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1

Using Radar, Lidar, and Radiometer measurements to Classify Cloud Type and Study Middle-Level Cloud Properties  

Microsoft Academic Search

The project is concerned with the characterization of cloud macrophysical and microphysical properties by combining radar, lidar, and radiometer measurements available from the U.S. Department of Energy's ARM Climate Research Facility (ACRF). To facilitate the production of integrated cloud product by applying different algorithms to the ARM data streams, an advanced cloud classification algorithm was developed to classified clouds into

Zhien

2006-01-01

2

Investigating cloud radar sensitivity to optically thin cirrus using collocated Raman lidar observations  

NASA Astrophysics Data System (ADS)

The sensitivity of the millimeter cloud radar (MMCR) to optically thin single-layer cirrus at the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site is investigated using collocated Raman lidar observations. The sensitivity is characterized in terms of cloud optical depth (OD) and infrared (IR) radiative flux using over three years of coincident Raman lidar and MMCR observations. For cases when the Raman lidar is not fully attenuated (OD < 2.0) the MMCR detects approximately 70% of the total cloud OD with the majority of missed cloud OD occurring near cloud top. If only MMCR observations are used for computing cloudy top-of-the-atmosphere (TOA) IR flux, the missed cloud OD results in TOA flux biases from 0 to over 100 W/m2; however, the most frequently occurring bias is approximately 16 W/m2. This result highlights the importance of combining Raman lidar, or other sensitive cloud lidars that are able to measure cloud extinction directly, with the MMCR in order to accurately characterize the cloud radiative forcing for thin cirrus cases.

Borg, Lori A.; Holz, Robert E.; Turner, David D.

2011-03-01

3

Toward a quantitative characterization of heterogeneous ice formation with lidar/radar: Comparison of CALIPSO/CloudSat with ground-based observations  

NASA Astrophysics Data System (ADS)

We analyze and compare the different sensitivities of aerosol/cloud lidar and 35-GHz cloud radar to detect ice formation in midlevel clouds in order to harmonize mixed phase cloud observations performed with lidar and radar. We found good agreement between spaceborne Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO)/CloudSat and ground-based lidar/radar observations at Leipzig, Germany. However, large differences were found to a previous study with an 11-year cloud statistics solely based on lidar observations which is caused by significantly higher sensitivity of the cloud radar to detect ice crystals. By introducing a lidar detection threshold for the ice water content of 10-6kgm-3, we find that lidar and radar cloud statistics become increasingly similar.

Bühl, J.; Ansmann, A.; Seifert, P.; Baars, H.; Engelmann, R.

2013-08-01

4

Cloud effects on radiative heating rate profiles over Darwin using ARM and A-train radar/lidar observations  

NASA Astrophysics Data System (ADS)

Observations of clouds from the ground-based U.S. Department of Energy Atmospheric Radiation Measurement (ARM) program and satellite-based A-train are used to compute cloud radiative forcing profiles over the ARM Darwin, Australia site. Cloud properties are obtained from both radar (the ARM Millimeter Cloud Radar (MMCR) and the CloudSat satellite in the A-train) and lidar (the ARM Micropulse lidar (MPL) and the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite in the A-train) observations. Cloud microphysical properties are taken from combined radar and lidar retrievals for ice clouds and radar-only or lidar-only retrievals for liquid clouds. Large, statistically significant differences of up to 1.43 K/d exist between the mean ARM and A-train net cloud radiative forcing profiles. The majority of the difference in cloud radiative forcing profiles is shown to be due to a large difference in the cloud fraction above 12 km. Above this altitude, the A-train cloud fraction is significantly larger because many more clouds are detected by CALIPSO than by the ground-based MPL. It is shown that the MPL is unable to observe as many high clouds as CALIPSO due to being more frequently attenuated and a poorer sensitivity. We also isolate the difference in cloud radiative forcing due to sampling and retrieval differences which are of comparable importance but are of smaller impact than cloud fraction differences. This study demonstrates that A-train observations are better suited for the calculation of cloud radiative forcing profiles at Darwin. In addition, we find that it is necessary to supplement CloudSat with CALIPSO observations to obtain accurate cloud radiative forcing profiles.

Thorsen, Tyler J.; Fu, Qiang; Comstock, Jennifer M.

2013-06-01

5

Vertical Cloud Climatology During TC4 Derived from High-Altitude Aircraft Merged Lidar and Radar Profiles  

NASA Technical Reports Server (NTRS)

Aircraft lidar works by shooting laser pulses toward the earth and recording the return time and intensity of any of the light returning to the aircraft after scattering off atmospheric particles and/or the Earth s surface. The scattered light signatures can be analyzed to tell the exact location of cloud and aerosol layers and, with the aid of a few optical assumptions, can be analyzed to retrieve estimates of optical properties such as atmospheric transparency. Radar works in a similar fashion except it sends pulses toward earth at a much larger wavelength than lidar. Radar records the return time and intensity of cloud or rain reflection returning to the aircraft. Lidar can measure scatter from optically thin cirrus and aerosol layers whose particles are too small for the radar to detect. Radar can provide reflection profiles through thick cloud layers of larger particles that lidar cannot penetrate. Only after merging the two instrument products can accurate measurements of the locations of all layers in the full atmospheric column be achieved. Accurate knowledge of the vertical distribution of clouds is important information for understanding the Earth/atmosphere radiative balance and for improving weather/climate forecast models. This paper describes one such merged data set developed from the Tropical Composition, Cloud and Climate Coupling (TC4) experiment based in Costa Rica in July-August 2007 using the nadir viewing Cloud Physics Lidar (CPL) and the Cloud Radar System (CRS) on board the NASA ER-2 aircraft. Statistics were developed concerning cloud probability through the atmospheric column and frequency of the number of cloud layers. These statistics were calculated for the full study area, four sub-regions, and over land compared to over ocean across all available flights. The results are valid for the TC4 experiment only, as preferred cloud patterns took priority during mission planning. The TC4 Study Area was a very cloudy region, with cloudy profiles occurring 94 percent of the time during the ER-2 flights. One to three cloud layers were common, with the average calculated at 2.03 layers per profile. The upper troposphere had a cloud frequency generally over 30%, reaching 42 percent near 13 km during the study. There were regional differences. The Caribbean was much clearer than the Pacific regions. Land had a much higher frequency of high clouds than ocean areas. One region just south and west of Panama had a high probability of clouds below 15 km altitude with the frequency never dropping below 25% and reaching a maximum of 60% at 11-13 km altitude. These cloud statistics will help characterize the cloud volume for TC4 scientists as they try to understand the complexities of the tropical atmosphere.

Hlavka, Dennis; Tian, Lin; Hart, William; Li, Lihua; McGill, Matthew; Heymsfield, Gerald

2009-01-01

6

Mapping tropical forest biomass with radar and spaceborne LiDAR: overcoming problems of high biomass and persistent cloud  

NASA Astrophysics Data System (ADS)

Spatially-explicit maps of aboveground biomass are essential for calculating the losses and gains in forest carbon at a regional to national level. The production of such maps across wide areas will become increasingly necessary as international efforts to protect primary forests, such as the REDD+ (Reducing Emissions from Deforestation and forest Degradation) mechanism, come into effect, alongside their use for management and research more generally. However, mapping biomass over high-biomass tropical forest is challenging as (1) direct regressions with optical and radar data saturate, (2) much of the tropics is persistently cloud-covered, reducing the availability of optical data, (3) many regions include steep topography, making the use of radar data complex, (4) while LiDAR data does not suffer from saturation, expensive aircraft-derived data are necessary for complete coverage. We present a solution to the problems, using a combination of terrain-corrected L-band radar data (ALOS PALSAR), spaceborne LiDAR data (ICESat GLAS) and ground-based data. We map Gabon's Lopé National Park (5000 km2) because it includes a range of vegetation types from savanna to closed-canopy tropical forest, is topographically complex, has no recent cloud-free high-resolution optical data, and the dense forest is above the saturation point for radar. Our 100 m resolution biomass map is derived from fusing spaceborne LiDAR (7142 ICESat GLAS footprints), 96 ground-based plots (average size 0.8 ha) and an unsupervised classification of terrain-corrected ALOS PALSAR radar data, from which we derive the aboveground biomass stocks of the park to be 78 Tg C (173 Mg C ha-1). This value is consistent with our field data average of 181 Mg C ha-1, from the field plots measured in 2009 covering a total of 78 ha, and which are independent as they were not used for the GLAS-biomass estimation. We estimate an uncertainty of ± 25 % on our carbon stock value for the park. This error term includes uncertainties resulting from the use of a generic tropical allometric equation, the use of GLAS data to estimate Lorey's height, and the necessity of separating the landscape into distinct classes. As there is currently no spaceborne LiDAR satellite in operation (GLAS data is available for 2003-2007 only), this methodology is not suitable for change-detection. This research underlines the need for new satellite LiDAR data to provide the potential for biomass-change estimates, although this need will not be met before 2015.

Mitchard, E. T. A.; Saatchi, S. S.; White, L. J. T.; Abernethy, K. A.; Jeffery, K. J.; Lewis, S. L.; Collins, M.; Lefsky, M. A.; Leal, M. E.; Woodhouse, I. H.; Meir, P.

2011-08-01

7

Measuring Cloud Heights: The Micropulse Lidar (MPL)  

NSDL National Science Digital Library

This middle/junior high school computer activity requires students to compare the lidar method with millimeter wave cloud radar to measure cloud heights using real data, and to identify cloud types using micropulse lidar. It is part of the Atmospheric Visualization Collection (AVC), which focuses on data from the Atmospheric Radiation Measurement (ARM) program's Southern Great Plains Cloud and Radiation Testbed site in Kansas and Oklahoma.

2003-05-09

8

Characterization of ice cloud properties obtained by shipborne radar/lidar over the tropical western Pacific Ocean for evaluation of an atmospheric general circulation model  

NASA Astrophysics Data System (ADS)

This study analyzed 95-GHz radar/lidar data collected from the R/V Mirai over the tropical western Pacific to characterize the vertical distribution of ice cloud effective radius reff, ice water content IWC, and in-cloud vertical velocity of the region in conjunction with weather regimes classified by International Satellite Cloud Climatology Project (ISCCP) cluster analysis. Ice clouds observed from the Mirai were roughly consistent with the ISCCP weather regimes; more convectively active regimes had larger amounts of high cloud consisting of deeper cloud with larger ice water path (IWP) and precipitating ice fraction. Ice cloud microphysics of the Center for Climate System Research, National Institute for Environmental Studies, Frontier Research Center for Global Change atmospheric general circulation model (AGCM) was then evaluated using the radar-lidar simulator and ISCCP weather regimes for comparison of the statistics at different scales. The model tended to produce a high cloud fraction that was two times larger in the cirrus regimes but 50% lower in the deepest convective regime. The simulated IWP could only weakly reproduce the observed variety and generally underestimated the observed values despite the weather regimes. Cutoff in the simulated grid mean IWC around 0.1 g-3 was too small, especially above 11 km. The AGCM successfully predicted the observed frequency distribution for reff above 11 km, but produced large overestimation in the peak value below 11 km due to the excessively large fraction of reff ˜100 ?m. Establishing a cutoff for cloud ice at reff > 120 ?m was found to be quite reasonable, although it would miss some of the larger particles that were observed.

Sato, Kaori; Okamoto, Hajime; Takemura, Toshihiko; Kumagai, Hiroshi; Sugimoto, Nobuo

2010-08-01

9

Using Radar, Lidar and Radiometer Data from NSA and SHEBA to Quantify Cloud Property Effects on the Surface Heat Budget in the Arctic  

SciTech Connect

Cloud and radiation data from two distinctly different Arctic areas are analyzed to study the differences between coastal Alaskan and open Arctic Ocean region clouds and their respective influence on the surface radiation budget. The cloud and radiation datasets were obtained from (1) the DOE North Slope of Alaska (NSA) facility in the coastal town of Barrow, Alaska, and (2) the SHEBA field program, which was conducted from an icebreaker frozen in, and drifting with, the sea-ice for one year in the Western Arctic Ocean. Radar, lidar, radiometer, and sounding measurements from both locations were used to produce annual cycles of cloud occurrence and height, atmospheric temperature and humidity, surface longwave and shortwave broadband fluxes, surface albedo, and cloud radiative forcing. In general, both regions revealed a similar annual trend of cloud occurrence fraction with minimum values in winter (60-75%) and maximum values during spring, summer and fall (80-90%). However, the annual average cloud occurrence fraction for SHEBA (76%) was lower than the 6-year average cloud occurrence at NSA (92%). Both Arctic areas also showed similar annual cycle trends of cloud forcing with clouds warming the surface through most of the year and a period of surface cooling during the summer, when cloud shading effects overwhelm cloud greenhouse effects. The greatest difference between the two regions was observed in the magnitude of the cloud cooling effect (i.e., shortwave cloud forcing), which was significantly stronger at NSA and lasted for a longer period of time than at SHEBA. This is predominantly due to the longer and stronger melt season at NSA (i.e., albedo values that are much lower coupled with Sun angles that are somewhat higher) than the melt season observed over the ice pack at SHEBA. Longwave cloud forcing values were comparable between the two sites indicating a general similarity in cloudiness and atmospheric temperature and humidity structure between the two regions.

Janet Intrieri; Mathhew Shupe

2005-01-01

10

Mapping tropical forest biomass with radar and spaceborne LiDAR in Lopé National Park, Gabon: overcoming problems of high biomass and persistent cloud  

NASA Astrophysics Data System (ADS)

Spatially-explicit maps of aboveground biomass are essential for calculating the losses and gains in forest carbon at a regional to national level. The production of such maps across wide areas will become increasingly necessary as international efforts to protect primary forests, such as the REDD+ (Reducing Emissions from Deforestation and forest Degradation) mechanism, come into effect, alongside their use for management and research more generally. However, mapping biomass over high-biomass tropical forest is challenging as (1) direct regressions with optical and radar data saturate, (2) much of the tropics is persistently cloud-covered, reducing the availability of optical data, (3) many regions include steep topography, making the use of radar data complex, (5) while LiDAR data does not suffer from saturation, expensive aircraft-derived data are necessary for complete coverage. We present a solution to the problems, using a combination of terrain-corrected L-band radar data (ALOS PALSAR), spaceborne LiDAR data (ICESat GLAS) and ground-based data. We map Gabon's Lopé National Park (5000 km2) because it includes a range of vegetation types from savanna to closed-canopy tropical forest, is topographically complex, has no recent contiguous cloud-free high-resolution optical data, and the dense forest is above the saturation point for radar. Our 100 m resolution biomass map is derived from fusing spaceborne LiDAR (7142 ICESat GLAS footprints), 96 ground-based plots (average size 0.8 ha) and an unsupervised classification of terrain-corrected ALOS PALSAR radar data, from which we derive the aboveground biomass stocks of the park to be 78 Tg C (173 Mg C ha-1). This value is consistent with our field data average of 181 Mg C ha-1, from the field plots measured in 2009 covering a total of 78 ha, and which are independent as they were not used for the GLAS-biomass estimation. We estimate an uncertainty of ±25% on our carbon stock value for the park. This error term includes uncertainties resulting from the use of a generic tropical allometric equation, the use of GLAS data to estimate Lorey's height, and the necessity of separating the landscape into distinct classes. As there is currently no spaceborne LiDAR satellite in operation (GLAS data is available for 2003-2009 only), this methodology is not suitable for change-detection. This research underlines the need for new satellite LiDAR data to provide the potential for biomass-change estimates, although this need will not be met before 2015.

Mitchard, E. T. A.; Saatchi, S. S.; White, L. J. T.; Abernethy, K. A.; Jeffery, K. J.; Lewis, S. L.; Collins, M.; Lefsky, M. A.; Leal, M. E.; Woodhouse, I. H.; Meir, P.

2012-01-01

11

The Cloud Radar System  

NASA Technical Reports Server (NTRS)

Improvement in our understanding of the radiative impact of clouds on the climate system requires a comprehensive view of clouds including their physical dimensions, dynamical generation processes, and detailed microphysical properties. To this end, millimeter vave radar is a powerful tool by which clouds can be remotely sensed. The NASA Goddard Space Flight Center has developed the Cloud Radar System (CRS). CRS is a highly sensitive 94 GHz (W-band) pulsed-Doppler polarimetric radar that is designed to fly on board the NASA high-altitude ER-2 aircraft. The instrument is currently the only millimeter wave radar capable of cloud and precipitation measurements from above most all clouds. Because it operates from high-altitude, the CRS provides a unique measurement perspective for cirrus cloud studies. The CRS emulates a satellite view of clouds and precipitation systems thus providing valuable measurements for the implementation and algorithm validation for the upcoming NASA CloudSat mission that is designed to measure ice cloud distributions on the global scale using a spaceborne 94 GHz radar. This paper describes the CRS instrument and preliminary data from the recent Cirrus Regional Study of Tropical Anvils and Cirrus Layers - Florida Area Cirrus Experiment (CRYSTAL-FACE). The radar design is discussed. Characteristics of the radar are given. A block diagram illustrating functional components of the radar is shown. The performance of the CRS during the CRYSTAL-FACE campaign is discussed.

Racette, Paul; Heymsfield, Gerald; Li, Lihua; Tian, Lin; Zenker, Ed

2003-01-01

12

Radar, lidar, and optical observations in the polar summer mesosphere shortly after a space shuttle launch  

Microsoft Academic Search

In the summer of 2007, a noctilucent cloud (NLC) campaign was organized in Alaska. Radar, lidar, and photographic methods were used. Due to lighting conditions, the campaign was carried out near the end of the NLC season. Sporadic radar and lidar echoes were obtained until the very end of the campaign, when an exceptionally intense event occurred on the local

M. C. Kelley; M. J. Nicolls; R. H. Varney; R. L. Collins; R. Doe; J. M. C. Plane; J. Thayer; M. Taylor; B. Thurairajah; K. Mizutani

2010-01-01

13

The variability of tropical ice cloud properties as a function of the large-scale context from ground-based radar-lidar observations over Darwin, Australia  

NASA Astrophysics Data System (ADS)

The high complexity of cloud parameterizations now held in models puts more pressure on observational studies to provide useful means to evaluate them. One approach to the problem put forth in the modelling community is to evaluate under what atmospheric conditions the parameterizations fail to simulate the cloud properties and under what conditions they do a good job. It is the ambition of this paper to characterize the variability of the statistical properties of tropical ice clouds in different tropical "regimes" recently identified in the literature to aid the development of better process-oriented parameterizations in models. For this purpose, the statistical properties of non-precipitating tropical ice clouds over Darwin, Australia are characterized using ground-based radar-lidar observations from the Atmospheric Radiation Measurement (ARM) Program. The ice cloud properties analysed are the frequency of ice cloud occurrence, the morphological properties (cloud top height and thickness), and the microphysical and radiative properties (ice water content, visible extinction, effective radius, and total concentration). The variability of these tropical ice cloud properties is then studied as a function of the large-scale cloud regimes derived from the International Satellite Cloud Climatology Project (ISCCP), the amplitude and phase of the Madden-Julian Oscillation (MJO), and the large-scale atmospheric regime as derived from a long-term record of radiosonde observations over Darwin. The vertical variability of ice cloud occurrence and microphysical properties is largest in all regimes (1.5 order of magnitude for ice water content and extinction, a factor 3 in effective radius, and three orders of magnitude in concentration, typically). 98 % of ice clouds in our dataset are characterized by either a small cloud fraction (smaller than 0.3) or a very large cloud fraction (larger than 0.9). In the ice part of the troposphere three distinct layers characterized by different statistically-dominant microphysical processes are identified. The variability of the ice cloud properties as a function of the large-scale atmospheric regime, cloud regime, and MJO phase is large, producing mean differences of up to a factor 8 in the frequency of ice cloud occurrence between large-scale atmospheric regimes and mean differences of a factor 2 typically in all microphysical properties. Finally, the diurnal cycle of the frequency of occurrence of ice clouds is also very different between regimes and MJO phases, with diurnal amplitudes of the vertically-integrated frequency of ice cloud occurrence ranging from as low as 0.2 (weak diurnal amplitude) to values in excess of 2.0 (very large diurnal amplitude). Modellers should now use these results to check if their model cloud parameterizations are capable of translating a given atmospheric forcing into the correct statistical ice cloud properties.

Protat, A.; Delanoë, J.; May, P. T.; Haynes, J.; Jakob, C.; O'Connor, E.; Pope, M.; Wheeler, M. C.

2011-08-01

14

The variability of tropical ice cloud properties as a function of the large-scale context from ground-based radar-lidar observations over Darwin, Australia  

NASA Astrophysics Data System (ADS)

The statistical properties of non-precipitating tropical ice clouds over Darwin, Australia are characterized using ground-based radar-lidar observations from the Atmospheric Radiation Measurement (ARM) Program. The ice cloud properties analysed are the frequency of ice cloud occurrence, the morphological properties (cloud top height and thickness, cloud fraction as derived considering a typical large-scale model grid box), and the microphysical and radiative properties (ice water content, visible extinction, effective radius, terminal fall speed, and total concentration). The variability of these tropical ice cloud properties is then studied as a function of the large-scale cloud regimes derived from the International Satellite Cloud Climatology Project (ISCCP), the amplitude and phase of the Madden-Julian Oscillation (MJO), and the large-scale atmospheric regime as derived from a long-term record of radiosonde observations over Darwin. The rationale for characterizing this variability is to provide an observational basis to which model outputs can be compared for the different regimes or large-scale characteristics and from which new parameterizations accounting for the large-scale context can be derived. The mean vertical variability of ice cloud occurrence and microphysical properties is large (1.5 order of magnitude for ice water content and extinction, a factor 3 in effective radius, and three orders of magnitude in concentration, typically). 98% of ice clouds in our dataset are characterized by either a small cloud fraction (smaller than 0.3) or a very large cloud fraction (larger than 0.9). Our results also indicate that, at least in the northern Australian region, the upper part of the troposphere can be split into three distinct layers characterized by different statistically-dominant microphysical processes. The variability of the ice cloud properties as a function of the large-scale atmospheric regime, cloud regime, and MJO phase is found to be large, producing mean differences of up to a factor of 8 in the frequency of ice cloud occurrence between large-scale atmospheric regimes, a factor of 3 to 4 for the ISCCP regimes and the MJO phases, and mean differences of a factor of 2 typically in all microphysical properties analysed in the present paper between large-scale atmospheric regimes or MJO phases. Large differences in occurrence (up to 60-80%) are also found in the main patterns of the cloud fraction distribution of ice clouds (fractions smaller than 0.3 and larger than 0.9). Finally, the diurnal cycle of the frequency of occurrence of ice clouds is also very different between regimes and MJO phases, with diurnal amplitudes of the vertically-integrated frequency of ice cloud occurrence ranging from as low as 0.2 (almost no detectable diurnal cycle) to values in excess of 2.0 (very large diurnal amplitude).

Protat, A.; Delanoë, J.; May, P. T.; Haynes, J.; Jakob, C.; O'Connor, E.; Pope, M.; Wheeler, M. C.

2010-08-01

15

Weather Radars and Lidar for Observing the Atmosphere  

NASA Astrophysics Data System (ADS)

The Earth Observing Laboratory (EOL) at the National Center for Atmospheric Research (NCAR) in Boulder, Colorado develops and deploys state-of-the-art ground-based radar, airborne radar and lidar instruments to advance scientific understanding of the earth system. The ground-based radar (S-Pol) is equipped with dual-wavelength capability (S-band and Ka-band). S-Pol is the only transportable radar in the world. In order to capture faster moving weather events such as tornadoes and record observations of clouds over rugged mountainous terrain and ocean, an airborne radar (ELDORA) is used. It is the only airborne Doppler meteorological radar that is able to detect motions in the clear air. The EOL is in the process of building the first phase of a three phase dual wavelength W/Ka-band airborne cloud radar to be called the HIAPER Cloud Radar (HCR). This phase is a pod based W-band radar system with scanning capability. The second phase will add pulse compression and polarimetric capability to the W-band system, while the third phase will add complementary Ka-band radar. The pod-based radar is primarily designed to fly on the Gulfstream V (GV) and C-130 aircraft. The envisioned capability of a millimeter wave radar system on GV is enhanced by coordination with microwave radiometer, in situ probes, and especially by the NCAR GV High-Spectral Resolution Lidar (HSRL) which is also under construction. The presentation will describe the capabilities of current instruments and also planned instrumentation development.

(Vivek) Vivekanandan, J.

2010-05-01

16

Comparison of Cloud Boundaries Measured with 8.6 mm Radar and 10.6 Micrometer Lidar.  

National Technical Information Service (NTIS)

One of the most basic cloud properties is location; the height of cloud base and the height of cloud top. The glossary of meteorology defines cloud base (top) as follows: 'For a given cloud or cloud layer, that lowest (highest) level in the atmosphere at ...

T. Uttal J. M. Intrieri

1993-01-01

17

Intercomparisons of cloud-top and cloud-base heights from ground-based Lidar, CloudSat and CALIPSO measurements  

Microsoft Academic Search

This study presents results of the intercomparison of cloud-top height (CTH) and cloud-bottom height (CBH) obtained from a space-borne active sensor Cloud Profiling Radar (CPR), the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), the space-borne passive sensor Moderate Resolution Imaging Spectroradiometer (MODIS) and ground-based Lidar measurements. Three selected cases (one daytime and two night-time cases) involving various cloud conditions such as

Sang-Woo Kim; Eui-Seok Chung; Soon-Chang Yoon; Byung-Ju Sohn; Nobuo Sugimoto

2011-01-01

18

Simple building reconstruction from LIDAR point cloud  

Microsoft Academic Search

This paper presents a method for simple regular building reconstruction from LIDAR point cloud. At First, TIN model of the extracted building point from discrete LIDAR point cloud is built. Those points in triangle facet which having the similar normal vector value are clustered into the same plane point set. Then, every plane point set is fitted into plane using

Qihong Zeng; Jiazhen Lai; Xianhua Li; Jianhua Mao; Xuefeng Liu

2008-01-01

19

Micropulse Lidar Cloud Mask Value-Added Product Technical Report.  

National Technical Information Service (NTIS)

Lidar backscattered signal is a useful tool for identifying vertical cloud structure in the atmosphere in optically thin clouds. Cloud boundaries derived from lidar signals are a necessary input for popular ARM data products, such as the Active Remote Sen...

C. Sivaraman J. Comstock

2011-01-01

20

Lidar Studies of Clouds at Toronto During the ECLIPS Program.  

National Technical Information Service (NTIS)

The Experimental Cloud Lidar Pilot Study (ECLIPS) measurement program involves the measurement of cloud optical and physical parameters with vertically pointing ground-based lidars simultaneously with satellites observing the same cloud system from above....

S. R. Pal, A. I. Carswell, A. Y. Fong, I. Pribluda, W. Steinbrecht

1992-01-01

21

THOR: Cloud Thickness from Off beam Lidar Returns  

NASA Technical Reports Server (NTRS)

Conventional wisdom is that lidar pulses do not significantly penetrate clouds having optical thickness exceeding about tau = 2, and that no returns are detectable from more than a shallow skin depth. Yet optically thicker clouds of tau much greater than 2 reflect a larger fraction of visible photons, and account for much of Earth s global average albedo. As cloud layer thickness grows, an increasing fraction of reflected photons are scattered multiple times within the cloud, and return from a diffuse concentric halo that grows around the incident pulse, increasing in horizontal area with layer physical thickness. The reflected halo is largely undetected by narrow field-of-view (FoV) receivers commonly used in lidar applications. THOR - Thickness from Off-beam Returns - is an airborne wide-angle detection system with multiple FoVs, capable of observing the diffuse halo, detecting wide-angle signal from which physical thickness of optically thick clouds can be retrieved. In this paper we describe the THOR system, demonstrate that the halo signal is stronger for thicker clouds, and validate physical thickness retrievals for clouds having z > 20, from NASA P-3B flights over the Department of Energy/Atmospheric Radiation Measurement/Southern Great Plains site, using the lidar, radar and other ancillary ground-based data.

Cahalan, Robert F.; McGill, Matthew; Kolasinski, John; Varnai, Tamas; Yetzer, Ken

2004-01-01

22

Cloud Thickness from Offbeam Returns - Thor Lidar  

NASA Technical Reports Server (NTRS)

Physical thickness of a cloud layer, and sometimes multiple cloud layers, can be estimated from the time delay of off-beam returns from a pulsed laser source illuminating one side of the cloud layer. In particular, the time delay of light returning from the outer diffuse halo of light surrounding the beam entry point, relative to the time delay at beam center, determines the cloud physical thickness. The delay combined with the pulse stretch gives the optical thickness. The halo method works best for thick cloud layers, typically optical thickness exceeding 2, and thus compliments conventional lidar which cannot penetrate thick clouds. Cloud layer top and base have been measured independently over the ARM/SGP site using conventional laser ranging (lidar) and the top minus base thickness are compared with a cloud top halo estimate obtained from the NASA/Goddard THOR System (THOR = THickness from Offbeam Returns). THOR flies on the NASA P3, and measures the halo timings from several km above cloud top, at the same time providing conventional lidar cloud top height. The ARM/SGP micropulse lidar provides cloud base height for validation.

Cahalan, R.; Kolasinski, J.; McGill, M.; Lau, William K. M. (Technical Monitor)

2002-01-01

23

Combined Lidar-Radar Remote Sensing: Initial Results from CRYSTAL-FACE and Implications for Future Spaceflight Missions  

NASA Technical Reports Server (NTRS)

In the near future NASA plans to fly satellites carrying a multi-wavelength backscatter lidar and a 94-GHz cloud profiling radar in formation to provide complete global profiling of cloud and aerosol properties. The CRYSTAL-FACE field campaign, conducted during July 2002, provided the first high-altitude colocated measurements from lidar and cloud profiling radar to simulate these spaceborne sensors. The lidar and radar provide complementary measurements with varying degrees of measurement overlap. This paper presents initial results of the combined airborne lidar-radar measurements during CRYSTAL-FACE. The overlap of instrument sensitivity is presented, within the context of particular CRYSTAL-FACE conditions. Results are presented to quantify the portion of atmospheric profiles sensed independently by each instrument and the portion sensed simultaneously by the two instruments.

McGill, Matthew J.; Li, Li-Hua; Hart, William D.; Heymsfield, Gerald M.; Hlavka, Dennis L.; Vaughan, Mark A.; Winker, David M.

2003-01-01

24

Lidar  

NASA Technical Reports Server (NTRS)

Lidar is an optical radar technique employing laser energy. Variations in signal intensity as a function of range provide information on atmospheric constituents, even when these are too tenuous to be normally visible. The theoretical and technical basis of the technique is described and typical values of the atmospheric optical parameters given. The significance of these parameters to atmospheric and meteorological problems is discussed. While the basic technique can provide valuable information about clouds and other material in the atmosphere, it is not possible to determine particle size and number concentrations precisely. There are also inherent difficulties in evaluating lidar observations. Nevertheless, lidar can provide much useful information as is shown by illustrations. These include lidar observations of: cirrus cloud, showing mountain wave motions; stratification in clear air due to the thermal profile near the ground; determinations of low cloud and visibility along an air-field approach path; and finally the motion and internal structure of clouds of tracer materials (insecticide spray and explosion-caused dust) which demonstrate the use of lidar for studying transport and diffusion processes.

Collis, R. T. H.

1969-01-01

25

RADAR AND LIDAR SYNERGY STUDIES BY MODEL SIMULATION  

Microsoft Academic Search

The use of lidar and radar instruments to measure forest structure attributes such as height and biomass are being considered for future Earth Observation satellite missions. Large footprint lidar makes a direct measurement of the heights of scatterers in the illuminated footprint and can yield information about the vertical profile of the canopy. Synthetic Aperture Radar (SAR) is known to

Guoqing Sun; Z. Guo; W. Ni; K. Jon Ranson; D. Kimes

26

Micropulse Lidar Cloud Mask Value-Added Product Technical Report  

SciTech Connect

Lidar backscattered signal is a useful tool for identifying vertical cloud structure in the atmosphere in optically thin clouds. Cloud boundaries derived from lidar signals are a necessary input for popular ARM data products, such as the Active Remote Sensing of Clouds (ARSCL) product. An operational cloud boundary algorithm (Wang and Sassen 2001) has been implemented for use with the ARM Micropulse Lidar (MPL) systems. In addition to retrieving cloud boundaries above 500 m, the value-added product (VAP) named Micropulse Lidar Cloud Mask (MPLCMASK) applies lidar-specific corrections (i.e., range-square, background, deadtime, and overlap) as described in Campbell et al. (2002) to the measured backscattered lidar. Depolarization ratio is computed using the methodology developed by Flynn et al. (2007) for polarization-capable MPL systems. The cloud boundaries output from MPLCMASK will be the primary lidar cloud mask for input to the ARSCL product and will be applied to all MPL systems, including historical data sets.

Sivaraman, C; Comstock, J

2011-07-25

27

Sensitivity of FMCW 95GHz cloud radar for high clouds  

Microsoft Academic Search

Studying the vertical structure of cloud is essential to make better atmospheric modellings for simulations of the global warming. Cloud observation requires very high sensitivity for radar. Although pulse radar is the mainstream of MMCR (millimeter wave cloud radar), FMCW radar has some advantages. FMCW signal has high spatial and time resolution, and enables high durability and cost-performance because all

J. Yamaguchi; T. Takano; T. Nakajima; T. Takamura; H. K. Y. Ohno; Y. Nakanishi; K. Akita; Y. Kawamura; H. A. Futaba; S. Yokote

2006-01-01

28

LIDAR, Point Clouds, and their Archaeological Applications  

SciTech Connect

It is common in contemporary archaeological literature, in papers at archaeological conferences, and in grant proposals to see heritage professionals use the term LIDAR to refer to high spatial resolution digital elevation models and the technology used to produce them. The goal of this chapter is to break that association and introduce archaeologists to the world of point clouds, in which LIDAR is only one member of a larger family of techniques to obtain, visualize, and analyze three-dimensional measurements of archaeological features. After describing how point clouds are constructed, there is a brief discussion on the currently available software and analytical techniques designed to make sense of them.

White, Devin A [ORNL

2013-01-01

29

Cloud properties derived from two lidars over the ARM SGP site  

NASA Astrophysics Data System (ADS)

Active remote sensors such as lidars or radars can be used with other data to quantify the cloud properties at regional scale and at global scale. Relative to radar, lidar remote sensing is sensitive to very thin and high clouds but has a significant limitation due to signal attenuation in the ability to precisely quantify the properties of clouds with a cloud optical thickness larger than 3. The cloud properties for all levels of clouds are derived and distributions of cloud base height (CBH), top height (CTH), physical cloud thickness (CT), and optical thickness (COT) from local statistics are compared. The goal of this study is (1) to establish a climatology of macrophysical and optical properties for all levels of clouds observed over the ARM SGP site and (2) to estimate the discrepancies between the two remote sensing systems (pulse energy, sampling, resolution, etc.). Our first results tend to show that the MPL, which are the primary ARM lidars, have a distinctly limited range within which all of these cloud properties are detectable, especially cloud top and cloud thickness, but this can include cloud base particularly during summer daytime period. According to the comparisons between RL and MPL, almost 50% of situations show a signal to noise ratio too low (smaller than 3) for the MPL in order to detect clouds higher than 7km during daytime period in summer. Consequently, the MPL-derived annual cycle of cirrus cloud base (top) altitude is biased low, especially for daylight periods, compared with those derived from the RL data, which detects cloud base ranging from 7.5 km in winter to 9.5 km in summer (and tops ranging from 8.6 to 10.5 km). The optically thickest cirrus clouds (COT > 0.3) reach 50% of the total population for the Raman lidar and only 20% for the Micropulse lidar due to the difference of pulse energy and the effect of solar irradiance contamination. A complementary study using the cloud fraction derived from the Micropulse lidar for clouds below 5 km and from the Raman lidar for cloud above 5 km allows for better estimation of the total cloud fraction between the ground and the top of the atmosphere. This study presents the diurnal cycle of cloud fraction for each season in comparisons with Long et al.'s (2006) cloud fraction calculation derived from radiative flux analysis.

