenberg, Scott; Belnap, Jayne; Okin, Gregory S.; Flagg, Cody; Reed, Sasha C.

2017-03-01

Drylands represent the planet’s largest terrestrial biome and evidence suggests these landscapes have large potential for creating feedbacks to future climate. Recent studies also indicate that dryland ecosystems are responding markedly to climate change. Biological soil crusts (biocrusts) ‒ soil surface communities of lichens, mosses, and/or cyanobacteria ‒ comprise up to 70% of dryland cover and help govern fundamental ecosystem functions, including soil stabilization and carbon uptake. Drylands are expected to experience significant changes in temperature and precipitation regimes, and such alterations may impact biocrust communities by promoting rapid mortality of foundational species. In turn, biocrust community shifts affect land surface cover and roughness—changes that can dramatically alter albedo. We tested this hypothesis in a full-factorial warming (+4 °C above ambient) and altered precipitation (increased frequency of 1.2 mm monsoon-type watering events) experiment on the Colorado Plateau, USA. We quantified changes in shortwave albedo via multi-angle, solar-reflectance measurements. Warming and watering treatments each led to large increases in albedo (>30%). This increase was driven by biophysical factors related to treatment effects on cyanobacteria cover and soil surface roughness following treatment-induced moss and lichen mortality. A rise in dryland surface albedo may represent a previously unidentified feedback to future climate.

Albedo feedbacks to future climate via climate change impacts on dryland biocrusts

USGS Publications Warehouse

Rutherford, William A.; Painter, Thomas H.; Ferrenberg, Scott; Belnap, Jayne; Okin, Gregory S.; Flagg, Cody B.; Reed, Sasha C.

2017-01-01

Drylands represent the planet’s largest terrestrial biome and evidence suggests these landscapes have large potential for creating feedbacks to future climate. Recent studies also indicate that dryland ecosystems are responding markedly to climate change. Biological soil crusts (biocrusts) ‒ soil surface communities of lichens, mosses, and/or cyanobacteria ‒ comprise up to 70% of dryland cover and help govern fundamental ecosystem functions, including soil stabilization and carbon uptake. Drylands are expected to experience significant changes in temperature and precipitation regimes, and such alterations may impact biocrust communities by promoting rapid mortality of foundational species. In turn, biocrust community shifts affect land surface cover and roughness—changes that can dramatically alter albedo. We tested this hypothesis in a full-factorial warming (+4 °C above ambient) and altered precipitation (increased frequency of 1.2 mm monsoon-type watering events) experiment on the Colorado Plateau, USA. We quantified changes in shortwave albedo via multi-angle, solar-reflectance measurements. Warming and watering treatments each led to large increases in albedo (>30%). This increase was driven by biophysical factors related to treatment effects on cyanobacteria cover and soil surface roughness following treatment-induced moss and lichen mortality. A rise in dryland surface albedo may represent a previously unidentified feedback to future climate.

Relating C-band Microwave and Optical Satellite Observations as A Function of Snow Thickness on First-Year Sea Ice during the Winter to Summer Transition

NASA Astrophysics Data System (ADS)

Zheng, J.; Yackel, J.

2015-12-01

The Arctic sea ice and its snow cover have a direct impact on both the Arctic and global climate system through their ability to moderate heat exchange across the ocean-sea ice-atmosphere (OSA) interface. Snow cover plays a key role in the OSA interface radiation and energy exchange, as it controls the growth and decay of first-year sea ice (FYI). However, meteoric accumulation and redistribution of snow on FYI is highly stochastic over space and time, which makes it poorly understood. Previous studies have estimated local-scale snow thickness distributions using in-situ technique and modelling but it is spatially limited and challenging due to logistic difficulties. Moreover, snow albedo is also critical for determining the surface energy balance of the OSA during the critical summer ablation season. Even then, due to persistent and widespread cloud cover in the Arctic at various spatio-temporal scales, it is difficult and unreliable to remotely measure albedo of snow cover on FYI in the optical spectrum. Previous studies demonstrate that only large-scale sea ice albedo was successfully estimated using optical-satellite sensors. However, space-borne microwave sensors, with their capability of all-weather and 24-hour imaging, can provide enhanced information about snow cover on FYI. Daily spaceborne C-band scatterometer data (ASCAT) and MODIS data are used to investigate the the seasonal co-evolution of the microwave backscatter coefficient and optical albedo as a function of snow thickness on smooth FYI. The research focuses on snow-covered FYI near Cambridge Bay, Nunavut (Fig.1) during the winter to advanced-melt period (April-June, 2014). The ACSAT time series (Fig.2) show distinct increase in scattering at melt onset indicating the first occurrence of melt water in the snow cover. The corresponding albedo exhibits no decrease at this stage. We show how the standard deviation of ASCAT backscatter on FYI during winter can be used as a proxy for surface roughness and subsequent snow thickness (ie. Rougher surfaces acquire thicker snow covers) and then how this surface manifests into statistically distinguishable surface melt pond fractions which largely governs the optical derived albedo. Such relationships are useful for modelling the subsequent summer melt pond fraction and albedo from winter snow cover.

Intercomparison of Models Representing Direct Shortwave Radiative Forcing by Sulfate Aerosols

NASA Technical Reports Server (NTRS)

Boucher, O.; Schwartz, S. E.; Ackerman, T. P.; Anderson, T. L.; Bergstrom, B.; Bonnel, B.; Dahlback, A.; Fouquart, Y.; Chylek, P.; Fu, Q.;

Photometric studies of Saturn's ring and eclipses of the Galilean satellites

NASA Technical Reports Server (NTRS)

Brunk, W. E.

1972-01-01

Reliable data defining the photometric function of the Saturn ring system at visual wavelengths are interpreted in terms of a simple scattering model. To facilitate the analysis, new photographic photometry of the ring has been carried out and homogeneous measurements of the mean surface brightness are presented. The ring model adopted is a plane parallel slab of isotropically scattering particles; the single scattering albedo and the perpendicular optical thickness are both arbitrary. Results indicate that primary scattering is inadequate to describe the photometric properties of the ring: multiple scattering predominates for all angles of tilt with respect to the Sun and earth. In addition, the scattering phase function of the individual particles is significantly anisotropic: they scatter preferentially towards the sun. Photoelectric photometry of Ganymede during its eclipse by Jupiter indicate that neither a simple reflecting-layer model nor a semi-infinite homogeneous scattering model provides an adequate physical description of the Jupiter atmosphere.

Uranus' (3-0) H2 quadrupole line profiles

NASA Technical Reports Server (NTRS)

Trafton, L.

1987-01-01

Spectra of Uranus' S3(0) and S3(1) H2 quadrupole lines, obtained during the 1978-1980 apparitions, are analyzed, and are found to require the presence of a deep cloud. Modifications of the Baines and Bergstralh (1986) standard model, including an additional haze layer above the 16-km-am H2 level which contains strongly absorbing particles, are needed to fit the observations. For a Rayleigh phase function, such a haze (uniformly mixed with the gas above this level) would have an absorption optical depth of 0.16 and a single scattering particle albedo of 0.30. This modification would imply a fraction of normal H2 equal to 0.25 + or - 0.10, in agreement with the Baines and Bergstralh standard model.

Investigating the influence of photocatalytic cool wall adoption on meteorology and air quality in the Los Angeles basin

NASA Astrophysics Data System (ADS)

Zhang, J.; Tang, X.; Levinson, R.; Destaillats, H.; Mohegh, A.; Li, Y.; Tao, W.; Liu, J.; Ban-Weiss, G. A.

2017-12-01

Solar reflective "cool materials" can be used to lower urban temperatures, useful for mitigating the urban heat island effect and adapting to the local impacts of climate change. While numerous past studies have investigated the climate impacts of cool surfaces, few studies have investigated their effects on air pollution. Meteorological changes from increases in surface albedo can lead to temperature and transport induced modifications in air pollutant concentrations. In an effort to maintain high albedos in polluted environments, cool surfaces can also be made using photocatalytic "self-cleaning" materials. These photocatalytic materials can also remove NOx from ambient air, with possible consequences on ambient gas and particle phase pollutant concentrations. In this research, we investigate the impact of widespread deployment of cool walls on urban meteorology and air pollutant concentrations in the Los Angeles basin. Both photocatalytic and standard (not photocatalytic) high albedo wall materials are investigated. Simulations using a coupled meteorology-chemistry model (WRF-Chem) show that cool walls could effectively decrease urban temperatures in the Los Angeles basin. Preliminary results indicate that meteorology-induced changes from adopting standard cool walls could lead to ozone concentration reductions of up to 0.5 ppb. NOx removal induced by photocatalytic materials was modeled by modifying the WRF-Chem dry deposition scheme, with deposition rates informed by laboratory measurements of various commercially available materials. Simulation results indicate that increased deposition of NOx by photocatalytic materials could increase ozone concentrations, analogous to the ozone "weekend effect" in which reduced weekend NOx emissions can lead to increases in ozone. The impacts of cool walls on particulate matter concentrations are also discussed. Changes in particulate matter concentrations are found to be driven by albedo-induced changes in air pollutant transport in the basin, temperature induced changes in photochemistry and aerosol phase partitioning, and changes to secondary organic aerosol.

Compositional characterization of asteroid (16) Psyche

NASA Astrophysics Data System (ADS)

Sanchez, Juan; Reddy, Vishnu; Shepard, Michael K.; Thomas, Cristina; Cloutis, Edward

2016-10-01

We present near-infrared spectra (0.7-2.5 microns) of asteroid (16) Psyche obtained with the NASA Infrared Telescope Facility. Rotationally-resolved spectra were obtained during three nights between December 2015 and February 2016. These data have been combined with three-dimensional shape models of Psyche generated with the SHAPE software package (Magri et al. 2007). From each spectrum, the band center, band depth and spectral slope were measured. We found that the band center varies from 0.92 to 0.94 microns with rotation phase, with an average value of 0.932±0.006 microns. The band depth was found to vary from 1.0 to 1.5±0.1%. Spectral slope values range from 0.25 to 0.35±0.01 microns-1, with rotation phase. We observed a possible anti-correlation between band depth and radar albedo. Using the band depth along with a new laboratory spectral calibration we estimated that Psyche has an average orthopyroxene abundance of 6±1%. The mass-deficit region of Psyche (longitudes ~ 0°-40°), characterized by having the highest radar albedo of the asteroid, also shows the highest value for the spectral slope and the minimum band depth, while the antipode of this region (longitudes ~ 180°-230°), where the radar albedo reaches its lowest value, shows a maximum in band depth and less steep spectral slopes. These results could suggest that the metal-poor antipode region has thicker regolith rich in pyroxene compared to the mass-deficit region.

Photometric Characteristics of Lunar Terrains

NASA Astrophysics Data System (ADS)

Sato, Hiroyuki; Hapke, Bruce W.; Denevi, Brett W.; Robinson, Mark

2016-10-01

The photometric properties of the lunar depend on albedo, surface roughness, porosity, and the internal/external structure of particles. Hapke parameter maps derived using a bidirectional reflectance model [Hapke, 2012] from Lunar Reconnaissance Orbiter Camera (LROC) Wide Angle Camera (WAC) images demonstrated the spatial and spectral variation of the photometric properties of the Moon [Sato et al., 2014]. Using the same methodology, here we present the photometric characteristics of typical lunar terrains, which were not systematically analyzed in the previous study.We selected five representative terrain types: mare, highland, swirls, and two Copernican (fresh) crater ejecta (one mare and one highlands example). As for the datasets, we used ~39 months of WAC repeated observations, and for each image pixel, we computed latitude, longitude, incidence, emission, and phase angles using the WAC GLD100 stereo DTM [Scholten et al., 2012]. To obtain similar phase and incidence angle ranges, all sampling sites are near the equator and in the vicinity of Reiner Gamma. Three free Hapke parameters (single scattering albedo: w, HG2 phase function parameter: c, and angular width of SHOE: hs) were then calculated for the seven bands (321-689 nm). The remaining parameters were fixed by simplifying the model [Sato et al., 2014].The highlands, highland ejecta, and swirl (Reiner Gamma) showed clearly higher w than the mare and mare ejecta. The derived c values were lower (less backscattering) for the swirl and higher (more backscattering) for the highlands (and ejecta) relative to the other sites. Forward scattering materials such as unconsolidated transparent crystalline materials might be relatively enriched in the swirl. In the highlands, anorthositic agglutinates with dense internal scattering could be responsible for the strong backscattering. The mare and mare ejecta showed continuously decreasing c from UV to visible wavelengths. This might be caused by the FeO-rich pyroxene and glass in the mare becoming more translucent at longer wavelengths.

Angular radiation models for Earth-atmosphere system. Volume 1: Shortwave radiation

NASA Technical Reports Server (NTRS)

Suttles, J. T.; Green, R. N.; Minnis, P.; Smith, G. L.; Staylor, W. F.; Wielicki, B. A.; Walker, I. J.; Young, D. F.; Taylor, V. R.; Stowe, L. L.

1988-01-01

Presented are shortwave angular radiation models which are required for analysis of satellite measurements of Earth radiation, such as those fro the Earth Radiation Budget Experiment (ERBE). The models consist of both bidirectional and directional parameters. The bidirectional parameters are anisotropic function, standard deviation of mean radiance, and shortwave-longwave radiance correlation coefficient. The directional parameters are mean albedo as a function of Sun zenith angle and mean albedo normalized to overhead Sun. Derivation of these models from the Nimbus 7 ERB (Earth Radiation Budget) and Geostationary Operational Environmental Satellite (GOES) data sets is described. Tabulated values and computer-generated plots are included for the bidirectional and directional modes.

Relative Photometry of HAT-P-1b Occultations

NASA Astrophysics Data System (ADS)

Béky, Bence; Holman, Matthew J.; Gilliland, Ronald L.; Bakos, Gáspár Á.; Winn, Joshua N.; Noyes, Robert W.; Sasselov, Dimitar D.

2013-06-01

We present Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph observations of two occultations of the transiting exoplanet HAT-P-1b. By measuring the planet to star flux ratio near opposition, we constrain the geometric albedo of the planet, which is strongly linked to its atmospheric temperature gradient. An advantage of HAT-P-1 as a target is its binary companion ADS 16402 A, which provides an excellent photometric reference, simplifying the usual steps in removing instrumental artifacts from HST time-series photometry. We find that without this reference star, we would need to detrend the lightcurve with the time of the exposures as well as the first three powers of HST orbital phase, and this would introduce a strong bias in the results for the albedo. However, with this reference star, we only need to detrend the data with the time of the exposures to achieve the same per-point scatter, therefore we can avoid most of the bias associated with detrending. Our final result is a 2σ upper limit of 0.64 for the geometric albedo of HAT-P-1b between 577 and 947 nm.

Direct estimation of land surface albedo from VIIRS data: Algorithm improvement and preliminary validation

NASA Astrophysics Data System (ADS)

Wang, Dongdong; Liang, Shunlin; He, Tao; Yu, Yunyue

2013-11-01

surface albedo (LSA), part of the Visible Infrared Imaging Radiometer Suite (VIIRS) surface albedo environmental data record (EDR), is an essential variable regulating shortwave energy exchange between the land surface and the atmosphere. Two sub-algorithms, the dark pixel sub-algorithm (DPSA) and the bright pixel sub-algorithm (BPSA), were proposed for retrieving LSA from VIIRS data. The BPSA estimates LSA directly from VIIRS top-of-atmosphere (TOA) reflectance through simulation of atmospheric radiative transfer. Several changes have been made to improve the BPSA since the deployment of VIIRS. A database of the Moderate Resolution Imaging Spectroradiometer (MODIS) bidirectional reflectance distribution function (BRDF) is collected and converted to bidirectional reflectance at VIIRS bands. The converted reflectance is then used as input to the atmospheric radiative transfer model to generate a look-up table (LUT) of regression coefficients with consideration of surface BRDF. Before its implementation in the operational system, the new BPSA is tested on the local infrastructure. The incorporation of the surface BRDF improves the accuracy of LSA estimation and reduces the temporal variation of LSA over stable surfaces. VIIRS LSA retrievals agree well with the MODIS albedo products. Comparison with field measurements at seven Surface Radiation (SURFRAD) Network sites shows that VIIRS LSA retrieved from the LUT with surface BRDF has an R2 value of 0.80 and root mean square error of 0.049, better than MODIS albedo products. The VIIRS results have a slight negative bias of 0.004, whereas the MODIS albedo is underestimated with a larger negative bias of 0.026.

Origin of Dark Material on VESTA from DAWN FC Data: Remnant Carbonaceous Chondrite Impators

NASA Technical Reports Server (NTRS)

Reddy, V.; LeCorre, L.; Nathues, A.; Mittlefehldt, David W.; Cloutis, E. A.; OBrien, D. P.; Durda, D. D.; Bottke, W. F.; Buczkowski, D.; Scully, J. E. C.;

The AKARI IRC asteroid flux catalogue: updated diameters and albedos

NASA Astrophysics Data System (ADS)

Alí-Lagoa, V.; Müller, T. G.; Usui, F.; Hasegawa, S.

2018-05-01

The AKARI IRC all-sky survey provided more than twenty thousand thermal infrared observations of over five thousand asteroids. Diameters and albedos were obtained by fitting an empirically calibrated version of the standard thermal model to these data. After the publication of the flux catalogue in October 2016, our aim here is to present the AKARI IRC all-sky survey data and discuss valuable scientific applications in the field of small body physical properties studies. As an example, we update the catalogue of asteroid diameters and albedos based on AKARI using the near-Earth asteroid thermal model (NEATM). We fit the NEATM to derive asteroid diameters and, whenever possible, infrared beaming parameters. We fit groups of observations taken for the same object at different epochs of the survey separately, so we compute more than one diameter for approximately half of the catalogue. We obtained a total of 8097 diameters and albedos for 5170 asteroids, and we fitted the beaming parameter for almost two thousand of them. When it was not possible to fit the beaming parameter, we used a straight line fit to our sample's beaming parameter-versus-phase angle plot to set the default value for each fit individually instead of using a single average value. Our diameters agree with stellar-occultation-based diameters well within the accuracy expected for the model. They also match the previous AKARI-based catalogue at phase angles lower than 50°, but we find a systematic deviation at higher phase angles, at which near-Earth and Mars-crossing asteroids were observed. The AKARI IRC All-sky survey is an essential source of information about asteroids, especially the large ones, since, it provides observations at different observation geometries, rotational coverages and aspect angles. For example, by comparing in more detail a few asteroids for which dimensions were derived from occultations, we discuss how the multiple observations per object may already provide three-dimensional information about elongated objects even based on an idealised model like the NEATM. Finally, we enumerate additional expected applications for more complex models, especially in combination with other catalogues. Full Table 1 is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/612/A85

Land Surface Albedo from MERIS Reflectances Using MODIS Directional Factors

NASA Technical Reports Server (NTRS)

Schaaf, Crystal L. B.; Gao, Feng; Strahler, Alan H.

2004-01-01

MERIS Level 2 surface reflectance products are now available to the scientific community. This paper demonstrates the production of MERIS-derived surface albedo and Nadir Bidirectional Reflectance Distribution Function (BRDF) adjusted reflectances by coupling the MERIS data with MODIS BRDF products. Initial efforts rely on the specification of surface anisotropy as provided by the global MODIS BRDF product for a first guess of the shape of the BRDF and then make use all of the coincidently available, partially atmospherically corrected, cloud cleared, MERIS observations to generate MERIS-derived BRDF and surface albedo quantities for each location. Comparisons between MODIS (aerosol-corrected) and MERIS (not-yet aerosol-corrected) surface values from April and May 2003 are also presented for case studies in Spain and California as well as preliminary comparisons with field data from the Devil's Rock Surfrad/BSRN site.

Deriving Albedo from Coupled MERIS and MODIS Surface Products

NASA Technical Reports Server (NTRS)

Gao, Feng; Schaaf, Crystal; Jin, Yu-Fang; Lucht, Wolfgang; Strahler, Alan

2004-01-01

MERIS Level 2 surface reflectance products are now available to the scientific community. This paper demonstrates the production of MERIS-derived surface albedo and Nadir Bidirectional Reflectance Distribution Function (BRDF) adjusted reflectances by coupling the MERIS data with MODIS BRDF products. Initial efforts rely on the specification of surface anisotropy as provided by the global MODIS BRDF product for a first guess of the shape of the BRDF and then make use all of the coincidently available, partially atmospherically corrected, cloud cleared, MERIS observations to generate MERIS-derived BRDF and surface albedo quantities for each location. Comparisons between MODIS (aerosol-corrected) and MERIS (not-yet aerosol-corrected) surface values from April and May 2003 are also presented for case studies in Spain and California as well as preliminary comparisons with field data from the Devil's Rock Surfrad/BSRN site.

Solar flux incident on an orbiting surface after reflection from a planet

NASA Technical Reports Server (NTRS)

Modest, M. F.

1980-01-01

Algorithms describing the solar radiation impinging on an infinitesimal surface after reflection from a gray and diffuse planet are derived. The following conditions apply: only radiation from the sunny half of the planet is taken into account; the radiation must fall on the top of the orbiting surface, and radiation must come from that part of the planet that can be seen from the orbiting body. A simple approximate formula is presented which displays excellent accuracy for all significant situations, with an error which is always less than 5% of the maximum possible reflected flux. Attention is also given to solar albedo flux on a surface directly facing the planet, the influence of solar position on albedo flux, and to solar albedo flux as a function of the surface-planet tilt angle.

Impact of Sulfur Hazes on the Reflected Light Spectra of Giant Exoplanets

NASA Astrophysics Data System (ADS)

Gao, Peter; Marley, Mark S.; Zahnle, Kevin; Robinson, Tyler D.; Lewis, Nikole K.

2017-01-01

Recent work has shown that photochemical hazes composed of elemental sulfur and its allotropes may arise in the atmospheres of warm and temperate giant exoplanets due to the photolysis of H2S. We investigate the impact such a haze would have on an exoplanet's geometric albedo spectrum using a suite of established radiative-convective, cloud, and albedo models, and how this may impact future direct imaging missions, such as WFIRST. For Jupiter-massed planets, photochemical destruction of H2S results in the production of ~1 ppmv of S8 between 100 and 0.1 mbar. The S8 mixing ratio is largely independent of the stellar UV flux, vertical mixing rates, and atmospheric temperature for expected ranges of those values, such that the S8 haze mass is dependent only on the S8 supersaturation, controlled by the local temperature. Nominal haze masses are found to drastically alter a planet's geometric albedo spectrum: whereas a clear atmosphere is dark at wavelengths between 0.5 and 1 μm due to molecular absorption, the addition of a sulfur haze boosts the albedo there to ~0.7 due to its purely scattering nature. Strong absorption by the haze shortward of 0.4 μm results in albedos <0.1, contrasting the high albedos produced by Rayleigh scattering in a clear atmosphere. These dramatic alteration in the geometric albedo spectra will lead to substantial color changes for hazy planets away from that expected for more Jupiter-like planets. For this reason colors are unlikely to provide definitive identification of warm Jupiter-like planets. The albedo change due to a sulfur haze is largely independent of the location of the haze in the atmosphere, but is a strong function of the haze optical depth as controlled by its column number density and mean particle size, though the absorption feature at short wavelengths remains robust. Detection of such a haze by future direct imaging missions like WFIRST is possible, though discriminating between a sulfur haze and any other reflective material, such as water ice, will require observations shortward of 0.4 μm, which is currently beyond WFIRST's grasp.

Revisiting surface albedo changes over Greenland since 1980s using satellite data from GLASS, CLARA, MODIS, and Landsat

NASA Astrophysics Data System (ADS)

He, T.; Liang, S.; Zhang, Y.

2017-12-01

Massive melting events over Greenland have been observed over the past few decades. Accompanying the melting events are the surface albedo changes, which had temporal and spatial variations. Albedo changes over Greenland during the past few decades have been reported in previous studies with the help of satellite observations; however, magnitudes and timing in albedo trends differ greatly in those studies. This has limited our understanding of albedo change mechanisms over Greenland. In this study, we present an analysis of surface albedo change over Greenland since 1980s combining four satellite albedo datasets, namely MODIS, GLASS, CLARA, and Landsat. MODIS, GLASS, and CLARA albedo data are publicly available and Landsat albedos were derived in our earlier study trying to bridge the scale difference between coarse resolution data and ground measurements available from early 1980s. Inter-comparisons were made among the satellite albedos and against ground measurements. We have several new findings. First, trends in surface albedo change among the satellite albedo datasets generally agree with each other and with ground measurements. Second, all datasets showed negative albedo trends after 2000, but magnitudes differ greatly. Third, trends before 2000 from coarse resolution data are not significant but Landsat data observed positive albedo changes. Fourth, the turning point of albedo trend was found to be earlier than 2000. Those findings may bring new research topics on timing and magnitude, and an improved understanding mechanisms of the albedo changes over Greenland during the past few decades.

The New Global Gapless GLASS Albedo Product from 1981 to 2014

NASA Astrophysics Data System (ADS)

Dou, B.; Liu, Q.; Qu, Y.; Wang, L.; Feng, Y.; Nie, A.; Li, X.; Zhang, J.; Niu, H.; Cai, E.; Zhao, L.

2016-12-01

Long-time series and various spatial resolution albedo products are needed for climate change and environmental studies at both global and regional scale. To meet these requirements, GLASS (Global LAnd Surface Satellites) gapless albedo product from 1981 to 2010 was firstly released in 2012 and widely used in long-term earth change researches. However, only shortwave albedo product in spatial resolution of 0.05 degree and 1 km were provided, which limits extensive applications for visible and near-infrared bands. Thus, new GLASS albedo product are produced and comprehensively enhanced in time series, algorithm and product content. Five major updates are conducted: 1) Time region is expanded from 1981-2010 to 1981-2014; 2) Physically ART (radiative transfer theory) and TCOWA (Three-Component Ocean Water Albedo) models rather than previous RTLSR (Rose-Thick Li-Sparse Reciprocal kernel combination) model are adopted for snow and inland water albedo estimation, respectively; 3) global shortwave, visible, and near-infrared albedos in spatial resolution of 0.05 degree and 1 km are released; 4) Clear-sky albedo is provided beyond the traditional black-sky albedo and white sky-albedo for amateurish user; 5) 250 m albedo product is provided in part of global for regional application. In this study, we firstly detail the updates of this inspiring product. Then the product is compared with the previous GLASS albedo product and preliminary assessed against field measurements under various land covers. Significant improvements are reported for snow and water albedo. The results demonstrate that the new GLASS albedo product is a gapless, long-term continuous, and self-consistent data-set. Comparing to previous GLASS albedo product, lower black-sky albedo and higher white-sky albedo are proved for permanent snow-cover region. Moreover, higher albedo of inland water and seasonal snow-cover mountain are captured. This product brings new chance and view to understanding long-term earth process and change.

Spectral properties of ice-particulate mixtures and implications for remote sensing. 1. Intimate mixtures.

USGS Publications Warehouse

Clark, R.N.; Lucey, P.G.

1984-01-01

The spectral properties of water ice-partitioning mixtures are studied for the purpose of deriving the ice and particulate abundances from remotely obtained spectra (particulates referring to non-icy materials in the form of grains). Reflectance levels and ice absorption band depths are a complex function of the single scattering albedo of the particulates embedded in the ice. The ice absorption band depths are related to the mean optical path length of photons in ice through Beers law, Fresnel reflection from the ice-crystal faces on the surface, and ice absorption coefficient as a function of wavelength. Laboratory spectra of many ice- particulate mixtures are studied with high-, medium-, and low-albedo particulates.-from Authors

THE PHYSICAL CHARACTERIZATION OF THE POTENTIALLY HAZARDOUS ASTEROID 2004 BL86: A FRAGMENT OF A DIFFERENTIATED ASTEROID

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reddy, Vishnu; Sanchez, Juan A.; Takir, Driss

The physical characterization of potentially hazardous asteroids (PHAs) is important for impact hazard assessment and evaluating mitigation options. Close flybys of PHAs provide an opportunity to study their surface photometric and spectral properties that enable the identification of their source regions in the main asteroid belt. We observed PHA (357439) 2004 BL86 during a close flyby of the Earth at a distance of 1.2 million km (0.0080 AU) on 2015 January 26, with an array of ground-based telescopes to constrain its photometric and spectral properties. Lightcurve observations showed that the asteroid was a binary and subsequent radar observations confirmed themore » binary nature and gave a primary diameter of 300 m and a secondary diameter of 50–100 m. Our photometric observations were used to derive the phase curve of 2004 BL86 in the V-band. Two different photometric functions were fitted to this phase curve, the IAU H–G model and the Shevchenko model. From the fit of the H–G function we obtained an absolute magnitude of H = 19.51 ± 0.02 and a slope parameter of G = 0.34 ± 0.02. The Shevchenko function yielded an absolute magnitude of H = 19.03 ± 0.07 and a phase coefficient b = 0.0225 ± 0.0006. The phase coefficient was used to calculate the geometric albedo (Ag) using the relationship found by Belskaya and Schevchenko, obtaining a value of Ag = 40% ± 8% in the V-band. With the geometric albedo and the absolute magnitudes derived from the H–G and the Shevchenko functions we calculated the diameter (D) of 2004 BL86, obtaining D = 263 ± 26 and D = 328 ± 35 m, respectively. 2004 BL86 spectral band parameters and pyroxene chemistry are consistent with non-cumulate eucrite meteorites. A majority of these meteorites are derived from Vesta and are analogous with surface lava flows on a differentiated parent body. A non-diagnostic spectral curve match using the Modeling for Asteroids tool yielded a best-match with non-cumulate eucrite Bereba. Three other near-Earth asteroids (1993 VW, 1998 KK17, and 2000 XH44) that were observed by Burbine et al. also have spectral properties similar to 2004 BL86. The presence of eucrites with anomalous oxygen isotope ratios compared to the howardites, eucrites, and diogenites meteorites from Vesta suggests the possible presence of multiple differentiated bodies in the inner main belt or the contamination of Vesta’s surface with exogenic material. The spectral properties of both anomalous and Vestan eucrites are degenerate, making it difficult to identify the parent bodies of anomalous eucrites in the main belt and the NEO population using remote sensing. This makes it difficult to link 2004 BL86 directly to Vesta, although the Vesta family is the largest contributor of V-types to near-Earth space.« less

MGS-TES Phase Effects and Thermal Infrared Directional Emissivity Field Measurements of Martian Analog Sites

NASA Astrophysics Data System (ADS)

Pitman, K. M.; Bandfield, J. L.; Wolff, M. J.

2006-03-01

We present a set of on- and off-nadir thermal IR field and laboratory emissivity spectra for three undisturbed Mars terrain analog sites and analyze them for presence or absence of directional emissivity effects. Comparisons to moderate and low albedo surface MGS-TES EPF sequences are discussed.

Ultraviolet photometry from the orbiting astronomical observatory. XXX - The Orion reflection nebulosity

NASA Technical Reports Server (NTRS)

Witt, A. N.; Lillie, C. F.

1978-01-01

Surface-brightness measurements are presented that cover the region of Orion in nine intermediate-width bandpasses ranging from 4250 to 1550 A. The existence of an extended ultraviolet reflection nebulosity in this area is confirmed, and the characteristics of its spectrum and spatial distribution are derived. The observations are consistent with a model in which the dense molecular cloud complex in Orion is illuminated by the foreground Orion aggregate of early-type stars. The interpretation is complicated by the fact that foreground dust may contribute to the observed scattered light. The scattering particles in the cloud appear to exhibit a wavelength-dependent albedo similar to that found for interstellar grains in general, with a strong indication that the phase function changes to a less forward-scattering form in the ultraviolet.

Computer simulation of position and maximum of linear polarization of asteroids

NASA Astrophysics Data System (ADS)

Petrov, Dmitry; Kiselev, Nikolai

2018-01-01

The ground-based observations of near-Earth asteroids at large phase angles have shown some feature: the linear polarization maximum position of the high-albedo E-type asteroids shifted markedly towards smaller phase angles (αmax ≈ 70°) with respect to that for the moderate-albedo S-type asteroids (αmax ≈ 110°), weakly depending on the wavelength. To study this phenomenon, the theoretical approach and the modified T-matrix method (the so-called Sh-matrices method) were used. Theoretical approach was devoted to finding the values of αmax, corresponding to maximal values of positive polarization Pmax. Computer simulations were performed for an ensemble of random Gaussian particles, whose scattering properties were averaged over with different particle orientations and size parameters in the range X = 2.0 ... 21.0, with the power law distribution X - k, where k = 3.6. The real parts of the refractive index mr were 1.5, 1.6 and 1.7. Imaginary part of refractive index varied from mi = 0.0 to mi = 0.5. Both theoretical approach and computer simulation showed that the value of αmax strongly depends on the refractive index. The increase of mi leads to increased αmax and Pmax. In addition, computer simulation shows that the increase of the real part of the refractive index reduces Pmax. Whereas E-type high-albedo asteroids have smaller values of mi, than S -type asteroids, we can conclude, that value of αmax of E-type asteroids should be smaller than for S -type ones. This is in qualitative agreement with the observed effect in asteroids.

Spatial distribution of Ion Precipitation into the High Latitude Inner Magnetosphere using Energetic Neutral Atom (ENA) images over the Declining Phase of Solar Cycle 23

NASA Astrophysics Data System (ADS)

Mackler, D. A.; Jahn, J.; Pollock, C. J.

2013-12-01

Plamasheet particles transported Earthward during times of active magnetic convection can interact with thermospheric neutrals through charge exchange. The resulting ENAs are free to leave the influence of the magnetosphere and can be remotely detected. ENAs associated with low altitude (300-800 km) ion precipitation in the high latitude inner mangetosphere are termed Low Altitude Emissions (LAEs). LAEs are highly non-isotropic in velocity space such that the pitch angle distribution at the time of charge exchange is near 90 degrees. The observed Geomagnetic Emission Cone (GEC) of LAEs can be mapped spatially, showing where energy is deposited during storm/sub-storm times. In this study we present a statistical look at the particulate albedo of LAEs over the declining phase of solar cycle 23. The particulate albedo is defined as the ratio of the emitting energetic neutrals to the precipitating ions. The precipitating ion differential directional flux maps are built up from combining NOAA 14/15/16 TED and DMSP 13/14/15 SSJ4 data. Low altitude ENA signatures are identified manually using IMAGE/MENA images and selected out. The geomagnetic location of each pixel representing a LAE source region in the neutral images is computed assuming an altitude of 650 km. Before taking the ratio of the resulting flux of neutrals and ions, the Magnetic Local Time (MLT) and Invariant Latitude (IL) bin sizes are changed such that each has less than 20% error in counting statistics. The particulate albedo maps are then evaluated over changes in geomagnetic storm activity.

An investigation of ESSA 7 radiation data for use in long-term earth energy experiments, phases 1 and 2

NASA Technical Reports Server (NTRS)

House, F. B.

1974-01-01

The results are presented of an investigation of ESSA 7 satellite radiation data for use in long-term earth energy experiments. Satellite systems for performing long-term earth radiation balance measurements over geographical areas, hemispheres, and the entire earth for periods of 10 to 30 years are examined. The ESSA 7 satellite employed plate and cone radiometers to measure earth albedo and emitted radiation. Each instrument had a black and white radiometer which discriminated the components of albedo and emitted radiation. Earth measurements were made continuously from ESSA 7 for ten months. The ESSA 7 raw data is processed to a point where it can be further analyzed for: (1) development of long-term earth energy experiments; and (2) document climate trends.

Variability of albedo and utility of the MODIS albedo product in forested wetlands

USGS Publications Warehouse

Sumner, David M.; Wu, Qinglong; Pathak, Chandra S.

2011-01-01

Albedo was monitored over a two-year period (beginning April 2008) at three forested wetland sites in Florida, USA using up- and down-ward facing pyranometers. Water level, above and below land surface, is the primary control on the temporal variability of daily albedo. Relatively low reflectivity of water accounts for the observed reductions in albedo with increased inundation of the forest floor. Enhanced canopy shading of the forest floor was responsible for lower sensitivity of albedo to water level at the most dense forest site. At one site, the most dramatic reduction in daily albedo was observed during the inundation of a highly-reflective, calcareous periphyton-covered land surface. Satellite-based Moderate-Resolution Imaging Spectroradiometer (MODIS) estimates of albedo compare favorably with measured albedo. Use of MODIS albedo values in net radiation computations introduced a root mean squared error of less than 4.7 W/m2 and a mean, annual bias of less than 2.3 W/m2 (1.7%). These results suggest that MODIS-estimated albedo values can reliably be used to capture areal and temporal variations in albedo that are important to the surface energy balance.

Wavelength dependence of dust aerosol single scattering albedo as observed by the Compact Reconnaissance Imaging Spectrometer

NASA Astrophysics Data System (ADS)

Wolff, M. J.; Smith, M. D.; Clancy, R. T.; Arvidson, R.; Kahre, M.; Seelos, F.; Murchie, S.; Savijärvi, H.

2009-06-01

Observations by the Compact Reconnaissance Imaging Spectrometer (CRISM) onboard the Mars Reconnaissance Orbiter (MRO) over the range 440-2920 nm of the very dusty Martian atmosphere of the 2007 planet-encircling dust event are combined with those made by both Mars Exploration Rovers (MERs) to better characterize the single scattering albedo (ω 0) of Martian dust aerosols. Using the diagnostic geometry of the CRISM emission phase function (EPF) sequences and the “ground truth” connection provided at both MER locations allows one to more effectively isolate the single scattering albedo (ω 0). This approach eliminates a significant portion of the type of uncertainty involved in many of the earlier radiative transfer analyses. Furthermore, the use of a “first principles” or microphysical representation of the aerosol scattering properties offers a direct path to produce a set of complex refractive indices (m = n + ik) that are consistent with the retrieved ω 0 values. We consider a family of effective particle radii: 1.2, 1.4, 1.6, and 1.8 μm. The resulting set of model data comparisons, ω 0, and m are presented along with an assessment of potential sources of error and uncertainty. We discuss our results within the context of previous work, including the apparent dichotomy of the literature values: “dark” (solar band ω 0 = 0.89-0.90) and “bright” (solar band ω 0 = 0.92-0.94). Previous work suggests that a mean radius of 1.8 μm is representative for the conditions sampled by the CRISM observations. Using the m for this case and a smaller effective particle radius more appropriate for diffuse dust conditions (1.4 μm), we examine EPF-derived optical depths relative to the MER 880 nm optical depths. Finally, we explore the potential impact of the resulting brighter solar band ω 0 of 0.94 to atmospheric temperatures in the planetary boundary layer.

Simulating the biogeochemical and biogeophysical impacts of transient land cover change and wood harvest in the Community Climate System Model (CCSM4) from 1850 to 2100

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lawrence, Peter J.; Feddema, Johannes J.; Bonan, Gordon B.

To assess the climate impacts of historical and projected land cover change and land use in the Community Climate System Model (CCSM4) we have developed new time series of transient Community Land Model (CLM4) Plant Functional Type (PFT) parameters and wood harvest parameters. The new parameters capture the dynamics of the Coupled Model Inter-comparison Project phase 5 (CMIP5) land cover change and wood harvest trajectories for the historical period from 1850 to 2005, and for the four Representative Concentration Pathways (RCP) periods from 2006 to 2100. Analysis of the biogeochemical impacts of land cover change in CCSM4 with the parametersmore » found the model produced an historical cumulative land use flux of 148.4 PgC from 1850 to 2005, which was in good agreement with other global estimates of around 156 PgC for the same period. The biogeophysical impacts of only applying the transient land cover change parameters in CCSM4 were cooling of the near surface atmospheric over land by -0.1OC, through increased surface albedo and reduced shortwave radiation absorption. When combined with other transient climate forcings, the higher albedo from land cover change was overwhelmed at global scales by decreases in snow albedo from black carbon deposition and from high latitude warming. At regional scales however the land cover change forcing persisted resulting in reduced warming, with the biggest impacts in eastern North America. The future CCSM4 RCP simulations showed that the CLM4 transient PFT and wood harvest parameters could be used to represent a wide range of human land cover change and land use scenarios. Furthermore, these simulations ranged from the RCP 4.5 reforestation scenario that was able to draw down 82.6 PgC from the atmosphere, to the RCP 8.5 wide scale deforestation scenario that released 171.6 PgC to the atmosphere.« less

Surface roughness retrieval by inversion of the Hapke model: A multiscale approach

NASA Astrophysics Data System (ADS)

Labarre, S.; Ferrari, C.; Jacquemoud, S.

2017-07-01

Surface roughness is a key property of soils that controls many surface processes and influences the scattering of incident electromagnetic waves at a wide range of scales. Hapke (2012b) designed a photometric model providing an approximate analytical solution of the Bidirectional Reflectance Distribution Function (BRDF) of a particulate medium: he introduced the effect of surface roughness as a correction factor of the BRDF of a smooth surface. This photometric roughness is defined as the mean slope angle of the facets composing the surface, integrated over all scales from the grain size to the local topography. Yet its physical meaning is still a question at issue, as the scale at which it occurs is not clearly defined. This work aims at better understanding the relative influence of roughness scales on soil BRDF and to test the ability of the Hapke model to retrieve a roughness that depicts effectively the ground truth. We apply a wavelet transform on millimeter digital terrain models (DTM) acquired over volcanic terrains. This method allows splitting the frequency band of a signal in several sub-bands, each corresponding to a spatial scale. We demonstrate that sub-centimeter surface features dominate both the integrated roughness and the BRDF shape. We investigate the suitability of the Hapke model for surface roughness retrieval by inversion on optical data. A global sensitivity analysis of the model shows that soil BRDF is very sensitive to surface roughness, nearly as much as the single scattering albedo according to the phase angle, but also that these two parameters are strongly correlated. Based on these results, a simplified two-parameter model depending on surface albedo and roughness is proposed. Inversion of this model on BRDF data simulated by a ray-tracing code over natural targets shows a good estimation of surface roughness when the assumptions of the model are verified, with a priori knowledge on surface albedo.

Land Surface Albedo From EPS/AVHRR : Method For Retrieval and Validation

NASA Astrophysics Data System (ADS)

Jacob, G.

2015-12-01

The scope of Land Surface Analysis Satellite Applications Facility (LSA-SAF) is to increase benefit from EUMETSAT Satellites (MSG and EPS) data by providing added value products for the meteorological and environmental science communities with main applications in the fields of climate modelling, environmental management, natural hazards management, and climate change detection. The MSG/SEVIRI daily albedo product is disseminated operationally by the LSA-SAF processing centre based in Portugal since 2009. This product so-called MDAL covers Europe and Africa includes in the visible, near infrared and shortwave bands at a resolution of 3km at the equator. Recently, an albedo product at 1km so-called ETAL has been built from EPS/AVHRR observations in order to primarily MDAL product outside the MSG disk, while ensuring a global coverage. The methodology is common to MSG and EPS data and relies on the inversion of the BRDF (Bidirectional Reflectance Distribution Function) model of Roujean et al. On a given target, ETAL products exploits the variability of viewing angles whereas MDAL looks at the variations of solar illumination. The comparison of ETAL albedo product against MODIS and MSG/SEVIRI products over the year 2015 is instructive in many ways and shows in general a good agreement between them. The dispersion may be accounted by different factors that will be explained The additional information provided by EPS appears to be particularly beneficial for high latitudes during winter and for snow albedo.

A model for rotation and shape of Asteroid 9969 Braille from ground-based observations and images obtained during the deep space 1 (DS1) flyby

USGS Publications Warehouse

Oberst, J.; Mottola, S.; Di, Martino M.; Hicks, M.; Buratti, B.; Soderblom, L.; Thomas, N.

2001-01-01

Image data from the DS1 encounter with Asteroid 9969 Braille and data from a coordinated ground-based photometric observing campaign are combined to study the physical properties of this small Mars crosser. From telescope data the object's brightness was found to vary by up to 0.5 mag from night to night, with the most probable synodic rotational period being 226.4 ?? 1.3 h (9.4 days) and a mean lightcurve magnitude R(1, ?? = 24??) = 17.04 ?? 0.10. During the flyby of the spacecraft, two frame images from a range of approximately 13,500 km and phase angle 82.4??, which impose strong constraints on size, shape, and albedo of the object, were obtained. Using telescope and flyby data in combination, the asteroid is estimated to have a size of 2.1 ?? 1 ?? 1 km3 and shown to have photometric properties similar to the asteroid 4 Vesta, notably a comparably high albedo. The high albedo supports the notion (L. Soderblom et al. 1999, Bull. Am. Astron. Soc. 31,) that Braille is of the V or Q taxonomic type. ?? 2001 Academic Press.

New particle formation leads to cloud dimming

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sullivan, Ryan C.; Crippa, Paola; Matsui, Hitoshi

New particle formation (NPF), nucleation of condensable vapors to the solid or liquid phase, is a significant source of atmospheric aerosol particle number concentrations. With sufficient growth, these nucleated particles may be a significant source of cloud condensation nuclei (CCN), thus altering cloud albedo, structure, and lifetimes, and insolation reaching the Earth's surface. Herein we present one of the first numerical experiments to quantify the impact of NPF on cloud radiative properties that is conducted at a convection permitting resolution and that explicitly simulates cloud droplet number concentrations. Consistent with observations, these simulations suggest that in spring over the Midwesternmore » U.S.A., NPF occurs frequently and on regional scales. However, the simulations suggest that NPF is not associated with enhancement of regional cloud albedos as would be expected from an increase of CCN. These simulations indicate that NPF reduces ambient sulfuric acid concentrations sufficiently to inhibit growth of preexisting particles to CCN sizes. This reduction in CCN-sized particles reduces cloud albedo, resulting in a domain average positive top of atmosphere cloud radiative forcing of 10 W m-2 and up to ~ 50 W m-2 in individual grid cells relative to a simulation in which NPF is excluded.« less

RELATIVE PHOTOMETRY OF HAT-P-1b OCCULTATIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beky, Bence; Holman, Matthew J.; Noyes, Robert W.

2013-06-01

We present Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph observations of two occultations of the transiting exoplanet HAT-P-1b. By measuring the planet to star flux ratio near opposition, we constrain the geometric albedo of the planet, which is strongly linked to its atmospheric temperature gradient. An advantage of HAT-P-1 as a target is its binary companion ADS 16402 A, which provides an excellent photometric reference, simplifying the usual steps in removing instrumental artifacts from HST time-series photometry. We find that without this reference star, we would need to detrend the lightcurve with the time of the exposures as wellmore » as the first three powers of HST orbital phase, and this would introduce a strong bias in the results for the albedo. However, with this reference star, we only need to detrend the data with the time of the exposures to achieve the same per-point scatter, therefore we can avoid most of the bias associated with detrending. Our final result is a 2{sigma} upper limit of 0.64 for the geometric albedo of HAT-P-1b between 577 and 947 nm.« less

The Effects of the Mountain Pine Beetle on Snow Accumulation and Melt Timing in the Headwaters of the Colorado River

NASA Astrophysics Data System (ADS)

Pugh, E. T.; Small, E. E.

2010-12-01

The high-elevation forests that are a primary source for Colorado’s domestic and agricultural water needs are changing rapidly due to an infestation by the mountain pine beetle (MPB). MPB are native to Colorado’s high elevation forests. However, the frequency of MPB infestation and resulting tree death has increased dramatically over the past 15 years. In Colorado, over 8,000 km2 of Lodgepole (Pinus contorta) and Ponderosa Pine (Pinus ponderosa) forest have been infested by MPB since 1996. It is predicted that the current epidemic will kill most of the pines in these areas; MPB are very destructive to forest canopies, often killing all of the overhead trees within lodgepole pine stands. Current widespread MPB outbreaks are not limited to Colorado; they are also impacting forests in much of the Western US and British Columbia, Canada. This study is focused on quantifying the impacts of widespread tree death on Colorado’s mountain snowpack. The data were collected one to three years after beetle infestation, at various stages of tree mortality. During the winters of 2009 and 2010, snowpack and meteorological properties were measured at eight pairs of dead and living lodgepole pine stands. All stands are located at an elevation of 2720 ± 32m, in a subalpine region along the headwaters of the Colorado River. Trees in living stands were generally smaller in diameter and more densely populated than trees in dead stands. In the red phase of tree death, snowpack accumulated equally beneath living and dead tree stands. Additionally, snow under all tree stands became isothermal on the same date regardless of mortality. However, the snow was depleted as much as one week earlier beneath red phase dead stands. Canopy transmission of solar radiation was not consistently different between living and red phase dead stands. We noted more ground litter in red phase dead stands which would decrease snowpack albedo and lead to the snowmelt differences observed. We also performed an albedo experiment to quantify the impact of surface litter on snow albedo. Results are also reported for more advanced grey phase dead stands. Lastly, we present a conceptual model of how the primary snow processes change with time as tree mortality progresses through various stages and introduce future work.

Constraining martian atmospheric dust particle size distributions from MER Navcam observations.

NASA Astrophysics Data System (ADS)

Soderblom, J. M.; Smith, M. D.

2017-12-01

Atmospheric dust plays an important role in atmospheric dynamics by absorbing energy and influencing the thermal structure of the atmosphere [1]. The efficiency by which dust absorbs energy depends on its size and single-scattering albedo. Characterizing these properties and their variability is, thus, important in modeling atmospheric circulation. Near-sun observations of the martian sky from Viking Lander, Mars Pathfinder, and MER Pancam images have been used to characterize the atmospheric scattering phase function. The forward-scattering peak the atmospheric phase function is primarily controlled by the size of aerosol particles and is less sensitive to atmospheric opacity or particle shape and single-scattering albedo [2]. These observations, however, have been limited to scattering angles >5°. We use the MER Navcams, which experience little-to-no debilitating internal instrumental scattered light during near-Sun imaging, enabling measurements of the brightness of the martian sky down to very small scattering angles [3], making them more sensitive to aerosol particle size. Additionally, the Navcams band-pass wavelength is similar to the dust effective particle size, further increasing this sensitivity. These data sample a wide range of atmospheric conditions, including variations in the atmospheric dust loading across the entire martian year, as well as more rapid variations during the onset and dissipation of a global-scale dust storm. General circulation models (GCMs) predict a size-dependence for the transport of dust during dust storms that would result in both spatial (on regional-to-global scales) and temporal (days-to-months) variations in the dust size distribution [4]. The absolute calibration of these data, however, is limited. The instrument temperature measurement is limited to a single thermocouple on the Opportunity left Navcam CCD, and observations of the calibration target by Navcam are infrequent. We discuss ways to mitigate these uncertainties and provide improved recovery of dust particle size distributions from these data. [1] Gierasch and Goody, 1972, J. Atmos. Sci., 29, 400-402. [2] Hansen and Travis, 1974, Space Sci. Rev., 16, 527-610. [3] Soderblom et al., 2008; JGR E06S19. [4] Murphy et al., 1993, JGR 98(E2), 3197-3220.

Prediction of Viking lander camera image quality

NASA Technical Reports Server (NTRS)

Huck, F. O.; Burcher, E. E.; Jobson, D. J.; Wall, S. D.

1976-01-01

Formulations are presented that permit prediction of image quality as a function of camera performance, surface radiance properties, and lighting and viewing geometry. Predictions made for a wide range of surface radiance properties reveal that image quality depends strongly on proper camera dynamic range command and on favorable lighting and viewing geometry. Proper camera dynamic range commands depend mostly on the surface albedo that will be encountered. Favorable lighting and viewing geometries depend mostly on lander orientation with respect to the diurnal sun path over the landing site, and tend to be independent of surface albedo and illumination scattering function. Side lighting with low sun elevation angles (10 to 30 deg) is generally favorable for imaging spatial details and slopes, whereas high sun elevation angles are favorable for measuring spectral reflectances.

Ground-based Characterization of Hayabusa2 Mission Target Asteroid 162173 Ryugu

NASA Astrophysics Data System (ADS)

Le Corre, Lucille; Reddy, Vishnu; Sanchez, Juan A.; Takir, Driss; Cloutis, Edward; Thirouin, Audrey; Becker, Kris J.; Li, Jian-Yang; Sugita, Seiji; Tatsumi, Eri

2017-10-01

In preparation for the arrival of the Japanese Space Agency’s (JAXA) Hayabusa2 sample return mission to near-Earth asteroid (NEA) (162173) Ryugu, we took the opportunity to characterize the target with a ground-based telescope. We observed Ryugu using the SpeX instrument in Prism mode on NASA Infrared Telescope Facility on Mauna Kea, Hawaii, on July, 12 2016 when the asteroid was 18.87 visual magnitude, at a phase angle of 13.3°. The NIR spectra were used to constrain Ryugu’s surface composition, meteorite analogs and spectral affinity to other asteroids. We also modeled its photometric properties using archival data. Using the Lommel-Seeliger model we computed the predicted flux for Ryugu at a wide range of viewing geometries as well as albedo quantities such as geometric albedo, phase integral, and spherical Bond albedo. Our computed albedo quantities are consistent with results from Masateru et al. (2014). Our spectrum of Ryugu has a broad absorption band at 1 µm, a slope change at 1.6 µm, and a second broad absorption band near 2.2 µm, but no well-defined absorption features over the 0.8-2.5 µm range. The two broad absorption features, if confirmed, are consistent with CO and CV chondrites. The shape of Ryugu’s spectrum matches very well those of NEA (85275) 1994 LY and Mars-crossing asteroid (316720) 1998 BE7, suggesting that their surface regolith have similar composition. We also compared the spectrum of Ryugu with that of main belt asteroid (302) Clarissa, the largest asteroid in the Clarissa asteroid family, suggested as the source of Ryugu by Campins et al. (2013). We found that the spectrum of Clarissa shows significant differences with our NIR spectrum of Ryugu. Our analysis shows Ryugu’s spectrum best matches two CM2 carbonaceous chondrites, Mighei and ALH83100. We expect the surface regolith of Ryugu to be altered by a range of factors including temperature, contamination by exogenic material, and space weathering, posing challenges to link spacecraft and ground-based data, and sample site selection.

[Temporal and Spatial Characteristics of Lake Taihu Surface Albedo and Its Impact Factors].

PubMed

Cao, Chang; Li, Xu-hui; Zhang, Mi; Liu, Shou-dong; Xiao, Wei; Xiao, Qi-tao; Xu, Jia-ping

2015-10-01

Lake surface albedo determines energy balance of water-atmospheric interface and water physical environment. Solar elevation angle, cloudiness, wind speed, water quality and other factors can affect lake surface albedo. Using solar radiation, wind speed, and water quality data (turbidity and chlorophyll-a concentration) which were observed in four eddy covariance sites (Meiliangwan, Dapukou, Bifenggang and Xiaoleishan i. e. MLW, DPK, BFG and XLS) in Lake Taihu and clearness index (k(t)), the influence of these factors on Lake Taihu surface albedo and the reasons that led to its spatial difference were investigated. The results showed that solar elevation angle played a leading role in the diurnal and seasonal change of lake surface albedo; lake surface albedo reached two peaks in 0 < k(t) < 0.1 and 0.4 < k(t) < 0.6 respectively, when solar elevation angle was below 35 degrees. The surface albedo increased with the increasing wind speed, turbidity and chlorophyll-a concentration. However, wind could indirectly affect surface albedo through leading to the changes in sediment resuspension and chlorophyll-a distribution. The sequence of albedo in the four sites was XLS > BFG > DPK > MLW. XLS and BFG belonged to the higher albedo group, while DPK and MLW belonged to the lower albedo group. The different biological environments caused by aquatic macrophytes and algae resulting in the spatial variation of Lake Taihu surface albedo. The relationship between albedo and chlorophyll-a concentration was not a very sensitive factor for indicating the outbreak of algae. This study can provide theoretical reference for lake albedo parameterization.

Using Directional Emissivity as a Probe of Particle Microphysical Properties

NASA Astrophysics Data System (ADS)

Pitman, K. M.; Wolff, M. J.; Bandfield, J. L.; Clayton, G. C.

2002-09-01

Real surfaces are not expected to be diffuse emitters, thus observed emissivity values are a function of viewing geometry. This fact has strong implications for analyses of the MGS/TES emission phase function (EPF) sequences and the upcoming Mars Exploration Rover mini-TES dataset. As reviewed previously [1], in the absence of strong thermal gradients, directional emissivity may be obtained via a combination of reciprocity and Kirchhoff's Law. Here we focus on the potential utility of directional emissivity as a direct probe of surface particle microphysical properties. We explore the effects of particle size and composition on observed radiances in the TES spectral regime using a combination of multiple scattering radiative transfer and Mie scattering algorithms. Comparisons of these simulated spectra to TES EPF observations of typical surface units (e.g., high and low albedo regions) will also be made. This work is supported through NASA grant NAGS-9820 (MJW) and LSU Board of Regents (KMP). [1] Pitman, K.M., et al. (2001), AAS-DPS meeting # 33, # 36.01.

Snow particles extracted from X-ray computed microtomography imagery and their single-scattering properties

NASA Astrophysics Data System (ADS)

Ishimoto, Hiroshi; Adachi, Satoru; Yamaguchi, Satoru; Tanikawa, Tomonori; Aoki, Teruo; Masuda, Kazuhiko

2018-04-01

Sizes and shapes of snow particles were determined from X-ray computed microtomography (micro-CT) images, and their single-scattering properties were calculated at visible and near-infrared wavelengths using a Geometrical Optics Method (GOM). We analyzed seven snow samples including fresh and aged artificial snow and natural snow obtained from field samples. Individual snow particles were numerically extracted, and the shape of each snow particle was defined by applying a rendering method. The size distribution and specific surface area distribution were estimated from the geometrical properties of the snow particles, and an effective particle radius was derived for each snow sample. The GOM calculations at wavelengths of 0.532 and 1.242 μm revealed that the realistic snow particles had similar scattering phase functions as those of previously modeled irregular shaped particles. Furthermore, distinct dendritic particles had a characteristic scattering phase function and asymmetry factor. The single-scattering properties of particles of effective radius reff were compared with the size-averaged single-scattering properties. We found that the particles of reff could be used as representative particles for calculating the average single-scattering properties of the snow. Furthermore, the single-scattering properties of the micro-CT particles were compared to those of particle shape models using our current snow retrieval algorithm. For the single-scattering phase function, the results of the micro-CT particles were consistent with those of a conceptual two-shape model. However, the particle size dependence differed for the single-scattering albedo and asymmetry factor.

The determination of surface albedo from meteorological satellites

NASA Technical Reports Server (NTRS)

Johnson, W. T.

1977-01-01

A surface albedo was determined from visible data collected by the NOAA-4 polar orbiting meteorological satellite. To filter out the major cause of atmospheric reflectivity, namely clouds, techniques were developed and applied to the data resulting in a map of global surface albedo. Neglecting spurious surface albedos for regions with persistent cloud cover, sun glint effects, insufficient reflected light and, at this time, some unresolved influences, the surface albedos retrieved from satellite data closely matched those of a global surface albedo map produced from surface and aircraft measurements and from characteristic albedos for land type and land use.

Initial Polarimetric Analysis of the Vestoid Asteroid Family

NASA Astrophysics Data System (ADS)

Maleszewski, C.; McMillan, R. S.; Smith, P.

2013-12-01

Observations of polarized light scattered off of asteroid regolith have been used to compare the major asteroid taxonomic types. Members within a taxonomic type tend to have similar polarimetric phase curves (linear polarization vs. phase angle). The polarization also exhibits a wavelength dependence. For the S-complex, the polarization decreases linearly with increasing wavelength. This is different from the C-complex, which has the opposite dependence of polarization on wavelength. The slope of wavelength dependence also changes with phase angle for both complexes; at higher phase angles, the wavelength dependence is steeper. One of the less analyzed taxonomic types with regards to polarization is the V-type. Focus has been placed on the largest member of the V-types: Vesta. However, the Vestoids, which are thought to be collisional remnants of Vesta, have not been analyzed. Due to Vesta's differentiation, the Vestoids as a whole should contain members with significant differences in composition. This in turn should mean significant variations in the polarization observed from these bodies. In order to confirm such differences, we have begun a polarimetric survey of Vestoids. Over thirty observations of six different Vestoids were obtained using the SPOL spectropolarimeter (http://james.as.arizona.edu/~psmith/SPOL/ ) and Steward Observatory telescopes. The wavelength dependence of linear polarization was plotted with respect to the observed phase angle. The linear polarization trends in each of the synthesized B, V, and R bandpasses do not fit a single curve, contrary to that displayed by ensembles of asteroids in other taxonomic complexes. This suggests that these particular targets have dissimilar albedos. This is consistent with the range of albedos measured for the Vestoids through thermal models. However, there is no discernable trend for individual Vestoids with regards to wavelength dependence. Unlike the S- and C-complexes, our data show examples in which the polarization both increases and decreases with wavelength. When our Vestoid data are combined, the wavelength dependence becomes more negative (i.e. polarization tends to decrease with wavelength) as phase angle increases. This is similar to the trend observed in the S-complex, but the opposite trend when compared to the C-complex. The wavelength dependence of Vestoids suggests that this dependence is not strongly affected by albedo. The Vestoids are significantly smaller in size than the asteroids for which other measurements of the wavelength dependence have been analyzed. Possible grain size effects could be a cause of the dissimilar wavelength dependence between the Vestoids and other taxonomic complexes. However, further investigation is needed to explore this possibility.

Regional scale albedo of first year Arctic drift ice during summer melt estimated from synthesis of in situ measurements and airborne imagery

NASA Astrophysics Data System (ADS)

Divine, Dmitry; Granskog, Mats A.; Hudson, Stephen R.; Pedersen, Christina A.; Karlsen, Tor I.; Gerland, Sebastian

2014-05-01

The paper presents the results of analysis of the radiative properties of first year sea ice in advanced stages of melt. The presented technique is based on the upscaling in situ point measurements of surface albedo to the regional (150 km) spatial scale using aerial photographs of sea ice captured by a helicopter borne camera setup. The sea ice imagery as well as in situ snow and ice data were collected during the eight day ICE12 drift experiment carried out by the Norwegian Polar Institute in the Arctic north of Svalbard at 83.5 N during 27 July-03 August 2012. In total some 100 ground albedo measurements were made on melting sea ice in locations representative of the four main types of sea ice surface identified using the discriminant analysis -based classification technique. Some 11000 images from a total of six ice survey flights adding up to some 770 km of flight tracks covering about 28 km2 of sea ice surface were classified to yield the along-track distributions of four major surface classes: bare ice, dark melt ponds, bright melt ponds and open water. Results demonstrated a relative homogeneity of sea ice cover in the study area allowing for upscaling the local optical measurements to the regional scale. For the typical 10% open water fraction and 25% melt pond coverage, with a ratio of dark to bright ponds of 2 identified from selected images, the aggregate scale surface albedo of the area was estimated to be 0.42(0.40;0.44). The confidence intervals on the estimate were derived using the moving block bootstrap approach applied to the sequences of classified sea ice images and albedo of the four surface classes treated as random variables. Uncertainty in the mean estimates of local albedo from in situ measurements contributed some 65% to the variance of the estimated regional albedo with the remaining variance to be associated with the spatial inhomogeneity of sea ice cover. The results of the study are of relevance for the modeling of sea ice processes in climate simulations. It particularly concerns the period of summer melt when the optical properties of sea ice undergo substantial changes which the existing sea ice models experience most difficulties to accurately reproduce. That phase of a season is especially crucial for climate and ecosystem processes in the polar regions.

Effect of land cover change on snow free surface albedo across the continental United States

USGS Publications Warehouse

Wickham, J.; Nash, M.S.; Barnes, Christopher A.

2016-01-01

Land cover changes (e.g., forest to grassland) affect albedo, and changes in albedo can influence radiative forcing (warming, cooling). We empirically tested albedo response to land cover change for 130 locations across the continental United States using high resolution (30 m-×-30 m) land cover change data and moderate resolution (~ 500 m-×-500 m) albedo data. The land cover change data spanned 10 years (2001 − 2011) and the albedo data included observations every eight days for 13 years (2001 − 2013). Empirical testing was based on autoregressive time series analysis of snow free albedo for verified locations of land cover change. Approximately one-third of the autoregressive analyses for woody to herbaceous or forest to shrub change classes were not significant, indicating that albedo did not change significantly as a result of land cover change at these locations. In addition, ~ 80% of mean differences in albedo arising from land cover change were less than ± 0.02, a nominal benchmark for precision of albedo measurements that is related to significant changes in radiative forcing. Under snow free conditions, we found that land cover change does not guarantee a significant albedo response, and that the differences in mean albedo response for the majority of land cover change locations were small.

Areal-Averaged Spectral Surface Albedo in an Atlantic Coastal Area: Estimation from Ground-Based Transmission

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kassianov, Evgueni; Barnard, James; Flynn, Connor

Tower-based data combined with high-resolution satellite products have been used to produce surface albedo at various spatial scales over land. Because tower-based albedo data are available at only a few sites, surface albedos using these combined data are spatially limited. Moreover, tower-based albedo data are not representative of highly heterogeneous regions. To produce areal-averaged and spectrally-resolved surface albedo for regions with various degrees of surface heterogeneity, we have developed a transmission-based retrieval and demonstrated its feasibility for relatively homogeneous land surfaces. Here we demonstrate its feasibility for a highly heterogeneous coastal region. We use the atmospheric transmission measured during amore » 19-month period (June 2009 – December 2010) by a ground-based Multi-Filter Rotating Shadowband Radiometer (MFRSR) at five wavelengths (0.415, 0.5, 0.615, 0.673 and 0.87 µm) at the Department of Energy’s Atmospheric Radiation Measurement (ARM) Mobile Facility (AMF) site located on Graciosa Island. We compare the MFRSR-retrieved areal-averaged surface albedo with albedo derived from Moderate Resolution Imaging Spectroradiometer (MODIS) observations, and also a composite-based albedo. Lastly, we demonstrate that these three methods produce similar spectral signatures of surface albedo; however, the MFRSR-retrieved albedo, is higher on average (≤0.04) than the MODIS-based areal-averaged surface albedo and the largest difference occurs in winter.« less

Areal-Averaged Spectral Surface Albedo in an Atlantic Coastal Area: Estimation from Ground-Based Transmission

DOE PAGES

Kassianov, Evgueni; Barnard, James; Flynn, Connor; ...

2017-07-12

Tower-based data combined with high-resolution satellite products have been used to produce surface albedo at various spatial scales over land. Because tower-based albedo data are available at only a few sites, surface albedos using these combined data are spatially limited. Moreover, tower-based albedo data are not representative of highly heterogeneous regions. To produce areal-averaged and spectrally-resolved surface albedo for regions with various degrees of surface heterogeneity, we have developed a transmission-based retrieval and demonstrated its feasibility for relatively homogeneous land surfaces. Here we demonstrate its feasibility for a highly heterogeneous coastal region. We use the atmospheric transmission measured during amore » 19-month period (June 2009 – December 2010) by a ground-based Multi-Filter Rotating Shadowband Radiometer (MFRSR) at five wavelengths (0.415, 0.5, 0.615, 0.673 and 0.87 µm) at the Department of Energy’s Atmospheric Radiation Measurement (ARM) Mobile Facility (AMF) site located on Graciosa Island. We compare the MFRSR-retrieved areal-averaged surface albedo with albedo derived from Moderate Resolution Imaging Spectroradiometer (MODIS) observations, and also a composite-based albedo. Lastly, we demonstrate that these three methods produce similar spectral signatures of surface albedo; however, the MFRSR-retrieved albedo, is higher on average (≤0.04) than the MODIS-based areal-averaged surface albedo and the largest difference occurs in winter.« less

ASTEROID LIGHT CURVES FROM THE PALOMAR TRANSIENT FACTORY SURVEY: ROTATION PERIODS AND PHASE FUNCTIONS FROM SPARSE PHOTOMETRY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Waszczak, Adam; Chang, Chan-Kao; Cheng, Yu-Chi

We fit 54,296 sparsely sampled asteroid light curves in the Palomar Transient Factory survey to a combined rotation plus phase-function model. Each light curve consists of 20 or more observations acquired in a single opposition. Using 805 asteroids in our sample that have reference periods in the literature, we find that the reliability of our fitted periods is a complicated function of the period, amplitude, apparent magnitude, and other light-curve attributes. Using the 805-asteroid ground-truth sample, we train an automated classifier to estimate (along with manual inspection) the validity of the remaining ∼53,000 fitted periods. By this method we findmore » that 9033 of our light curves (of ∼8300 unique asteroids) have “reliable” periods. Subsequent consideration of asteroids with multiple light-curve fits indicates a 4% contamination in these “reliable” periods. For 3902 light curves with sufficient phase-angle coverage and either a reliable fit period or low amplitude, we examine the distribution of several phase-function parameters, none of which are bimodal though all correlate with the bond albedo and with visible-band colors. Comparing the theoretical maximal spin rate of a fluid body with our amplitude versus spin-rate distribution suggests that, if held together only by self-gravity, most asteroids are in general less dense than ∼2 g cm{sup −3}, while C types have a lower limit of between 1 and 2 g cm{sup −3}. These results are in agreement with previous density estimates. For 5–20 km diameters, S types rotate faster and have lower amplitudes than C types. If both populations share the same angular momentum, this may indicate the two types’ differing ability to deform under rotational stress. Lastly, we compare our absolute magnitudes (and apparent-magnitude residuals) to those of the Minor Planet Center’s nominal (G = 0.15, rotation-neglecting) model; our phase-function plus Fourier-series fitting reduces asteroid photometric rms scatter by a factor of ∼3.« less

Shadow mechanism and the opposition effect of brightness of atmosphereless celestial bodies

NASA Astrophysics Data System (ADS)

Morozhenko, A. V.; Vidmachenko, A. P.

2013-09-01

We consider the Irvine-Yanovistkii modification of the shadow model developed by Hapke for the opposition effect of brightness. The relation between the single scattering albedo ω and the transparency coefficient of particles κ is suggested to be used in the form κ = (1 - ω) n, which allows the number of unknowns in the model to be reduced to two parameters (the packing density of particles g and ω) and the single-scattering phase function Ξ(α). The analysis of spectrophotometric measurements of the moon and Mars showed that the data on the observed opposition effect and the changes in the color index with the phase angle α well agree if the values of n = 0.25 and g = 0.4 (the moon) and 0.6 (Mars) are assumed in calculations. When being applied to asteroids of several types, this method also yielded a satisfactory agreement. For the E-type asteroids, the sets of parameters are [g = 0.6, ω = 0.6, A g = 0.21, and q = 0.83] or [g = 0.3, ω = 0.4, A g = 0.15, and q = 0.71] under the Martian single-scattering phase function; for the M-type asteroids, it is [g = 0.4, ω ≤ 0.1, A g ≤ 0.075, and q ≤ 0.42] under the lunar single-scattering phase function; for the S-type asteroids, it is [g = 0.4, ω = 0.4, A g = 0.28, and q = 0.49] under the lunar single-scattering phase function; and for the C-type asteroids, it is [g = 0.6, ω ≤ 0.1, A g ≤ 0.075, and q = 0.43] under the modified lunar single-scattering phase function. The polarization measurements fulfilled by Gehrels et al. (1964) for the bright feature on the lunar surface, Copernicus (L = -20°08', φ = +10°11'), at a phase angle α = 1.6° revealed the deviations in the position of the polarization plane from that typical for the negative branch. They were 22° and 12° in the G and I filters, respectively. At the same time, the deviation was within the error (±3° in the U filter and for the dark feature Plato (L = -10°32', φ = +51°25'), which can be caused by the coherent mechanism of the formation of the polarization peak.

Historical photometric evidence for volatile migration on Triton

NASA Technical Reports Server (NTRS)

Buratti, Bonnie J.; Goguen, Jay D.; Gibson, James; Mosher, Joel

1994-01-01

Analysis of CCD images of Triton obtained with the 1.5-m telescope on Palomar Mountain shows that in the time period surrounding the Voyager 2 encounter with the satellite (1985-1990), no changes in the satellite's visual albedo or color occurred. The published observations of Triton in the 0.35- to 0.60-micrometer spectral region obtained between 1950 and 1990 were reanalyzed to detect historical variability in both its albedo and visual color. Analysis of the photometry indicates that there is little, if any, change in Triton's visual geometric albedo. This result is consistent with the albedo pattern observed by Voyager and the change in sub-Earth latitude. Two distinct types of color changes are evident: a significant secular increase in the blue region of the visual spectrum since at least the 1950s, and the reported dramatic reddening of Triton's spectrum in the late 1970s. The latter change can be explained only by a short-lived geological phenomenon. Triton's changing pole orientation with respect to a terrestrial observer cannot explain the secular color changes. These changes imply volatile transport on a global scale on Triton's surface during the past 4 decades. We present two models which show that either removal of a red volatile from Triton's polar cap or deposition of a blue volatile in the equatorial regions can explain the secular color changes. A third possibility is that the changes are the result of the alpha-beta phase transition of nitrogen and subsequent fracturing of the polar cap region (N. S. Duxbury and R. H. Brown (1993).

Ground-based characterization of Hayabusa2 mission target asteroid 162173 Ryugu: constraining mineralogical composition in preparation for spacecraft operations

NASA Astrophysics Data System (ADS)

Le Corre, Lucille; Sanchez, Juan A.; Reddy, Vishnu; Takir, Driss; Cloutis, Edward A.; Thirouin, Audrey; Becker, Kris J.; Li, Jian-Yang; Sugita, Seiji; Tatsumi, Eri

2018-03-01

Asteroids that are targets of spacecraft missions are interesting because they present us with an opportunity to validate ground-based spectral observations. One such object is near-Earth asteroid (NEA) (162173) Ryugu, which is the target of the Japanese Space Agency's (JAXA) Hayabusa2 sample return mission. We observed Ryugu using the 3-m NASA Infrared Telescope Facility on Mauna Kea, Hawaii, on 2016 July 13 to constrain the object's surface composition, meteorite analogues, and link to other asteroids in the main belt and NEA populations. We also modelled its photometric properties using archival data. Using the Lommel-Seeliger model we computed the predicted flux for Ryugu at a wide range of viewing geometries as well as albedo quantities such as geometric albedo, phase integral, and spherical Bond albedo. Our computed albedo quantities are consistent with results from Ishiguro et al. Our spectral analysis has found a near-perfect match between our spectrum of Ryugu and those of NEA (85275) 1994 LY and Mars-crossing asteroid (316720) 1998 BE7, suggesting that their surface regoliths have similar composition. We compared Ryugu's spectrum with that of main belt asteroid (302) Clarissa, the largest asteroid in the Clarissa asteroid family, suggested as a possible source of Ryugu by Campins et al. We found that the spectrum of Clarissa shows significant differences with our spectrum of Ryugu, but it is similar to the spectrum obtained by Moskovitz et al. The best possible meteorite analogues for our spectrum of Ryugu are two CM2 carbonaceous chondrites, Mighei and ALH83100.

Analysis of global land surface albedo climatology and spatial-temporal variation during 1981-2010 from multiple satellite products

NASA Astrophysics Data System (ADS)

He, Tao; Liang, Shunlin; Song, Dan-Xia

2014-09-01

For several decades, long-term time series data sets of multiple global land surface albedo products have been generated from satellite observations. These data sets have been used as one of the key variables in climate change studies. This study aims to assess the surface albedo climatology and to analyze long-term albedo changes, from nine satellite-based data sets for the period 1981-2010, on a global basis. Results show that climatological surface albedo data sets derived from satellite observations can be used to validate, calibrate, and further improve surface albedo simulations and parameterizations in current climate models. However, the albedo products derived from the International Satellite Cloud Climatology Project and the Global Energy and Water Exchanges Project have large seasonal biases. At latitudes higher than 50°, the maximal difference in winter zonal albedo ranges from 0.1 to 0.4 among the nine satellite data sets. Satellite-based albedo data sets agree relatively well during the summer at high latitudes, with a standard deviation of 0.04 for the 70°-80° zone in both hemispheres. The fine-resolution (0.05°) data sets agree well with each other for all the land cover types in middle to low latitudes; however, large spread was identified for their albedos at middle to high latitudes over land covers with mixed snow and sparse vegetation. By analyzing the time series of satellite-based albedo products over the past three decades, albedo of the Northern Hemisphere was found to be decreasing in July, likely due to the shrinking snow cover. Meanwhile, albedo in January was found to be increasing, likely because of the expansion of snow cover in northern winter. However, to improve the albedo estimation at high latitudes, and ultimately the climate models used for long-term climate change studies, a still better understanding of differences between satellite-based albedo data sets is required.

Spectrophotometric properties of materials observed by Pancam on the Mars Exploration Rovers: 2. Opportunity

USGS Publications Warehouse

Johnson, J. R.; Grundy, W.M.; Lemmon, M.T.; Bell, J.F.; Johnson, M.J.; Deen, R.; Arvidson, R. E.; Farrand, W. H.; Guinness, E.; Hayes, A.G.; Herkenhoff, K. E.; Seelos, F.; Soderblom, J.; Squyres, S.

2006-01-01

The Panoramic Camera (Pancam) on the Mars Exploration Rover Opportunity acquired visible/near-infrared multispectral observations of soils and rocks under varying viewing and illumination geometries that were modeled using radiative transfer theory to improve interpretations of the microphysical and surface scattering nature of materials in Meridiani Planum. Nearly 25,000 individual measurements were collected of rock and soil units identified by their color and morphologic properties over a wide range of phase angles (0-150??) at Eagle crater, in the surrounding plains, in Endurance crater, and in the plains between Endurance and Erebus craters through Sol 492. Corrections for diffuse skylight incorporated sky models based on observations of atmospheric opacity throughout the mission. Disparity maps created from Pancam stereo images allowed inclusion of local facet orientation estimates. Outcrop rocks overall exhibited the highest single scattering albedos (???0.9 at 753 nm), and most spherule-rich soils exhibited the lowest (???0.6 at 753 nm). Macroscopic roughness among outcrop rocks varied but was typically larger than spherule-rich soils. Data sets with sufficient phase angle coverage (resulting in well-constrained Hapke parameters) suggested that models using single-term and two-term Henyey-Greenstein phase functions exhibit a dominantly broad backscattering trend for most undisturbed spherule-rich soils. Rover tracks and other compressed soils exhibited forward scattering, while outcrop rocks were intermediate in their scattering behaviors. Some phase functions exhibited wavelength-dependent trends that may result from variations in thin deposits of airfall dust that occurred during the mission. Copyright 2006 by the American Geophysical Union.

Validation of Quasi-Invariant Ice Cloud Radiative Quantities with MODIS Satellite-Based Cloud Property Retrievals

NASA Technical Reports Server (NTRS)

Ding, Jiachen; Yang, Ping; Kattawar, George W.; King, Michael D.; Platnick, Steven; Meyer, Kerry G.

2017-01-01

Similarity relations applied to ice cloud radiance calculations are theoretically analyzed and numerically validated. If t(1v) and t(1vg) are conserved where t is optical thickness, v the single-scattering albedo, and g the asymmetry factor, it is possible that substantially different phase functions may give rise to similar radiances in both conservative and non-conservative scattering cases, particularly in the case of large optical thicknesses. In addition to theoretical analysis, this study uses operational ice cloud optical thickness retrievals from the Moderate Resolution Imaging Spectroradiometer (MODIS) Level 2 Collection5 (C5) and Collection 6 (C6) cloud property products to verify radiative similarity relations. It is found that, if the MODIS C5 and C6 ice cloud optical thickness values are multiplied by their respective (1wg)factors, the resultant products referred to as the effective optical thicknesses become similar with their ratio values around unity. Furthermore, the ratios of the C5 and C6 ice cloud effective optical thicknesses display an angular variation pattern similar to that of the corresponding ice cloud phase function ratios. The MODIS C5 and C6 values of ice cloud similarity parameter, defined as [(1w)(1(exp. 1/2)wg)]12, also tend to be similar.

[A review of atmospheric aerosol research by using polarization remote sensing].

PubMed

Guo, Hong; Gu, Xing-Fa; Xie, Dong-Hai; Yu, Tao; Meng, Qing-Yan

2014-07-01

In the present paper, aerosol research by using polarization remote sensing in last two decades (1993-2013) was reviewed, including aerosol researches based on POLDER/PARASOL, APS(Aerosol Polarimetry Sensor), Polarized Airborne camera and Ground-based measurements. We emphasize the following three aspects: (1) The retrieval algorithms developed for land and marine aerosol by using POLDER/PARASOL; The validation and application of POLDER/PARASOL AOD, and cross-comparison with AOD of other satellites, such as MODIS AOD. (2) The retrieval algorithms developed for land and marine aerosol by using MICROPOL and RSP/APS. We also introduce the new progress in aerosol research based on The Directional Polarimetric Camera (DPC), which was produced by Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences (CAS). (3) The aerosol retrieval algorithms by using measurements from ground-based instruments, such as CE318-2 and CE318-DP. The retrieval results from spaceborne sensors, airborne camera and ground-based measurements include total AOD, fine-mode AOD, coarse-mode AOD, size distribution, particle shape, complex refractive indices, single scattering albedo, scattering phase function, polarization phase function and AOD above cloud. Finally, based on the research, the authors present the problems and prospects of atmospheric aerosol research by using polarization remote sensing, and provide a valuable reference for the future studies of atmospheric aerosol.

Snow Cover and Vegetation-Induced Decrease in Global Albedo From 2002 to 2016

NASA Astrophysics Data System (ADS)

Li, Qiuping; Ma, Mingguo; Wu, Xiaodan; Yang, Hong

2018-01-01

Land surface albedo is an essential parameter in regional and global climate models, and it is markedly influenced by land cover change. Variations in the albedo can affect the surface radiation budget and further impact the global climate. In this study, the interannual variation of albedo from 2002 to 2016 was estimated on the global scale using Moderate Resolution Imaging Spectroradiometer (MODIS) datasets. The presence and causes of the albedo changes for each specific region were also explored. From 2002 to 2016, the MODIS-based albedo decreased globally, snow cover declined by 0.970 (percent per pixel), while the seasonally integrated normalized difference vegetation index increased by 0.175. Some obvious increases in the albedo were detected in Central Asia, northeastern China, parts of the boreal forest in Canada, and the temperate steppe in North America. In contrast, noticeable decreases in the albedo were found in the Siberian tundra, Europe, southeastern Australia, and northeastern regions of North America. In the Northern Hemisphere, the greening trend at high latitudes made more contribution to the decline in the albedo. However, the dramatic fluctuation of snow-cover at midlatitudes predominated in the change of albedo. Our analysis can help to understand the roles that vegetation and snow cover play in the variation of albedo on global and regional scales.

A Continental United States High Resolution NLCD Land Cover – MODIS Albedo Database to Examine Albedo and Land Cover Change Relationships

EPA Science Inventory

Surface albedo influences climate by affecting the amount of solar radiation that is reflected at the Earth’s surface, and surface albedo is, in turn, affected by land cover. General Circulation Models typically use modeled or prescribed albedo to assess the influence of land co...

Estimating big bluestem albedo from directional reflectance measurements

NASA Technical Reports Server (NTRS)

Irons, J. R.; Ranson, K. J.; Daughtry, C. S. T.

1988-01-01

Multidirectional reflectance factor measurements acquired in the summer of 1986 are used to make estimates of big bluestem grass albedo, evaluating the variation of albedo with changes in solar zenith angle and phenology. On any given day, the albedo was observed to increase by at least 19 percent as solar zenith angle increased. Changes in albedo were found to correspond to changes in the green leaf area index of the grass canopy. Estimates of albedo made using reflectance data acquired within only one or two azimuthal planes and at a restricted range of view zenith angle were evaluated and compared to 'true' albedos derived from all available reflectance factor data. It was found that even a limited amount of multiple direction reflectance data was preferable to a single nadir reflectance factor for the estimation of prarie grass albedo.

Long-term record of top-of-atmosphere albedo generated from AVHRR data

NASA Astrophysics Data System (ADS)

Song, Z.

2017-12-01

Top-of-Atmosphere (TOA) albedo is a fundamental component of Earth's energy budget. Previously, long-term accurate TOA albedo products did not exist due to the lack of stable broadband observations. With a new albedo estimation methodology based on multispectral observations, TOA albedo since 1981 has been retrieved using data from the Advanced Very High Resolution Radiometer (AVHRR), which provides the longest record of satellite observations across the globe. To develop the long-term TOA albedo record, the instantaneous TOA albedo was calculated by the direct estimation method, which was built on training data pairs from coincident AVHRR TOA reflectance and Moderate Resolution Imaging Spectroradiometer (MODIS) TOA albedo. The instantaneous TOA albedo was then converted to daily mean and monthly mean albedo based on the diurnal curves from geostationary satellites. The TOA albedo results (AVHRR-TAL) were compared with Clouds and the Earth's Radiant Energy System (CERES) flux products for 2007. The monthly mean AVHRR-TAL agreed well with the CERES products, with a root mean square difference (RMSD) of 0.032 and a bias of 0.013. In addition, AVHRR-TAL showed similar seasonal variations to those seen in the CERES products. Further analysis on long-term time series showed good consistency between the two datasets (R2 > 0.95 and relative RMSD < 4%) from 2000 to 2015. Although some calibration issues remain to be solved, our datasets show the potential ability to observe the global TOA albedo from 1981 to the present.

Taking the Temperature of a Lava Planet

NASA Astrophysics Data System (ADS)

Kreidberg, Laura; Lopez, Eric; Cowan, Nick; Lupu, Roxana; Stevenson, Kevin; Louden, Tom; Malavolta, Luca

2018-05-01

Ultra-short period rocky planets (USPs) are an exotic class of planet found around less than 1% of stars. With orbital periods shorter than 24 hours, these worlds are blasted with stellar radiation that is expected to obliterate any traces of a primordial atmosphere and melt the dayside surface into a magma ocean. Observations of USPs have yielded several surprising results, including the measurement of an offset hotspot in the thermal phase curve of 55 Cancri e (which may indicate a thick atmosphere has survived), and a high Bond albedo for Kepler-10b, which suggests the presence of unusually reflective lava on its surface. To further explore the properties of USPs and put these results in context, we propose to observe a thermal phase curve of the newly discovered USP K2- 141b. This planet is a rocky world in a 6.7 hour orbit around a bright, nearby star. When combined with optical phase curve measured by K2, our observations will uniquely determine the planet's Bond albedo, precisely measure the offset of the thermal curve, and determine the temperature of the dayside surface. These results will cement Spitzer's role as a pioneer in the study of terrestrial planets beyond the Solar System, and provide a critical foundation for pursuing the optimal follow-up strategy for K2-141b with JWST.

Photometric correction of VIR high space resolution data of Ceres

NASA Astrophysics Data System (ADS)

Longobardo, Andrea; Palomba, Ernesto; De Sanctis, Maria Cristina; Ciarniello, Mauro; Tosi, Federico; Giacomo Carrozzo, Filippo; Capria, Maria Teresa; Zambon, Francesca; Raponi, Andrea; Ammannito, Eleonora; Zinzi, Angelo; Raymond, Carol; Russell, Christopher T.; VIR-Dawn Team

2016-10-01

NASA's Dawn spacecraft [1] has been orbiting Ceres since early 2015. The mission is divided into five stages, characterized by different spacecraft altitudes corresponding to different space resolutions, i.e. Approach (CSA), Rotational Characterization (CSR), Survey (CSS), High Altitude Mapping Orbit (HAMO), and Low Altitude Mapping Orbit (LAMO).Ceres is a dark body (i.e. average albedo at 1.2 um is 0.08 [2]), hence photometric correction is much more important than for brighter asteroids (e.g. S-type and achondritric). Indeed, the negligible role of multiple scattering increases the reflectance dependence on phase angle.A photometric correction of VIR data at low spatial resolution (i.e. CSA, CSR, CSS) has already been applied with different methodologies (e.g. [2], [3]), These techniques highlight a reflectance and band depths dependency on the phase angle which is homogeneous on the entire surface in agreement with C-type taxonomy.However, with increasing spatial resolution (i.e. HAMO and LAMO data), the retrieval of a unique set of parameters for the photometric correction is no longer sufficient to obtain reliable albedo/band depth maps. In this work, a new photometric correction is obtained and applied to all the high resolution VIR data of Ceres, taking into account the reflectance variations observed at small scales. The developed algorithm will be implemented on the MATISSE tool [4] in order to be visualized on the Ceres shape model.Finally, an interpretation of the obtained phase functions is given in terms of optical and physical properties of the Ceres regolith.AcknowledgementsVIR was funded and coordinated by the Italian Space Agency, and built by SELEX ES, with the scientific leadership of IAPS-INAF, Rome, Italy, and is operated by IAPS-INAF, Rome, Italy. Support of the Dawn Science, Instrument, and Operation Teams is gratefully acknowledged.References[1] Russell, C. T. et al., 2012, Science 336, 686[2] Longobardo A., et al., 2016, LPSC, 2239[3] Ciarniello, M. et al., 2016, submitted to A&A[4] Zinzi, A. et al., 2016, A&C, 15, 16-28

Characterizing bidirectional reflectance and spectral albedo of various land cover types in Midwest using GeoTASO Summer-2014 campaign

NASA Astrophysics Data System (ADS)

Wulamu, A.; Fishman, J.; Maimaitiyiming, M.; Leitch, J. W.; Zoogman, P.; Liu, X.; Chance, K.; Marshall, B.

2015-12-01

Understanding the bi-directional reflectance function (BRDF) and spectral albedo of various land-cover types is critical for retrieval of trace gas measurements from planned geostationary satellites such as the Tropospheric Emissions: Monitoring of Pollution (TEMPO). Radiant energy, which will be measured by these instruments at the top of atmosphere (TOA) at unprecedented spectral resolution, is strongly influenced by how this energy is reflected by the underlying surface. Thus, it is critical that we understand this phenomenon at comparable wavelength resolution. As part of the NASA ESTO-funded Geostationary Trace gas and Aerosol Sensor Optimization (GeoTASO) development project, we carried out synchronous field and airborne data collection campaigns in the St Louis Metro region in Summer 2014. We collected spectral reflectance data of various land cover types on the ground within hours of a GeoTASO overpass using a field-based hyperspectral spectroradiometer (model PSR3500 from Spectral Evolution). Field measurements collecting in-situ spectral albedo and bidirectional reflectance factors were also obtained in July and August of 2015. In this study, we present our preliminary findings from in-situ and airborne GeoTASO derived spectral albedo and BRDF characteristics of major land cover types at TEMPO spectral profiles, which are necessary for the accurate retrieval of tropospheric trace gases and aerosols. First, a spectral database of various targets (e.g., plants, soils, rocks, man-made objects and water) was developed using field measurements. Next, the GeoTASO airborne data were corrected using MODTRAN and field measurements to derive spectral albedo and BRDF. High spatial resolution land-cover types were extracted using satellite images (e.g., Landsat, WorldView, IKONOS, etc.) at resolutions from 2 m - 30 m. Lastly, spectral albedo/BRDFs corresponding to various land cover types were analyzed using both field and GeoTASO measurements.

Predicting Clear-Sky Reflectance Over Snow/Ice in Polar Regions

NASA Technical Reports Server (NTRS)

Chen, Yan; Sun-Mack, Sunny; Arduini, Robert F.; Hong, Gang; Minnis, Patrick

2015-01-01

Satellite remote sensing of clouds requires an accurate estimate of the clear-sky radiances for a given scene to detect clouds and aerosols and to retrieve their microphysical properties. Knowing the spatial and angular variability of clear-sky albedo is essential for predicting clear-sky radiance at solar wavelengths. The Clouds and the Earth's Radiant Energy System (CERES) Project uses the nearinfrared (NIR; 1.24, 1.6 or 2.13 micrometers), visible (VIS; 0.63 micrometers) and vegetation (VEG; 0.86 micrometers) channels available on the Terra and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) to help identify clouds and retrieve their properties in both snow-free and snow-covered conditions. Thus, it is critical to have reliable distributions of clear-sky albedo for all of these channels. In CERES Edition 4 (Ed4), the 1.24-micrometer channel is used to retrieve cloud optical depth over snow/ice-covered surfaces. Thus, it is especially critical to accurately predict the 1.24-micrometer clear-sky albedo alpha and reflectance rho for a given location and time. Snow albedo and reflectance patterns are very complex due to surface texture, particle shapes and sizes, melt water, and vegetation protrusions from the snow surface. To minimize those effects, this study focuses on the permanent snow cover of Antarctica where vegetation is absent and melt water is minimal. Clear-sky albedos are determined as a function of solar zenith angle (SZA) from observations over all scenes determined to be cloud-free to produce a normalized directional albedo model (DRM). The DRM is used to develop alpha(SZA=0 degrees) on 10 foot grid for each season. These values provide the basis for predicting r at any location and set of viewing & illumination conditions. This paper examines the accuracy of this approach for two theoretical snow surface reflectance models.

Assessment of NPP VIIRS Albedo Over Heterogeneous Crop Land in Northern China

NASA Astrophysics Data System (ADS)

Wu, Xiaodan; Wen, Jianguang; Xiao, Qing; Yu, Yunyue; You, Dongqin; Hueni, Andreas

2017-12-01

In this paper, the accuracy of Suomi National Polar-orbiting Partnership Visible Infrared Imaging Radiometer Suite (VIIRS) land surface albedo, which is derived from the direct estimation algorithm, was assessed using ground-based albedo observations from a wireless sensor network over a heterogeneous cropland in the Huailai station, northern China. Data from six nodes spanning 2013-2014 over vegetation, bare soil, and mixed terrain surfaces were utilized to provide ground reference at VIIRS pixel scale. The performance of VIIRS albedo was also compared with Global LAnd Surface Satellite (GLASS) and Moderate Resolution Imaging Spectroradiometer (MODIS) albedos (Collection 5 and 6). The results indicate that the current granular VIIRS albedo has a high accuracy with a root-mean-square error of 0.02 for typical land covers. They are significantly correlated with ground references indicated by a correlation coefficient (R) of 0.73. The VIIRS albedo shows distinct advantages to GLASS and MODIS albedos over bare soil and mixed-cover surfaces, while it is inferior to the other two products over vegetated surfaces. Furthermore, its time continuity and the ability to capture the abrupt change of surface albedo are better than that of GLASS and MODIS albedo.

MISR Level 3 Products

Atmospheric Science Data Center

2015-06-04

... nm), approximated from visible bands. Derived from a linear combination of MISR bands found in the Level 2 LAND, DHR field. Weiss et ... Level 2 ALBEDO, AlbedoRestrictive field. Local Albedo Local albedo, for 4 MISR spectral bands + broadband ...

Sea Ice, Clouds, Sunlight, and Albedo: The Umbrella Versus the Blanket

NASA Astrophysics Data System (ADS)

Perovich, D. K.

2017-12-01

The Arctic sea ice cover has undergone a major decline in recent years, with reductions in ice extent, ice thickness, and ice age. Understanding the feedbacks and forcing driving these changes is critical in improving predictions. The surface radiation budget plays a central role in summer ice melt and is governed by clouds and surface albedo. Clouds act as an umbrella reducing the downwelling shortwave, but also serve as a blanket increasing the downwelling longwave, with the surface albedo also determining the net balance. Using field observations from the SHEBA program, pairs of clear and cloudy days were selected for each month from May through September and the net radiation flux was calculated for different surface conditions and albedos. To explore the impact of albedo we calculated a break even albedo, where the net radiation for cloudy skies is the same as clear skies. For albedos larger than the break-even value the net radiation flux is smaller under clear skies compared to cloudy skies. Break-even albedos ranged from 0.30 in September to 0.58 in July. For snow covered or bare ice, clear skies always resulted in less radiative heat input. In contrast, leads always had, and ponds usually had, more radiative heat input under clear skies than cloudy skies. Snow covered ice had a net radiation flux that was negative or near zero under clear skies resulting in radiative cooling. We combined the albedo of individual ice types with the area of those ice types to calculate albedos averaged over a 50 km x 50 km area. The July case had the smallest areally averaged albedo of 0.50. This was less than the breakeven albedo, so cloudy skies had a smaller net radiation flux than clear skies. For the cases from the other four months, the areally averaged albedo was greater than the break-even albedo. The areally averaged net radiation flux was negative under clear skies for the May and September cases.

Assessing spatio-temporal variability and trends in modelled and measured Greenland Ice Sheet albedo (2000-2013)

NASA Astrophysics Data System (ADS)

Alexander, P. M.; Tedesco, M.; Fettweis, X.; van de Wal, R. S. W.; Smeets, C. J. P. P.; van den Broeke, M. R.

2014-12-01

Accurate measurements and simulations of Greenland Ice Sheet (GrIS) surface albedo are essential, given the role of surface albedo in modulating the amount of absorbed solar radiation and meltwater production. In this study, we assess the spatio-temporal variability of GrIS albedo during June, July, and August (JJA) for the period 2000-2013. We use two remote sensing products derived from data collected by the Moderate Resolution Imaging Spectroradiometer (MODIS), as well as outputs from the Modèle Atmosphérique Régionale (MAR) regional climate model (RCM) and data from in situ automatic weather stations. Our results point to an overall consistency in spatio-temporal variability between remote sensing and RCM albedo, but reveal a difference in mean albedo of up to ~0.08 between the two remote sensing products north of 70° N. At low elevations, albedo values simulated by the RCM are positively biased with respect to remote sensing products by up to ~0.1 and exhibit low variability compared with observations. We infer that these differences are the result of a positive bias in simulated bare ice albedo. MODIS albedo, RCM outputs, and in situ observations consistently indicate a decrease in albedo of -0.03 to -0.06 per decade over the period 2003-2013 for the GrIS ablation area. Nevertheless, satellite products show a decline in JJA albedo of -0.03 to -0.04 per decade for regions within the accumulation area that is not confirmed by either the model or in situ observations. These findings appear to contradict a previous study that found an agreement between in situ and MODIS trends for individual months. The results indicate a need for further evaluation of high elevation albedo trends, a reconciliation of MODIS mean albedo at high latitudes, and the importance of accurately simulating bare ice albedo in RCMs.

Generalized Calibration of the Polarimetric Albedo Scale of Asteroids

NASA Astrophysics Data System (ADS)

Lupishko, D. F.

2018-03-01

Six different calibrations of the polarimetric albedo scale of asteroids have been published so far. Each of them contains its particular random and systematic errors and yields its values of geometric albedo. On the one hand, this complicates their analysis and comparison; on the other hand, it becomes more and more difficult to decide which of the proposed calibrations should be used. Moreover, in recent years, new databases on the albedo of asteroids obtained from the radiometric surveys of the sky with the orbital space facilities (the InfraRed Astronomical Satellite (IRAS), the Japanese astronomical satellite AKARI (which means "light"), the Wide-field Infrared Survey Explorer (WISE), and the Near-Earth Object Wide-field Survey Explorer (NEOWISE)) have appeared; and the database on the diameters and albedos of asteroids obtained from their occultations of stars has substantially increased. Here, we critically review the currently available calibrations and propose a new generalized calibration derived from the interrelations between the slope h and the albedo and between P min and the albedo. This calibration is based on all of the available series of the asteroid albedos and the most complete data on the polarization parameters of asteroids. The generalized calibration yields the values of the polarimetric albedo of asteroids in the system unified with the radiometric albedos and the albedos obtained from occultations of stars by asteroids. This, in turn, removes the difficulties in their comparison, joint analysis, etc.

Close packing effects on clean and dirty snow albedo and associated climatic implications

NASA Astrophysics Data System (ADS)

He, C.; Liou, K. N.; Takano, Y.

2017-12-01

Previous modeling of snow albedo, a key climate feedback parameter, follows the independent scattering approximation (ISA) such that snow grains are considered as a number of separate units with distances longer than wavelengths. Here we develop a new snow albedo model for widely observed close-packed snow grains internally mixed with black carbon (BC) and demonstrate that albedo simulations match closer to observations. Close packing results in a stronger light absorption for clean and BC-contaminated snow. Compared with ISA, close packing reduces pure snow albedos by up to 0.05, whereas it enhances BC-induced snow albedo reduction and associated surface radiative forcing by up to 15% (20%) for fresh (old) snow, with larger enhancements for stronger structure packing. Finally, our results suggest that BC-snow albedo forcing and snow albedo feedback (climate sensitivity) are underestimated in previous modeling studies, making snow close packing consideration a necessity in climate modeling and analysis.