Dupont, Jean-Charles; Haeffelin, Martial; Morille, Yohann; Comstock, Jennifer M.; Flynn, Connor; Long, Charles N.; Sivaraman, Chitra; Newson, Rob K.

2011-04-01

30

Aircraft-protection radar for use with atmospheric lidars  

Microsoft Academic Search

A modified X-band radar system designed to detect aircraft during atmospheric lidar operations is described and characterized. The capability of the radar to identify aircraft approaching from a variety of directions was tested, and first detections were found to occur between the 10 and 3 dB perimeters of the gain horn's antenna pattern. A model based on the radar equation

Bernard Firanski; Dwight Sipler

2005-01-01

31

94 GHz FMCW cloud radar  

NASA Astrophysics Data System (ADS)

A compact, solid state, zenith looking 94 GHz meteorological radar is described. Samples of the reflectivity data obtained from representative samples of hydrometeors, including cirrus cloud and fog, are presented. This bistatic FMCW radar delivers continuous information on the distribution and thickness of cloud layers, permitting accurate determination of the cloud base altitude and upper limit. The maximum range is 16 km, with a corresponding resolution of 30 m: both range and averaging time are user selectable in ranges 2-16 km and 5-60 s respectively. A radiated millimetre wave power of below 200 mW yields a dynamic range of over 60 dB in the received signal.

Huggard, P. G.; Oldfield, M. L.; Moyna, B. P.; Ellison, B. N.; Matheson, D. N.; Bennett, A. J.; Gaffard, C.; Oakley, T.; Nash, J.

2008-10-01

32

Forest Biomass retrieval strategies from Lidar and Radar modeling  

NASA Astrophysics Data System (ADS)

Estimates of regional and global forest biomass and forest structure are essential for understanding and monitoring ecosystem responses to human activities and climate change. Lidars with capabilities of recording the time-varying return signals provide vegetation height, ground surface height, and vertical distribution of vegetated surfaces intercepted by laser pulses. Large footprint lidar has been shown to be an effective technique for measuring forest canopy height, and biomass from space. Essentially, radar responds to the amount of water in a forest canopy, as well as its spatial structure. Data from these sensors contain information relevant to different aspects of the biophysical properties of the vegetation canopy including above ground biomass. The planned NASA new mission DESDynI will provide global systematic lidar sampling data and complete global coverage of L-band high resolution SAR and InSAR data for vegetation 3D structure mapping. By combining lidar and high-resolution SAR data, our quantitative knowledge of global carbon dynamics and ecosystem structure and function can be improved. This requires some new data processing and fusion technologies. What is the proper lidar sampling design and how to expand the vegetation spatial structural parameters estimated at lidar footprints to global spatial coverage in high resolution need to be resolved. Current configuration of DESDynI may also require lidar observations with variable looking angles, which creates a new challenge in lidar data processing. Models designed to simulate lidar and radar response from a variety of forest canopies can help answer these questions. In this paper we present an overview of our spatially explicit lidar and radar models and their use for examining the questions above. Specifically we will discuss sensitivities of large-footprint lidar and L-band polarimetric and interferometric radar to forest

Sun, G.; Ranson, J.

2008-12-01

33

Improved Snowfall Measurements using High Spectral Resolution Lidar and Radar  

Microsoft Academic Search

Lidar and radar measurements can be combined to estimate the effective diameter of precipitation particles(Donovan and Lammeren, J. Geophys. Res. 106, 2001). When these size estimates are combined with radar vertical velocity measurements it is possible to estimate precipitation rates in a layer a short distance above the ground. These retrievals are made much more robust when a high spectral

E. W. Eloranta

2008-01-01

34

Cloud properties derived from two lidars over the ARM SGP site  

SciTech Connect

[1] Active remote sensors such as lidars or radars can be used with other data to quantify the cloud properties at regional scale and at global scale (Dupont et al., 2009). Relative to radar, lidar remote sensing is sensitive to very thin and high clouds but has a significant limitation due to signal attenuation in the ability to precisely quantify the properties of clouds with a 20 cloud optical thickness larger than 3. In this study, 10-years of backscatter lidar signal data are analysed by a unique algorithm called STRucture of ATmosphere (STRAT, Morille et al., 2007). We apply the STRAT algorithm to data from both the collocated Micropulse lidar (MPL) and a Raman lidar (RL) at the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site between 1998 and 2009. Raw backscatter lidar signal is processed and 25 corrections for detector deadtime, afterpulse, and overlap are applied. (Campbell et al.) The cloud properties for all levels of clouds are derived and distributions of cloud base height (CBH), top height (CTH), physical cloud thickness (CT), and optical thickness (COT) from local statistics are compared. The goal of this study is (1) to establish a climatology of macrophysical and optical properties for all levels of clouds observed over the ARM SGP site 30 and (2) to estimate the discrepancies induced by the two remote sensing systems (pulse energy, sampling, resolution, etc.). Our first results tend to show that the MPLs, which are the primary ARM lidars, have a distinctly limited range where all of these cloud properties are detectable, especially cloud top and cloud thickness, but even actual cloud base especially during summer daytime period. According to the comparisons between RL and MPL, almost 50% of situations show a signal to noise ratio too low (smaller than 3) for the MPL in order to detect clouds higher than 7km during daytime period in summer. Consequently, the MPLderived annual cycle of cirrus cloud base (top) altitude is biased low, especially for daylight periods, compared with those derived from the RL data, which detects 5 cloud base ranging from 7.5 km in winter to 9.5 km in summer (and tops ranging from 8.6 to 10.5 km). The optically thickest cirrus clouds (COT>0.3) reach 50% of the total population for the Raman lidar and only 20% for the Micropulse lidar due to the difference of pulse energy and the effect of solar irradiance contamination. A complementary study using the cloud fraction 10 derived from the Micropulse lidar for clouds below 5 km and from the Raman lidar for cloud above 5 km allows for better estimation of the total cloud fraction between the ground and the top of the atmosphere. This study presents the diurnal cycle of cloud fraction for each season in comparisons with the Long et al. (2006) cloud fraction calculation derived from radiative flux analysis.

Dupont, Jean-Charles; Haeffelin, Martial; Morille, Y.; Comstock, Jennifer M.; Flynn, Connor J.; Long, Charles N.; Sivaraman, Chitra; Newsom, Rob K.

2011-02-16

35

Ice cloud microphysical property retrieval using airborne two-frequency radars  

NASA Astrophysics Data System (ADS)

An algorithm to retrieve the optically thick ice cloud microphysical property profiles is developed by using the GSFC 9.6 GHz ER-2 Doppler Radar (EDOP) and the 94 GHz Cloud Radar System (CRS) measurements aboard the high-altitude ER-2 aircraft. In situ size distribution and total water content data from the CRYSTAL-FACE field campaign are used for algorithm development. To reduce uncertainty in calculated radar reflectivity factors (Ze) at these wavelengths, coincident radar measurements and size distribution data are used to guide the selection of mass-length relationship and to deal with the density and non-spherical effects of ice crystals on Ze. The algorithm is able to retrieve microphysical property profiles of optically thick ice clouds, such as, deep convective and anvil clouds, which are very challenge for single frequency radar and lidar. An example of retrieved microphysical properties of a deep convective cloud is presented.

Wang, Zhien; Heymsfield, Gerald M.; Li, Lihua; Heymsfield, Andrew J.

2004-12-01

36

Cloud top liquid water from lidar observations of marine stratocumulus  

NASA Technical Reports Server (NTRS)

Marine stratus clouds were simultaneously observed by nadir Nd:YAG lidar measurements and in situ cloud physics measurements. A procedure was applied to derive the two-dimensional vertical cross section of the liquid water from within the cloud top lidar observations. A comparison to direct in-cloud liquid water observations gave good results. The liquid water retrieval was limited to an effective optical depth of 1.5. The true cloud optical thickness was also obtained from the retrieval procedure to a corresponding limit of 3.8. The optical thickness of the observed marine stratus clouds was predominantly below 3.0.

Spinhirne, J. D.; Boers, R.; Hart, W. D.

1989-01-01

37

Forest Biomass Mapping From Lidar and Radar Synergies  

NASA Technical Reports Server (NTRS)

The use of lidar and radar instruments to measure forest structure attributes such as height and biomass at global scales is being considered for a future Earth Observation satellite mission, DESDynI (Deformation, Ecosystem Structure, and Dynamics of Ice). Large footprint lidar makes a direct measurement of the heights of scatterers in the illuminated footprint and can yield accurate information about the vertical profile of the canopy within lidar footprint samples. Synthetic Aperture Radar (SAR) is known to sense the canopy volume, especially at longer wavelengths and provides image data. Methods for biomass mapping by a combination of lidar sampling and radar mapping need to be developed. In this study, several issues in this respect were investigated using aircraft borne lidar and SAR data in Howland, Maine, USA. The stepwise regression selected the height indices rh50 and rh75 of the Laser Vegetation Imaging Sensor (LVIS) data for predicting field measured biomass with a R(exp 2) of 0.71 and RMSE of 31.33 Mg/ha. The above-ground biomass map generated from this regression model was considered to represent the true biomass of the area and used as a reference map since no better biomass map exists for the area. Random samples were taken from the biomass map and the correlation between the sampled biomass and co-located SAR signature was studied. The best models were used to extend the biomass from lidar samples into all forested areas in the study area, which mimics a procedure that could be used for the future DESDYnI Mission. It was found that depending on the data types used (quad-pol or dual-pol) the SAR data can predict the lidar biomass samples with R2 of 0.63-0.71, RMSE of 32.0-28.2 Mg/ha up to biomass levels of 200-250 Mg/ha. The mean biomass of the study area calculated from the biomass maps generated by lidar- SAR synergy 63 was within 10% of the reference biomass map derived from LVIS data. The results from this study are preliminary, but do show the potential of the combined use of lidar samples and radar imagery for forest biomass mapping. Various issues regarding lidar/radar data synergies for biomass mapping are discussed in the paper.

Sun, Guoqing; Ranson, K. Jon; Guo, Z.; Zhang, Z.; Montesano, P.; Kimes, D.

2011-01-01

38

Radar, lidar, and optical observations in the polar summer mesosphere shortly after a space shuttle launch  

NASA Astrophysics Data System (ADS)

In the summer of 2007, a noctilucent cloud (NLC) campaign was organized in Alaska. Radar, lidar, and photographic methods were used. Due to lighting conditions, the campaign was carried out near the end of the NLC season. Sporadic radar and lidar echoes were obtained until the very end of the campaign, when an exceptionally intense event occurred on the local time night of 10-11 August. This late-season event followed the launch of the space shuttle on 8 August. At least twice before, solstice launches of the shuttle have been followed by unique observations of NLC and sporadic iron layers in the polar regions. This was the case here as well. The iron layer increased in altitude and density, the latter by a factor of 20, compared to the previous night. And, for the first time, (1) polar mesospheric summer echoes (PMSE) were recorded by a radar in an event of this nature and (2) an intense sporadic E layer was collocated with the iron atom layer. At the UHF radar frequency used, very large Schmidt numbers are required for PMSE. Indeed, the PMSE was found at and just above the particles responsible for Mie scatter. Such large particles are likely needed to yield large Schmidt numbers. Additionally, similar lidar and sporadic E layers were detected over Greenland on the previous night. Here we consider the ion chemistry that could lead to the collocated atom and iron layers and conclude that considerably enhanced water vapor content was required.

Kelley, M. C.; Nicolls, M. J.; Varney, R. H.; Collins, R. L.; Doe, R.; Plane, J. M. C.; Thayer, J.; Taylor, M.; Thurairajah, B.; Mizutani, K.

2010-05-01

39

Simultaneous Radar and Lidar Observations During the DYANA-Campaign.  

National Technical Information Service (NTIS)

During the Dynamics Adapted Network for the Atmosphere (DYANA) campaign from Jan. - Mar. 1990 the SOUSY-VHF-Radar and the SOUSY-UV-Lidar were operated simultaneously at 15 clear nights near Andenes on the island of Andoya (northern Norway) to investigate ...

P. Czechowsky B. Inhester J. Klostermeyer R. Ruester G. Schmidt

1991-01-01

40

Potential of airborne lidar measurements for cirrus cloud studies  

NASA Astrophysics Data System (ADS)

Aerosol and water vapour measurements were performed with the lidar system WALES of Deutsches Zentrum für Luft- und Raumfahrt (DLR) in October and November 2010 during the first mission with the new German research aircraft G55-HALO. Curtains composed of lidar profiles beneath the aircraft show the vertical and horizontal distribution and variability of water vapour mixing ratio and backscatter ratio above Germany. Two missions on 3 and 4 November 2010 were selected to derive the water vapour mixing ratio inside cirrus clouds from the lidar instrument. A good agreement was found with in-situ observations performed on a second research aircraft flying below HALO. ECMWF analysis temperature data are used to derive relative humidity fields (RHi) inside and outside of cirrus clouds from the lidar water vapour observations. The RHi variability is dominated by small scale fluctuations in the water vapour fields while the temperature variation has a minor impact. The most frequent in-cloud RHi value from lidar observations is 98%. The RHi variance is smaller inside the cirrus than outside of the cloud. 2-dimensional histograms of relative humidity and backscatter ratio show significant differences for in-cloud and out-of cloud situations for two different cirrus cloud regimes. Combined with accurate temperature measurements, the lidar observations have a great potential for detailed statistical cirrus cloud and related humidity studies.

Groß, S.; Wirth, M.; Schäfler, A.; Fix, A.; Kaufmann, S.; Voigt, C.

2014-04-01

41

Vertical Cloud Profiles: The Millimeter Wave Cloud Radar (MMCR)  

NSDL National Science Digital Library

This middle/junior high school level activity requires students to color velocity and reflectivity radar images from the millimeter wave cloud radar (MMCR) in Oklahoma and to interpret their features including cloud thickness and height. The exercise is part of the Atmospheric Visualization Collection (AVC), which focuses on data from the Atmospheric Radiation Measurement (ARM) program's Southern Great Plains Cloud and Radiation Testbed site.

2003-05-09

42

Lidar observations of high-altitude aerosol layers (cirrus clouds)  

NASA Astrophysics Data System (ADS)

Aerosols, clouds and aerosol-cloud interactions are recognized as the key factors influencing the climate. Clouds are the primary modulators of the Earth's radiative budget. This paper focuses on the detection of high-altitude aerosol layers in the troposphere over mid-latitude lidar station in Sofia, Bulgaria. They are situated in the height-region 6 km÷16 km, with thickness in the range 0.2 km÷5 km and have varying optical characteristics. On the basis of the general utilized classification of the Cirrus clouds, high values of the calculated atmospheric backscatter coefficient and Angströmexponent estimation results we conclude that the registered strongly scattered aerosol layers are Cirrus clouds. Lidar measurements are performed with an aerosol lidar, equipped with Nd:YAG laser at wavelengths 532 nm and 1064 nm. Mainly, lidar data are presented in terms of vertical atmospheric backscatter coefficient profiles. We also include 2Dcolormap in height-time coordinates build on the basis of so called range corrected signals. It shows in general changes of the aerosol stratification over the lidar station during the measurement period. We employed HYSPLIT backward trajectories and DREAM forecasts to analyze the lidar profile outlines and characterize the events during which Cirrus cloud samples were observed. So was remarked that most of the results were obtained during Saharan dust long-way transport over the city of Sofia. Reported experimental examples are extracted from regular lidar investigations of the atmosphere within the frame of European project EARLINET.

Deleva, Atanaska D.; Grigorov, Ivan V.

2013-03-01

43

Feature enhancing aerial lidar point cloud refinement  

NASA Astrophysics Data System (ADS)

Raw aerial LiDAR point clouds often suffer from noise and under-sampling, which can be alleviated by feature preserving refinement. However, existing approaches are limited to only preserving normal discontinuous features (ridges, ravines and crest lines) while position discontinuous features (boundaries) are also universal in urban scenes. We present a new refinement approach to accommodate unique properties of aerial LiDAR building points. By extending recent developments in geometry refinement to explicitly regularize boundary points, both normal and position discontinuous features are preserved and enhanced. The refinement includes two steps: i) the smoothing step applies a two-stage feature preserving bilateral filtering, which first filters normals and then updates positions under the guidance of the filtered normals. In a separate similar process, boundary points are smoothed directed by tangent directions of underlying lines, and ii) the up-sampling step interpolates new points to fill gaps/holes for both interior surfaces and boundary lines, through a local gap detector and a feature-aware bilateral projector. Features can be further enhanced by limiting the up-sampling near discontinuities. The refinement operates directly on points with diverse density, shape and complexity. It is memory-efficient, easy to implement, and easily extensible.

Gao, Zhenzhen; Neumann, Ulrich

2014-03-01

44

Climatology of Ice clouds Derived from Polarization Lidar at AFARS, Fairbanks, Alaska  

NASA Astrophysics Data System (ADS)

Arctic clouds play a crucial role in the global climate system through their radiative impacts and climate-feedback mechanisms. While it is generally recognized that changes in arctic cloud characteristics are due to large-scale atmospheric and oceanic circulation features, regional patterns and types of clouds are more sensitive to orography and weather phenomenon, which are poorly understood because of sparse measurements and are not well represented in climate models. A cloud research station (Arctic Facility for Atmospheric Remote Sensing, AFARS) established in central Alaska at the University of Alaska Fairbanks (64.85N-147.85W) supports a cloud polarization lidar (0.694?m) and W-band Doppler radar (3.2 mm) since 2004 with cloud and aerosol measurements during the local overpass times of the A-Train satellite constellation. Here we present a climatology of all ice clouds derived from our unique ~6 year lidar dataset and local radiosonde measurements. The clouds have been categorized by type according to the visual identification scheme of WMO by a single trained observer. The purpose of this study is to understand the conditions under which these types of cloud form with their macrophysical properties and associated weather patterns. In future these derived synoptic conditions and cloud properties will be used in algorithm development utilizing the present spaceborne active sensing datasets.

Kayetha, V. K.; Sassen, K.

2011-12-01

45

Airborne Lidar and Radiometric Observations of PBL- and Low Clouds.  

National Technical Information Service (NTIS)

Boundary layer- and low altitude clouds over open ocean and continent areas have been studied during several field campaigns since mid-1990 using the French airborne backscatter lidar LEANDRE in conjunction with on-board IR and visible radiometers. LEANDR...

P. H. Flamant R. Valentin J. Pelon

1992-01-01

46

Initial assessment of space-based lidar CALIOP aerosol and cloud layer structures through inter-comparison with a ground-based back-scattering lidar and CloudSat  

NASA Astrophysics Data System (ADS)

This study presents results of the intercomparison of aerosol/cloud top and bottom heights obtained from a space-borne active sensor Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) onboard CALIPSO, and the Cloud Profiling Radar (CPR) onboard CloudSat, and the space-borne passive sensor Moderate Resolution Imaging Spectroradiometer (MODIS) onboard Aqua, and ground-based 2-wavelenght polarization lidar system (532 and 1064 nm) at Seoul National University (SNU), Seoul, South Korea. This result confirms that the CALIPSO science team algorithms for the discrimination of cloud and aerosol as well as for the detection of layer top and base altitude provide reliable information both under cloud-free conditions and in cases of multiple aerosol layers underlying semi-transparent cirrus clouds. Simultaneous space-borne CALIOP, CPR and ground-based SNU lidar (SNU-L) measurements complement each other and can be combined to provide full information on the vertical distribution of aerosols and clouds, especially for thick opaque clouds. The aerosol extinction profiles from both lidars show good agreement for aerosols within the planetary boundary layer under cloud-free conditions and for the night-time CALIOP flight.

Kim, S.-W.; Yoon, S.-C.; Chung, E.-S.; Sohn, B.-J.; Berthier, S.; Raut, J.-C.; Chazette, P.; Dulac, F.

2009-03-01

47

Relation of Cloud Occurrence Frequency, Overlap, and Effective Thickness Derived from CALIPSO and CloudSat Merged Cloud Vertical Profiles.  

National Technical Information Service (NTIS)

A cloud frequency of occurrence matrix is generated using merged cloud vertical profile derived from Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and Cloud Profiling Radar (CPR). The matrix contains vertical profiles of cloud occurrence frequ...

B. A. Wielicki F. G. Rose P. Minnis S. Kato S. Sun-Mack W. F. Miller Y. Chen

2009-01-01

48

IMPROVING CLOUD CLIMATOLOGY ANALYSIS USING SPACE LIDAR OBSERVATIONS: COMPARISON OF SEVIRI AND PARASOL WITH CALIPSO  

Microsoft Academic Search

Coincident cloud occurrence, cloud type and cloud pressure data from the lidar CALIOP on board the CALIPSO (Cloud-Aerosol Lidar with Orthogonal Polarization) platform flying in the A-train Constellation, the POLDER (Polarization and Directionality of the Earth's Reflectances) radiometer on board the PARASOL (Polarization and Anisotropy of Reflectances for Atmospheric Sciences coupled with Observations from a Lidar) platform flying also in

G. Sèze; J. Pelon; C. Vanbauce; F. Parol; H. Legleau; M. Derrien; J. Riedi

49

Polarization lidar liquid cloud detection algorithm for winter mountain storms  

NASA Technical Reports Server (NTRS)

We have collected an extensive polarization lidar dataset from elevated sites in the Tushar Mountains of Utah in support of winter storm cloud seeding research and experiments. Our truck-mounted ruby lidar collected zenith, dual-polarization lidar data through a roof window equipped with a wiper system to prevent snowfall accumulation. Lidar returns were collected at a rate of one shot every 1 to 5 min during declared storm periods over the 1985 and 1987 mid-Jan. to mid-Mar. Field seasons. The mid-barrier remote sensor field site was located at 2.57 km MSL. Of chief interest to weather modification efforts are the heights of supercooled liquid water (SLW) clouds, which must be known to assess their 'seedability' (i.e., temperature and height suitability for artificially increasing snowfall). We are currently re-examining out entire dataset to determine the climatological properties of SLW clouds in winter storms using an autonomous computer algorithm.

Sassen, Kenneth; Zhao, Hongjie

1992-01-01

50

Amplification of radar and lidar signatures using quantum sensors  

NASA Astrophysics Data System (ADS)

One of the major scientific thrusts from recent years has been to try to harness quantum phenomena to dramat­ ically increase the performance of a wide variety of classical devices. These advances in quantum information science have had a considerable impact on the development of photonic-based quantum sensors. Even though quantum radar and quantum lidar remain theoretical proposals, preliminary results suggest that these sensors have the potential of becoming disruptive technologies able to revolutionize reconnaissance systems. In this paper we will discuss how quantum entanglement can be exploited to increase the radar and lidar signature of rectangular targets. In particular, we will show how the effective visibility of the target is increased if observed with an entangled multi-photon quantum sensor.

Lanzagorta, Marco

2013-05-01

51

Nanosecond gated PMT for LIDAR-RADAR applications  

Microsoft Academic Search

Wide dynamic range gating photosensor modules has been design for LIDAR-RADAR applications on base R7400U (active area 8 mm. diameter) R7600U (active area 18x18 mm.) Hamamatsu photomultiplier tubes. The photomultiplier tubes R7400U, series have two kinds of photocathode: low resistance semitransparent multialkali photocathodes and semitransparent bialkali photocathodes with large resistance. Different kinds of photocathodes require different approach to gating circuits

Pavlo A. Molchanov; Vincent M. Contarino; Brian M. Concannon; Olha V. Asmolova; Yulia Y. Podobna

2006-01-01

52

Ground-based microwave radar and optical lidar signatures of volcanic ash plumes: models, observations and retrievals  

NASA Astrophysics Data System (ADS)

The detection and quantitative retrieval of volcanic ash clouds is of significant interest due to its environmental, climatic and socio-economic effects. Real-time monitoring of such phenomena is crucial, also for the initialization of dispersion models. Satellite visible-infrared radiometric observations from geostationary platforms are usually exploited for long-range trajectory tracking and for measuring low level eruptions. Their imagery is available every 15-30 minutes and suffers from a relatively poor spatial resolution. Moreover, the field-of-view of geostationary radiometric measurements may be blocked by water and ice clouds at higher levels and their overall utility is reduced at night. Ground-based microwave radars may represent an important tool to detect and, to a certain extent, mitigate the hazard from the ash clouds. Ground-based weather radar systems can provide data for determining the ash volume, total mass and height of eruption clouds. Methodological studies have recently investigated the possibility of using ground-based single-polarization and dual-polarization radar system for the remote sensing of volcanic ash cloud. A microphysical characterization of volcanic ash was carried out in terms of dielectric properties, size distribution and terminal fall speed, assuming spherically-shaped particles. A prototype of volcanic ash radar retrieval (VARR) algorithm for single-polarization systems was proposed and applied to S-band and C-band weather radar data. The sensitivity of the ground-based radar measurements decreases as the ash cloud is farther so that for distances greater than about 50 kilometers fine ash might be not detected anymore by microwave radars. In this respect, radar observations can be complementary to satellite, lidar and aircraft observations. Active remote sensing retrieval from ground, in terms of detection, estimation and sensitivity, of volcanic ash plumes is not only dependent on the sensor specifications, but also on the range and ash cloud distribution. The minimum detectable signal can be increased, for a given system and ash plume scenario, by decreasing the observation range and increasing the operational frequency using a multi-sensor approach, but also exploiting possible polarimetric capabilities. In particular, multi-wavelengths lidars can be complementary systems useful to integrate radar-based ash particle measurement. This work, starting from the results of a previous study and from above mentioned issues, is aimed at quantitatively assessing the optimal choices for microwave and millimeter-wave radar systems with a dual-polarization capability for real-time ash cloud remote sensing to be used in combination with an optical lidar. The physical-electromagnetic model of ash particle distributions is systematically reviewed and extended to include non-spherical particle shapes, vesicular composition, silicate content and orientation phenomena. The radar and lidar scattering and absorption response is simulated and analyzed in terms of self-consistent polarimetric signatures for ash classification purposes and correlation with ash concentration and mean diameter for quantitative retrieval aims. A sensitivity analysis to ash concentration, as a function of sensor specifications, range and ash category, is carried out trying to assess the expected multi-sensor multi-spectral system performances and limitations. The multi-sensor multi-wavelength polarimetric model-based approach can be used within a particle classification and estimation scheme, based on the VARR Bayesian metrics. As an application, the ground-based observation of the Eyjafjallajökull volcanic ash plume on 15-16 May 2010, carried out at the Atmospheric Research Station at Mace Head, Carna (Ireland) with MIRA36 35-GHz Ka-Band Doppler cloud radar and CHM15K lidar/ceilometer at 1064-nm wavelength, has been considered. Results are discussed in terms of retrievals and intercomparison with other ground-based and satellite-based sensors.

Mereu, Luigi; Marzano, Frank; Mori, Saverio; Montopoli, Mario; Cimini, Domenico; Martucci, Giovanni

2013-04-01

53

Towards an automatic lidar cirrus cloud retrieval for climate studies  

NASA Astrophysics Data System (ADS)

This paper presents a methodology to calculate lidar ratios for distinct cirrus clouds that has been developed and implemented for a site located in the Southern Hemisphere. The cirrus cloud lidar data processing aims to consider a large cloud variability and cirrus cloud monitoring through a robust retrieval process. Among cirrus features estimates for complex scenes that lidar systems can provide, we highlight cloud geometrical information and extinction-to-backscatter ratio (known as lidar ratio or LR). In general, direct information on cirrus cloud microphysics is difficult to derive because LR depends on the presence of ice crystals and their properties such as shape, size, composition and orientation of particles. An iterative process to derive a stable LR value has been proposed. One of the keys is to restrict the analysis to conditions allowing accurate multilayer events. This method uses nonparametric statistical approaches to identify stationary periods according to cloud features and variability. Measurements performed in the region of the metropolitan city of São Paulo (MSP) have been used to implement and test the methodology developed for cirrus cloud characterization. Good results are represented by examining specific cases with multilayer cirrus cloud occurrence. In addition to the geometrical parameters obtained, cirrus LR values were calculated for a single day ranging from 19 ± 01 sr to 74 ± 13 sr for 2 observed layers. This large difference in LR can indicate a mixture of ice crystal particles with different sizes and shapes in both layers of the cirrus clouds. Trajectory analyses indicate that both of these cloud layers can be associated with different air mass and should be considered as 2 distinct clouds in climatology.

Larroza, E. G.; Nakaema, W. M.; Bourayou, R.; Hoareau, C.; Landulfo, E.; Keckhut, P.

2013-11-01

54

Lidar detection of temporal and spatial anomalies of multiple clouds  

Microsoft Academic Search

An algorithm using N-way analysis for the detection of multiple clouds in multi-wavelength lidar data is presented. Nway analysis is a tool for algebraic manipulation of N-dimensional (ND) data arrays, and it allows for spatial (range), temporal (time), and spectral (wavelength) information to be extracted simultaneously from 3D lidar data. The algorithm tracks the spectral signal strength and location of

Charles E. Davidson; Avishai Ben-David

2008-01-01

55

Surface Complexity Component of LIDAR Point Cloud Error Characterization  

NASA Astrophysics Data System (ADS)

There are several data product characterization methods to describe LiDAR data quality. Typically based on guidelines developed by government or professional societies, these techniques require the statistical analysis of vertical differences at known checkpoints (surface patches) to obtain a measure of the vertical accuracy. More advanced methods attempt to also characterize the horizontal accuracy of the LiDAR point cloud, using measurements at LiDAR-specific targets or other man-made objects that can be distinctly extracted from both horizontal and vertical representation in the LiDAR point cloud. There are two concerns with these methods. First, the number of check points/features is relatively small with respect to the point cloud size that is typically measured, at least, in millions. Second, these locations are usually selected in relatively benign areas, such as hard flat surfaces at easily accessible locations. The problem with this characterization is that it is not likely that a statistically representative analysis can be obtained from a limited number of points at locations that may not properly represent the overall object space composition. There is an ongoing effort to address these issues, and some of the newer methods to characterize LiDAR data include an average points spacing measure, computed from the LiDAR point cloud. Clearly, it is an important step forward but it ignores the surface complexity. The objective of this study is to elaborate only on the requirements for adequate surface representation in combination with the LiDAR error characterization techniques to identify the relation between the two surfaces, the measured and reference (ideal), and thus, to support better LiDAR or, in general, point cloud error characterization.

Toth, C.; Grejner-Brzezinska, D.

2012-07-01

56

Multi-year measurements of cloud base heights at South Pole by lidar  

Microsoft Academic Search

The Micropulse Lidar Network has operated a full-time lidar measurement program at South Pole Station since 2000. Observations from this instrument are an important multi-year record of clouds over the Antarctic plateau. Earlier South Pole observations relied mostly on passive measurements to characterize clouds; the lidar's active profiles present an opportunity to validate current understanding of Antarctic clouds, as well

Ashwin Mahesh; James R. Campbell; James D. Spinhirne

2005-01-01

57

Airborne Lidar Point Cloud Density Indices  

NASA Astrophysics Data System (ADS)

Airborne lidar is useful for collecting a large volume and high density of points with three dimensional coordinates. Among these points are terrain points, as well as those points located aboveground. For DEM production, the density of the terrain points is an important quality index. While the penetration rate of laser points is dependent on the surface type characteristics, there are also different ways to present the point density. Namely, the point density could be measured by subdividing the surveyed area into cells, then computing the ratio of the number of points in each respective cell to its area. In this case, there will be one density value for each cell. The other method is to construct the TIN, and count the number of triangles in the cell, divided by the area of the cell. Aside from counting the number of triangles, the area of the largest, or the 95% ranking, triangle, could be used as an index as well. The TIN could also be replaced by Voronoi diagrams (Thiessen Polygon), and a polygon with even density could be derived from human interpretation. The nature of these indices is discussed later in this research paper. Examples of different land cover types: bare earth, built-up, low vegetation, low density forest, and high density forest; are extracted from point clouds collected in 2005 by ITRI under a contract from the Ministry of the Interior. It is found that all these indices are capable of reflecting the differences of the land cover type. However, further investigation is necessary to determine which the most descriptive one is.

Shih, P. T.; Huang, C.-M.

2006-12-01

58

CloudSat as a Global Radar Calibrator  

SciTech Connect

The calibration of the CloudSat spaceborne cloud radar has been thoroughly assessed using very accurate internal link budgets before launch, comparisons with predicted ocean surface backscatter at 94 GHz, direct comparisons with airborne cloud radars, and statistical comparisons with ground-based cloud radars at different locations of the world. It is believed that the calibration of CloudSat is accurate to within 0.5 to 1 dB. In the present paper it is shown that an approach similar to that used for the statistical comparisons with ground-based radars can now be adopted the other way around to calibrate other ground-based or airborne radars against CloudSat and / or detect anomalies in long time series of ground-based radar measurements, provided that the calibration of CloudSat is followed up closely (which is the case). The power of using CloudSat as a Global Radar Calibrator is demonstrated using the Atmospheric Radiation Measurement cloud radar data taken at Barrow, Alaska, the cloud radar data from the Cabauw site, The Netherlands, and airborne Doppler cloud radar measurements taken along the CloudSat track in the Arctic by the RASTA (Radar SysTem Airborne) cloud radar installed in the French ATR-42 aircraft for the first time. It is found that the Barrow radar data in 2008 are calibrated too high by 9.8 dB, while the Cabauw radar data in 2008 are calibrated too low by 8.0 dB. The calibration of the RASTA airborne cloud radar using direct comparisons with CloudSat agrees well with the expected gains and losses due to the change in configuration which required verification of the RASTA calibration.

Protat, Alain; Bouniol, Dominique; O'Connor, E. J.; Baltink, Henk K.; Verlinde, J.; Widener, Kevin B.

2011-03-01

59

A Wing Pod-based Millimeter Wave Cloud Radar on HIAPER  

NASA Astrophysics Data System (ADS)

One of the attractive features of a millimeter wave radar system is its ability to detect micron-sized particles that constitute clouds with lower than 0.1 g m-3 liquid or ice water content. Scanning or vertically-pointing ground-based millimeter wavelength radars are used to study stratocumulus (Vali et al. 1998; Kollias and Albrecht 2000) and fair-weather cumulus (Kollias et al. 2001). Airborne millimeter wavelength radars have been used for atmospheric remote sensing since the early 1990s (Pazmany et al. 1995). Airborne millimeter wavelength radar systems, such as the University of Wyoming King Air Cloud Radar (WCR) and the NASA ER-2 Cloud Radar System (CRS), have added mobility to observe clouds in remote regions and over oceans. Scientific requirements of millimeter wavelength radar are mainly driven by climate and cloud initiation studies. Survey results from the cloud radar user community indicated a common preference for a narrow beam W-band radar with polarimetric and Doppler capabilities for airborne remote sensing of clouds. For detecting small amounts of liquid and ice, it is desired to have -30 dBZ sensitivity at a 10 km range. Additional desired capabilities included a second wavelength and/or dual-Doppler winds. Modern radar technology offers various options (e.g., dual-polarization and dual-wavelength). Even though a basic fixed beam Doppler radar system with a sensitivity of -30 dBZ at 10 km is capable of satisfying cloud detection requirements, the above-mentioned additional options, namely dual-wavelength, and dual-polarization, significantly extend the measurement capabilities to further reduce any uncertainty in radar-based retrievals of cloud properties. This paper describes a novel, airborne pod-based millimeter wave radar, preliminary radar measurements and corresponding derived scientific products. Since some of the primary engineering requirements of this millimeter wave radar are that it should be deployable on an airborne platform, occupy minimum cabin space and maximize scan coverage, a pod-based configuration was adopted. Currently, the radar system is capable of collecting observations between zenith and nadir in a fixed scanning mode. Measurements are corrected for aircraft attitude changes. The near-nadir and zenith pointing observations minimize the cross-track Doppler contamination in the radial velocity measurements. An extensive engineering monitoring mechanism is built into the recording system status such as temperature, pressure, various electronic components' status and receiver characteristics. Status parameters are used for real-time system stability estimates and correcting radar system parameters. The pod based radar system is mounted on a modified Gulfstream V aircraft, which is operated and maintained by the National Center for Atmospheric Research (NCAR) on behalf of the National Science Foundation (NSF). The aircraft is called the High-Performance Instrumented Airborne Platform for Environmental Research (HIAPER) (Laursen et al., 2006). It is also instrumented with high spectral resolution lidar (HSRL) and an array of in situ and remote sensors for atmospheric research. As part of the instrument suite for HIAPER, the NSF funded the development of the HIAPER Cloud Radar (HCR). The HCR is an airborne, millimeter-wavelength, dual-polarization, Doppler radar that serves the atmospheric science community by providing cloud remote sensing capabilities for the NSF/NCAR G-V (HIAPER) aircraft. An optimal radar configuration that is capable of maximizing the accuracy of both qualitative and quantitative estimated cloud microphysical and dynamical properties is the most attractive option to the research community. The Technical specifications of cloud radar are optimized for realizing the desired scientific performance for the pod-based configuration. The radar was both ground and flight tested and preliminary measurements of Doppler and polarization measurements were collected. HCR observed sensitivity as low as -37 dBZ at 1 km range and resolved linear depolarization ratio (LDR) si

Vivekanandan, Jothiram; Tsai, Peisang; Ellis, Scott; Loew, Eric; Lee, Wen-Chau; Emmett, Joanthan

2014-05-01

60

Lidar-radar synergy for characterizing properties of ultragiant volcanic aerosol  

NASA Astrophysics Data System (ADS)

The atmospheric aerosol has a relevant effect on our life influencing climate, aviation safety, air quality and natural hazards. The identification of aerosol layers through inspection of continuous measurements is strongly recommended for quantifying their contribution to natural hazards and air quality and to establish suitable alerting systems. In particular, the study of ultragiant aerosols may improve the knowledge of physical-chemical processes underlying the aerosol-cloud interactions and the effect of giant nuclei as a potential element to expedite the warm-rain process. Moreover, the identification and the characterization of ultragiant aerosols may strongly contribute to quantify their impact on human health and their role in airplane engine damages or in visibility problems, especially in case of extreme events as explosive volcanic eruptions. During spring 2010, volcanic aerosol layers coming from Eyjafjallajökull volcano were observed over most of the European countries, using lidar technique. From 19 April to 19 May 2010, they were also observed at CNR-IMAA Atmospheric Observatory (CIAO) with the multi-wavelength Raman lidar systems of the Potenza EARLINET station (40.60N, 15.72E, 760 m a.s.l), Southern Italy. During this period, ultragiant aerosol were also observed at CIAO using a co-located Ka-band MIRA-36 Doppler microwave radar operating at 8.45 mm (35.5 GHz). The Ka-band radar observed in four separate days (19 April, 7, 10, 13 May) signatures consistent with the observations of non-spherical ultragiant aerosol characterized by anomalous values of linear depolarization ratio higher than -4 dB, probably related to the occurrence of multiple effects as particle alignment and presence of an ice coating. 7-days backward trajectory analysis shows that the air masses corresponding to the ultragiant aerosol observed by the radar were coming from the Eyjafjallajökull volcano area. Only in one case the trajectories do not come directly from Iceland, but from Central Europe where many lidar observations confirm the presence of volcanic aerosol in the previous days. Therefore, both CIAO lidar observations and the backtrajectory analysis suggests a volcanic origin of the ultragiant aerosol observed by the radar, revealing that these particles might have travelled for more than 4000 km after their injection into the atmosphere. The reported observation fostered a study, reported in this work, about the performances of multi-wavelength Raman lidars in the identification and the characterization of ultragiant aerosols layers in the troposphere. Results from simulations using Mie, T-Matrix and ray-tracing codes will be presented and compared with the observations performed in April-May 2010 during the Eyjafjallajökull eruption. Sensitivity ranges in detection of aerosol layer are pointed out in terms of experimental limits of both lidar and radar techniques and of aerosol optical depth. Moreover, recommendations for use of a combined lidar-radar approach for the aerosol typing and for the retrieval of their microphysical properties are reported.

Madonna, F.; Amodeo, A.; D'Amico, G.; Giunta, A.; Mona, L.; Pappalardo, G.

2011-12-01

61

ARM Value-Added Products for New Scanning and Zenith-pointing Cloud Radars  

NASA Astrophysics Data System (ADS)

The Department of Energy's Atmospheric Radiation Measurement (ARM) Climate Research Facility has extended and improved its cloud observing capabilities with the addition of the dual-frequency Scanning ARM Cloud Radars (SACRs) and the upgrade of the vertically pointing 35GHz cloud radars to become the Ka-band ARM Zenith-pointing Radars (KAZRs). These radars are now installed at each of the facility's existing fixed sites and as part of both ARM mobile facilities. While these radars are capable of producing unprecedented continuous long-term cloud property data sets, the measurements will be most utilized if scientists can readily incorporate the observations into their research, without the need for extensive radar analysis and expertise. For this reason, value-added products (VAPs) are being developed to provide quality-controlled gridded radar moments (reflectivity, radial velocity, spectrum width) as well as derived products, such as hydrometeor masks and cloud boundaries. The Active Remote Sensing of Clouds (ARSCL) VAP has been producing a first generation of these products for over 10 years. The VAP combines zenith-pointing cloud radar data with micropulse lidar, ceilometer and rain gauge data to produce best-estimate quality-controlled radar moments and cloud boundaries. ARSCL has been rewritten and improved to take advantage of the upgraded KAZR radars. In addition, a new product is being developed for the polarization-diverse scanning Ka/W-band and X/Ka-band cloud radars. Initially, moments from each individual radar will be corrected for water vapor attenuation as well as range and velocity folding. Next, three-dimensional gridded moments will be produced, followed by combined-frequency, synergistic products. The new products will be described and examples of available and anticipated data products will be shown. Example of best-estimate reflectivity produced by ARSCL-KAZR product. Image is for date 2011.05.20, using measurements from the KAZR radar at the ARM Southern Great Plains site. Corresponding cloud boundaries produced by ARSCL-KAZR product.

Johnson, K. L.; Troyan, D.; Kollias, P.; Kalesse, H.; Luke, E. P.; Giangrande, S. E.; Jensen, M. P.

2012-12-01

62

Performance of the GLAS Satellite Lidar Cloud and Aerosol Measurements  

Microsoft Academic Search

Launched in early 2003, the geoscience laser altimeter system (GLAS) on the Ice, Cloud and Land Elevation Satellite is the first polar orbiting satellite lidar and is intended for comprehensive earth science applications covering surface altimetry for ice sheets and vegetation and atmospheric profiling. The instrument design includes high performance observations of the distribution and optical scattering cross sections of

James D. Spinhirne

2008-01-01

63

Data segmentation for geometric feature extraction from lidar point clouds  

Microsoft Academic Search

Data Segmentation is the basis of 3D feature ex- traction. This paper is aim to partition 3D point clouds into useful segments from Light Detection and Ranging (LIDAR) data directly without previous digital surface model (DSM) generation. The proposed method is based on watershed segmentation scheme which is employed prominently in image segmentation and now is gradually applied to the

Jingjue Jiang; Zuxun Zhang; Ying Ming

2005-01-01

64

Airborne lidar and radiometric observations of PBL- and low clouds  

NASA Technical Reports Server (NTRS)

Boundary layer- and low altitude clouds over open ocean and continent areas have been studied during several field campaigns since mid-1990 using the French airborne backscatter lidar LEANDRE in conjunction with on-board IR and visible radiometers. LEANDRE is an automatic system, and a modification of the instrumental parameters, when airborne, is computer controlled through an operator keyboard. The vertical range squared lidar signals and instrument status are displayed in real time on two dedicated monitors. The lidar is used either down- or up-looking while the aircraft is flying above or below clouds. A switching of the viewing configuration takes about a minute. The lidar measurements provide a high resolution description of cloud morphology and holes in cloud layers. The flights were conducted during various meteorological conditions on single or multilayer stratocumulus and cumulus decks. Analysis on a single shot basis of cloud top (or bottom) altitude and a plot of the corresponding histogram allows one to determine a probability density function (PDF). The preliminary results show the PDFs for cloud top are not Gaussian and symmetric about the mean value. The skewness varies with atmospheric conditions. An example of results recorded over the Atlantic ocean near Biarritz is displayed, showing: (1) the range squared lidar signals as a function of time (here 100 s corresponds to about 8 km, 60 shots are averaged on horizontal); the Planetary Boundary Layer (PBL) - up to 600 m - is observed at the beginning of the leg as well as on surface returns, giving an indication of the porosity; (2) the cloud top altitude variation between 2.4 to 2.8 km during the 150 to 320 s section; and (3) the corresponding PDF. Similar results are obtained on stratocumulus over land. Single shot measurements can be used also to determine an optical porosity at a small scale as well as a fractional cloudiness at a larger scale. A comparison of cloud top altitude retrieved from lidar and narrowbeam IR radiometer is conducted to study the scale integration problem. A good agreement within less than 100 m relies on spatial uniformity and an optically thick layer. In the presence of holes, a discrepancy is observed. This is illustrated in figure 2, displaying as a function of time (1) the lidar signals; (2) the target temperature (either clouds or sea surface) retreived from a narrowbeam IR radiometer, 17 C is the sea surface temperature on that day; and (3) the visible flux, linked to cloud albedo, measured by a pyranometer. In preparation of ASTEX, down- and up-looking measurements where conducted on stratocumulus clouds over the Atlantic Ocean near Quimper in Brittany. Depending on the flight pattern orientation with respect to the wind, the top and bottom cloud morphologies are different. Preliminary results are given on cloud morphology, cloud top PDFs, optical porosity, fractional cloudiness, and comparison of lidar and radiometric measurements.

Flamant, P. H.; Valentin, R.; Pelon, J.

1992-01-01

65

Observation of aerosols and clouds planned with the Mission Demonstration Satellite Lidar (ELISE)  

Microsoft Academic Search

The space lidar which is named Experimental Lidar-In-Space Equipment (ELISE) is being developed by the National Space Development Agency of Japan (NASDA) for the Mission Demonstration Satellite II planned for launch in 2002. The primary purpose of ELISE is to demonstrate the space lidar technology and the feasibility of the Mie scattering lidar observation of clouds and aerosols from space.

N. Sugimoto; Y. Sasano

1999-01-01

66

Nanosecond gated PMT for LIDAR-RADAR applications  

NASA Astrophysics Data System (ADS)

Wide dynamic range gating photosensor modules has been design for LIDAR-RADAR applications on base R7400U (active area 8 mm. diameter) R7600U (active area 18x18 mm.) Hamamatsu photomultiplier tubes. The photomultiplier tubes R7400U, series have two kinds of photocathode: low resistance semitransparent multialkali photocathodes and semitransparent bialkali photocathodes with large resistance. Different kinds of photocathodes require different approach to gating circuits design. High-speed pulse gating (gating rise time 10 nsec, setting time 40 nsec for 99%) has been used for enhancing of target contrast at ocean optic application for both kinds: semitransparent bialkali and semitransparent multialkali photocathodes. Wide dynamic range (50 dB of optical power) has been achieved by optimizing of applied to dynodes voltages. Compression up to 30 dB has been used for following output signal digital processing. Hamamatsu photosensitive modules were used in the two system receivers in pulsed LIDAR system. The system was mounted on the bow of the R/V New Horizon and collected data from August 25 thru September 8, 2005 as part of the LOCO field test in Monterey Bay. Approximately 4 million LIDAR profiles were collected during this period. During the field test the profiles were processed to show relative changes in water optical properties and to reveal water column structure in real time.

Molchanov, Pavlo A.; Contarino, Vincent M.; Concannon, Brian M.; Asmolova, Olha V.; Podobna, Yulia Y.

2006-09-01

67

Aerosol Scavenging by Cirrus Clouds: Evidence from Polarization Lidar Measurements  

NASA Astrophysics Data System (ADS)

Under some conditions polarization lidar observations of ice clouds suggest the depletion of aerosol particles in the vicinity of the cloud margins and just below cloud base. This is particularly evident for cirrus that form in connection with transported desert dust layers, because these dust particles can be relatively large and hence strongly backscattering and depolarizing. Indications of aerosol scavenging primarily through the ice nucleation and gravitational capture processes, as well as phoretic forces where ice crystals are evaporating, can then produce a noticeable decrease in lidar backscattering and depolarization in clear (but recently cloudy) air. (In contrast, aerosol loss due to Brownian diffusion may not be as noticeable because these generally smaller particles are relatively weak backscatterers.) Presumably, previously cloudy air with its depleted interstitial aerosol is disclosed by variable fallstreak production and evaporation effects. The action of clouds is of great importance to the redistribution and removal (through precipitation) of aerosols suspended in the atmosphere. Polarization lidar examples will be given of aerosol-depleted halos surrounding cirrus cloud elements and backscatter troughs just below the base of undulating cirrus layers.

Sassen, K.; Zhu, J.

2007-12-01

68

Simultaneous PMC and PMSE observations with a ground-based lidar and SuperDARN HF radar at Syowa Station, Antarctica  

NASA Astrophysics Data System (ADS)

A Rayleigh-Raman lidar system was installed in January 2011 at Syowa Station, Antarctica (69.0° S, 39.6° E). Polar mesospheric clouds (PMCs) were detected by lidar at around 22:30 UTC (LT -3 h) on 4 February 2011, which was the first day of observation. This was the first detection of PMCs over Syowa Station by lidar. On the same day, a Super Dual Auroral Radar Network (SuperDARN) HF radar with oblique-incidence beams detected polar mesospheric summer echoes (PMSE) between 21:30 and 23:00 UTC. This event is regarded as the last PMC activity around Syowa Station during the austral summer season (2010-2011), since no other PMC signals were detected by lidar in February 2011. This is consistent with results of PMC and mesopause temperature observations by satellite-born instruments of AIM (Aeronomy of Ice in the Mesosphere)/CIPS (Cloud Imaging and Particle Size) and AURA/MLS (Microwave Limb Sounder) and horizontal wind measurements taken by a separate MF radar. Doppler velocity of PMSE observed by the HF radar showed motion toward Syowa Station (westward). This westward motion is consistent with the wind velocities obtained by the MF radar. However, the PMSE region showed horizontal motion from a north-to-south direction during the PMC event. This event indicates that the apparent horizontal motion of the PMSE region can deviate from neutral wind directions and observed Doppler velocities.

Suzuki, H.; Nakamura, T.; Ejiri, M. K.; Ogawa, T.; Tsutsumi, M.; Abo, M.; Kawahara, T. D.; Tomikawa, Y.; Yukimatu, A. S.; Sato, N.

2013-10-01

69

Cloud Coverage and Height Distribution from the GLAS Polar Orbiting Lidar: Comparison to Passive Cloud Retrievals  

NASA Technical Reports Server (NTRS)

The Geoscience Laser Altimeter System (GLAS) began full on orbit operations in September 2003. A main application of the two-wavelength GLAS lidar is highly accurate detection and profiling of global cloud cover. Initial analysis indicates that cloud and aerosol layers are consistently detected on a global basis to cross-sections down to 10(exp -6) per meter. Images of the lidar data dramatically and accurately show the vertical structure of cloud and aerosol to the limit of signal attenuation. The GLAS lidar has made the most accurate measurement of global cloud coverage and height to date. In addition to the calibrated lidar signal, GLAS data products include multi level boundaries and optical depth of all transmissive layers. Processing includes a multi-variable separation of cloud and aerosol layers. An initial application of the data results is to compare monthly cloud means from several months of GLAS observations in 2003 to existing cloud climatologies from other satellite measurement. In some cases direct comparison to passive cloud retrievals is possible. A limitation of the lidar measurements is nadir only sampling. However monthly means exhibit reasonably good global statistics and coverage results, at other than polar regions, compare well with other measurements but show significant differences in height distribution. For polar regions where passive cloud retrievals are problematic and where orbit track density is greatest, the GLAS results are particularly an advance in cloud cover information. Direct comparison to MODIS retrievals show a better than 90% agreement in cloud detection for daytime, but less than 60% at night. Height retrievals are in much less agreement. GLAS is a part of the NASA EOS project and data products are thus openly available to the science community (see http://glo.gsfc.nasa.gov).

Spinhime, J. D.; Palm, S. P.; Hlavka, D. L.; Hart, W. D.; Mahesh, A.

2004-01-01

70

The interdependence of continental warm cloud properties derived from unexploited solar background signal in ground-based lidar measurements  

NASA Astrophysics Data System (ADS)

We have extensively analysed the interdependence between cloud optical depth, droplet effective radius, liquid water path (LWP) and geometric thickness for stratiform warm clouds using ground-based observations. In particular, this analysis uses cloud optical depths retrieved from untapped solar background signal that is previously unwanted and needs to be removed in most lidar applications. Combining these new optical depth retrievals with radar and microwave observations at the Atmospheric Radiation Measurement (ARM) Climate Research Facility in Oklahoma during 2005-2007, we have found that LWP and geometric thickness increase and follow a power-law relationship with cloud optical depth regardless of the presence of drizzle; LWP and geometric thickness in drizzling clouds can be generally 20-40% and at least 10% higher than those in non-drizzling clouds, respectively. In contrast, droplet effective radius shows a negative correlation with optical depth in drizzling clouds, while it increases with optical depth and reaches an asymptote of 10 ?m in non-drizzling clouds. This asymptotic behaviour in non-drizzling clouds is found in both droplet effective radius and optical depth, making it possible to use simple thresholds of optical depth, droplet size, or a combination of these two variables for drizzle delineation. This paper demonstrates a new way to enhance ground-based cloud observations and drizzle delineations using existing lidar networks.

Chiu, J. C.; Holmes, J. A.; Hogan, R. J.; O'Connor, E. J.

2014-04-01

71

Classifying clouds around the globe with the CloudSat radar: 1-year of results  

Microsoft Academic Search

CloudSat supports a 94 GHz cloud profiling radar as part of the innovative A-train formation of satellites studying the Earths clouds and atmosphere. Using the vertical profiles of clouds and precipitation, an algorithm has been developed to determine the type of clouds present. Because cloud type corresponds to specific cloud physical properties, this step is needed to apply other algorithms

Kenneth Sassen; Zhien Wang

2008-01-01

72

Lidar Observations of the Optical Properties and 3-Dimensional Structure of Cirrus Clouds  

NASA Technical Reports Server (NTRS)

The scientific research conducted under this grant have been reported in a series of journal articles, dissertations, and conference proceedings. This report consists of a compilation of these publications in the following areas: development and operation of a High Spectral Resolution Lidar, cloud physics and cloud formation, mesoscale observations of cloud phenomena, ground-based and satellite cloud cover observations, impact of volcanic aerosols on cloud formation, visible and infrared radiative relationships as measured by satellites and lidar, and scattering cross sections.

Eloranta, E. W.

1996-01-01

73

ESTIMATION OF TROPICAL FOREST STRUCTURE AND BIOMASS FROM FUSION OF RADAR AND LIDAR MEASUREMENTS (Invited)  

NASA Astrophysics Data System (ADS)

Radar and Lidar instruments are active remote sensing sensors with the potential of measuring forest vertical and horizontal structure and the aboveground biomass (AGB). In this paper, we present the analysis of radar and lidar data acquired over the La Selva Biological Station in Costa Rica. Radar polarimetry at L-band (25 cm wavelength), P-band (70 cm wavelength) and interferometry at C-band (6 cm wavelength) and VV polarization were acquired by the NASA/JPL airborne synthetic aperture radar (AIRSAR) system. Lidar images were provided by a large footprint airborne scanning Lidar known as the Laser Vegetation Imaging Sensor (LVIS). By including field measurements of structure and biomass over a variety of forest types, we examined: 1) sensitivity of radar and lidar measurements to forest structure and biomass, 2) accuracy of individual sensors for AGB estimation, and 3) synergism of radar imaging measurements with lidar imaging and sampling measurements for improving the estimation of 3-dimensional forest structure and AGB. The results showed that P-band radar combined with any interformteric measurement of forest height can capture approximately 85% of the variation of biomass in La Selva at spatial scales larger than 1 hectare. Similar analysis at L-band frequency captured only 70% of the variation. However, combination of lidar and radar measurements improved estimates of forest three-dimensional structure and biomass to above 90% for all forest types. We present a novel data fusion approach based on a Baysian estimation model with the capability of incorporating lidar samples and radar imagery. The model was used to simulate the potential of data fusion in future satellite mission scenarios as in BIOMASS (planned by ESA) at P-band and DESDynl (planned by NASA) at L-band. The estimation model was also able to quantify errors and uncertainties associated with the scale of measurements, spatial variability of forest structure, and differences in radar and lidar geometry and pixel locations. Keywords: Amazon, Biomass, Carbon, Forest Structure, Tropical forests, Radar, Polarimetry, Interferometry, Lidar This work is performed partially at the Jet Propulsion Laboratory, California Institute of Technology, under contract from National Aeronautic and Space Administration.

Saatchi, S. S.; Dubayah, R.; Clark, D. B.; Chazdon, R.

2009-12-01

74

Cirrus Cloud Properties from a Cloud-Resolving Model Simulation Compared to Cloud Radar Observations.  

NASA Astrophysics Data System (ADS)

Cloud radar data collected at the Atmospheric Radiation Measurement (ARM) Program's Southern Great Plains site were used to evaluate the properties of cirrus clouds that occurred in a cloud-resolving model (CRM) simulation of the 29-day summer 1997 intensive observation period (IOP). The simulation was `forced' by the large-scale advective temperature and water vapor tendencies, horizontal wind velocity, and turbulent surface fluxes observed at the Southern Great Plains site. The large-scale advective condensate tendency was not observed. The correlation of CRM cirrus amount with Geostationary Operational Environmental Satellite (GOES) high cloud amount was 0.70 for the subperiods during which cirrus formation and decay occurred primarily locally, but only 0.30 for the entire IOP. This suggests that neglecting condensate advection has a detrimental impact on the ability of a model (CRM or single-column model) to properly simulate cirrus cloud occurrence.The occurrence, vertical location, and thickness of cirrus cloud layers, as well as the bulk microphysical properties of thin cirrus cloud layers, were determined from the cloud radar measurements for June, July, and August 1997. The composite characteristics of cirrus clouds derived from this dataset are well suited for evaluating CRMs because of the close correspondence between the timescales and space scales resolved by the cloud radar measurements and by CRMs. The CRM results were sampled at eight grid columns spaced 64 km apart using the same definitions of cirrus and thin cirrus as the cloud radar dataset. The composite characteristics of cirrus clouds obtained from the CRM were then compared to those obtained from the cloud radar.Compared with the cloud radar observations, the CRM cirrus clouds occur at lower heights and with larger physical thicknesses. The ice water paths in the CRM's thin cirrus clouds are similar to those observed. However, the corresponding cloud-layer-mean ice water contents are significantly less than observed due to the CRM's larger cloud-layer thicknesses. The strong dependence of cirrus microphysical properties on layer-mean temperature and layer thickness as revealed by the observations is reproduced by the CRM. In addition, both the CRM and the observations show that the thin cirrus ice water path during large-scale ascent is only slightly greater than during no ascent or descent.

Luo, Yali; Krueger, Steven K.; Mace, Gerald G.; Xu, Kuan-Man

2003-02-01

75

Tropical cirrus cloud macrophysical properties over Darwin from CALIPSO, the ARM MPL and the ARM Raman lidar  

NASA Astrophysics Data System (ADS)

Tropical cirrus clouds occur frequently and are important for regulating radiative heating in the tropical tropopause layer. From a remote sensing perspective, a significant number of tropical cirrus are sufficiently optical thin to be below the minimum threshold of passive imagers and contain small ice crystals making them undetectable by cloud radars. Detecting all tropical cirrus clouds requires the use of lidar observations. Thorsen et al. (JGR, 2011) compared CALIPSO and ARM MPL observations of cirrus clouds over the three ARM TWP sites. In general this study showed that statistics of cirrus properties agree well between the two sets of observations when comparisons where made with profiles transparent to the lidar. However differences exist between the MPL and CALIPSO observations. Specifically this study found that (1) the frequency of occurrence of cirrus in the MPL observations is significantly smaller, (2) the MPL is more frequently completely attenuated, particularly during the daytime (3) Transparent daytime MPL clouds boundaries are biased to lower altitudes relative to CALIPSO, presumably due to the poor sampling of transparent profiles and increased noise in the MPL observations. In the current study we intend to revisit these issues using the new ARM Raman lidar at Darwin. We will examine cloud occurrence profiles, cloud top height, base height and geometrical thicknesses from CALIPSO, the MPL and the Raman lidar to determine if the discrepancies between CALIPSO and the MPL are resolved by using the Raman lidar. In addition we'll examine the finding by Thorsen et al. (JGR, 2011) that both CALIPSO and the MPL show the same diurnal cycle of geometrical thickness with geometrically thicker cirrus clouds during the nighttime. It is not clear if this diurnal cycle is physical or an effect of improved single-to-noise at night, which allows for better detection of cloud top and base and therefore a thicker cloud. While CALIPSO and the MPL operate at wavelengths in the visible, the Raman lidar operates in the ultra-violet and therefore is subjected to less noise from the solar background making it a better tool for determining the diurnal cycle of cirrus geometrical thickness.

Thorsen, T. J.; Fu, Q.; Comstock, J. M.

2012-12-01

76

A High Resolution Hydrometer Phase Classifier Based on Analysis of Cloud Radar Doppler Spectra.  

SciTech Connect

The lifecycle and radiative properties of clouds are highly sensitive to the phase of their hydrometeors (i.e., liquid or ice). Knowledge of cloud phase is essential for specifying the optical properties of clouds, or else, large errors can be introduced in the calculation of the cloud radiative fluxes. Current parameterizations of cloud water partition in liquid and ice based on temperature are characterized by large uncertainty (Curry et al., 1996; Hobbs and Rangno, 1998; Intriery et al., 2002). This is particularly important in high geographical latitudes and temperature ranges where both liquid droplets and ice crystal phases can exist (mixed-phase cloud). The mixture of phases has a large effect on cloud radiative properties, and the parameterization of mixed-phase clouds has a large impact on climate simulations (e.g., Gregory and Morris, 1996). Furthermore, the presence of both ice and liquid affects the macroscopic properties of clouds, including their propensity to precipitate. Despite their importance, mixed-phase clouds are severely understudied compared to the arguably simpler single-phase clouds. In-situ measurements in mixed-phase clouds are hindered due to aircraft icing, difficulties distinguishing hydrometeor phase, and discrepancies in methods for deriving physical quantities (Wendisch et al. 1996, Lawson et al. 2001). Satellite-based retrievals of cloud phase in high latitudes are often hindered by the highly reflecting ice-covered ground and persistent temperature inversions. From the ground, the retrieval of mixed-phase cloud properties has been the subject of extensive research over the past 20 years using polarization lidars (e.g., Sassen et al. 1990), dual radar wavelengths (e.g., Gosset and Sauvageot 1992; Sekelsky and McIntosh, 1996), and recently radar Doppler spectra (Shupe et al. 2004). Millimeter-wavelength radars have substantially improved our ability to observe non-precipitating clouds (Kollias et al., 2007) due to their excellent sensitivity that enables the detection of thin cloud layers and their ability to penetrate several non-precipitating cloud layers. However, in mixed-phase clouds conditions, the observed Doppler moments are dominated by the highly reflecting ice crystals and thus can not be used to identify the cloud phase. This limits our ability to identify the spatial distribution of cloud phase and our ability to identify the conditions under which mixed-phase clouds form.

Luke,E.; Kollias, P.

2007-08-06

77

A comparison of ambipolar diffusion coefficients in meteor trains using VHF radar and UV lidar  

Microsoft Academic Search

In this paper we present the first comparative estimations of ionic diffusion rates for sporadic meteor trains near the mesopause made using VHF radar and UV Rayleigh lidar observations. In both cases we initially assumed that the meteor trains dissipate primarily through ambipolar diffusion. For the radar data, the diffusion coefficient within the meteor train was determined from the decay

Phillip B. Chilson; Peter Czechowsky; Gerhard Schmidt

1996-01-01

78

Fog monitoring using a new 94 GHz FMCW cloud radar  

Microsoft Academic Search

A new solid state frequency modulated continuous wave (FMCW) cloud radar and its potential for monitoring the life cycle of fog and low stratus is presented. The radar operates at a frequency of 94 GHz, which is ideal for observing clouds as it lies within a part of the spectrum which experiences relatively low absorption in the atmosphere. With a

B. Thies; K. Müller; F. Maier; J. Bendix

2010-01-01

79

Surface Roughness Impact on the Sea Ice Thickness Measurements Based on LIDAR/Radar Altimetry  

NASA Astrophysics Data System (ADS)

The Radar and/or LIDAR measurements of sea ice freeboard provide an indirect approach to infer sea ice thickness via isostasy. The underlying assumption is that the LIDAR signal returns at the air/snow interface and radar signal at the snow/ice interface. Thus the surface roughness at the air, snow and ice interface has a significant impact on the LIDAR/Radar returns, which can lead to very significant errors in the ice thickness retrievals. Recent Cryosat-2 validation results suggest that its altimetry-based technique is very effective in mapping hemispheric sea ice thickness. However, in some cases significant bias exists in the Cryosat-2 data product. To understand the performance of those data depends on our skills in quantifying the impacts of the secondary parameters, such as surface roughness of snow and ice surfaces and the penetration depth of the snow/ice by the radar. To this end, we analyze airborne radar and lidar altimeter data collected during a Cryosat-2 under-flight by the NRL and the NASA IceBridge missions, as well as the in-situ data from the coordinated CRREL/NRL field campaign. In this presentation we will show some surface roughness data from airborne LIDAR for leveled and deformed first year ice, and ice pressure ridges. Their impacts on radar returns and sea ice thickness retrieval will be presented.

Li, L.; Truesdale, D.; Posey, P.; Allard, R.; Gardner, J. M.; Brozena, J. M.; Richter-Menge, J.

2013-12-01

80

A self-directing elastic backscatter lidar system for debris cloud tracking and characterization  

SciTech Connect

An elastic backscatter lidar that utilizes the lidar signal itself to direct the system towards fast moving isolated aerosol clouds has been developed. However, detecting and tracking invisible transient effluents from unknown locations, though conceptually straightforward, has still remained experimentally challenging. Accurate cloud volume, cloud density distribution, and track information have been obtained on small, fast moving, subvisible debris clouds resulting from above ground tests in which conventional explosives were detonated.

Clark, D.A.; Dighe, K.A. [Los Alamos National Lab., NM (United States); Tunnell, T.W. [Bechtel Nevada, Los Alamos, NM (United States). Los Alamos Operations

1996-06-01

81

W-band ARM Cloud Radar (WACR) Handbook  

SciTech Connect

The W-band Atmospheric Radiation Measurement (ARM) Program Cloud Radar (WACR) systems are zenith pointing Doppler radars that probe the extent and composition of clouds at 95.04 GHz. The main purpose of this radar is to determine cloud boundaries (e.g., cloud bottoms and tops). This radar reports estimates for the first three spectra moments for each range gate up to 15 km. The 0th moment is reflectivity, the 1st moment is radial velocity, and the 2nd moment is spectral width. Also available are the raw spectra files. Unlike the millimeter wavelength cloud radar (MMCR), the WACR does not use pulse coding and operates in only copolarization and cross-polarization modes.

Widener, KB; Johnson, K

2005-01-05

82

Exploring Stratocumulus Cloud-Top Entrainment Processes and Parameterizations Using Doppler Cloud Radar Observations  

NASA Astrophysics Data System (ADS)

Observations from an upward-pointing Doppler cloud radar are used to examine the vertical velocity variance and energy dissipation rate at the top of continental stratocumulus clouds. These observations are used to examine terms in the turbulence kinetic energy (TKE) budget in the entrainment zone that are related to the entrainment rate. When this budget (without wind shear) is applied to the entrainment zone, the entrainment rate is proportional to a vertical transport and pressure perturbation term minus a dissipation term and inversely proportional to the strength of the inversion. The transport-pressure term is usually assumed to be proportional to the vertical velocity variance to the 3/2 power and inversely proportional to the boundary layer depth (called the variance term in this study). In this study the observations are made in a continental stratocumulus cloud observed over the Southern Great Plains (SGP) at the DOE ARM site for a 14-hour period. Clouds were solid during this entire period and had thicknesses of 300-400 meters and tops increasing from 800-1200 m. The turbulence forcing due to surface buoyancy fluxes and radiative cooling at cloud top is obtained from surface flux measurements and radiative transfer calculations based on the cloud characteristics derived from cloud radar and lidar observations. During the day surface forcing dominates as the radiative warming at cloud top by solar absorption compensates the cloud-top longwave cooling. At night the surface buoyancy fluxes are close to zero and the longwave cooling at cloud top dominates the turbulence forcing. Vertical velocity and spectrum width observations from the upward pointing millimeter cloud radar (MMCR) at the SGP site are used to examine the turbulence in the top 20% (60-80 m) of the cloud, which is define as the entrainment zone. The spectrum width is used to define energy dissipation rates directly in the entrainment zone and the vertical velocity observations are used to define vertical velocity variance for one-hour periods. These quantities are then used to examine the terms in the TKE budget in this layer. It is found for the 14 hours of observations used in this study that the variance term is strongly correlated to the dissipation rates in the entrainment zone. However, the ratio of the variance term to the dissipation rate term is 0.12 during the day and 0.06 at night. This difference indicates that the length scales involved in the turbulence and entrainment processes may depend on whether the turbulence is forced by the surface fluxes or cloud-top cooling. To further explore this possibility, the relationships among the convective velocity scales, the vertical velocity variances, and the dissipation rates are examined and compared with entrainment rates from parameterizations based on the convective velocity scale and the strength of the inversion.

Albrecht, B. A.; Fang, M.

2012-12-01

83

The radar simulator: deriving the radar signal using the cloud model output  

Microsoft Academic Search

We present an approach to simulate cloud radar signals on the basis of cloud model output, the radar simulator. The simulator is being developed to aid validation of the cloud model. The cloud model applies double-moment bulk warm-rain and ice schemes developed by Morrison and Grabowski.1, 2 As an input, the simulator uses profiles of the mixing ratios and number

Aleksandra E. Kardas; Sally McFarlane; Hugh Morrison; Jennifer Comstock; Wojciech W. Grabowski; Szymon P. Malinowski

2009-01-01

84

Cirrus cloud characteristics derived from volume imaging lidar, high spectral resolution lidar, HIS radiometer, and satellite  

NASA Technical Reports Server (NTRS)

Preliminary measurement results are presented from the Cirrus Remote Sensing Pilot Experiment which used a unique suite of instruments to simultaneously retrieve cirrus cloud visible and IR optical properties, while addressing the disparities between satellite volume averages and local point measurements. The experiment employed a ground-based high resolution interferometer sounder (HIS) and a second Fourier transform spectrometer to measure the spectral radiance in the 4-20 micron band, a correlated high spectral resolution lidar, a volume imaging lidar, a CLASS radiosonde system, the Scripps Whole Sky Imager, and multispectral VAS, HIRS, and AVHRR satellite data from polar orbiting and geostationary satellites. Data acquired during the month long experiment included continuous daytime monitoring with the Whole Sky Imager.

Grund, Christian J.; Ackerman, Steven A.; Eloranta, Edwin W.; Knutsen, Robert O.; Revercomb, Henry E.; Smith, William L.; Wylie, Donald P.

1990-01-01

85

Mie lidar observations of lower tropospheric aerosols and clouds.  