Close packing effects on clean and dirty snow albedo and associated climatic implications

NASA Astrophysics Data System (ADS)

He, Cenlin; Takano, Yoshi; Liou, Kuo-Nan

2017-04-01

Previous modeling of snow albedo, a key climate feedback parameter, follows the independent scattering approximation (ISA) such that snow grains are considered as a number of separate units with distances longer than wavelengths. Here we develop a new snow albedo model for widely observed close-packed snow grains internally mixed with black carbon (BC) and demonstrate that albedo simulations match closer to observations. Close packing results in a stronger light absorption for clean and BC-contaminated snow. Compared with ISA, close packing reduces pure snow albedos by up to 0.05, whereas it enhances BC-induced snow albedo reduction and associated surface radiative forcing by up to 15% (20%) for fresh (old) snow, with larger enhancements for stronger structure packing. Finally, our results suggest that BC-snow albedo forcing and snow albedo feedback (climate sensitivity) are underestimated in previous modeling studies, making snow close packing consideration a necessity in climate modeling and analysis.

Assessing the aerosol direct and first indirect effects using ACM/GCM simulation results

NASA Astrophysics Data System (ADS)

Huang, H.; Gu, Y.; Xue, Y.; Lu, C. H.

2016-12-01

Atmospheric aerosols have been found to play an important role in global climate change but there are still large uncertainty in evaluating its role in the climate system. The aerosols generally affect global and regional climate through the scattering and the absorption of solar radiation (direct effect) and through their influences on cloud particle, number and sizes (first indirect effect). The indirect effect will further affects cloud water content, cloud top albedo and surface precipitations. In this study, we investigate the global climatic effect of aerosols using a coupled NCEP Global Forecast System (GFS) and a land surface model (SSiB2) The OPAC (Optical Properties of Aerosols and Clouds) database is used for aerosol effect. The OPAC data provides the optical properties (i.e., the extinction, scattering and absorption coefficient, single-scattering albedo, asymmetry factor and phase function) of ten types of aerosols under various relative humidity conditions for investigating the global direct and first indirect effects of dust aerosols. For indirect forcings due to liquid water, we follow the approach presented by Jiang et al (2011), in which a parameterization of cloud effective radius was calculated to describe its variance with convective strength and aerosol concentration. Since the oceans also play an important role on aerosol climatic effect, we also design a set of simulations using a coupled atmosphere/ocean model (CFS) to evaluate the sensitivity of aerosol effect with two-way atmosphere-ocean interactions.

Asymptotic radiance and polarization in optically thick media: ocean and clouds.

PubMed

Kattawar, G W; Plass, G N

1976-12-01

Deep in a homogeneous medium that both scatters and absorbs photons, such as a cloud, the ocean, or a thick planetary atmosphere, the radiance decreases exponentially with depth, while the angular dependence of the radiance and polarization is independent of depth. In this diffusion region, the asymptotic radiance and polarization are also independent of the incident distribution of radiation at the upper surface of the medium. An exact expression is derived for the asymptotic radiance and polarization for Rayleigh scattering. The approximate expression for the asymptotic radiance derived from the scalar theory is shown to be in error by as much as 16.4%. An exact expression is also derived for the relation between the diffusion exponent k and the single scattering albedo. A method is developed for the numerical calculation of the asymptotic radiance and polarization for any scattering matrix. Results are given for scattering from the haze L and cloud C3 distributions for a wide range of single scattering albedos. When the absorption is large, the polarization in the diffusion region approaches the values obtained for single scattered photons, while the radiance approaches the value calculated from the expression: phase function divided by (1 + kmicro), where micro is the cosine of the zenith angle. The asymptotic distribution of the radiation is of interest since it depends only on the inherent optical properties of the medium. It is, however, difficult to observe when the absorption is large because of the very low radiance values in the diffusion region.

Matrix operator theory of radiative transfer. 1: rayleigh scattering.

PubMed

Plass, G N; Kattawar, G W; Catchings, F E

1973-02-01

An entirely rigorous method for the solution of the equations for radiative transfer based on the matrix operator theory is reviewed. The advantages of the present method are: (1) all orders of the reflection and transmission matrices are calculated at once; (2) layers of any thickness may be combined, so that a realistic model of the atmosphere can be developed from any arbitrary number of layers, each with different properties and thicknesses; (3) calculations can readily be made for large optical depths and with highly anisotropic phase functions; (4) results are obtained for any desired value of the surface albedo including the value unity and for a large number of polar and azimuthal angles including the polar angle theta = 0 degrees ; (5) all fundamental equations can be interpreted immediately in terms of the physical interactions appropriate to the problem; (6) both upward and downward radiance can be calculated at interior points from relatively simple expressions. Both the general theory and its history together with the method of calculation are discussed. As a first example of the method numerous curves are given for both the reflected and transmitted radiance for Rayleigh scattering from a homogeneous layer for a range of optical thicknesses from 0.0019 to 4096, surface albedo A = 0, 0.2, and 1, and cosine of solar zenith angle micro = 1, 0.5397, and 0.1882. It is shown that the matrix operator approach contains the doubling method as a special case.

Albedo Spatial Variability and Causes on the Western Greenland Ice Sheet Percolation Zone

NASA Astrophysics Data System (ADS)

Lewis, G.; Osterberg, E. C.; Hawley, R. L.; Koffman, B. G.; Marshall, H. P.; Birkel, S. D.; Dibb, J. E.

2016-12-01

Many recent studies have concluded that Greenland Ice Sheet (GIS) mass loss has been accelerating over recent decades, but spatial and temporal variations in GIS mass balance remain poorly understood due to a complex relationship among precipitation and temperature changes, increasing melt and runoff, ice discharge, and surface albedo. Satellite measurements from MODerate resolution Imaging Spectroradiometer (MODIS) indicate that albedo has been declining over the past decade, but the cause and extent of GIS albedo change remains poorly constrained by field data. As fresh snow (albedo > 0.85) warms and melts, its albedo decreases due to snow grain growth, promoting solar absorption, higher snowpack temperatures and further melt. However, dark impurities like soot and dust can also significantly reduce snow albedo, even in the dry snow zone. While many regional climate models (e.g. the Regional Atmospheric Climate MOdel - RACMO2) calculate albedo spatial resolutions on the order of 10-30 km, and MODIS averages albedo over 500 m, surface features like sastrugi can affect albedo on much smaller scales. Here we assess the relative importance of grain size and shape vs. impurity concentrations on albedo in the western GIS percolation zone. We collected broadband albedo measurements (300-2500 nm at 3-8 nm resolution) at 35 locations using an ASD FieldSpec4 spectroradiometer to simultaneously quantify radiative fluxes and spectral reflectance. Measurements were collected on 10 x 10 m, 1 x 1 km, 5 x 5 km, and 10 x 10 km grids to determine the spatial variability of albedo as part of the 850-km Greenland Traverse for Accumulation and Climate Studies (GreenTrACS) traverse from Raven/Dye 2 to Summit. Additionally, we collected shallow (0-50 cm) snow pit samples every 5 cm at ASD measurement sites to quantify black carbon and mineral dust concentrations and size distributions using a Single Particle Soot Photometer and Coulter Counter, respectively. Preliminary results indicate larger albedo variability in the infrared than visible and near infrared. We compare our in situ field measurements with co-located albedo data from airplanes, satellites, and climate models, and discuss implications for GIS surface mass balance.

Evaluation of Operational Albedo Algorithms For AVHRR, MODIS and VIIRS: Case Studies in Southern Africa

NASA Astrophysics Data System (ADS)

Privette, J. L.; Schaaf, C. B.; Saleous, N.; Liang, S.

2004-12-01

Shortwave broadband albedo is the fundamental surface variable that partitions solar irradiance into energy available to the land biophysical system and energy reflected back into the atmosphere. Albedo varies with land cover, vegetation phenological stage, surface wetness, solar angle, and atmospheric condition, among other variables. For these reasons, a consistent and normalized albedo time series is needed to accurately model weather, climate and ecological trends. Although an empirically-derived coarse-scale albedo from the 20-year NOAA AVHRR record (Sellers et al., 1996) is available, an operational moderate resolution global product first became available from NASA's MODIS sensor. The validated MODIS product now provides the benchmark upon which to compare albedo generated through 1) reprocessing of the historic AVHRR record and 2) operational processing of data from the future National Polar-Orbiting Environmental Satellite System's (NPOESS) Visible/Infrared Imager Radiometer Suite (VIIRS). Unfortunately, different instrument characteristics (e.g., spectral bands, spatial resolution), processing approaches (e.g., latency requirements, ancillary data availability) and even product definitions (black sky albedo, white sky albedo, actual or blue sky albedo) complicate the development of the desired multi-mission (AVHRR to MODIS to VIIRS) albedo time series -- a so-called Climate Data Record. This presentation will describe the different albedo algorithms used with AVHRR, MODIS and VIIRS, and compare their results against field measurements collected over two semi-arid sites in southern Africa. We also describe the MODIS-derived VIIRS proxy data we developed to predict NPOESS albedo characteristics. We conclude with a strategy to develop a seamless Climate Data Record from 1982- to 2020.

Saturn Ring Data Analysis and Thermal Modeling

NASA Technical Reports Server (NTRS)

Dobson, Coleman

2011-01-01

CIRS, VIMS, UVIS, and ISS (Cassini's Composite Infrared Specrtometer, Visual and Infrared Mapping Spectrometer, Ultra Violet Imaging Spectrometer and Imaging Science Subsystem, respectively), have each operated in a multidimensional observation space and have acquired scans of the lit and unlit rings at multiple phase angles. To better understand physical and dynamical ring particle parametric dependence, we co-registered profiles from these three instruments, taken at a wide range of wavelengths, from ultraviolet through the thermal infrared, to associate changes in ring particle temperature with changes in observed brightness, specifically with albedos inferred by ISS, UVIS and VIMS. We work in a parameter space where the solar elevation range is constrained to 12 deg - 14 deg and the chosen radial region is the B3 region of the B ring; this region is the most optically thick region in Saturn's rings. From this compilation of multiple wavelength data, we construct and fit phase curves and color ratios using independent dynamical thermal models for ring structure and overplot Saturn, Saturn ring, and Solar spectra. Analysis of phase curve construction and color ratios reveals thermal emission to fall within the extrema of the ISS bandwidth and a geometrical dependence of reddening on phase angle, respectively. Analysis of spectra reveals Cassini CIRS Saturn spectra dominate Cassini CIRS B3 Ring Spectra from 19 to 1000 microns, while Earth-based B Ring Spectrum dominates Earth-based Saturn Spectrum from 0.4 to 4 microns. From our fits we test out dynamical thermal models; from the phase curves we derive ring albedos and non-lambertian properties of the ring particle surfaces; and from the color ratios we examine multiple scattering within the regolith of ring particles.

Global Albedo

Atmospheric Science Data Center

2013-04-19

... the albedo. Bright surfaces have albedo near unity, and dark surfaces have albedo near zero. The DHR refers to the amount of spectral ... Atmospheric Science Data Center's  MISR Level 3 Imagery web site . The Multi-angle Imaging SpectroRadiometer observes the daylit ...

Impacts of Satellite-Based Snow Albedo Assimilation on Offline and Coupled Land Surface Model Simulations.

PubMed

Wang, Tao; Peng, Shushi; Krinner, Gerhard; Ryder, James; Li, Yue; Dantec-Nédélec, Sarah; Ottlé, Catherine

2015-01-01

Seasonal snow cover in the Northern Hemisphere is the largest component of the terrestrial cryosphere and plays a major role in the climate system through strong positive feedbacks related to albedo. The snow-albedo feedback is invoked as an important cause for the polar amplification of ongoing and projected climate change, and its parameterization across models is an important source of uncertainty in climate simulations. Here, instead of developing a physical snow albedo scheme, we use a direct insertion approach to assimilate satellite-based surface albedo during the snow season (hereafter as snow albedo assimilation) into the land surface model ORCHIDEE (ORganizing Carbon and Hydrology In Dynamic EcosystEms) and assess the influences of such assimilation on offline and coupled simulations. Our results have shown that snow albedo assimilation in both ORCHIDEE and ORCHIDEE-LMDZ (a general circulation model of Laboratoire de Météorologie Dynamique) improve the simulation accuracy of mean seasonal (October throughout May) snow water equivalent over the region north of 40 degrees. The sensitivity of snow water equivalent to snow albedo assimilation is more pronounced in the coupled simulation than the offline simulation since the feedback of albedo on air temperature is allowed in ORCHIDEE-LMDZ. We have also shown that simulations of air temperature at 2 meters in ORCHIDEE-LMDZ due to snow albedo assimilation are significantly improved during the spring in particular over the eastern Siberia region. This is a result of the fact that high amounts of shortwave radiation during the spring can maximize its snow albedo feedback, which is also supported by the finding that the spatial sensitivity of temperature change to albedo change is much larger during the spring than during the autumn and winter. In addition, the radiative forcing at the top of the atmosphere induced by snow albedo assimilation during the spring is estimated to be -2.50 W m-2, the magnitude of which is almost comparable to that due to CO2 (2.83 W m-2) increases since 1750. Our results thus highlight the necessity of realistic representation of snow albedo in the model and demonstrate the use of satellite-based snow albedo to improve model behaviors, which opens new avenues for constraining snow albedo feedback in earth system models.

Impacts of Satellite-Based Snow Albedo Assimilation on Offline and Coupled Land Surface Model Simulations

PubMed Central

Wang, Tao; Peng, Shushi; Krinner, Gerhard; Ryder, James; Li, Yue; Dantec-Nédélec, Sarah; Ottlé, Catherine

2015-01-01

Seasonal snow cover in the Northern Hemisphere is the largest component of the terrestrial cryosphere and plays a major role in the climate system through strong positive feedbacks related to albedo. The snow-albedo feedback is invoked as an important cause for the polar amplification of ongoing and projected climate change, and its parameterization across models is an important source of uncertainty in climate simulations. Here, instead of developing a physical snow albedo scheme, we use a direct insertion approach to assimilate satellite-based surface albedo during the snow season (hereafter as snow albedo assimilation) into the land surface model ORCHIDEE (ORganizing Carbon and Hydrology In Dynamic EcosystEms) and assess the influences of such assimilation on offline and coupled simulations. Our results have shown that snow albedo assimilation in both ORCHIDEE and ORCHIDEE-LMDZ (a general circulation model of Laboratoire de Météorologie Dynamique) improve the simulation accuracy of mean seasonal (October throughout May) snow water equivalent over the region north of 40 degrees. The sensitivity of snow water equivalent to snow albedo assimilation is more pronounced in the coupled simulation than the offline simulation since the feedback of albedo on air temperature is allowed in ORCHIDEE-LMDZ. We have also shown that simulations of air temperature at 2 meters in ORCHIDEE-LMDZ due to snow albedo assimilation are significantly improved during the spring in particular over the eastern Siberia region. This is a result of the fact that high amounts of shortwave radiation during the spring can maximize its snow albedo feedback, which is also supported by the finding that the spatial sensitivity of temperature change to albedo change is much larger during the spring than during the autumn and winter. In addition, the radiative forcing at the top of the atmosphere induced by snow albedo assimilation during the spring is estimated to be -2.50 W m-2, the magnitude of which is almost comparable to that due to CO2 (2.83 W m-2) increases since 1750. Our results thus highlight the necessity of realistic representation of snow albedo in the model and demonstrate the use of satellite-based snow albedo to improve model behaviors, which opens new avenues for constraining snow albedo feedback in earth system models. PMID:26366564

Soil texture and granulometry at the surface of Mars

NASA Technical Reports Server (NTRS)

Dollfus, A.; Deschamps, M.; Zimbelman, J.

1992-01-01

The microtexture of the near-surface Martian soil was sensed with three diagnostic parameters: (1) the albedo A at normal incidence and phase angle 5 degrees, which relates to the composition of the top surface exposed layer; (2) the polarization parameter b characterizes the texture of the top surface layer in terms of grain size; and (3) the thermal inertia parameter I which refers to the soil compaction through the first few decimeters below the top surface sensed by polarimetry, in terms of size for the pieces making a granular regolith. Parameter b was derived from instrument VPM on board the Soviet spacecraft MARS-5, inertial I is from IRTM on the American Viking, and albedo A from both. The polarimetric scans racked strips covering two contrasted regions, the dark hued Mare Erythraeum, and the adjacent bright orange Thaumasia. Erythraem is characterized everywhere by a same type of terrain, despite the large geomorphological diversity of the surface. There is an ubiquitous coating or mantling with small dark grains, of both albedo 12.7 percent and particle size 10 to 20 microns, above a subsurface dislocation in pieces around 300 to 600 microns. A simple model is with sand-size particles completely coated with 15 micron dark grains.

Simulated cold bias being improved by using MODIS time-varying albedo in the Tibetan Plateau in WRF model

NASA Astrophysics Data System (ADS)

Meng, X.; Lyu, S.; Zhang, T.; Zhao, L.; Li, Z.; Han, B.; Li, S.; Ma, D.; Chen, H.; Ao, Y.; Luo, S.; Shen, Y.; Guo, J.; Wen, L.

2018-04-01

Systematic cold biases exist in the simulation for 2 m air temperature in the Tibetan Plateau (TP) when using regional climate models and global atmospheric general circulation models. We updated the albedo in the Weather Research and Forecasting (WRF) Model lower boundary condition using the Global LAnd Surface Satellite Moderate-Resolution Imaging Spectroradiometer albedo products and demonstrated evident improvement for cold temperature biases in the TP. It is the large overestimation of albedo in winter and spring in the WRF model that resulted in the large cold temperature biases. The overestimated albedo was caused by the simulated precipitation biases and over-parameterization of snow albedo. Furthermore, light-absorbing aerosols can result in a large reduction of albedo in snow and ice cover. The results suggest the necessity of developing snow albedo parameterization using observations in the TP, where snow cover and melting are very different from other low-elevation regions, and the influence of aerosols should be considered as well. In addition to defining snow albedo, our results show an urgent call for improving precipitation simulation in the TP.

Intercomparison Between in situ and AVHRR Polar Pathfinder-Derived Surface Albedo over Greenland

NASA Technical Reports Server (NTRS)

Stroeve, Julienne C.; Box, Jason E.; Fowler, Charles; Haran, Terence; Key, Jeffery

2001-01-01

The Advanced Very High Resolution (AVHRR) Polar Pathfinder Data (APP) provides the first long time series of consistent, calibrated surface albedo and surface temperature data for the polar regions. Validations of these products have consisted of individual studies that analyzed algorithm performance for limited regions and or time periods. This paper reports on comparisons made between the APP-derived surface albedo and that measured at fourteen automatic weather stations (AWS) around the Greenland ice sheet from January 1997 to August 1998. Results show that satellite-derived surface albedo values are on average 10% less than those measured by the AWS stations. However, the station measurements tend to be biased high by about 4% and thus the differences in absolute albedo may be less (e.g. 6%). In regions of the ice sheet where the albedo variability is small, such as the dry snow facies, the APP albedo uncertainty exceeds the natural variability. Further work is needed to improve the absolute accuracy of the APP-derived surface albedo. Even so, the data provide temporally and spatially consistent estimates of the Greenland ice sheet albedo.

A stability theorem for energy-balance climate models

NASA Technical Reports Server (NTRS)

Cahalan, R. F.; North, G. R.

1979-01-01

The paper treats the stability of steady-state solutions of some simple, latitude-dependent, energy-balance climate models. For north-south symmetric solutions of models with an ice-cap-type albedo feedback, and for the sum of horizontal transport and infrared radiation given by a linear operator, it is possible to prove a 'slope stability' theorem, i.e., if the local slope of the steady-state iceline latitude versus solar constant curve is positive (negative) the steady-state solution is stable (unstable). Certain rather weak restrictions on the albedo function and on the heat transport are required for the proof, and their physical basis is discussed.

The nature of albedo features on Mercury, with maps for the telescopic observer. Part II: The nature of the albedo markings

NASA Astrophysics Data System (ADS)

Graham, D. L.

1995-04-01

Part One of this paper (J. Brit. Astron. Assoc., 105(1), 1995) reviewed the classical telescopic observations of albedo markings on Mercury and reproduced the definitive albedo map to assist visual observers of the planet. In Part Two, an investigation into the relationship between albedo and physiography is conducted, and the significance of the historical observations is discussed.

High-Albedo Salt Crusts on the Tropical Ocean of Snowball Earth: Measurements and Modeling

NASA Astrophysics Data System (ADS)

Carns, R.; Light, B.; Warren, S. G.

2014-12-01

During a Snowball Earth event, almost all of the ocean surface first freezes as sea ice. As in modern sea ice, trapped inclusions of liquid brine permeate the ice cover. As the ice grows and cools, salt crystals precipitate within the inclusions. At -23C, the most abundant salt in seawater, sodium chloride, begins to precipitate as the dihydrate mineral hydrohalite (NaCl·2H2O). Crystals of hydrohalite within the sea ice scatter light. Measurements of cold, natural sea ice show a broadband albedo increase of 10-20% when salt precipitates. Such snow-free natural sea ice with a surface temperature below -23C is rare on modern Earth, but would have been common in tropical regions of a Snowball Earth where evaporation exceeded precipitation. The persistent cold and lack of summer melt on the Snowball ocean surface, combined with net evaporation, is hypothesized to yield lag deposits of hydrohalite crystals on the ice surface. To investigate this process, we prepared laboratory-grown sea ice in a 1000 liter tank in a walk-in freezer laboratory. The ice was cooled below -23 C and the surface sprayed with a 23% NaCl solution to create a layer of hydrohalite-enriched ice, a proxy for lag deposits that would have formed over long periods of surface sublimation. We have developed a novel technique for measuring the spectral albedo of ice surfaces in the laboratory; this technique was used to monitor the evolution of the surface albedo of our salt crust as the ice matrix sublimated away leaving a layer of fine-grained hydrohalite crystals. Measurements of this hydrohalite surface crust show a very high albedo, comparable to fresh snow at visible wavelengths and significantly larger than fresh snow at near infrared wavelengths. Broadband albedos are 0.55 for bare artificial sea ice at -30C, 0.75 for ice containing 25% hydrohalite by volume, 0.84 after five days of desiccation and 0.93 after 47 days of desiccation. Using our laboratory measurements, along with estimates of grain size and crust optical depth, as inputs to Mie scattering and radiative transfer models allowed us to infer the imaginary refractive index of hydrohalite. The model can calculate albedo for pure hydrohalite crusts of varying thickness and for mixtures of ice and hydrohalite. A parameterization is presented for albedo as a function of the thickness of the hydrohalite crust.

Impact of weather events on Arctic sea ice albedo evolution

NASA Astrophysics Data System (ADS)

Arntsen, A. E.; Perovich, D. K.; Polashenski, C.; Stwertka, C.

2015-12-01

Arctic sea ice undergoes a seasonal evolution from cold snow-covered ice to melting snow to bare ice with melt ponds. Associated with this physical evolution is a decrease in the albedo of the ice cover. While the change in albedo is often considered as a steady seasonal decrease, weather events during melt, such as rain or snow, can impact the albedo evolution. Measurements on first year ice in the Chukchi Sea showed a decrease in visible albedo to 0.77 during the onset of melt. New snow from 4 - 6 June halted melting and increased the visible albedo to 0.87. It took 12 days for the albedo to decrease to levels prior to the snowfall. Incident solar radiation is large in June and thus a change in albedo has a large impact on the surface heat budget. The snowfall increased the albedo by 0.1 and reduced the absorbed sunlight from 5 June to 17 June by approximately 32 MJ m-2. The total impact of the snowfall will be even greater, since the delay in albedo reduction will be propagated throughout the entire summer. A rain event would have the opposite impact, increasing solar heat input and accelerating melting. Snow or rain in May or June can impact the summer melt cycle of Arctic sea ice.

Inclusion of Solar Elevation Angle in Land Surface Albedo Parameterization Over Bare Soil Surface.

PubMed

Zheng, Zhiyuan; Wei, Zhigang; Wen, Zhiping; Dong, Wenjie; Li, Zhenchao; Wen, Xiaohang; Zhu, Xian; Ji, Dong; Chen, Chen; Yan, Dongdong

2017-12-01

Land surface albedo is a significant parameter for maintaining a balance in surface energy. It is also an important parameter of bare soil surface albedo for developing land surface process models that accurately reflect diurnal variation characteristics and the mechanism behind the solar spectral radiation albedo on bare soil surfaces and for understanding the relationships between climate factors and spectral radiation albedo. Using a data set of field observations, we conducted experiments to analyze the variation characteristics of land surface solar spectral radiation and the corresponding albedo over a typical Gobi bare soil underlying surface and to investigate the relationships between the land surface solar spectral radiation albedo, solar elevation angle, and soil moisture. Based on both solar elevation angle and soil moisture measurements simultaneously, we propose a new two-factor parameterization scheme for spectral radiation albedo over bare soil underlying surfaces. The results of numerical simulation experiments show that the new parameterization scheme can more accurately depict the diurnal variation characteristics of bare soil surface albedo than the previous schemes. Solar elevation angle is one of the most important factors for parameterizing bare soil surface albedo and must be considered in the parameterization scheme, especially in arid and semiarid areas with low soil moisture content. This study reveals the characteristics and mechanism of the diurnal variation of bare soil surface solar spectral radiation albedo and is helpful in developing land surface process models, weather models, and climate models.

Dependence on Solar Phase Angle and Grain Size of the Spectral Reflectance of the Railroad Valley Playa for GOSAT/GOSAT-2 Vicarious Calibration

NASA Astrophysics Data System (ADS)

Arai, T.; Matsunaga, T.

2017-12-01

GOSAT and the next generation GOSAT-2 satellites estimate the concentration of greenhouse gasses, and distribution of aerosol and cloud to observe solar light reflection and radiation from surface and atmosphere of the Earth. Precise information of the surface and the bidirectional reflectance distribution function (BRDF) are required for the estimation because the surface reflectance of solar light varies with the observation geometry and the surface condition. The purpose of this study is to search an appropriate BRDF model of the GOSAT calibration site (Railroad Valley playa). In 2017, JAXA, NIES, and NASA/OCO-2 teams collaboratively performed 9th vicarious experiments by the simultaneous observation with GOSAT, OCO-2, and ground-based equipment (Kuze et al., 2014) at the Railroad Valley from June 25 to 30. We performed the BRDF measurement to observe solar light reflection by varying with observed angles using a spectroradiometer (FieldSpec4, ASD Inc.) mounted on a one-axis goniometer. The surface sand was shifted to several sizes of grain (75, 125, 250, 500, and 1000 μm), which was measured for the limited area of 5mm diameter with a collimating lens (74-UV, OceanOptics). The BRDF parameters for the observed reflectance were determined by the least squares fitting with the free parameters of a single scattering albedo and an asymmetric factor (Hapke, 2012) for the ultraviolet to near infrared wavelength bands of GOSAT. The resulting value of the single scattering albedo increased with decreasing the grain size of the sands. The observed reflectance of the fine grain sands (below 250 μm) is not varied with observed phase angles (solar incident light - surface sand - detector) as a Lambertian reflectance, but the spectra of coarse grain sands (above 500 μm) are varied with the observation angles. Therefore, a priori information of the target surface such as grain size is required for the determination of the precise reflectance of the target.

Simulation and Analysis of Topographic Effect on Land Surface Albedo over Mountainous Areas

NASA Astrophysics Data System (ADS)

Hao, D.; Wen, J.; Xiao, Q.

2017-12-01

Land surface albedo is one of the significant geophysical variables affecting the Earth's climate and controlling the surface radiation budget. Topography leads to the formation of shadows and the redistribution of incident radiation, which complicates the modeling and estimation of the land surface albedo. Some studies show that neglecting the topography effect may lead to significant bias in estimating the land surface albedo for the sloping terrain. However, for the composite sloping terrain, the topographic effects on the albedo remain unclear. Accurately estimating the sub-topographic effect on the land surface albedo over the composite sloping terrain presents a challenge for remote sensing modeling and applications. In our study, we focus on the development of a simplified estimation method for land surface albedo including black-sky albedo (BSA) and white-sky albedo (WSA) of the composite sloping terrain at a kilometer scale based on the fine scale DEM (30m) and quantitatively investigate and understand the topographic effects on the albedo. The albedo is affected by various factors such as solar zenith angle (SZA), solar azimuth angle (SAA), shadows, terrain occlusion, and slope and aspect distribution of the micro-slopes. When SZA is 30°, the absolute and relative deviations between the BSA of flat terrain and that of rugged terrain reaches 0.12 and 50%, respectively. When the mean slope of the terrain is 30.63° and SZA=30°, the absolute deviation of BSA caused by SAA can reach 0.04. The maximal relative and relative deviation between the WSA of flat terrain and that of rugged terrain reaches 0.08 and 50%. These results demonstrate that the topographic effect has to be taken into account in the albedo estimation.

Composition and Mineralogy of Low Albedo Northern Circumpolar Deposits on Mars Using MGS/TES Data

NASA Astrophysics Data System (ADS)

Bell, J. F.; Horgan, B.; Noe Dobrea, E. Z.

2009-12-01

The northern high latitude non-ice geology of Mars is dominated by large, low-albedo sand dunes and sand sheet deposits. These materials have experienced a complex geologic history, including evidence preserved in the morphology for aeolian deposition, transport, and erosion (e.g., Tanaka et al., Icarus, 196, 318, 2008), and evidence preserved in the mineralogy for aqueous alteration processes (e.g., Langevin et al., Science, 307, 1584, 2005). These low-albedo materials span the circumpolar plains of Vastitas Borealis north of about 75 deg. latitude, and extend down to about 30 deg. north in the Acidalia Planitia region (from about 15 to 45 deg. west) where they are the type locality for the Mars Global Surveyor Thermal Emission Spectrometer (MGS/TES) "Surface Type 2" global compositional endmember. We are assessing both the morphology and primary (mafic) and secondary mineralogy of north polar sand deposits using high spatial and spectral resolution data sets, working to test hypotheses for the formation and evolution of these materials throughout Martian history. Here we report on our initial mineralogic analyses of TES mid-IR spectra of these low albedo materials. Because of the relatively low surface temperatures at high northern latitudes on Mars, assembling a high-quality TES data set that covers a significant fraction of representative terrains is a challenge. Ultimately we were able to identify and assemble a data subset of more than 5000 TES emissivity spectra having temperatures above 250K and covering surface regions with bolometric albedo below 0.15 during times of relatively clear atmospheric conditions. These spectra cover only a few percent of the north polar low albedo deposits, but they provide representative sampling of many terrains. We are performing atmospheric corrections and deriving estimated mineral abundances for these spectra using an iterative linear matrix inversion spectral unmixing method (Noe Dobrea et al., JGR, 111, 2006) and laboratory-derived mineral endmembers from the publicly-available TES library. This method allows us to compute best-fit abundances for all possible endmember combinations within a user-defined library subset, and to estimate average abundances for each modeled mineral. Minerals not detected above a minimum detection threshold are discarded, which then allows us to converge on models with the most statistically accurate representation of the likely mineral assemblage. The best-fit models of our average polar sand deposit spectra (using 68 spectrally-unique endmembers chosen to represent a range of potential primary and secondary mineralogies relevant to Mars) included "expected" mafic minerals (olivine, pyroxene, feldspar) plus a silica-bearing amorphous phase. The best models also included minor amounts of other phases, however, like Mg-, Al-, and Fe-bearing sulfates and iron oxides. Our TES mid-IR results enhance and augment previous interpretations (Horgan et al., JGR, 114, 2009) of the composition and mineralogy of these regions from Mars Express/OMEGA near-IR imaging spectroscopic observations, allowing us to explore the processes and relationships between primary minerals and previously-identified secondary alteration products in the region like polyhydrated sulfates.

Hubble PanCET: an isothermal day-side atmosphere for the bloated gas-giant HAT-P-32Ab

NASA Astrophysics Data System (ADS)

Nikolov, N.; Sing, D. K.; Goyal, J.; Henry, G. W.; Wakeford, H. R.; Evans, T. M.; López-Morales, M.; García Muñoz, A.; Ben-Jaffel, L.; Sanz-Forcada, J.; Ballester, G. E.; Kataria, T.; Barstow, J. K.; Bourrier, V.; Buchhave, L. A.; Cohen, O.; Deming, D.; Ehrenreich, D.; Knutson, H.; Lavvas, P.; Lecavelier des Etangs, A.; Lewis, N. K.; Mandell, A. M.; Williamson, M. H.

2018-02-01

We present a thermal emission spectrum of the bloated hot Jupiter HAT-P-32Ab from a single eclipse observation made in spatial scan mode with the Wide Field Camera 3 (WFC3) aboard the Hubble Space Telescope (HST). The spectrum covers the wavelength regime from 1.123 to 1.644 μm which is binned into 14 eclipse depths measured to an averaged precision of 104 parts-per million. The spectrum is unaffected by a dilution from the close M-dwarf companion HAT-P-32B, which was fully resolved. We complemented our spectrum with literature results and performed a comparative forward and retrieval analysis with the 1D radiative-convective ATMO model. Assuming solar abundance of the planet atmosphere, we find that the measured spectrum can best be explained by the spectrum of a blackbody isothermal atmosphere with Tp = 1995 ± 17 K, but can equally well be described by a spectrum with modest thermal inversion. The retrieved spectrum suggests emission from VO at the WFC3 wavelengths and no evidence of the 1.4 μm water feature. The emission models with temperature profiles decreasing with height are rejected at a high confidence. An isothermal or inverted spectrum can imply a clear atmosphere with an absorber, a dusty cloud deck or a combination of both. We find that the planet can have continuum of values for the albedo and recirculation, ranging from high albedo and poor recirculation to low albedo and efficient recirculation. Optical spectroscopy of the planet's day-side or thermal emission phase curves can potentially resolve the current albedo with recirculation degeneracy.

Errors induced by the neglect of polarization in radiance calculations for Rayleigh-scattering atmospheres

NASA Technical Reports Server (NTRS)

Mishchenko, M. I.; Lacis, A. A.; Travis, L. D.

1994-01-01

Although neglecting polarization and replacing the rigorous vector radiative transfer equation by its approximate scalar counterpart has no physical background, it is a widely used simplification when the incident light is unpolarized and only the intensity of the reflected light is to be computed. We employ accurate vector and scalar multiple-scattering calculations to perform a systematic study of the errors induced by the neglect of polarization in radiance calculations for a homogeneous, plane-parallel Rayleigh-scattering atmosphere (with and without depolarization) above a Lambertian surface. Specifically, we calculate percent errors in the reflected intensity for various directions of light incidence and reflection, optical thicknesses of the atmosphere, single-scattering albedos, depolarization factors, and surface albedos. The numerical data displayed can be used to decide whether or not the scalar approximation may be employed depending on the parameters of the problem. We show that the errors decrease with increasing depolarization factor and/or increasing surface albedo. For conservative or nearly conservative scattering and small surface albedos, the errors are maximum at optical thicknesses of about 1. The calculated errors may be too large for some practical applications, and, therefore, rigorous vector calculations should be employed whenever possible. However, if approximate scalar calculations are used, we recommend to avoid geometries involving phase angles equal or close to 0 deg and 90 deg, where the errors are especially significant. We propose a theoretical explanation of the large vector/scalar differences in the case of Rayleigh scattering. According to this explanation, the differences are caused by the particular structure of the Rayleigh scattering matrix and come from lower-order (except first-order) light scattering paths involving right scattering angles and right-angle rotations of the scattering plane.

Searching for reflected light from τ Bootis b with high-resolution ground-based spectroscopy: Approaching the 10-5 contrast barrier

NASA Astrophysics Data System (ADS)

Hoeijmakers, H. J.; Snellen, I. A. G.; van Terwisga, S. E.

2018-02-01

Context. It is challenging to measure the starlight reflected from exoplanets because of the extreme contrast with their host stars. For hot Jupiters, this contrast is in the range of 10-6 to 10-4, depending on their albedo, radius and orbital distance. Searches for reflected light have been performed since the first hot Jupiters were discovered, but with very limited success because hot Jupiters tend to have low albedo values due to the general absence of reflective cloud decks. Aim. The aim of this study is to search for reflected light from τ Boo b, a hot Jupiter with one of the brightest host stars. Since its discovery in 1997, it has been the subject of several reflected-light searches using high-dispersion spectroscopy. Here we aim to combine these data in to a single meta-analysis. Methods: We analysed more than 2000 archival high-dispersion spectra obtained with the UVES, ESPaDOnS, NARVAL UES and HARPS-N spectrographs during various epochs between 1998 and 2013. Each spectrum was first cleaned of the stellar spectrum and subsequently cross-correlated with a PHOENIX model spectrum. These were then Doppler shifted to the planet rest-frame and co-added in time, weighted according to the expected signal-to-noise of the planet signal. Results: We reach a 3σ upper limit of the planet-to-star contrast of 1.5 × 10-5. Assuming a planet radius of 1.15 RJ, this corresponds to an optical albedo of between 400-700 nm. A low albedo is in line with secondary eclipse and phase curve observations of other hot Jupiters using space-based observatories, as well as theoretical predictions of their reflective properties.

VizieR Online Data Catalog: AKARI IRC asteroid sample diameters & albedos (Ali-Lagoa+, 2018)

NASA Astrophysics Data System (ADS)

Ali-Lagoa, V.; Mueller, T. G.; Usui, F.; Hasegawa, S.

2017-11-01

Table 1 contains the best-fitting values of size and beaming parameter and corresponding visible geometric albedos for the full AKARI IRC sample. We fitted the near-Earth asteroid thermal model (NEATM) of Harris (1998Icar..131..291H) to the AKARI IRC thermal infrared data (Murakami et al., 2007PASJ...59S.369M, Onaka et al., 2007PASJ...59S.401O, Ishihara et al., 2010A&A...514A...1I, Cat. II/297, Usui et al., 2011PASJ...63.1117U, Cat. J/PASJ/63/1117, Takita et al., 2012PASJ...64..126T, Hasegawa et al., 2013PASJ...65...34H, Cat. J/PASJ/65/34). The NEATM implementation is described in Ali-Lagoa and Delbo' (2017A&A...603A..55A, cat. J/A+A/603/A55). Minimum relative errors of 10, 15, and 20 percent are given for size, beaming parameter and albedo in those cases where the beaming parameter could be fitted. Otherwise, a default value of the beaming parameter is assumed based on Eq. 1 in the article, and the minimum relative errors in size and albedo increase to 20 and 40 percent (see the discussions in Mainzer et al., 2011ApJ...736..100M, Ali-Lagoa et al., 2016A&A...591A..14A, Cat. J/A+A/591/A14). We also provide the asteroid absolute magnitudes and G12 slope parameters retrieved from Oszkiewicz et al. (2012), the number of observations used in each IRC band (S9W and L18W), plus the heliocentric and geocentric distances and phase angle (r, Delta, alpha) based on the ephemerides taken from the MIRIADE service (http://vo.imcce.fr/webservices/miriade/?ephemph). (1 data file).

Observed increase in local cooling effect of deforestation at higher latitudes.

PubMed

Lee, Xuhui; Goulden, Michael L; Hollinger, David Y; Barr, Alan; Black, T Andrew; Bohrer, Gil; Bracho, Rosvel; Drake, Bert; Goldstein, Allen; Gu, Lianhong; Katul, Gabriel; Kolb, Thomas; Law, Beverly E; Margolis, Hank; Meyers, Tilden; Monson, Russell; Munger, William; Oren, Ram; Paw U, Kyaw Tha; Richardson, Andrew D; Schmid, Hans Peter; Staebler, Ralf; Wofsy, Steven; Zhao, Lei

2011-11-16

Deforestation in mid- to high latitudes is hypothesized to have the potential to cool the Earth's surface by altering biophysical processes. In climate models of continental-scale land clearing, the cooling is triggered by increases in surface albedo and is reinforced by a land albedo-sea ice feedback. This feedback is crucial in the model predictions; without it other biophysical processes may overwhelm the albedo effect to generate warming instead. Ongoing land-use activities, such as land management for climate mitigation, are occurring at local scales (hectares) presumably too small to generate the feedback, and it is not known whether the intrinsic biophysical mechanism on its own can change the surface temperature in a consistent manner. Nor has the effect of deforestation on climate been demonstrated over large areas from direct observations. Here we show that surface air temperature is lower in open land than in nearby forested land. The effect is 0.85 ± 0.44 K (mean ± one standard deviation) northwards of 45° N and 0.21 ± 0.53 K southwards. Below 35° N there is weak evidence that deforestation leads to warming. Results are based on comparisons of temperature at forested eddy covariance towers in the USA and Canada and, as a proxy for small areas of cleared land, nearby surface weather stations. Night-time temperature changes unrelated to changes in surface albedo are an important contributor to the overall cooling effect. The observed latitudinal dependence is consistent with theoretical expectation of changes in energy loss from convection and radiation across latitudes in both the daytime and night-time phase of the diurnal cycle, the latter of which remains uncertain in climate models. © 2011 Macmillan Publishers Limited. All rights reserved

The Dependence of the Ice-Albedo Feedback on Atmospheric Properties

PubMed Central

Selsis, F.; Kitzmann, D.; Rauer, H.

2013-01-01

Abstract Ice-albedo feedback is a potentially important destabilizing effect for the climate of terrestrial planets. It is based on the positive feedback between decreasing surface temperatures, an increase of snow and ice cover, and an associated increase in planetary albedo, which then further decreases surface temperature. A recent study shows that for M stars, the strength of the ice-albedo feedback is reduced due to the strong spectral dependence of stellar radiation and snow/ice albedos; that is, M stars primarily emit in the near IR, where the snow and ice albedo is low, and less in the visible, where the snow/ice albedo is high. This study investigates the influence of the atmosphere (in terms of surface pressure and atmospheric composition) on this feedback, since an atmosphere was neglected in previous studies. A plane-parallel radiative transfer model was used for the calculation of planetary albedos. We varied CO2 partial pressures as well as the H2O, CH4, and O3 content in the atmosphere for planets orbiting Sun-like and M type stars. Results suggest that, for planets around M stars, the ice-albedo effect is significantly reduced, compared to planets around Sun-like stars. Including the effects of an atmosphere further suppresses the sensitivity to the ice-albedo effect. Atmospheric key properties such as surface pressure, but also the abundance of radiative trace gases, can considerably change the strength of the ice-albedo feedback. For dense CO2 atmospheres of the order of a few to tens of bar, atmospheric rather than surface properties begin to dominate the planetary radiation budget. At high CO2 pressures, the ice-albedo feedback is strongly reduced for planets around M stars. The presence of trace amounts of H2O and CH4 in the atmosphere also weakens the ice-albedo effect for both stellar types considered. For planets around Sun-like stars, O3 could also lead to a very strong decrease of the ice-albedo feedback at high CO2 pressures. Key Words: Atmospheric compositions—Extrasolar terrestrial planets—Snowball Earth—Planetary atmospheres—Radiative transfer. Astrobiology 13, 899–909. PMID:24111995

Measurements and Modeling of Aerosol Absorption and Single Scattering Albedo at Ambient Relative Hum

NASA Technical Reports Server (NTRS)

Redemann, J.; Russell, P. B.; Hamill, P.

2000-01-01

Uncertainties in the aerosol single scattering albedo have been identified to be an important source of errors in current large-scale model estimates of the direct aerosol radiative forcing of climate. A number of investigators have obtained estimates of the single scattering albedo from a variety of remote sensing and in situ measurements during aerosol field experiments. During the Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX, 1996) for example, estimates of the aerosol single scattering albedo were obtained (1) as a best-fit parameter in comparing radiative flux changes measured by airborne pyranometer to those computed from independently measured aerosol properties; (2) from estimates of the aerosol complex index of refraction derived using a combination of airborne sunphotometer, lidar backscatter and in situ size distribution measurements; and (3) from airborne measurements of aerosol scattering and absorption using nephelometers and absorption photometers. In this paper, we briefly compare the results of the latter two methods for two TARFOX case studies, since those techniques provide height-resolved information about the aerosol single scattering albedo. Estimates of the aerosol single scattering albedo from nephelometer and absorption photometer measurements require knowledge of the scattering and absorption humidification (i.e., the increase in these properties in response to an increase in ambient relative humidity), since both measurements are usually carried out at a relative humidity different from the ambient atmosphere. In principle, the scattering humidification factor can be measured, but there is currently no technique widely available to measure the absorption of an aerosol sample as a function of relative humidity. Frequently, for lack of better knowledge, the absorption humidification is assumed to be unity (meaning that there is no change in aerosol absorption due to an increase in ambient relative humidity). This assumption then enters the estimate of the single scattering albedo at ambient relative humidity. To investigate the validity of this assumption we have carried out modeling studies of the absorption humidification factor, assuming that the aerosols contain an insoluble soot core and a coating which determines its hygroscopic growth behavior. The aerosol optical properties are then computed on the basis of the shell/core particle morphology using a Mie-code for concentric shells. From basic physical principles, it is conceivable that aerosol absorption increases when an atmospheric aerosol particle collects a non-absorbing shell, since the soot core is then exposed to an increased (focused) electric field strength. Indeed, our preliminary modeling studies show that the absorption of an atmospheric aerosol particle composed of a soot core and an aqueous sulfuric acid shell may increase by a factor of 50% due to a change in ambient relative humidity from 30 to 95%. We will show how this increased absorption is a function of the initial particle size and soot mass fraction.

Surface albedo in relation to disturbance and early stand dynamics in the boreal forest: Implications for climate models

NASA Astrophysics Data System (ADS)

Halim, M. A.; Thomas, S. C.

2017-12-01

Surface albedo is the most important biophysical radiative forcing in the boreal forest. General Circulation Model studies have suggested that harvesting of boreal forest has a net cooling effect, in contrast to other terrestrial biomes, by increasing surface albedo. However, albedo estimation in these models has been achieved by simplifying processes governing albedo at a coarse scale (both spatial and temporal). Biophysical processes that determine albedo likely operate on small spatial and temporal scales, requiring more direct estimates of effects of landcover change on net radiation. We established a chronosequence study in post-fire and post-clearcut sites (2013, 2006, 1998), logging data from July 2013 to July 2017 in boreal forest sites in northwestern Ontario, Canada. Each age-class X disturbance had 3 three replicates, matched to 18 permanent circular plots (10-m radius) each with an instrumented tower measuring surface albedo, air and soil temperature, and soil moisture. We also measured leaf area index, species composition and soil organic matter content at each site. BRDF-corrected surface albedo was calculated from daily 30m x 30m reflectance data fused from the MODIS MOD09GA product and Landsat 7 reflectance data. Calculated albedo was verified using ground-based measurements. Results show that fire sites generally had lower (15-25%) albedo than clearcut sites in all seasons. Because of rapid forest regrowth, large perturbations of clearcut harvests on forest albedo started to fade out within a year. Albedo differences between fire and clearcut sites also declined sharply with stand age. Younger stands generally had higher albedo than older stands mainly due to the presence of broadleaf species (for example, Populus tremuloides). In spring, snow melted 10-12 days earlier in recent (2013) clearcut sites compared to closed-canopy sites, causing a sharp reduction in surface albedo in comparison to old clearcut/fire sites (2006 and 1998). Snow melted faster in post-fire sites than in clearcut sites, with concomitant effects on albedo associated with snow. Findings of this study strongly suggest that harvests in boreal forest do not have as strong a radiative cooling effect as previously inferred from GCM experiments based on coarse-resolution data or "biome substitution" approaches.

Multiplatform observations enabling albedo retrievals with high temporal resolution

NASA Astrophysics Data System (ADS)

Riihelä, Aku; Manninen, Terhikki; Key, Jeffrey; Sun, Qingsong; Sütterlin, Melanie; Lattanzio, Alessio; Schaaf, Crystal

2017-04-01

In this paper we show that combining observations from different polar orbiting satellite families (such as AVHRR and MODIS) is physically justifiable and technically feasible. Our proposed approach will lead to surface albedo retrievals at higher temporal resolution than the state of the art, with comparable or better accuracy. This study is carried out in the World Meteorological Organization (WMO) Sustained and coordinated processing of Environmental Satellite data for Climate Monitoring (SCOPE-CM) project SCM-02 (http://www.scope-cm.org/projects/scm-02/). Following a spectral homogenization of the Top-of-Atmosphere reflectances of bands 1 & 2 from AVHRR and MODIS, both observation datasets are atmospherically corrected with a coherent atmospheric profile and algorithm. The resulting surface reflectances are then fed into an inversion of the RossThick-LiSparse-Reciprocal surface bidirectional reflectance distribution function (BRDF) model. The results of the inversion (BRDF kernels) may then be integrated to estimate various surface albedo quantities. A key principle here is that the larger number of valid surface observations with multiple satellites allows us to invert the BRDF coefficients within a shorter time span, enabling the monitoring of relatively rapid surface phenomena such as snowmelt. The proposed multiplatform approach is expected to bring benefits in particular to the observation of the albedo of the polar regions, where persistent cloudiness and long atmospheric path lengths present challenges to satellite-based retrievals. Following a similar logic, the retrievals over tropical regions with high cloudiness should also benefit from the method. We present results from a demonstrator dataset of a global combined AVHRR-GAC and MODIS dataset covering the year 2010. The retrieved surface albedo is compared against quality-monitored in situ albedo observations from the Baseline Surface Radiation Network (BSRN). Additionally, the combined retrieval dataset is compared against MODIS C6 albedo/BRDF datasets to assess the quality of the multiplatform approach against current state of the art. This approach is not limited to AHVRR and MODIS observations. Provided that the spectral homogenization produces an acceptably good match, any instrument observing the Earth's surface in the visible and near-infrared wavelengths could, in principal, be included to further enhance the temporal resolution and accuracy of the retrievals. The SCOPE-CM initiative provides a potential framework for such expansion in the future.