PubMed

Mie lidar system is developed at Laser Science and Technology Centre, Delhi (28.38°N, 77.12°E) by using minimal number of commercially available off-the-shelf components. Neodymium Yttrium Aluminum Garnet (Nd:YAG) laser operating at 1064nm with variable pulse energies between 25 and 400 mJ with 10 Hz repetition rate and 7ns pulse duration is used as a transmitter and off-axis CASSEGRAIN telescope with 100mm diameter as a receiver. Silicon avalanche photodiode (Si-APD) module with built-in preamplifier and front-end optics is used as detector. This system has been developed for the studies of lower tropospheric aerosols and clouds. Some experiments have been conducted using this set up and preliminary results are discussed. The characteristics of backscattered signals for various transmitter pulse energies are also studied. Atmospheric aerosol extinction coefficient values are calculated using Klett lidar inversion algorithm. The extinction coefficient, in general, falls with range in the lower troposphere and the values lie typically in the range 7.5×10(-5) m(-1) to 1.12×10(-4) m(-1) in the absence of any cloud whereas this value shoots maximum up to 1.267×10(-3) m(-1) (peak extinction) in the presence of clouds. PMID:21975046

Veerabuthiran, S; Razdan, A K; Jindal, M K; Dubey, D K; Sharma, R C

2011-12-15

86

The Cloud Physics Lidar: Instrument Description and Initial Measurement Results  

NASA Technical Reports Server (NTRS)

The new Cloud Physics Lidar (CPL) has been built for use on the NASA ER-2 high altitude aircraft. The purpose of the CPL is to provide multi-wavelength measurements of cirrus, subvisual cirrus, and aerosols with high temporal and spatial resolution. The CPL utilizes state-of-the-art technology with a high repetition rate, a low pulse energy laser, and photon-counting detection. The first deployment for the CPL was the SAFARI-2000 field campaign during August-September 2000. We provide here an overview of the instrument and initial data results to illustrate the measurement capability of the CPL.

McGill, Matthew; Hlavka, Dennis; Hart, William; Spinhirne, James; Scott, V. Stanley; Starr, David OC. (Technical Monitor)

2001-01-01

87

Comparison of CloudSat and TRMM radar reflectivities  

NASA Astrophysics Data System (ADS)

Comparison of reflectivity data of radars onboard CloudSat and TRMM is performed using coincident overpasses. The contoured frequency by altitude diagrams (CFADs) are constructed for two cases: (a) only include collocated vertical profiles that are most likely to be raining and (b) include all collocated profiles along with cloudy pixels falling within a distance of about 50 km from the centre point of coincidence. Our analysis shows that for both cases, CloudSat underestimates the radar reflectivity by about 10 dBZ compared to that of TRMM radar below 15 km altitude. The difference is well outside the uncertainty value of ~2 dBZ of each radar. Further, CloudSat reflectivity shows a decreasing trend while that of TRMM radar an increasing trend below 4 km height. Basically W-band radar that CloudSat flies suffers strong attenuation in precipitating clouds and its reflectivity value rarely exceeds 20 dBZ though its technical specification indicates the upper measurement limit to be 40 dBZ. TRMM radar, on the other hand, cannot measure values below 17 dBZ. In fact combining data from these two radars seems to give a better overall spatial structure of convective clouds.

Sindhu, K. D.; Bhat, G. S.

2013-08-01

88

Dimensionality Based Scale Selection in 3d LIDAR Point Clouds  

NASA Astrophysics Data System (ADS)

This papers presents a multi-scale method that computes robust geometric features on lidar point clouds in order to retrieve the optimal neighborhood size for each point. Three dimensionality features are calculated on spherical neighborhoods at various radius sizes. Based on combinations of the eigenvalues of the local structure tensor, they describe the shape of the neighborhood, indicating whether the local geometry is more linear (1D), planar (2D) or volumetric (3D). Two radius-selection criteria have been tested and compared for ?nding automatically the optimal neighborhood radius for each point. Besides, such procedure allows a dimensionality labelling, giving signi?cant hints for classi?cation and segmentation purposes. The method is successfully applied to 3D point clouds from airborne, terrestrial, and mobile mapping systems since no a priori knowledge on the distribution of the 3D points is required. Extracted dimensionality features and labellings are then favorably compared to those computed from constant size neighborhoods.

Demantké, J.; Mallet, C.; David, N.; Vallet, B.

2011-09-01

89

Comparison of meteor radar and Na Doppler lidar measurements of winds in the mesopause region above Maui, Hawaii  

Microsoft Academic Search

Simultaneous sodium (Na) Doppler lidar and meteor radar measurements of horizontal winds in the mesopause region over Maui, Hawaii, were collected in July 2002 and October\\/November 2003. The coincident measurements span 96 hours and altitudes between 80 and 100 km. Statistical comparisons are carried out on radar\\/lidar winds with 1 hour and 4 km time and height resolution, respectively. The

S. J. Franke; X. Chu; A. Z. Liu; W. K. Hocking

2005-01-01

90

Enhanced Simulation of Radar Backscatter From Forests Using LiDAR and Optical Data  

Microsoft Academic Search

Focusing on a forest dominated by Poplar Box (Eucalyptus populnea) near Injune in Queensland, Australia, light detection and ranging (LiDAR) and optical remote sensing data are integrated with tree- and stand-level information to parameterize a coherent L-band synthetic aperture radar (SAR) imaging simulation that models microwave penetration and interaction with the canopy, understory, and ground. The approach used LiDAR data

Richard M. Lucas; Alex C. Lee; Mark L. Williams

2006-01-01

91

Lidar measurements of boundary layers, aerosol scattering and clouds during project FIFE  

NASA Technical Reports Server (NTRS)

A detailed account of progress achieved under this grant funding is contained in five journal papers. The titles of these papers are: The calculation of area-averaged vertical profiles of the horizontal wind velocity using volume imaging lidar data; Volume imaging lidar observation of the convective structure surrounding the flight path of an instrumented aircraft; Convective boundary layer mean depths, cloud base altitudes, cloud top altitudes, cloud coverages, and cloud shadows obtained from Volume Imaging Lidar data; An accuracy analysis of the wind profiles calculated from Volume Imaging Lidar data; and Calculation of divergence and vertical motion from volume-imaging lidar data. Copies of these papers form the body of this report.

Eloranta, Edwin W. (Principal Investigator)

1995-01-01

92

On the horizontal and temporal structure of noctilucent clouds as observed by satellite and lidar at ALOMAR (69N)  

NASA Astrophysics Data System (ADS)

Simultaneous and common volume observations of Noctilucent Clouds (NLC) and Polar Mesospheric Clouds (PMC) have been performed above the ALOMAR research station in Northern Norway (69°N, 16°E) from ground and space, respectively. A detailed case study on August 5, 2008 shows that the measured particle sizes and T-matrix simulations of the optical properties allow to combine the two observation techniques. From the ground, the observations were performed by lidar sounding of the temporal evolution of the cloud at two locations separated by about 40 km, before, during and after the coincidence. From space, the CIPS instrument onboard the AIM satellite observed the horizontal structure of the cloud. Using mesospheric radar wind measurements at ALOMAR the advection of the cloud particles is calculated and the temporal evolution of the cloud as seen from ground is compared with the horizontal structure observed from satellite. This comparison allows estimation of the timescales during which the clouds behave as passive tracers. We find that during this case study cloud structures larger than about 5 km × 5 km and oscillations slower than about one minute behaved like a passive tracer for up to one hour corresponding to horizontal scales of about 300 km. However, if the cloud shows wave structures with brightness modulations of 20% microphysical changes might take place on scales of minutes and kilometers.

Baumgarten, G.; Chandran, A.; Fiedler, J.; Hoffmann, P.; Kaifler, N.; Lumpe, J.; Merkel, A.; Randall, C. E.; Rusch, D.; Thomas, G.

2012-01-01

93

Simultaneous Observations of Cirrus Clouds with a Millimeter-Wave Radar and the MU Radar  

Microsoft Academic Search

Observations of frontal cirrus clouds were conducted with the scanning millimeter-wave radar at the Shigaraki Middle and Upper Atmosphere (MU) Radar Observatory in Shiga, Japan, during 30 September-13 October 2000. The three-dimensional background winds were also observed with the very high frequency (VHF) band MU radar. Comparing the observational results of the two radars, it was found that the cirrus

Eiko Wada; Hiroyuki Hashiguchi; Masayuki K. Yamamoto; Michihiro Teshiba; Shoichiro Fukao

2005-01-01

94

Study for external calibration method for cloud profiling radar on EarthCARE  

NASA Astrophysics Data System (ADS)

EarthCARE mission has objectives to reveal aerosol and cloud interaction and to reveal relationships with radiation budget. For this purpose, the EarthCARE satellite has four instruments, which are Atmospheric LIDAR (ATLID), Multi Spectral Imager (MSI) and Broad Band Radiometer (BBR) in addition to Cloud Profiling Radar (CPR). CPR is developed under cooperation of Japanese Aerospace Exploration Agency (JAXA) and National Institute of Information and Communications Technology (NICT) in Japan. The requirement of sensitivity is -35dBZ, therefore CPR uses W-band frequency and needs a large (2.5m) antenna reflector. The large antenna has small footprint and is to give up antenna scanning. From this, some difficulty of external calibration using active radar calibrator (ARC) is recognized. One solution of external calibration is using scattering from natural distributed target, such as sea surface. Then the measurement of sea surface scattering using airborne cloud radar was performed. The sea surface scattering property is being prepared. Second solution is that ARC puts on exact location of sub-satellite track. Precise sub-satellite track prediction is necessary. We focus second solution in this paper. The test experiment was demonstrated using CloudSat of NASA/JPL, which is provided CPR using W-band frequency. The feasibility of this calibration method is discussed.

Horie, Hiroaki; Kimura, Toshiyoshi; Okada, Kazuyuki; Ohno, Yuichi; Sato, Kenji; Kumagai, Hiroshi

2008-10-01

95

Radar Evaluation of Optical Cloud Constraints to Space Launch Operations  

NASA Technical Reports Server (NTRS)

Weather constraints to launching space vehicles are designed to prevent loss of the vehicle or mission due to weather hazards (See, e.g., Ref 1). Constraints include Lightning Launch Commit Criteria (LLCC) designed to avoid natural and triggered lightning. The LLCC currently in use at most American launch sites including the Eastern Range and Kennedy Space Center require the Launch Weather Officer to determine the height of cloud bases and tops, the location of cloud edges, and cloud transparency. The preferred method of making these determinations is visual observation, but when that isn't possible due to darkness or obscured vision, it is permissible to use radar. This note examines the relationship between visual and radar observations in three ways: A theoretical consideration of the relationship between radar reflectivity and optical transparency. An observational study relating radar reflectivity to cloud edge determined from in-situ measurements of cloud particle concentrations that determine the visible cloud edge. An observational study relating standard radar products to anvil cloud transparency. It is shown that these three approaches yield results consistent with each other and with the radar threshold specified in Reference 2 for LLCC evaluation.

Merceret, Francis J.; Short, David A.; Ward, Jennifer G.

2005-01-01

96

Methods of discriminating cloud systems by their radar characteristics  

NASA Technical Reports Server (NTRS)

The connection of the radar characteristics of cloud systems with the genetics of their formation, the microphysical structure, and the spatial extent of the clouds is examined. The relation of the probability of detecting clouds at various distances by their microphysical structure and the capabilities of the equipment are also considered. A method of discriminating cloud systems is proposed on the basis of obtained relations.

Divinskaya, B. S.

1975-01-01

97

New Cloud Science from the New ARM Cloud Radar Systems (Invited)  

NASA Astrophysics Data System (ADS)

The DOE ARM Program is deploying over $30M worth of scanning polarimetric Doppler radars at its four fixed and two mobile sites, with the object of advancing cloud lifecycle science, and cloud-aerosol-precipitation interaction science, by a quantum leap. As of 2011, there will be 13 scanning radar systems to complement its existing array of profiling cloud radars: C-band for precipitation, X-band for drizzle and precipitation, and two-frequency radars for cloud droplets and drizzle. This will make ARM the world’s largest science user of, and largest provider of data from, ground-based cloud radars. The philosophy behind this leap is actually quite simple, to wit: dimensionality really does matter. Just as 2D turbulence is fundamentally different from 3D turbulence, so observing clouds only at zenith provides a dimensionally starved, and sometimes misleading, picture of real clouds. In particular, the zenith view can say little or nothing about cloud lifecycle and the second indirect effect, nor about aerosol-precipitation interactions. It is not even particularly good at retrieving the cloud fraction (no matter how that slippery quantity is defined). This talk will review the history that led to this development and then discuss the aspirations for how this will propel cloud-aerosol-precipitation science forward. The step by step plan for translating raw radar data into information that is useful to cloud and aerosol scientists and climate modelers will be laid out, with examples from ARM’s recent scanning cloud radar deployments in the Azores and Oklahoma . In the end, the new systems should allow cloud systems to be understood as 4D coherent entities rather than dimensionally crippled 2D or 3D entities such as observed by satellites and zenith-pointing radars.

Wiscombe, W. J.

2010-12-01

98

Phoenix Lidar Observations of the Cloud Topped Boundary Layer on Mars  

Microsoft Academic Search

The NASA Phoenix mission to Mars landed on 25 May 2008 and operated for five months. The LIDAR instrument on Phoenix observed water ice clouds in the atmosphere of Mars that were similar to cirrus clouds on Earth. Fall streaks in the cloud structure traced the precipitation of ice crystals toward the ground. Measurements of atmospheric dust indicated that the

J. A. Whiteway; L. Komguem; C. Dickinson; C. Cook; M. Illnicki; J. Seabrook; V. Popovici; T. Duck; R. Davy; P. Taylor; J. Pathak; D. Fisher; A. Carswell; M. Daly; V. Hipkin; L. Tamppari; N. Renno; J. Moores; M. Lemmon; F. Daerden; P. H. Smith

2009-01-01

99

Arctic polar stratospheric cloud observations by airborne lidar  

NASA Technical Reports Server (NTRS)

Lidar observations obtained from January 24 to February 2, 1989, during the Airborne Arctic Stratospheric expedition (AASE) mission further support the existence of two distinct classes (Types 1 and 2) of polar stratospheric clouds (PSCs). Most of the Type 1 PSCs observed were formed by rapid adiabatic cooling and exhibited very low depolarization ratios and low-to-intermediate scattering ratios. Type 2 PSCs were observed in regions of lowest temperature and showed much larger depolarization and scattering ratios, as would be expected from larger ice crystals. PSCs with low scattering ratios but moderate depolarization ratios were observed near the center of the vortex on one flight. These may have been either sparse Type 2 PSCs or Type 1 PSCs formed by less rapid cooling.

Mccormick, M. P.; Poole, L. R.; Kent, G. S.; Hunt, W. H.; Osborn, M. T.

1990-01-01

100

Polar Cirrus Cloud Properties Through Long-Term Lidar and Radiometer Observations  

NASA Technical Reports Server (NTRS)

In comparison to mid latitude cloud cover, knowledge of polar cirrus and other cloud cover is limited. The interpretations of satellite-based cloud imaging and retrievals in polar regions have major problems due to factors such as darkness and extreme low temperatures. Beginning in 2002 a NASA orbiting lidar instrument, GLAS, (Geoscience Laser Altimeter System) will unambiguously define cloud type and fraction with good coverage of polar regions. Active laser sensing gives the spatial and temporal distribution of clouds and diamond dust. In preparation for, and supplementing the GLAS measurements are ground based MP (micro pulse) lidar experiments providing continuous profiling. MP lidar installations have been operating at the South Pole since December 1999 and at the Atmospheric Radiation Measurement (ARM) program arctic site since 1996. Both at the ARM Barrow, Alaska site and at the South Pole station, Fourier-transform interferometers also observe clouds in the wavelength intervals between approximately 5 and 18 microns. Spectral instruments can yield cloud microphysical properties with additional information from lidar about the vertical extent of clouds being modeled. We examine the simultaneous lidar and spectral data from both Barrow and South Pole, to obtain cloud properties (optical depth, particle size) by the use of both instruments. The results have applications to interpretation of current satellite data, and GLAS measurements when available.

Spinhirne, James; Campbell, James; Mahesh, Ashwin; Welton, Judd; Starr, David OC. (Technical Monitor)

2001-01-01

101

Min-Cut Based Segmentation of Airborne LIDAR Point Clouds  

NASA Astrophysics Data System (ADS)

Introducing an organization to the unstructured point cloud before extracting information from airborne lidar data is common in many applications. Aggregating the points with similar features into segments in 3-D which comply with the nature of actual objects is affected by the neighborhood, scale, features and noise among other aspects. In this study, we present a min-cut based method for segmenting the point cloud. We first assess the neighborhood of each point in 3-D by investigating the local geometric and statistical properties of the candidates. Neighborhood selection is essential since point features are calculated within their local neighborhood. Following neighborhood determination, we calculate point features and determine the clusters in the feature space. We adapt a graph representation from image processing which is especially used in pixel labeling problems and establish it for the unstructured 3-D point clouds. The edges of the graph that are connecting the points with each other and nodes representing feature clusters hold the smoothness costs in the spatial domain and data costs in the feature domain. Smoothness costs ensure spatial coherence, while data costs control the consistency with the representative feature clusters. This graph representation formalizes the segmentation task as an energy minimization problem. It allows the implementation of an approximate solution by min-cuts for a global minimum of this NP hard minimization problem in low order polynomial time. We test our method with airborne lidar point cloud acquired with maximum planned post spacing of 1.4 m and a vertical accuracy 10.5 cm as RMSE. We present the effects of neighborhood and feature determination in the segmentation results and assess the accuracy and efficiency of the implemented min-cut algorithm as well as its sensitivity to the parameters of the smoothness and data cost functions. We find that smoothness cost that only considers simple distance parameter does not strongly conform to the natural structure of the points. Including shape information within the energy function by assigning costs based on the local properties may help to achieve a better representation for segmentation.

Ural, S.; Shan, J.

2012-07-01

102

Simulated polarization diversity lidar returns from water and precipitating mixed phase clouds  

SciTech Connect

The dependence of polarization lidar returns on basic microphysical and thermodynamic variables is assessed by using a cloud model to simulate the growth of water and mixed (water and ice) phase clouds. Cloud contents that evolve with height in updrafts are converted, by using Mie theory, into cloud droplet single and double backscattering and attenuation coefficients. The lidar equation includes forward multiple scattering attenuation corrections based on diffraction theory for droplets and ice crystals, whose relative scattering contributions are treated empirically. Lidar depolarization is computed from droplet and crystal single scattering and an analytical treatment of droplet double scattering. Water cloud results reveal the expected increases in linear depolarization ratios ({delta}) with increasing lidar field of view and distance to cloud but also show that depolarization is a function of cloud liquid water content, which depends primarily on temperature. Ice crystals modulate mixed phase cloud liquid water contents through water vapor competition effects, thereby affecting multiple scattering {delta} values as functions of updraft velocity, temperature, and crystal size and concentration. Although the minimum {delta} at cloud base increases with increasing ice content, the peak measurable {delta} in the cloud decreases. Comparison with field data demonstrate that this modeling approach is a valuable supplement to cloud measurements.

Sassen, K.; Zhao, H.; Dodd, G.C. (Department of Meteorology, University of Utah, Salt Lake City, Utah 84112 (United States))

1992-05-20

103

Use of probability distribution functions for discriminating between cloud and aerosol in lidar backscatter data  

Microsoft Academic Search

In this paper, we describe the algorithm that will be used during the upcoming Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) mission for discriminating between clouds and aerosols detected in two-wavelength backscatter lidar profiles. We first analyze single-test and multiple-test classification approaches based on one-dimensional (1-D) and multidimensional probability distribution functions (PDFs) in the context of a two-class feature

Zhaoyan Liu; Mark A. Vaughan; David M. Winker; Chris A. Hostetler; Lamont R. Poole; Dennis Hlavka; William Hart; Matthew McGill

2004-01-01

104

Fog monitoring using a new 94 GHz FMCW cloud radar  

NASA Astrophysics Data System (ADS)

A new solid state frequency modulated continuous wave (FMCW) cloud radar and its potential for monitoring the life cycle of fog and low stratus is presented. The radar operates at a frequency of 94 GHz, which is ideal for observing clouds as it lies within a part of the spectrum which experiences relatively low absorption in the atmosphere. With a wavelength of approximately 3 mm, scattering from cloud droplets is by Rayleigh scattering. So the new 94 GHz FMCW radar provides best resolution of cloud and fog in the lower troposphere. Due to the FMCW technique, the radar can detect clouds with a minimum range of ~30 m making it ideal for monitoring fog and low stratus. A vertical resolution of 4 m from the surface to 2 km permits fine vertical cloud structures to be resolved. The high temporal resolution of 10 seconds makes it highly suitable to capture and analyze the dynamics of fog development and its evolutionary stages. Since the radar reflectivity is strongly related to the cloud liquid water content within the respective scan level, it is possible to retrieve and analyze this essential microphysical cloud parameter with a high vertical and temporal resolution. Only some studies investigated the profile of the liquid water content during fog events so far. Very few of them combined the vertical and the temporal component by investigating the variation of the liquid water content profile during different fog evolutionary stages. This is mainly due to the laborious measurement techniques using balloon-borne sensor platforms. In this context the radar offers new insights into fog development and the associated liquid water content based on continuous profile measurements. Such a continuous monitoring of fog and its vertical structure has applications for aviation as well as for climatological and meteorological research. The poster presents the vertical fog structure and its temporal dynamic for selected fog events and investigate the existence of distinct evolutionary stages as concluded from former studies.

Thies, B.; Müller, K.; Maier, F.; Bendix, J.

2010-07-01

105

A 3D Cloud-Construction Algorithm for the EarthCARE Satellite Mission  

NASA Technical Reports Server (NTRS)

This article presents and assesses an algorithm that constructs 3D distributions of cloud from passive satellite imagery and collocated 2D nadir profiles of cloud properties inferred synergistically from lidar, cloud radar and imager data.

Barker, H. W.; Jerg, M. P.; Wehr, T.; Kato, S.; Donovan, D. P.; Hogan, R. J.

2011-01-01

106

Cloud Distribution Statistics from LITE  

NASA Technical Reports Server (NTRS)

The Lidar In-Space Technology Experiment (LITE) mission has demonstrated the utility of spaceborne lidar in observing multilayer clouds and has provided a dataset showing the distribution of tropospheric clouds and aerosols. These unambiguous observations of the vertical distribution of clouds will allow improved verification of current cloud climatologies and GCM cloud parameterizations. Although there is now great interest in cloud profiling radar, operating in the mm-wave region, for the spacebased observation of cloud heights the results of the LITE mission have shown that satellite lidars can also make significant contributions in this area.

Winker, David M.

1998-01-01

107

Space-Based Lidar Systems  

NASA Technical Reports Server (NTRS)

An overview of space-based lidar systems is presented. from the first laser altimeter on APOLLO 15 mission in 1971 to the Mercury Laser Altimeter on MESSENGER mission currently in orbit, and those currently under development. Lidar, which stands for Light Detection And Ranging, is a powerful tool in remote sensing from space. Compared to radars, lidars operate at a much shorter wavelength with a much narrower beam and much smaller transmitter and receiver. Compared to passive remote sensing instruments. lidars carry their own light sources and can continue measuring day and night. and over polar regions. There are mainly two types of lidars depending on the types of measurements. lidars that are designed to measure the distance and properties of hard targets are often called laser rangers or laser altimeters. They are used to obtain the surface elevation and global shape of a planet from the laser pulse time-of-night and the spacecraft orbit position. lidars that are designed to measure the backscattering and absorption of a volume scatter, such as clouds and aerosols, are often just called lidars and categorized by their measurements. such as cloud and aerosol lidar, wind lidar, CO2 lidar, and so on. The advantages of space-based lidar systems over ground based lidars are the abilities of global coverage and continuous measurements.

Sun, Xiaoli

2012-01-01

108

Scanning Cloud Radar Observations at the ARM sites  

NASA Astrophysics Data System (ADS)

Recently, the DOE Atmospheric Radiation Measurement (ARM) program upgraded its fixed and mobile facilities with the acquisition of state-of-the-art scanning, dual-wavelength, polarimetric, Doppler cloud radars. The scanning ARM cloud radars (SACR's) are the most expensive and significant radar systems at all ARM sites and eight SACR systems will be operational at ARM sites by the end of 2013. The SACR's are the primary instruments for the detection of 3D cloud properties (boundaries, volume cloud fractional coverage, liquid water content, dynamics, etc.) beyond the soda-straw (profiling) limited view. Having scanning capabilities with two frequencies and polarization allows more accurate probing of a variety of cloud systems (e.g., drizzle and shallow, warm rain), better correction for attenuation, use of attenuation for liquid water content retrievals, and polarimetric and dual-wavelength ratio characterization of non-spherical particles for improved ice crystal habit identification. Examples of SACR observations from four ARM sites are presented here: the fixed sites at Southern Great Plains (SGP) and North Slope of Alaska (NSA), and the mobile facility deployments at Graciosa Island, Azores and Cape Cod, Massachusetts. The 3D cloud structure is investigated both at the macro-scale (20-50 km) and cloud-scale (100-500 m). Doppler velocity measurements are corrected for velocity folding and are used either to describe the in-cloud horizontal wind profile or the 3D vertical air motions.

Kollias, P.; Clothiaux, E. E.; Shupe, M.; Widener, K.; Bharadwaj, N.; Miller, M. A.; Verlinde, H.; Luke, E. P.; Johnson, K. L.; Jo, I.; Tatarevic, A.; Lamer, K.

2012-12-01

109

Building blocks for a two-frequency laser lidar-radar: a preliminary study  

NASA Astrophysics Data System (ADS)

A new principle of lidar-radar is theoretically and experimentally investigated. The proposed architecture is based on the use of an rf modulation of the emitted light beam and a direct detection of the backscattered intensity. Use of a radar-processing chain allows one to obtain range and Doppler measurements with the advantages of lidar spatial resolution. We calculate the maximum range of this device, taking into account different possible improvements. In particular, we show that use of a pulsed two-frequency laser and a spatially multimode optical preamplification of the backscattered light leads to calculated ranges larger than 20 km, including the possibility of both range and Doppler measurements. The building blocks of this lidar-radar are tested experimentally: The radar processing of an rf-modulated backscattered cw laser beam is demonstrated at 532 nm, illustrating the Doppler and identification capabilities of the system. In addition, signal-to-noise ratio improvement by optical preamplification is demonstrated at 1.06 mum. Finally, a two-frequency passively Q-switched Nd:YAG laser is developed. This laser then permits two-frequency pulses with tunable pulse duration (from 18 to 240 ns) and beat frequency (from 0 to 2.65 GHz) to be obtained.

Morvan, Loic; Lai, Ngoc D.; Dolfi, Daniel; Huignard, Jean-Pierre; Brunel, Marc; Bretenaker, Fabien; Le Floch, Albert

2002-09-01

110

Comparison of Meteor Radar and Na Doppler Lidar Measurements of Winds in the Mesopause Region Above Maui, HI  

Microsoft Academic Search

Abstract. Simultaneous sodium (Na) Doppler lidar and meteor radar mea- surements of horizontal winds in the mesopause region over Maui, HI were collected in July, 2002 and October\\/November 2003. The coincident mea- surements span 96 hours and altitudes between 80-100 km. Statistical com- parisons are carried out on radar\\/lidar winds with 1 h and 4 km time and height resolution,

S. J. Franke; X. Chu; A. Z. Liu; W. K. Hocking

2004-01-01

111

Evaluation of Radar Reflectivity (Z) for FMCW Millimeter-Wave Cloud Radar “FALCON-I”  

NASA Astrophysics Data System (ADS)

We have developed an FMCW Millimeter-Wave Cloud Radar (MMCR) at 95 GHz named FALCON-I for observations of thin clouds, which are not easily detected with microwave radars. Sensitivities in radar reflectivity Z of FALCON-I are evaluated by comparing simultaneously observed data with the pulse type MMCR named SPIDER of National Institute of Information and Communications Technology (NICT). Evaluated sensitivity of FALCON-I at the height of 5km is more sensitive than -30dBZ in 1 minute resolution, which is comparable to the calculated value from the noise figure of the receiver: -37dBZ. FALCON-I can detect clouds with -30dBZ upto the height of 9km. This is good enough performance for thin cloud observations.

Yamaguchi, Jun; Takano, Toshiaki; Nakanishi, Yuji; Abe, Hideji; Kawamura, Youhei; Yokote, Shinichi; Kumagai, Hiroshi; Ohno, Yuichi; Horie, Hiroaki

112

Aerosol and Cloud Interaction Observed From High Spectral Resolution Lidar Data  

NASA Technical Reports Server (NTRS)

Recent studies utilizing satellite retrievals have shown a strong correlation between aerosol optical depth (AOD) and cloud cover. However, these retrievals from passive sensors are subject to many limitations, including cloud adjacency (or 3D) effects, possible cloud contamination, uncertainty in the AOD retrieval. Some of these limitations do not exist in High Spectral Resolution Lidar (HSRL) observations; for instance, HSRL observations are not a ected by cloud adjacency effects, are less prone to cloud contamination, and offer accurate aerosol property measurements (backscatter coefficient, extinction coefficient, lidar ratio, backscatter Angstrom exponent,and aerosol optical depth) at a neospatial resolution (less than 100 m) in the vicinity of clouds. Hence, the HSRL provides an important dataset for studying aerosol and cloud interaction. In this study, we statistically analyze aircraft-based HSRL profiles according to their distance from the nearest cloud, assuring that all profile comparisons are subject to the same large-scale meteorological conditions. Our results indicate that AODs from HSRL are about 17% higher in the proximity of clouds (approximately 100 m) than far away from clouds (4.5 km), which is much smaller than the reported cloud 3D effect on AOD retrievals. The backscatter and extinction coefficients also systematically increase in the vicinity of clouds, which can be explained by aerosol swelling in the high relative humidity (RH) environment and/or aerosol growth through in cloud processing (albeit not conclusively). On the other hand, we do not observe a systematic trend in lidar ratio; we hypothesize that this is caused by the opposite effects of aerosol swelling and aerosol in-cloud processing on the lidar ratio. Finally, the observed backscatter Angstrom exponent (BAE) does not show a consistent trend because of the complicated relationship between BAE and RH. We demonstrate that BAE should not be used as a surrogate for Angstrom exponent, especially at high RH.

Su, Wenying; Schuster, Gregory L.; Loeb, Norman G.; Rogers, Raymond R.; Ferrare, Richard A.; Hostetler, Chris A.; Hair, Johnathan W.; Obland, Michael D.

2008-01-01

113

An Automated Cloud-edge Detection Algorithm Using Cloud Physics and Radar Data  

NASA Technical Reports Server (NTRS)

An automated cloud edge detection algorithm was developed and extensively tested. The algorithm uses in-situ cloud physics data measured by a research aircraft coupled with ground-based weather radar measurements to determine whether the aircraft is in or out of cloud. Cloud edges are determined when the in/out state changes, subject to a hysteresis constraint. The hysteresis constraint prevents isolated transient cloud puffs or data dropouts from being identified as cloud boundaries. The algorithm was verified by detailed manual examination of the data set in comparison to the results from application of the automated algorithm.

Ward, Jennifer G.; Merceret, Francis J.; Grainger, Cedric A.

2003-01-01

114

The radar simulator: deriving the radar signal using the cloud model output  

NASA Astrophysics Data System (ADS)

We present an approach to simulate cloud radar signals on the basis of cloud model output, the radar simulator. The simulator is being developed to aid validation of the cloud model. The cloud model applies double-moment bulk warm-rain and ice schemes developed by Morrison and Grabowski.1, 2 As an input, the simulator uses profiles of the mixing ratios and number concentrations of cloud droplets, rain/drizzle drops, and ice crystals, as well as the air temperature. For the ice crystals, the rimed mass fraction predicted by the ice scheme is also used. The simulator applies precomputed look-up tables containing scattering properties of cloud and precipitation particles, such as reflectivities, extinction and absorption coefficients. For each grid point, the coefficients are integrated over particle size distributions and summed over hydrometeor types. Consistent with assumptions in the cloud model microphysical scheme, modified gamma size distributions are assumed for cloud droplets and ice crystals, whereas the exponential Marshall-Palmer size distribution is assumed for the rain/drizzle drops. Application of the radar simulator to a simulation of clouds observed during the TWP-ICE campaign over northern Australia is presented.

Kardas, Aleksandra E.; McFarlane, Sally; Morrison, Hugh; Comstock, Jennifer; Grabowski, Wojciech W.; Malinowski, Szymon P.

2009-09-01

115

Airborne lidar/radiometric measurements of cirrus cloud parameters and their application to LOWTRAN radiance evaluations  

NASA Technical Reports Server (NTRS)

SRI has assembled an airborne lidar/radiometric instrumentation suite for mapping cirrus cloud distribution and analyzing cirrus cloud optical properties. Operation of upward viewing infrared radiometers from an airborne platform provides the optimum method of measuring high altitude cold cloud radiative properties with minimum interference from the thermal emission by the earth's surface and lower atmospheric components. Airborne installed sensors can also operate over large regional areas including water, urban, and mountain surfaces and above lower atmospheric convective clouds and haze layers. Currently available sensors installed on the SRI Queen Air aircraft are illustrated. Lidar and radiometric data records are processed for real time viewing on a color video screen. A cirrus cloud data example is presented as a black and white reproduction of a color display of data at the aircraft altitude of 12,000 ft, the 8 to 14 micron atmospheric radiation background was equivalent to a blackbody temperature of about -60 C and, therefore, the radiometer did not respond strongly to low density cirrus cloud concentrations detected by the lidar. Cloud blackbody temperatures (observed by radiometer) are shown plotted against midcloud temperatures (derived from lidar observed cloud heights and supporting temperature profiles) for data collected on 30 June and 28 July.

Uthe, Edward E.

1990-01-01

116

Millimeter-wave radars for remotely sensing clouds and precipitation  

Microsoft Academic Search

Millimeter-wave radars have been used since the early 1950s to study clouds and precipitation, but until recently these early instruments were limited to simple backscatter power measurements and were plagued by hardware problems. However, development of solid-state millimeter-wave componentry and high-power klystron amplifiers has spurred the evolution of reliable, coherent radars operating up to 95 GHz. In addition, advances in

JAMES B. MEAD; ANDREW L. PAZMANY; STEPHEN M. SEKELSKY; ROBERT E. MCINTOSH

1994-01-01

117

95 GHz Doppler Polarimetric Cloud Radar Based on a Magnetron Transmitter  

Microsoft Academic Search

This paper presents the development and first operation of a 95 GHz Doppler polarimetric cloud radar. The radar provides high-resolution, real-time measurements of reflectivity, linear depolarisation ratio, Doppler spectrum, radial velocity mean, and velocity variance of clouds and precipitation. Compared to similar existing radars, the discussed one takes advantages from several innovative key components. In particular, the radar essentially benefits

D. M. Vavriv; V. A. Volkov; V. V. Vinogradov; R. V. Kozhyn; K. Schunemann

2002-01-01

118

The 1973-1974 lidar observations of cirrus clouds at Kwajalein  

NASA Technical Reports Server (NTRS)

A series of surface-based lidar measurements was made in support of reentry tests at Kwajalein. The measurement periods were conducted during May to June, Aug., Dec. 1973, and Mar. to Apr. 1974. The lidar used was the SRI Mark IX, a ruby lidar installed within a van complete with its own power supplies, azimuth and elevation scanning capabilities and real time digital data recording, processing, and display systems. The digital data system was used to estimate cirrus cloud equivalent ice water content as the cloud was being observed. Other supporting equipment included an instrumented WB-57 aircraft used for sampling cirrus cloud ice crystals. An altitude time intensity modulated video display of cirrus cloud structure observed on 17 Dec. 1973 is presented.

Uthe, Edward E.