Regional Climate Modeling over the Glaciated Regions of the Canadian High Arctic

NASA Astrophysics Data System (ADS)

Gready, Benjamin P.

The Canadian Arctic Islands (CAI) contain the largest concentration of terrestrial ice outside of the continental ice sheets. Mass loss from this region has recently increased sharply due to above average summer temperatures. Thus, increasing the understanding of the mechanisms responsible for mass loss from this region is critical. Previously, Regional Climate Models (RCMs) have been utilized to estimate climatic balance over Greenland and Antarctica. This method offers the opportunity to study a full suite of climatic variables over extensive spatially distributed grids. However, there are doubts of the applicability of such models to the CAI, given the relatively complex topography of the CAI. To test RCMs in the CAI, the polar version of the regional climate model MM5 was run at high resolution over Devon Ice Cap. At low altitudes, residuals (computed through comparisons with in situ measurements) in the net radiation budget were driven primarily by residuals in net shortwave (NSW) radiation. Residuals in NSW are largely due to inaccuracies in modeled cloud cover and modeled albedo. Albedo on glaciers and ice sheets is oversimplified in Polar MM5 and its successor, the Polar version of the Weather Research and Forecast model (Polar WRF), and is an obvious place for model improvement. Subsequently, an inline parameterization of albedo for Polar WRF was developed as a function of the depth, temperature and age of snow. The parameterization was able to reproduce elevation gradients of seasonal mean albedo derived from satellite albedo measurements (MODIS MOD10A1 daily albedo), on the western slope of the Greenland Ice Sheet for three years. Feedbacks between modelled albedo and modelled surface energy budget components were identified. The shortwave radiation flux feeds back positively with changes to albedo, whereas the longwave, turbulent and ground energy fluxes all feed back negatively, with a maximum combined magnitude of two thirds of the shortwave feedback magnitude. These strong feedbacks demonstrate that an accurate albedo parameterization must be run inline within an RCM, to accurately quantify the net surface energy budget of an ice sheet. Finally, Polar WRF, with the improved albedo parameterization, was used to simulate climatic balance over the Queen Elizabeth Islands for the summers of 2001 to 2008. Climatic balance was derived from the output using energy balance and temperature index melt models. Regional mass balance was calculated by combining climatic balance with estimates of iceberg discharge. Mass balance estimates from the model agreed, within the bounds of uncertainty, with estimates from previous studies, thus supporting the assertion that mass loss from the QEI accelerated during the first decade of the 21st century. Melt rates on the seven major icecaps of the QEI became more correlated to one another during the period 2001-2008. However, precipitation became less correlated from 2003-2008. These observations are coincident with dramatic increases in melt on all of the ice caps, and it is speculated that both are caused by decreases in the scale of disturbances delivering precipitation to the region over time.

Increase in surface albedo caused by agricultural plastic film

NASA Astrophysics Data System (ADS)

Fan, X.; Chen, H.; Xia, X.

2016-12-01

The area of agricultural greenhouses and cropland covered by plastic film has increased inChina over the past three decades. Construction of large-area plastic greenhouse potentiallychanges the physical and radiative properties of the surface and its albedo, thereby potentiallyaffecting the surface energy budget and climate change. This study aims to investigate theeffect of the plastic-film cover on surface albedo based on computationswith a simplified modeland several field observation experiments. The results showed that surface albedo increasedby ˜23.5 and ˜33.9% on clear and overcast days, respectively, if grassland was covered byplastic film. Surface albedo of bare soil covered by plastic film increased by ˜16.6% underclear sky conditions. A larger increase in surface albedo was derived for surface types withsmaller surface albedo. Model calculations were in good agreement with field observations.

The potential impacts of climate change induced changes to tropical leaf albedo and its feedback on global climate

NASA Astrophysics Data System (ADS)

Doughty, C.; Shenkin, A.; Bentley, L. P.; Malhi, Y.

2017-12-01

Tropical forest leaf albedo plays a critical role in global climate by determining how much radiation the planet absorbs near the equator. However, little is known about how tropical leaf albedo could be affected by climate change and how any such changes in albedo could, in turn, impact global climate. Here we measure sunlit leaf albedo along two elevation temperature gradients (a 3000-meter gradient in Peru (10 plots) and a 1500 m gradient in Australia (10 plots) and along two wet to dry transects (a 2000 mm yr-1 gradient in Ghana (10 plots) and a 2000 mm yr-1 gradient in Brazil (10 plots). We found a highly significant increase in visible leaf albedo with wetness at both wet to dry gradients. We also found a marginally significant trend of increased albedo with warmer temperatures along one of the elevation gradients. Leaf albedo can also be impacted by changes in species composition, variations in interspecific variation, and changes in leaf chlorophyll concentrations. We removed the dominant two species from the basal area weighting for each plots but found no significant change, a directional change of interspecific variation could change albedo by 0.01 in the NIR, and changes in chlorophyll could decrease visible albedo by 0.005. We then simulated changes in tropical leaf albedo with a climate model and show that such changes could act as a small negative feedback on climate, but most likely will not have a large impact on future climate.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mainzer, A.; Masiero, J.; Hand, E.

The NEOWISE data set offers the opportunity to study the variations in albedo for asteroid classification schemes based on visible and near-infrared observations for a large sample of minor planets. We have determined the albedos for nearly 1900 asteroids classified by the Tholen, Bus, and Bus-DeMeo taxonomic classification schemes. We find that the S-complex spans a broad range of bright albedos, partially overlapping the low albedo C-complex at small sizes. As expected, the X-complex covers a wide range of albedos. The multiwavelength infrared coverage provided by NEOWISE allows determination of the reflectivity at 3.4 and 4.6 {mu}m relative to themore » visible albedo. The direct computation of the reflectivity at 3.4 and 4.6 {mu}m enables a new means of comparing the various taxonomic classes. Although C, B, D, and T asteroids all have similarly low visible albedos, the D and T types can be distinguished from the C and B types by examining their relative reflectance at 3.4 and 4.6 {mu}m. All of the albedo distributions are strongly affected by selection biases against small, low albedo objects, as all objects selected for taxonomic classification were chosen according to their visible light brightness. Due to these strong selection biases, we are unable to determine whether or not there are correlations between size, albedo, and space weathering. We argue that the current set of classified asteroids makes any such correlations difficult to verify. A sample of taxonomically classified asteroids drawn without significant albedo bias is needed in order to perform such an analysis.« less

Effect of land cover change on snow free surface albedo across the continental United States

EPA Science Inventory

Land cover changes (e.g., forest to grassland) affect albedo, and changes in albedo can influence radiative forcing (warming, cooling). We empirically tested albedo response to land cover change for 130 locations across the continental United States using high resolution (30 m-&t...

Matrix operator theory of radiative transfer. I - Rayleigh scattering.

NASA Technical Reports Server (NTRS)

Plass, G. N.; Kattawar, G. W.; Catchings, F. E.

1973-01-01

An entirely rigorous method for the solution of the equations for radiative transfer based on the matrix operator theory is reviewed. The advantages of the present method are: (1) all orders of the reflection and transmission matrices are calculated at once; (2) layers of any thickness may be combined, so that a realistic model of the atmosphere can be developed from any arbitrary number of layers, each with different properties and thicknesses; (3) calculations can readily be made for large optical depths and with highly anisotropic phase functions; (4) results are obtained for any desired value of the surface albedo including the value unity and for a large number of polar and azimuthal angles; (5) all fundamental equations can be interpreted immediately in terms of the physical interactions appropriate to the problem; and (6) both upward and downward radiance can be calculated at interior points from relatively simple expressions.

Assessment and validation of the community radiative transfer model for ice cloud conditions

NASA Astrophysics Data System (ADS)

Yi, Bingqi; Yang, Ping; Weng, Fuzhong; Liu, Quanhua

2014-11-01

The performance of the Community Radiative Transfer Model (CRTM) under ice cloud conditions is evaluated and improved with the implementation of MODIS collection 6 ice cloud optical property model based on the use of severely roughened solid column aggregates and a modified Gamma particle size distribution. New ice cloud bulk scattering properties (namely, the extinction efficiency, single-scattering albedo, asymmetry factor, and scattering phase function) suitable for application to the CRTM are calculated by using the most up-to-date ice particle optical property library. CRTM-based simulations illustrate reasonable accuracy in comparison with the counterparts derived from a combination of the Discrete Ordinate Radiative Transfer (DISORT) model and the Line-by-line Radiative Transfer Model (LBLRTM). Furthermore, simulations of the top of the atmosphere brightness temperature with CRTM for the Crosstrack Infrared Sounder (CrIS) are carried out to further evaluate the updated CRTM ice cloud optical property look-up table.

Radiative transfer in dusty nebulae. III - The effects of dust albedo

NASA Technical Reports Server (NTRS)

Petrosian, V.; Dana, R. A.

1980-01-01

The effects of an albedo of internal dust, such as ionization structure and temperature of dust grain, were studied by the quasi-diffusion method with an iterative technique for solving the radiative heat transfer equations. It was found that the generalized on-the-spot approximation solution is adequate for most astrophysical applications for a zero albedo; for a nonzero albedo, the Eddington approximation is more accurate. The albedo increases the average energy of the diffuse photons, increasing the ionization level of hydrogen and heavy elements if the Eddington approximation is applied; the dust thermal gradient is reduced so that the infrared spectrum approaches blackbody spectrum with an increasing albedo.

Space Weathering of Silicate Asteroids: An Observational Investigation

NASA Astrophysics Data System (ADS)

MacLennan, Eric M.; Emery, Joshua; Lindsay, Sean S.

2017-10-01

Solar wind exposure and micrometeoroid bombardment are known to cause mineralogical changes in the upper few microns of silicate grains (by forming amorphous “composition” rims with embedded nano-phase Fe0). These processes, jointly called space weathering (SW), affect the light-scattering properties and subsequently the geometric albedo and spectral parameters (spectral slope and band depth). Earth’s Moon exhibits the well known “lunar-style” of SW: albedo decrease, spectral slope increase, and absorption band suppression. However, space mission images of (243) Ida and (433) Eros suggest that different SW “styles” exist among the silicate-bearing (olivine and pyroxene) S-complex asteroids, which exhibit diagnostic absorption features near 1 & 2 μm. While Eros generally shows only albedo differences between younger and older locations, Ida’s surface only shows changes in spectral slope and band depth. It is not clear if these SW styles are unique to Ida and Eros or if they can be observed throughout the entire asteroid population.We hypothesize that the SW styles seen on Eros and Ida also exist on other asteroid surfaces. Additionally, we hypothesize that increased solar wind exposure, smaller regolith particles, higher olivine abundance, and older asteroid surfaces will increase the observed degree of SW. Our dataset includes publicly available Visible (0.4-0.8 μm) and Near Infrared (~0.7-2.5 μm) reflectance spectra of silicate-bearing asteroids (those with 1 & 2 μm bands) from the PDS and the SMASS, S3OS2 and MIT-UH-IRTF spectral surveys. We have also conducted a spectral survey with the IRTF/SpeX targeting 52 silicate asteroids for which we have constraints for regolith grain sizes from interpretation of thermal-IR data. The relevant band parameters to SW and to interpreting mineralogical properties are calculated using the band analysis code, SARA. Geometric albedos are calculated using thermal-IR data from WISE/NEOWISE. Using these derived parameters, we search for potential SW styles among different spectral classes and for correlations with the factors listed above. Analysis on a subset of S-types suggests that heliocentric distance correlates with spectral slope and band depth but not albedo.

The impact of future forest dynamics on climate: interactive effects of changing vegetation and disturbance regimes.

PubMed

Thom, Dominik; Rammer, Werner; Seidl, Rupert

2017-11-01

Currently, the temperate forest biome cools the earth's climate and dampens anthropogenic climate change. However, climate change will substantially alter forest dynamics in the future, affecting the climate regulation function of forests. Increasing natural disturbances can reduce carbon uptake and evaporative cooling, but at the same time increase the albedo of a landscape. Simultaneous changes in vegetation composition can mitigate disturbance impacts, but also influence climate regulation directly (e.g., via albedo changes). As a result of a number of interactive drivers (changes in climate, vegetation, and disturbance) and their simultaneous effects on climate-relevant processes (carbon exchange, albedo, latent heat flux) the future climate regulation function of forests remains highly uncertain. Here we address these complex interactions to assess the effect of future forest dynamics on the climate system. Our specific objectives were (1) to investigate the long-term interactions between changing vegetation composition and disturbance regimes under climate change, (2) to quantify the response of climate regulation to changes in forest dynamics, and (3) to identify the main drivers of the future influence of forests on the climate system. We investigated these issues using the individual-based forest landscape and disturbance model (iLand). Simulations were run over 200 yr for Kalkalpen National Park (Austria), assuming different future climate projections, and incorporating dynamically responding wind and bark beetle disturbances. To consistently assess the net effect on climate the simulated responses of carbon exchange, albedo, and latent heat flux were expressed as contributions to radiative forcing. We found that climate change increased disturbances (+27.7% over 200 yr) and specifically bark beetle activity during the 21st century. However, negative feedbacks from a simultaneously changing tree species composition (+28.0% broadleaved species) decreased disturbance activity in the long run (-10.1%), mainly by reducing the host trees available for bark beetles. Climate change and the resulting future forest dynamics significantly reduced the climate regulation function of the landscape, increasing radiative forcing by up to +10.2% on average over 200 yr. Overall, radiative forcing was most strongly driven by carbon exchange. We conclude that future changes in forest dynamics can cause amplifying climate feedbacks from temperate forest ecosystems.

Correction of broadband albedo measurements affected by unknown slope and sensor tilts

NASA Astrophysics Data System (ADS)

Weiser, Ursula; Olefs, Marc; Schöner, Wolfgang; Weyss, Gernot; Hynek, Bernhard

2017-02-01

Geometric effects induced by the underlying terrain slope or by tilt errors of radiation sensors lead to an erroneous measurement of snow or ice albedo. Consequently, diurnal albedo variations are observed. A general method to correct tilt errors of albedo measurements in cases where tilts of both the sensors and the slopes are not accurately measured or known is presented. Atmospheric parameters for this correction method can either be taken from a nearby well-maintained and horizontally levelled measurement of global radiation or alternatively from a solar radiation model. In a next step the model is fitted to the measured data to determine tilts and directions of the sensors and the underlying terrain slope. This then allows to correct the measured albedo, the radiative balance and the energy balance. Depending on the direction of the slope and the sensors a comparison between measured and corrected albedo values reveals obvious over-or underestimations of albedo.

Lambert Reflectance Albedo And Temperature Mapping Of Thermal Emission Spectrometer Data During The Mars Global Surveyor Aerobraking Phase

NASA Astrophysics Data System (ADS)

Badri, K. M.; Alqasim, A.; Altunaiji, E. S.; Edwards, C. S.; Smith, M. D.

2017-12-01

The goal of this work is to create multiple sets of maps using Thermal Emission Spectrometer (TES) data that encompass the aerobraking phase of the Mars Global Surveyor mission. This work will serve as a proof of concept for the upcoming Emirates Mars Mission, where the Emirates Mars Infrared Spectrometer (EMRIS) will generate data acquired in a similar manner to that acquired by TES during aerobraking. To generate maps of these data on a global scale, python will be used in combination with the Spacecraft Planet Instrument Camera Matrix and Event (SPICE) toolkit to determine the geometry of the pixels on the planet surface. TES is an instrument within the Mars Global Surveyor (MGS) spacecraft. It is a Fourier transform infrared spectrometer developed to study the surface and atmosphere of Mars using thermal infrared emission spectroscopy. TES consists of six detectors arranged in a 2x3 array with a nominal spot size of 3 × 6 km when in its nominal mapping orbit. Over the southern hemisphere during aerobraking the footprint is significantly larger (10s of km) due to the elliptical nature of the orbit during this phase of the mission. TES aerobraking spectra were taken between Mars Year 23, Ls=180° and Mars Year 24, Ls=30°. Here we map TES footprints to the surface during MGS aerobraking, binned by solar longitude to observe differences on the surface in both temperature and Lambert albedo.

Generating multi-scale albedo look-up maps using MODIS BRDF/Albedo products and landsat imagery

USDA-ARS?s Scientific Manuscript database

Surface albedo determines radiative forcing and is a key parameter for driving Earth’s climate. Better characterization of surface albedo for individual land cover types can reduce the uncertainty in estimating changes to Earth’s radiation balance due to land cover change. This paper presents a mult...

Correction of broadband snow albedo measurements affected by unknown slope and sensor tilts

NASA Astrophysics Data System (ADS)

Weiser, Ursula; Olefs, Marc; Schöner, Wolfgang; Weyss, Gernot; Hynek, Bernhard

2016-04-01

Geometric effects induced by the underlying terrain slope or by tilt errors of the radiation sensors lead to an erroneous measurement of snow or ice albedo. Consequently, artificial diurnal albedo variations in the order of 1-20 % are observed. The present paper proposes a general method to correct tilt errors of albedo measurements in cases where tilts of both the sensors and the slopes are not accurately measured or known. We demonstrate that atmospheric parameters for this correction model can either be taken from a nearby well-maintained and horizontally levelled measurement of global radiation or alternatively from a solar radiation model. In a next step the model is fitted to the measured data to determine tilts and directions of sensors and the underlying terrain slope. This then allows us to correct the measured albedo, the radiative balance and the energy balance. Depending on the direction of the slope and the sensors a comparison between measured and corrected albedo values reveals obvious over- or underestimations of albedo. It is also demonstrated that differences between measured and corrected albedo are generally highest for large solar zenith angles.

Albedo indicating land degradation around the Badain Jaran Desert for better land resources utilization.

PubMed

Liu, Fengshan; Chen, Ying; Lu, Haiying; Shao, Hongbo

2017-02-01

Surface albedo is an easy access parameter in reflecting the status of both human disturbed soil and indirectly influenced area, whose characteristic is an important indicator in sustainable development under the background of global climate change. In this study, we employed meteorological data, MODIS 8-day BRDF/Albedo and LAI products from 2000 to 2014 to show the amelioration and mechanism around the Badain Jaran Desert. Results showed that the human-dominated afforestation activities significantly increased the leaf area index (LAI) in summer and autumn. Lower reflectance at visible band was sensed inside the desert compared with the ecozone and the lowest albedo at forested area. The contribution of soil and vegetation reflectance to surface albedo determined the linear sensitivity of albedo to LAI variation. Decreased albedo dominated the spatial-temporal pattern of the Badain Jaran Desert. This study suggested that surface albedo can be regarded as a useful index in indicating the change process and evaluating the sustainable development of biological management around the Badain Jaran Desert. Copyright © 2016. Published by Elsevier B.V.

Analysis on variability and trend in Antarctic sea ice albedo between 1983 and 2009

NASA Astrophysics Data System (ADS)

Seo, Minji; Kim, Hyun-cheol; Choi, Sungwon; Lee, Kyeong-sang; Han, Kyung-soo

2017-04-01

Sea ice is key parameter in order to understand the cryosphere climate change. Several studies indicate the different trend of sea ice between Antarctica and Arctic. Albedo is important factor for understanding the energy budget and factors for observing of environment changes of Cryosphere such as South Pole, due to it mainly covered by ice and snow with high albedo value. In this study, we analyzed variability and trend of long-term sea ice albedo data to understand the changes of sea ice over Antarctica. In addiction, sea ice albedo researched the relationship with Antarctic oscillation in order to determine the atmospheric influence. We used the sea ice albedo data at The Satellite Application Facility on Climate Monitoring and Antarctic Oscillation data at NOAA Climate Prediction Center (CPC). We analyzed the annual trend in albedo using linear regression to understand the spatial and temporal tendency. Antarctic sea ice albedo has two spatial trend. Weddle sea / Ross sea sections represent a positive trend (0.26% ˜ 0.04% yr-1) and Bellingshausen Amundsen sea represents a negative trend (- 0.14 ˜ -0.25%yr-1). Moreover, we performed the correlation analysis between albedo and Antarctic oscillation. As a results, negative area indicate correlation coefficient of - 0.3639 and positive area indicates correlation coefficient of - 0.0741. Theses results sea ice albedo has regional trend according to ocean. Decreasing sea ice trend has negative relationship with Antarctic oscillation, its represent a possibility that sea ice influence atmospheric factor.

Changes in summer sea ice, albedo, and portioning of surface solar radiation in the Pacific sector of Arctic Ocean during 1982-2009

NASA Astrophysics Data System (ADS)

Lei, Ruibo; Tian-Kunze, Xiangshan; Leppäranta, Matti; Wang, Jia; Kaleschke, Lars; Zhang, Zhanhai

2016-08-01

SSM/I sea ice concentration and CLARA black-sky composite albedo were used to estimate sea ice albedo in the region 70°N-82°N, 130°W-180°W. The long-term trends and seasonal evolutions of ice concentration, composite albedo, and ice albedo were then obtained. In July-August 1982-2009, the linear trend of the composite albedo and the ice albedo was -0.069 and -0.046 units per decade, respectively. During 1 June to 19 August, melting of sea ice resulted in an increase of solar heat input to the ice-ocean system by 282 MJ·m-2 from 1982 to 2009. However, because of the counter-balancing effects of the loss of sea ice area and the enhanced ice surface melting, the trend of solar heat input to the ice was insignificant. The summer evolution of ice albedo matched the ice surface melting and ponding well at basin scale. The ice albedo showed a large difference between the multiyear and first-year ice because the latter melted completely by the end of a melt season. At the SHEBA geolocations, a distinct change in the ice albedo has occurred since 2007, because most of the multiyear ice has been replaced by first-year ice. A positive polarity in the Arctic Dipole Anomaly could be partly responsible for the rapid loss of summer ice within the study region in the recent years by bringing warmer air masses from the south and advecting more ice toward the north. Both these effects would enhance ice-albedo feedback.

Impact of Grain Shape and Multiple Black Carbon Internal Mixing on Snow Albedo: Parameterization and Radiative Effect Analysis

NASA Astrophysics Data System (ADS)

He, Cenlin; Liou, Kuo-Nan; Takano, Yoshi; Yang, Ping; Qi, Ling; Chen, Fei

2018-01-01

We quantify the effects of grain shape and multiple black carbon (BC)-snow internal mixing on snow albedo by explicitly resolving shape and mixing structures. Nonspherical snow grains tend to have higher albedos than spheres with the same effective sizes, while the albedo difference due to shape effects increases with grain size, with up to 0.013 and 0.055 for effective radii of 1,000 μm at visible and near-infrared bands, respectively. BC-snow internal mixing reduces snow albedo at wavelengths < 1.5 μm, with negligible effects at longer wavelengths. Nonspherical snow grains show less BC-induced albedo reductions than spheres with the same effective sizes by up to 0.06 at ultraviolet and visible bands. Compared with external mixing, internal mixing enhances snow albedo reduction by a factor of 1.2-2.0 at visible wavelengths depending on BC concentration and snow shape. The opposite effects on albedo reductions due to snow grain nonsphericity and BC-snow internal mixing point toward a careful investigation of these two factors simultaneously in climate modeling. We further develop parameterizations for snow albedo and its reduction by accounting for grain shape and BC-snow internal/external mixing. Combining the parameterizations with BC-in-snow measurements in China, North America, and the Arctic, we estimate that nonspherical snow grains reduce BC-induced albedo radiative effects by up to 50% compared with spherical grains. Moreover, BC-snow internal mixing enhances the albedo effects by up to 30% (130%) for spherical (nonspherical) grains relative to external mixing. The overall uncertainty induced by snow shape and BC-snow mixing state is about 21-32%.

The influence of canopy shading of snow on effective albedo in forested environments

NASA Astrophysics Data System (ADS)

Webster, C.; Jonas, T.

2017-12-01

The overlap of highly reflective snow and absorbent forested areas creates strong heterogeneity in the effective surface albedo compared to forest-free areas. Current errors in calculations of effective forest snow albedo arise due to uncertainties in how models should treat masking of snow by vegetation but improvement of local and large scale models is currently limited by a lack of measurements that demonstrate both spatial and temporal variability over forests. We present above-canopy measurements of winter-time effective forest snow albedo using up- and down-looking radiometers mounted on an octocopter UAV for a total of fifteen flights on eight different days. Ground-view fractions across the flight path were between 0.12 and 0.81. Correlations between effective albedo and both ground-view fraction and canopy height were statistically significant during 14 out of 15 flights, but varied between flights due to solar angle and snow cover. Measured effective albedo across the flight path differed by up to 0.33 during snow-on canopy conditions. A comparison between maximum interception and no interception showed effective albedo varied by up 0.17, which was the same variation between effective albedo during high (46°) and low (23°) solar elevation angles. Temporal and spatial variations in effective albedo caused by canopy shading of the snow surface are therefore as important as temporal variations caused by interception of snow by the canopy. Calculation of effective albedo over forested areas therefore requires careful consideration of canopy height, canopy coverage, solar angle and interception load. The results of this study should be used to inform snow albedo and canopy structure parametrisations in local and larger scale land surface models.

Estimation of snow albedo reduction by light absorbing impurities using Monte Carlo radiative transfer model

NASA Astrophysics Data System (ADS)

Sengupta, D.; Gao, L.; Wilcox, E. M.; Beres, N. D.; Moosmüller, H.; Khlystov, A.

2017-12-01

Radiative forcing and climate change greatly depends on earth's surface albedo and its temporal and spatial variation. The surface albedo varies greatly depending on the surface characteristics ranging from 5-10% for calm ocean waters to 80% for some snow-covered areas. Clean and fresh snow surfaces have the highest albedo and are most sensitive to contamination with light absorbing impurities that can greatly reduce surface albedo and change overall radiative forcing estimates. Accurate estimation of snow albedo as well as understanding of feedbacks on climate from changes in snow-covered areas is important for radiative forcing, snow energy balance, predicting seasonal snowmelt, and run off rates. Such information is essential to inform timely decision making of stakeholders and policy makers. Light absorbing particles deposited onto the snow surface can greatly alter snow albedo and have been identified as a major contributor to regional climate forcing if seasonal snow cover is involved. However, uncertainty associated with quantification of albedo reduction by these light absorbing particles is high. Here, we use Mie theory (under the assumption of spherical snow grains) to reconstruct the single scattering parameters of snow (i.e., single scattering albedo ῶ and asymmetry parameter g) from observation-based size distribution information and retrieved refractive index values. The single scattering parameters of impurities are extracted with the same approach from datasets obtained during laboratory combustion of biomass samples. Instead of using plane-parallel approximation methods to account for multiple scattering, we have used the simple "Monte Carlo ray/photon tracing approach" to calculate the snow albedo. This simple approach considers multiple scattering to be the "collection" of single scattering events. Using this approach, we vary the effective snow grain size and impurity concentrations to explore the evolution of snow albedo over a wide wavelength range (300 nm - 2000 nm). Results will be compared with the SNICAR model to better understand the differences in snow albedo computation between plane-parallel methods and the statistical Monte Carlo methods.

Spatio-temporal Variability of Albedo and its Impact on Glacier Melt Modelling

NASA Astrophysics Data System (ADS)

Kinnard, C.; Mendoza, C.; Abermann, J.; Petlicki, M.; MacDonell, S.; Urrutia, R.

2017-12-01

Albedo is an important variable for the surface energy balance of glaciers, yet its representation within distributed glacier mass-balance models is often greatly simplified. Here we study the spatio-temporal evolution of albedo on Glacier Universidad, central Chile (34°S, 70°W), using time-lapse terrestrial photography, and investigate its effect on the shortwave radiation balance and modelled melt rates. A 12 megapixel digital single-lens reflex camera was setup overlooking the glacier and programmed to take three daily images of the glacier during a two-year period (2012-2014). One image was chosen for each day with no cloud shading on the glacier. The RAW images were projected onto a 10m resolution digital elevation model (DEM), using the IMGRAFT software (Messerli and Grinsted, 2015). A six-parameter camera model was calibrated using a single image and a set of 17 ground control points (GCPs), yielding a georeferencing accuracy of <1 pixel in image coordinates. The camera rotation was recalibrated for new images based on a set of common tie points over stable terrain, thus accounting for possible camera movement over time. The reflectance values from the projected image were corrected for topographic and atmospheric influences using a parametric solar irradiation model, following a modified algorithm based on Corripio (2004), and then converted to albedo using reference albedo measurements from an on-glacier automatic weather station (AWS). The image-based albedo was found to compare well with independent albedo observations from a second AWS in the glacier accumulation area. Analysis of the albedo maps showed that the albedo is more spatially-variable than the incoming solar radiation, making albedo a more important factor of energy balance spatial variability. The incorporation of albedo maps within an enhanced temperature index melt model revealed that the spatio-temporal variability of albedo is an important factor for the calculation of glacier-wide meltwater fluxes.

Phenology and species determine growing-season albedo increase at the altitudinal limit of shrub growth in the sub-Arctic.

PubMed

Williamson, Scott N; Barrio, Isabel C; Hik, David S; Gamon, John A

2016-11-01

Arctic warming is resulting in reduced snow cover and increased shrub growth, both of which have been associated with altered land surface-atmospheric feedback processes involving sensible heat flux, ground heat flux and biogeochemical cycling. Using field measurements, we show that two common Arctic shrub species (Betula glandulosa and Salix pulchra), which are largely responsible for shrub encroachment in tundra, differed markedly in albedo and that albedo of both species increased as growing season progressed when measured at their altitudinal limit. A moveable apparatus was used to repeatedly measure albedo at six precise spots during the summer of 2012, and resampled in 2013. Contrary to the generally accepted view of shrub-covered areas having low albedo in tundra, full-canopy prostrate B. glandulosa had almost the highest albedo of all surfaces measured during the peak of the growing season. The higher midsummer albedo is also evident in localized MODIS albedo aggregated from 2000 to 2013, which displays a similar increase in growing-season albedo. Using our field measurements, we show the ensemble summer increase in tundra albedo counteracts the generalized effect of earlier spring snow melt on surface energy balance by approximately 40%. This summer increase in albedo, when viewed in absolute values, is as large as the difference between the forest and tundra transition. These results indicate that near future (<50 years) changes in growing-season albedo related to Arctic vegetation change are unlikely to be particularly large and might constitute a negative feedback to climate warming in certain circumstances. Future efforts to calculate energy budgets and a sensible heating feedback in the Arctic will require more detailed information about the relative abundance of different ground cover types, particularly shrub species and their respective growth forms and phenology. © 2016 John Wiley & Sons Ltd.

Opposition effect on comet 67P/Churyumov-Gerasimenko using Rosetta-OSIRIS images

NASA Astrophysics Data System (ADS)

Masoumzadeh, N.; Oklay, N.; Kolokolova, L.; Sierks, H.; Fornasier, S.; Barucci, M. A.; Vincent, J.-B.; Tubiana, C.; Güttler, C.; Preusker, F.; Scholten, F.; Mottola, S.; Hasselmann, P. H.; Feller, C.; Barbieri, C.; Lamy, P. L.; Rodrigo, R.; Koschny, D.; Rickman, H.; A'Hearn, M. F.; Bertaux, J.-L.; Bertini, I.; Cremonese, G.; Da Deppo, V.; Davidsson, B. J. R.; Debei, S.; De Cecco, M.; Fulle, M.; Gicquel, A.; Groussin, O.; Gutiérrez, P. J.; Hall, I.; Hofmann, M.; Hviid, S. F.; Ip, W.-H.; Jorda, L.; Keller, H. U.; Knollenberg, J.; Kovacs, G.; Kramm, J.-R.; Kührt, E.; Küppers, M.; Lara, L. M.; Lazzarin, M.; Lopez Moreno, J. J.; Marzari, F.; Naletto, G.; Shi, X.; Thomas, N.

2017-03-01

Aims: We aim to explore the behavior of the opposition effect as an important tool in optical remote sensing on the nucleus of comet 67P/ Churyumov-Gerasimenko (67P), using Rosetta-OSIRIS images acquired in different filters during the approach phase, July-August 2014 and the close flyby images on 14 of February 2015, which contain the spacecraft shadow. Methods: We based our investigation on the global and local brightness from the surface of 67P with respect to the phase angle, also known as phase curve. The local phase curve corresponds to a region that is located at the Imhotep-Ash boundary of 67P. Assuming that the region at the Imhotep-Ash boundary and the entire nucleus have similar albedo, we combined the global and local phase curves to study the opposition-surge morphology and constrain the structure and properties of 67P. The model parameters were furthermore compared with other bodies in the solar system and existing laboratory study. Results: We found that the morphological parameters of the opposition surge decrease monotonically with wavelength, whereas in the case of coherent backscattering this behavior should be the reverse. The results from comparative analysis place 67P in the same category as the two Mars satellites, Phobos and Deimos, which are notably different from all airless bodies in the solar system. The similarity between the surface phase function of 67P and a carbon soot sample at extremely small angles is identified, introducing regolith at the boundary of the Imhotep-Ash region of 67P as a very dark and fluffy layer.

Mars aerosol studies with the MGS TES emission phase function observations: Optical depths, particle sizes, and ice cloud types versus latitude and solar longitude

NASA Astrophysics Data System (ADS)

Clancy, R. Todd; Wolff, Michael J.; Christensen, Philip R.

2003-09-01

Emission phase function (EPF) observations taken in 1999-2001 by Mars Global Surveyor Thermal Emission Spectrometer (MGS TES) support the broadest study of Martian aerosol properties to date. TES solar band and infrared (IR) spectral EPF sequences are analyzed to obtain first-time seasonal/latitudinal distributions of visible optical depths, particle sizes, and single scattering phase functions. This combined angular and wavelength coverage enables identification of two distinct ice cloud types over 45°S-45°N. Type 1 ice clouds exhibit small particle sizes (reff = 1-2 μm) and a distinctive backscattering increase. They are most prevalent in the southern hemisphere during aphelion, but also appear more widely distributed in season and latitude as topographic and high-altitude (>=20 km) ice hazes. Type 2 ice clouds exhibit larger particle sizes (reff = 3-4 μm), a distinct side-scattering minimum at 90-100° phase angles (characteristic of a change in particle shape relative to the type 1), and appear most prominently in the northern subtropical aphelion cloud belt. The majority of retrieved dust visible-to-IR optical depth ratios are indicative of reff = 1.5 +/- 0.1 μm, consistent with Pathfinder and Viking/Mariner 9 reanalyses. However, increased ratios (2.7 versus 1.7) appear frequently in the northern hemisphere over LS = 50-200°, indicating substantially smaller dust particles sizes (reff = 1.0 +/- 0.2 μm) at this time. In addition, larger (reff = 1.8-2.5 μm) dust particles were observed locally in the southern hemisphere during the peak of the 2001 global dust storm. Detailed spectral modeling of the TES visible band pass indicates agreement of EPF-derived dust single scattering albedos (0.92-0.94) with the spectrally resolved results from Pathfinder observations.

Vertical Structure and Optical Properties of Titans Aerosols from Radiance Measurements Made Inside and Outside the Atmosphere

NASA Technical Reports Server (NTRS)

Doose, Lyn R.; Karkoschka, Erich; Tomasko, Martin G.; Anderson, Carrie M.

2017-01-01

Prompted by the detection of stratospheric cloud layers by Cassini's Composite Infrared Spectrometer (CIRS; see Anderson, C.M., Samuelson, R.E. [2011]. Icarus 212, 762-778), we have re-examined the observations made by the Descent Imager/Spectral Radiometer (DISR) in the atmosphere of Titan together with two constraints from measurements made outside the atmosphere. No evidence of thin layers (<1 km) in the DISR image data sets is seen beyond the three previously reported layers at 21 km, 11 km, and 7 km by Karkoschka and Tomasko (Karkoschka, E., Tomasko, M.G. [2009]. Icarus 199, 442-448). On the other hand, there is evidence of a thicker layer centered at about 55 km. A rise in radiance gradients in the Downward-Looking Visible Spectrometer (DLVS) data below 55 km indicates an increase in the volume extinction coefficient near this altitude. To fit the geometric albedo measured from outside the atmosphere the decrease in the single scattering albedo of Titan's aerosols at high altitudes, noted in earlier studies of DISR data, must continue to much higher altitudes. The altitude of Titan's limb as a function of wavelength requires that the scale height of the aerosols decrease with altitude from the 65 km value seen in the DISR observations below 140 km to the 45 km value at higher altitudes. We compared the variation of radiance with nadir angle observed in the DISR images to improve our aerosol model. Our new aerosol model fits the altitude and wavelength variations of the observations at small and intermediate nadir angles but not for large nadir angles, indicating an effect that is not reproduced by our radiative transfer model. The volume extinction profiles are modeled by continuous functions except near the enhancement level near 55 km altitude. The wavelength dependence of the extinction optical depth is similar to earlier results at wavelengths from 500 to 700 nm, but is smaller at shorter wavelengths and larger toward longer wavelengths. A Hapke-like model is used for the ground reflectivity, and the variation of the Hapke single scattering albedo with wavelength is given. Fits to the visible spectrometers looking upward and downward are achieved except in the methane bands longward of 720 nm. This is possibly due to uncertainties in extrapolation of laboratory measurements from 1 km-am paths to much longer paths at lower pressures. It could also be due to changes in the single scattering phase functions at low altitudes, which strongly affect the path length through methane that the photons travel. We demonstrate the effects on the model fits by varying each model parameter individually in order to illustrate the sensitivity of our determination of each model parameter.

Monitoring land surface albedo and vegetation dynamics using high spatial and temporal resolution synthetic time series from Landsat and the MODIS BRDF/NBAR/albedo product

NASA Astrophysics Data System (ADS)

Wang, Zhuosen; Schaaf, Crystal B.; Sun, Qingsong; Kim, JiHyun; Erb, Angela M.; Gao, Feng; Román, Miguel O.; Yang, Yun; Petroy, Shelley; Taylor, Jeffrey R.; Masek, Jeffrey G.; Morisette, Jeffrey T.; Zhang, Xiaoyang; Papuga, Shirley A.

2017-07-01

Seasonal vegetation phenology can significantly alter surface albedo which in turn affects the global energy balance and the albedo warming/cooling feedbacks that impact climate change. To monitor and quantify the surface dynamics of heterogeneous landscapes, high temporal and spatial resolution synthetic time series of albedo and the enhanced vegetation index (EVI) were generated from the 500 m Moderate Resolution Imaging Spectroradiometer (MODIS) operational Collection V006 daily BRDF/NBAR/albedo products and 30 m Landsat 5 albedo and near-nadir reflectance data through the use of the Spatial and Temporal Adaptive Reflectance Fusion Model (STARFM). The traditional Landsat Albedo (Shuai et al., 2011) makes use of the MODIS BRDF/Albedo products (MCD43) by assigning appropriate BRDFs from coincident MODIS products to each Landsat image to generate a 30 m Landsat albedo product for that acquisition date. The available cloud free Landsat 5 albedos (due to clouds, generated every 16 days at best) were used in conjunction with the daily MODIS albedos to determine the appropriate 30 m albedos for the intervening daily time steps in this study. These enhanced daily 30 m spatial resolution synthetic time series were then used to track albedo and vegetation phenology dynamics over three Ameriflux tower sites (Harvard Forest in 2007, Santa Rita in 2011 and Walker Branch in 2005). These Ameriflux sites were chosen as they are all quite nearby new towers coming on line for the National Ecological Observatory Network (NEON), and thus represent locations which will be served by spatially paired albedo measures in the near future. The availability of data from the NEON towers will greatly expand the sources of tower albedometer data available for evaluation of satellite products. At these three Ameriflux tower sites the synthetic time series of broadband shortwave albedos were evaluated using the tower albedo measurements with a Root Mean Square Error (RMSE) less than 0.013 and a bias within the range of ±0.006. These synthetic time series provide much greater spatial detail than the 500 m gridded MODIS data, especially over more heterogeneous surfaces, which improves the efforts to characterize and monitor the spatial variation across species and communities. The mean of the difference between maximum and minimum synthetic time series of albedo within the MODIS pixels over a subset of satellite data of Harvard Forest (16 km by 14 km) was as high as 0.2 during the snow-covered period and reduced to around 0.1 during the snow-free period. Similarly, we have used STARFM to also couple MODIS Nadir BRDF Adjusted Reflectances (NBAR) values with Landsat 5 reflectances to generate daily synthetic times series of NBAR and thus Enhanced Vegetation Index (NBAR-EVI) at a 30 m resolution. While normally STARFM is used with directional reflectances, the use of the view angle corrected daily MODIS NBAR values will provide more consistent time series. These synthetic times series of EVI are shown to capture seasonal vegetation dynamics with finer spatial and temporal details, especially over heterogeneous land surfaces.

Monitoring land surface albedo and vegetation dynamics using high spatial and temporal resolution synthetic time series from Landsat and the MODIS BRDF/NBAR/albedo product

USGS Publications Warehouse

Wang, Zhuosen; Schaaf, Crystal B.; Sun, Qingson; Kim, JiHyun; Erb, Angela M.; Gao, Feng; Roman, Miguel O.; Yang, Yun; Petroy, Shelley; Taylor, Jeffrey; Masek, Jeffrey G.; Morisette, Jeffrey T.; Zhang, Xiaoyang; Papuga, Shirley A.

2017-01-01

Seasonal vegetation phenology can significantly alter surface albedo which in turn affects the global energy balance and the albedo warming/cooling feedbacks that impact climate change. To monitor and quantify the surface dynamics of heterogeneous landscapes, high temporal and spatial resolution synthetic time series of albedo and the enhanced vegetation index (EVI) were generated from the 500 m Moderate Resolution Imaging Spectroradiometer (MODIS) operational Collection V006 daily BRDF/NBAR/albedo products and 30 m Landsat 5 albedo and near-nadir reflectance data through the use of the Spatial and Temporal Adaptive Reflectance Fusion Model (STARFM). The traditional Landsat Albedo (Shuai et al., 2011) makes use of the MODIS BRDF/Albedo products (MCD43) by assigning appropriate BRDFs from coincident MODIS products to each Landsat image to generate a 30 m Landsat albedo product for that acquisition date. The available cloud free Landsat 5 albedos (due to clouds, generated every 16 days at best) were used in conjunction with the daily MODIS albedos to determine the appropriate 30 m albedos for the intervening daily time steps in this study. These enhanced daily 30 m spatial resolution synthetic time series were then used to track albedo and vegetation phenology dynamics over three Ameriflux tower sites (Harvard Forest in 2007, Santa Rita in 2011 and Walker Branch in 2005). These Ameriflux sites were chosen as they are all quite nearby new towers coming on line for the National Ecological Observatory Network (NEON), and thus represent locations which will be served by spatially paired albedo measures in the near future. The availability of data from the NEON towers will greatly expand the sources of tower albedometer data available for evaluation of satellite products. At these three Ameriflux tower sites the synthetic time series of broadband shortwave albedos were evaluated using the tower albedo measurements with a Root Mean Square Error (RMSE) less than 0.013 and a bias within the range of ±0.006. These synthetic time series provide much greater spatial detail than the 500 m gridded MODIS data, especially over more heterogeneous surfaces, which improves the efforts to characterize and monitor the spatial variation across species and communities. The mean of the difference between maximum and minimum synthetic time series of albedo within the MODIS pixels over a subset of satellite data of Harvard Forest (16 km by 14 km) was as high as 0.2 during the snow-covered period and reduced to around 0.1 during the snow-free period. Similarly, we have used STARFM to also couple MODIS Nadir BRDF Adjusted Reflectances (NBAR) values with Landsat 5 reflectances to generate daily synthetic times series of NBAR and thus Enhanced Vegetation Index (NBAR-EVI) at a 30 m resolution. While normally STARFM is used with directional reflectances, the use of the view angle corrected daily MODIS NBAR values will provide more consistent time series. These synthetic times series of EVI are shown to capture seasonal vegetation dynamics with finer spatial and temporal details, especially over heterogeneous land surfaces.

Using Remote Sensing to Quantify Roof Albedo in Seven California Cities

NASA Astrophysics Data System (ADS)

Ban-Weiss, G. A.; Woods, J.; Millstein, D.; Levinson, R.

2013-12-01

Cool roofs reflect sunlight and therefore can reduce cooling energy use in buildings. Further, since roofs cover about 20-25% of cities, wide spread deployment of cool roofs could mitigate the urban heat island effect and partially counter urban temperature increases associated with global climate change. Accurately predicting the potential for increasing urban albedo using reflective roofs and its associated energy use and climate benefits requires detailed knowledge of the current stock of roofs at the city scale. Until now this knowledge has been limited due to a lack of availability of albedo data with sufficient spatial coverage, spatial resolution, and spectral information. In this work we use a novel source of multiband aerial imagery to derive the albedos of individual roofs in seven California cities: Los Angeles, Long Beach, San Diego, Bakersfield, Sacramento, San Francisco, and San Jose. The radiometrically calibrated, remotely sensed imagery has high spatial resolution (1 m) and four narrow (less than 0.1 μm wide) band reflectances: blue, green, red, and near-infrared. To derive the albedo of roofs in each city, we first locate roof pixels within GIS building outlines. Next we use laboratory measurements of the solar spectral reflectances of 190 roofing products to empirically relate solar reflectance (albedo) to reflectances in the four narrow bands; the root-mean-square of the residuals for the albedo prediction is 0.016. Albedos computed from remotely sensed reflectances are calibrated to ground measurements of roof albedo in each city. The error (both precision and accuracy) of albedo values is presented for each city. The area-weighted mean roof albedo (× standard deviation) for each city ranges from 0.17 × 0.08 (Los Angeles) to 0.29 × 0.15 (San Diego). In each city most roofs have low albedo in the range of 0.1 to 0.3. Roofs with albedo greater than 0.4 comprise less than 3% of total roofs and 7% of total roof area in each city. The California Building Energy Efficiency Standard (Title-24, Part 6) includes the use of high-albedo surfaces on low-sloped roofs on non-residential buildings. Analyzing a subset of large presumably commercial buildings, we find high albedo roofs represent 0.5% and 10% of total roofs and roof surface area, respectively. The potential for high albedo roofs to reduce urban temperatures was investigated for a California city (Bakersfield) with warm summers using a state-of-the-art meteorological model (Weather Research and Forecasting, WRF). Base case and cool roof scenarios were simulated with the only difference being that the surface albedo was increased under the cool roof scenario. Roof albedos derived from the aerial imagery were used as an input to the climate model in the base case scenario. Simulation results indicate that seasonal average afternoon (1500 h) temperatures could be reduced by up to 0.2 °C across Bakersfield during both the summer and winter. While temperature changes are similar during winter and summer, only summer shows statistically significant temperature changes downwind (southeast) from Bakersfield. This indicates that reduced summertime temperatures may be felt over a distance that is 2 or 3 times the length scale of the region with high albedo roofs.

Analytic Reflected Lightcurves for Exoplanets

NASA Astrophysics Data System (ADS)

Haggard, Hal M.; Cowan, Nicolas B.

2018-04-01

The disk-integrated reflected brightness of an exoplanet changes as a function of time due to orbital and rotational motion coupled with an inhomogeneous albedo map. We have previously derived analytic reflected lightcurves for spherical harmonic albedo maps in the special case of a synchronously-rotating planet on an edge-on orbit (Cowan, Fuentes & Haggard 2013). In this letter, we present analytic reflected lightcurves for the general case of a planet on an inclined orbit, with arbitrary spin period and non-zero obliquity. We do so for two different albedo basis maps: bright points (δ-maps), and spherical harmonics (Y_l^m-maps). In particular, we use Wigner D-matrices to express an harmonic lightcurve for an arbitrary viewing geometry as a non-linear combination of harmonic lightcurves for the simpler edge-on, synchronously rotating geometry. These solutions will enable future exploration of the degeneracies and information content of reflected lightcurves, as well as fast calculation of lightcurves for mapping exoplanets based on time-resolved photometry. To these ends we make available Exoplanet Analytic Reflected Lightcurves (EARL), a simple open-source code that allows rapid computation of reflected lightcurves.

Report on the ALPO LTP observing program. [for establishing albedo scale for lunar features

NASA Technical Reports Server (NTRS)

Cameron, W. S.

1974-01-01

Observations of lunar transient phenomena for the Association of Lunar and Planetary Observers (ALPO) are reported. The procedures for making visual observations for estimating albedo are described, and the reported albedo analyzed for lunar topographic features. It is shown that a catalog or scale of albedos can be established for each feature.

Ground based planetary research

NASA Technical Reports Server (NTRS)

1973-01-01

High spatial resolution spectrophotometric observations made in the wavelength region lambda lambda 0.6 - 2.0 micrometers are used to study the Jovian and Saturnian limb darkening. Limb darkening coefficients (k) of the Minnaert function are derived for the cloud layers of both planets. A value of k = 1.0 is found for Jupiter over the entire disk while values of between 0.75 and 0.90 are found for different latitudes for Saturn. These data are used to derive geometric albedoes (G) for the various belts, zones, spots and regions observed on Jupiter and Saturn. These values of G and k are in turn used to show that an isotropic scattering model is invalid for Jupiter and that at least an asymmetric scattering function, such as the Euler function, is needed to fit the Jovian data. The Jovian scattering function is found to generally vary between 0.960 and 0.994 as a function of wavelength and the feature observed. The Saturn geometric albedoes and values of k indicate that Euler's function fails to adequately model the scattering properties of the Saturnian clouds. As a result it is suggested that simple scattering theory may not apply to the Saturn clouds or that they are better represented by a cumulus cloud model.

Opposing effects of fire severity on climate feedbacks in Siberian larch forests

NASA Astrophysics Data System (ADS)

Loranty, M. M.; Alexander, H. D.; Natali, S.; Kropp, H.; Mack, M. C.; Bunn, A. G.; Davydov, S. P.; Erb, A.; Kholodov, A. L.; Schaaf, C.; Wang, Z.; Zimov, N.; Zimov, S. A.