1990-01-01

119

Three-dimensional lidar point-cloud visualization and analysis of coseismic deformation using LidarViewer  

NASA Astrophysics Data System (ADS)

We summarize new point-cloud analysis techniques, and results obtained from lidar data collected from the 2010 El Mayor-Cucapah earthquake surface rupture, using LidarViewer, an open-source software platform developed at the UC Davis KeckCAVES. Imaging of earthquake deformation with multi-resolution and multi-temporal lidar presents several challenges for visualization and analysis. Instruments, data resolution, and even the geodetic reference frame may change significantly between surveys. Grid-based techniques fail to adequately represent fully 3-D features, such as scarps and vegetation, and introduce aliasing artifacts that are especially troublesome when the deformation signal sought is less than the point spacing. Once obtained, the resulting dense field of 3-D vectors derived from differential lidar are difficult to visualize together with the terrain, limiting interpretation of these results. Points are the native, resolution-independent format of lidar, but working with massive point data sets can overwhelm system memory. LidarViewer overcomes these challenges using hierarchal data storage, view-dependent rendering, and an efficient, recursive data analysis framework. Pre-earthquake airborne lidar, collected as part of a regional survey, are very sparse (0.013 pts/m2) compared to the post-earthquake survey (9 pts/m2). A simple, \\chi2 minimization approach to matching these data sets takes advantage of this dramatic resolution difference to extract 3-D ground motion. We visualize the resulting displacement field in a 3-D environment using streamline-based approaches, colored by elevation change, and superimposed on the post-earthquake topography. This fused data product encourages exploration and assessment of the deformation signal and its relationship to landscape features, such as fault scarps, vegetation, and topographic relief. Terrestrial lidar scans collected within two weeks of the earthquake reveal the surface rupture at centimeter resolution. Virtual field measurements of offset features were collected using the full point-cloud in an immersive 3-D cave environment. Repeat measurements, both at a point and along strike, reveal substantial epistemic (interpretive) uncertainty that is generally greater than that reported by geologists working in the field after an earthquake. Combining observations from differential airborne and post-earthquake terrestrial lidar from the strike-slip Borrego fault reveals smooth coseismic slip gradients of ˜ 10-3, similar to strains measured from ground-surface deformation across strike. Higher strains are found along the Paso Superior normal fault surface rupture, due largely to distributed faulting and sagging of the hangingwall.

Oskin, M. E.; Kreylos, O.; Banesh, D.; Hamann, B.; Gold, P. O.; Elliott, A. J.; Hinojosa, A.; Kellogg, L. H.

2012-12-01

120

Accuracy of biomass estimates from radar and lidar over temperate forests  

NASA Astrophysics Data System (ADS)

A better understanding of ecosystem processes requires accurate estimates of forest biomass and structure on global scales. Recently, there have been demonstrations of the ability of remote sensing instruments, such as radar and lidar, for the estimation of forest parameters from spaceborne platforms in a consistent manner. These advances can be exploited for global forest biomass accounting and structure characterization, leading to a better understanding of the global carbon cycle. The popular techniques for estimation of forest parameters from radar instruments in particular, use backscatter intensity, interferometry and polarimetric interferometry. In this paper we analyze the accuracy of biomass estimates over temperate forests of the North-Eastern United States from lidar and radar backscatter. We adopt an empirical approach, relying on ground truth data collected during DESDynI field campaigns over the Harvard and Howland Forests in 2009 and remote sensing data from LVIS, the GSFC full-waveform lidar and NASA JPL's L-band UAVSAR. UAVSAR collected data over the Harvard and Howland Forests during a deployment in 2009 where it was flown in a repeat-pass configuration collecting several fully polarimetric scenes. In a concurrent deployment of the GSFC LVIS instrument, full waveform lidar data was collected over the same region. Diameter and species information from fifteen hectares at the Harvard Forest and twenty three hectares at the Howland forest was collected during the July 2009 DESDynI field campaigns as well. We assess the accuracy of biomass estimates based on diameter measurements by using a classic statistical approach to characterize the impact of the diameter-biomass allometry at both field sites. Using a lidar error model and estimates of error in field biomass, we attempt to characterize the error in biomass estimates from common full waveform lidar metrics from LVIS data over the Harvard and Howland forests. Similarly, using a radar backscatter error model and data from UAVSAR, we analyze the accuracy of the backscatter-biomass relationship and characterize the uncertainty in biomass estimates from radar in a non-linear regression setting with measurement error. A discussion will be provided on the implications of this analysis on the design and science outcomes of the proposed DESDynI mission.

Ahmed, R.; Siqueira, P. R.; Hensley, S.

2011-12-01

121

First results from an iron lidar and a VHF radar at Davis, Antarctica  

NASA Astrophysics Data System (ADS)

We present temperature measurements at Davis, Antarctica (69°S, 78°E), and compare with simultaneous and co-located radar measurements of polar mesosphere summer echoes (PMSE). The mobile scanning iron lidar of the IAP in Kuehlungsborn was installed at Davis in December 2010. It measures iron densities, vertical winds, and temperatures in the iron layer, i. e. from approximately 80 to 100 km. It is based on probing the Doppler broadened resonance line of iron atoms at 386 nm and can operate under daylight conditions. Typical values for temperature uncertainty, altitude and time resolution are 3-5 K, 1 km, and 1 hour, respectively. The lidar also measures neutral air densities and temperatures in the stratosphere and lower mesosphere. At Davis the lidar has up to now achieved approximately 2700 hours of data which is presumably the largest nearly continuous data set in Antarctica. The mesopause altitude changes throughout the summer season by several kilometers, significantly different from the northern hemisphere summer. Depending on altitude, temperatures can be warmer or colder compared to the NH summer. Temperatures at Davis near 86 km are rather similar to the NH, but they are much colder at higher altitudes. The thermal structure around the mesopause at Davis is closely related to the general circulation in the stratosphere, namely to the transition from winter to summer conditions. Different from expectations we sometimes find the mesopause significantly higher and colder(!) compared to the NH. Furthermore, we find large thermal tides in the summer months with amplitudes of up to 6-7~K, which is much larger than expected from models. The Australien Antarctic Division operates a 55 MHz VHF radar at Davis since February 2003. We report first simultaneous measurements of PMSE and temperatures by the Fe lidar. PMSE are strong radar echoes related to ice particles and therefore require atmospheric temperatures being lower than the frost point temperature. Several hours of simultaneous lidar/radar observations are now available from the Antarctic summer seasons 2010/2011 and 2011/2012. The VHF radar frequently detected PMSE. Temperatures at PMSE altitudes are below the frost point. To our surprise PMSE were sometimes absent at altitudes where temperatures are much lower than the frost point. We note that (apart from low temperatures) more ingredients are required for PMSE, for example, background electrons and neutral air turbulence. We will discuss potential explanations for the presence and absence of PMSE.Thermal tide from the iron resonance lidar located at Davis, Antarctica (from Lübken et al., Geophys. Res. Lett., 2011).

Luebken, F.; Morris, R. J.; Hoeffner, J.; Kaifler, B.; Viehl, T.

2012-12-01

122

Validation of aerosol and cloud layer structures from the space-borne lidar CALIOP using Seoul National University ground-based lidar  

NASA Astrophysics Data System (ADS)

We present first observationally based validations of the space-borne lidar CALIOP onboard CALIPSO satellite using coincidental observations from a ground-based SNU lidar for 3 different types of atmospheric scenes. Both lidar measurements were taken in nearly same airmass in space and time. Total attenuated backscatters at 532 nm from the two instruments show similar aerosol and cloud layer structures (the top and bottom heights) both under cloud-free conditions and in case of multi-aerosol layers underlying semi-transparent cirrus clouds. This result confirms that the CALIPSO science team algorithms of the discrimination of cloud and aerosol as well as of their layer top and base altitudes are sound. Under thick clouds conditions, only information on the cloud top (bottom) height is reliable from CALIOP (ground-based lidar) observations due to strong signal attenuations. However, simultaneous space-borne CALIOP and ground-based SNU lidar measurements complement each other and provide full information on the vertical distribution of aerosols and clouds. Discrepancies between space-borne and ground-based lidar signals are partly explained by the strong spatial and vertical inhomogeneous distributions of clouds at few kilometer horizontal scales.

Kim, S.-W.; Berthier, S.; Chazette, P.; Raut, J.-C.; Dulac, F.; Yoon, S.-C.

2007-08-01

123

Dual-FOV Raman and Doppler lidar studies of aerosol-cloud interactions: Simultaneous profiling of aerosols, warm-cloud properties, and vertical wind  

NASA Astrophysics Data System (ADS)

For the first time, colocated dual-field of view (dual-FOV) Raman lidar and Doppler lidar observations (case studies) of aerosol and cloud optical and microphysical properties below and within thin layered liquid water clouds are presented together with an updraft and downdraft characterization at cloud base. The goal of this work is to investigate the relationship between aerosol load close to cloud base and cloud characteristics of warm (purely liquid) clouds and the study of the influence of vertical motions and turbulent mixing on this relationship. We further use this opportunity to illustrate the applicability of the novel dual-FOV Raman lidar in this field of research. The dual-FOV lidar combines the well-established multiwavelength Raman lidar technique for aerosol retrievals and the multiple-scattering Raman lidar technique for profiling of the single-scattering extinction coefficient, effective radius, number concentration of the cloud droplets, and liquid water content. Key findings of our 3 year observations are presented in several case studies of optically thin altocumulus layers occurring in the lower free troposphere between 2.5 and 4 km height over Leipzig, Germany, during clean and polluted situations. For the clouds that we observed, the most direct link between aerosol proxy (particle extinction coefficient) and cloud proxy (cloud droplet number concentration) was found at cloud base during updraft periods. Above cloud base, additional processes resulting from turbulent mixing and entrainment of dry air make it difficult to determine the direct impact of aerosols on cloud processes.

Schmidt, Jörg; Ansmann, Albert; Bühl, Johannes; Baars, Holger; Wandinger, Ulla; Müller, Detlef; Malinka, Aleksey V.

2014-05-01

124

Macrophysical and optical properties of midlatitude high-altitude clouds from 4 ground-based lidars and collocated CALIOP observations  

NASA Astrophysics Data System (ADS)

Cirrus clouds not only play a major role in the energy budget of the Earth-Atmosphere system, but are also important in the hydrological cycle [Stephens et al., 1990; Webster, 1994]. According to satellite passive remote sensing, high-altitude clouds cover as much as 40% of the earth's surface on average (Liou 1986; Stubenrauch et al., 2006) and can reach 70% of cloud cover over the Tropics (Wang et al., 1996; Nazaryan et al., 2008). Hence, given their very large cloud cover, they have a major role in the climate system (Lynch et al. 2001). Cirrus clouds can be classified into three distinct families according to their optical thickness, namely subvisible clouds (OD<0.03), semi-transparent clouds (0.03clouds (0.3Lidar measurements however show that subvisible and semi-transparent clouds represent 50% or more of cirrus cloud population. The radiative effects of cirrus clouds are found to be significant by many studies both at the top of the atmosphere and surface. The contribution of the subvisible and semi-transparent classes is strongly affected by levels of other scatterers in the atmosphere (gases, aerosols). This makes them quite an important topic of study at the global scale. In the present work, we applied the cloud structure analysis algorithm STRAT to long time series of lidar backscatter profiles from multiple locations around the world. Our goal was to establish a Mid-Latitude climatology of cirrus clouds macrophysical properties based on active remote sensing: ground-based lidars at four mid-latitude observatories and the spaceborne instrument CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization). Lidar sampling, macrophysical (cloud base height, cloud top height, cloud thickness) and optical (cloud optical thickness) properties statistics are then evaluated and compared between the four observatories ground-based lidar measurements and quasi-simultaneously CALIOP overpasses. We note an overall good consistency in the macrophysical properties statistics derived from ground- based Lidar and CALIOP. For high altitude clouds, using consistent transmission-based retrieval methods, discrepancies are found in COT retrievals between ground Lidars and CALIOP. Ground-based Lidar retrievals contain less thick cirrus clouds than CALIOP. Overall, the results show that cirrus clouds with COD<0.1 (not included in historical cloud climatologies) represent 30-50% of the non-opaque cirrus class (COD<3, Pressure<440mb from ISCCP). Finally, we analyze the statistic consistencies between each dataset and investigate the possible bias due to lidar sampling and instrument/algorithm differences between ground-based lidar and CALIOP.

Dupont, J. C.; Haeffelin, M.; Morille, Y.; Noel, V.; Keckhut, P.; Comstock, J.; Winker, D.; Chervet, P.; Roblin, A.

2009-04-01

125

G band atmospheric radars: new frontiers in cloud physics  

NASA Astrophysics Data System (ADS)

Clouds and associated precipitation are the largest source of uncertainty in current weather and future climate simulations. Observations of the microphysical, dynamical and radiative processes that act at cloud scales are needed to improve our understanding of clouds. The rapid expansion of ground-based super-sites and the availability of continuous profiling and scanning multi-frequency radar observations at 35 and 94 GHz have significantly improved our ability to probe the internal structure of clouds in high temporal-spatial resolution, and to retrieve quantitative cloud and precipitation properties. However, there are still gaps in our ability to probe clouds due to large uncertainties in the retrievals. The present work discusses the potential of G band (frequency between 110 and 300 GHz) Doppler radars in combination with lower frequencies to further improve the retrievals of microphysical properties. Our results show that, thanks to a larger dynamic range in dual-wavelength reflectivity, dual-wavelength attenuation and dual-wavelength Doppler velocity (with respect to a Rayleigh reference), the inclusion of frequencies in the G band can significantly improve current profiling capabilities in three key areas: boundary layer clouds, cirrus and mid-level ice clouds, and precipitating snow.

Battaglia, A.; Westbrook, C. D.; Kneifel, S.; Kollias, P.; Humpage, N.; Löhnert, U.; Tyynelä, J.; Petty, G. W.

2014-06-01

126

G-band atmospheric radars: new frontiers in cloud physics  

NASA Astrophysics Data System (ADS)

Clouds and associated precipitation are the largest source of uncertainty in current weather and future climate simulations. Observations of the microphysical, dynamical and radiative processes that act at cloud-scales are needed to improve our understanding of clouds. The rapid expansion of ground-based super-sites and the availability of continuous profiling and scanning multi-frequency radar observations at 35 and 94 GHz have significantly improved our ability to probe the internal structure of clouds in high temporal-spatial resolution, and to retrieve quantitative cloud and precipitation properties. However, there are still gaps in our ability to probe clouds due to large uncertainties in the retrievals. The present work discusses the potential of G-band (frequency between 110 and 300 GHz) Doppler radars in combination with lower frequencies to further improve the retrievals of microphysical properties. Our results show that, thanks to a larger dynamic range in dual-wavelength reflectivity, dual-wavelength attenuation and dual-wavelength Doppler velocity (with respect to a Rayleigh reference), the inclusion of frequencies in the G-band can significantly improve current profiling capabilities in three key areas: boundary layer clouds, cirrus and mid-level ice clouds, and precipitating snow.

Battaglia, A.; Westbrook, C. D.; Kneifel, S.; Kollias, P.; Humpage, N.; Löhnert, U.; Tyynelä, J.; Petty, G. W.

2014-01-01

127

Influence of daylight and noise current on cloud and aerosol observations by spaceborne elastic scattering lidar.  

PubMed

The influence of daylight and noise current on cloud and aerosol observations by realistic spaceborne lidar was examined by computer simulations. The reflected solar radiations, which contaminate the daytime return signals of lidar operations, were strictly and explicitly estimated by accurate radiative transfer calculations. It was found that the model multilayer cirrus clouds and the boundary layer aerosols could be observed during the daytime and the nighttime with only a few laser shots. However, high background noise and noise current make it difficult to observe volcanic aerosols in middle and upper atmospheric layers. Optimal combinations of the laser power and receiver field of view are proposed to compensate for the negative influence that is due to these noises. For the computer simulations, we used a realistic set of lidar parameters similar to the Experimental Lidar in-Space Equipment of the National Space Development Agency of Japan. PMID:18324021

Nakajima, T Y; Imai, T; Uchino, O; Nagai, T

1999-08-20

128

Autonomous, Full-Time Cloud Profiling at Arm Sites with Micro Pulse Lidar  

NASA Technical Reports Server (NTRS)

Since the early 1990's technology advances permit ground based lidar to operate full time and profile all significant aerosol and cloud structure of the atmosphere up to the limit of signal attenuation. These systems are known as Micro Pulse Lidars (MPL), as referenced by Spinhirne (1993), and were first in operation at DOE Atmospheric Radiation Measurement (ARM) sites. The objective of the ARM program is to improve the predictability of climate change, particularly as it relates to cloud-climate feedback. The fundamental application of the MPL systems is towards the detection of all significant hydrometeor layers, to the limit of signal attenuation. The heating and cooling of the atmosphere are effected by the distribution and characteristics of clouds and aerosol concentration. Aerosol and cloud retrievals in several important areas can only be adequately obtained with active remote sensing by lidar. For cloud cover, the height and related emissivity of thin clouds and the distribution of base height for all clouds are basic parameters for the surface radiation budget, and lidar is essetial for accurate measurements. The ARM MPL observing network represents the first long-term, global lidar study known within the community. MPL systems are now operational at four ARM sites. A six year data set has been obtained at the original Oklahoma site, and there are several years of observations at tropical and artic sites. Observational results include cloud base height distributions and aerosol profiles. These expanding data sets offer a significant new resource for cloud, aerosol and atmospheric radiation analysis. The nature of the data sets, data processing algorithms, derived parameters and application results are presented.

Spinhirne, James D.; Campbell, James R.; Hlavka, Dennis L.; Scott, V. Stanley; Flynn, Connor J.

2000-01-01

129

Multilayer cloud monitoring by micro-Joule lidar based on photon counting receiver and diode laser  

Microsoft Academic Search

Multilayers clouds layer's horizons have been detected in strong snowing condition by using the micro-Joule eye-safe lidar. Lidar is based on the 1 muJ (30 ns length) pulsed diode laser, which operates with high repetition rate (up to 10 kHz) and silica (Si) photon counting receiver (Single Photon Avalanche Diode, SPAD) from Czech Technical University. Note that the unique low

S. M. Pershin; A. N. Lyash; V. S. Makarov; K. Hamal; I. Prochazka; B. Sopko

2009-01-01

130

Noctilucent cloud in the western Arctic in 2005: Simultaneous lidar and camera observations and analysis  

Microsoft Academic Search

We report observations of a noctilucent cloud (NLC) over central Alaska by a ground-based lidar and camera on the night of 9–10 August 2005. The lidar at Poker Flat Research Range (PFRR), Chatanika (65°N, 147°W) measured a maximum integrated backscatter coefficient of 2.4×10?6sr?1 with a peak backscatter coefficient of 2.6×10?9m?1sr?1 corresponding to an aerosol backscatter ratio of 120 at an

R. L. Collins; M. J. Taylor; K. Nielsen; K. Mizutani; Y. Murayama; K. Sakanoi; M. T. DeLand

2009-01-01

131

Portable standoff Raman and Mie-Rayleigh lidar for cloud, aerosol, and chemical monitoring  

Microsoft Academic Search

There is a need for portable, low-cost lidar systems that can be used for cloud, aerosols and chemical monitoring from a stand-off distance. At the University of Hawaii we have developed lidar systems based on a 12.7-cm diameter telescope and a 20 Hz frequency-doubled Nd:YAG laser source. For stand off Raman detection of organic liquid and vapors, and plastic explosives,

Shiv K. Sharma; John N. Porter; Anupum K. Misra; Hugh W. Hubble; Premlata Menon

2003-01-01

132

Airborne lidar observations of cirrus clouds in the Tropics, Mid-latitudes, and the Arctic  

Microsoft Academic Search

Airborne lidar systems have demonstrated an unsurpassed capability to detect and profile optically thin cirrus. The airborne Lidar Atmospheric Sensing Experiment (LASE) has demonstrated a capability to detect thin cirrus at aerosol scattering levels of <2.0× 10-9 m-1 sr-1 at 815 nm, and this makes it well suited for deriving many cirrus cloud properties. LASE has been operated from high-

S. Ismail; E. Browell; R. Ferrare; W. Grant; S. Kooi; V. Brackett; M. Mahoney

2003-01-01

133

Cloud radar Doppler spectra in drizzling stratiform clouds: 2. Observations and microphysical modeling of drizzle evolution  

NASA Astrophysics Data System (ADS)

In part I, the influence of cloud microphysics and dynamics on the shape of cloud radar Doppler spectra in warm stratiform clouds was discussed. The traditional analysis of radar Doppler moments was extended to include skewness and kurtosis as additional descriptors of the Doppler spectrum. Here, a short climatology of observed Doppler spectra moments as a function of the radar reflectivity at continental and maritime ARM sites is presented. The evolution of the Doppler spectra moments is consistent with the onset and growth of drizzle particles and can be used to assist modeling studies of drizzle onset and growth. Time-height radar observations are used to exhibit the coherency of the Doppler spectra shape parameters and demonstrate their potential to improve the interpretation and use of radar observations. In addition, a simplified microphysical approach to modeling the vertical evolution of the drizzle particle size distribution in warm stratiform clouds is described and used to analyze the observations. The formation rate of embryonic drizzle droplets due to the autoconversion process is not calculated explicitly; however, accretion and evaporation processes are explicitly modeled. The microphysical model is used as input to a radar Doppler spectrum forward model, and synthetic radar Doppler spectra moments are generated. Three areas of interest are studied in detail: early drizzle growth near the cloud top, growth by accretion of the well-developed drizzle, and drizzle depletion below the cloud base due to evaporation. The modeling results are in good agreement with the continental and maritime observations. This demonstrates that steady state one-dimensional explicit microphysical models coupled with a forward model and comprehensive radar Doppler spectra observations offer a powerful method to explore the vertical evolution of the drizzle particle size distribution.

Kollias, Pavlos; Szyrmer, Wanda; RéMillard, Jasmine; Luke, Edward

2011-07-01

134

Cloud radar Doppler spectra in drizzling stratiform clouds: 2. Observations and microphysical modeling of drizzle evolution  

SciTech Connect

In part I, the influence of cloud microphysics and dynamics on the shape of cloud radar Doppler spectra in warm stratiform clouds was discussed. The traditional analysis of radar Doppler moments was extended to include skewness and kurtosis as additional descriptors of the Doppler spectrum. Here, a short climatology of observed Doppler spectra moments as a function of the radar reflectivity at continental and maritime ARM sites is presented. The evolution of the Doppler spectra moments is consistent with the onset and growth of drizzle particles and can be used to assist modeling studies of drizzle onset and growth. Time-height radar observations are used to exhibit the coherency of the Doppler spectra shape parameters and demonstrate their potential to improve the interpretation and use of radar observations. In addition, a simplified microphysical approach to modeling the vertical evolution of the drizzle particle size distribution in warm stratiform clouds is described and used to analyze the observations. The formation rate of embryonic drizzle droplets due to the autoconversion process is not calculated explicitly; however, accretion and evaporation processes are explicitly modeled. The microphysical model is used as input to a radar Doppler spectrum forward model, and synthetic radar Doppler spectra moments are generated. Three areas of interest are studied in detail: early drizzle growth near the cloud top, growth by accretion of the well-developed drizzle, and drizzle depletion below the cloud base due to evaporation. The modeling results are in good agreement with the continental and maritime observations. This demonstrates that steady state one-dimensional explicit microphysical models coupled with a forward model and comprehensive radar Doppler spectra observations offer a powerful method to explore the vertical evolution of the drizzle particle size distribution.

Kollias, P.; Luke, E.; Szyrmer, W.; Rémillard, J.

2011-07-02

135

Millimeter Wave Polarimetric Radar Remote Sensing of Ice Clouds  

Microsoft Academic Search

Ice clouds play important roles in many practical and theoretical researches. This thesis investigates the electromagnetic scattering properties of ice crystals at 94 and 220 GHz, and polarimetric radar techniques for ice crystal type discrimination and ice mass content estimation. The scattering amplitude matrix is computed for pristine ice crystals of different sizes and from different incidence directions using the

Chengxian Tang

1994-01-01

136

Ice crystal properties retrieval using radar spectral polarimetric measurements within ice\\/mixed-phase clouds  

Microsoft Academic Search

In the field of atmospheric research, ground-based radar systems are often employed to study ice\\/mixed-phase cloud properties based on retrieval techniques. These techniques convert the radar signal backscattered by each bulk of ice crystals being probed within the same radar resolution volume to cloud’s microphysical characteristics. However, the size of a radar resolution volume is often too large compared to

Y. Dufournet

2010-01-01

137

Micropulse Lidar (MPL) Handbook  

SciTech Connect

The micropulse lidar (MPL) is a ground-based optical remote sensing system designed primarily to determine the altitude of clouds overhead. The physical principle is the same as for radar. Pulses of energy are transmitted into the atmosphere; the energy scattered back to the transceiver is collected and measured as a time-resolved signal. From the time delay between each outgoing transmitted pulse and the backscattered signal, the distance to the scatterer is infered. Besides real-time detection of clouds, post-processing of the lidar return can also characterize the extent and properties of aerosol or other particle-laden regions.

Mendoza, A; Flynn, C

2006-05-01

138

Coherent lidar imaging of dust clouds: waveform comparison with the poly-phase (P4) modulation waveform  

NASA Astrophysics Data System (ADS)

A dust or aerosol cloud represents a convenient target to examine the capabilities of range-resolved Doppler and intensity (RRDI) or inverse synthetic aperture ladar (ISAR) imaging coherent laser radar, known as coherent "lidar" for optically thin targets. The poly-phase P4 ladar waveform and its RRDI images are described and compared with previous pulse-burst, linear-FM chirp pulse-compression, pseudo-random phase modulation waveforms, and several other waveforms which have not been utilized to date. A "dust cloud" has very many independently moving point scatterers with velocities that are approximately Gaussian randomly distributed in x,y,z with standard deviations of about 10% of the mean wind + aerosol velocity. This is contrary to a hard-target where the point scatterers are rigidly attached and moving together. The dust cloud produced speckle effects for the various ladar waveforms are compared. In addition, a reference set of four corner-cube retro-reflectors within the dust cloud further illustrates the differences in the various waveform capabilities and resolution.

Youmans, Douglas G.

2008-05-01

139

Cloud track wind using synergism of backscatter lidar and sky digital picture  

NASA Astrophysics Data System (ADS)

Cloud altitude measurements by a 532nm backscatter Lidar and time lapsed digital photography are combined to monitor the cloud velocity profile. The cloud images are recorded in time steps of two seconds by a Nikon D100 digital camera through a 63° solid angle while the Lidar was measuring the cloud altitude. The images are recorded in 8 bits gray scale JPG format in an array of 2240×1488 pixels. To measure the angular displacement of different parts of the cloud, each image is meshed into an array of 44×29 cells, each cell contains 50×50 pixels. The grayscale density cross correlations between similar cells of successive images are computed using a MATLAB code developed by us for this application. The output products are the direction and the amount of displacement of each cell, in pixels. combining the results on cloud displacement with Lidar measurements enable to calculate the velocity vector in each cell. The resolution in velocity is about 1 ms-1 and 2° in direction. The calculation technique also is tested by simulating the cloud motion by moving the image pixels with a computer generated Gaussian velocity distribution.

Khalesifard, Hamid R.; Abdi, Farhad; Flamant, Pierre H.

2005-10-01

140

Aerosol and Cloud Observations and Data Products by the GLAS Polar Orbiting Lidar Instrument  

NASA Technical Reports Server (NTRS)

The Geoscience Laser Altimeter System (GLAS) launched in 2003 is the first polar orbiting satellite lidar. The instrument was designed for high performance observations of the distribution and optical scattering cross sections of clouds and aerosol. The backscatter lidar operates at two wavelengths, 532 and 1064 nm. Both receiver channels meet and exceed their design goals, and beginning with a two month period through October and November 2003, an excellent global lidar data set now exists. The data products for atmospheric observations include the calibrated, attenuated backscatter cross section for cloud and aerosol; height detection for multiple cloud layers; planetary boundary layer height; cirrus and aerosol optical depth and the height distribution of aerosol and cloud scattering cross section profiles. The data sets are now in open release through the NASA data distribution system. The initial results on global statistics for cloud and aerosol distribution has been produced and in some cases compared to other satellite observations. The sensitivity of the cloud measurements is such that the 70% global cloud coverage result should be the most accurate to date. Results on the global distribution of aerosol are the first that produce the true height distribution for model inter-comparison.

Spinhirne, J. D.; Palm, S. P.; Hlavka, D. L.; Hart, W. D.; Mahesh, A.; Welton, E. J.

2005-01-01

141

Lidar observations of the Pinatubo volcanic cloud over Hampton, Virginia  

NASA Technical Reports Server (NTRS)

A series of eruptions of Mt. Pinatubo climaxed in a cataclysmic eruption on June 15-16, which greatly perturbed the stratospheric aerosol layer. These eruptions yielded an estimated 20 megatons of SO2, which is three times the amount produced by El Chichon. Lidar measurements taken by the 48-inch lidar system at Langley Research Center show the vertical distribution, intensity and spread of the Pinatubo aerosol layers over the middle latitude locations. A few observations have also been made using an airborne lidar system which measures scattering and depolarization. The magnitude and transport time of the volcanic aerosols following Pinatubo and El Chichon are compared. In addition, comparisons are made between the ground-based lidar measurements and near-coincident Stratospheric Aerosol and Gas Experiment (SAGE) 2 satellite observations of the Pinatubo aerosol layers.

Osborn, M. T.; Winker, D. M.; Woods, D. C.; Decoursey, R. J.

1992-01-01

142

Polar winter cloud depolarization measurements with the CANDAC Rayleigh-Mie-Raman Lidar  

NASA Astrophysics Data System (ADS)

Clouds introduce a significant positive forcing to the Arctic radiation budget and this is strongest during the polar winter when shortwave radiation is absent (Intrieri et al., 2002). The amount of forcing depends on the occurrence probability and optical depth of the clouds as well as the cloud particle phase (Ebert and Curry 1992). Mixed-phase clouds are particularly complex as they involve interactions between three phases of water (vapour, liquid and ice) coexisting in the same cloud. Although significant progress has been made in characterizing wintertime Arctic clouds (de Boer et al., 2009 and 2011), there is considerable variability in the relative abundance of particles of each phase, in the morphology of solid particles, and in precipitation rates depending on the meteorology at the time. The Canadian Network for the Detection of Atmospheric Change (CANDAC) Rayleigh-Mie-Raman Lidar (CRL) was installed in the Canadian High Arctic at Eureka, Nunavut (80°N, 86°W) in 2008-2009. The remotely-operated system began with measurement capabilities for multi-wavelength aerosol extinction, water vapour mixing ratio, and tropospheric temperature profiles, as well as backscatter cross section coefficient and colour ratio. In 2010, a new depolarization channel was added. The capability to measure the polarization state of the return signal allows the characterization of the cloud in terms of liquid and ice water content, enabling the lidar to probe all three phases of water in these clouds. Lidar depolarization results from 2010 and 2011 winter clouds at Eureka will be presented, with a focus on differences in downwelling radiation between mixed phase clouds and ice clouds. de Boer, G., E.W. Eloranta, and M.D. Shupe (2009), Arctic mixed-phase stratiform cloud properties from multiple years of surface-based measurements at two high-latitude locations, Journal of Atmospheric Sciences, 66 (9), 2874-2887. de Boer, G., H. Morrison, M. D. Shupe, and R. Hildner (2011), Evidence of liquid dependent ice nucleation in high-latitude stratiform clouds from surface remote sensors, Geophysical Research Letters, 38, L01803. Ebert, EE and J.A .Curry (1992), A parameterization of ice cloud optical properties for climate models, Journal of Geophysical Research 97:3831-3836. Intrieri JM, Fairall CW, Shupe MD, Persson POG, Andreas EL, Guest PS, Moritz RE. 2002. An annual cycle of Arctic surface cloud forcing at SHEBA. Journal of Geophysical Research 107 NO. C10, 8039 . Noel, V., H. Chepfer, M. Haeffelin, and Y. Morille (2006), Classification of ice crystal shapes in midlatitude ice clouds from three years of lidar observations over the SIRTA observatory. Journal of the Atmospheric Sciences, 63:2978 - 2991.

McCullough, E. M.; Nott, G. J.; Duck, T. J.; Sica, R. J.; Doyle, J. G.; Pike-thackray, C.; Drummond, J. R.

2011-12-01

143

Retrieval of atmospheric attenuation using combined ground-based and airborne 95-GHz cloud radar measurements  

NASA Technical Reports Server (NTRS)

This paper discusses cloud radar calibration and intercomparison of airborne and ground-based radar measurements and presents a unique algorithm for attenuation retrieval. This algorithm is based on dual 95-GHz radar measurements of the same cloud and precipitation volumes collected from opposing viewing angles.

Li, L.; Sekelsky, S.; Reising, S.; Swift, C.; Durden, S.; Sadowy, G.; Dinardo, S.; Li, F.; Huffman, A.; Stephens, G.; Babb, D.; Rosenberger, H.

2001-01-01

144

DC-8 scanning lidar characterization of aircraft contrails and cirrus clouds  

NASA Technical Reports Server (NTRS)

A Subsonic Assessment (SASS) element of the overall Atmospheric Effects of Aviation Project (AEAP) was initiated by NASA to assess the atmospheric impact of subsonic aircraft. SRI was awarded a project to develop and test a scanning backscatter lidar for installation on the NASA DC-8 (year 1), participate in the Subsonic Aircraft: Contrail and Cloud Effects Special Study (SUCCESS) field program (year 2), and conduct a comprehensive analysis of field data (year 3). A scanning mirror pod attached to the DC-8 aircraft provides for scanning lidar observations ahead of the DC-8 and fixed-angle upward or downward observations. The lidar system installed within the DC-8 transmits 275 MJ at 1.06 gm wavelength or about 130 mJ at 1.06 and 0.53 gm simultaneously. Range-resolved aerosol backscatter is displayed in real time in terms of cloud/contrail spatial distributions. The objectives of the project are to map contrail/cloud vertical distributions ahead of DC-8; provide DC-8 guidance into enhanced scattering layers; document DC-8 flight path intersection of contrail and cloud geometries (in-situ measurement positions relative to cloud/contrail shape and an extension of in-situ measurements into the vertical -- integrated contrail/cloud properties); analyze contrail/cloud radiative properties with LIRAD (combined lidar and radiometry) technique; evaluate mean particle sizes of aircraft emissions from two-wavelength observations; study contrail/cloud interactions, diffusion, and mass decay/growth; and make observations in the near-field of aircraft engine emissions. The scanning mirror pod may also provide a scanning capability for other remote sensing instruments.

Nielsen, Norman B.; Uthe, Edward E. (Principal Investigator)

1996-01-01

145

Arctic polar stratospheric cloud measurements by means of a four wavelength depolarization lidar  

NASA Technical Reports Server (NTRS)

A four wavelength depolarization backscattering lidar has been operated during the European Arctic Stratospheric Ozone Experiment (EASOE) in Sodankyl, in the Finnish Arctic. The lidar performed measurements during the months of December 1991, January, February and March 1992. The Finnish Meteorological Institute during the same period launched regularly three Radiosondes per day, and three Ozone sondes per week. Both Mt. Pinatubo aerosols and Polar Stratospheric Clouds were measured. The use of four wavelengths, respectively at 355 nm, 532 nm , 750 nm, and 850 nm permits an inversion of the lidar data to determine aerosol particle size. The depolarization technique permits the identification of Polar Stratospheric Clouds. Frequent correlation between Ozone minima and peaks in the Mt. Pinatubo aerosol maxima were detected. Measurements were carried out both within and outside the Polar Vortex.

Stefanutti, L.; Castagnoli, F.; Delguasta, M.; Flesia, C.; Godin, S.; Kolenda, J.; Kneipp, H.; Kyro, Esko; Matthey, R.; Morandi, M.

1994-01-01

146

Modeling urban LIDAR point clouds with combined 2D TIN and 3D tetrahedron structure  

NASA Astrophysics Data System (ADS)

This paper presents our research on exploring the combined 2D TIN and 3D Tetrahedra structure to quickly model large-range Urban LIDAR point clouds for 3D visualization purpose. To this end, Morphological grayscale reconstruction is first implemented to segment LIDAR point clouds into terrain and non-terrain regions. After that, segmented Lidar terrain points are modeled with Constrained Delaunay Triangulation under constrain of building boundary as well as non-terrain points are modeled with Power Crust algorithm to obtain reconstructed building surface. Next, two kinds of model are combined based on shared building boundary. Finally, 3D visualization of selected urban area with presented technique clearly demonstrates higherefficiency. Valuable conclusions are given as well.

Wu, Jun; Liao, Honggang; Chen, Menmen; Peng, Zhiyong

2013-10-01

147

High-precision DEM reconstruction based on airborne LiDAR point clouds  

NASA Astrophysics Data System (ADS)

Airborne LiDAR point clouds have become important data sources for DEM generation recently; however the problem of low precision and low efficiency in DEM production still exists. This paper proposes a new technical scheme for high-precision DEM production based on airborne LiDAR point clouds systematically. Firstly, an elevation and density analysis method is applied to filter out outliers. Secondly, ground points are detected by an improved filter algorithm based on the hierarchical smoothing method. Finally, feature lines are extracted by the planar surface fitting and intersecting method, and a simple data structure of feature lines preserved DEM is proposed to achieve reconstructing high accuracy DEM, combing feature lines with ground points. Experimental results show that the proposed scheme is able to compensate for deficiencies of existing DEM reconstruction techniques and can meet the needs of high precision DEM production based on LiDAR data.

Xu, Jingzhong; Kou, Yuan; Wang, Jun

2014-05-01

148

Backscattered signal modulation and emitting module design for a cloud lidar  

NASA Astrophysics Data System (ADS)

The cloud lidar, with the character of high precision and good stability, is an effective way to detect the cloud height. Pulse diode laser (PLD), as an essential part of the lidar system, needs the triggering pulse. In this paper, the emitting part of the lidar is studied - including the simulation of the backscatter SNR, the choose of the PLD and the design of trigging circuit to drive the 905nm PLD with the consideration of the optical system. A circuit for trigging the laser pulse with adjustable power and pulse width is contrived. Then the software Systemview is used to emulate the design and finally the making of PCB is finished. The results show whatever the parameters of the pulse, namely trigging pulse width, the rising edge, dithering , all these can be qualified to be in use in the practice and enjoys the merits of the low cost and convenience. The emitting module operates well.

Shu, Xiaowen; Chen, Zhenyi; Lian, Xu; Jin, Hui; Zhang, Xiaofu

2014-02-01

149

DC-8 Scanning Lidar Characterization of Aircraft Contrails and Cirrus Clouds  

NASA Technical Reports Server (NTRS)

An angular-scanning large-aperture (36 cm) backscatter lidar was developed and deployed on the NASA DC-8 research aircraft as part of the SUCCESS (Subsonic Aircraft: Contrail and Cloud Effects Special Study) program. The lidar viewing direction could be scanned continuously during aircraft flight from vertically upward to forward to vertically downward, or the viewing could be at fixed angles. Real-time pictorial displays generated from the lidar signatures were broadcast on the DC-8 video network and used to locate clouds and contrails above, ahead of, and below the DC-8 to depict their spatial structure and to help select DC-8 altitudes for achieving optimum sampling by onboard in situ sensors. Several lidar receiver systems and real-time data displays were evaluated to help extend in situ data into vertical dimensions and to help establish possible lidar configurations and applications on future missions. Digital lidar signatures were recorded on 8 mm Exabyte tape and generated real-time displays were recorded on 8mm video tape. The digital records were transcribed in a common format to compact disks to facilitate data analysis and delivery to SUCCESS participants. Data selected from the real-time display video recordings were processed for publication-quality displays incorporating several standard lidar data corrections. Data examples are presented that illustrate: (1) correlation with particulate, gas, and radiometric measurements made by onboard sensors, (2) discrimination and identification between contrails observed by onboard sensors, (3) high-altitude (13 km) scattering layer that exhibits greatly enhanced vertical backscatter relative to off-vertical backscatter, and (4) mapping of vertical distributions of individual precipitating ice crystals and their capture by cloud layers. An angular scan plotting program was developed that accounts for DC-8 pitch and velocity.

Uthe, Edward E.; Nielsen, Norman B.; Oseberg, Terje E.

1998-01-01

150

A four-wavelength depolarization backscattering LIDAR for polar stratospheric cloud monitoring  

Microsoft Academic Search

A four wavelength backscattering depolarization LIDAR designed for polar stratospheric cloud and stratospheric aerosol measurement is described. The system uses the following wavelengths: 355 nm, 532 nm, 750 nm, and 850 nm. These wavelengths, obtained by means of the third- and second-harmonic of a Nd: YAG laser and by means of a tunable Ti: Sapphire laser, are chosen in a

L. Stefanutti; F. Castagnoli; M. Del Guasta; M. Morandi; V. M. Sacco; V. Venturi; L. Zuccagnoli; J. Kolenda; H. Kneipp; P. Rairoux; B. Stein; D. Weidauer; J. P. Wolf

1992-01-01

151

A method of deriving features of building from LIDAR point clouds in urban area  

Microsoft Academic Search

This research paper aims at extracting features, especially the plane feature, of building from Light Detection And Ranging (LiDAR) point clouds in Urban Area, and with these features and information to build the model of object. Unlike modeling object in other fields, such as reverse engineering, surfaces of building usually consist of abundant big and plane surfaces which are significant

Weian Wang; Bo Zheng; Jue Lu; Jiao Lu; Yi Liu

2009-01-01

152

Efficient segmentation of 3D LIDAR point clouds handling partial occlusion  

Microsoft Academic Search

This paper presents a novel approach to segmen- tation of a dense 3D point cloud, generated by a flash lidar type camera. Incorporating symmetries of the sensor, the algorithm is using a 2D grid approach to cluster data points and extrude object segments in complex scenes. The data representation allows for the handling of partially occluded, but connected objects at

Jan Aue; Dirk Langer; Bernhard Muller-Bessler; Burkhard Huhnke

2011-01-01

153

Analysis of airborne Doppler lidar, Doppler radar and tall tower measurements of atmospheric flows in quiescent and stormy weather  

NASA Technical Reports Server (NTRS)

The first experiment to combine airborne Doppler Lidar and ground-based dual Doppler Radar measurements of wind to detail the lower tropospheric flows in quiescent and stormy weather was conducted in central Oklahoma during four days in June-July 1981. Data from these unique remote sensing instruments, coupled with data from conventional in-situ facilities, i.e., 500-m meteorological tower, rawinsonde, and surface based sensors, were analyzed to enhance understanding of wind, waves and turbulence. The purposes of the study were to: (1) compare winds mapped by ground-based dual Doppler radars, airborne Doppler lidar, and anemometers on a tower; (2) compare measured atmospheric boundary layer flow with flows predicted by theoretical models; (3) investigate the kinematic structure of air mass boundaries that precede the development of severe storms; and (4) study the kinematic structure of thunderstorm phenomena (downdrafts, gust fronts, etc.) that produce wind shear and turbulence hazardous to aircraft operations. The report consists of three parts: Part 1, Intercomparison of Wind Data from Airborne Lidar, Ground-Based Radars and Instrumented 444 m Tower; Part 2, The Structure of the Convective Atmospheric Boundary Layer as Revealed by Lidar and Doppler Radars; and Part 3, Doppler Lidar Observations in Thunderstorm Environments.

Bluestein, H. B.; Doviak, R. J.; Eilts, M. D.; Mccaul, E. W.; Rabin, R.; Sundara-Rajan, A.; Zrnic, D. S.

1986-01-01

154

ETO lidar studies of cirrostratus altocumulogenitus: Another role for supercooled liquid water in cirrus cloud formation  

NASA Technical Reports Server (NTRS)

Cirrus clouds have traditionally been viewed as cold, wispy, or stratiform ice clouds, typically displaying optical phenomena such as haloes. A composition entirely of hexagonal ice crystals, of one habit or another could only have a transitory existence in cirrus, since the concentrations of ice nuclei (IN) measured by various techniques (at the surface or in the lower troposphere) indicate an enormous number of IN that should be active at cirrus cloud temperatures. In light of recent instrumental aircraft and polarization lidar studies of cirrus clouds, it is clear that highly supercooled cloud droplets can sometimes be a component of cirrus clouds. It remains to be determined if supercooled liquid water (SLW) is present abundantly enough in cirrus to play a significant role in earth's radiance balance, or is merely a curious, infrequent occurrence. To help evaluate this issue, the UH polarization lidar FIRE Extended Time Observation (ETO) of cirrus clouds are being utilized to compile, among other parameters, a climatological record of SLW clouds associated with and within cirrus.

Sassen, Kenneth

1990-01-01

155

Retrieval of ice cloud microphysical parameters using the CloudSat millimeter-wave radar and temperature  

Microsoft Academic Search

A new remote sensing retrieval of ice cloud microphysics has been developed for use with millimeter-wave radar from ground-, air-, or space-based sensors. Developed from an earlier retrieval that used measurements of radar reflectivity factor together with a priori information about the likely cloud targets, the new retrieval includes temperature information as well to assist in determining the correct region

Richard T. Austin; Andrew J. Heymsfield; Graeme L. Stephens

2009-01-01

156

A 95 GHz airborne cloud radar: Statistics of cloud reflectivity and analysis of beam-filling errors for a proposed spaceborn cloud radar  

NASA Astrophysics Data System (ADS)

The Microwave Remote Sensing Laboratory (MIRSL) at the University of Massachusetts, in collaboration with The Jet Propulsion Laboratory, has developed a new radar designed to facilitate measurements of the radiative properties of clouds. Details of this new design are described with particular emphasis on improvements from previous systems. This radar system was used to collect cloud data during three experiment campaigns. During these experiments, reflectivity data from all prevalent cloud types were collected over a wide range of geographical locations. The observations were then used to examine the reflectivity vs. altitude and temperature characteristics and layer structure for various types of cloud complexes. To increase the representation of tropical cirrus clouds in the composite data set, the airborne data was supplemented with data from MCTEX collected by the UMass CPRS radar. All observations were classified into four classes of clouds and histograms of altitude and temperature vs. reflectivity were used to demonstrate the reflectivity characteristics of various clouds types. Statistics of layer base and top altitudes, thickness and number of layers were also computed. Also, the relationship between cirrus cloud thickness, reflectivity and ice water path (IWP) is examined. The data sets from the four experiments were then used to address performance issues for a spaceborne radar. The problem of cloud detectability is discussed and an analysis of the ice water content (IWC) estimation error resulting from spatial inhomogeneity is presented. The fraction of clouds thinner than one range gate of the CloudSat radar was found to be 14% for all data sets combined. The data sets are used to simulate satellite radar pixels and the distributions of errors in IWC estimates due to inhomogeneity are calculated. On average, 40% of the pixels were partially filled and the relative IWC error was 24%. The distribution of the relative errors vs. IWC values indicated that the largest relative error occurred at vary small values of IWC and the mean error for all experiments was only 15% for IWC values larger than 10 -3 gm3.

Sadowy, Gregory A.

1999-11-01

157

Global Monitoring of Clouds and Aerosols Using a Network of Micro-Pulse Lidar Systems  

NASA Technical Reports Server (NTRS)

Long-term global radiation programs, such as AERONET and BSRN, have shown success in monitoring column averaged cloud and aerosol optical properties. Little attention has been focused on global measurements of vertically resolved optical properties. Lidar systems are the preferred instrument for such measurements. However, global usage of lidar systems has not been achieved because of limits imposed by older systems that were large, expensive, and logistically difficult to use in the field. Small, eye-safe, and autonomous lidar systems are now currently available and overcome problems associated with older systems. The first such lidar to be developed is the Micro-pulse lidar System (MPL). The MPL has proven to be useful in the field because it can be automated, runs continuously (day and night), is eye-safe, can easily be transported and set up, and has a small field-of-view which removes multiple scattering concerns. We have developed successful protocols to operate and calibrate MPL systems. We have also developed a data analysis algorithm that produces data products such as cloud and aerosol layer heights, optical depths, extinction profiles, and the extinction-backscatter ratio. The algorithm minimizes the use of a priori assumptions and also produces error bars for all data products. Here we present an overview of our MPL protocols and data analysis techniques. We also discuss the ongoing construction of a global MPL network in conjunction with the AERONET program. Finally, we present some early results from the MPL network.

Welton, Ellsworth J.; Campbell, James R.; Spinhirne, James D.; Scott, V. Stanley

2000-01-01

158

First results of combined Fe-lidar/Radar measurements at Davis, 69° S.  

NASA Astrophysics Data System (ADS)

The mobile scanning Fe-lidar of the IAP-Kühlungsborn was moved to Davis, Antarctica, 69° S, 78° E during November 2010. This location was chosen because PMSE/NLC observations by MST-radar/RMR-lidar have been performed since 2003/2001 by the Australian Antarctic Division. Davis is the only station in Antarctica where comparable long-term observations to Alomar, 69° N are available. A comparison of both locations allows a detailed comparison of differences or similarities between the northern (NH) / southern hemisphere (SH) at mesopause altitudes. The Fe-lidar is a two wavelength system which measures Doppler temperature/vertical wind and iron densities by resonance scattering at 386 nm. The fundamental wavelength at 772 nm is used for aerosol measurements from the stratosphere to the mesosphere including NLC in summer or PSC in winter. Measurements are almost background free which allows year round operation independent of sunlight. At Davis the lidar was in operation 24% of the first year (2150 hours) which has not been achieved elsewhere with a mesospheric lidar. This unusual and already largest lidar data base of Antarctica shows the thermal structure of the mesopause region and the iron layer in great detail. Strong tides throughout the year have been observed and a link of the early part of the PMSE season to the stratospheric vortex has been found. More than 700 hours of temperature observation during the PMSE-season are compared with common volume PMSE/NLC observations. For the first time temperature and vertical wind measurements through PMSE and NLC have been achieved by a lidar showing that the SH in particular in December/January differs significantly from the NH in June/July. The temperature measurements near 86 km altitude show that the summer mesopause is surprisingly similar to the NH at PMSE altitudes but differs significantly at higher altitudes. Unlike the NH the southern mesopause altitude changes throughout the season by several kilometres. Depending on altitude temperatures can be warmer but also much colder than at the NH causing a change in PMSE altitude over the season.

Höffner, J.; Morris, R. J.; Kaifler, B.; Viehl, T.; Lübken, F.-J.

2012-04-01

159

Validation of aerosol and cloud layer structures from the space-borne lidar CALIOP using a ground-based lidar in Seoul, Korea  

NASA Astrophysics Data System (ADS)

We present initial validation results of the space-borne lidar CALIOP onboard CALIPSO satellite using coincidental observations from a ground-based lidar in Seoul National University (SNU), Seoul, Korea (37.46° N, 126.95° E). We analyze six selected cases between September 2006 and February 2007, including 3 daytime and 3 night-time observations and covering different types of clear and cloudy atmospheric conditions. Apparent scattering ratios calculated from the two lidar measurements of total attenuated backscatter at 532 nm show similar aerosol and cloud layer structures both under cloud-free conditions and in cases of multiple aerosol layers underlying semi-transparent cirrus clouds. Agreement on top and base heights of cloud and aerosol layers is generally within 0.10 km, particularly during night-time. This result confirms that the CALIPSO science team algorithms for the discrimination of cloud and aerosol as well as for the detection of layer top and base altitude provide reliable information in such atmospheric conditions. This accuracy of the planetary boundary layer top height under cirrus cloud appears, however, limited during daytime. Under thick cloud conditions, however, information on the cloud top (bottom) height only is reliable from CALIOP (ground-based lidar) due to strong signal attenuations. However, simultaneous space-borne CALIOP and ground-based SNU lidar (SNU-L) measurements complement each other and can be combined to provide full information on the vertical distribution of aerosols and clouds. An aerosol backscatter-to-extinction ratio (BER) estimated from lidar and sunphotometer synergy at the SNU site during the CALIOP overpass is assessed to be 0.023±0.004 sr-1 (i.e. a lidar ratio of 43.2±6.2 sr) from CALIOP and 0.027±0.006 sr-1 (37.4±7.2 sr) from SNU-L. For aerosols within the planetary boundary layer under cloud-free conditions, the aerosol extinction profiles from both lidars are in agreement within about 0.02 km-1. Under semi-transparent cirrus clouds, such profiles also show good agreement for the night-time CALIOP flight, but large discrepancies are found for the daytime flights due to a small signal-to-noise ratio of the CALIOP data.

Kim, S.-W.; Berthier, S.; Raut, J.-C.; Chazette, P.; Dulac, F.; Yoon, S.-C.

2008-07-01

160

Depolarization ratio and attenuated backscatter for nine cloud types: analyses based on collocated CALIPSO lidar and MODIS measurements.  

PubMed

This paper reports on the relationship between lidar backscatter and the corresponding depolarization ratio for nine types of cloud systems. The data used in this study are the lidar returns measured by the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) aboard the Cloud- Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite and the collocated cloud products derived from the observations made by the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard Aqua satellite. Specifically, the operational MODIS cloud optical thickness and cloud-top pressure products are used to classify cloud types on the basis of the International Satellite Cloud Climatology Project (ISCCP) cloud classification scheme. While the CALIPSO observations provide information for up to 10 cloud layers, in the present study only the uppermost clouds are considered. The layer-averaged attenuated backscatter (gamma') and layer-averaged depolarization ratio (delta) from the CALIPSO measurements show both water- and ice-phase features for global cirrus, cirrostratus, and deep convective cloud classes. Furthermore, we screen both the MODIS and CALIPSO data to eliminate cases in which CALIPSO detected two- or multi-layered clouds. It is shown that low gamma' values corresponding to uppermost thin clouds are largely eliminated in the CALIPSO delta-gamma' relationship for single-layered clouds. For mid-latitude and polar regions corresponding, respectively, to latitude belts 30 degrees -60 degrees and 60 degrees -90 degrees in both the hemispheres, a mixture of water and ice is also observed in the case of the altostratus class. MODIS cloud phase flags are also used to screen ice clouds. The resultant water clouds flagged by the MODIS algorithm show only water phase feature in the delta-gamma' relation observed by CALIOP; however, in the case of the ice clouds flagged by the MODIS algorithm, the co-existence of ice- and water-phase clouds is still observed in the CALIPSO delta-gamma' relationship. PMID:18542490

Cho, Hyoun-Myoung; Yang, Ping; Kattawar, George W; Nasiri, Shaima L; Hu, Yongxiang; Minnis, Patrick; Trepte, Charles; Winker, David

2008-03-17

161

Improved Boundary Layer and Cloud Heights from the NASA Micro Pulse Lidar Network (MPLNET)  

NASA Astrophysics Data System (ADS)

The NASA Micro Pulse Lidar Network (MPLNET) Level 1.5b data product provides identification of aerosol and cloud layers. New algorithms have been developed for determining planetary boundary layer (PBL) heights and cloud heights from MPLNET data. An overview of the new methods will be discussed, along with their advantages and limitations. Seasonal and diurnal trends observed at the Goddard Space Flight Center site in Greenbelt, MD will also be evaluated. Results from the improved algorithms are compared to the current operational MPLNET cloud and PBL height products as well as the corresponding products from the GEOS-5 model.

Lewis, J.; Welton, E. J.; Belcher, L. R.; Mplnet Team

2011-12-01

162

CALIPSO: Global Aerosol and Cloud Observations from Lidar and Passive Instruments  

NASA Technical Reports Server (NTRS)

CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Spaceborne Observations) is an approved satellite mission being developed through collaboration between NASA and the French space agency CNES. The mission is scheduled for launch in 2004 and will operate for 3 years as part of a five-satellite formation called the Aqua constellation. This constellation will provide a unique data set on aerosol and cloud optical and physical properties and aerosol-cloud interactions that will substantially increase our understanding of the climate system and the potential for climate change.

Poole, L. R.; Winker, D. M.; Pelon, J. R.; McCormick, M. P.

2002-01-01

163

Lidar retrievals of cloud droplet number concentration at the cumulus base: A feasibility study  

NASA Astrophysics Data System (ADS)

The properties of atmospheric aerosol under a cumulus base were studied using three-wavelength lidar. A growth of hygroscopic aerosol particles in a convective updraft and the activation of cloud condensation nuclei (CCN) were observed. A simple and robust model of droplet formation in a rising parcel was used as a closing assumption to the original approach of cloud droplet number concentration (CDNC) retrieval. The potential to retrieve the vertical profile of the effective radius of droplets near the cloud base and the height of activation and condensation of nuclei is demonstrated.

Stacewicz, T.; Posyniak, M.; Sitarek, S.; Malinowski, S. P.

2014-06-01

164

An approach to DSM refinement with fusion of airborne lidar point cloud data and optical imagery  

NASA Astrophysics Data System (ADS)

The airborne LiDAR system, which usually integrated with optical camera, is an efficient way of acquiring 3D geographic information and enjoys widely application in building DSM. However, when the airborne LiDAR is used in urban area, where there are a large amount of tall buildings, the characteristic points of buildings are seldom measured and the measured points are frequently too sparse to create precise building models. In this paper, an approach to DSM refining DSM in urban area with fusion of airborne LiDAR point cloud data and optical imagery is put forward. Firstly, the geometric relationship between the airborne LiDAR point and the correspondent pixel on the image synchronously taken by optical camera is analyzed. The relative position and attitude parameters between the laser rangefinder and the camera are determined in the process of alignment and calibration. Secondly, the building roof edges on the optical image are extracted by edge detection. By tracing the building roof edges, the contours of building roofs in vector format are acquired and the characteristic points of buildings are further extracted. Thirdly, all the LiDAR measured points on the roof of specific building are separated from the point cloud data by judging the geometric relation between LiDAR measured points and the building outline, which is represented by a polygon, according to their plane coordinates. Finally, the DSM refinement for buildings can be implemented. All pixels representing the building roof are given heights as same as that of nearer LiDAR point inside the polygon. Ortho-photo map and virtual building models of urban area with higher quality can be reached with the refined DSM and optical images.

Hao, Xiangyang; Zhang, Weiqiang; Jiang, Lixing

2013-05-01

165

Comparisons of Aerosol-Cloud Observations Between a Ground-based Raman-Mie Lidar and CALIPSO  

NASA Astrophysics Data System (ADS)

Global vertical profiles of aerosol and cloud are currently being observed by satellite CALIPSO. Based on the inherent properties of elastic-scattering lidar, the lidar ratio (extinction-to-backscatter ratio) becomes very important to quantitatively retrieve the distribution of aerosol/cloud extinction or backscatter coefficient. In this presentation, we examine the feasibility of using MODIS-retrieved aerosol optical depth over ocean to constrain the aerosol lidar ratio in the CALIPSO retrieval of aerosol extinction profile with Fernald algorithm, and then compare these lidar-ratios to those derived from both column measurements by the CIMEL Sunphotometer and a combination of the ground-based lidar and radiometer. We explore the variability of lidar ratios for the different types of aerosol over the US east coast. In addition, we present our validation measurements for aerosol vertical profiles. So far, 13 near simultaneous observations by our ground-based multi-wavelength Raman-Mie lidar which operated in New York City (40.821N, 73.949W), have been obtained together with other supporting measurements. In particular, comparisons of aerosol extinction profiles are performed between the ground- based lidar and CALIPSO observations and the vertical distribution of smoke plumes, aloft aerosol layer, urban aerosol and PBL height are presented and compared. Retrievals of optically thin clouds heights and optical depth in the low- and high-altitude from CALIPSO and MODIS/Aqua, respectively, are examined with respect to ground- based lidar measurements and several biases in the measurements are presented.

Wu, Y.; Chaw, S.; Gross, B.; Charles, L.; Vladutescu, V.; Cao, N.; Moshary, F.; Ahmed, S.

2007-12-01

166

A Assessment of the Effects of Cloud Inhomogeneity on Ice Cloud Radiative Properties  

Microsoft Academic Search

This research focuses on understanding and quantifying the effects of microphysics and cloud inhomogeneity on the radiative properties of cirrus clouds. The Spherical Harmonic Spatial Grid method of radiative transfer is used to simulate the radiances and fluxes of two-dimensional (2D) cirrus cloud fields. Two types of 2D cloud fields are inferred from ground based radar and lidar measurements; one

Paul Wesley Stackhouse Jr.

1995-01-01

167

Effects of Cloud on Goddard Lidar Observatory for Wind (GLOW) Performance and Analysis of Associated Errors  

NASA Astrophysics Data System (ADS)

The Goddard Lidar Observatory for Wind (GLOW), a mobile direct detection Doppler LIDAR based on molecular backscattering for measurement of wind in the troposphere and lower stratosphere region of atmosphere is operated and its errors characterized. It was operated at Howard University Beltsville Center for Climate Observation System (BCCOS) side by side with other operating instruments: the NASA/Langely Research Center Validation Lidar (VALIDAR), Leosphere WLS70, and other standard wind sensing instruments. The performance of Goddard Lidar Observatory for Wind (GLOW) is presented for various optical thicknesses of cloud conditions. It was also compared to VALIDAR under various conditions. These conditions include clear and cloudy sky regions. The performance degradation due to the presence of cirrus clouds is quantified by comparing the wind speed error to cloud thickness. The cloud thickness is quantified in terms of aerosol backscatter ratio (ASR) and cloud optical depth (COD). ASR and COD are determined from Howard University Raman Lidar (HURL) operating at the same station as GLOW. The wind speed error of GLOW was correlated with COD and aerosol backscatter ratio (ASR) which are determined from HURL data. The correlation related in a weak linear relationship. Finally, the wind speed measurements of GLOW were corrected using the quantitative relation from the correlation relations. Using ASR reduced the GLOW wind error from 19% to 8% in a thin cirrus cloud and from 58% to 28% in a relatively thick cloud. After correcting for cloud induced error, the remaining error is due to shot noise and atmospheric variability. Shot-noise error is the statistical random error of backscattered photons detected by photon multiplier tube (PMT) can only be minimized by averaging large number of data recorded. The atmospheric backscatter measured by GLOW along its line-of-sight direction is also used to analyze error due to atmospheric variability within the volume of measurement. GLOW scans in five different directions (vertical and at elevation angles of 45° in north, south, east, and west) to generate wind profiles. The non-uniformity of the atmosphere in all scanning directions is a factor contributing to the measurement error of GLOW. The atmospheric variability in the scanning region leads to difference in the intensity of backscattered signals for scanning directions. Taking the ratio of the north (east) to south (west) and comparing the statistical differences lead to a weak linear relation between atmospheric variability and line-of-sights wind speed differences. This relation was used to make correction which reduced by about 50%.

Bacha, Tulu

168

The eyesafe visioceilometer - A tactical visibility and cloud height lidar  

NASA Astrophysics Data System (ADS)

A recent breakthrough in the mathematical solution to the lidar equation combined with state-of-the-art microelectronics has made it possible to produce the first portable ceiling, visibility, and rangefinding device suitable for tactical use by the U.S. Army. The signal processor of the former XE-2 (Nd:YAG) can be adapted to an eyesafe unit by making use of an erbium glass laser and a GaInAs PIN photodiode detector. It is pointed out that the XE-3 (Eyesafe Visioceilometer) provides tactical real-time data when and where the user needs it, with an accuracy superior to existing nonportable runway equipment. Attention is given to system evolution, lidar theory, the relationship of backscattering and extinction coefficients, a system description, the transient recorder, the analysis of data, and details regarding tactical applications.

Barnes, E. S.; Lentz, W. J.

169

Predicting Biomass in Temperate Hardwood and Mixed Forests Using VHF Radar, Interferometric SAR and Discrete-Return Lidar Data  

NASA Astrophysics Data System (ADS)

Our working hypothesis is that biomass models derived from radar variables or radar-lidar synergy will provide greater accuracy in hardwood and mixed forests than those derived using lidar variables only. To provide the data to test this hypothesis, BioSAR, profiling lidar (PALS), imaging lidar, GeoSAR, and field data were collected over hardwood and mixed forests of Appomattox-Buckingham State Forest, Virginia, USA in 2007 and 2008. We are evaluating BioSAR, GeoSAR and lidar data for their ability to provide reliable biomass estimates both individually and collectively. Lidar derived variables include canopy height, crown diameter, and distributional parameters (mean, standard deviation, percentiles, etc.). GeoSAR variables include the canopy height model produced by differencing the X- and P-band interferometric heights. The BioSAR variables consist of the cross-sectional areas from six different frequencies. Field data consist of a network of 64 fixed plots and 256 variable radius plots on which standard forest measurements were made. Both parametric (best subsets regression) and non-parametric (regression tree) approaches are being used for variable selection and model evaluation.

Banskota, A.; Wynne, R.; Thomas, V.; Kayastha, N.; Peduzzi, A.

2008-12-01

170

Raman Lidar Measurements of Water Vapor and Cirrus Clouds During the Passage of Hurricane Bonnie  

NASA Technical Reports Server (NTRS)

The NASA/GSFC Scanning Raman Lidar (SRL) was stationed on Andros Island in the Bahamas during August - September, 1998 as a part of the third Convection and Moisture Experiment (CAMEX-3) which focussed on hurricane development and tracking. During the period August 21 - 24, hurricane Bonnie passed near Andros Island and influenced the water vapor and cirrus cloud measurements acquired by the SRL. Two drying signatures related to the hurricane were recorded by the SRL (Scanning Raman Lidar) and other sensors. Cirrus cloud optical depths (at 351 nm) were also measured during this period. Optical depth values ranged from approximately 0.01 to 1.4. The influence of multiple scattering on these optical depth measurements was studied with the conclusion that the measured values of optical depth are less than the actual value by up to 20% . The UV/IR cirrus cloud optical depth ratio was estimated based on a comparison of lidar and GOES measurements. Simple radiative transfer model calculations compared with GOES satellite brightness temperatures indicate that satellite radiances are significantly affected by the presence of cirrus clouds if IR optical depths are approximately 0.02 or greater. This has implications for satellite cirrus detection requirements.

Whiteman, D. N.; Evans, K. D.; Demoz, B.; Starr, D. OC; Tobin, D.; Feltz, W.; Jedlovec, G. J.; Gutman, S. I.; Schwemmer, G. K.; Cardirola, M.; Melfi, S. H.; Schmidlin, F. J.

2000-01-01

171

Eigen-feature analysis of weighted covariance matrices for LiDAR point cloud classification  

NASA Astrophysics Data System (ADS)

The features used in the separation of different objects are important for successful point cloud classification. Eigen-features from a covariance matrix of a point set with the sample mean are commonly used geometric features that can describe the local geometric characteristics of a point cloud and indicate whether the local geometry is linear, planar, or spherical. However, eigen-features calculated by the principal component analysis of a covariance matrix are sensitive to LiDAR data with inherent noise and incomplete shapes because of the non-robust statistical analysis. To obtain reliable eigen-features from LiDAR data and to improve classification accuracy, we introduce a method of analyzing local geometric characteristics of a point cloud by using a weighted covariance matrix with a geometric median. Each point is assigned a weight to represent its spatial contribution in the weighted principal component analysis and to estimate the geometric median which can be regarded as a localized center of a shape. In the experiments, qualitative and quantitative analyses on airborne LiDAR data and simulated point clouds show a clear improvement of the proposed method compared with the standard eigen-features. The classification accuracy is improved by 1.6-4.5% using a supervised classifier.

Lin, Chao-Hung; Chen, Jyun-Yuan; Su, Po-Lin; Chen, Chung-Hao

2014-08-01

172

Registration of ground?based LiDAR point clouds by means of 3D line features  

Microsoft Academic Search

Techniques for extracting data from LiDAR point clouds can be refined for increased accuracy. In this paper, the authors elaborate on an innovative approach for registering ground?based LiDAR point clouds using overlapping scans based on 3D line features. The proposed working scheme consists of three major kernels: a 3D line feature extractor, a 3D line feature matching mechanism, and a

2008-01-01

173

Comparisons of Aerosol-Cloud Observations Between a Ground-based Raman-Mie Lidar and CALIPSO  

Microsoft Academic Search

Global vertical profiles of aerosol and cloud are currently being observed by satellite CALIPSO. Based on the inherent properties of elastic-scattering lidar, the lidar ratio (extinction-to-backscatter ratio) becomes very important to quantitatively retrieve the distribution of aerosol\\/cloud extinction or backscatter coefficient. In this presentation, we examine the feasibility of using MODIS-retrieved aerosol optical depth over ocean to constrain the aerosol

Y. Wu; S. Chaw; B. Gross; L. Charles; V. Vladutescu; N. Cao; F. Moshary; S. Ahmed

2007-01-01

174

Remote sensing of vegetation 3-D structure for biodiversity and habitat: Review and implications for lidar and radar spaceborne missions  

NASA Astrophysics Data System (ADS)

Biodiversity and habitat face increasing pressures due to human and natural influences that alter vegetation structure. Because of the inherent difficulty of measuring forested vegetation three-dimensional (3-D) structure on the ground, this important component of biodiversity and habitat has been, until recently, largely restricted to local measurements, or at larger scales to generalizations. New lidar and radar remote sensing instruments such as those proposed for spaceborne missions will provide the capability to fill this gap. This paper reviews the state of the art for incorporatinginformation on vegetation 3-D structure into biodiversity and habitat science and management approaches, with emphasis on use of lidar and radar data. First we review relationships between vegetation 3-D structure, biodiversity and habitat, and metrics commonly used to describe those relationships. Next, we review the technical capabilities of new lidar and radar sensors and their application to biodiversity and habitat studies to date. We then define variables that have been identified as both useful and feasible to retrieve from spaceborne lidar and radar observations and provide their accuracy and precision requirements. We conclude with a brief discussion of implications for spaceborne missions and research programs. The possibility to derive vegetation 3-D measurements from spaceborne active sensors and to integrate them into science and management comes at a critical juncture for global biodiversity conservation and opens new possibilities for advanced scientific analysis of habitat and biodiversity.

Bergen, K. M.; Goetz, S. J.; Dubayah, R. O.; Henebry, G. M.; Hunsaker, C. T.; Imhoff, M. L.; Nelson, R. F.; Parker, G. G.; Radeloff, V. C.

2009-06-01

175

Arctic Mixed-Phase Cloud Properties from AERI Lidar Observations: Algorithm and Results from SHEBA  

SciTech Connect

A new approach to retrieve microphysical properties from mixed-phase Arctic clouds is presented. This mixed-phase cloud property retrieval algorithm (MIXCRA) retrieves cloud optical depth, ice fraction, and the effective radius of the water and ice particles from ground-based, high-resolution infrared radiance and lidar cloud boundary observations. The theoretical basis for this technique is that the absorption coefficient of ice is greater than that of liquid water from 10 to 13 ?m, whereas liquid water is more absorbing than ice from 16 to 25 ?m. MIXCRA retrievals are only valid for optically thin (?visible < 6) single-layer clouds when the precipitable water vapor is less than 1 cm. MIXCRA was applied to the Atmospheric Emitted Radiance Interferometer (AERI) data that were collected during the Surface Heat Budget of the Arctic Ocean (SHEBA) experiment from November 1997 to May 1998, where 63% of all of the cloudy scenes above the SHEBA site met this specification. The retrieval determined that approximately 48% of these clouds were mixed phase and that a significant number of clouds (during all 7 months) contained liquid water, even for cloud temperatures as low as 240 K. The retrieved distributions of effective radii for water and ice particles in single-phase clouds are shown to be different than the effective radii in mixed-phase clouds.

Turner, David D.

2005-04-01

176

Raman Lidar Measurements of Water Vapor and Cirrus Clouds During The Passage of Hurricane Bonnie  

NASA Technical Reports Server (NTRS)

The NASA/GSFC Scanning Raman Lidar (SRL) was stationed on Andros Island in the Bahamas during August - September, 1998 as a part of the third Convection and Moisture Experiment (CAMEX-3) which focussed on hurricane development and tracking. During the period August 21 - 24, hurricane Bonnie passed near Andros Island and influenced the water vapor and cirrus cloud measurements acquired by the SRL. Two drying signatures related to the hurricane were recorded by the SRL and other sensors. Cirrus cloud optical depths (at 351 nm) were also measured during this period. Optical depth values ranged from less than 0.01 to 1.5. The influence of multiple scattering on these optical depth measurements was studied. A correction technique is presented which minimizes the influences of multiple scattering and derives information about cirrus cloud optical and physical properties. The UV/IR cirrus cloud optical depth ratio was estimated based on a comparison of lidar and GOES measurements. Simple radiative transfer model calculations compared with GOES satellite brightness temperatures indicate that satellite radiances are significantly affected by the presence of cirrus clouds if IR optical depths are approximately 0.005 or greater. Using the ISCCP detection threshold for cirrus clouds on the GOES data presented here, a high bias of up to 40% in the GOES precipitable water retrieval was found.