2017-12-01

Boreal larch forests in northeastern Siberia comprise nearly 25% of the continuous permafrost zone. Structural and functional changes in these ecosystems will have important climate feedbacks at regional and global scales. Like boreal ecosystems in North America, fire is an important determinant of landscape scale forest distribution, and fire regimes are intensifying as climate warms. In Siberian larch forests are dominated by a single tree species, and there is evidence that fire severity influences post-fire forest density via impacts on seedling establishment. The extent to which these effects occur, or persist, and the associated climate feedbacks are not well quantified. In this study we use forest stand inventories, in situ observations, and satellite remote sensing to examine: 1) variation in forest density within and between fire scars, and 2) changes in land surface albedo and active layer dynamics associated with forest density variation. At the landscape scale we observed declines in Landsat derived albedo as forests recovered in the first several decades after fire, though canopy cover varied widely within and between individual fire scars. Within an individual mid-successional fire scar ( 75 years) we observed canopy cover ranging from 15-90% with correspondingly large ranges of albedo during periods of snow cover, and relatively small differences in albedo during the growing season. We found an inverse relationship between canopy density and soil temperature within this fire scar; high-density low-albedo stands had cooler soils and shallower active layers, while low-density stands had warmer soils and deeper active layers. Intensive energy balance measurements at a high- and low- density site show that canopy cover alters the magnitude and timing of ground heat fluxes that affect active layer properties. Our results show that fire impacts on stand structure in Siberian larch forests affect land surface albedo and active layer dynamics in ways that may lead to opposing climate feedbacks. At effectively large scales these changes constitute positive and negative climate feedbacks, respectively. Accurate predictive understanding of terrestrial Arctic climate feedbacks requires improved knowledge regarding the ecological consequences of changing fire regimes in Siberian boreal forests.

Auroral Data Analysis

DTIC Science & Technology

1979-01-31

LT) sector, distinct and repeatable electron lair - and disceearrlrgos epetvI.Tepro tde tudinal distributions \\%ere observed as a function of substorm...of surface a ,wcond time by using the same procedure, Next the)’ were optical albedo and east-%est nonuniformities in precipitation grouped together

Surface BRDF estimation from an aircraft compared to MODIS and ground estimates at the Southern Great Plains site

DOE Office of Scientific and Technical Information (OSTI.GOV)

Knobelspiesse, Kirk D.; Cairns, Brian; Schmid, Beat

2008-10-21

The surface spectral albedo is an important component of climate models since it determines the amount of incident solar radiation that is absorbed by the ground. The albedo can be highly heterogeneous, both in space and time, and thus adequate measurement and modeling is challenging. One source of measurements that constrain the surface albedo are satellite instruments that observe the Earth, such as the Moderate Resolution Imaging Spectroradiometer (MODIS). Satellites estimate the surface bidirectional reflectance distribution function (BRDF) by correcting top of the atmosphere (TOA) radiances for atmospheric effects and accumulating observations at a variety of viewing geometries. The BRDFmore » can then be used to determine the albedo that is required in climate modeling. Other measurements that provide a more direct constraint on surface albedo are those made by upward and downward looking radiometers at the ground. One product in particular, the Best Estimate Radiation Flux (BEFLUX) value added product of the Department of Energy’s Atmospheric Radiation Measurement (ARM) Program at the Southern Great Plains Central Facility (SGP CF) in central Oklahoma, has been used to evaluate the quality of the albedo products derived from MODIS BRDF estimates. These comparisons have highlighted discrepancies between the energy absorbed at the surface that is calculated from the BEFLUX products and that is predicted from the MODIS BRDF product. This paper attempts to investigate these discrepancies by using data from an airborne scanning radiometer, the Research Scanning Polarimeter (RSP) that was flown at low altitude in the vicinity of the SGP CF site during the Aerosol Lidar Validation Experiment (ALIVE) in September of 2005. The RSP is a polarimeter that scans in the direction of the aircraft ground track, and can thus estimate the BRDF in a period of seconds, rather than the days required by MODIS to accumulate enough viewing angles. Atmospheric correction is aided by the Ames Airborne Tracking Sunphotometer (AATS-14), which was operated on the same aircraft as the RSP. The RSP data can therefore be used to validate the MODIS BRDF product and diagnose the reason for the discrepancies with BEFLUX. Our analysis indicates that MODIS and RSP estimates of surface absorption and BEFLUX measurements do agree and that previously noticed differences between MODIS albedo products and BEFLUX were due as much to the analysis techniques used as to any instrumental effects. We conclude that the MODIS BRDF products provide a useful measure of surface albedo that can be used to determine whether the surface radiative heating in climate models has a realistic spatial and seasonal variation.« less

Application and Evaluation of MODIS LAI, FPAR, and Albedo ...

EPA Pesticide Factsheets

MODIS vegetation and albedo products provide a more realistic representation of surface conditions for input to the WRF/CMAQ modeling system. However, the initial evaluation of ingesting MODIS data into the system showed mixed results, with increased bias and error for 2-m temperature and reduced bias and error for 2-m mixing ratio. Recently, the WRF/CMAQ land surface and boundary laywer processes have been updated. In this study, MODIS vegetation and albedo data are input to the updated WRF/CMAQ meteorology and air quality simulations for 2006 over a North American (NA) 12-km domain. The evaluation of the simulation results shows that the updated WRF/CMAQ system improves 2-m temperature estimates over the pre-update base modeling system estimates. The MODIS vegetation input produces a realistic spring green-up that progresses through time from the south to north. Overall, MODIS input reduces 2-m mixing ration bias during the growing season. The NA west shows larger positive O3 bias during the growing season because of reduced gas phase deposition resulting from lower O3 deposition velocities driven by reduced vegetation cover. The O3 bias increase associated with the realistic vegetation representation indicates that further improvement may be needed in the WRF/CMAQ system. The National Exposure Research Laboratory’s Atmospheric Modeling Division (AMAD) conducts research in support of EPA’s mission to protect human health and the environment. AMAD’s rese

A cavity radiometer for Earth albedo measurement, phase 1

NASA Technical Reports Server (NTRS)

1987-01-01

Radiometric measurements of the directional albedo of the Earth requires a detector with a flat response from 0.2 to 50 microns, a response time of about 2 seconds, a sensitivity of the order of 0.02 mw/sq cm, and a measurement uncertainty of less than 5 percent. Absolute cavity radiometers easily meet the spectral response and accuracy requirements for Earth albedo measurements, but the radiometers available today lack the necessary sensitivity and response time. The specific innovations addressed were the development of a very low thermal mass cavity and printed/deposited thermocouple sensing elements which were incorporated into the radiometer design to produce a sensitive, fast response, absolute radiometer. The cavity is applicable to the measurement of the reflected and radiated fluxes from the Earth surface and lower atmosphere from low Earth orbit satellites. The effort consisted of requirements and thermal analysis; design, construction, and test of prototype elements of the black cavity and sensor elements to show proof-of-concept. The results obtained indicate that a black body cavity sensor that has inherently a flat response from 0.2 to 50 microns can be produced which has a sensitivity of at least 0.02 mw/sq cm per micro volt ouput and with a time constant of less than two seconds. Additional work is required to develop the required thermopile.

VizieR Online Data Catalog: WISE/NEOWISE Mars-crossing asteroids (Ali-Lagoa+, 2017)

NASA Astrophysics Data System (ADS)

Ali-Lagoa, V.; Delbo, M.

2017-07-01

We fitted the near-Earth asteroid thermal model of Harris (1998, Icarus, 131, 29) to WISE/NEOWISE thermal infrared data (see, e.g., Mainzer et al. 2011ApJ...736..100M, and Masiero et al. 2014, Cat. J/ApJ/791/121). The table contains the best-fitting values of size and beaming parameter. We note that the beaming parameter is a strictly positive quantity, but a negative sign is given to indicate whenever we could not fit it and had to assume a default value. We also provide the visible geometric albedos computed from the diameter and the tabulated absolute magnitudes. Minimum relative errors of 10, 15, and 20 percent should be considered for size, beaming parameter and albedo in those cases for which the beaming parameter could be fitted. Otherwise, the minimum relative errors in size and albedo increase to 20 and 40 percent (see, e.g., Mainzer et al. 2011ApJ...736..100M). The asteroid absolute magnitudes and slope parameters retrieved from the Minor Planet Center (MPC) are included, as well as the number of observations used in each WISE band (nW2, nW3, nW4) and the corresponding average values of heliocentric and geocentric distances and phase angle of the observations. The ephemerides were retrieved from the MIRIADE service (http://vo.imcce.fr/webservices/miriade/?ephemph). (1 data file).

Surface albedo observations at Gusev Crater and Meridiani Planum, Mars

NASA Astrophysics Data System (ADS)

Bell, J. F.; Rice, M. S.; Johnson, J. R.; Hare, T. M.

2008-05-01

During the Mars Exploration Rover mission, the Pancam instrument has periodically acquired large-scale panoramic images with its broadband (739 +/- 338 nm) filter in order to estimate the Lambert bolometric albedo of the surface along each rover's traverse. In this work we present the full suite of such estimated albedo values measured to date by the Spirit and Opportunity rovers along their traverses in Gusev Crater and Meridiani Planum, respectively. We include estimated bolometric albedo values of individual surface features (e.g., outcrops, dusty plains, aeolian bed forms, wheel tracks, light-toned soils, and crater walls) as well as overall surface averages of the 43 total panoramic albedo data sets acquired to date. We also present comparisons to estimated Lambert albedo values taken from the Mars Global Surveyor Mars Orbiter Camera (MOC) along the rovers' traverses, and to the large-scale bolometric albedos of the sites from the Viking Orbiter Infrared Thermal Mapper (IRTM) and Mars Global Surveyor/Thermal Emission Spectrometer (TES). The ranges of Pancam-derived albedos at Gusev Crater (0.14 to 0.25) and in Meridiani Planum (0.10 to 0.18) are in good agreement with IRTM, TES, and MOC orbital measurements. These data sets will be a useful tool and benchmark for future investigations of albedo variations with time, including measurements from orbital instruments like the Context Camera and High Resolution Imaging Science Experiment on Mars Reconnaissance Orbiter. Long-term, accurate albedo measurements could also be important for future efforts in climate modeling as well as for studies of active surface processes.

Impacts of Synoptic Weather Patterns on Snow Albedo at Sites in New England

NASA Astrophysics Data System (ADS)

Adolph, A. C.; Albert, M. R.; Lazarcik, J.; Dibb, J. E.; Amante, J.; Price, A. N.

2015-12-01

Winter snow in the northeastern United States has changed over the last several decades, resulting in shallower snow packs, fewer days of snow cover and increasing precipitation falling as rain in the winter. In addition to these changes which cause reductions in surface albedo, increasing winter temperatures also lead to more rapid snow grain growth, resulting in decreased snow reflectivity. We present in-situ measurements and analyses to test the sensitivity of seasonal snow albedo to varying weather conditions at sites in New England. In particular, we investigate the impact of temperature on snow albedo through melt and grain growth, the impact of precipitation event frequency on albedo through snow "freshening," and the impact of storm path on snow structure and snow albedo. Over three winter seasons between 2013 and 2015, in-situ snow characterization measurements were made at three non-forested sites across New Hampshire. These near-daily measurements include spectrally resolved albedo, snow optical grain size determined through contact spectroscopy, snow depth, snow density and local meteorological parameters. Combining this information with storm tracks derived from HYSPLIT modeling, we quantify the current sensitivity of northeastern US snow albedo to temperature as well as precipitation type, frequency and path. Our analysis shows that southerly winter storms result in snow with a significantly lower albedo than storms which come from across the continental US or the Atlantic Ocean. Interannual variability in temperature and statewide spatial variability in snowfall rates at our sites show the relative importance of snowfall amount and temperatures in albedo evolution over the course of the winter.

Improvement of Mars surface snow albedo modeling in LMD Mars GCM with SNICAR

NASA Astrophysics Data System (ADS)

Singh, D.; Flanner, M.; Millour, E.

2017-12-01

The current version of Laboratoire de Météorologie Dynamique (LMD) Mars GCM (original-MGCM) uses annually repeating (prescribed) albedo values from the Thermal Emission Spectrometer observations. We integrate the Snow, Ice, and Aerosol Radiation (SNICAR) model with MGCM (SNICAR-MGCM) to prognostically determine H2O and CO2 ice cap albedos interactively in the model. Over snow-covered regions mean SNICAR-MGCM albedo is higher by about 0.034 than original-MGCM. Changes in albedo and surface dust content also impact the shortwave energy flux at the surface. SNICAR-MGCM model simulates a change of -1.26 W/m2 shortwave flux on a global scale. Globally, net CO2 ice deposition increases by about 4% over one Martian annual cycle as compared to original-MGCM simulations. SNICAR integration reduces the net mean global surface temperature, and the global surface pressure of Mars by about 0.87% and 2.5% respectively. Changes in albedo also show a similar distribution as dust deposition over the globe. The SNICAR-MGCM model generates albedos with higher sensitivity to surface dust content as compared to original-MGCM. For snow-covered regions, we improve the correlation between albedo and optical depth of dust from -0.91 to -0.97 with SNICAR-MGCM as compared to original-MGCM. Using new diagnostic capabilities with this model, we find that cryospheric surfaces (with dust) increase the global surface albedo of Mars by 0.022. The cryospheric effect is severely muted by dust in snow, however, which acts to decrease the planet-mean surface albedo by 0.06.

Examples of cooler reflective streets for urban heat-island mitigation : Portland cement concrete and chip seals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pomerantz, M.; Akbari, H.; Chang, S.-C.

Part of the urban heat island effect can be attributed to dark pavements that are commonly used on streets and parking lots. In this paper we consider two light colored, hence cooler, alternative paving materials that are in actual use in cities today. These are Portland cement concrete (PCC) pavements and chip seals. We report measurements of the albedos of some PCC and chip sealed pavements in the San Francisco Bay Area. The albedos of the PCC pavements ranged from about 0.18 to 0.35. The temperatures of some PCC pavements are also measured and calculated. We then consider how themore » albedos of the constituent materials of the PCC (stone, sand and cement) contribute to the albedos of the resulting finished concrete. The albedos of a set of chip sealed pavements in San Jose, CA, were measured and correlated with the times of their placement. It is found that the albedos decrease with age (and use) but remain higher than that of standard asphalt concrete (AC) for about five years. After t hat, the albedos of the chip seals are about 0.12, similar to aged AC. The fact that many PCC pavements have albedos at least twice as high as aged AC suggests that it is possible to have pavement albedos that remain high for many years.« less

Topographic Controls on Southern California Ecosystem Function and Post-fire Recovery: a Satellite and Near-surface Remote Sensing Approach

NASA Astrophysics Data System (ADS)

Azzari, George

Southern Californian wildfires can influence climate in a variety of ways, including changes in surface albedo, emission of greenhouse gases and aerosols, and the production of tropospheric ozone. Ecosystem post-fire recovery plays a key role in determining the strength, duration, and relative importance of these climate forcing agents. Southern California's ecosystems vary markedly with topography, creating sharp transitions with elevation, aspect, and slope. Little is known about the ways topography influences ecosystem properties and function, particularly in the context of post-fire recovery. We combined images from the USGS satellite Landsat 5 with flux tower measurements to analyze pre- and post-fire albedo and carbon exchanged by Southern California's ecosystems in the Santa Ana Mountains. We reduced the sources of external variability in Landsat images using several correction methods for topographic and bidirectional effects. We used time series of corrected images to infer the Net Ecosystem Exchange and surface albedo, and calculated the radiative forcing due to CO2 emissions and albedo changes. We analyzed the patterns of recovery and radiative forcing on north- and south-facing slopes, stratified by vegetation classes including grassland, coastal sage scrub, chaparral, and evergreen oak forest. We found that topography strongly influenced post-fire recovery and radiative forcing. Field observations are often limited by the difficulty of collecting ground validation data. Current instrumentation networks do not provide adequate spatial resolution for landscape-level analysis. The deployment of consumer-market technology could reduce the cost of near-surface measurements, allowing the installation of finer-scale instrument networks. We tested the performance of the Microsoft Kinect sensor for measuring vegetation structure. We used Kinect to acquire 3D vegetation point clouds in the field, and used these data to compute plant height, crown diameter, and volume. We found good agreement between Kinect-derived and manual measurements.

Aerosol optical properties measurements by a CAPS single scattering albedo monitor: Comparisons between summer and winter in Beijing, China

NASA Astrophysics Data System (ADS)

Han, Tingting; Xu, Weiqi; Li, Jie; Freedman, Andrew; Zhao, Jian; Wang, Qingqing; Chen, Chen; Zhang, Yingjie; Wang, Zifa; Fu, Pingqing; Liu, Xingang; Sun, Yele

2017-02-01

Aerosol optical properties were measured in Beijing in summer and winter using a state-of-the-art cavity attenuated phase shift single scattering albedo monitor (CAPS PMssa) along with aerosol composition measurements by aerosol mass spectrometers and aethalometers. The SSA directly measured by the CAPS PMssa showed overall agreements with those derived from colocated measurements. However, substantial differences were observed during periods with low SSA values in both summer and winter, suggesting that interpretation of low SSA values needs to be cautious. The average (±σ) extinction coefficient (bext) and absorption coefficient (bap) were 336 (±343) Mm-1 and 44 (±41) Mm-1, respectively, during wintertime, which were approximately twice those observed in summer, while the average SSA was relatively similar, 0.86 (±0.06) and 0.85 (±0.04) in summer and winter, respectively. Further analysis showed that the variations in SSA can be approximately parameterized as a function of mass fraction of secondary particulate matter (fSPM), which is SSA = 0.74 + 0.19 × fSPM (fSPM > 0.3, r2 = 0.85). The contributions of aerosol species to extinction coefficients during the two seasons were also estimated. Our results showed that the light extinction was dominantly contributed by ammonium sulfate (30%) and secondary organic aerosol (22%) in summer, while organic aerosol was the largest contributor (51%) in winter. Consistently, SPM played the major role in visibility degradation in both seasons by contributing 70% of the total extinction.

Attenuation of Ultraviolet Radiation by Dust in Interstellar Clouds

NASA Astrophysics Data System (ADS)

Escalante, V.

1994-07-01

Se han obtenido soluciones de la ecuación de transporte para la dispersión coherente, no conservativa y anisotrópica para estimar la precisión de métodos aproximados, usados en modelos de nubes en que la luz es atenuada principalmente por el polvo. En los cálculos se ha aplicado el metodo de armónicos esféricos para distintos parámetros del polvo. Se ha explorado la posibilidad de descubrir cambios en las caracterísiticas del polvo mediante observaciones de regiones fotodisociadas. Se muestra que para altos valores del albedo de dispersión simple y del parametro de asimetria de Ia función de fase que son adecuados para el polvo galáctico, no es posible determinar variaciones de más de un factor de 2 en el cociente de gas a polvo. Solutions to the transfer equation for coherent, non-conservative, anisotropic scattering have been obtained in order to estimate the accuracy of approximate methods used in models of clouds where light is attenuated mostly by dust. In the calculations the spherical harmonic method has been applied for different grain parameters. The possibility of discovering changes of dust characteristics through observations of photodissociation regions has been considered. It is shown that for the high values of the single scattering albedo and the asymmetry parameter of the phase function for redistribution that appear to be appropriate for galactic dust, it is not possible to determine variations of more than a factor of 2 in the gas to dust ratio.

4STAR Sky-Scanning Retrievals of Aerosol Intensive Optical Properties from Multiple Field Campaigns with Detailed Comparisons of SSA Reported During SEAC4RS

NASA Technical Reports Server (NTRS)

Flynn, Connor; Dahlgren, R. P.; Dunagan, S.; Johnson, R.; Kacenelenbogen, M.; LeBlanc, S.; Livingston, J.; Redemann, J.; Schmid, B.; Segal Rozenhaimer, M.;

Evaluation of the global MODIS 30 arc-second spatially and temporally complete snow-free land surface albedo and reflectance anisotropy dataset

NASA Astrophysics Data System (ADS)

Sun, Qingsong; Wang, Zhuosen; Li, Zhan; Erb, Angela; Schaaf, Crystal B.

2017-06-01

Land surface albedo is an essential variable for surface energy and climate modeling as it describes the proportion of incident solar radiant flux that is reflected from the Earth's surface. To capture the temporal variability and spatial heterogeneity of the land surface, satellite remote sensing must be used to monitor albedo accurately at a global scale. However, large data gaps caused by cloud or ephemeral snow have slowed the adoption of satellite albedo products by the climate modeling community. To address the needs of this community, we used a number of temporal and spatial gap-filling strategies to improve the spatial and temporal coverage of the global land surface MODIS BRDF, albedo and NBAR products. A rigorous evaluation of the gap-filled values shows good agreement with original high quality data (RMSE = 0.027 for the NIR band albedo, 0.020 for the red band albedo). This global snow-free and cloud-free MODIS BRDF and albedo dataset (established from 2001 to 2015) offers unique opportunities to monitor and assess the impact of the changes on the Earth's land surface.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Masiero, Joseph R.; Mainzer, A. K.; Nugent, C. R.

We present revised near-infrared albedo fits of 2835 main-belt asteroids observed by WISE/NEOWISE over the course of its fully cryogenic survey in 2010. These fits are derived from reflected-light near-infrared images taken simultaneously with thermal emission measurements, allowing for more accurate measurements of the near-infrared albedos than is possible for visible albedo measurements. Because our sample requires reflected light measurements, it undersamples small, low-albedo asteroids, as well as those with blue spectral slopes across the wavelengths investigated. We find that the main belt separates into three distinct groups of 6%, 16%, and 40% reflectance at 3.4 μm. Conversely, the 4.6more » μm albedo distribution spans the full range of possible values with no clear grouping. Asteroid families show a narrow distribution of 3.4 μm albedos within each family that map to one of the three observed groupings, with the (221) Eos family being the sole family associated with the 16% reflectance 3.4 μm albedo group. We show that near-infrared albedos derived from simultaneous thermal emission and reflected light measurements are important indicators of asteroid taxonomy and can identify interesting targets for spectroscopic follow-up.« less

Albedo Boundary

NASA Technical Reports Server (NTRS)

2003-01-01

MGS MOC Release No. MOC2-510, 11 October 2003

The sharp, nearly straight line that runs diagonally across the center of this April 2003 Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image is an albedo boundary. Albedois a term that refers to reflectance of sunlight. A surface with a low albedo is one that appears dark because it reflects less light than a high albedo (bright) surface. On Mars, albedo boundaries occur between two materials of differing texture, particle size, or composition, or some combination of these three factors. The boundary shown here is remarkable because it is so sharp and straight. This is caused by wind. Most likely, the entire surface was once covered with the lower-albedo (darker) material that is now seen in the upper half of the image. At some later time, wind stripped away this darker material from the surfaces in the lower half of the image. The difference in albedo here might be related to composition, and possibly particle size. This picture is located near the southwest rim of Schiaparelli Basin at 5.5oS, 345.9oW. The picture covers an area 3 km (1.9 mi) wide and is illuminated by sunlight from the left.

Field Measured Spectral Albedo-Four Years of Data from the Western U.S. Prairie

NASA Astrophysics Data System (ADS)

Michalsky, Joseph J.; Hodges, Gary B.

2013-01-01

This paper presents an initial look at four years of spectral measurements used to calculate albedo for the Colorado prairie just east of the Rocky Mountain range foothills. Some issues associated with calculating broadband albedo from thermopile sensors are discussed demonstrating that uncorrected instrument issues have led to incorrect conclusions. Normalized Difference Vegetative Index (NDVI) is defined for the spectral instruments in this study and used to demonstrate the dramatic changes that can be monitored with this very sensitive product. Examples of albedo wavelength and solar-zenith angle dependence for different stages of vegetative growth and senescence are presented. The spectral albedo of fresh snow and its spectral and solar-zenith angle dependence are discussed and contrasted with other studies of these dependencies. We conclude that fresh snow is consistent with a Lambertian reflector over the solar incidence angles measured; this is contrary to most snow albedo results. Even a slope of a degree or two in the viewed surface can explain the asymmetry in the morning and afternoon albedos for snow and vegetation. Plans for extending these spectral measurements for albedo to longer wavelengths and to additional sites are described.

Climate changes impact the surface albedo of a forest ecosystem based on MODIS satellite data

NASA Astrophysics Data System (ADS)

Zoran, M. A.; Nemuc, A. V.

2007-10-01

Surface albedo is one of the most important biophysical parameter responsible for energy balance control and the surface temperature and boundary-layer structure of the atmosphere. Forest land surface albedo is also highly variable temporally showing both diurnal as well as seasonal variations. In forest systems, albedo controls the microclimate conditions which affects ecosystem physical, physiological, and biogeochemical processes such as energy balance, evapotranspiration, photosynthesis. Due to anthropogenic and natural factors, land cover and land use changes result is the land surfaces albedo change. The main aim of this paper is to investigate the albedo patterns due to the impact of atmospheric pollution and climate variations of a forest ecosystem Branesti-Cernica, placed to the North-East of Bucharest city, Romania based on satellite Landsat ETM+, IKONOS and MODIS data and climate station observations. Our study focuses on 3 years of data (2003-2005), each of which had a different climatic regime. As the physical climate system is very sensitive to surface albedo, forest ecosystems could significantly feedback to the projected climate change modeling scenarios through albedo changes. The results of this research have a number of applications in weather forecasting, climate change, and forest ecosystem studies.

A model predicting the evolution of ice particle size spectra and radiative properties of cirrus clouds. Part 2: Dependence of absorption and extinction on ice crystal morphology

NASA Technical Reports Server (NTRS)

Mitchell, David L.; Arnott, W. Patrick

1994-01-01

This study builds upon the microphysical modeling described in Part 1 by deriving formulations for the extinction and absorption coefficients in terms of the size distribution parameters predicted from the micro-physical model. The optical depth and single scatter albedo of a cirrus cloud can then be determined, which, along with the asymmetry parameter, are the input parameters needed by cloud radiation models. Through the use of anomalous diffraction theory, analytical expressions were developed describing the absorption and extinction coefficients and the single scatter albedo as functions of size distribution parameters, ice crystal shapes (or habits), wavelength, and refractive index. The extinction coefficient was formulated in terms of the projected area of the size distribution, while the absorption coefficient was formulated in terms of both the projected area and mass of the size distribution. These properties were formulated as explicit functions of ice crystal geometry and were not based on an 'effective radius.' Based on simulations of the second cirrus case study described in Part 1, absorption coefficients predicted in the near infrared for hexagonal columns and rosettes were up to 47% and 71% lower, respectively, than absorption coefficients predicted by using equivalent area spheres. This resulted in single scatter albedos in the near-infrared that were considerably greater than those predicted by the equivalent area sphere method. Reflectances in this region should therefore be underestimated using the equivalent area sphere approach. Cloud optical depth was found to depend on ice crystal habit. When the simulated cirrus cloud contained only bullet rosettes, the optical depth was 142% greater than when the cloud contained only hexagonal columns. This increase produced a doubling in cloud albedo. In the near-infrared (IR), the single scatter albedo also exhibited a significant dependence on ice crystal habit. More research is needed on the geometrical properties of ice crystals before the influence of ice crystal shape on cirrus radiative properties can be adequately understood. This study provides a way of coupling the radiative properties of absorption, extinction, and single scatter albedo to the microphysical properties of cirrus clouds. The dependence of extinction and absorption on ice crystal shape was not just due to geometrical differences between crystal types, but was also due to the effect these differences had on the evolution of ice particle size spectra. The ice particle growth model in Part 1 and the radiative properties treated here are based on analytical formulations, and thus represent a computationally efficient means of modeling the microphysical and radiative properties of cirrus clouds.

Albedo Drop on the Greenland Ice Sheet: Relative Impacts of Wet and Dry Snow Processes

NASA Astrophysics Data System (ADS)

Chen, J.; Polashenski, C.

2014-12-01

The energy balance of the Greenland Ice Sheet (GIS) is strongly impacted by changes in snow albedo. MODIS (Moderate Resolution Imaging Spectroradiometer) observations indicate that the GIS albedo has dropped since the early part of this century. We analyze data from the MODIS products MOD10A1 for broadband snow albedo and MOD09A1 for surface spectral reflectance since 2001 to better explain the physical mechanisms driving these changes. The MODIS products are filtered, and the data is masked using microwave-derived surface melt maps to isolate albedo changes due to dry snow processes from those driven by melt impacts. Results show that the majority of recent changes in the GIS albedo - even at high elevations - are driven by snow wetting rather than dry snow processes such as grain metamorphosis and aerosol impurity deposition. The spectral signature of the smaller changes occurring within dry snow areas suggests that grain metamorphosis dominates the albedo decline in these regions.

Postfire influences of snag attrition on albedo and radiative forcing

NASA Astrophysics Data System (ADS)

O'Halloran, Thomas L.; Acker, Steven A.; Joerger, Verena M.; Kertis, Jane; Law, Beverly E.

2014-12-01

This paper examines albedo perturbation and radiative forcing after a high-severity fire in a mature forest in the Oregon Cascade Range. Correlations between postfire albedo and seedling, sapling, and snag (standing dead tree) density were investigated across fire severity classes and seasons for years 4-15 after fire. Albedo perturbation was 14 times larger in winter compared to summer and increased with fire severity class for the first several years. Albedo perturbation increased linearly with time over the study period. Correlations between albedo perturbations and the vegetation densities were strongest with snags, and significant in all fire classes in both summer and winter (R < -0.92, p < 0.01). The resulting annual radiative forcing at the top of the atmosphere became more negative linearly at a rate of -0.86 W m-2 yr-1, reaching -15 W m-2 in year 15 after fire. This suggests that snags can be the dominant controller of postfire albedo on decadal time scales.

Surface features on Mars: Ground-based albedo and radar compared with Mariner 9 topography

NASA Technical Reports Server (NTRS)

Frey, H.

1973-01-01

Earth-based albedo maps of Mars were compared with Mariner 9 television data and ground-based radar profiles to investigate the nature of the bright and dark albedo features. Little correlation was found except at the boundaries of classical albedo features, where some topographic control is indicated. Wind-blown dust models for seasonal and secular albedo variations are supported, but it is not clear whether the fines are derived from bright or dark parent rock. Mars, like the Earth and Moon, has probably generated two distinct types of crustal material.

Natural versus anthropogenic factors affecting low-level cloud albedo over the North Atlantic

NASA Technical Reports Server (NTRS)

Falkowski, Paul G.; Kim, Yongseung; Kolber, Zbigniew; Wilson, Cara; Wirick, Creighton; Cess, Robert

1992-01-01

Cloud albedo plays a key role in regulating earth's climate. Cloud albedo depends on column-integrated liquid water content and the density of cloud condensation nuclei, which consists primarily of submicrometer-sized aerosol sulfate particles. A comparison of two independent satellite data sets suggests that, although anthropogenic sulfate emissions may enhance cloud albedo immediately adjacent to the east coast of the United States, over the central North Atlantic Ocean the variability in albedo can be largely accounted for by natural marine and atmospheric processes that probably have remained relatively constant since the beginning of the industrial revolution.

Putting the Capital 'A' in CoCoRAHS: A Pilot Program to Measure Albedo using the Community Collaborative Rain, Hail, and Snow (CoCoRaHS) Network

NASA Astrophysics Data System (ADS)

Burakowski, E. A.; Stampone, M. D.; Wake, C. P.; Dibb, J. E.

2012-12-01

The Community Collaborative Rain, Hail, and Snow (CoCoRaHS) Network, started in 1998 as a community-based network of volunteer weather observer in Colorado, is the single largest provider of daily precipitation observations in the United States. We embrace the CoCoRaHS mission to use low-cost measurement tools, provide training and education, and utilize an interactive website to collect high quality albedo data for research and education applications. We trained a select sub-set of CoCoRaHS's eighteen most enthusiastic, self-proclaimed 'weather nuts' in the state of New Hampshire to collect surface albedo, snow depth, and snow density measurements between 23-Nov-2011 and 15-Mar-2012. At less than 700 per observer, the low-cost albedo data falls within ±0.05 of albedo values collected from a First Class Kipp and Zonen Albedometer (CMA6) at local solar noon. CoCoRaHS albedo values range from 0.99 for fresh snow to 0.34 for shallow, aged snow. Snow-free albedo ranges from 0.09 to 0.39, depending on ground cover. Albedo is found to increase logarithmically with snow depth and decrease linearly with snow density. The latter relationship with snow density is inferred to be a proxy for increasing snow grain size as snowpack ages and compacts, supported by spectral albedo measurements collected with an ASD FieldSpec4 spectrometer. The newly established albedo network also serves as a development test bed for interactive online mapping and graphing applications for CoCoRaHS observers to investigate spatial and temporal patterns in albedo, snow depth, and snow density (www.cocorahs-albedo.org). The 2012-2013 field season will include low-cost infrared temperature guns (<40 each) to investigate the relationship between surface albedo and skin temperature. We have also recruited middle- and high-schools as volunteer observers and are working with the teachers to develop curriculum and lesson plans that utilize the low-cost measurement tools provided by CoCoRAHS. CoCoRAHS data will provide critical spatially distributed measurements of surface data that will be used to validate and improve land surface modeling of New Hampshire climate under different land cover scenarios. Building on the success of the first season, the newly established albedo network shows promise to put the capital 'A' in CoCoRAHS.Figure 1. (a) Map of Community Collaborative Rain, Hail, and Snow (CoCoRAHS) volunteers participating in the pilot albedo project, and (b) CoCoRAHS snow measurement kit.

Global warming related transient albedo feedback in the Arctic and its relation to the seasonality of sea ice

NASA Astrophysics Data System (ADS)

Andry, Olivier; Bintanja, Richard; Hazeleger, Wilco

2015-04-01

The Arctic is warming two to three times faster than the global average. Arctic sea ice cover is very sensitive to this warming and has reached historic minima in late summer in recent years (i.e. 2007, 2012). Considering that the Arctic Ocean is mainly ice-covered and that the albedo of sea ice is very high compared to that of open water, the change in sea ice cover is very likely to have a strong impact on the local surface albedo feedback. Here we quantify the temporal changes in surface albedo feedback in response to global warming. Usually feedbacks are evaluated as being representative and constant for long time periods, but we show here that the strength of climate feedbacks in fact varies strongly with time. For instance, time series of the amplitude of the surface albedo feedback, derived from future climate simulations (CIMP5, RCP8.5 up to year 2300) using a kernel method, peaks around the year 2100. This maximum is likely caused by an increased seasonality in sea-ice cover that is inherently associated with sea ice retreat. We demonstrate that the Arctic average surface albedo has a strong seasonal signature with a maximum in spring and a minimum in late summer/autumn. In winter when incoming solar radiation is minimal the surface albedo doesn't have an important effect on the energy balance of the climate system. The annual mean surface albedo is thus determined by the seasonality of both downwelling shortwave radiation and sea ice cover. As sea ice cover reduces the seasonal signature is modified, the transient part from maximum sea ice cover to its minimum is shortened and sharpened. The sea ice cover is reduced when downwelling shortwave radiation is maximum and thus the annual surface albedo is drastically smaller. Consequently the change in annual surface albedo with time will become larger and so will the surface albedo feedback. We conclude that a stronger seasonality in sea ice leads to a stronger surface albedo feedback, which accelerates melting of sea ice. Hence, the change in seasonality and the associated change in feedback strength is an integral part of the positive surface albedo feedback leading to Arctic amplification and diminishing sea ice cover in the next century when global climate warms.

Albedo and its Relationship to Land Cover and the Urban Heat Island in the Boston Metropolitan Region

NASA Astrophysics Data System (ADS)

Trlica, A.; Hutyra, L.; Wang, J.; Schaaf, C.; Erb, A.

2016-12-01

The urban built environment creates key changes in the biophysical character of the landscape, including the creation of Urban Heat Islands (UHIs) with increased near-surface temperatures in and around cities. Alteration in surface albedo is believed to partially drive UHIs through greater absorption of solar energy, but few empirical studies have specifically quantified albedo across a heterogeneous urban landscape, or investigated linkages between albedo, the UHI, and other surface socio-biophysical characteristics at a high enough spatial resolution to discern urban-scale features. This study used data derived from observations by Landsat and other remote sensing platforms to measure albedo across a varied urban landscape centered on Boston, Massachusetts, and examined the relationship between albedo, several key indicators of urban surface character (canopy cover, impervious fraction, and population density) and land surface temperature at resolutions of both 30 and 500 m. Albedo tended to be lower in areas with highest urbanization intensity indicators compared to rural undeveloped areas, and areas with lower albedo tended also to have higher median daytime summer surface temperatures. A k-means classification utilizing all the data available for each pixel revealed several distinct patterns of urban land cover corresponding mainly to the density of population and constructed surfaces and their impact on tree canopy cover. Mean 30-m summer surface temperatures ranged from 40.0 °C (SD = 2.6) in urban core areas to 26.2 °C (SD = 1.1) in nearby forest, but we only observed correspondingly large albedo decreases in the highest density urban core, with mean albedo of 0.116 (SD = 0.015) compared with 0.155 (SD = 0.015) in forest. Observations show that lower albedo in the Boston metropolitan region may be an important component of the local UHI in the most densely built-up urban core regions, while the UHI temperature effect in less densely settled peripheral regions is more likely to be driven primarily by reduced evapotranspiration due to diminished tree canopy and greater impervious surface coverage. These results empirically characterize surface albedo across a suite of land cover categories and biophysical characteristics and reveal how albedo relates to surface temperatures in this urbanized region.

Albedo boundaries on Mars in 1972: Results from Mariner 9

USGS Publications Warehouse

Batson, R.M.; Inge, J.L.

1976-01-01

A map of "albedo" boundaries (light and dark markings) on Mars was prepared from Mariner 9 images. After special digital processing, these pictures provide detailed locations of albedo boundaries, which is significant in interpreting recent eolian activity. Derivation of absolute albedo values from the spacecraft data was not attempted. The map correlates well with telescopic observations of Mars after the 1971 dust storm. ?? 1976.

Evaluation of MODIS albedo product (MCD43A) over grassland, agriculture and forest surface types during dormant and snow-covered periods

Treesearch

Zhuosen Wang; Crystal B. Schaaf; Alan H. Strahler; Mark J. Chopping; Miguel O. Román; Yanmin Shuai; Curtis E. Woodcock; David Y. Hollinger; David R. Fitzjarrald

2014-01-01

This study assesses the Moderate-resolution Imaging Spectroradiometer (MODIS) BRDF/albedo 8 day standard product and products from the daily Direct Broadcast BRDF/albedo algorithm, and shows that these products agree well with ground-based albedo measurements during the more difficult periods of vegetation dormancy and snow cover. Cropland, grassland, deciduous and...

Snow driven Radiative Forcing in High Latitude Areas of Disturbance Using Higher Resolution Albedo Products from Landsat and Sentinel-2

NASA Astrophysics Data System (ADS)

Erb, A.; Li, Z.; Schaaf, C.; Wang, Z.; Rogers, B. M.

2017-12-01

Land surface albedo plays an important role in the surface energy budget and radiative forcing by determining the proportion of absorbed incoming solar radiation available to drive photosynthesis and surface heating. In Arctic regions, albedo is particularly sensitive to land cover and land use change (LCLUC) and modeling efforts have shown it to be the primary driver of effective radiative forcing from the biogeophysical effects of LCLUC. In boreal forests, the effects of these changes are complicated during snow covered periods when newly exposed, highly reflective snow can serve as the primary driver of radiative forcing. In Arctic biomes disturbance scars from fire, pest and harvest can remain in the landscape for long periods of time. As such, understanding the magnitude and persistence of these disturbances, especially in the shoulder seasons, is critical. The Landsat and Sentinel-2 Albedo Products couple 30m and 20m surface reflectances with concurrent 500m BRDF Products from the MODerate resolution Imaging Spectroradiometer (MODIS). The 12 bit radiometric fidelity of Sentinel-2 and Landsat-8 allow for the inclusion of high-quality, unsaturated albedo calculations over snow covered surfaces at scales more compatible with fragmented landscapes. Recent work on the early spring albedo of fire scars has illustrated significant post-fire spatial heterogeneity of burn severity at the landscape scale and highlights the need for a finer spatial resolution albedo record. The increased temporal resolution provided by multiple satellite instruments also allows for a better understanding of albedo dynamics during the dynamic shoulder seasons and in historically difficult high latitude locations where persistent cloud cover limits high quality retrievals. Here we present how changes in the early spring albedo of recent boreal forest disturbance in Alaska and central Canada affects landscape-scale radiative forcing. We take advantage of the long historical Landsat record to examine pre-disturbance albedo trends and to link historical land cover and disturbance history to post-disturbance early spring albedo values. We examine the impact of landscape heterogeneity on albedo in the growing and dormant seasons and quantify the effects of snow exposure changes from over-story canopy loss.

A Comparison of the Seasonal Change of Albedo across Glaciers and Ice-Covered Lakes of the Taylor Valley, Antarctica

NASA Astrophysics Data System (ADS)

Gooseff, M. N.; Bergstrom, A.

2016-12-01

The Dry Valleys of Antarctica are a polar desert ecosystem consisting of piedmont and alpine glaciers, ice-covered lakes, and vast expanses of bare soil. The ecosystem is highly dependent on glacial melt a water source. Because average summer temperatures are close to freezing, glacier ice and lake ice are very closely linked to the energy balance. A slight increase in incoming radiation or decrease in albedo can have large effects on the timing and volume of available liquid water. However, we have yet to fully characterize the seasonal evolution of albedo in the valleys. In this study, we used a camera, gps, and short wave radiometer to characterize the albedo within and across landscape types in the Taylor Valley. These instruments were attached to a helicopter and flown on a prescribed path along the valley at approximately 300 feet above the ground surface five different times throughout the season from mid-November to mid-January, 2015-2016. We used these data to calculate the albedo of each glacier, lake, and the soil surface of the lake basins in the valley for each flight. As expected, we found that all landscape types had significantly different albedo, with the glaciers consistently the highest throughout the season and the bare soils the lowest (p-value < 0.05). We hypothesized that albedo would decrease throughout the season with snow melt and increasing sediment exposure on the glacier and lake surfaces. However, small snow events (< 3 cm) caused somewhat persistent high albedo on the lakes and glaciers. Furthermore, there was a range in albedo across glaciers and each responded to seasonal snow and melt differently. These findings highlight the importance of understanding the spatial and temporal variability in albedo and the close coupling of climate and landscape response. We can use this new understanding of landscape albedo to better predict how the Dry Valley ecosystems will respond to changing climate at the basin scale.

a Physical Parameterization of Snow Albedo for Use in Climate Models.

NASA Astrophysics Data System (ADS)

Marshall, Susan Elaine

The albedo of a natural snowcover is highly variable ranging from 90 percent for clean, new snow to 30 percent for old, dirty snow. This range in albedo represents a difference in surface energy absorption of 10 to 70 percent of incident solar radiation. Most general circulation models (GCMs) fail to calculate the surface snow albedo accurately, yet the results of these models are sensitive to the assumed value of the snow albedo. This study replaces the current simple empirical parameterizations of snow albedo with a physically-based parameterization which is accurate (within +/- 3% of theoretical estimates) yet efficient to compute. The parameterization is designed as a FORTRAN subroutine (called SNOALB) which can be easily implemented into model code. The subroutine requires less then 0.02 seconds of computer time (CRAY X-MP) per call and adds only one new parameter to the model calculations, the snow grain size. The snow grain size can be calculated according to one of the two methods offered in this thesis. All other input variables to the subroutine are available from a climate model. The subroutine calculates a visible, near-infrared and solar (0.2-5 μm) snow albedo and offers a choice of two wavelengths (0.7 and 0.9 mu m) at which the solar spectrum is separated into the visible and near-infrared components. The parameterization is incorporated into the National Center for Atmospheric Research (NCAR) Community Climate Model, version 1 (CCM1), and the results of a five -year, seasonal cycle, fixed hydrology experiment are compared to the current model snow albedo parameterization. The results show the SNOALB albedos to be comparable to the old CCM1 snow albedos for current climate conditions, with generally higher visible and lower near-infrared snow albedos using the new subroutine. However, this parameterization offers a greater predictability for climate change experiments outside the range of current snow conditions because it is physically-based and not tuned to current empirical results.

Validation of GEOLAND-2 Spot/vgt Albedo Products by Using Ceos Olive Methodology

NASA Astrophysics Data System (ADS)

Camacho de Coca, F.; Sanchez, J.; Schaaf, C.; Baret, F.; Weiss, M.; Cescatti, A.; Lacaze, R. N.

2012-12-01

This study evaluates the scientific merit of the global surface albedo products developed in the framework of the Geoland-2 project based on SPOT/VEGETATION observations. The methodology follows the OLIVE (On-Line Validation Exercise) approach supported by the CEOS Land Product Validation subgroup (calvalportal.ceos.org/cvp/web/olive). First, the spatial and temporal consistency of SPOT/VGT albedo products was assessed by intercomparison with reference global products (MODIS/Terra+Aqua and POLDER-3/PARASOL) for the period 2006-2007. A bulk statistical analysis over a global network of 420 homogeneous sites (BELMANIP-2) was performed and analyzed per biome types. Additional sites were included to study albedo under snow conditions. Second, the accuracy and realism of temporal variations were evaluated using a number of ground measurements from FLUXNET sites suitable for use in direct comparison to the co-located satellite data. Our results show that SPOT/VGT albedo products present reliable spatial and temporal distribution of retrievals. The SPOT/VGT albedo performs admirably with MODIS, with a mean bias and RMSE for the shortwave black-sky albedo over BELMANIP-2 sites lower than 0.006 and 0.03 (13% in relative terms) respectively, and even better for snow free pixels. Similar results were found for the white-sky albedo quantities. Discrepancies are larger when comparing with POLDER-3 products: for the shortwave black-sky albedo a mean bias of -0.014 and RMSE of 0.04 (20%) was found. This overall performance figures are however land-cover dependent and larger uncertainties were found over some biomes (or regions) or specific periods (e.g. winter in the north hemisphere). The comparison of SPOT/VGT blue-sky albedo estimates with ground measurements (mainly over Needle-leaf forest sites) show a RMSE of 0.04 and a bias of 0.003 when only snow-free pixels are considered. Moreover, this work shows that the OLIVE tool is also suitable for validation of global albedo products.

Evaluation of MODIS and VIIRS Albedo Products Using Ground and Airborne Measurements and Development of Ceos/Wgcv/Lpv Albedo Ecv Protocols

NASA Astrophysics Data System (ADS)

Wang, Z.; Roman, M. O.; Schaaf, C.; Sun, Q.; Liu, Y.; Saenz, E. J.; Gatebe, C. K.

2014-12-01

Surface albedo, defined as the ratio of the hemispheric reflected solar radiation flux to the incident flux upon the surface, is one of the essential climate variables and quantifies the radiation interaction between the atmosphere and the land surface. An absolute accuracy of 0.02-0.05 for global surface albedo is required by climate models. The MODerate resolution Imaging Spectroradiometer (MODIS) standard BRDF/albedo product makes use of a linear "kernel-driven" RossThick-LiSparse Reciprocal (RTLSR) BRDF model to describe the reflectance anisotropy. The surface albedo is calculated by integrating the BRDF over the above ground hemisphere. While MODIS Terra was launched in Dec 1999 and MODIS Aqua in 2002, the Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi-NPP satellite was launched more recently on October 28, 2011. Thus a long term record of BRDF, albedo and Nadir BRDF-Adjusted Reflectance (NBAR) products from VIIRS can be generated through MODIS heritage algorithms. Several investigations have evaluated the MODIS albedo products during the growing season, as well as during dormant and snow covered periods. The Land Product Validation (LPV) sub-group of the Committee on Earth Observation Satellites (CEOS) Working Group on Calibration and Validation (WGCV) aims to address the challenges associated with the validation of global land products. The validation of global surface radiation/albedo products is one of the LPV subgroup activities. In this research, a reference dataset covering various land surface types and vegetation structure is assembled to assess the accuracy of satellite albedo products. This dataset includes in situ data (Baseline Surface Radiation Network (BSRN), FLUXNET and Long Term Ecological Research network (LTER) etc.) and airborne measurements (e.g. Cloud Absorption Radiometer (CAR)). Spatially representative analysis is applied to each site to establish whether the ground measurements can adequately represent moderate spatial resolution remotely sensed albedo products.

Arctic sea ice albedo from AVHRR

NASA Technical Reports Server (NTRS)

Lindsay, R. W.; Rothrock, D. A.

1994-01-01

The seasonal cycle of surface albedo of sea ice in the Arctic is estimated from measurements made with the Advanced Very High Resolution Radiometer (AVHRR) on the polar-orbiting satellites NOAA-10 and NOAA-11. The albedos of 145 200-km-square cells are analyzed. The cells are from March through September 1989 and include only those for which the sun is more than 10 deg above the horizon. Cloud masking is performed manually. Corrections are applied for instrument calibration, nonisotropic reflection, atmospheric interference, narrowband to broadband conversion, and normalization to a common solar zenith angle. The estimated albedos are relative, with the instrument gain set to give an albedo of 0.80 for ice floes in March and April. The mean values for the cloud-free portions of individual cells range from 0.18 to 0.91. Monthly averages of cells in the central Arctic range from 0.76 in April to 0.47 in August. The monthly averages of the within-cell standard deviations in the central Arctic are 0.04 in April and 0.06 in September. The surface albedo and surface temperature are correlated most strongly in March (R = -0.77) with little correlation in the summer. The monthly average lead fraction is determined from the mean potential open water, a scaled representation of the temperature or albedo between 0.0 (for ice) and 1.0 (for water); in the central Arctic it rises from an average 0.025 in the spring to 0.06 in September. Sparse data on aerosols, ozone, and water vapor in the atmospheric column contribute uncertainties to instantaneous, area-average albedos of 0.13, 0.04, and 0.08. Uncertainties in monthly average albedos are not this large. Contemporaneous estimation of these variables could reduce the uncertainty in the estimated albedo considerably. The poor calibration of AVHRR channels 1 and 2 is another large impediment to making accurate albedo estimates.

Observations of Surfzone Albedo

NASA Astrophysics Data System (ADS)

Sinnett, G.; Feddersen, F.

2014-12-01

The surfzone environment (where waves break) contains several unique and previously unconsidered processes that affect the heat budget. Entering short-wave radiation is a dominant term in both shelf and surfzone heat budgets. In contrast to the shelf, however, depth limited wave breaking in the surfzone generates spray, whitewater and suspended sediments, elevating the surface albedo (ratio of reflected to incident short-wave radiation). Elevated albedo reduces the level of solar short-wave radiation entering the water, potentially resulting in less heating. Additionally, surfzone water quality is often impacted by fecal bacteria contamination. As bacteria mortality is related to short-wave solar radiation, elevated surfzone albedo could reduce pathogen mortality, impacting human health. Albedo in the open ocean has been frequently studied and parameterizations often consider solar zenith angle, wind speed and ocean chlorophyll concentration, producing albedo values typically near 0.06. However, surfzone albedo observations have been extremely sparse, yet show depth limited wave breaking may increase the albedo by nearly a factor of 10 up to 0.5. Here, we present findings from a field study at the Scripps Institution of Oceanography pier to observe the affect of waves on surfzone albedo. Concurrent measurements were taken with a four-way radiometer (to measure both downwelling and upwelling short-wave and long wave radiation) mounted above the surfzone. A co-located GoPro camera was used to relate visual aspects of the surfzone to measured reflectance, and wave height and period were observed with a bottom mounted pressure sensor in 5 m water depth just outside the surfzone. Wind speed and direction were observed on the pier 10 m above the water surface. Here, we will examine the surfzone albedo dependence on surfzone parameters, such as wave height.

Quantification of seasonal to annual mass balances from glacier surface albedo derived from optical satellite images, application on 30 glaciers in the French Alps for the period 2000-2015.

NASA Astrophysics Data System (ADS)

Davaze, Lucas; Rabatel, Antoine; Arnaud, Yves; Sirguey, Pascal; Six, Delphine; Letreguilly, Anne; Dumont, Marie

2017-04-01

Increasing the number of glaciers monitored for surface mass balance is very challenging, especially using laborious methods based on in situ data. Complementary methods are therefore required to quantify the surface mass balance of unmonitored glaciers. The current study relies on the so-called albedo method, based on the analysis of albedo maps retrieved from optical satellite imagery acquired since 2000 by the MODIS sensor, onboard of TERRA satellite. Recent studies performed on single glaciers in the French Alps, the Himalayas or the Southern Alps of New Zealand revealed substantial relationships between summer minimum glacier-wide surface albedo and annual mass balance, because this minimum surface albedo is directly related to accumulation-area ratio and the equilibrium-line altitude. On the basis of 30 glaciers located in the French Alps where annual surface mass balance are available, our study conducted on the period 2000-2015 confirms the robustness and reliability of the relationship between the summer minimum surface albedo and the annual surface mass balance. At the seasonal scale, the integrated summer surface albedo is significantly correlated with the summer mass balance of the six glaciers seasonally surveyed. For the winter season, four of the six glaciers showed a significant correlation when linking the winter surface mass balance and the integrated winter surface albedo, using glacier-dependent thresholds to filter the albedo signal. Sensitivity study on the computed cloud detection algorithm revealed high confidence in retrieved albedo maps. These results are promising to monitor both annual and seasonal glacier-wide surface mass balances of individual glaciers at a regional scale using optical satellite images.

Evaluation of MuSyQ land surface albedo based on LAnd surface Parameters VAlidation System (LAPVAS)

NASA Astrophysics Data System (ADS)

Dou, B.; Wen, J.; Xinwen, L.; Zhiming, F.; Wu, S.; Zhang, Y.

2016-12-01

satellite derived Land surface albedo is an essential climate variable which controls the earth energy budget and it can be used in applications such as climate change, hydrology, and numerical weather prediction. However, the accuracy and uncertainty of surface albedo products should be evaluated with a reliable reference truth data prior to applications. A new comprehensive and systemic project of china, called the Remote Sensing Application Network (CRSAN), has been launched recent years. Two subjects of this project is developing a Multi-source data Synergized Quantitative Remote Sensin g Production System ( MuSyQ ) and a Web-based validation system named LAnd surface remote sensing Product VAlidation System (LAPVAS) , which aims to generate a quantitative remote sensing product for ecosystem and environmental monitoring and validate them with a reference validation data and a standard validation system, respectively. Land surface BRDF/albedo is one of product datasets of MuSyQ which has a pentad period with 1km spatial resolution and is derived by Multi-sensor Combined BRDF Inversion ( MCBI ) Model. In this MuSyQ albedo evaluation, a multi-validation strategy is implemented by LAPVAS, including directly and multi-scale validation with field measured albedo and cross validation with MODIS albedo product with different land cover. The results reveal that MuSyQ albedo data with a 5-day temporal resolution is in higher sensibility and accuracy during land cover change period, e.g. snowing. But results without regard to snow or changed land cover, MuSyQ albedo generally is in similar accuracy with MODIS albedo and meet the climate modeling requirement of an absolute accuracy of 0.05.

Factors controlling the initiation of Snowball Earth events

NASA Astrophysics Data System (ADS)

Voigt, A.

2012-12-01

During the Neoproterozoic glaciations tropical continents were covered by active glaciers that extended down to sea level. To explain these glaciers, the Snowball Earth hypothesis assumes that oceans were completely sea-ice covered during these glaciation, but there is an ongoing debate whether or not some regions of the tropical oceans remained open. In this talk, I will describe past and ongoing climate modelling activities with the comprehensive coupled climate model ECHAM5/MPI-OM that identify and compare factors that control the initiation of Snowball Earth events. I first show that shifting the continents from their present-day location to their Marinoan (635 My BP) low-latitude location increases the planetary albedo, cools the climate, and thereby allows Snowball Earth initiation at higher levels of total solar irradiance and atmospheric CO2. I then present simulations with successively lowered bare sea-ice albedo, disabled sea-ice dynamics, and switched-off ocean heat transport. These simulations show that both lowering the bare sea-ice albedo and disabling sea-ice dynamics increase the critical sea-ice cover in ECHAM5/MPI-OM, but sea-ice dynamics due to strong equatorward sea-ice transport have a much larger influence on the critical CO2. Disabling sea-ice transport allows a state with sea-ice margin at 10 deg latitude by virtue of the Jormungand mechanism. The accumulation of snow on land, in combination with tropical land temperatures below or close to freezing, suggests that tropical land glaciers could easily form in such a state. However, in contrast to aquaplanet simulations without ocean heat transport, there is no sign of a Jormungand hysteresis in the coupled simulations. Ocean heat transport is not responsible for the lack of a Jormungand hysteresis in the coupled simulations. By relating the above findings to previous studies, I will outline promising future avenues of research on the initiation of Snowball Earth events. In particular, an improved understanding and modelling of sea-ice dynamics is needed.ea-ice cover as a function of CO2 for ECHAM5/MPI-OM simulations with high bare sea-ice albedo (black circles), low bare sea-ice albedo (blue squares), low bare sea-ice albedo and disabled sea-ice dynamics (red triangles), and low bare sea-ice albedo, disabled sea-ice dynamics and zero ocean heat transport (green diamonds). All simulations use Marinoan low-latitude continents and a solar constant reduced to 94% of its modern value.

Glacier albedo change and its relationship to surface temperature change from MODIS data: Queen Elizabeth Islands, Arctic Canada, 2001-2015

NASA Astrophysics Data System (ADS)

Mortimer, C.; Sharp, M. J.

2016-12-01

Glacier and ice cap surface albedo change over the Canadian High Arctic is assessed using measurements from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensors for the period 2001-2015. Mean summer black-sky broadband surface albedo (MCD43A3 v05) over all glaciated surfaces in the Queen Elizabeth Islands south of 80°N decreased at a rate of 0.0038 ± 0.0037 yr-1 over that period. The bulk of this albedo decrease occurred from 2008 to 2012 when mean summer albedo was anomalously low. Albedo declines were greatest in the west of the QEI and at lower elevations on the ice caps. The period 2005-2012 included some of the warmest summers in the region since at least the 1950s. Between 2001 and 2015, mean summer glacier surface temperatures for the QEI (south of 80°N), derived from MODIS data (MOD11A2 v05), increased at a rate of 0.034 ± 0.037 °C yr-1. Net shortwave energy is modulated by changes in the surface albedo and is the largest source of summer melt energy in the QEI. During 2001-2015, the summer albedo record was negatively correlated with the mean summer glacier surface temperature record across 91% of the region; clusters of positive correlations between surface temperature and albedo were observed at high elevations in eastern Ellesmere Island.

Dominance of grain size impacts on seasonal snow albedo at open sites in New Hampshire

NASA Astrophysics Data System (ADS)

Adolph, Alden C.; Albert, Mary R.; Lazarcik, James; Dibb, Jack E.; Amante, Jacqueline M.; Price, Andrea

2017-01-01

Snow cover serves as a major control on the surface energy budget in temperate regions due to its high reflectivity compared to underlying surfaces. Winter in the northeastern United States has changed over the last several decades, resulting in shallower snowpacks, fewer days of snow cover, and increasing precipitation falling as rain in the winter. As these climatic changes occur, it is imperative that we understand current controls on the evolution of seasonal snow albedo in the region. Over three winter seasons between 2013 and 2015, snow characterization measurements were made at three open sites across New Hampshire. These near-daily measurements include spectral albedo, snow optical grain size determined through contact spectroscopy, snow depth, snow density, black carbon content, local meteorological parameters, and analysis of storm trajectories using the Hybrid Single-Particle Lagrangian Integrated Trajectory model. Using analysis of variance, we determine that land-based winter storms result in marginally higher albedo than coastal storms or storms from the Atlantic Ocean. Through multiple regression analysis, we determine that snow grain size is significantly more important in albedo reduction than black carbon content or snow density. And finally, we present a parameterization of albedo based on days since snowfall and temperature that accounts for 52% of variance in albedo over all three sites and years. Our improved understanding of current controls on snow albedo in the region will allow for better assessment of potential response of seasonal snow albedo and snow cover to changing climate.

Inversion of the Earth spherical albedo from radiation-pressure

NASA Astrophysics Data System (ADS)

Wilkman, Olli; Herranen, Joonas; Näränen, Jyri; Virtanen, Jenni; Koivula, Hannu; Poutanen, Markku; Penttilä, Antti; Gritsevich, Maria; Muinonen, Karri

2017-04-01

We are studying the retrieval of the spherical albedo and net radiation of the Earth from the perturbations caused by the planet's radiation on the dynamics of its satellites. The spherical or Bond albedo gives the ratio of the fluxes incident on and scattered by the planet. The net radiation represents the net heat input into the planet's climate system and drives changes in its atmospheric, surface, and ocean temperatures. The ultimate aim of the study is inverting the problem and estimating the Earth albedo based on observations of satellites, simultaneously improving the space-geodetic positioning accuracy. Here we investigate the effect of the spherical albedo on satellite orbits with the help of a simplified model. We simulate the propagation of satellite orbits using a new simulation software. The simulation contains the main perturbing forces on medium and high Earth orbits, used by, e.g., navigation satellites, including the radiation pressure of reflected sunlight from the Earth. An arbitrary satellite shape model can be used, and the rotation of the satellite is modeled. In this first study, we use a box-wing satellite model with a simple surface BRDF. We also assume a diffusely reflecting Earth with a single global albedo value. We vary the Earth albedo and search for systematic effects on different orbits. Thereafter, we estimate the dependence of the albedo accuracy on the satellite positioning and timing data available. We show that the inversion of the spherical albedo with reasonable accuracy is feasible from the current space-geodetic measurements.

The first UV spectrum of a Uranian satellite - IUE observations of Oberon from 2650-3200 A

NASA Technical Reports Server (NTRS)

Stern, S. A.; Festou, M. C.; Van Santvoort, J.; Buratti, B. J.

1990-01-01

Using the International Ultraviolet Explorer (IUE) observatory, the first vacuum UV spectrum of Oberon was obtained. The data contain useful information in the spectral range 2650-3200 A. Oberon's UV geometric albedo is found to be flat and essentially featureless with an average value of p(UV) = 0.19 + or - 0.025, and making it possible to extend Oberon's phase curve into the opposite region.

Sunlight, Sea Ice, and the Ice Albedo Feedback in a Changing Arctic Sea Ice Cover

DTIC Science & Technology

2013-09-30

Sea Ice , and the Ice Albedo Feedback in a...COVERED 00-00-2013 to 00-00-2013 4. TITLE AND SUBTITLE Sunlight, Sea Ice , and the Ice Albedo Feedback in a Changing Arctic Sea Ice Cover 5a...during a period when incident solar irradiance is large increasing solar heat input to the ice . Seasonal sea ice typically has a smaller albedo

Albedo of Surface CO2 Deposits in Mars' Residual South Polar Cap

NASA Astrophysics Data System (ADS)

James, P. B.; Wolff, M. J.; Bonev, B.

2014-12-01

The albedo of surface CO2 deposits in the Residual South Polar Cap (RSPC) of Mars controls their net condensation / sublimation over a martian year and is therefore a crucial parameter in determining RSPC stability. The albedo used in previous analyses is obtained by dividing I/F, determined from radiometrically calibrated imaging data, by the cosine of the incidence angle. Because of atmospheric aerosols, the albedo calculated from I/F above the atmosphere is not the surface albedo that enters into stability considerations. In order to determine the surface albedo, we interpolate optical depths determined from CRISM EPF measurements to provide estimates of the dust and ice opacities over the RSPC (Wolff et al., 2009) and use these to determine the actual surface albedos from MARCI images using the radiative transport program DISORT (Stamnes et al., 1988). Assuming that dust is the only contributor to atmospheric opacity, the retrieved surface albedos for the longer wavelength MARCI filters in MY 28 and 29 are found to be consistent despite very different dust opacities in the two years (James et al., 2014). However, this model fails to reproduce the short wavelength behavior in early summer. We consider possible modifications of the dust only model that could explain the discrepancy.

Spectral Reflectance and Albedo of Snow-Covered Heterogeneous Landscapes in New Hampshire, USA: Comparison of Ground-based, Airborne Hyperspectral, and MODIS Satellite Data

NASA Astrophysics Data System (ADS)

Burakowski, E. A.; Ollinger, S. V.; Martin, M.; Lepine, L. C.; Hollinger, D. Y.; Dibb, J. E.

2013-12-01

This study evaluates the accuracy of hyperspectral imagery (HSI) and MODIS daily 500-m snow albedo over forested, deforested, and mixed land use types under snow-covered conditions in New Hampshire, USA. HSI spectral reflectance generally agrees well with tower-based measurements above a mixed forest canopy. Over cleared pasture, HSI spectral reflectance is lower than ground-based measurements collected using a spectrometer, and greatly underestimates reflectance at wavelengths less than 430 nm. Based on tower-based albedo measurements, HSI shortwave broadband albedo meets the absolute accuracy requirement of ×0.05 recommended for climate modeling. When HSI 5-m fine-resolution imagery is aggregated to MODIS 500-m resolution and integrated to shortwave broadband albedo, MOD10A1 daily snow-covered surface albedo exhibits a negative bias of -0.0033 and root mean square error (RMSE) of 0.067 compared to HSI shortwave broadband albedo, just outside the range of the absolute accuracy requirement of ×0.05 recommended for climate modeling. Spectral albedo collected over a deciduous broadleaf canopy under snow-covered and snow-free conditions will expand the existing spectral library and contribute to future validation efforts of multi-spectral remote sensing products (e.g., HyspIRI).

Estimation of shortwave hemispherical reflectance (albedo) from bidirectionally reflected radiance data

NASA Technical Reports Server (NTRS)

Starks, Patrick J.; Norman, John M.; Blad, Blaine L.; Walter-Shea, Elizabeth A.; Walthall, Charles L.

1991-01-01

An equation for estimating albedo from bidirectional reflectance data is proposed. The estimates of albedo are found to be greater than values obtained with simultaneous pyranometer measurements. Particular attention is given to potential sources of systematic errors including extrapolation of bidirectional reflectance data out to a view zenith angle of 90 deg, the use of inappropriate weighting coefficients in the numerator of the albedo equation, surface shadowing caused by the A-frame instrumentation used to measure the incoming and outgoing radiation fluxes, errors in estimates of the denominator of the proposed albedo equation, and a 'hot spot' contribution in bidirectional data measured by a modular multiband radiometer.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mainzer, A.; Bauer, J.; Masiero, J.

NASA's Wide-field Infrared Survey Explorer (WISE) spacecraft has been brought out of hibernation and has resumed surveying the sky at 3.4 and 4.6 μm. The scientific objectives of the NEOWISE reactivation mission are to detect, track, and characterize near-Earth asteroids and comets. The search for minor planets resumed on 2013 December 23, and the first new near-Earth object (NEO) was discovered 6 days later. As an infrared survey, NEOWISE detects asteroids based on their thermal emission and is equally sensitive to high and low albedo objects; consequently, NEOWISE-discovered NEOs tend to be large and dark. Over the course of itsmore » three-year mission, NEOWISE will determine radiometrically derived diameters and albedos for ∼2000 NEOs and tens of thousands of Main Belt asteroids. The 32 months of hibernation have had no significant effect on the mission's performance. Image quality, sensitivity, photometric and astrometric accuracy, completeness, and the rate of minor planet detections are all essentially unchanged from the prime mission's post-cryogenic phase.« less

Spectrophotometry and organic matter on Iapetus. 1: Composition models

NASA Technical Reports Server (NTRS)

Wilson, Peter D.; Sagan, Carl

1995-01-01

Iapetus shows a greater hemispheric albedo asymmetry than any other body in the solar system. Hapke scattering theory and optical constants measured in the laboratory are used to identify possible compositions for the dark material on the leading hemisphere of Iapetus. The materials considered are poly-HCN, kerogen, Murchison organic residue, Titan tholin, ice tholin, and water ice. Three-component mixtures of these materials are modeled in intraparticle mixture of 25% poly-HCN, 10% Murchison residue, and 65% water ice is found to best fit the spectrum, albedo, and phase behavior of the dark material. The Murchison residue and/or water ice can be replaced by kerogen and ice tholin, respectively, and still produce very good fits. Areal and particle mixtures of poly-HCN, Titan tholin, and either ice tholin or Murchison residue are also possible models. Poly-HCN is a necessary component in almost all good models. The presence of poly-HCN can be further tested by high-resolution observations near 4.5 micrometers.

Mars: Detaching of the Free Water Signature (FWS) Presence Regions on the Base of HEND/ODYSSEY Data and Their Correlation with Some Permafrost Features from MOC Data

NASA Technical Reports Server (NTRS)

Kuzmin, R. O.; Mitrofanov, I. G.; Litvak, M. L.; Boynton, M. V.; Saunders, R. S.

2003-01-01

The first results from global mapping of the neutron albedo from Mars by HEND instrument have shown the noticeable deficit of both the epithermal (EN) and the fast (FN) neutrons counts rate in the high latitudes regions of both hemispheres of the planet. The deficit is indicative for high enriching of the surface regolith by hydrogen, which may correspond to amount of any water phases and forms. The objectives of our study are the spatial and temporal variations of the free water (ice) signature in the Martian surface layer on the base of HEND/ODYSSEY data and their correlation with spatial spreading of some permafrost features, mapped on the base of MOC images. For the study we used the results of the global mapping (pixel 5 x5 ) of EN and FN albedo, realized by HEND/ODYSSEY in the period from 17 February to 10 December 2002 year.

[Characteristics and numerical simulation of surface albedo in temperate desert steppe in Inner Mongolia].

PubMed

Yang, Fu-lin; Zhou, Guang-sheng; Zhang, Feng; Wang, Feng-yu; Bao, Fang; Ping, Xiao-yan

2009-12-01

Based on the meteorological and biological observation data from the temperate desert steppe ecosystem research station in Sunitezuoqi of Inner Mongolia during growth season (from May 1st to October 15th, 2008), the diurnal and seasonal characteristics of surface albedo in the steppe were analyzed, with related model constructed. In the steppe, the diurnal variation of surface albedo was mainly affected by solar altitude, being higher just after sunrise and before sunset and lower in midday. During growth season, the surface albedo was from 0.20 to 0.34, with an average of 0.25, and was higher in May, decreased in June, kept relatively stable from July to September, and increased in October. This seasonal variation was related to the phenology of canopy leaf, and affected by precipitation process. Soil water content (SWC) and leaf area index (LAI) were the key factors affecting the surface albedo. A model for the surface albedo responding to SWC and LAI was developed, which showed a good performance in consistent between simulated and observed surface albedo.

Albedo of surface CO2 deposits in Mars' Residual South Polar Cap

NASA Astrophysics Data System (ADS)

James, P. B.; Wolff, M. J.; Bonev, B.

2013-12-01

The albedo of surface CO2 deposits in the Residual South Polar Cap (RSPC) controls their net condensation / sublimation over a martian year and is therefore a crucial parameter in determining RSPC stability. The Lambert albedo used in previous analyses is obtained by dividing I/F, determined from radiometrically calibrated imaging data, by the cosine of the incidence angle. Because of atmospheric dust, this albedo calculated from I/F above the atmosphere is not the surface albedo that enters into stability considerations. In order to investigate the real surface albedo, we interpolate optical depths determined from CRISM EPF measurements to provide estimates of the opacites over the RSPC and use these to determine the actual surface albedos from MARCI images using the radiative transport program DISORT (Stamnes et al., 1988). The assumption that the surface is a Lambertian diffuse reflector can then also be tested. MARCI images acquired in one-day span a significant range of emission angles; the set of images acquired during one sol is similar to EPF observations except that diurnal opacity variations could be important.

Early Student Support to Investigate the Role of Sea Ice-Albedo Feedback in Sea Ice Predictions

DTIC Science & Technology

2014-09-30

Ice - Albedo Feedback in Sea Ice Predictions Cecilia M. Bitz Atmospheric Sciences MS351640 University of Washington Seattle, WA 98196-1640 phone...TERM GOALS The overarching goals of this project are to understand the role of sea ice - albedo feedback on sea ice predictability, to improve how... sea - ice albedo is modeled and how sea ice predictions are initialized, and then to evaluate how these improvements

Albedos of Small Hilda Asteroids

NASA Astrophysics Data System (ADS)

Ryan, Erin L.; Woodward, C. E.

2010-10-01

We present albedo results for 70 small Hilda dynamical family members detected by the Spitzer Space Telescope in multiple archival programs. This Spitzer data samples Hildas with diameters between 2 and 11 kilometers. Our preliminary analysis reveals that the mean geometric albedo for this sample is pv = 0.05, matching the mean albedo derived for large (20 to 160 km) Hilda asteroids observed by IRAS (Ryan and Woodward 2010). This mean albedo is significantly darker than the mean albedo of asteroids in the outer main belt (2.8 AU < a < 3.5 AU), possibly suggesting that these asteroids did not originate from the outer main belt . This is in direct conflict with some dynamical models which suggest that the HIldas are field asteroids trapped from an inward migration of Jupiter (Franklin et al. 2004), and may provide additional observation support for delivery of dark Kuiper Belt contaminants to the inner solar system as per the Nice Model (Levison et al. 2009).

Surface albedo observations at Gusev Crater and Meridiani Planum, Mars

USGS Publications Warehouse

Bell, J.F.; Rice, M.S.; Johnson, J. R.; Hare, T.M.

2008-01-01

During the Mars Exploration Rover mission, the Pancam instrument has periodically acquired large-scale panoramic images with its broadband (739??338 nm) filter in order to estimate the Lambert bolometric albedo of the surface along each rover's traverse. In this work we present the full suite of such estimated albedo values measured to date by the Spirit and Opportunity rovers along their traverses in Gusev Crater and Meridiani Planum, respectively. We include estimated bolometric albedo values of individual surface features (e.g., outcrops, dusty plains, aeolian bed forms, wheel tracks, light-toned soils, and crater walls) as well as overall surface averages of the 43 total panoramic albedo data sets acquired to date. We also present comparisons to estimated Lambert albedo values taken from the Mars Global Surveyor Mars Orbiter Camera (MOC) along the rovers' traverses, and to the large-scale bolometric albedos of the sites from the Viking Orbiter Infrared Thermal Mapper (IRTM) and Mars Global Surveyor/Thermal Emission Spectrometer (TES). The ranges of Pancam-derived albedos at Gusev Crater (0.14 to 0.25) and in Meridiani Planum. (0.10 to 0.18) are in good agreement with IRTM, TES, and MOC orbital measurements. These data sets will be a useful tool and benchmark for future investigations of albodo variations with time, including measurements from orbital instruments like the Context Camera and High Resolution Imaging Science Experiment on Mars Reconnaissance Orbiter. Long-term, accurate albedo measurements could also be important for future efforts in climate modeling as well as for studies of active surface processes. Copyright 2008 by the American Geophysical Union.

Validation and application of MODIS-derived clean snow albedo and dust radiative forcing

NASA Astrophysics Data System (ADS)

Rittger, K. E.; Bryant, A. C.; Seidel, F. C.; Bair, E. H.; Skiles, M.; Goodale, C. E.; Ramirez, P.; Mattmann, C. A.; Dozier, J.; Painter, T.

2012-12-01

Snow albedo is an important control on snowmelt. Though albedo evolution of aging snow can be roughly modeled from grain growth, dust and other light absorbing impurities are extrinsic and therefore must be measured. Estimates of clean snow albedo and surface radiative forcing from impurities, which can be inferred from MODIS 500 m surface reflectance products, can provide this driving data for snowmelt models. Here we use MODSCAG (MODIS snow covered area and grain size) to estimate the clean snow albedo and MODDRFS (MODIS dust radiative forcing of snow) to estimate the additional absorbed solar radiation from dust and black carbon. With its finer spatial (20 m) and spectral (10 nm) resolutions, AVIRIS provides a way to estimate the accuracy of MODIS products and understand variability of snow albedo at a finer scale that we explore though a range of topography. The AVIRIS database includes images from late in the accumulation season through the melt season when we are most interested in changes in snow albedo. In addition to the spatial validation, we employ the best estimate of albedo from MODIS in an energy balance reconstruction model to estimate the maximum snow water equivalent. MODDRFS calculates radiative forcing only in pixels that are completely snow-covered, so we spatially interpolate the product to estimate the forcing in all pixels where MODSCAG has given us estimates of clean snow albedo. Comparisons with snow pillows and courses show better agreement when the radiative forcing from absorbing impurities is included in the energy balance reconstruction.

Bright is the New Black - Multi-Year Performance of Generic High-Albedo Roofs in an Urban Climate

NASA Technical Reports Server (NTRS)

Gaffin, S. R.; Imhoff, M.; Rosenzweig, C.; Khanbilvardi, R.; Pasqualini, A.; Kong, A. Y. Y.; Grillo, D.; Freed, A.; Hillel, D.; Hartung, E.

2012-01-01

High-albedo white and cool roofing membranes are recognized as a fundamental strategy that dense urban areas can deploy on a large scale, at low cost, to mitigate the urban heat island effect. We are monitoring three generic white membranes within New York City that represent a cross-section of the dominant white membrane options for U.S. flat roofs: (1) an ethylene propylene diene monomer (EPDM) rubber membrane; (2) a thermoplastic polyolefin (TPO) membrane and; (3) an asphaltic multi-ply built-up membrane coated with white elastomeric acrylic paint. The paint product is being used by New York City s government for the first major urban albedo enhancement program in its history. We report on the temperature and related albedo performance of these three membranes at three different sites over a multi-year period. The results indicate that the professionally installed white membranes are maintaining their temperature control effectively and are meeting the Energy Star Cool Roofing performance standards requiring a three-year aged albedo above 0.50. The EPDM membrane however shows evidence of low emissivity. The painted asphaltic surface shows high emissivity but lost about half of its initial albedo within two years after installation. Given that the acrylic approach is an important "do-it-yourself," low-cost, retrofit technique, and, as such, offers the most rapid technique for increasing urban albedo, further product performance research is recommended to identify conditions that optimize its long-term albedo control. Even so, its current multi-year performance still represents a significant albedo enhancement for urban heat island mitigation.

The Influence of a Sandy Substrate, Seagrass, or Highly Turbid Water on Albedo and Surface Heat Flux

NASA Astrophysics Data System (ADS)

Fogarty, M. C.; Fewings, M. R.; Paget, A. C.; Dierssen, H. M.

2018-01-01

Sea-surface albedo is a combination of surface-reflected and water-leaving irradiance, but water-leaving irradiance typically contributes less than 15% of the total albedo in open-ocean conditions. In coastal systems, however, the bottom substrate or suspended particulate matter can increase the amount of backscattered light, thereby increasing albedo and decreasing net shortwave surface heat flux. Here a sensitivity analysis using observations and models predicts the effect of light scattering on albedo and the net shortwave heat flux for three test cases: a bright sand bottom, a seagrass canopy, and turbid water. After scaling to the full solar shortwave spectrum, daytime average albedo for the test cases is up to 0.20 and exceeds the value of 0.05 predicted using a commonly applied parameterization. Daytime net shortwave heat flux into the water is significantly reduced, particularly for waters with bright sediments, dense horizontal seagrass canopies < 0.25 m from the sea surface, or highly turbid waters with suspended particulate matter concentration ≥ 50 g m-3. Observations of a more vertical seagrass canopy within 0.2 and 1 m of the surface indicate the increase in albedo compared to the common parameterization is negligible. Therefore, we suggest that the commonly applied albedo lookup table can be used in coastal heat flux estimates in water as shallow as 1 m unless the bottom substrate is highly reflective or the water is highly turbid. Our model results provide guidance to researchers who need to determine albedo in highly reflective or highly turbid conditions but have no direct observations.

Surface Albedo Darkening from wildfires in Northern Sub-Saharan Africa

NASA Technical Reports Server (NTRS)

Gatebe, C. K.; Ichoku, C. M.; Poudal, R.; Roman, M. O.; Wilcox, E.

2014-01-01

Wildfires are recognized as a key physical disturbance of terrestrial ecosystems and a major source of atmospheric trace gases and aerosols. They are known to produce changes in landscape patterns and lead to changes in surface albedo that can persist for long periods. Here, we estimate the darkening of surface albedo due to wildfires in different land cover ecosystems in the Northern Sub-Saharan Africa using data from the Moderate Resolution Imaging Spectroradiometer (MODIS). We determined a decrease in albedo after fires over most land cover types (e.g. woody savannas: (-0.00352 0.00003) and savannas: (- 0.003910.00003), which together accounted for >86% of the total MODIS fire count between 2003 and 2011). Grasslands had a higher value (-0.00454 0.00003) than the savannas, but accounted for only about 5% of the total fire count. A few other land cover types (e.g. Deciduous broad leaf: (0.00062 0.00015), and barren: 0.00027 0.00019), showed an increase in albedo after fires, but accounted for less than 1% of the total fires. Albedo change due to wildfires is more important during the fire season (October-February). The albedo recovery progresses rapidly during the first year after fires, where savannas show the greatest recovery (>77%) within one year, while deciduous broadleaf, permanent wetlands and barren lands show the least one-year recovery (56%). The persistence of surface albedo darkening in most land cover types is limited to about six to seven years, after which at least 98% of the burnt pixels recover to their pre-fire albedo.

Could we constrain some major properties of hot Super-Earths with NIRSPEC-JWT spectra?

NASA Astrophysics Data System (ADS)

Rouan, D.; Samuel, B.; Leconte, J.; Léger, A.

2014-03-01

CoRot-7b and Kepler-10b were the first super-earths with solid surfaces identified thanks to transits detection from space using ultra-precise photometry. At only a few stellar radii from their host stars, these two rocky planets are very hot. The current model (Leger et al., 2011) is that they are atmosphere-free, in a synchronous rotation state, receive strong stellar winds and fluxes and that they feature a lava ocean on their hot dayside. We show how observations with NIRSPEC-JWST could further confirm and constrain, or reject the atmosphere-free lava ocean planet model for very hot super earths. Taking CoRoT-7b as a baseline, we explore the consequences on the phase-curve of a non tidal-locked rotation, of the presence/absence of an atmosphere, and of different values of the surface albedo. Simulated observations of the reflected light and thermal emission using NIRSPEC-JWST are used to look for detectable signatures of those peculiar conditions. We also study how to retrieve the temperature map of the surface. We demonstrate that thanks to the broad range of wavelengths accessible with JWST, we should be able to constrain several parameters: i) the Bond albedo is retrieved to within ±0.03 in most cases; ii) the lag effect allows to retrieve the rotation period of a non phaselocked planet to within 3 hours; iii) the shortest rotation period compatible with an actually phase-locked planet is in the range 30 - 800 h depending on the thermal properties of the soil; iv) the presence of a thick atmosphere with a pressure of one bar, and an specific opacity higher than 10-5m-2kg-1 is detectable; v) The latitudinal temperature profile can be retrieved to within 30 K for a signal to noise ratio of 7.5. We conclude that it should thus be possible to distinguish the situation of a lava ocean with phase-locking and no atmosphere from other cases. In addition, obtaining the surface temperature map and the albedo will bring important constraints on the nature or the physical state of the soil of hot super-earths. We examine the extension of this method to other cases of super-earths.

Atmospheric effects on the mapping of Martian thermal inertia and thermally derived albedo

NASA Technical Reports Server (NTRS)

Hayashi, J. N.; Jakosky, B. M.; Haberle, R. M.

1994-01-01

The most widely used thermal inertia data for Mars assumes the atmospheric contribution is constant and equal to 2 percent of the maximum solar insolation. Haberle and Jakosky investigated the effect of including a dusty CO2 atmosphere and sensible heat exchange with the surface on thermal inertia. We recently utilized Haberle and Jakosky's coupled surface-atmosphere model to investigate the effects of such an atmosphere on the thermally derived albedo. The thermally derived albedo is the albedo which, together with the thermal inertia, provides model surface temperatures which best match the observed temperatures. New maps are presented of thermal inertia and thermally derived albedo which incorporate dust opacities derived from IRTM data.

Analytic reflected light curves for exoplanets

NASA Astrophysics Data System (ADS)

Haggard, Hal M.; Cowan, Nicolas B.

2018-07-01

The disc-integrated reflected brightness of an exoplanet changes as a function of time due to orbital and rotational motions coupled with an inhomogeneous albedo map. We have previously derived analytic reflected light curves for spherical harmonic albedo maps in the special case of a synchronously rotating planet on an edge-on orbit (Cowan, Fuentes & Haggard). In this paper, we present analytic reflected light curves for the general case of a planet on an inclined orbit, with arbitrary spin period and non-zero obliquity. We do so for two different albedo basis maps: bright points (δ-maps), and spherical harmonics (Y_ l^m-maps). In particular, we use Wigner D-matrices to express an harmonic light curve for an arbitrary viewing geometry as a non-linear combination of harmonic light curves for the simpler edge-on, synchronously rotating geometry. These solutions will enable future exploration of the degeneracies and information content of reflected light curves, as well as fast calculation of light curves for mapping exoplanets based on time-resolved photometry. To these ends, we make available Exoplanet Analytic Reflected Lightcurves, a simple open-source code that allows rapid computation of reflected light curves.

Simulating polarized light scattering in terrestrial snow based on bicontinuous random medium and Monte Carlo ray tracing

NASA Astrophysics Data System (ADS)

Xiong, Chuan; Shi, Jiancheng

2014-01-01

To date, the light scattering models of snow consider very little about the real snow microstructures. The ideal spherical or other single shaped particle assumptions in previous snow light scattering models can cause error in light scattering modeling of snow and further cause errors in remote sensing inversion algorithms. This paper tries to build up a snow polarized reflectance model based on bicontinuous medium, with which the real snow microstructure is considered. The accurate specific surface area of bicontinuous medium can be analytically derived. The polarized Monte Carlo ray tracing technique is applied to the computer generated bicontinuous medium. With proper algorithms, the snow surface albedo, bidirectional reflectance distribution function (BRDF) and polarized BRDF can be simulated. The validation of model predicted spectral albedo and bidirectional reflectance factor (BRF) using experiment data shows good results. The relationship between snow surface albedo and snow specific surface area (SSA) were predicted, and this relationship can be used for future improvement of snow specific surface area (SSA) inversion algorithms. The model predicted polarized reflectance is validated and proved accurate, which can be further applied in polarized remote sensing.

Greenland surface albedo changes in July 1981-2012 from satellite observations

NASA Astrophysics Data System (ADS)

He, Tao; Liang, Shunlin; Yu, Yunyue; Wang, Dongdong; Gao, Feng; Liu, Qiang

2013-12-01

Significant melting events over Greenland have been observed over the past few decades. This study presents an analysis of surface albedo change over Greenland using a 32-year consistent satellite albedo product from the global land surface satellite (GLASS) project together with ground measurements. Results show a general decreasing trend of surface albedo from 1981 to 2012 (-0.009 ± 0.002 decade-1, p < 0.01). However, a large decrease has occurred since 2000 (-0.028 ± 0.008 decade-1, p < 0.01) with most significant decreases at elevations between 1000 and 1500 m (-0.055 decade-1, p < 0.01) which may be associated with surface temperature increases. The surface radiative forcing from albedo changes is 2.73 W m-2 decade-1 and 3.06 W m-2 decade-1 under full-sky and clear-sky conditions, respectively, which indicates that surface albedo changes are likely to have a larger impact on the surface shortwave radiation budget than that caused by changes in the atmosphere over Greenland. A comparison made between satellite albedo products and data output from the Coupled Model Inter-comparison Project 5 (CMIP5) general circulation models (GCMs) shows that most of the CMIP5 models do not detect the significantly decreasing trends of albedo in recent decades. This suggests that more efforts are needed to improve our understanding and simulation of climate change at high latitudes.

Changes in Arctic Vegetation Amplify High-Latitude Warming Through Greenhouse Effect

NASA Astrophysics Data System (ADS)

Swann, A.; Fung, I.; Levis, S.; Bonan, G. B.; Doney, S. C.

2009-12-01

Changes in vegetation cover are recognized to modify climate and the energy budget of the Earth through changes in albedo in high latitudes and evapotranspiration (ET) in the tropics. In snow-covered regions, the springtime growth of leaves enhances solar absorption because surface albedo is reduced from the albedo of snow (~0.8) towards the albedo of leaves (~0.1). Leaves also play a hydrologic role, transpiring soil water to the atmosphere. It has been suggested that broad-leaf deciduous trees may invade warming tundra more effectively than boreal evergreen trees and these trees have higher rates of transpiration than needle-leaf trees. Here we use a global climate model with an interactive biosphere to investigate the effects of adding deciduous trees on bare ground at high northern latitudes. We find that the top-of-atmosphere radiative imbalance from enhanced transpiration (associated with the expanded forest cover) is 2.4 times larger than the direct forcing due to albedo change from the forest. Albedo change is considered to be the dominant mechanism by which trees directly modify climate at high-latitudes, but our findings suggest an additional mechanism through transpiration. Furthermore, the greenhouse warming by additional water vapor melts sea ice and triggers a positive feedback through changes in ocean albedo and evaporation. Vegetation feedbacks through albedo and transpiration produce a strong warming if they act in combination with sea-ice processes.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Usui, Fumihiko; Hasegawa, Sunao; Matsuhara, Hideo

We present an analysis of the albedo properties of main belt asteroids (MBAs) detected by the All-Sky Survey of the infrared astronomical satellite AKARI. The characteristics of 5120 asteroids detected by the survey, including their sizes and albedos, were cataloged in the Asteroid Catalog Using AKARI (AcuA). Size and albedo measurements were based on the standard thermal model, using inputs of infrared fluxes and absolute magnitudes measured at optical wavelengths. MBAs, which account for 4722 of the 5120 AcuA asteroids, have semimajor axes of 2.06-3.27 AU, except for the near-Earth asteroids. AcuA provides a complete data set of all MBAsmore » brighter than the absolute magnitude of H < 10.3, which corresponds to the diameter of d > 20 km. We confirmed that the albedo distribution of the MBAs is strongly bimodal as was already known from the past observations, and that the bimodal distribution occurs not only in the total population, but also within inner, middle, and outer regions of the main belt. The bimodal distribution in each group consists of low-albedo components in C-type asteroids and high-albedo components in S-type asteroids. We found that the small asteroids have much more variety in albedo than the large asteroids. In spite of the albedo transition process like space weathering, the heliocentric distribution of the mean albedo of asteroids in each taxonomic type is nearly flat. The mean albedo of the total, on the other hand, gradually decreases with an increase in semimajor axis. This can be explained by the compositional ratio of taxonomic types; that is, the proportion of dark asteroids such as C- and D-types increases, while that of bright asteroids such as S-type decreases, with increasing heliocentric distance. The heliocentric distributions of X-subclasses: E-, M-, and P-types, which can be divided based on albedo values, are also examined. P-types, which are the major component in X-types, are distributed throughout the main belt regions, and the abundance of P-types increases beyond 3 AU. This distribution is similar to that of C- or D-types.« less

Understanding the drivers of post-fire albedo and radiative forcing across Alaska and Canada: implications for management.

NASA Astrophysics Data System (ADS)

Potter, S.; Solvik, K.; Erb, A.; Goetz, S. J.; Johnstone, J. F.; Mack, M. C.; Randerson, J. T.; Roman, M. O.; Schaaf, C. L.; Turetsky, M. R.; Veraverbeke, S.; Wang, Z.; Rogers, B. M.

2017-12-01

Boreal forest dynamics including succession, composition, carbon cycling, and surface-atmosphere energy exchanges are largely driven by fire. In Alaska and Canada, burned area and fire frequency have increased since the 1970s, and are projected to continue increasing into the 21st century. In contrast to other biomes, alterations to surface albedo from fires in North American boreal forests are one of the primary feedbacks to climate. Understanding how altered fire regimes impact vegetation composition and energy budgets is therefore critical to forecasting regional and global climate change. High-severity fires cause winter and spring albedo to increase due to increased snow exposure and replacement of evergreen conifers by deciduous broadleaf trees. Although summer albedo decreases initially due to the deposition of black carbon and charred surfaces, it typically increases for several decades thereafter when younger and brighter deciduous trees dominate. The net effect of these albedo changes is expected to result in substantive radiative cooling, but there has been little research to examine how albedo trajectories differ spatially and temporally as a result of differences in burn severity, species composition, topography, climate and soil properties, and what the associated implications for future energy balances are. Here we investigate drivers of post-fire monthly albedo trajectories across Canada and Alaska using a new Collection V006 500 m MODIS daily blue-sky albedo product and historical fires from the Canadian and Alaskan National Fire Databases. The impacts of varying fuel type, landscape position, soils, climate, and burn severity on monthly albedo trajectories are explored using a Random Forest model. This information is then used to predict long-term monthly albedo and radiative forcing for fires that occurred during the MODIS era (2001-2012). We find that higher severity burns in denser forests and environmental conditions that promote either deciduous vegetation or slower tree growth result in the largest increases in post fire albedo and radiative cooling. This understanding and our geospatial products may be relevant for management focused on limiting the climate impacts from intensifying boreal fire regimes.

The impact of future forest dynamics on climate: interactive effects of changing vegetation and disturbance regimes

PubMed Central

Thom, Dominik; Rammer, Werner; Seidl, Rupert

2018-01-01

Currently, the temperate forest biome cools the earth’s climate and dampens anthropogenic climate change. However, climate change will substantially alter forest dynamics in the future, affecting the climate regulation function of forests. Increasing natural disturbances can reduce carbon uptake and evaporative cooling, but at the same time increase the albedo of a landscape. Simultaneous changes in vegetation composition can mitigate disturbance impacts, but also influence climate regulation directly (e.g., via albedo changes). As a result of a number of interactive drivers (changes in climate, vegetation, and disturbance) and their simultaneous effects on climate-relevant processes (carbon exchange, albedo, latent heat flux) the future climate regulation function of forests remains highly uncertain. Here we address these complex interactions to assess the effect of future forest dynamics on the climate system. Our specific objectives were (1) to investigate the long-term interactions between changing vegetation composition and disturbance regimes under climate change, (2) to quantify the response of climate regulation to changes in forest dynamics, and (3) to identify the main drivers of the future influence of forests on the climate system. We investigated these issues using the individual-based forest landscape and disturbance model (iLand). Simulations were run over 200 yr for Kalkalpen National Park (Austria), assuming different future climate projections, and incorporating dynamically responding wind and bark beetle disturbances. To consistently assess the net effect on climate the simulated responses of carbon exchange, albedo, and latent heat flux were expressed as contributions to radiative forcing. We found that climate change increased disturbances (+27.7% over 200 yr) and specifically bark beetle activity during the 21st century. However, negative feedbacks from a simultaneously changing tree species composition (+28.0% broadleaved species) decreased disturbance activity in the long run (−10.1%), mainly by reducing the host trees available for bark beetles. Climate change and the resulting future forest dynamics significantly reduced the climate regulation function of the landscape, increasing radiative forcing by up to +10.2% on average over 200 yr. Overall, radiative forcing was most strongly driven by carbon exchange. We conclude that future changes in forest dynamics can cause amplifying climate feedbacks from temperate forest ecosystems. PMID:29628526

Ship track observations of a reduced shortwave aerosol indirect effect in mixed-phase clouds

NASA Astrophysics Data System (ADS)

Christensen, M. W.; Suzuki, K.; Zambri, B.; Stephens, G. L.

2014-10-01

Aerosol influences on clouds are a major source of uncertainty to our understanding of forced climate change. Increased aerosol can enhance solar reflection from clouds countering greenhouse gas warming. Recently, this indirect effect has been extended from water droplet clouds to other types including mixed-phase clouds. Aerosol effects on mixed-phase clouds are important because of their fundamental role on sea ice loss and polar climate change, but very little is known about aerosol effects on these clouds. Here we provide the first analysis of the effects of aerosol emitted from ship stacks into mixed-phase clouds. Satellite observations of solar reflection in numerous ship tracks reveal that cloud albedo increases 5 times more in liquid clouds when polluted and persist 2 h longer than in mixed-phase clouds. These results suggest that seeding mixed-phase clouds via shipping aerosol is unlikely to provide any significant counterbalancing solar radiative cooling effects in warming polar regions.

The Statistics of Albedo and Heat Recirculation on Hot Exoplanets

NASA Astrophysics Data System (ADS)

Cowan, Nicolas B.; Agol, Eric

2011-03-01

If both the day-side and night-side effective temperatures of a planet can be measured, it is possible to estimate its Bond albedo, 0 < AB < 1, as well as its day-night heat redistribution efficiency, 0 < ɛ < 1. We attempt a statistical analysis of the albedo and redistribution efficiency for 24 transiting exoplanets that have at least one published secondary eclipse. For each planet, we show how to calculate a sub-stellar equilibrium temperature, T 0, and associated uncertainty. We then use a simple model-independent technique to estimate a planet's effective temperature from planet/star flux ratios. We use thermal secondary eclipse measurements—those obtained at λ>0.8 μm—to estimate day-side effective temperatures, T d, and thermal phase variations—when available—to estimate night-side effective temperature. We strongly rule out the "null hypothesis" of a single AB and ɛ for all 24 planets. If we allow each planet to have different parameters, we find that low Bond albedos are favored (AB < 0.35 at 1σ confidence), which is an independent confirmation of the low albedos inferred from non-detections of reflected light. Our sample exhibits a wide variety of redistribution efficiencies. When normalized by T 0, the day-side effective temperatures of the 24 planets describe a uni-modal distribution. The two biggest outliers are GJ 436b (abnormally hot) and HD 80606b (abnormally cool), and these are the only eccentric planets in our sample. The dimensionless quantity T d/T 0 exhibits no trend with the presence or absence of stratospheric inversions. There is also no clear trend between T d/T 0 and T 0. That said, the six planets with the greatest sub-stellar equilibrium temperatures (T > 2400 K) have low ɛ, as opposed to the 18 cooler planets, which show a variety of recirculation efficiencies. This hints that the very hottest transiting giant planets are qualitatively different from the merely hot Jupiters. We propose an explanation of this trend based on how a planet's radiative and advective times scale with temperature: both timescales are expected to be shorter for hotter planets, but the temperature dependence of the radiative timescale is stronger, leading to decreased heat recirculation efficiency.

The Costs of Climate Change: Impact of Future Snow Cover Projections on Valuation of Albedo in Forest Management

NASA Astrophysics Data System (ADS)

Burakowski, E. A.; Lutz, D. A.

2014-12-01

Surface albedo provides an important climate regulating ecosystem service, particularly in the mid-latitudes where seasonal snow cover influences surface radiation budgets. In the case of substantial seasonal snow cover, the influence of albedo can equal or surpass the climatic benefits of carbon sequestration from forest growth. Climate mitigation platforms should therefore consider albedo in their framework in order to integrate these two climatic services in an economic context for the effective design and implementation of forest management projects. Over the next century, the influence of surface albedo is projected to diminish under higher emissions scenarios due to an overall decrease in snow depth and duration of snow cover in the mid-latitudes. In this study, we focus on the change in economic value of winter albedo in the northeastern United States projected through 2100 using the Special Report on Emissions Scenarios (SRES) a1 and b1 scenarios. Statistically downscaled temperature and precipitation are used as input to the Variable Infiltration Capacity (VIC) model to provide future daily snow depth fields through 2100. Using VIC projections of future snow depth, projected winter albedo fields over deforested lands were generated using an empirical logarithmic relationship between snow depth and albedo derived from a volunteer network of snow observers in New Hampshire over the period Nov 2011 through 2014. Our results show that greater reductions in snow depth and the number of winter days with snow cover in the a1 compared to the b1 scenario reduce wintertime albedo when forested lands are harvested. This result has implications on future trade-offs among albedo, carbon storage, and timber value that should be investigated in greater detail. The impacts of forest harvest on radiative forcing associated with energy redistribution (e.g., latent heat and surface roughness length) should also be considered in future work.