Whiteman, D. N.; Evans, K. D.; Demoz, B.; Starr, D OC.; Eloranta, E. W.; Tobin, D.; Feltz, W.; Jedlovec, G. J.; Gutman, S. I.; Schwemmer, G. K.; Smith, David E. (Technical Monitor)

2000-01-01

177

Lidar Investigation of Tropical Nocturnal Boundary Layer Aerosols and Cloud Macrophysics  

SciTech Connect

Observational evidence of two-way association between nocturnal boundary layer aerosols and cloud macrophysical properties under different meteorological conditions is reported in this paper. The study has been conducted during 2008-09 employing a high space-time resolution polarimetric micro-pulse lidar over a tropical urban station in India. Firstly, the study highlights the crucial role of boundary layer aerosols and background meteorology on the formation and structure of low-level stratiform clouds in the backdrop of different atmospheric stability conditions. Turbulent mixing induced by the wind shear at the station, which is associated with a complex terrain, is found to play a pivotal role in the formation and structural evolution of nocturnal boundary layer clouds. Secondly, it is shown that the trapping of energy in the form of outgoing terrestrial radiation by the overlying low-level clouds can enhance the aerosol mixing height associated with the nocturnal boundary layer. To substantiate this, the long-wave heating associated with cloud capping has been quantitatively estimated in an indirect way by employing an Advanced Research Weather Research and Forecasting (WRF-ARW) model version 2.2 developed by National Center for Atmospheric Research (NCAR), Colorado, USA, and supplementary data sets; and differentiated against other heating mechanisms. The present investigation as well establishes the potential of lidar remote-sensing technique in exploring some of the intriguing aspects of the cloud-environment relationship.

Manoj, M. G.; Devara, PC S.; Taraphdar, Sourav

2013-10-01

178

Portable standoff Raman and Mie-Rayleigh lidar for cloud, aerosol, and chemical monitoring  

NASA Astrophysics Data System (ADS)

There is a need for portable, low-cost lidar systems that can be used for cloud, aerosols and chemical monitoring from a stand-off distance. At the University of Hawaii we have developed lidar systems based on a 12.7-cm diameter telescope and a 20 Hz frequency-doubled Nd:YAG laser source. For stand off Raman detection of organic liquid and vapors, and plastic explosives, we are using a 0.25-m HoloSpec f/2.2 spectrometer equipped with a gated intensified detector (PI Model I-MAX-1024-E). The samples of interest are excited with 532-nm laser light (35 mJ/pulse). The operational range of the Raman system is in 10's of meters and has been tested at distance of 66 m. This system can also be operated as a Raman lidar by using appropriate filters for atmospheric nitrogen, oxygen and other gaseous species of interest. The Mie-Rayleigh lidar system uses the same telescope and laser, but we have three (1064, 532 and 355-nm) wavelengths available for monitoring clouds and aerosols. A small Hamamatsu H6779 photomultiplier tube (PMT) located near the focal point of telescope detects 532-nm backscatter signal. An avalanche photodiode (APD, EG & G C3095) detector equipped with a 2.5-cm diameter aspheric lens is used for detecting 1064-nm backscatter. The Mie-Rayleigh lidar has usable range of 60 - 4000 m. Results obtained with this system for marine aerosols and clouds are discussed.

Sharma, Shiv K.; Porter, John N.; Misra, Anupum K.; Hubble, Hugh W.; Menon, Premlata

2003-12-01

179

Retrieval of Polar Stratospheric Cloud Microphysical Properties from Lidar Measurements: Dependence on Particle Shape Assumptions  

NASA Technical Reports Server (NTRS)

A retrieval algorithm has been developed for the microphysical analysis of polar stratospheric cloud (PSC) optical data obtained using lidar instrumentation. The parameterization scheme of the PSC microphysical properties allows for coexistence of up to three different particle types with size-dependent shapes. The finite difference time domain (FDTD) method has been used to calculate optical properties of particles with maximum dimensions equal to or less than 2 mu m and with shapes that can be considered more representative of PSCs on the scale of individual crystals than the commonly assumed spheroids. Specifically. these are irregular and hexagonal crystals. Selection of the optical parameters that are input to the inversion algorithm is based on a potential data set such as that gathered by two of the lidars on board the NASA DC-8 during the Stratospheric Aerosol and Gas Experiment 0 p (SAGE) Ozone Loss Validation experiment (SOLVE) campaign in winter 1999/2000: the Airborne Raman Ozone and Temperature Lidar (AROTEL) and the NASA Langley Differential Absorption Lidar (DIAL). The 0 microphysical retrieval algorithm has been applied to study how particle shape assumptions affect the inversion of lidar data measured in leewave PSCs. The model simulations show that under the assumption of spheroidal particle shapes, PSC surface and volume density are systematically smaller than the FDTD-based values by, respectively, approximately 10-30% and approximately 5-23%.

Reichardt, J.; Reichardt, S.; Yang, P.; McGee, T. J.; Bhartia, P. K. (Technical Monitor)

2001-01-01

180

Automated Extraction of 3D Trees from Mobile LiDAR Point Clouds  

NASA Astrophysics Data System (ADS)

This paper presents an automated algorithm for extracting 3D trees directly from 3D mobile light detection and ranging (LiDAR) data. To reduce both computational and spatial complexities, ground points are first filtered out from a raw 3D point cloud via blockbased elevation filtering. Off-ground points are then grouped into clusters representing individual objects through Euclidean distance clustering and voxel-based normalized cut segmentation. Finally, a model-driven method is proposed to achieve the extraction of 3D trees based on a pairwise 3D shape descriptor. The proposed algorithm is tested using a set of mobile LiDAR point clouds acquired by a RIEGL VMX-450 system. The results demonstrate the feasibility and effectiveness of the proposed algorithm.

Yu, Y.; Li, J.; Guan, H.; Zai, D.; Wang, C.

2014-06-01

181

A Comparison of Simulated Cloud Radar Output from the Multiscale Modeling Framework Global Climate Model with CloudSat Cloud Radar Observations  

SciTech Connect

Over the last few years a new type of global climate model (GCM) has emerged in which a cloud-resolving model is embedded into each grid cell of a GCM. This new approach is frequently called a multiscale modeling framework (MMF) or superparameterization. In this article we present a comparison of MMF output with radar observations from the NASA CloudSat mission, which uses a near-nadir-pointing millimeter-wavelength radar to probe the vertical structure of clouds and precipitation. We account for radar detection limits by simulating the 94 GHz radar reflectivity that CloudSat would observe from the high-resolution cloud-resolving model output produced by the MMF. Overall, the MMF does a good job of reproducing the broad pattern of tropical convergence zones, subtropical belts, and midlatitude storm tracks, as well as their changes in position with the annual solar cycle. Nonetheless, the comparison also reveals a number of model shortfalls including (1) excessive hydrometeor coverage at all altitudes over many convectively active regions, (2) a lack of low-level hydrometeors over all subtropical oceanic basins, (3) excessive low-level hydrometeor coverage (principally precipitating hydrometeors) in the midlatitude storm tracks of both hemispheres during the summer season (in each hemisphere), and (4) a thin band of low-level hydrometeors in the Southern Hemisphere of the central (and at times eastern and western) Pacific in the MMF, which is not observed by CloudSat. This band resembles a second much weaker ITCZ but is restricted to low levels.

Marchand, Roger T.; Haynes, J. M.; Mace, Gerald G.; Ackerman, Thomas P.; Stephens, Graeme L.

2009-01-13

182

Cloud and Aerosol Measurements from the GLAS Polar Orbiting Lidar: First Year Results  

NASA Technical Reports Server (NTRS)

The Geoscience Laser Altimeter System (GLAS) launched in 2003 is the first polar orbiting satellite lidar. The instrument was designed for high performance observations of the distribution and optical scattering cross sections of clouds and aerosol. GLAS is approaching six months of on orbit data operation. These data from thousands of orbits illustrate the ability of space lidar to accurately and dramatically measure the height distribution of global cloud and aerosol to an unprecedented degree. There were many intended science applications of the GLAS data and significant results have already been realized. One application is the accurate height distribution and coverage of global cloud cover with one goal of defining the limitation and inaccuracies of passive retrievals. Comparison to MODIS cloud retrievals shows notable discrepancies. Initial comparisons to NOAA 14&15 satellite cloud retrievals show basic similarity in overall cloud coverage, but important differences in height distribution. Because of the especially poor performance of passive cloud retrievals in polar regions, and partly because of high orbit track densities, the GLAS measurements are by far the most accurate measurement of Arctic and Antarctica cloud cover from space to date. Global aerosol height profiling is a fundamentally new measurement from space with multiple applications. A most important aerosol application is providing input to global aerosol generation and transport models. Another is improved measurement of aerosol optical depth. Oceanic surface energy flux derivation from PBL and LCL height measurements is another application of GLAS data that is being pursued. A special area of work for GLAS data is the correction and application of multiple scattering effects. Stretching of surface return pulses in excess of 40 m from cloud propagation effects and other interesting multiple scattering phenomena have been observed. As an EOS project instrument, GLAS data products are openly available to the science community. First year results from GLAS are summarized.

Spinhirne, J. D.; Palm, S. P.; Hlavka, D. L.; Hart, W. D.; Mahesh, A.; Welton, E. J.

2004-01-01

183

Microphysical characterization of microwave Radar reflectivity due to volcanic ash clouds  

Microsoft Academic Search

Ground-based microwave radar systems can have a valuable role in volcanic ash cloud monitoring as evidenced by available radar imagery. Their use for ash cloud detection and quantitative retrieval has been so far not fully investigated. In order to do this, a forward electromagnetic model is set up and examined taking into account various operating frequencies such as S-, C-,

Frank Silvio Marzano; Gianfranco Vulpiani; William I. Rose

2006-01-01

184

Second annual progress report of the Millimeter Wave Cloud Profiling Radar System (CPRS)  

SciTech Connect

The Cloud Profiling Radar System (CPRS) is a single antenna, two frequency (33 GHz and 95 GHz) polarimetric radar which is currently under the development at the University of Massachusetts (UMASS). This system will be capable of making four dimensional Doppler and polarimetric measurements of clouds. This report gives details about the status of the various subsystems under development and discusses current research activities.

Pazmany, A.L.; Sekelsky, S.M.; McIntosh, R.E.

1992-06-07

185

Airborne lidar observation of mountain-wave-induced polar stratospheric clouds during EASOE  

Microsoft Academic Search

The airborne backscatter lidar Leandre was flown during the EASOE campaign on board the French ARAT-Fokker 27, to provide mesoscale observations of scattering layers in the stratosphere. The use of crosspolarization channels at the 532 nm laser emitted wavelength, allowed discrimination between the quasi-spherical particles of the Pinatubo aerosol and the non-spherical frozen particles of polar stratospheric clouds. Measurements taken

S. Godin; G. Mégie; C. David; D. Haner; C. Flesia; Y. Emery

1994-01-01

186

Applications of GLAS Satellite Lidar Cloud, Aerosol and PBL Measurements at High Spatial Resolution  

Microsoft Academic Search

The Geoscience Laser Altimeter System, GLAS, beginning in 2003, provides space borne lidar observations of global clouds and aerosol from polar orbit. The measurements in fall 2003 and spring 2004 include highly sensitive aerosol detection and profiling by photon counting detection at 532 nm wavelength to backscatter cross section below 10-7 1\\/m-sr. Data products from the measurements include aerosol optical

J. D. Spinhirne; S. P. Palm

2007-01-01

187

Lidar studies of interannual, seasonal, and diurnal variations of polar mesospheric clouds at the South Pole  

Microsoft Academic Search

Polar mesospheric clouds (PMC) were observed by an Fe Boltzmann temperature lidar at the South Pole in the 1999-2000 and 2000-2001 austral summer seasons. We report the study of interannual, seasonal, and diurnal variations of PMC using more than 430 h of PMC data. The most significant differences between the two seasons are that in the 2000-2001 season, the PMC

Xinzhao Chu; Chester S. Gardner; Raymond G. Roble

2003-01-01

188

Lidar studies of interannual, seasonal, and diurnal variations of polar mesospheric clouds at the South Pole  

Microsoft Academic Search

Polar mesospheric clouds (PMC) were observed by an Fe Boltzmann temperature lidar at the South Pole in the 1999–2000 and 2000–2001 austral summer seasons. We report the study of interannual, seasonal, and diurnal variations of PMC using more than 430 h of PMC data. The most significant differences between the two seasons are that in the 2000–2001 season, the PMC

Xinzhao Chu; Chester S. Gardner; Raymond G. Roble

2003-01-01

189

High Spectral Resolution Lidar Measurements of Extinction and Particle Size in Clouds  

NASA Technical Reports Server (NTRS)

The University of Wisconsin High Spectral Resolution Lidar (HSRL) measures optical properties of the atmosphere by separating the Doppler broadened molecular backscatter return from the unbroadened aerosol return. In the past, the HSRL employed a 150 mm diameter Fabry-Perot etalon to separate the aerosol and molecular signals. The replacement of the etalon with an I2 absorption filter significantly improved the ability of the HSRL to separate weak molecular signals inside dense clouds.

Eloranta, E. W.; Piirronen, P.

1996-01-01

190

Macrophysical Properties of Tropical Cirrus Clouds from the CALIPSO Satellite and from Ground-based Micropulse and Raman Lidars  

SciTech Connect

Lidar observations of cirrus cloud macrophysical properties over the U.S. Department of Energy Atmospheric Radiation Measurement (ARM) program Darwin, Australia site are compared from the Cloud-Aerosol Lidar and In- frared Pathfinder Satellite Observation (CALIPSO) satellite, the ground-based ARM micropulse lidar (MPL), and the ARM Raman lidar (RL). Comparisons are made using the subset of profiles where the lidar beam is not fully attenuated. Daytime measurements using the RL are shown to be relatively unaffected by the solar background and are therefore suited for checking the validity of diurnal cycles. RL and CALIPSO cloud fraction profiles show good agreement while the MPL detects significantly less cirrus, particularly during the daytime. Both MPL and CALIPSO observations show that cirrus clouds occur less frequently during the day than at night at all altitudes. In contrast, the RL diurnal cy- cle is significantly different than zero only below about 11 km; where it is the opposite sign (i.e. more clouds during the daytime). For cirrus geomet- rical thickness, the MPL and CALIPSO observations agree well and both datasets have signficantly thinner clouds during the daytime than the RL. From the examination of hourly MPL and RL cirrus cloud thickness and through the application of daytime detection limits to all CALIPSO data we find that the decreased MPL and CALIPSO cloud thickness during the daytime is very likely a result of increased daytime noise. This study highlights the vast im- provement the RL provides (compared to the MPL) in the ARM program's ability to observe tropical cirrus clouds as well as a valuable ground-based lidar dataset for the validation of CALIPSO observations and to help im- prove our understanding of tropical cirrus clouds.

Thorsen, Tyler J.; Fu, Qiang; Comstock, Jennifer M.; Sivaraman, Chitra; Vaughan, Mark A.; Winker, D.; Turner, David D.

2013-08-27

191

Macrophysical properties of tropical cirrus clouds from the CALIPSO satellite and from ground-based micropulse and Raman lidars  

NASA Astrophysics Data System (ADS)

Lidar observations of cirrus cloud macrophysical properties over the U.S. Department of Energy Atmospheric Radiation Measurement (ARM) program Darwin, Australia, site are compared from the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite, the ground-based ARM micropulse lidar (MPL), and the ARM Raman lidar (RL). Comparisons are made using the subset of profiles where the lidar beam is not fully attenuated. Daytime measurements using the RL are shown to be relatively unaffected by the solar background and are therefore suited for checking the validity of diurnal cycles. RL and CALIPSO cloud fraction profiles show good agreement while the MPL detects significantly less cirrus, particularly during the daytime. Both MPL and CALIPSO observations show that cirrus clouds occur less frequently during the day than at night at all altitudes. In contrast, the RL diurnal cycle is significantly different from zero only below about 11 km; where it is of opposite sign (i.e., more clouds during the daytime). For cirrus geometrical thickness, the MPL and CALIPSO observations agree well and both data sets have significantly thinner clouds during the daytime than the RL. From the examination of hourly MPL and RL cirrus cloud thickness and through the application of daytime detection limits to all CALIPSO data, we find that the decreased MPL and CALIPSO cloud thickness during the daytime is very likely a result of increased daytime noise. This study highlights the significant improvement the RL provides (compared to the MPL) in the ARM program's ability to observe tropical cirrus clouds and will help improve our understanding of these clouds. The RL also provides a valuable ground-based lidar data set for the evaluation of CALIPSO observations.

Thorsen, Tyler J.; Fu, Qiang; Comstock, Jennifer M.; Sivaraman, Chitra; Vaughan, Mark A.; Winker, David M.; Turner, David D.

2013-08-01

192

Pseudorandom noise-continuous-wave laser radar for surface and cloud measurements  

Microsoft Academic Search

Laser radar (lidar) application may require an instrument with compact size, long life of the components, low consumption and eye-safety. One possibility to achieve these features is to use a continuous-wave (cw) diode laser as lidar transmitter. A practical way to perform range-resolved measurements with a cw laser diode is the pseudo-random noise (PRN) modulation. This paper presents a compact

Renaud Matthey; Valentin Mitev

2005-01-01

193

A Compact Airborne High Spectral Resolution Lidar for Observations of Aerosol and Cloud Optical Properties  

NASA Technical Reports Server (NTRS)

We are in the process of developing a nadir-viewing, aircraft-based high spectral resolution lidar (HSRL) at NASA Langley Research Center. The system is designed to measure backscatter and extinction of aerosols and tenuous clouds. The primary uses of the instrument will be to validate spaceborne aerosol and cloud observations, carry out regional process studies, and assess the predictions of chemical transport models. In this paper, we provide an overview of the instrument design and present the results of simulations showing the instrument's capability to accurately measure extinction and extinction-to-backscatter ratio.

Hostetler, Chris A.; Hair, John W.; Cook, Anthony L.

2002-01-01

194

Extracting vertical winds from simulated clouds with ground-based coherent Doppler lidar.  

PubMed

The performance of mean velocity estimators is determined by computer simulations for solid-state coherent Doppler lidar measurements of wind fields at a cloud interface with deterministic profiles of velocity and aerosol backscatter. Performance of the velocity estimates is characterized by the standard deviation about the estimated mean and the bias referenced to the input velocity. A new class of estimators are required for cloud conditions, as traditional techniques result in biased estimates. We consider data with high signal energy that produces negligible random outliers. PMID:18301652

Lottman, B T; Frehlich, R G

1998-12-20

195

Range determination for generating point clouds from airborne small footprint LiDAR waveforms.  

PubMed

This paper presents a range determination approach for generating point clouds from small footprint LiDAR waveforms. Waveform deformation over complex terrain area is simulated using convolution. Drift of the peak center position is analyzed to identify the first echo returned by the illuminated objects in the LiDAR footprint. An approximate start point of peak in the waveform is estimated and adopted as the indicator of range calculation; range correction method is proposed to correct pulse widening over complex terrain surface. The experiment was carried out on small footprint LiDAR waveform data acquired by RIEGL LMS-Q560. The results suggest that the proposed approach generates more points than standard commercial products; based on field measurements, a comparative analysis between the point clouds generated by the proposed approach and the commercial software GeocodeWF indicates that: 1). the proposed approach obtained more accurate tree heights; 2). smooth surface can be achieved with low standard deviation. In summary, the proposed approach provides a satisfactory solution for range determination in estimating 3D coordinate values of point clouds, especially for correcting range information of waveforms containing deformed peaks. PMID:23187409

Qin, Yuchu; Vu, Tuong Thuy; Ban, Yifang; Niu, Zheng

2012-11-01

196

Improved simulation of aerosol, cloud, and density measurements by shuttle lidar  

NASA Technical Reports Server (NTRS)

Data retrievals are simulated for a Nd:YAG lidar suitable for early flight on the space shuttle. Maximum assumed vertical and horizontal resolutions are 0.1 and 100 km, respectively, in the boundary layer, increasing to 2 and 2000 km in the mesosphere. Aerosol and cloud retrievals are simulated using 1.06 and 0.53 microns wavelengths independently. Error sources include signal measurement, conventional density information, atmospheric transmission, and lidar calibration. By day, tenuous clouds and Saharan and boundary layer aerosols are retrieved at both wavelengths. By night, these constituents are retrieved, plus upper tropospheric, stratospheric, and mesospheric aerosols and noctilucent clouds. Density, temperature, and improved aerosol and cloud retrievals are simulated by combining signals at 0.35, 1.06, and 0.53 microns. Particlate contamination limits the technique to the cloud free upper troposphere and above. Error bars automatically show effect of this contamination, as well as errors in absolute density nonmalization, reference temperature or pressure, and the sources listed above. For nonvolcanic conditions, relative density profiles have rms errors of 0.54 to 2% in the upper troposphere and stratosphere. Temperature profiles have rms errors of 1.2 to 2.5 K and can define the tropopause to 0.5 km and higher wave structures to 1 or 2 km.

Russell, P. B.; Morley, B. M.; Livingston, J. M.; Grams, G. W.; Patterson, E. W.

1981-01-01

197

Polarization properties of lidar scattering from clouds at 347 nm and 694 nm.  

PubMed

The polarization characteristics of lidar scattering from cumulus and low-lying shower clouds have been measured with a system operating at 694 nm (red) and 347 nm (blue). The backscatter profiles of the polarization components as well as of the total intensity of the return are presented and discussed for the two wavelengths. The linear depolarization ratio delta, which can be used as a measure of the unpolarized multiple scattering, has been obtained at both wavelengths. This quantity has a very low value at cloud base for both wavelengths and increases with pulse penetration. The blue registers generally higher values of a within the cloud. The measured total intensity backscatter functions for both wavelengths are presented and discussed in relation to theoretical calculations of cloud models. PMID:20203781

Pal, S R; Carswell, A I

1978-08-01

198

Orbiting lidar simulations. I - Aerosol and cloud measurements by an independent-wavelength technique  

NASA Technical Reports Server (NTRS)

Aerosol and cloud measurements have been simulated for a Space Shuttle lidar. Expected errors - in signal, transmission, density, and calibration - are calculated algebraically and checked by simulating measurements and retrievals using random-number generators. By day, vertical structure is retrieved for tenuous clouds, Saharan aerosols, and boundary layer aerosols (at 0.53 and 1.06 micron) as well as strong volcanic stratospheric aerosols (at 0.53 micron). By night, all these constituents are retrieved plus upper tropospheric and stratospheric aerosols (at 1.06 micron), mesospheric aerosols (at 0.53 micron), and noctilucent clouds (at 1.06 and 0.53 micron). The vertical resolution was 0.1-0.5 km in the troposphere, 0.5-2.0 km above, except 0.25-1.0 km in the mesospheric cloud and aerosol layers; horizontal resolution was 100-2000 km.

Russell, P. B.; Morley, B. M.; Livingston, J. M.; Grams, G. W.; Patterson, E. M.

1982-01-01

199

Operational processing and cloud boundary detection from micro pulse lidar data  

NASA Technical Reports Server (NTRS)

Micro Pulse Lidar (MPL) was developed at NASA Goddard Space Flight Center (GSFC) as the result of research on space-borne lidar techniques. It was designed to provide continuous, unattended observations of all significant atmospheric cloud and aerosol structure with a rugged, compact system design and the benefit of eye safety (Spinhirne 1993). The significant eye safety feature is achieved by using low pulse energies and high pulse repetition rates compared to standard lidar systems. MPL systems use a diode pumped 10 microj, 2500 Hz doubled Nd:YLF laser. In addition, a solid state Geiger mode avalanche photo diode (GAPD) photon counting detector is used allowing for quantum efficiencies approaching 70%. Other design features have previously been noted by Spinhirne (1995). Though a commercially available instrument, with nearly 20 systems operating around the world, the most extensive MPL work has come from those operated by the Atmospheric Radiation Measurement (ARM) (Stokes and Schwartz 1994) program. The diverse ability of the instrument relating to the measurement of basic cloud macrophysical structure and both cloud and aerosol radiative properties well suits the ARM research philosophy. MPL data can be used to yield many parameters including cloud boundary heights to the limit of signal attenuation, cloud scattering cross sections and optical thicknesses, planetary boundary layer heights and aerosol scattering profiles, including those into the stratosphere in nighttime cases (Hlavka et al 1996). System vertical resolution ranges from 30 m to 300 m (i.e. high and low resolution respectively) depending on system design. The lidar research group at GSFC plays an advisory role in the operation, calibration and maintenance of NASA and ARM owned MPL systems. Over the past three years, processing software and system correction techniques have been developed in anticipation of the increasing population of systems amongst the community. Datasets produced by three ARM-owned systems have served as the basis for this development. With two operating at the southern Great Plains Cloud and Radiation Testbed Site (SGP CART) since December 1993 and another at the Manus Island Atmospheric Radiation and Cloud Station (TWP ARCS) location in the tropical western Pacific since February 1997, the ARM archive contains over 4 years of observations. In addition, high resolution systems planning to come on-line at the North Slope, AK CART shortly with another scheduled to follow at the TWP ARCS-II will diversify this archive with more extensive observations.

Campbell, James R.; Hlavka, Dennis L.; Spinhirne, James D.; Scott, V. Stanley., III; Turner, David D.

1998-01-01

200

A 35-GHz polarimetrie Doppler radar and its application for observing clouds associated with Typhoon Nuri  

NASA Astrophysics Data System (ADS)

Millimeter-wavelength radar has proved to be an effective instrument for cloud observation and research. In this study, 8-mm-wavelength cloud radar (MMCR) with Doppler and polarization capabilities was used to investigate cloud dynamics in China for the first time. Its design, system specifications, calibration, and application in measuring clouds associated with typhoon are discussed in this article. The cloud radar measurements of radar reflectivity ( Z), Doppler velocity ( V r), velocity spectrum width ( S w) and the depolarization ratio ( L DR) at vertical incidence were used to analyze the microphysical and dynamic processes of the cloud system and precipitation associated with Typhoon Nuri, which occurred in southern China in August 2008. The results show the reflectivity observed using MMCR to be consistent with the echo height and the melting-layer location data obtained by the nearby China S-band new-generation weather radar (SA), but the Ka-band MMCR provided more detailed structural information about clouds and weak precipitation data than did the SA radar. The variation of radar reflectivity and L DR in vertical structure reveals the transformation of particle phase from ice to water. The vertical velocity and velocity spectrum width of MMCR observations indicate an updraft and strong turbulence in the stratiform cloud layer. MMCR provides a valuable new technology for meteorological research in China.

Zhong, Lingzhi; Liu, Lipingt; Feng, Sheng; Ge, Runsheng; Zhang, Zhe

2011-07-01

201

The building blocks for a pulsed dual-frequency lidar-radar: concept and preliminary experimental results  

NASA Astrophysics Data System (ADS)

A new principle of lidar-radar is theoretically and experimentally investigated. The proposed architecture is based on the use of a RF modulation of the emitted light beam and direct detection of the backscattered intensity. The use of a radar processing chain allows to obtain range and Doppler measurements with the advantages of lidar spatial resolution. The maximum range of this device is calculated, taking different possible improvements into account. In particular, it is shown that the use of a pulsed two-frequency laser and a spatially multimode optical pre-amplification of the backscattered light leads to calculated ranges larger than 20 km, including the possibility for both range and Doppler measurements. The building blocks of this lidar-radar are tested experimentally : the radar processing of an RF modulated backscattered cw laser beam is demonstrated at 532 nm, illustrating the Doppler and identification capabilities of the system. Besides, signal-to-noise ratio improvement by optical pre-amplification and filtering of the ASE noise is demonstrated at 1.55 ?m. Finally, a two-frequency passively Q-switched Nd:YAG laser is developed. This laser then permits to obtain two-frequency pulses with tunable pulse duration and beat frequency.

Morvan, Loic; Lai, N. D.; Dolfi, Daniel; Huignard, Jean-Pierre; Brunel, Michel; Bretenaker, Fabien; Le Floch, Albert

2003-02-01

202

Cloud-Free Line of Sight (CFLOS) derived from CloudSat Cloud Profiling Radar Data  

NASA Astrophysics Data System (ADS)

Numerous global "Cloud-Free Line of Sight" climatologies have been derived from satellite observations of cloud. All have inherent limitations due to the fact that they rely on data from passive meteorological sensors which provide a reasonable measurement of the cloud tops, but provide no information about cloud bases or multi-layered clouds below the highest opaque cloud layer. NASA's exciting new CloudSat mission will provide, for the first time from space, a direct measurement of the vertical profile of cloud including cloud bases and the elusive "hidden layers". This presentation will describe a technique for producing a CFLOS database from CloudSat and some early results and comparisons with existing climatologies.

Reinke, D. L.; Eis, K. E.; Vonder Haar, T. H.

2006-12-01

203

First temperature measurements within Polar Stratospheric Clouds with the Esrange lidar  

NASA Astrophysics Data System (ADS)

In the winter stratosphere polar stratospheric clouds (PSCs) provide the surface for heterogeneous reactions which transform stable chlorine and bromine species into their highly reactive ozone-destroying states. PSCs are classified into three types (PSC Ia: nitric acid di- or trihydrate crystals, NAD or NAT; PSC Ib: supercooled liquid ternary solutions, STS; PSC II: ice) according to their particle composition and to their physical phase. The formation of PSCs depends strongly on temperature. For a comprehensive understanding of such temperature-dependent processes in the lower stratosphere, lidar measurements using the rotational-Raman technique are most suitable. The rotational-Raman technique allows for temperature measurements without a priori assumptions of the state of the atmosphere. The technique is feasible in aerosol layers and clouds, such as PSCs. A rotational-Raman channel for temperature measurements in the upper troposphere and lower stratosphere was added to the Esrange lidar in late 2010. The Esrange lidar operates at Esrange (68°N, 21°E) near the Swedish city of Kiruna. By combining rotational-Raman measurements (4-35 km height) and the integration technique (30-80 km height), the Esrange lidar is now capable of measuring atmospheric temperature profiles from the upper troposphere up to the mesosphere. Such measurements could be used to validate current lidar-based PSC classification schemes and the current understanding of PSC formation. The new capability of the instrument furthermore enables the studies of other clouds layers, temperature variations and exchange processes in the upper troposphere/lower stratosphere. These studies will take advantage of the geographical location of Esrange where mountain wave activity in the lee of the Scandinavian mountain range gives rise to a wide range of PSC growth conditions. Although several lidars are operated at polar latitudes, there are few instruments that are capable of measuring temperature profiles in the troposphere, stratosphere, and mesosphere, as well as aerosols extinction in the troposphere and lower stratosphere. In this study, we utilize measurements of PSCs and temperature during the winters 2010/11, 2011/12, and 2012/13 to gain insight into the temperature dependence of different PSC types.

Achtert, Peggy; Khaplanov, Mikhail; Khosrawi, Farahnaz; Gumbel, Jörg

2013-04-01

204

Aerosol and cloud sensing with the Lidar In-space Technology Experiment (LITE)  

NASA Technical Reports Server (NTRS)

The Lidar In-space Technology Experiment (LITE) is a multi-wavelength backscatter lidar developed by NASA Langley Research Center to fly on the Space Shuttle. The LITE instrument is built around a three-wavelength ND:YAG laser and a 1-meter diameter telescope. The laser operates at 10 Hz and produces about 500 mJ per pulse at 1064 nm and 532 nm, and 150 mJ per pulse at 355 nm. The objective of the LITE program is to develop the engineering processes required for space lidar and to demonstrate applications of space-based lidar to remote sensing of the atmosphere. The LITE instrument was designed to study a wide range of cloud and aerosol phenomena. To this end, a comprehensive program of scientific investigations has been planned for the upcoming mission. Simulations of on-orbit performance show the instrument has sufficient sensitivity to detect even thin cirrus on a single-shot basis. Signal averaging provides the capability of measuring the height and structure of the planetary boundary layer, aerosols in the free troposphere, the stratospheric aerosol layer, and density profiles to an altitude of 40 km. The instrument has successfully completed a ground-test phase and is scheduled to fly on the Space Shuttle Discovery for a 9-day mission in September 1994.

Winker, D. M.; McCormick, M. P.

1994-01-01

205

Performance of the Lidar Design and Data Algorithms for the GLAS Global Cloud and Aerosol Measurements  

NASA Technical Reports Server (NTRS)

The Geoscience Laser Altimeter System (GLAS) launched in early 2003 is the first polar orbiting satellite lidar. The instrument design includes high performance observations of the distribution and optical scattering cross sections of atmospheric clouds and aerosol. The backscatter lidar operates at two wavelengths, 532 and 1064 nm. For the atmospheric cloud and aerosol measurements, the 532 nm channel was designed for ultra high efficiency with solid state photon counting detectors and etalon filtering. Data processing algorithms were developed to calibrate and normalize the signals and produce global scale data products of the height distribution of cloud and aerosol layers and their optical depths and particulate scattering cross sections up to the limit of optical attenuation. The paper will concentrate on the effectiveness and limitations of the lidar channel design and data product algorithms. Both atmospheric receiver channels meet and exceed their design goals. Geiger Mode Avalanche Photodiode modules are used for the 532 nm signal. The operational experience is that some signal artifacts and non-linearity require correction in data processing. As with all photon counting detectors, a pulse-pile-up calibration is an important aspect of the measurement. Additional signal corrections were found to be necessary relating to correction of a saturation signal-run-on effect and also for daytime data, a small range dependent variation in the responsivity. It was possible to correct for these signal errors in data processing and achieve the requirement to accurately profile aerosol and cloud cross section down to 10-7 llm-sr. The analysis procedure employs a precise calibration against molecular scattering in the mid-stratosphere. The 1064 nm channel detection employs a high-speed analog APD for surface and atmospheric measurements where the detection sensitivity is limited by detector noise and is over an order of magnitude less than at 532 nm. A unique feature of the GLAS is a full acquisition of the surface return pulse, which has important application to the atmospheric transmission retrieval.

Spinhirne, James D.; Palm, Stephen P.; Hlavka, Dennis L.; Hart, William D.

2007-01-01

206

Microphysical modeling of a midlatitude “polar stratospheric cloud” event: Comparisons against multiwavelength ground-based and spaceborne lidar data  

NASA Astrophysics Data System (ADS)

A high-resolution transport model containing a fully explicit size-resolving microphysical scheme is used to study a large-scale polar stratospheric cloud (PSC) case detected by lidar at midlatitudes between 17 and 23 February 2008. The model simulations, initialized using European Centre for Medium-Range Weather Forecasts (ECMWF) fields and Microwave Limb Sounder (MLS) Aura data, are validated locally against ground-based (Institute for Tropospheric Research Multiwavelength Atmospheric Raman lidar for Temperature, Humidity, and Aerosol profiling (IfT MARTHA)) lidar measurements at Leipzig and globally against spaceborne (Cloud-Aerosol LIdar with Orthogonal Polarization/Cloud-Aerosol-Lidar and Infrared Pathfinder Satellite Observations (CALIOP/CALIPSO)) lidar backscatter measurements. By assuming a 1 K cold bias on the ECMWF temperatures and under the assumption of equilibrated spherical PSC particles, our model produces fields of optical and microphysical parameters like the total surface area density (A) and volume (V). A, and V, as well as the median radius of the PSC size distribution, compare favorably to the corresponding values derived from multiwavelength lidar backscatter measurements. Around 21 km, A and V are found to be around 10 ?m2 cm-3 and 1 ?m3 cm-3, respectively. The median radius of the Supercooled Ternary Solution particle size distribution is estimated to be around 0.3 ?m using both the model calculations and the lidar-derived size distribution parameters. Overall, despite the simplifications on the microphysical scheme, the model is able to reproduce the salient features of the local and global lidar observations. The results clearly demonstrate the value of CALIOP products for large-scale studies, exploiting chemistry-transport models.