Remote sensing albedo product validation over heterogenicity surface based on WSN: preliminary results and its uncertainty

NASA Astrophysics Data System (ADS)

Wu, Xiaodan; Wen, Jianguang; Xiao, Qing; Peng, Jingjing; Liu, Qiang; Dou, Baocheng; Tang, Yong; Li, Xiuhong

2014-11-01

The evaluation of uncertainty in satellite-derived albedo products is critical to ensure their accuracy, stability and consistency for studying climate change. In this study, we assess the Moderate-resolution Imaging Spectroradiometer(MODIS) albedo 8 day standard product MOD43B3 using the ground-based albedometer measurement based on the wireless sensor network (WSN) technology. The experiment have been performed in Huailai, Hubei province. A 1.5 km*2 km area are selected as study region, which locates between 115.78° E-115.80° E and 40.35° N-40.37° N. This area is characterized by its distinct landscapes: bare ground between January and April, corn from May to Octorber. That is, this area is relatively homegeneous from January to Octorber, but in Novermber and December, the surface is very heterogeneous because of straw burning, as well as snow fall and snow melting. It is a big challenge to validate the MODIS albedo products because of the vast difference in spatial resolution between ground measurement and satellite measurement. Here, we use the HJ albedo products as the bridge that link the ground measurement with satellite data. Firstly, we analyses the spatial representativeness of the WSN site under green-up, dormant and snow covered situations to decide whether direct comparison between ground-based measurement and MODIS albedo can be made. The semivariogram is used here to describe the ground hetergeneity around the WSN site. In addition, the bias between the average albedo of the certain neighborhood centered at the WSN site and the center pixel albedo is also calculated.Then we compare the MOD43B3 value with the ground-based value. Result shows that MOD43B3 agree with in situ well during the growing season, however, there are relatively large difference between ground albedos and MCD43B3 albedos during dormant and snow-coverd periods.

Description of Mixed-Phase Clouds in Weather Forecast and Climate Models

DTIC Science & Technology

2014-09-30

deficits, leading to freeze-up of both sea ice and the ocean surface. The surface albedo and processes impacting the energy content of the upper ocean...appear key to producing a temporal difference be- tween the freeze-up of the sea - ice surface and adjacent open water. While synoptic conditions, atmos...Leck, 2013: Cloud and boundary layer interactions over the Arctic sea - ice in late summer, Atmos. Chem. Phys. Discuss., 13, 13191-13244, doi

Changes in the Albedo of the Pegasus and Phoenix Runways, 2000-2017

DTIC Science & Technology

2017-07-18

further reducing pavement strength and promoting more melting. To prevent or delay reaching the melt tipping point, it is critical to maintain the...2013. McMurdo Consolidated Airfields Study: Phase I, Basis of Design . ERDC/CRREL TR-13-5. Hanover, NH: U.S. Army Engineer Research and Development...Center. Haehnel, R., M. A. Knuth, T. Melendy, C. Hiemstra, and R. Davis. 2014. Design and Implementation of a Consolidated Airfield at McMurdo

Quantifying the ice-albedo feedback through decoupling

NASA Astrophysics Data System (ADS)

Kravitz, B.; Rasch, P. J.

2017-12-01

The ice-albedo feedback involves numerous individual components, whereby warming induces sea ice melt, inducing reduced surface albedo, inducing increased surface shortwave absorption, causing further warming. Here we attempt to quantify the sea ice albedo feedback using an analogue of the "partial radiative perturbation" method, but where the governing mechanisms are directly decoupled in a climate model. As an example, we can isolate the insulating effects of sea ice on surface energy and moisture fluxes by allowing sea ice thickness to change but fixing Arctic surface albedo, or vice versa. Here we present results from such idealized simulations using the Community Earth System Model in which individual components are successively fixed, effectively decoupling the ice-albedo feedback loop. We isolate the different components of this feedback, including temperature change, sea ice extent/thickness, and air-sea exchange of heat and moisture. We explore the interactions between these different components, as well as the strengths of the total feedback in the decoupled feedback loop, to quantify contributions from individual pieces. We also quantify the non-additivity of the effects of the components as a means of investigating the dominant sources of nonlinearity in the ice-albedo feedback.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mainzer, A.; Masiero, J.; Bauer, J.

We have combined the NEOWISE and Sloan Digital Sky Survey data to study the albedos of 24,353 asteroids with candidate taxonomic classifications derived using Sloan photometry. We find a wide range of moderate to high albedos for candidate S-type asteroids that are analogous to the S complex defined by previous spectrophotometrically based taxonomic systems. The candidate C-type asteroids, while generally very dark, have a tail of higher albedos that overlaps the S types. The albedo distribution for asteroids with a photometrically derived Q classification is extremely similar to those of the S types. Asteroids with similar colors to (4) Vestamore » have higher albedos than the S types, and most have orbital elements similar to known Vesta family members. Finally, we show that the relative reflectance at 3.4 and 4.6 {mu}m is higher for D-type asteroids and suggest that their red visible and near-infrared spectral slope extends out to these wavelengths. Understanding the relationship between size, albedo, and taxonomic classification is complicated by the fact that the objects with classifications were selected from the visible/near-infrared Sloan Moving Object Catalog, which is biased against fainter asteroids, including those with lower albedos.« less

XCO2 retrieval error over deserts near critical surface albedo

NASA Astrophysics Data System (ADS)

Zhang, Qiong; Shia, Run-Lie; Sander, Stanley P.; Yung, Yuk L.

2016-02-01

Large retrieval errors in column-weighted CO2 mixing ratio (XCO2) over deserts are evident in the Orbiting Carbon Observatory 2 version 7 L2 products. We argue that these errors are caused by the surface albedo being close to a critical surface albedo (αc). Over a surface with albedo close to αc, increasing the aerosol optical depth (AOD) does not change the continuum radiance. The spectral signature caused by changing the AOD is identical to that caused by changing the absorbing gas column. The degeneracy in the retrievals of AOD and XCO2 results in a loss of degrees of freedom and information content. We employ a two-stream-exact single scattering radiative transfer model to study the physical mechanism of XCO2 retrieval error over a surface with albedo close to αc. Based on retrieval tests over surfaces with different albedos, we conclude that over a surface with albedo close to αc, the XCO2 retrieval suffers from a significant loss of accuracy. We recommend a bias correction approach that has significantly improved the XCO2 retrieval from the California Laboratory for Atmospheric Remote Sensing data in the presence of aerosol loading.

Landsat monitoring of albedo changes in northwestern Arizona, 1977-1980

USGS Publications Warehouse

Robinove, Charles Joseph

1982-01-01

As part of a cooperative project between the U.S. Geological Survey and the Bureau of Land Management, changes in albedo (percentage of light reflected from the ground) were calculated and mapped from Landsat images for an area in northwestern Arizona for three periods: August 26, 1977, to September 3, 1979; September 3, 1979, to August 28, 1980; and August 26, 1977, to August 28, 1980. The mapped albedo changes were field checked in April 1981. Decreases in albedo were associated with increases in vegetation, primarily the flush of annual vegetation and the regrowth of vegetation in chained areas and sites of past fires. Increases in albedo were due to recent fires. Continuous monitoring of changes in albedo using current, rather than historical, Landsat images can provide the Bureau of Land Management with a means of monitoring vegetation growth, determining areas of high fire potential, and more efficiently deploying of field personnel to sites where severe changes are occuring in the quality of the land and vegetation resources. For example, an albedo change could be an indication of encroachment by an invader species. Similarly, it could indicate where rangeland is being lost to desertification.

Kotov during Albedo Experiment in the SM

NASA Image and Video Library

2013-11-18

ISS038-E-005022 (20 Nov. 2013) --- At a window in the International Space Station?s Zvezda Service Module, Russian cosmonaut Oleg Kotov, Expedition 38 commander, uses a digital camera photospectral system to perform a session for the Albedo Experiment. The experiment measures Earth?s albedo, or the amount of solar radiation reflected from the surface, in the hopes to develop methods to harness the reflected radiation to supplement the station?s power supply. The light reflection phenomenon is measured in units called albedo.

Kotov during Albedo Experiment in the SM

NASA Image and Video Library

2013-11-18

ISS038-E-005014 (20 Nov. 2013) --- At a window in the International Space Station’s Zvezda Service Module, Russian cosmonaut Oleg Kotov, Expedition 38 commander, uses a digital camera photospectral system to perform a session for the Albedo Experiment. The experiment measures Earth’s albedo, or the amount of solar radiation reflected from the surface, in the hopes to develop methods to harness the reflected radiation to supplement the station’s power supply. The light reflection phenomenon is measured in units called albedo.

Kotov during Albedo Experiment in the SM

NASA Image and Video Library

2013-11-18

ISS038-E-005023 (20 Nov. 2013) --- At a window in the International Space Station?s Zvezda Service Module, Russian cosmonaut Oleg Kotov, Expedition 38 commander, uses a digital camera photospectral system to perform a session for the Albedo Experiment. The experiment measures Earth?s albedo, or the amount of solar radiation reflected from the surface, in the hopes to develop methods to harness the reflected radiation to supplement the station?s power supply. The light reflection phenomenon is measured in units called albedo.

Kotov during Albedo Experiment in the SM

NASA Image and Video Library

2013-11-18

ISS038-E-005031 (20 Nov. 2013) --- At a window in the International Space Station?s Zvezda Service Module, Russian cosmonaut Oleg Kotov, Expedition 38 commander, uses a digital camera photospectral system to perform a session for the Albedo Experiment. The experiment measures Earth?s albedo, or the amount of solar radiation reflected from the surface, in the hopes to develop methods to harness the reflected radiation to supplement the station?s power supply. The light reflection phenomenon is measured in units called albedo.

Kotov during Albedo Experiment in the SM

NASA Image and Video Library

2013-11-18

ISS038-E-005016 (20 Nov. 2013) --- At a window in the International Space Station?s Zvezda Service Module, Russian cosmonaut Oleg Kotov, Expedition 38 commander, uses a digital camera photospectral system to perform a session for the Albedo Experiment. The experiment measures Earth?s albedo, or the amount of solar radiation reflected from the surface, in the hopes to develop methods to harness the reflected radiation to supplement the station?s power supply. The light reflection phenomenon is measured in units called albedo.

Kotov during Albedo Experiment in the SM

NASA Image and Video Library

2013-11-18

ISS038-E-005019 (20 Nov. 2013) --- At a window in the International Space Station?s Zvezda Service Module, Russian cosmonaut Oleg Kotov, Expedition 38 commander, uses a digital camera photospectral system to perform a session for the Albedo Experiment. The experiment measures Earth?s albedo, or the amount of solar radiation reflected from the surface, in the hopes to develop methods to harness the reflected radiation to supplement the station?s power supply. The light reflection phenomenon is measured in units called albedo.

Neutron Fading Characteristics of Copper Doped Lithium Fluoride (LiF: MCP) Thermoluminescent Dosimeters (TLDs)

DTIC Science & Technology

2008-05-21

Albedo Dosimetry TLDs that are used for neutron or neutron-photon personnel dosimetry are albedo dosimeters. The word albedo simply means the proportion... dosimetry . When LiF: MCP is exposed to thermal neutron irradiation, there is no obvious change in the glow curve shape. In the case of TLD -100, the...LiF: MCP undergoes compared to TLD -100. Therefore, LET results in significant variations in TL output for LiF: MCP. Limitations of Albedo Dosimetry

Earth albedo neutrons from 10 to 100 MeV.

NASA Technical Reports Server (NTRS)

Preszler, A. M.; Simnett, G. M.; White, R. S.

1972-01-01

We report the measurement of the energy and angular distributions of earth albedo neutrons from 10 to 100 MeV at 40 deg N geomagnetic latitude from a balloon at 120,000 ft, below 4.65 g/sq cm. The albedo-neutron omnidirectional energy distribution is flat to 50 MeV, then decreases with energy. The absolute neutron energy distribution is of the correct strength and shape for the albedo neutrons to be the source of the protons trapped in earth's inner radiation belt.

Exploiting Surface Albedos Products to Bridge the Gap Between Remote Sensing Information and Climate Models

NASA Astrophysics Data System (ADS)

Pinty, Bernard; Andredakis, Ioannis; Clerici, Marco; Kaminski, Thomas; Taberner, Malcolm; Stephen, Plummer

2011-01-01

We present results from the application of an inversion method conducted using MODIS derived broadband visible and near-infrared surface albedo products. This contribution is an extension of earlier efforts to optimally retrieve land surface fluxes and associated two- stream model parameters based on the Joint Research Centre Two-stream Inversion Package (JRC-TIP). The discussion focuses on products (based on the mean and one-sigma values of the Probability Distribution Functions (PDFs)) obtained during the summer and winter and highlight specific issues related to snowy conditions. This paper discusses the retrieved model parameters including the effective Leaf Area Index (LAI), the background brightness and the scattering efficiency of the vegetation elements. The spatial and seasonal changes exhibited by these parameters agree with common knowledge and underscore the richness of the high quality surface albedo data sets. At the same time, the opportunity to generate global maps of new products, such as the background albedo, underscores the advantages of using state of the art algorithmic approaches capable of fully exploiting accurate satellite remote sensing datasets. The detailed analyses of the retrieval uncertainties highlight the central role and contribution of the LAI, the main process parameter to interpret radiation transfer observations over vegetated surfaces. The posterior covariance matrix of the uncertainties is further exploited to quantify the knowledge gain from the ingestion of MODIS surface albedo products. The estimation of the radiation fluxes that are absorbed, transmitted and scattered by the vegetation layer and its background is achieved on the basis of the retrieved PDFs of the model parameters. The propagation of uncertainties from the observations to the model parameters is achieved via the Hessian of the cost function and yields a covariance matrix of posterior parameter uncertainties. This matrix is propagated to the radiation fluxes via the model’s Jacobian matrix of first derivatives. A definite asset of the JRC-TIP lies in its capability to control and ultimately relax a number of assumptions that are often implicit in traditional approaches. These features greatly help understand the discrepancies between the different data sets of land surface properties and fluxes that are currently available. Through a series of selected examples, the inverse procedure implemented in the JRC-TIP is shown to be robust, reliable and compliant with large scale processing requirements. Furthermore, this package ensures the physical consistency between the set of observations, the two-stream model parameters and radiation fluxes. It also documents the retrieval of associated uncertainties. The knowledge gained from the availability of remote sensing surface albedo products can be expressed in quantitative terms using a simple metric. This metric helps identify the geographical locations and periods of the year where the remote sensing products fail in reducing the uncertainty on the process model parameters as can be specified from current knowledge.

Geenland Glacier Albedo Variability

NASA Astrophysics Data System (ADS)

2004-01-01

The program for Arctic Regional Climate Assessment (PARCA) is a NASA-funded project with the prime goal of addressing the mass balance of the Greenland ice sheet. Since the formal initiation of the program in 1995, there has been a significant improvement in the estimates of the mass balance of the ice sheet. Results from this program reveal that the high-elevation regions of the ice sheet are approximately in balance, but the margins are thinning. Laser surveys reveal significant thinning along 70 percent of the ice sheet periphery below 2000 m elevations, and in at least one outlet glacier, Kangerdlugssuaq in southeast Greenland, thinning has been as much as 10 m/yr. This study examines the albedo variability in four outlet glaciers to help separate out the relative contributions of surface melting versus ice dynamics to the recent mass balance changes. Analysis of AVHRR Polar Pathfinder albedo shows that at the Petermann and Jakobshavn glaciers, there has been a negative trend in albedo at the glacier terminus from 1981 to 2000, whereas the Stor+strommen and Kangerdlugssuaq glaciers show slightly positive trends in albedo. These findings are consistent with recent observations of melt extent from passive microwave data which show more melt on the western side of Greenland and slightly less on the eastern side. Significance of albedo trends will depend on where and when the albedo changes occur. Since the majority of surface melt occurs in the shallow sloping western margin of the ice sheet where the shortwave radiation dominates the energy balance in summer (e.g. Jakobshavn region) this region will be more sensitive to changes in albedo than in regions where this is not the case. Near the Jakobshavn glacier, even larger changes in albedo have been observed, with decreases as much as 20 percent per decade.

Greenland Glacier Albedo Variability

NASA Technical Reports Server (NTRS)

2004-01-01

The program for Arctic Regional Climate Assessment (PARCA) is a NASA-funded project with the prime goal of addressing the mass balance of the Greenland ice sheet. Since the formal initiation of the program in 1995, there has been a significant improvement in the estimates of the mass balance of the ice sheet. Results from this program reveal that the high-elevation regions of the ice sheet are approximately in balance, but the margins are thinning. Laser surveys reveal significant thinning along 70 percent of the ice sheet periphery below 2000 m elevations, and in at least one outlet glacier, Kangerdlugssuaq in southeast Greenland, thinning has been as much as 10 m/yr. This study examines the albedo variability in four outlet glaciers to help separate out the relative contributions of surface melting versus ice dynamics to the recent mass balance changes. Analysis of AVHRR Polar Pathfinder albedo shows that at the Petermann and Jakobshavn glaciers, there has been a negative trend in albedo at the glacier terminus from 1981 to 2000, whereas the Stor+strommen and Kangerdlugssuaq glaciers show slightly positive trends in albedo. These findings are consistent with recent observations of melt extent from passive microwave data which show more melt on the western side of Greenland and slightly less on the eastern side. Significance of albedo trends will depend on where and when the albedo changes occur. Since the majority of surface melt occurs in the shallow sloping western margin of the ice sheet where the shortwave radiation dominates the energy balance in summer (e.g. Jakobshavn region) this region will be more sensitive to changes in albedo than in regions where this is not the case. Near the Jakobshavn glacier, even larger changes in albedo have been observed, with decreases as much as 20 percent per decade.

Bright is the new black—multi-year performance of high-albedo roofs in an urban climate

NASA Astrophysics Data System (ADS)

Gaffin, S. R.; Imhoff, M.; Rosenzweig, C.; Khanbilvardi, R.; Pasqualini, A.; Kong, A. Y. Y.; Grillo, D.; Freed, A.; Hillel, D.; Hartung, E.

2012-03-01

High-albedo white and cool roofing membranes are recognized as a fundamental strategy that dense urban areas can deploy on a large scale, at low cost, to mitigate the urban heat island effect. We are monitoring three generic white membranes within New York City that represent a cross section of the dominant white membrane options for US flat roofs: (1) an ethylene-propylene-diene monomer (EPDM) rubber membrane; (2) a thermoplastic polyolefin (TPO) membrane; and (3) an asphaltic multi-ply built-up membrane coated with white elastomeric acrylic paint. The paint product is being used by New York City’s government for the first major urban albedo enhancement program in its history. We report on the temperature and related albedo performance of these three membranes at three different sites over a multi-year period. The results indicate that the professionally installed white membranes are maintaining their temperature control effectively and are meeting the Energy Star Cool Roofing performance standards requiring a three-year aged albedo above 0.50. The EPDM membrane shows evidence of low emissivity; however this had the interesting effect of avoiding any ‘winter heat penalty’ for this building. The painted asphaltic surface shows high emissivity but lost about half of its initial albedo within two years of installation. Given that the acrylic approach is such an important ‘do-it-yourself’, low-cost, retrofit technique, and, as such, offers the most rapid technique for increasing urban albedo, further product performance research is recommended to identify conditions that optimize its long-term albedo control. Even so, its current multi-year performance still represents a significant albedo enhancement for urban heat island mitigation.

Areal-averaged and Spectrally-resolved Surface Albedo from Ground-based Transmission Data Alone: Toward an Operational Retrieval

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kassianov, Evgueni I.; Barnard, James C.; Flynn, Connor J.

We present here a simple retrieval of the areal-averaged and spectrally resolved surface albedo using only ground-based measurements of atmospheric transmission under fully overcast conditions. Our retrieval is based on a one-line equation and widely accepted assumptions regarding the weak spectral dependence of cloud optical properties in the visible and near-infrared spectral range. The feasibility of our approach for the routine determinations of albedo is demonstrated for different landscapes with various degrees of heterogeneity using three sets of measurements:(1) spectrally resolved atmospheric transmission from Multi-Filter Rotating Shadowband Radiometer (MFRSR) at wavelength 415, 500, 615, 673, and 870 nm, (2) tower-basedmore » measurements of local surface albedo at the same wavelengths, and (3) areal-averaged surface albedo at four wavelengths (470, 560, 670 and 860 nm) from collocated and coincident Moderate Resolution Imaging Spectroradiometer (MODIS) observations. These integrated datasets cover both long (2008-2013) and short (April-May, 2010) periods at the ARM Southern Great Plains (SGP) site and the NOAA Table Mountain site, respectively. The calculated root mean square error (RMSE), which is defined here as the root mean squared difference between the MODIS-derived surface albedo and the retrieved area-averaged albedo, is quite small (RMSE≤0.01) and comparable with that obtained previously by other investigators for the shortwave broadband albedo. Good agreement between the tower-based daily averages of surface albedo for the completely overcast and non-overcast conditions is also demonstrated. This agreement suggests that our retrieval originally developed for the overcast conditions likely will work for non-overcast conditions as well.« less

An Algorithm for the Retrieval of 30-m Snow-Free Albedo from Landsat Surface Reflectance and MODIS BRDF

NASA Technical Reports Server (NTRS)

Shuai, Yanmin; Masek, Jeffrey G.; Gao, Feng; Schaaf, Crystal B.

2011-01-01

We present a new methodology to generate 30-m resolution land surface albedo using Landsat surface reflectance and anisotropy information from concurrent MODIS 500-m observations. Albedo information at fine spatial resolution is particularly useful for quantifying climate impacts associated with land use change and ecosystem disturbance. The derived white-sky and black-sky spectral albedos maybe used to estimate actual spectral albedos by taking into account the proportion of direct and diffuse solar radiation arriving at the ground. A further spectral-to-broadband conversion based on extensive radiative transfer simulations is applied to produce the broadband albedos at visible, near infrared, and shortwave regimes. The accuracy of this approach has been evaluated using 270 Landsat scenes covering six field stations supported by the SURFace RADiation Budget Network (SURFRAD) and Atmospheric Radiation Measurement Southern Great Plains (ARM/SGP) network. Comparison with field measurements shows that Landsat 30-m snow-free shortwave albedos from all seasons generally achieve an absolute accuracy of +/-0.02 - 0.05 for these validation sites during available clear days in 2003-2005,with a root mean square error less than 0.03 and a bias less than 0.02. This level of accuracy has been regarded as sufficient for driving global and regional climate models. The Landsat-based retrievals have also been compared to the operational 16-day MODIS albedo produced every 8-days from MODIS on Terra and Aqua (MCD43A). The Landsat albedo provides more detailed landscape texture, and achieves better agreement (correlation and dynamic range) with in-situ data at the validation stations, particularly when the stations include a heterogeneous mix of surface covers.

Monitoring glacier albedo as a proxy to derive summer and annual surface mass balances from optical remote-sensing data

NASA Astrophysics Data System (ADS)

Davaze, Lucas; Rabatel, Antoine; Arnaud, Yves; Sirguey, Pascal; Six, Delphine; Letreguilly, Anne; Dumont, Marie

2018-01-01

Less than 0.25 % of the 250 000 glaciers inventoried in the Randolph Glacier Inventory (RGI V.5) are currently monitored with in situ measurements of surface mass balance. Increasing this archive is very challenging, especially using time-consuming methods based on in situ measurements, and complementary methods are required to quantify the surface mass balance of unmonitored glaciers. The current study relies on the so-called albedo method, based on the analysis of albedo maps retrieved from optical satellite imagery acquired since 2000 by the MODIS sensor, on board the TERRA satellite. Recent studies revealed substantial relationships between summer minimum glacier-wide surface albedo and annual surface mass balance, because this minimum surface albedo is directly related to the accumulation-area ratio and the equilibrium-line altitude. On the basis of 30 glaciers located in the French Alps where annual surface mass balance data are available, our study conducted on the period 2000-2015 confirms the robustness and reliability of the relationship between the summer minimum surface albedo and the annual surface mass balance. For the ablation season, the integrated summer surface albedo is significantly correlated with the summer surface mass balance of the six glaciers seasonally monitored. These results are promising to monitor both annual and summer glacier-wide surface mass balances of individual glaciers at a regional scale using optical satellite images. A sensitivity study on the computed cloud masks revealed a high confidence in the retrieved albedo maps, restricting the number of omission errors. Albedo retrieval artifacts have been detected for topographically incised glaciers, highlighting limitations in the shadow correction algorithm, although inter-annual comparisons are not affected by systematic errors.

Fire-induced albedo change and surface radiative forcing in sub-Saharan Africa savanna ecosystems: Implications for the energy balance

NASA Astrophysics Data System (ADS)

Dintwe, Kebonye; Okin, Gregory S.; Xue, Yongkang

2017-06-01

Surface albedo is a critical parameter that controls surface energy balance. In dryland ecosystems, fires play a significant role in decreasing surface albedo, resulting in positive radiative forcing. Here we investigate the long-term effect of fire on surface albedo. We devised a method to calculate short-, medium-, and long-term effect of fire-induced radiative forcing and their relative effects on energy balance. We used Moderate Resolution Imaging Spectroradiometer (MODIS) data in our analysis, covering different vegetation classes in sub-Saharan Africa (SSA). Our analysis indicated that mean short-term fire-induced albedo change in SSA was -0.022, -0.035, and -0.041 for savannas, shrubland, and grasslands, respectively. At regional scale, mean fire-induced albedo change in savannas was -0.018 and -0.024 for northern sub-Saharan of Africa and the southern hemisphere Africa, respectively. The short-term mean fire-induced radiative forcing in burned areas in sub-Saharan Africa (SSA) was 5.41 W m-2, which contributed continental and global radiative forcings of 0.25 and 0.058 W m-2, respectively. The impact of fire in surface albedo has long-lasting effects that varies with vegetation type. The long-term energetic effects of fire-induced albedo change and associated radiative forcing were, on average, more than 19 times greater across SSA than the short-term effects, suggesting that fires exerted far more radiative forcing than previously thought. Taking into account the actual duration of fire's effect on surface albedo, we conclude that the contribution of SSA fires, globally and throughout the year, is 0.12 W m-2. These findings provide crucial information on possible impact of fire on regional climate variability.

Global Climate Forcing from Albedo Change Caused by Large-scale Deforestation and Reforestation: Quantification and Attribution of Geographic Variation

NASA Technical Reports Server (NTRS)

Gao, Feng; Ghimire, Bardan; Jiao, Tong; Williams, Christopher A.; Masek, Jeffrey; Schaaf, Crystal

2017-01-01

Large-scale deforestation and reforestation have contributed substantially to historical and contemporary global climate change in part through albedo-induced radiative forcing, with meaningful implications for forest management aiming to mitigate climate change. Associated warming or cooling varies widely across the globe due to a range of factors including forest type, snow cover, and insolation, but resulting geographic variation remain spoorly described and has been largely based on model assessments. This study provides an observation-based approach to quantify local and global radiative forcings from large-scale deforestation and reforestation and further examines mechanisms that result in the spatial heterogeneity of radiative forcing. We incorporate a new spatially and temporally explicit land cover-specific albedo product derived from Moderate Resolution Imaging Spectroradiometer with a historical land use data set (Land Use Harmonization product). Spatial variation in radiative forcing was attributed to four mechanisms, including the change in snow-covered albedo, change in snow-free albedo, snow cover fraction, and incoming solar radiation. We find an albedo-only radiative forcing (RF) of -0.819 W m(exp -2) if year 2000 forests were completely deforested and converted to croplands. Albedo RF from global reforestation of present-day croplands to recover year 1700 forests is estimated to be 0.161 W m)exp -2). Snow-cover fraction is identified as the primary factor in determining the spatial variation of radiative forcing in winter, while the magnitude of the change in snow-free albedo is the primary factor determining variations in summertime RF. Findings reinforce the notion that, for conifers at the snowier high latitudes, albedo RF diminishes the warming from forest loss and the cooling from forest gain more so than for other forest types, latitudes, and climate settings.

The influence of burn severity on post-fire vegetation recovery and albedo change during early succession in North American boreal forests

NASA Astrophysics Data System (ADS)

Jin, Y.; Randerson, J. T.; Goetz, S. J.; Beck, P. S.; Loranty, M. M.; Goulden, M.

2011-12-01

Severity of burning can influence multiple aspects of forest composition, carbon cycling, and climate forcing. We quantified how burn severity affected vegetation recovery and albedo change during early succession in Canadian boreal regions by combining satellite observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Canadian Large Fire Data Base (LFDB). We used the difference Normalized Burn Ratio (dNBR) and changes in spring albedo derived from MODIS 500m albedo product as measures of burn severity. We found that the most severe burns had the greatest reduction in summer EVI in first year after fire, indicating greater loss of vegetation cover immediately following fire. By 5-7 years after fire, summer EVI for all severity classes had recovered to within 90-110% of pre-fire levels. Burn severity had a positive effect on the increase of post-fire spring albedo during the first 7 years after fire, and a shift from low to moderate or moderate to severe fires led to amplification of the post-fire albedo increase by approximately 30%. Fire-induced increases in both spring and summer albedo became progressively larger with stand age from years 1-7, with the trend in spring albedo likely driven by continued losses of needles and branches from trees killed by the fire (and concurrent losses of black carbon coatings on remaining debris), and the summer trend associated with increases in leaf area of short-stature herbs and shrubs. Our results suggest that increases in burn severity and carbon losses observed in some areas of boreal forests (e.g., Turetsky et al., 2011) may be at least partly offset by increases in negative forcing associated with changes in surface albedo.

Surface temperatures and retention of H2O frost on Ganymede and Callisto

NASA Technical Reports Server (NTRS)

Squyres, S. W.

1980-01-01

Surface temperatures and ice evaporation rates are calculated for Ganymede and Callisto as functions of latitude, time of day, and albedo, according to a model that uses surface thermal properties determined by eclipse radiometry and albedos determined from photometrically decalibrated Voyager images. The difference in temperature between Ganymede and Callisto is not great enough to account for the lack of bright polar caps on Callisto, which seems instead to reflect a real deficiency in the amount of available water frost relative to Ganymede. The temperature difference between Ganymede's grooved and cratered terrains also cannot account for the high concentration of bright ray craters in the former, suggesting that an internal geologic process has enriched the grooved terrain in ice content relative to the cratered terrain.

The Global Radiative Impact of the Sea-Ice-Albedo Feedback in the Arctic

NASA Astrophysics Data System (ADS)

Hudson, S. R.

2009-12-01

The sea-ice-albedo feedback is known to be an important element of climatic changes over and near regions of ocean with ice cover. It is one of several feedbacks that lead to the polar enhancement of observed and projected global warming. Many studies in the past have used climate models to look at the regional and global impact of the albedo feedback on specific climate variables, most often temperature. These studies generally report a strong regional effect, but also some global effects due to the feedback. Recent changes in Arctic sea ice have led to increased reference to the importance of the sea-ice-albedo feedback, but few studies have examined the global impact of the feedback specifically associated with changes to sea ice in the Arctic; most have included changes to sea ice in both hemispheres, and in many cases, also to snow. That reduced sea ice cover will have a local warming effect is clear from modeling studies. On the other hand, given the relatively small area of the globe that is covered by Arctic sea ice, and the relatively small amounts of sunlight incident on these areas annually, it should be investigated how important reductions in sea ice are to the global solar radiation budget. In this study I present calculations of the global radiative impact of the reduction in Earth’s albedo resulting from reduced sea-ice cover in the Arctic. The intended result is a number, in W m-2, that represents the total increase in absorbed solar radiation due to the reduction in Arctic sea-ice cover, averaged over the globe and over the year. This number is relevant to assessing the long-term, global importance of the sea-ice-albedo feedback to climate change, and can help put it into context by allowing a comparison of this radiative forcing with other forcings, such as those due to CO2 increases and to aerosols, as given in Figure SPM.2 from the IPCC AR4 WG1. Rather than try to determine this forcing with a model, in which the assumptions and approximations are difficult to see and understand, I use representative datasets and calculate the effect with relatively simple math. The solar zenith angle is calculated as a function of latitude and time for an entire year, giving the top-of-atmosphere (ToA) incident flux; the ToA albedo, as a function of solar zenith angle, is taken from observations by CERES, for clear and cloudy skies over sea ice (cold and melting) and ocean; cloud cover data are taken from the cloud atlas of Warren and Hahn; monthly gridded sea ice concentrations from passive microwave data were downloaded from NSIDC and are interpolated to daily concentrations. The total energy absorbed in each grid cell is then calculated in a very straightforward way for 2.5-minute time steps throughout the year. This is done both with the mean ice concentration from 1979 to 1998, and then with various modified concentration fields, including realistic current and future fields, as well as a permanently ice-free Arctic. Clouds are left unchanged, though because of their importance, their effect is investigated. The details of the calculation, including assumptions and approximations will be presented, along with a range of results for current and future changes, as well as for an estimate on the upper bound: a global-annual mean of about 0.7 W m-2.

Arctic sea ice albedo - A comparison of two satellite-derived data sets

NASA Technical Reports Server (NTRS)

Schweiger, Axel J.; Serreze, Mark C.; Key, Jeffrey R.

1993-01-01

Spatial patterns of mean monthly surface albedo for May, June, and July, derived from DMSP Operational Line Scan (OLS) satellite imagery are compared with surface albedos derived from the International Satellite Cloud Climatology Program (ISCCP) monthly data set. Spatial patterns obtained by the two techniques are in general agreement, especially for June and July. Nevertheless, systematic differences in albedo of 0.05 - 0.10 are noted which are most likely related to uncertainties in the simple parameterizations used in the DMSP analyses, problems in the ISCCP cloud-clearing algorithm and other modeling simplifications. However, with respect to the eventual goal of developing a reliable automated retrieval algorithm for compiling a long-term albedo data base, these initial comparisons are very encouraging.

Development of a Multilayer MODIS IST-Albedo Product of Greenland

NASA Technical Reports Server (NTRS)

Hall, D. K.; Comiso, J. C.; Cullather, R. I.; Digirolamo, N. E.; Nowicki, S. M.; Medley, B. C.

2017-01-01

A new multilayer IST-albedo Moderate Resolution Imaging Spectroradiometer (MODIS) product of Greenland was developed to meet the needs of the ice sheet modeling community. The multiple layers of the product enable the relationship between IST and albedo to be evaluated easily. Surface temperature is a fundamental input for dynamical ice sheet models because it is a component of the ice sheet radiation budget and mass balance. Albedo influences absorption of incoming solar radiation. The daily product will combine the existing standard MODIS Collection-6 ice-surface temperature, derived melt maps, snow albedo and water vapor products. The new product is available in a polar stereographic projection in NetCDF format. The product will ultimately extend from March 2000 through the end of 2017.

Using the Opposition Effect in Remotely Sensed Data to Assist in the Retrieval of Bulk Density

NASA Astrophysics Data System (ADS)

Ambeau, Brittany L.

Bulk density is an important geophysical property that impacts the mobility of military vehicles and personnel. Accurate retrieval of bulk density from remotely sensed data is, therefore, needed to estimate the mobility on "off-road" terrain. For a particulate surface, the functional form of the opposition effect can provide valuable information about composition and structure. In this research, we examine the relationship between bulk density and angular width of the opposition effect for a controlled set of laboratory experiments. Given a sample with a known bulk density, we collect reflectance measurements on a spherical grid for various illumination and view geometries -- increasing the amount of reflectance measurements collected at small phase angles near the opposition direction. Bulk densities are varied using a custom-made pluviation device, samples are measured using the Goniometer of the Rochester Institute of Technology-Two (GRIT-T), and observations are fit to the Hapke model using a grid-search method. The method that is selected allows for the direct estimation of five parameters: the single-scattering albedo, the amplitude of the opposition effect, the angular width of the opposition effect, and the two parameters that describe the single-particle phase function. As a test of the Hapke model, the retrieved bulk densities are compared to the known bulk densities. Results show that with an increase in the availability of multi-angular reflectance measurements, the prospects for retrieving the spatial distribution of bulk density from satellite and airborne sensors are imminent.

Generalized Rayleigh scattering. I. Basic theory.

NASA Astrophysics Data System (ADS)

Ivanov, V. V.

1995-11-01

The classsical problem of multiple molecular (in particular, Rayleigh) scattering in plane-parallel atmospheres is considered from a somewhat broader viewpoint than usual. The general approach and ideology are borrowed from non-LTE line formation theory. The main emphasis is on the depth dependence of the corresponding source matrix rather than on the emergent radiation. We study the azimuth-averaged radiation field of polarized radiation in a semi-infinite atmosphere with embedded primary sources. The corresponding 2x2 phase matrix of molecular scattering is P=(1-W) P_I_+W P_R_, where P_I_ and P_R_ are the phase matrices of the scalar isotropic scattering and of the Rayleigh scattering, respectively, and W is the depolarization parameter. Contrary to the usual assumption that W{in}[0,1], we assume W{in} [0,{infinity}) and call this generalized Rayleigh scattering (GRS). Using the factorization of P which is intimately related to its diadic expansion, we reduce the problem to an integral equation for the source matrix S(τ) with a matrix displacement kernel. In operator form this equation is S={LAMBDA}S+S^*^, where {LAMBDA} is the matrix {LAMBDA}-operator and S^*^ is the primary source term. This leads to a new concept, the matrix albedo of single scattering λ =diag(λ_I_,λ_Q_), where λ_I_ is the usual (scalar) single scattering albedo and λ_Q_=0.7Wλ_I_. Its use enables one to formulate matrix equivalents of many of the results of the scalar theory in exactly the same form as in the scalar case. Of crucial importance is the matrix equivalent of the sqrt(ɛ) law of the scalar theory. Another useful new concept is the λ-plane, i.e., the plane with the axes (λ_I_,λ_Q_). Systematic use of the matrix sqrt(ɛ) law and of the λ-plane proved to be a useful instrument in classifying various limiting and particular cases of GRS and in discussing numerical data on the matrix source functions (to be given in Paper II of the series).

Resolving Size Distribution of Black Carbon Internally Mixed With Snow: Impact on Snow Optical Properties and Albedo

NASA Astrophysics Data System (ADS)

He, Cenlin; Liou, Kuo-Nan; Takano, Yoshi

2018-03-01

We develop a stochastic aerosol-snow albedo model that explicitly resolves size distribution of aerosols internally mixed with various snow grains. We use the model to quantify black carbon (BC) size effects on snow albedo and optical properties for BC-snow internal mixing. Results show that BC-induced snow single-scattering coalbedo enhancement and albedo reduction decrease by a factor of 2-3 with increasing BC effective radii from 0.05 to 0.25 μm, while polydisperse BC results in up to 40% smaller visible single-scattering coalbedo enhancement and albedo reduction compared to monodisperse BC with equivalent effective radii. We further develop parameterizations for BC size effects for application to climate models. Compared with a realistic polydisperse assumption and observed shifts to larger BC sizes in snow, respectively, assuming monodisperse BC and typical atmospheric BC effective radii could lead to overestimates of 24% and 40% in BC-snow albedo forcing averaged over different BC and snow conditions.

Retrieval of Aerosol Optical Properties from Ground-Based Remote Sensing Measurements: Aerosol Asymmetry Factor and Single Scattering Albedo

NASA Astrophysics Data System (ADS)

Qie, L.; Li, Z.; Li, L.; Li, K.; Li, D.; Xu, H.

2018-04-01

The Devaux-Vermeulen-Li method (DVL method) is a simple approach to retrieve aerosol optical parameters from the Sun-sky radiance measurements. This study inherited the previous works of retrieving aerosol single scattering albedo (SSA) and scattering phase function, the DVL method was modified to derive aerosol asymmetric factor (g). To assess the algorithm performance at various atmospheric aerosol conditions, retrievals from AERONET observations were implemented, and the results are compared with AERONET official products. The comparison shows that both the DVL SSA and g were well correlated with those of AERONET. The RMSD and the absolute value of MBD deviations between the SSAs are 0.025 and 0.015 respectively, well below the AERONET declared SSA uncertainty of 0.03 for all wavelengths. For asymmetry factor g, the RMSD deviations are smaller than 0.02 and the absolute values of MBDs smaller than 0.01 at 675, 870 and 1020 nm bands. Then, considering several factors probably affecting retrieval quality (i.e. the aerosol optical depth (AOD), the solar zenith angle, and the sky residual error, sphericity proportion and Ångström exponent), the deviations for SSA and g of these two algorithms were calculated at varying value intervals. Both the SSA and g deviations were found decrease with the AOD and the solar zenith angle, and increase with sky residual error. However, the deviations do not show clear sensitivity to the sphericity proportion and Ångström exponent. This indicated that the DVL algorithm is available for both large, non-spherical particles and spherical particles. The DVL results are suitable for the evaluation of aerosol direct radiative effects of different aerosol types.

Triton, Pluto, and Titan: A Comparison of Haze Photometry

NASA Astrophysics Data System (ADS)

Buratti, Bonnie J.; Hillier, John K.; Abgarian, Mary; Kutsop, Nicholas; Devins, Spencer; Mosher, Joel A.; Stern, S. Alan; Weaver, Harold A.; Olkin, Catherine; Young, Leslie; Ennico, Kimberly; New Horizons Science Team

2017-10-01

As Kuiper Belt Objects of similar size and albedo, Triton and Pluto were thought to be kindred bodies exhibiting like geologic histories and features, with possible seasonal volatile transport in their polar regions. During the flyby of Pluto in July 2015, active geological processes were observed on the planet (Stern et al., 2015), and a substantial haze layer that was more akin to Titan’s was observed (Gladstone et. al., 2016). Multiple haze layers were discovered surrounding the dwarf planet (Cheng et al. 2017).Using a radiative transfer model based on Chandrasekhar’s “Planetary Problem” of an optically thin atmosphere and a surface of arbitrary single scattering albedo and single particle phase function (Chandrasekhar, 1960; Hillier et al., 1990, 1991; Buratti et al., 2011), we have characterized the optical depth and surface properties of Pluto, Triton, and Titan. The forward-scattering properties of the haze can also be quantified by this model. Optical imaging data was analyzed for Triton and Pluto. For Titan we made use of published data on Titan (Tomasko and West, 2009) plus new Cassini Visual Infrared Mapping Spectrometer (VIMS) data, which spans the wavelength range between 0.35 and 5.2 microns, and which has several channels in the mid-infrared where both the haze opacity is relatively low and the atmosphere is optically thin. Pluto’s atmosphere is more optically thick than Triton’s but both are far thinner than Titan’s. The composition of Triton’s haze layer differs markedly from Titan’s. Observations of Pluto’s haze reveal a bluish color (Gladstone et al., 2016), but the reddish tint of possible haze deposits on the surface (Stern et al., 2015; Buratti et al., 2015) suggest Pluto’s haze composition is Titan-like. Institute of Technology. Government sponsorship acknowledged.

Highlights from 4STAR Sky-Scanning Retrievals of Aerosol Intensive Optical Properties from Multiple Field Campaigns with Detailed Comparisons of SSA Reported During SEAC4RS

NASA Technical Reports Server (NTRS)

Dunagan, Stephen E.

2016-01-01

The 4STAR (Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research) instrument combines airborne sun tracking capabilities of the Ames Airborne Tracking Sun Photometer (AATS-14) with AERONET (Aerosol Robotic Network)-like sky-scanning capability and adds state-of-the-art fiber-coupled grating spectrometry to yield hyperspectral measurements of direct solar irradiance and angularly resolved sky radiance. The combination of sun-tracking and sky-scanning capability enables retrievals of wavelength-dependent aerosol optical depth (AOD), mode-resolved aerosol size distribution (SD), asphericity, and complex refractive index, and thus also the scattering phase function, asymmetry parameter, single-scattering albedo (SSA), and absorption aerosol optical thickness (AAOT). From 2012 to 2014 4STAR participated in four major field campaigns: the U.S. Dept. of Energy's TCAP (Two-Column Aerosol Project) I & II campaigns, and NASA's SEAC4RS (Studies of Emissions, Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys) and ARISE (Arctic Radiation - IceBridge Sea & Ice Experiment) campaigns. Establishing a strong performance record, 4STAR operated successfully on all flights conducted during each of these campaigns. Sky radiance spectra from scans in either constant azimuth (principal plane) or constant zenith angle (almucantar) were interspersed with direct beam measurements during level legs. During SEAC4RS and ARISE, 4STAR airborne measurements were augmented with flight-level albedo from the collocated Shortwave Spectral Flux Radiometer (SSFR) providing improved specification of below-aircraft radiative conditions for the retrieval. Calibrated radiances and retrieved products will be presented with particular emphasis on detailed comparisons of ambient SSA retrievals and measurements during SEAC4RS from 4STAR, AERONET, HSRL2 (High Spectral Resolution Lidar), and from in situ measurements.

Derivation of martian surface slope characteristics from directional thermal infrared radiometry

NASA Astrophysics Data System (ADS)

Bandfield, Joshua L.; Edwards, Christopher S.

2008-01-01

Directional thermal infrared measurements of the martian surface is one of a variety of methods that may be used to characterize surface roughness and slopes at scales smaller than can be obtained by orbital imagery. Thermal Emission Spectrometer (TES) emission phase function (EPF) observations show distinct apparent temperature variations with azimuth and emission angle that are consistent with the presence of warm, sunlit and cool, shaded slopes at typically ˜0.1 m scales. A surface model of a Gaussian distribution of azimuth independent slopes (described by θ-bar) is combined with a thermal model to predict surface temperature from each viewing angle and azimuth of the TES EPF observation. The models can be used to predict surface slopes using the difference in measured apparent temperature from 2 separate 60-70° emission angle observations taken ˜180° in azimuth relative to each other. Most martian surfaces are consistent with low to moderate slope distributions. The slope distributions display distinct correlations with latitude, longitude, and albedo. Exceptionally smooth surfaces are located at lower latitudes in both the southern highlands as well as in high albedo dusty terrains. High slopes are associated with southern high-latitude patterned ground and north polar sand dunes. There is little apparent correlation between high resolution imagery and the derived θ-bar, with exceptions such as duneforms. This method can be used to characterize potential landing sites by assuming fractal scaling behavior to meter scales. More precisely targeted thermal infrared observations from other spacecraft instruments are capable of significantly reducing uncertainty as well as reducing measurement spot size from 10s of kilometers to sub-kilometer scales.

Super-catastrophic disruption of asteroids at small perihelion distances.

PubMed

Granvik, Mikael; Morbidelli, Alessandro; Jedicke, Robert; Bolin, Bryce; Bottke, William F; Beshore, Edward; Vokrouhlický, David; Delbò, Marco; Michel, Patrick

2016-02-18

Most near-Earth objects came from the asteroid belt and drifted via non-gravitational thermal forces into resonant escape routes that, in turn, pushed them onto planet-crossing orbits. Models predict that numerous asteroids should be found on orbits that closely approach the Sun, but few have been seen. In addition, even though the near-Earth-object population in general is an even mix of low-albedo (less than ten per cent of incident radiation is reflected) and high-albedo (more than ten per cent of incident radiation is reflected) asteroids, the characterized asteroids near the Sun typically have high albedos. Here we report a quantitative comparison of actual asteroid detections and a near-Earth-object model (which accounts for observational selection effects). We conclude that the deficit of low-albedo objects near the Sun arises from the super-catastrophic breakup (that is, almost complete disintegration) of a substantial fraction of asteroids when they achieve perihelion distances of a few tens of solar radii. The distance at which destruction occurs is greater for smaller asteroids, and their temperatures during perihelion passages are too low for evaporation to explain their disappearance. Although both bright and dark (high- and low-albedo) asteroids eventually break up, we find that low-albedo asteroids are more likely to be destroyed farther from the Sun, which explains the apparent excess of high-albedo near-Earth objects and suggests that low-albedo asteroids break up more easily as a result of thermal effects.

Preferential cooling of hot extremes from cropland albedo management

PubMed Central

Davin, Edouard L.; Seneviratne, Sonia I.; Ciais, Philippe; Olioso, Albert; Wang, Tao

2014-01-01

Changes in agricultural practices are considered a possible option to mitigate climate change. In particular, reducing or suppressing tillage (no-till) may have the potential to sequester carbon in soils, which could help slow global warming. On the other hand, such practices also have a direct effect on regional climate by altering the physical properties of the land surface. These biogeophysical effects, however, are still poorly known. Here we show that no-till management increases the surface albedo of croplands in summer and that the resulting cooling effect is amplified during hot extremes, thus attenuating peak temperatures reached during heat waves. Using a regional climate model accounting for the observed effects of no-till farming on surface albedo, as well as possible reductions in soil evaporation, we investigate the potential consequences of a full conversion to no-till agriculture in Europe. We find that the summer cooling from cropland albedo increase is strongly amplified during hot summer days, when surface albedo has more impact on the Earth’s radiative balance due to clear-sky conditions. The reduced evaporation associated with the crop residue cover tends to counteract the albedo-induced cooling, but during hot days the albedo effect is the dominating factor. For heatwave summer days the local cooling effect gained from no-till practice is of the order of 2 °C. The identified asymmetric impact of surface albedo change on summer temperature opens new avenues for climate-engineering measures targeting high-impact events rather than mean climate properties. PMID:24958872

DOE Office of Scientific and Technical Information (OSTI.GOV)

Masiero, Joseph R.; Mainzer, A. K.; Bauer, J. M.

We present initial results from the Wide-field Infrared Survey Explorer (WISE), a four-band all-sky thermal infrared survey that produces data well suited for measuring the physical properties of asteroids, and the NEOWISE enhancement to the WISE mission allowing for detailed study of solar system objects. Using a NEATM thermal model fitting routine, we compute diameters for over 100,000 Main Belt asteroids from their IR thermal flux, with errors better than 10%. We then incorporate literature values of visible measurements (in the form of the H absolute magnitude) to determine albedos. Using these data we investigate the albedo and diameter distributionsmore » of the Main Belt. As observed previously, we find a change in the average albedo when comparing the inner, middle, and outer portions of the Main Belt. We also confirm that the albedo distribution of each region is strongly bimodal. We observe groupings of objects with similar albedos in regions of the Main Belt associated with dynamical breakup families. Asteroid families typically show a characteristic albedo for all members, but there are notable exceptions to this. This paper is the first look at the Main Belt asteroids in the WISE data, and only represents the preliminary, observed raw size, and albedo distributions for the populations considered. These distributions are subject to survey biases inherent to the NEOWISE data set and cannot yet be interpreted as describing the true populations; the debiased size and albedo distributions will be the subject of the next paper in this series.« less

Sea ice roughness: the key for predicting Arctic summer ice albedo

NASA Astrophysics Data System (ADS)

Landy, J.; Ehn, J. K.; Tsamados, M.; Stroeve, J.; Barber, D. G.

2017-12-01

Although melt ponds on Arctic sea ice evolve in stages, ice with smoother surface topography typically allows the pond water to spread over a wider area, reducing the ice-albedo and accelerating further melt. Building on this theory, we simulated the distribution of meltwater on a range of statistically-derived topographies to develop a quantitative relationship between premelt sea ice surface roughness and summer ice albedo. Our method, previously applied to ICESat observations of the end-of-winter sea ice roughness, could account for 85% of the variance in AVHRR observations of the summer ice-albedo [Landy et al., 2015]. Consequently, an Arctic-wide reduction in sea ice roughness over the ICESat operational period (from 2003 to 2008) explained a drop in ice-albedo that resulted in a 16% increase in solar heat input to the sea ice cover. Here we will review this work and present new research linking pre-melt sea ice surface roughness observations from Cryosat-2 to summer sea ice albedo over the past six years, examining the potential of winter roughness as a significant new source of sea ice predictability. We will further evaluate the possibility for high-resolution (kilometre-scale) forecasts of summer sea ice albedo from waveform-level Cryosat-2 roughness data in the landfast sea ice zone of the Canadian Arctic. Landy, J. C., J. K. Ehn, and D. G. Barber (2015), Albedo feedback enhanced by smoother Arctic sea ice, Geophys. Res. Lett., 42, 10,714-10,720, doi:10.1002/2015GL066712.

How Well Can We Estimate Areal-Averaged Spectral Surface Albedo from Ground-Based Transmission in an Atlantic Coastal Area?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kassianov, Evgueni I.; Barnard, James C.; Flynn, Connor J.

Areal-averaged albedos are particularly difficult to measure in coastal regions, because the surface is not homogenous, consisting of a sharp demarcation between land and water. With this difficulty in mind, we evaluate a simple retrieval of areal-averaged surface albedo using ground-based measurements of atmospheric transmission alone under fully overcast conditions. To illustrate the performance of our retrieval, we find the areal-averaged albedo using measurements from the Multi-Filter Rotating Shadowband Radiometer (MFRSR) at five wavelengths (415, 500, 615, 673, and 870 nm). These MFRSR data are collected at a coastal site in Graciosa Island, Azores supported by the U.S. Department ofmore » Energy’s (DOE’s) Atmospheric Radiation Measurement (ARM) Program. The areal-averaged albedos obtained from the MFRSR are compared with collocated and coincident Moderate Resolution Imaging Spectroradiometer (MODIS) white-sky albedo at four nominal wavelengths (470, 560, 670 and 860 nm). These comparisons are made during a 19-month period (June 2009 - December 2010). We also calculate composite-based spectral values of surface albedo by a weighted-average approach using estimated fractions of major surface types observed in an area surrounding this coastal site. Taken as a whole, these three methods of finding albedo show spectral and temporal similarities, and suggest that our simple, transmission-based technique holds promise, but with estimated errors of about ±0.03. Additional work is needed to reduce this uncertainty in areas with inhomogeneous surfaces.« less

Modelling Mean Albedo of Individual Roofs in Complex Urban Areas Using Satellite Images and Airborne Laser Scanning Point Clouds

NASA Astrophysics Data System (ADS)

Kalantar, B.; Mansor, S.; Khuzaimah, Z.; Sameen, M. Ibrahim; Pradhan, B.

2017-09-01

Knowledge of surface albedo at individual roof scale is important for mitigating urban heat islands and understanding urban climate change. This study presents a method for quantifying surface albedo of individual roofs in a complex urban area using the integration of Landsat 8 and airborne LiDAR data. First, individual roofs were extracted from airborne LiDAR data and orthophotos using optimized segmentation and supervised object based image analysis (OBIA). Support vector machine (SVM) was used as a classifier in OBIA process for extracting individual roofs. The user-defined parameters required in SVM classifier were selected using v-fold cross validation method. After that, surface albedo was calculated for each individual roof from Landsat images. Finally, thematic maps of mean surface albedo of individual roofs were generated in GIS and the results were discussed. Results showed that the study area is covered by 35% of buildings varying in roofing material types and conditions. The calculated surface albedo of buildings ranged from 0.16 to 0.65 in the study area. More importantly, the results indicated that the types and conditions of roofing materials significantly effect on the mean value of surface albedo. Mean albedo of new concrete, old concrete, new steel, and old steel were found to be equal to 0.38, 0.26, 0.51, and 0.44 respectively. Replacing old roofing materials with new ones should highly prioritized.

The Gamma-Ray Albedo of the Moon

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moskalenko, I.V.; /Stanford U., HEPL /KIPAC, Menlo Park; Porter, T.A.

2008-03-25

We use the GEANT4 Monte Carlo framework to calculate the {gamma}-ray albedo of the Moon due to interactions of cosmic ray (CR) nuclei with moon rock. Our calculation of the albedo spectrum agrees with the EGRET data. We show that the spectrum of {gamma}-rays from the Moon is very steep with an effective cutoff around 3-4 GeV (600 MeV for the inner part of the Moon disk) and exhibits a narrow pion-decay line at 67.5 MeV, perhaps unique in astrophysics. Apart from other astrophysical sources, the albedo spectrum of the Moon is well understood, including its absolute normalization; this makesmore » it a useful 'standard candle' for {gamma}-ray telescopes. The steep albedo spectrum also provides a unique opportunity for energy calibration of {gamma}-ray telescopes, such as the forthcoming Gamma Ray Large Area Space Telescope (GLAST). Since the albedo flux depends on the incident CR spectrum which changes over the solar cycle, it is possible to monitor the CR spectrum using the albedo {gamma}-ray flux. Simultaneous measurements of CR proton and helium spectra by the Payload for Antimatter-Matter Exploration and Light-nuclei Astrophysics (PAMELA), and observations of the albedo {gamma}-rays by the GLAST Large Area Telescope (LAT), can be used to test the model predictions and will enable the LAT to monitor the CR spectrum near the Earth beyond the lifetime of the PAMELA.« less

The Gamma-ray Albedo of the Moon

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moskalenko, Igor V.; /Stanford U., HEPL; Porter, Troy A.

2007-09-28

We use the GEANT4 Monte Carlo framework to calculate the {gamma}-ray albedo of the Moon due to interactions of cosmic ray (CR) nuclei with moon rock. Our calculation of the albedo spectrum agrees with the EGRET data. We show that the spectrum of {gamma}-rays from the Moon is very steep with an effective cutoff around 3-4 GeV (600 MeV for the inner part of the Moon disk) and exhibits a narrow pion-decay line at 67.5 MeV, perhaps unique in astrophysics. Apart from other astrophysical sources, the albedo spectrum of the Moon is well understood, including its absolute normalization; this makesmore » it a useful 'standard candle' for {gamma}-ray telescopes. The steep albedo spectrum also provides a unique opportunity for energy calibration of {gamma}-ray telescopes, such as the forthcoming Gamma Ray Large Area Space Telescope (GLAST). Since the albedo flux depends on the incident CR spectrum which changes over the solar cycle, it is possible to monitor the CR spectrum using the albedo {gamma}-ray flux. Simultaneous measurements of CR proton and helium spectra by the Payload for Antimatter-Matter Exploration and Light-nuclei Astrophysics (PAMELA), and observations of the albedo {gamma}-rays by the GLAST Large Area Telescope (LAT), can be used to test the model predictions and will enable the LAT to monitor the CR spectrum near the Earth beyond the lifetime of the PAMELA.« less

Arid land monitoring using Landsat albedo difference images

USGS Publications Warehouse

Robinove, Charles J.; Chavez, Pat S.; Gehring, Dale G.; Holmgren, Ralph

1981-01-01

The Landsat albedo, or percentage of incoming radiation reflected from the ground in the wavelength range of 0.5 [mu]m to 1.1 [mu]m, is calculated from an equation using the Landsat digital brightness values and solar irradiance values, and correcting for atmospheric scattering, multispectral scanner calibration, and sun angle. The albedo calculated for each pixel is used to create an albedo image, whose grey scale is proportional to the albedo. Differencing sequential registered images and mapping selected values of the difference is used to create quantitative maps of increased or decreased albedo values of the terrain. All maps and other output products are in black and white rather than color, thus making the method quite economical. Decreases of albedo in arid regions may indicate improvement of land quality; increases may indicate degradation. Tests of the albedo difference mapping method in the Desert Experimental Range in southwestern Utah (a cold desert with little long-term terrain change) for a four-year period show that mapped changes can be correlated with erosion from flash floods, increased or decreased soil moisture, and increases or decreases in the density of desert vegetation, both perennial shrubs and annual plants. All terrain changes identified in this test were related to variations in precipitation. Although further tests of this method in hot deserts showing severe "desertification" are needed, the method is nevertheless recommended for experimental use in monitoring terrain change in other arid and semiarid regions of the world.

A SmallSat Approach for Global Imaging Spectroscopy of the Earth SYSTEM Enabled by Advanced Technology

NASA Astrophysics Data System (ADS)

Green, R. O.; Asner, G. P.; Thompson, D. R.; Mouroulis, P.; Eastwood, M. L.; Chien, S.

2017-12-01

Global coverage imaging spectroscopy in the solar reflected energy portion of the spectrum has been identified by the Earth Decadal Survey as an important measurement that enables a diverse set of new and time critical science objectives/targets for the Earth system. These science objectives include biodiversity; ecosystem function; ecosystem biogeochemistry; initialization and constraint of global ecosystem models; fire fuel, combustion, burn severity, and recovery; surface mineralogy, geochemistry, geologic processes, soils, and hazards; global mineral dust source composition; cryospheric albedo, energy balance, and melting; coastal and inland water habitats; coral reefs; point source gas emission; cloud thermodynamic phase; urban system properties; and more. Traceability of these science objectives to spectroscopic measurement in the visible to short wavelength infrared portion of the spectrum is summarized. New approaches, including satellite constellations, to acquire these global imaging spectroscopy measurements is presented drawing from recent advances in optical design, detector technology, instrument architecture, thermal control, on-board processing, data storage, and downlink.

Optics of Water Microdroplets with Soot Inclusions: Exact Versus Approximate Results

NASA Technical Reports Server (NTRS)

Liu, Li; Mishchenko, Michael I.

2016-01-01

We use the recently generalized version of the multi-sphere superposition T-matrix method (STMM) to compute the scattering and absorption properties of microscopic water droplets contaminated by black carbon. The soot material is assumed to be randomly distributed throughout the droplet interior in the form of numerous small spherical inclusions. Our numerically-exact STMM results are compared with approximate ones obtained using the Maxwell-Garnett effective-medium approximation (MGA) and the Monte Carlo ray-tracing approximation (MCRTA). We show that the popular MGA can be used to calculate the droplet optical cross sections, single-scattering albedo, and asymmetry parameter provided that the soot inclusions are quasi-uniformly distributed throughout the droplet interior, but can fail in computations of the elements of the scattering matrix depending on the volume fraction of soot inclusions. The integral radiative characteristics computed with the MCRTA can deviate more significantly from their exact STMM counterparts, while accurate MCRTA computations of the phase function require droplet size parameters substantially exceeding 60.

Independent Pixel and Two Dimensional Estimates of LANDSAT-Derived Cloud Field Albedo

NASA Technical Reports Server (NTRS)

Chambers, L. H.; Wielicki, Bruce A.; Evans, K. F.

1996-01-01

A theoretical study has been conducted on the effects of cloud horizontal inhomogeneity on cloud albedo bias. A two-dimensional (2D) version of the Spherical Harmonic Discrete Ordinate Method (SHDOM) is used to estimate the albedo bias of the plane parallel (PP-IPA) and independent pixel (IPA-2D) approximations for a wide range of 2D cloud fields obtained from LANDSAT. They include single layer trade cumulus, open and closed cell broken stratocumulus, and solid stratocumulus boundary layer cloud fields over ocean. Findings are presented on a variety of averaging scales and are summarized as a function of cloud fraction, mean cloud optical depth, cloud aspect ratio, standard deviation of optical depth, and the gamma function parameter Y (a measure of the width of the optical depth distribution). Biases are found to be small for small cloud fraction or mean optical depth, where the cloud fields under study behave linearly. They are large (up to 0.20 for PP-IPA bias, -0.12 for IPA-2D bias) for large v. On a scene average basis PP-IPA bias can reach 0.30, while IPA-2D bias reaches its largest magnitude at -0.07. Biases due to horizontal transport (IPA-2D) are much smaller than PP-IPA biases but account for 20% RMS of the bias overall. Limitations of this work include the particular cloud field set used, assumptions of conservative scattering, constant cloud droplet size, no gas absorption or surface reflectance, and restriction to 2D radiative transport. The LANDSAT data used may also be affected by radiative smoothing.

Mars Aerosol Studies with the MGS TES Emission Phase Function Observations: Opacities, Particle Sizes, and Ice Cloud Types

NASA Astrophysics Data System (ADS)

Wolff, M. J.; Clancy, R. T.; Pitman, K. M.; Christensen, P. R.; Whitney, B. A.

2001-11-01

A full Mars year (1999-2001) of emission phase function (EPF) observations from Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES) provide the most complete study of Mars dust and ice aerosol properties to date. TES visible (solar band average) and infrared spectral EPF sequences are analyzed self-consistently with detailed multiple scattering radiative transfer codes. As a consequence of the combined angular and wavelength coverage, we are able to define two distinct ice cloud types at 45\\arcdeg S-45\\arcdeg N latitudes on Mars. Type I ice clouds exhibit small particle sizes (1-2 \\micron\\ radii), as well as a broad, deep minimum in side-scattering that are potentially indicative of aligned ice grains. Type I ice aerosols are most prevalent in the southern hemisphere during Mars aphelion, but also appear more widely distributed in season and latitude as topographic and high altitude (>20 km) ice hazes. Type II ice clouds exhibit larger particle sizes (3-5 \\micron) and a much narrower side-scattering minimum, indicative of poorer grain alignment or a change in particle shape relative to the type I ice clouds. Type II ice clouds appear most prominently in the northern subtropical aphelion cloud belt, where relatively low altitudes water vapor saturation (10 km) coincide with strong advective transport. Retrieved dust particle radii of 1.5-1.8 \\micron\\ are consistent with Pathfinder and recent Viking/Mariner 9 reanalyses. Our analyses also find EPF-derived dust single scattering albedos (ssa) in agreement with those from Pathfinder. Spatial and seasonal changes in the dust ssa (0.92-0.95, solar band average) and phase functions suggest possible dust property variations, but may also be a consequence of variable high altitude ice hazes. The annual variations of both dust and ice clouds at 45S-45N latitudes are predominately orbital rather than seasonal in character and have shown remarkable repeatability during the portions of two Mars years observed by MGS.

Earth's Reflection: Albedo

ERIC Educational Resources Information Center

Gillette, Brandon; Hamilton, Cheri

2011-01-01

When viewing objects of different colors, you might notice that some appear brighter than others. This is because light is reflected differently from various surfaces, depending on their physical properties. The word "albedo" is used to describe how reflective a surface is. The Earth-atmosphere has a combined albedo of about 30%, a number that is…

Climatic influence of background and volcanic stratosphere aerosol models

NASA Technical Reports Server (NTRS)

Deschamps, P. Y.; Herman, M.; Lenoble, J.; Tanre, D.

1982-01-01

A simple modelization of the earth atmosphere system including tropospheric and stratospheric aerosols has been derived and tested. Analytical expressions are obtained for the albedo variation due to a thin stratospheric aerosol layer. Also outlined are the physical procedures and the respective influence of the main parameters: aerosol optical thickness, single scattering albedo and asymmetry factor, and sublayer albedo. The method is applied to compute the variation of the zonal and planetary albedos due to a stratospheric layer of background H2SO4 particles and of volcanic ash.

Detecting Low-Contrast Features in the Cosmic Ray Albedo Proton Map of the Moon

NASA Technical Reports Server (NTRS)

Wilson, J. K.; Schwadron, N.; Spence, H. E.; Golightly, M. J.; Case, A. W.; Smith, S.; Blake, J. B.; Kasper, J.; Looper, M. D.; Mazur, J. E.;

Variable control of neutron albedo in toroidal fusion devices

DOEpatents

Jassby, Daniel L.; Micklich, Bradley J.

1986-01-01

An arrangement is provided for controlling neutron albedo in toroidal fusion devices having inboard and outboard vacuum vessel walls for containment of the neutrons of a fusion plasma. Neutron albedo material is disposed immediately adjacent the inboard wall, and is movable, preferably in vertical directions, so as to be brought into and out of neutron modifying communication with the fusion neutrons. Neutron albedo material preferably comprises a liquid form, but may also take pebble, stringer and curtain-like forms. A neutron flux valve, rotatable about a vertical axis is also disclosed.

Seasonal albedo of an urban/rural landscape from satellite observations

NASA Technical Reports Server (NTRS)

Brest, Christopher L.

1987-01-01

Using data from 27 calibrated Landsat observations of the Hartford, Connecticut area, the spatial distribution and seasonal variation of surface reflectance and albedo were examined. Mean values of visible reflectance, near-IR reflectance, and albedo are presented (for both snow-free and snow-cover observations) according to 14 land use/land cover categories. A diversity of albedo values was found to exist in this type of environment, associated with land cover. Many land-cover categories display a seasonal dependence, with intracategory seasonal differences being of comparable magnitude to intercategory differences. Key factors in determining albedo (and its seasonal dynamics) are the presence or absence of vegetation and the canopy structure. Snow-cover/snow-free differences range from a few percent (for urban land covers) to over 40 percent (for low-canopy vegetation).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nugent, C. R.; Cutri, R. M.; Mainzer, A.

The Near-Earth Object Wide-Field Infrared Survey Explorer (NEOWISE) mission continues to detect, track, and characterize minor planets. We present diameters and albedos calculated from observations taken during the second year since the spacecraft was reactivated in late 2013. These include 207 near-Earth asteroids (NEAs) and 8885 other asteroids. Of the NEAs, 84% NEAs did not have previously measured diameters and albedos by the NEOWISE mission. Comparison of sizes and albedos calculated from NEOWISE measurements with those measured by occultations, spacecraft, and radar-derived shapes shows accuracy consistent with previous NEOWISE publications. Diameters and albedos fall within ±∼20% and ±∼40%, 1-sigma, respectively,more » of those measured by these alternate techniques. NEOWISE continues to preferentially discover near-Earth objects which are large (>100 m), and have low albedos.« less

Radiative forcing impacts of boreal forest biofuels: a scenario study for Norway in light of albedo.

PubMed

Bright, Ryan M; Strømman, Anders Hammer; Peters, Glen P

2011-09-01

Radiative forcing impacts due to increased harvesting of boreal forests for use as transportation biofuel in Norway are quantified using simple climate models together with life cycle emission data, MODIS surface albedo data, and a dynamic land use model tracking carbon flux and clear-cut area changes within productive forests over a 100-year management period. We approximate the magnitude of radiative forcing due to albedo changes and compare it to the forcing due to changes in the carbon cycle for purposes of attributing the net result, along with changes in fossil fuel emissions, to the combined anthropogenic land use plus transport fuel system. Depending on albedo uncertainty and uncertainty about the geographic distribution of future logging activity, we report a range of results, thus only general conclusions about the magnitude of the carbon offset potential due to changes in surface albedo can be drawn. Nevertheless, our results have important implications for how forests might be managed for mitigating climate change in light of this additional biophysical criterion, and in particular, on future biofuel policies throughout the region. Future research efforts should be directed at understanding the relationships between the physical properties of managed forests and albedo, and how albedo changes in time as a result of specific management interventions.

Albedo impact on the suitability of biochar systems to mitigate global warming.

PubMed

Meyer, Sebastian; Bright, Ryan M; Fischer, Daniel; Schulz, Hardy; Glaser, Bruno

2012-11-20

Biochar application to agricultural soils can change the surface albedo which could counteract the climate mitigation benefit of biochar systems. However, the size of this impact has not yet been quantified. Based on empirical albedo measurements and literature data of arable soils mixed with biochar, a model for annual vegetation cover development based on satellite data and an assessment of the annual development of surface humidity, an average mean annual albedo reduction of 0.05 has been calculated for applying 30-32 Mg ha(-1) biochar on a test field near Bayreuth, Germany. The impact of biochar production and application on the carbon cycle and on the soil albedo was integrated into the greenhouse gas (GHG) balance of a modeled pyrolysis based biochar system via the computation of global warming potential (GWP) characterization factors. The analysis resulted in a reduction of the overall climate mitigation benefit of biochar systems by 13-22% due to the albedo change as compared to an analysis which disregards the albedo effect. Comparing the use of the same quantity of biomass in a biochar system to a bioenergy district heating system which replaces natural gas combustion, bioenergy heating systems achieve 99-119% of the climate benefit of biochar systems according to the model calculation.

NOAA AVHRR Land Surface Albedo Algorithm Development

NASA Technical Reports Server (NTRS)

Toll, D. L.; Shirey, D.; Kimes, D. S.

1997-01-01

The primary objective of this research is to develop a surface albedo model for the National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR). The primary test site is the Konza prairie, Kansas (U.S.A.), used by the International Satellite Land Surface Climatology Project (ISLSCP) in the First ISLSCP Field Experiment (FIFE). In this research, high spectral resolution field spectrometer data was analyzed to simulate AVHRR wavebands and to derive surface albedos. Development of a surface albedo algorithm was completed by analysing a combination of satellite, field spectrometer, and ancillary data. Estimated albedos from the field spectrometer data were compared to reference albedos derived using pyranometer data. Variations from surface anisotropy of reflected solar radiation were found to be the most significant albedo-related error. Additional error or sensitivity came from estimation of a shortwave mid-IR reflectance (1.3-4.0 micro-m) using the AVHRR red and near-IR bands. Errors caused by the use of AVHRR spectral reflectance to estimate both a total visible (0.4-0.7 micro-m) and near-IR (0.7-1.3 micro-m) reflectance were small. The solar spectral integration, using the derived ultraviolet, visible, near-IR and SW mid-IR reflectivities, was not sensitive to many clear-sky changes in atmospheric properties and illumination conditions.

Evaluation of the SMAP model calculated snow albedo at the SIGMA-A site, northwest Greenland, during the 2012 record surface melt event

NASA Astrophysics Data System (ADS)

Niwano, M.; Aoki, T.; Matoba, S.; Yamaguchi, S.; Tanikawa, T.; Kuchiki, K.; Motoyama, H.

2015-12-01

The snow and ice on the Greenland ice sheet (GrIS) experienced the extreme surface melt around 12 July, 2012. In order to understand the snow-atmosphere interaction during the period, we applied a physical snowpack model SMAP to the GrIS snowpack. In the SMAP model, the snow albedo is calculated by the PBSAM component explicitly considering effects of snow grain size and light-absorbing snow impurities such as black carbon and dust. Temporal evolution of snow grain size is calculated internally in the SMAP model, whereas mass concentrations of snow impurities are externally given from observations. In the PBSAM, the (shortwave) snow albedo is calculated from a weighted summation of visible albedo (primarily affected by snow impurities) and near-infrared albedo (mainly controlled by snow grain size). The weights for these albedos are the visible and near-infrared fractions of the downward shortwave radiant flux. The SMAP model forced by meteorological data obtained from an automated weather station at SIGMA-A site, northwest GrIS during 30 June to 14 July, 2012　(IOP) was evaluated in terms of surface (optically equivalent) snow grain size and snow albedo. Snow grain size simulated by the model was compared against that retrieved from in-situ spectral albedo measurements. Although the RMSE and ME were reasonable (0.21 mm and 0.17 mm, respectively), the small snow grain size associated with the surface hoar could not be simulated by the SMAP model. As for snow albedo, simulation results agreed well with observations throughout the IOP (RMSE was 0.022 and ME was 0.008). Under cloudy-sky conditions, the SMAP model reproduced observed rapid increase in the snow albedo. When cloud cover is present the near-infrared fraction of the downward shortwave radiant flux is decreased, while it is increased under clear-sky conditions. Therefore, the above mentioned performance of the SMAP model can be attributed to the PBSAM component driven by the observed near-infrared and visible fractions of the downward shortwave radiant flux. This result suggests that it is necessary for snowpack models to consider changes in the visible and near-infrared fractions of the downward shortwave radiant flux caused by the presence of cloud cover to reproduce realistic temporal changes in the snow albedo and consequently the surface energy balance.

Analysis of Surface Albedo to Improve Upper-Ocean Heat Budget Calculations

NASA Astrophysics Data System (ADS)

Hogikyan, A.; Zhang, D.; Cronin, M. F.

2016-12-01

Over 90% of the Earth's energy imbalance is stored in the oceans, so it is important to understand the ocean-atmosphere heat transfer. The Ocean Climate Stations group (OCS) at the Pacific Marine Environmental Laboratory maintains two moored surface buoys in the North Pacific (PAPA and KEO) as air-sea flux reference sites. The goal of the reference sites is to validate global air-sea flux products from atmospheric reanalyses and satellite products, that are critical to understand and model the variability and trend of the earth climate. As other air-sea flux reference buoys in the world ocean, PAPA and KEO only measure downward shortwave radiation (SWdown), but utilize the albedo and the directly measured SWdown to calculate the SWup. Since the open ocean albedo is small, the errors associated with this practice are thought to be comparable or smaller than the instrumentation errors in the air-sea flux measurements. In addition, it is generally accepted that ocean surface albedos can be derived with reasonable confidence from surface radiative fluxes in satellite products such as the Clouds and the Earth's Radiant Energy System (CERES) and the International Satellite Cloud Climatology Project (ISCCP). This project developed a CERES-based albedo product for derivation of SWnet at PAPA and KEO, and assessed the impact of CERES-based albedo on the net surface heat fluxes relative to the currently used ISCCP-based albedo in the OCS air-sea flux data (http://www.pmel.noaa.gov/ocs/data/fluxdisdel/). The high-resolution surface fluxes from CERES are more frequently updated, and consider more physical factors in the approximation, than those from ISCCP. There was a greater change between ISCCP and CERES albedo during wintertime than during summer. There was a greater change at Station PAPA in the northeastern sub-Arctic Pacific, than at Station KEO in the northwestern subtropical Pacific. The rate of temperature change of the mixed-layer is shown to increase based on the new source of albedo data, .08 and .5 °C/year at KEO and PAPA, respectively. The differences in the net surface heat flux due to different albedos used in this study suggest that more comprehensive investigations of the albedo in different products and radiative models, and their impacts on oceanic and atmospheric processes are needed.

Bacterial production of sunscreen pigments increase arid land soil surface temperature

NASA Astrophysics Data System (ADS)

Couradeau, Estelle; Karaoz, Ulas; Lim, HsiaoChien; Nunes da Rocha, Ulisses; Northern, Trent; Brodie, Eoin; Garcia-Pichel, Ferran

2015-04-01

Biological Soil Crusts (BSCs) are desert top soils formations built by complex microbial communities and dominated by the filamentous cyanobacterium Microcoleus sp. BSCs cover extensive desert areas where they correspond to millimeters size mantles responsible of soil stability and fertility. Despite their ecological importance, little is known about how these communities will endure climate change. It has been shown in North America that different species of Microcoleus showed distinct temperature preferences and that their continental biogeography may be susceptible to small changes in temperature with unknown consequences for the ecosystem function. Using a combination of physical, biochemical and microbiological analyses to characterize a successional gradient of crust maturity from light to dark BSCs (Moab, Utah) we found that the concentration of scytonemin (a cyanobacterial sunscreen pigment) increased with crust maturity. We also confirmed that scytonemin was by far the major pigment responsible of light absorption in the visible spectrum in BSCs, and is then responsible of the darkening of the BSCs (i.e decrease of albedo) with maturity. We measured the surface temperature and albedo and found, as predicted, a negative linear relationship between these two parameters. The decrease in albedo across the gradient of crust maturity corresponded to an increase in surface temperature up to 10° C. Upon investigation of microbial community composition using SSU rRNA gene analysis, we demonstrate that warmer crust surface temperatures (decreased albedo) are associated with a replacement of the dominant cyanobacterium; the thermosensitive Microcoleus sp. being replaced by a thermotolerant Microcoleus sp. in darker BSCs. This study supports at the local scale a finding previously made at the continental scale, but also sheds light on the importance of scytonemin as a significant warmer of soils with important consequences for BSC composition and function. Based on estimates of the global biomass of cyanobacteria in soil crusts, one can easily calculate that there must currently exist about 15 million metric tons of scytonemin accumulated on the surface of arid soils worldwide, whose role on soils temperature has been ignored so far.

Planets as background noise sources in free space optical communications

NASA Technical Reports Server (NTRS)

Katz, J.

1986-01-01

Background noise generated by planets is the dominant noise source in most deep space direct detection optical communications systems. Earlier approximate analyses of this problem are based on simplified blackbody calculations and can yield results that may be inaccurate by up to an order of magnitude. Various other factors that need to be taken into consideration, such as the phase angle and the actual spectral dependence of the planet albedo, in order to obtain a more accurate estimate of the noise magnitude are examined.

Change in Urban Albedo in London: A Multi-scale Perspective

NASA Astrophysics Data System (ADS)

Susca, T.; Kotthaus, S.; Grimmond, S.

2013-12-01

Urbanization-induced change in land use has considerable implications for climate, air quality, resources and ecosystems. Urban-induced warming is one of the most well-known impacts. This directly and indirectly can extend beyond the city. One way to reduce the size of this is to modify the surface atmosphere exchanges through changing the urban albedo. As increased rugosity caused by the morphology of a city results in lower albedo with constant material characteristics, the impacts of changing the albedo has impacts across a range of scales. Here a multi-scale assessment of the potential effects of the increase in albedo in London is presented. This includes modeling at the global and meso-scale informed by local and micro-scale measurements. In this study the first order calculations are conducted for the impact of changing the albedo (e.g. a 0.01 increase) on the radiative exchange. For example, when incoming solar radiation and cloud cover are considered, based on data retrieved from NASA (http://power.larc.nasa.gov/) for ~1600 km2 area of London, would produce a mean decrease in the instantaneous solar radiative forcing on the same surface of 0.40 W m-2. The nature of the surface is critical in terms of considering the impact of changes in albedo. For example, in the Central Activity Zone in London pavement and building can vary from 10 to 100% of the plan area. From observations the albedo is seen to change dramatically with changes in building materials. For example, glass surfaces which are being used increasingly in the central business district results in dramatic changes in albedo. Using the documented albedo variations determined across different scales the impacts are considered. For example, the effect of the increase in urban albedo is translated into the corresponding amount of avoided emission of carbon dioxide that produces the same effect on climate. At local scale, the effect that the increase in urban albedo can potentially have on local climate is calculated using numerical modelling to mitigate the urban heat island in London. The co-benefits from decreasing the urban temperature are then considered. These include a reduction in the peak of tropospheric ozone formation, a decrease heat stress to the city dwellers as well as in energy demand. The extreme summer temperatures have most of the impact on people socially and physically vulnerable people. The decrease in summer temperatures has positive effects on human health decreasing the mortality for natural causes as well as for respiratory and cardio-vascular diseases promoting socially equality. The increase in urban albedo - with a particular reference to changes in pavements and rooftops - can be easily integrated in urban and building maintenance plans. Since the increase in urban albedo can affect both the global and local scale, the results of this extensive and multi-level study are useful to address-policy-relevant strategies for coping with the effects of climate. In particular, they can provide insights for multi-level governance strategies and for shaping mitigation and adaptation strategies.

Ultraviolet Spectroscopy of Asteroid(4) Vesta

NASA Technical Reports Server (NTRS)

Li, Jian-Yang; Bodewits, Dennis; Feaga, Lori M.; Landsman, Wayne; A'Hearn, Michael F.; Mutchler, Max J.; Russell, Christopher T.; McFadden, Lucy A.; Raymond, Carol A.

2011-01-01

We report a comprehensive review of the UV-visible spectrum and rotational lightcurve of Vesta combining new observations by Hubble Space Telescope and Swift with archival International Ultraviolet Explorer observations. The geometric albedos of Vesta from 220 nm to 953 nm arc derived by carefully comparing these observations from various instruments at different times and observing geometries. Vesta has a rotationally averaged geometric albedo of 0.09 at 250 nm, 0.14 at 300 nm, 0.26 at 373 nm, 0.38 at 673 nm, and 0.30 at 950 nm. The linear spectral slope in the ultraviolet displays a sharp minimum ncar sub-Earth longitude of 20deg, and maximum in the eastern hemisphere. This is completely consistent with the distribution of the spectral slope in the visible wavelength. The uncertainty of the measurement in the ultraviolet is approx.20%, and in the visible wavelengths better than 10%. The amplitude of Vesta's rotational lightcurves is approx.10% throughout the range of wavelengths we observed, but is smaller at 950 nm (approx.6%) ncar the 1-micron mafic band center. Contrary to earlier reports, we found no evidence for any difference between the phasing of the ultraviolet and visible/ncar-infrared lightcurves with respect to sub-Earth longitude. Vesta's average spectrum between 220 and 950 nm can well be described by measured reflectance spectra of fine particle howardite-like materials of basaltic achondrite meteorites. Combining this with the in-phase behavior of the ultraviolet, visible. and ncar-infrared lightcurves, and the spectral slopes with respect to the rotational phase, we conclude that there is no global ultraviolet/visible reversal on Vesta. Consequently, this implies lack of global space weathering on Vesta. Keyword,: Asteroid Vesta; Spectrophotometry; Spectroscopy; Ultraviolet observations; Hubble Space Telescope observations

Spring snow albedo feedback in daily data over Russia: Comparing in-situ measurements with reanalysis products.

NASA Astrophysics Data System (ADS)

Wegmann, M.; Zolina, O.; Jacobi, H. W.

2016-12-01

Global warming is enhanced at high northern latitudes where the Arctic surface air temperature has risen at twice the rate of the global average in recent decades - a feature called Arctic amplification. This recent Arctic warming signal likely results from several factors such as the albedo feedback due to a diminishing cryosphere, enhanced poleward atmospheric and oceanic heat transport, and changes in humidity. Surface albedo feedback is stating that the additional amount of shortwave radiation at the top of the atmosphere decreases with decreasing surface albedo whereas surface air temperature increases with decreasing surface albedo. It is considered a positive feedback in that an initial warming perturbation than kicks off a strengthening warming. Looking at the Northern Hemisphere with its large landmasses, snow albedo feedback is especially strong since most of these landmasses experience snow cover during boreal wintertime. Unfortunately, so far there remains a lack of reliable observational data over large parts of the cryosphere. Satellite products cover large parts of the NH, however lack high temporal resolution and have problems with large solar zenith angles as well as over complex terrain (eg. Wang et al. 2014). Our analysis focuses at the Russian territory where we utilize in-situ radiation and snow depth measurements. We found 50 stations which measure both variables on a daily basis for the period 2000-2013. Since Hall (2004) found that 50% of the notal NH snow albedo feedback caused by global warming occurs during NH spring, we focus on the transition period of March to June (MAMJ). Thackeray & Fletcher 2006 compared albedo feedback processes CMIP3 and CMIP5 model families and found while the models represent the feedback process accurately, there are still inherent biases and outdated parameterizations. Therefore we use the daily observations and state of the art reanalysis products to 1) evaluate reanalysis and model products in respect to radiation properties, 2) investigate snow albedo feedbacks on a daily scale during spring and 3) to suggest climate change signals over Russia in albedo feedback between 2000 - 2013 based on in-situ measurements.

Aerosol cloud interactions in southeast Pacific stratocumulus: satellite observations, in situ data and regional modeling

NASA Astrophysics Data System (ADS)

George, Rhea

The influence of anthropogenic aerosols on cloud radiative properties in the persistent southeast Pacific stratocumulus deck is investigated using MODIS satellite observations, in situ data from the VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx), and WRF-Chem, a regional model with interactive chemistry and aerosols. An albedo proxy is derived based on the fractional coverage of low cloud (a macrophysical field) and the cloud albedo, with the latter broken down into contributions from microphysics (cloud droplet concentration, Nd and macrophysics (liquid water path). Albedo variability is dominated by low cloud fraction variability, except within 10-15° of the South American coast, where cloud albedo variability contributes significantly. Covariance between cloud fraction and cloud albedo also contributes significantly to the variance in albedo, which highlights how complex and inseparable the factors controlling albedo are. N d variability contributes only weakly, which emphasizes that attributing albedo variability to the indirect effects of aerosols against the backdrop of natural meteorological variability is extremely challenging. Specific cases of aerosol changes can have strong impacts on albedo. We identify a pathway for periodic anthropogenic aerosol transport to the unpolluted marine stratocumulus >1000 km offshore, which strongly enhances Nd and albedo in zonally-elongated 'hook'-shaped arc. Hook development occurs with Nd increasing to polluted levels over the remote ocean primarily due to entrainment of a large number of small aerosols from the free troposphere that contribute a relatively small amount of aerosol mass to the marine boundary layer. Strong, deep offshore flow needed to transport continental aerosols to the remote ocean is favored by a trough approaching the South American coast and a southeastward shift of the climatological subtropical high pressure system. DMS significantly influences the aerosol number and size distributions, but does not cause hooks. The Twomey effect contributes 50-80% of the total aerosol indirect effect (AIE) both near sources and offshore during hook events. Meteorological variability between simulations can swamp the signal of AIEs, particularly due to the binary model cloud fraction field and distinguishing AIE requires determination of appropriate spatial and temporal averaging scales over which AIE is significant above this noise.

Current and future darkening of the Greenland ice sheet

NASA Astrophysics Data System (ADS)

Tedesco, Marco; Stroeve, Julienne; Fettweis, Xavier; Warren, Stephen; Doherty, Sarah; Noble, Erik; Alexander, Patrick

2015-04-01

Surface melting over the Greenland ice sheet (GIS) promotes snow grains growth, reducing albedo and further enhancing melting through the increased amount of absorbed solar radiation. Using a combination of remote sensing data and outputs of a regional climate model, we show that albedo over the GIS decreased significantly from 1996 to 2012. Further, we show that most of this darkening can be accounted for by enhanced snow grain growth and the expansion of areas where bare ice is exposed, both of which are driven by increases in snow warming. An analysis of the impact of light-absorbing impurities on albedo trends detected from spaceborne measurements was inconclusive because the estimated impact for concentrations of impurities of order of magnitude found in Greenland is within the albedo uncertainty retrievable from space-based instruments. However, neither models nor observations show an increase in pollutants (black carbon and associated organics) in the atmosphere over the GIS in this time period. Additionally, we could not identify trends in the number of fires over North America and Russia, assumed to be among the sources of soot for Greenland. We did find that a 'dark band' of tilted ice plays a crucial role in decreasing albedo along the west margin, and there is some indication that dust deposition to the GIS may be decreasing albedo in this region but this is not conclusive. In addition to looking at the direct impact of impurities on albedo, we estimated the impact of impurities on albedo via their influence on grain growth and found it is relatively small (~ 1- 2 %), though more sophisticated analysis needs to be carried out. Projections obtained under different warming scenarios consistently point to a continued darkening, with anomalies in albedo driven solely by the effects of climate warming of as much as -0.12 along the west margin of the GIS by the end of this century (with respect to year 2000). Projected darkening is likely underestimated because of an underestimation in melting and because the model used to project albedo does not account for the influence of light-absorbing impurities.

SPIDERMAN: an open-source code to model phase curves and secondary eclipses

NASA Astrophysics Data System (ADS)

Louden, Tom; Kreidberg, Laura

2018-06-01

We present SPIDERMAN (Secondary eclipse and Phase curve Integrator for 2D tempERature MAppiNg), a fast code for calculating exoplanet phase curves and secondary eclipses with arbitrary surface brightness distributions in two dimensions. Using a geometrical algorithm, the code solves exactly the area of sections of the disc of the planet that are occulted by the star. The code is written in C with a user-friendly Python interface, and is optimized to run quickly, with no loss in numerical precision. Approximately 1000 models can be generated per second in typical use, making Markov Chain Monte Carlo analyses practicable. The modular nature of the code allows easy comparison of the effect of multiple different brightness distributions for the data set. As a test case, we apply the code to archival data on the phase curve of WASP-43b using a physically motivated analytical model for the two-dimensional brightness map. The model provides a good fit to the data; however, it overpredicts the temperature of the nightside. We speculate that this could be due to the presence of clouds on the nightside of the planet, or additional reflected light from the dayside. When testing a simple cloud model, we find that the best-fitting model has a geometric albedo of 0.32 ± 0.02 and does not require a hot nightside. We also test for variation of the map parameters as a function of wavelength and find no statistically significant correlations. SPIDERMAN is available for download at https://github.com/tomlouden/spiderman.

Impacts of ocean albedo alteration on Arctic sea ice restoration and Northern Hemisphere climate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cvijanovic, Ivana; Caldeira, Ken; MacMartin, Douglas G.

The Arctic Ocean is expected to transition into a seasonally ice-free state by mid-century, enhancing Arctic warming and leading to substantial ecological and socio-economic challenges across the Arctic region. It has been proposed that artificially increasing high latitude ocean albedo could restore sea ice, but the climate impacts of such a strategy have not been previously explored. Motivated by this, we investigate the impacts of idealized high latitude ocean albedo changes on Arctic sea ice restoration and climate. In our simulated 4xCO₂ climate, imposing surface albedo alterations over the Arctic Ocean leads to partial sea ice recovery and a modestmore » reduction in Arctic warming. With the most extreme ocean albedo changes, imposed over the area 70°–90°N, September sea ice cover stabilizes at ~40% of its preindustrial value (compared to ~3% without imposed albedo modifications). This is accompanied by an annual mean Arctic surface temperature decrease of ~2 °C but no substantial global mean temperature decrease. Imposed albedo changes and sea ice recovery alter climate outside the Arctic region too, affecting precipitation distribution over parts of the continental United States and Northeastern Pacific. For example, following sea ice recovery, wetter and milder winter conditions are present in the Southwest United States while the East Coast experiences cooling. We conclude that although ocean albedo alteration could lead to some sea ice recovery, it does not appear to be an effective way of offsetting the overall effects of CO₂ induced global warming.« less

Impacts of ocean albedo alteration on Arctic sea ice restoration and Northern Hemisphere climate

DOE PAGES

Cvijanovic, Ivana; Caldeira, Ken; MacMartin, Douglas G.

2015-04-01

The Arctic Ocean is expected to transition into a seasonally ice-free state by mid-century, enhancing Arctic warming and leading to substantial ecological and socio-economic challenges across the Arctic region. It has been proposed that artificially increasing high latitude ocean albedo could restore sea ice, but the climate impacts of such a strategy have not been previously explored. Motivated by this, we investigate the impacts of idealized high latitude ocean albedo changes on Arctic sea ice restoration and climate. In our simulated 4xCO₂ climate, imposing surface albedo alterations over the Arctic Ocean leads to partial sea ice recovery and a modestmore » reduction in Arctic warming. With the most extreme ocean albedo changes, imposed over the area 70°–90°N, September sea ice cover stabilizes at ~40% of its preindustrial value (compared to ~3% without imposed albedo modifications). This is accompanied by an annual mean Arctic surface temperature decrease of ~2 °C but no substantial global mean temperature decrease. Imposed albedo changes and sea ice recovery alter climate outside the Arctic region too, affecting precipitation distribution over parts of the continental United States and Northeastern Pacific. For example, following sea ice recovery, wetter and milder winter conditions are present in the Southwest United States while the East Coast experiences cooling. We conclude that although ocean albedo alteration could lead to some sea ice recovery, it does not appear to be an effective way of offsetting the overall effects of CO₂ induced global warming.« less

Improvement of Mars Surface Snow Albedo Modeling in LMD Mars GCM With SNICAR

NASA Astrophysics Data System (ADS)

Singh, D.; Flanner, M. G.; Millour, E.

2018-03-01

The current version of Laboratoire de Météorologie Dynamique (LMD) Mars GCM (original-MGCM) uses annually repeating (prescribed) CO2 snow albedo values based on the Thermal Emission Spectrometer observations. We integrate the Snow, Ice, and Aerosol Radiation (SNICAR) model with MGCM (SNICAR-MGCM) to prognostically determine H2O and CO2 snow albedos interactively in the model. Using the new diagnostic capabilities of this model, we find that cryospheric surfaces (with dust) increase the global surface albedo of Mars by 0.022. Over snow-covered regions, SNICAR-MGCM simulates mean albedo that is higher by about 0.034 than prescribed values in the original-MGCM. Globally, shortwave flux into the surface decreases by 1.26 W/m2, and net CO2 snow deposition increases by about 4% with SNICAR-MGCM over one Martian annual cycle as compared to the original-MGCM simulations. SNICAR integration reduces the mean global surface temperature and the surface pressure of Mars by about 0.87% and 2.5%, respectively. Changes in albedo also show a similar distribution to dust deposition over the globe. The SNICAR-MGCM model generates albedos with higher sensitivity to surface dust content as compared to original-MGCM. For snow-covered regions, we improve the correlation between albedo and optical depth of dust from -0.91 to -0.97 with SNICAR-MGCM as compared to the original-MGCM. Dust substantially darkens Mars's cryosphere, thereby reducing its impact on the global shortwave energy budget by more than half, relative to the impact of pure snow.

Radiative Forcing and Temperature Response to Changes in Urban Albedos and Associated CO2 Offsets

NASA Technical Reports Server (NTRS)

Menon, Surabi; Akbari, Hashem; Mahanama, Sarith; Sednev, Igor; Levinson, Ronnen

2009-01-01

The two main forcings that can counteract to some extent the positive forcings from greenhouse gases from pre-industrial times to present-day are the aerosol and related aerosol-cloud forcings, and the radiative response to changes in surface albedo. Here, we quantify the change in radiative forcing and surface temperature that may be obtained by increasing the albedos of roofs and pavements in urban areas in temperate and tropical regions of the globe. Using the catchment land surface model (the land model coupled to the GEOS-5 Atmospheric General Circulation Model), we quantify the response of the total outgoing (outgoing shortwave+longwave) radiation to urban albedo changes. Globally, the total outgoing radiation increased by 0.5 W/square m and temperature decreased by -0.008 K for an average 0.003 increase in albedo. For the U.S. the total outgoing total radiation increased by 2.3 W/square meter, and temperature decreased by approximately 0.03 K for an average 0.01 increase in albedo. These values are for the boreal summer (Tune-July-August). Based on these forcings, the expected emitted CO2 offset for a plausible 0.25 and 0.15 increase in albedos of roofs and pavements, respectively, for all global urban areas, was found to be approximately 57 Gt CO2 . A more meaningful evaluation of the impacts of urban albedo increases on climate and the expected CO2 offsets would require simulations which better characterizes urban surfaces and represents the full annual cycle.

Measuring cloud thermodynamic phase with shortwave infrared imaging spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thompson, David R.; McCubbin, Ian; Gao, Bo Cai

Shortwave Infrared imaging spectroscopy enables accurate remote mapping of cloud thermodynamic phase at high spatial resolution. We describe a measurement strategy to exploit signatures of liquid and ice absorption in cloud top apparent reflectance spectra from 1.4 to 1.8 μm. This signal is generally insensitive to confounding factors such as solar angles, view angles, and surface albedo. We first evaluate the approach in simulation and then apply it to airborne data acquired in the Calwater-2/ACAPEX campaign of Winter 2015. Here NASA’s “Classic” Airborne Visible Infrared Imaging Spectrometer (AVIRIS-C) remotely observed diverse cloud formations while the U.S. Department of Energy ARMmore » Aerial Facility G-1 aircraft measured cloud integral and microphysical properties in situ. Finally, the coincident measurements demonstrate good separation of the thermodynamic phases for relatively homogeneous clouds.« less

Radiative forcing over the conterminous United States due to contemporary land cover land use albedo change

USGS Publications Warehouse

Barnes, Christopher; Roy, David P.

2008-01-01

Recently available satellite land cover land use (LCLU) and albedo data are used to study the impact of LCLU change from 1973 to 2000 on surface albedo and radiative forcing for 36 ecoregions covering 43% of the conterminous United States (CONUS). Moderate Resolution Imaging Spectroradiometer (MODIS) snow-free broadband albedo values are derived from Landsat LCLU classification maps located using a stratified random sampling methodology to estimate ecoregion estimates of LCLU induced albedo change and surface radiative forcing. The results illustrate that radiative forcing due to LCLU change may be disguised when spatially and temporally explicit data sets are not used. The radiative forcing due to contemporary LCLU albedo change varies geographically in sign and magnitude, with the most positive forcings (up to 0.284 Wm−2) due to conversion of agriculture to other LCLU types, and the most negative forcings (as low as −0.247 Wm−2) due to forest loss. For the 36 ecoregions considered a small net positive forcing (i.e., warming) of 0.012 Wm−2 is estimated.

Spatially Complete Global Surface Albedos Derived from Terra/MODIS Data

NASA Technical Reports Server (NTRS)

King, Michael D.; Moody, Eric G.; Platnick, Steven; Schaaf, Crystal B.

2005-01-01

Spectral land surface albedo is an important parameter for describing the radiative properties of the Earth. Accordingly it reflects the consequences of natural and human interactions, such as anthropogenic, meteorological, and phenological effects, on global and local climatological trends. Consequently, albedos are integral parts in a variety of research areas, such as general circulation models (GCMs), energy balance studies, modeling of land use and land use change, and biophysical, oceanographic, and meteorological studies. Recent production of land surface anisotropy, diffuse bihemispherical (white-sky) albedo and direct beam directional hemispherical (black-sky) albedo from observations acquired by the MODIS instruments aboard NASA's Terra and &la satellite platforms have provided researchers with unprecedented spatial, spectral, and temporal information on the land surface's radiative characteristics. Cloud cover, which curtails retrievals, and the presence of ephemeral and seasonal snow limit the snow-free data to approximately half the global land surfaces on an annual equal-angle basis. This precludes the MOD43B3 albedo products from being used in some remote sensing and ground-based applications, &mate models, and global change research projects.