Jumelet, Julien; Bekki, Slimane; Seifert, Patric; Montoux, Nadège; Vernier, Jean-Paul; Pelon, Jacques

2009-08-01

207

Nineteenth International Laser Radar Conference. Part 2  

NASA Technical Reports Server (NTRS)

This publication contains extended abstracts of papers presented at the Nineteenth International Laser Radar Conference, held at Annapolis, Maryland, July 6-10, 1998; 260 papers were presented in both oral and poster sessions. The topics of the conference sessions were Aerosol Clouds, Multiple Scattering; Tropospheric Profiling, Stratospheric/Mesospheric Profiling; Wind Profiling; New Lidar Technology and Techniques; Lidar Applications, Including Altimetry and Marine; Space and Future Lidar; and Lidar Commercialization/Eye Safety. This conference reflects the breadth of research activities being conducted in the lidar field. These abstracts address subjects from lidar-based atmospheric investigations, development of new lasers and lidar system technology, and current and future space-based lidar systems.

Singh, Upendra N. (Editor); Ismail, Syed (Editor); Schwemmer, Geary K. (Editor)

1998-01-01

208

Vertical velocities within a Cirrus cloud from Doppler lidar and aircraft measurements during FIRE: Implications for particle growth  

NASA Technical Reports Server (NTRS)

A large and comprehensive data set taken by the NOAA CO2 Doppler lidar, the NCAR King Air, and rawinsondes on 31 October 1986 during the FIRE (First ISCCP Regional Experiment) field program which took place in Wisconsin are presented. Vertical velocities are determined from the Doppler lidar data, and are compared with velocities derived from the aircraft microphysical data. The data are used for discussion of particle growth and dynamical processes operative within the cloud.

Gultepe, Ismail; Heymsfield, Andrew J.

1990-01-01

209

Building a LiDAR point cloud simulator: Testing algorithms for high resolution topographic change  

NASA Astrophysics Data System (ADS)

Terrestrial laser technique (TLS) is becoming a common tool in Geosciences, with clear applications ranging from the generation of a high resolution 3D models to the monitoring of unstable slopes and the quantification of morphological changes. Nevertheless, like every measurement techniques, TLS still has some limitations that are not clearly understood and affect the accuracy of the dataset (point cloud). A challenge in LiDAR research is to understand the influence of instrumental parameters on measurement errors during LiDAR acquisition. Indeed, different critical parameters interact with the scans quality at different ranges: the existence of shadow areas, the spatial resolution (point density), and the diameter of the laser beam, the incidence angle and the single point accuracy. The objective of this study is to test the main limitations of different algorithms usually applied on point cloud data treatment, from alignment to monitoring. To this end, we built in MATLAB(c) environment a LiDAR point cloud simulator able to recreate the multiple sources of errors related to instrumental settings that we normally observe in real datasets. In a first step we characterized the error from single laser pulse by modelling the influence of range and incidence angle on single point data accuracy. In a second step, we simulated the scanning part of the system in order to analyze the shifting and angular error effects. Other parameters have been added to the point cloud simulator, such as point spacing, acquisition window, etc., in order to create point clouds of simple and/or complex geometries. We tested the influence of point density and vitiating point of view on the Iterative Closest Point (ICP) alignment and also in some deformation tracking algorithm with same point cloud geometry, in order to determine alignment and deformation detection threshold. We also generated a series of high resolution point clouds in order to model small changes on different environments (erosion, landslide monitoring, etc) and we then tested the use of filtering techniques using 3D moving windows along the space and time, which considerably reduces data scattering due to the benefits of data redundancy. In conclusion, the simulator allowed us to improve our different algorithms and to understand how instrumental error affects final results. And also, improve the methodology of scans acquisition to find the best compromise between point density, positioning and acquisition time with the best accuracy possible to characterize the topographic change.

Carrea, Dario; Abellán, Antonio; Derron, Marc-Henri; Jaboyedoff, Michel

2014-05-01

210

Retrieval of Polar Stratospheric Cloud Microphysical Properties From Lidar Measurements: Dependence on Particle Shape Assumptions  

NASA Technical Reports Server (NTRS)

Knowledge of particle sizes and number densities of polar stratospheric clouds (PSCs) is highly important, because they are critical parameters for the modeling of the ozone chemistry of the stratosphere. In situ measurements of PSC particles are rare. the main instrument for the accumulation of PSC data are lidar systems. Therefore the derivation of some microphysical properties of PSCS from the optical parameters measured by lidars would be highly beneficial for ozone research. Inversion of lidar data obtained in the presence of PSCs formed from crystalline particles type 11 and the various nitric acid tri Ydrrate (NAT) types cannot be easily accomplished, because a suitable scattering theory for small faceted crystals has not been readily available tip to now. As a consequence, the T-matrix method is commonly used for the interpretation of these PSC lidar data. Here the assumption is made that the optical properties of an ensemble of spheroids resemble those of crystalline PSCs, and microphysical properties of the PSC are inferred from the optical signatures of the PSC at two or more wavelengths. The problem with the T-matrix approach is that the assumption of spheroidal instead of faceted particles can lead to dramatically wrong results: Usually cloud particle properties are deduced from analysis of lidar profiles of backscatter ratio and depolarization ratio. The particle contribution to the backscatter ratio is given by the product of the particle number density and the backscattering cross section. The latter is proportional to the value of the particle's scattering phase function at 180 degrees scattering angle. At 180 degrees however, the phase functions of rough, faceted crystals and of spheroids with same maximum dimension differ by a factor of 6. From this it follows that for a PSC consisting of faceted crystals, the particle number density is underestimated by roughly the same factor if spheroidal particles are unrealistically assumed. We are currently developing a retrieval technique for determining the microphysical parameters of crystalline PSCs that takes into account the faceted shape of the PSC particles. This approach utilizes finite-difference time-domain (FDTD) calculations of particle optical properties. The accuracy and the free choice of the shape of the scattering particle make the FDTD technique a promising tool for the inversion of PSC lidar data. A first comparison of FDTD and T-matrix calculations will be presented.

Reichardt, Susanne; Reichardt, Jens; Yang, Ping; McGee, Thomas J.; Einaudi, Franco (Technical Monitor)

2001-01-01

211

Cloud base height determination in rain, snow, and fog with a low-cost eye-safe lidar  

NASA Astrophysics Data System (ADS)

The main obstacles for a reliable cloud base height determination with a lidar system are hydrometeors and precipitation scattering the emitted laser light on its way into the atmosphere. In order to fulfill the requirements of airport and aviation safety, modern commercial ceilometers have to be designed in a way that especially takes care of this problem, and the fact that a great part of the light received by the lidar originates from multiple scattering. Results of measuring campaigns performed in Canada and Germany show that the new Hagenuk cloud height lidar LD-WH X 06 also gives reliable results in difficult weather situations. Additionally it offers features like easy servicability, high MTBF, extended maintensance intervals, and long lifetime of laser being of special interest for commercial applications. This presentation contains some examples of the measuring compaigns mentioned above along with a comparison of the cloud heights measured with two different ceilometers in Canada.

Muenkel, Christoph

1995-09-01

212

Vertical distribution of clouds over Hampton, Virginia observed by lidar under the ECLIPS and FIRE ETO programs  

NASA Technical Reports Server (NTRS)

Intensive cloud lidar observations have been made by NASA Langley Research Center during the two observation phases of the ECLIPS project. Less intensive but longer term observations have been conducted as part of the FIRE extended time observation (ETO) program since 1987. We present a preliminary analysis of the vertical distribution of clouds based on these observations. A mean cirrus thickness of just under 1 km has been observed with a mean altitude of about 80 percent of the tropopause height. Based on the lidar data, cirrus coverage was estimated to be just under 20 percent, representing roughly 50 percent of all clouds studied. Cirrus was observed to have less seasonal variation than lower clouds. Mid-level clouds are found to occur primarily in association with frontal activity.

Vaughan, M. A.; Winker, D. M.

1994-01-01

213

CART Raman Lidar Aerosol and Water Vapor Measurements in the Vicinity of Clouds  

NASA Technical Reports Server (NTRS)

Aerosol and water vapor profiles acquired by the Raman lidar instrument located at the Climate Research Facility (CRF) at Southern Great Plains (SGP) provide data necessary to investigate the atmospheric variability in the vicinity of clouds near the top of the planetary boundary layer (PBL). Recent CARL upgrades and modifications to the routine processing algorithms afforded the necessarily high temporal and vertical data resolutions for these investigations. CARL measurements are used to investigate the behavior of aerosol backscattering and extinction and their correlation with water vapor and relative humidity.

Clayton, Marian B.; Ferrare, Richard A.; Turner, David; Newsom, Rob; Sivaraman, Chitra

2008-01-01

214

Cloud-Aerosol LIDAR and Infrared Pathfinder Satellite Observation (CALIPSO) Spacecraft: Independent Technical Assessment  

NASA Technical Reports Server (NTRS)

CALIPSO is a joint science mission between the CNES, LaRC and GSFC. It was selected as an Earth System Science Pathfinder satellite mission in December 1998 to address the role of clouds and aerosols in the Earth's radiation budget. The spacecraft includes a NASA light detecting and ranging (LIDAR) instrument, a NASA wide-field camera and a CNES imaging infrared radiometer. The scope of this effort was a review of the Proteus propulsion bus design and an assessment of the potential for personnel exposure to hydrazine propellant.

Gilbrech, Richard J.; McManamen, John P.; Wilson, Timmy R.; Robinson, Frank; Schoren, William R.

2004-01-01

215

Cloud-Aerosol LIDAR and Infrared Pathfinder Satellite Observation (CALIPSO) Spacecraft: Independent Technical Assessment  

NASA Technical Reports Server (NTRS)

CALIPSO is a joint science mission between the CNES, LaRC and GSFC. It was selected as an Earth System Science Pathfinder satellite mission in December 1998 to address the role of clouds and aerosols in the Earth's radiation budget. The spacecraft includes a NASA light detecting and ranging (LIDAR) instrument, a NASA wide-field camera and a CNES imaging infrared radiometer. The scope of this effort was a review of the Proteus propulsion bus design and an assessment of the potential for personnel exposure to hydrazine propellant.

Gilbrech, Richard J.; McManamen, John P.; Wilson, Timmy R.; Robinson, Frank; Schoren, William R.

2005-01-01

216

Horizontal and vertical structure of the Eyjafjallajökull ash cloud over the UK: a comparison of airborne lidar observations and simulations  

NASA Astrophysics Data System (ADS)

During April and May 2010 the ash cloud from the eruption of the Icelandic volcano Eyjafjallajökull caused widespread disruption to aviation over northern Europe. The location and impact of the eruption led to a wealth of observations of the ash cloud were being obtained which can be used to assess modelling of the long range transport of ash in the troposphere. The UK FAAM (Facility for Airborne Atmospheric Measurements) BAe-146-301 research aircraft overflew the ash cloud on a number of days during May. The aircraft carries a downward looking lidar which detected the ash layer through the backscatter of the laser light. In this study ash concentrations derived from the lidar are compared with simulations of the ash cloud made with NAME (Numerical Atmospheric-dispersion Modelling Environment), a general purpose atmospheric transport and dispersion model. The simulated ash clouds are compared to the lidar data to determine how well NAME simulates the horizontal and vertical structure of the ash clouds. Comparison between the ash concentrations derived from the lidar and those from NAME is used to define the fraction of ash emitted in the eruption that is transported over long distances compared to the total emission of tephra. In making these comparisons possible position errors in the simulated ash clouds are identified and accounted for. The ash layers seen by the lidar considered in this study were thin, with typical depths of 550-750 m. The vertical structure of the ash cloud simulated by NAME was generally consistent with the observed ash layers, although the layers in the simulated ash clouds that are identified with observed ash layers are about twice the depth of the observed layers. The structure of the simulated ash clouds were sensitive to the profile of ash emissions that was assumed. In terms of horizontal and vertical structure the best results were obtained by assuming that the emission occurred at the top of the eruption plume, consistent with the observed structure of eruption plumes. However, early in the period when the intensity of the eruption was low, assuming that the emission of ash was uniform with height gives better guidance on the horizontal and vertical structure of the ash cloud. Comparison of the lidar concentrations with those from NAME show that 2-5% of the total mass erupted by the volcano remained in the ash cloud over the United Kingdom.

Grant, A. L. M.; Dacre, H. F.; Thomson, D. J.; Marenco, F.

2012-11-01

217

Detecting and Updating Changes in Lidar Point Clouds for Automatic 3D Urban Cartography  

NASA Astrophysics Data System (ADS)

This work presents a method that automatically detects, analyses and then updates changes in LiDAR point clouds for accurate 3D urban cartography. In the proposed method, the 3D point cloud obtained in each passage is first classified into 2 main object classes: Permanent and Temporary. The Temporary objects are then removed from the 3D point cloud to leave behind a perforated 3D point cloud of the urban scene. These perforated 3D point clouds obtained from different passages (in the same place) at different days and times are then matched together to complete the 3D urban landscape by incremental updating. Different natural or man-made changes occurring in the urban landscape over this period of time are detected and analyzed using cognitive functions of similarity and the resulting 3D cartography is progressively modified and updated accordingly. The results, evaluated on real data using different standard evaluation metrics, not only demonstrate the efficacy of the proposed method but also shows that this method is easily applicable and well scalable, making it suitable for handling large urban scenes.

Aijazi, A. K.; Checchin, P.; Trassoudaine, L.

2013-10-01

218

Coherent lidar imaging of dust clouds: waveform comparison with the poly-phase (P4) modulation waveform  

Microsoft Academic Search

A dust or aerosol cloud represents a convenient target to examine the capabilities of range-resolved Doppler and intensity (RRDI) or inverse synthetic aperture ladar (ISAR) imaging coherent laser radar, known as coherent \\

Douglas G. Youmans

2008-01-01

219

Lidar observations of the Pinatubo stratospheric aerosol cloud over Frascati, Italy  

NASA Technical Reports Server (NTRS)

The Pinatubo eruption of June 1991 introduced large plumes into the local stratosphere. On several occasions, volcanic gases and particles reached altitudes of about 30 km, and spread towards the west. A lidar system has been operating to monitor the evolution of the stratospheric aerosol cloud. The backscattering ratio profiles of eight different measurements were chosen to summarize the most significant occurrences of the event. Since the beginning of the winter planetary wave activity, the Pinatubo cloud integrated backscatter exceeded El Chichon's. In this context, the perturbation generated by El Chichon can only be assumed as a lower limit of the one which will follow the Pinatubo eruption. Observations of the event are still in progress.

Congeduti, Fernando; Adriani, Alberto; Gobbi, Gian Paolo; Centurioni, Sante

1992-01-01

220

Validation of Satellite-Based Objective Overshooting Cloud-Top Detection Methods Using CloudSat Cloud Profiling Radar Observations  

NASA Technical Reports Server (NTRS)

Two satellite infrared-based overshooting convective cloud-top (OT) detection methods have recently been described in the literature: 1) the 11-mm infrared window channel texture (IRW texture) method, which uses IRW channel brightness temperature (BT) spatial gradients and thresholds, and 2) the water vapor minus IRW BT difference (WV-IRW BTD). While both methods show good performance in published case study examples, it is important to quantitatively validate these methods relative to overshooting top events across the globe. Unfortunately, no overshooting top database currently exists that could be used in such study. This study examines National Aeronautics and Space Administration CloudSat Cloud Profiling Radar data to develop an OT detection validation database that is used to evaluate the IRW-texture and WV-IRW BTD OT detection methods. CloudSat data were manually examined over a 1.5-yr period to identify cases in which the cloud top penetrates above the tropopause height defined by a numerical weather prediction model and the surrounding cirrus anvil cloud top, producing 111 confirmed overshooting top events. When applied to Moderate Resolution Imaging Spectroradiometer (MODIS)-based Geostationary Operational Environmental Satellite-R Series (GOES-R) Advanced Baseline Imager proxy data, the IRW-texture (WV-IRW BTD) method offered a 76% (96%) probability of OT detection (POD) and 16% (81%) false-alarm ratio. Case study examples show that WV-IRW BTD.0 K identifies much of the deep convective cloud top, while the IRW-texture method focuses only on regions with a spatial scale near that of commonly observed OTs. The POD decreases by 20% when IRW-texture is applied to current geostationary imager data, highlighting the importance of imager spatial resolution for observing and detecting OT regions.

Bedka, Kristopher M.; Dworak, Richard; Brunner, Jason; Feltz, Wayne

2012-01-01

221

A study of equatorial wave characteristics using rockets, balloons, lidar and radar  

NASA Astrophysics Data System (ADS)

A co-ordmated experimental campaign was conducted for 40 consecutive days from 21 February to 01 April 2000 using RH-200 rockets, balloons, Rayleigh lidar and MST radar, with the objective of delineating the equatorial waves and estimating momentum fluxes associated with them. Winds and temperatures in the troposphere, stratosphere and mesosphere over two low latitude stations Gadanki (13.5°N, 79.2°E) and SHAR (13.7°N, 80.2°E) were measured and were used for the study of equatorial waves and their interactions with the background mean flow in various atmospheric regions. The study shows the occurrence of a strong stratospheric cooling (˜25 K) anomaly along with a zonal wind anomaly and this low-latitude event appears to be linked to high-latitude stratospheric warming event and followed by subsequent generation of short period (˜5 days) oscillations lasting for a few cycles in the stratosphere. Slow and fast Kelvin waves and RG wave (˜-17-day and ˜7.2-day and ˜4.2-day periods respectively) have been identified. The mean flow acceleration produced by the divergence of the momentum flux due to the observed Kelvin waves in the 35-60 km height region were compared with the zonal flow accelerations computed from the observed zonal winds. Contribution by the slow and fast Kelvin waves was found to be only ˜25 % of the observed acceleration during the evolution of the westerly phase of the semi-annual oscillation.

Sasi, M. N.; Krishna Murthy, B. V.; Ramkumar, Geetha; Satheesan, K.; Parameswaran, K.; Rajeev, K.; Sunilkumar, S. V.; Nair, Prabha R.; Krishna Moorthy, K.; Bhavanikumar, Y.; Raghunath, K.; Jain, A. R.; Rao, P. B.; Krishnaiah, M.; Prabhakaran Nayars, S. R.; Revathy, K.; Devanarayanan, S.

2003-09-01

222

Lidar Measurements of Cirrus Clouds In The Northern and Southern Hemisphere (inca): An Interhemispheric Comparison.  

NASA Astrophysics Data System (ADS)

Cirrus cloud measurements were performed during the INCA field campaigns in Punta Arenas/Chile (53.12S, 70.88W) and in Prestwick/Scotland (55.51N, 4.60W) in 2000. From lidar backscatter profiles at 532 nm and 355 nm wavelength the optical depth of the clouds are retrieved as well as base and top altitude and the particle phase. The range of detection covers clouds with optical depth (OD) of 3 down to below 10- 3 setting the focus on thin and subvisual cirrus. Comparisons with climatologies of cloud properties suggest that the data obtained within a period of 3 weeks are to some extend representative. One main difference found is the observation of very faint layers of particles in the northern hemisphere in an altitude range of 5 to 8 km. Comparable structures in the SH have not been observed. For cirrus itself the distributions of the occurrence frequencies versus the optical depth (dt / dlogOD) look very similar. In Punta Arenas about 38 % of all detected ice clouds are found in the subvisible range (OD<.03) while 35% were characterized as thin cirrus (.03 .3) In Prestwick these fractions were 32%, 41% and 27%, respec- tively. Differences in the results from the southern and the northern hemisphere are found in the wavelength dependence of the backscatter coefficient and the depolariza- tion behaviour. These results suggest, that there are clouds consisting of rather large particles in Punta Arenas, which have not been detected in Prestwick. In summary our data suggest that the higher concentration of aerosol (including anthropogenic aerosols) in the northern hemisphere does not have an impact on the abundance of cirrus, including those in the subvisible range. However, there are indications for an influence on the microphysical properties of all high altitude clouds.

Immler, F.; Schrems, O.; Ström, J.

223

A new method for building roof segmentation from airborne LiDAR point cloud data  

NASA Astrophysics Data System (ADS)

A new method based on the combination of two kinds of clustering algorithms for building roof segmentation from airborne LiDAR (light detection and ranging) point cloud data is proposed. The K-plane algorithm is introduced to classify the laser footprints that cannot be correctly classified by the traditional K-means algorithm. High-precision classification can be obtained by combining the two aforementioned clustering algorithms. Furthermore, to improve the performance of the new segmentation method, a new initialization method is proposed to acquire the number and coordinates of the initial cluster centers for the K-means algorithm. In the proposed initialization method, the geometrical planes of a building roof are estimated from the elevation image of the building roof by using the mathematical morphology and Hough transform techniques. By calculating the number and normal vectors of the estimated geometrical planes, the number and coordinates of the initial cluster centers for the K-means algorithm are obtained. With the aid of the proposed initialization and segmentation methods, the point cloud of the building roof can be rapidly and appropriately classified. The proposed methods are validated by using both simulated and real LiDAR data.

Kong, Deming; Xu, Lijun; Li, Xiaolu

2013-09-01

224

Lidar observations of subvisual cirrus clouds in the tropics and the midlatitudes  

NASA Astrophysics Data System (ADS)

Measurements performed with the Mobile Aerosol Raman Lidar MARL in Punta Arenas/Chile (53.12^oS, 70.88^oW), in Prestwick /Scotland (55.5^oN, 4.60^oW), and aboard the German research vessel Polarstern within the German PAZI project are reported. MARL is able to measure backscatter profiles at the wavelengths of 532~nm and 355~nm with a vertical resolution of 7.5~m and a time resolution of 140~s. Additionally, the depolarization is detected at both wavelengths. With the help of a newly developed algorithm the detection of clouds by the lidar is very sensitive and enables us to observe thin layers with an estimated optical depth down to 10-4 by making use of the backscatter and the depolarization caused by the ice particles. During the northern and the southern hemispheric campaigns which were part of the European INCA project, about 60 hours of lidar measurements were gathered, respectively. At both sites, subvisual cirrus with an optical depth (OD)<0.03 were present in about 30% of the obtained data. An analysis of the depolarization and the color index suggests differences in the microphysical properties of the cloud particles. The measurements in the tropics aboard Polarstern revealed the frequent occurrence of tropical subvisual cirrus (TSC) in the equatorial Atlantic region. The TSCs differed significantly from their midlatitude counterparts with respect to their horizontal extent and their lifetime as well as in their optical and microphysical properties. Simultaneous radiosonde soundings performed aboard Polarstern allowed the determination of the temperature and other meteorological parameters of the tropical tropopause layer.

Immler, F.; Schrems, O.

2003-04-01

225

Radiative effects of African dust and smoke observed from Clouds and the Earth's Radiant Energy System (CERES) and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) data  

NASA Astrophysics Data System (ADS)

Cloud and aerosol effects have a significant impact on the atmospheric radiation budget in the tropical Atlantic because of the spatial and temporal extent of desert dust and smoke from biomass burning in the atmosphere. The influences of African dust and smoke aerosols on cloud radiative properties over the tropical Atlantic Ocean were analyzed for the month of July for 3 years (2006-2008) using colocated data collected by the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and Clouds and the Earth's Radiant Energy System (CERES) instruments on the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and Aqua satellites. Aerosol layer height and type can be accurately determined using CALIOP data through directly measured parameters such as optical depth, volume depolarization ratio, attenuated backscatter, and color ratio. On average, clouds below 5 km had a daytime instantaneous shortwave (SW) radiative flux of 270.2 ± 16.9 W/m2 and thin cirrus clouds had a SW radiative flux of 208.0 ± 12.7 W/m2. When dust aerosols interacted with clouds below 5 km, as determined from CALIPSO, the SW radiative flux decreased to 205.4 ± 13.0 W/m2. Similarly, smoke aerosols decreased the SW radiative flux of low clouds to a value of 240.0 ± 16.6 W/m2. These decreases in SW radiative flux were likely attributed to the aerosol layer height and changes in cloud microphysics. CALIOP lidar observations, which more accurately identify aerosol layer height than passive instruments, appear essential for better understanding of cloud-aerosol interactions, a major uncertainty in predicting the climate system.

Yorks, John E.; McGill, Matt; Rodier, Sharon; Vaughan, Mark; Hu, Yongxiang; Hlavka, Dennis

2009-09-01

226

Simulation of Space-borne Radar Observation from High Resolution Cloud Model - for GPM Dual frequency Precipitation Radar -  

NASA Astrophysics Data System (ADS)

A comprehensive space-borne radar simulator has been developed to support active microwave sensor satellite missions. The two major objectives of this study are: 1) to develop a radar simulator optimized for the Dual-frequency Precipitation Radar (KuPR and KaPR) on the Global Precipitation Measurement Mission satellite (GPM-DPR) and 2) to generate the synthetic test datasets for DPR algorithm development. This simulator consists of two modules: a DPR scanning configuration module and a forward module that generates atmospheric and surface radar observations. To generate realistic DPR test data, the scanning configuration module specifies the technical characteristics of DPR sensor and emulates the scanning geometry of the DPR with a inner swath of about 120 km, which contains matched-beam data from both frequencies, and an outer swath from 120 to 245 km over which only Ku-band data will be acquired. The second module is a forward model used to compute radar observables (reflectivity, attenuation and polarimetric variables) from input model variables including temperature, pressure and water content (rain water, cloud water, cloud ice, snow, graupel and water vapor) over the radar resolution volume. Presently, the input data to the simulator come from the Goddard Cumulus Ensemble (GCE) and Weather Research and Forecast (WRF) models where a constant mass density is assumed for each species with a particle size distribution given by an exponential distribution with fixed intercept parameter (N0) and a slope parameter (?) determined from the equivalent water content. Although the model data do not presently contain mixed phase hydrometeors, the Yokoyama-Tanaka melting model is used along with the Bruggeman effective dielectric constant to replace rain and snow particles, where both are present, with mixed phase particles while preserving the snow/water fraction. For testing one of the DPR retrieval algorithms, the Surface Reference Technique (SRT), the simulator uses the normalized radar cross sections of the surface,?0, at each frequency and incidence angle to generate the radar return power from the surface. The simulated ?0 data are modeled as realizations from jointly Gaussian random variables with means, variances and correlations obtained from measurements of ?0 from the JPL APR2 (2nd generation Airborne Precipitation Radar) data, which operates at approximately the same frequencies as the DPR. We will discuss the general capabilities of the radar simulator, present some sample results and show how they can be used to assess the performance of the radar retrieval algorithms proposed for the Dual-Frequency GPM radar. In addition, we will report on updates to the simulator using inputs from cloud models with spectral bin microphysics.

Kim, H.; Meneghini, R.; Jones, J.; Liao, L.

2011-12-01

227

Separation of millimeter-wave radar reflectivities of aggregates and pristine ice crystals in a cloud  

Microsoft Academic Search

Millimeter wave radars operating at 35 and 94 GHz are being used for the remote sensing of ice clouds. Two-dimensional particle probe measurements in clouds show that a single type of ice crystals (e.g., column, plate, stellar crystal, etc.) is often observed in a mixture with ice crystal aggregates. This may pose a problem for estimating the ice water content

K. Aydin; T. M. Walsh

1998-01-01

228

Extensive ground-based Lidar and Radiometer Measurements of Aerosol and Cloud for the Comparison and Validation of CALIPSO retrievals  

NASA Astrophysics Data System (ADS)

We present the results of collocated measurements from CCNY ground-based multiwavelength Raman-Mie lidar and a CIMEL Sun/sky radiometer with CALIPSO overpasses near New York City (40.821N,73.949W). The data set consists of 19 days of observations conducted under the clear, hazy, and cloudy skies. In particular, statistical comparisons are made between the CALIPSO Level-2 5-km layer products and the ground-based lidar observations. We find in general excellent correlations exist between both cloud base and cloud top even for multiple deck cases that are not to close. In the clear skies, the CALIPSO aerosol layer tops are consistent with ground-lidar derived PBL heights although the accuracy degrades if capped by cloud layers. In addition, we perform a detailed comparison for smoke and polluted dust entrainments including aerosol classification, derivation of extinction profiles and lidar ratios. Aerosol extinction profiles are shown to be in good agreement when processed directly using the Fernald algorithm. Problems are seen when CALIPSO misidentifies plumes as clouds and processes the extinction data incorrectly. Finally, we derive planetary boundary layer (PBL) heights directly from the CALIPSO level-1B profiles and show reasonable statistical agreement to the Level-2 layer height product. Comparisons to PBL heights in urban areas are also performed.

Wu, Y.; Herman, B.; Gross, B.; Moshary, F.; Ahmed, S.

2008-12-01

229

Lidar investigations on the optical and dynamical properties of cirrus clouds in the upper troposphere and lower stratosphere regions at a tropical station, Gadanki, India (13.5°N, 79.2°E)  

NASA Astrophysics Data System (ADS)

High altitude cirrus clouds are composed mainly of ice crystals with a variety of sizes and shapes. They have a large influence on Earth's energy balance and global climate. Recent studies indicate that the formation, dissipation, life time, optical, and micro-physical properties are influenced by the dynamical conditions of the surrounding atmosphere like background aerosol, turbulence, etc. In this work, an attempt has been made to quantify some of these characteristics by using lidar and mesosphere-stratosphere-troposphere (MST) radar. Mie lidar and 53 MHz MST radar measurements made over 41 nights during the period 2009 to 2010 from the tropical station, Gadanki, India (13.5°N, 79.2°E). The optical and microphysical properties along with the structure and dynamics of the cirrus are presented as observed under different atmospheric conditions. The study reveals the manifestation of different forms of cirrus with a preferred altitude of formation in the 13 to 14 km altitude. There are considerable differences in the properties obtained among 2009 and 2010 showing significant anomalous behavior in 2010. The clouds observed during 2010 show relatively high asymmetry and large multiple scattering effects. The anomalies found during 2010 may be attributed to the turbulence noticed in the surrounding atmosphere. The results show a clear correlation between the crystal morphology in the clouds and the dynamical conditions of the prevailing atmosphere during the observational period.

Krishnakumar, Vasudevannair; Satyanarayana, Malladi; Radhakrishnan, Soman R.; Dhaman, Reji K.; Jayeshlal, Glory Selvan; Motty, Gopinathan Nair S.; Pillai, Vellara P. Mahadevan; Raghunath, Karnam; Ratnam, Madineni Venkat; Rao, Duggirala Ramakrishna; Sudhakar, Pindlodi

2014-01-01

230

3-D earthquake surface displacements from differencing pre- and post-event LiDAR point clouds  

NASA Astrophysics Data System (ADS)

The explosion in aerial LiDAR surveying along active faults across the western United States and elsewhere provides a high-resolution topographic baseline against which to compare repeat LiDAR datasets collected after future earthquakes. We present a new method for determining 3-D coseismic surface displacements and rotations by differencing pre- and post-earthquake LiDAR point clouds using an adaptation of the Iterative Closest Point (ICP) algorithm, a point set registration technique widely used in medical imaging, computer vision and graphics. There is no need for any gridding or smoothing of the LiDAR data and the method works well even with large mismatches in the density of the two point clouds. To explore the method's performance, we simulate pre- and post-event point clouds using real ("B4") LiDAR data on the southern San Andreas Fault perturbed with displacements of known magnitude. For input point clouds with ~2 points per square meter, we are able to reproduce displacements with a 50 m grid spacing and with horizontal and vertical accuracies of ~20 cm and ~4 cm. In the future, finer grids and improved precisions should be possible with higher shot densities and better survey geo-referencing. By capturing near-fault deformation in 3-D, LiDAR differencing with ICP will complement satellite-based techniques such as InSAR which map only certain components of the surface deformation and which often break down close to surface faulting or in areas of dense vegetation. It will be especially useful for mapping shallow fault slip and rupture zone deformation, helping inform paleoseismic studies and better constrain fault zone rheology. Because ICP can image rotations directly, the technique will also help resolve the detailed kinematics of distributed zones of faulting where block rotations may be common.

Krishnan, A. K.; Nissen, E.; Arrowsmith, R.; Saripalli, S.

2012-12-01

231

Observations of Typhoon Melissa during the Lidar In-Space Technology Experiment (LITE)  

Microsoft Academic Search

The ability to predict the intensity and movement of tropical cyclones depends on understanding their structure. Information on tropical cyclone structure is provided by ground based Doppler radar; aircraft in situ, Doppler radar, and dropsonde measurements; and satellite soundings and images. Unfortunately, these instruments do not allow the vertical cloud structure of tropical cyclones to be studied. The Lidar In-space

T. A. Kovacs; M. P. McCormick

2002-01-01

232

Noctilucent cloud variability and mean parameters from 15 years of lidar observations at a mid-latitude site (54°N, 12°E)  

NASA Astrophysics Data System (ADS)

Noctilucent clouds (NLC) are an important tracer of temperature and dynamics of the summer mesopause region. Our site at Kühlungsborn (Germany, 54°N) is at the equatorward edge of the NLC region and therefore of special interest for the understanding of these clouds. 41 nights (63 h) of NLC are observed since 1997. They form the largest lidar data set from mid-latitudes. NLC are typically weak, with nearly 70% having a backscatter coefficient ?max,532nm < 2 ? 10-10 m-1 sr-1. The seasonal variation of NLC shows maximum occurrence around the temperature minimum (saturation maximum) but lower temperatures (higher saturation) at the beginning compared to the end of the season. Mean centroid altitude is 82.7 ± 0.03 km, with strong NLC being typically lower and vertically thinner compared to weak clouds. NLC occurrence was lowest in the years 2000-2002 and reached a maximum in 2009 with a rate of 19%. Overall, NLC are less frequent and dimmer compared to higher latitudes. The occurrence is highly anti-correlated with solar activity. Beside NLC, we are measuring mesospheric temperatures since 2002 by lidars, complemented by microwave observations of water vapor (since October 2009) and radar observations of mesospheric winds. NLC occurrence is found anti-correlated with ambient temperatures (r = -0.85 at 84 km), while low temperatures are necessary but not sufficient for individual events. Meridional winds at 84 km are weakly anti-correlated with NLC occurrence (r = -0.58 at 84 km). Furthermore, we find some biennial variation of NLC occurrence in part of the time series. Any additional trend has not yet been detected.

Gerding, M.; HöFfner, J.; Hoffmann, P.; Kopp, M.; Lübken, F.-J.

2013-01-01

233

ESYRO Lidar system developments for troposphere monitoring of aerosols and clouds properties  

NASA Astrophysics Data System (ADS)

Aiming the remote sensing low cost, up-gradable and modular tools development for monitoring relevant atmospheric parameters and processes in the whole troposphere (from 250 m to 12-15 Km altitude), a new configuration LIDAR system, i.e. ESYROLIDAR, dedicated for tropospheric aerosols and clouds high temporal (minutes) and spatial resolutions (meters) monitoring have been developed and tested. This extremely up-gradable configuration of ESYROLIDAR is based on: a multi -wavelengths (1064, 532 and 355 nm) powerful (200, 100 and 45 mJ/pulse) and relatively high variable repetition rate (up to 30 Hz) Nd:YAG pulsed laser, a large Newtonian telescope (40 cm diameter of collector mirror) and a new opto-mechanics detection module built in an original "eye geometry" consideration. The firsts tests and measurements were performed at the site of Science and Technology Park TehnopolIS (Iasi city located on the northeastern region of Romania), using a basic configuration with a 532 nm elastic detection with depolarization study module. Different types of clouds up to 12 km in daylight are highlighted from this first measurement. Measurements and tests made in other recent campaigns for 355 nm elastic channel are also presented. The ability of the new LIDAR system to determine the height of planetary boundary layer (PBL) determined from the LIDAR signals, as well as the aerosols load and optical parameters (extinction and backscatter) and the evaluation of atmospheric dynamics at high spatial-temporal resolutions are clearly confirmed. This paper presents the ESYROLIDAR basic configuration with its two VIS elastic channels (532 nm, parallel and cross). The first measurements made with the UV (355 nm - interchangeable channel) and VIS (532 nm) elastic channels are illustrated by typical examples. The quality of ESYROLIDAR atmospheric profiles is based on advantages of low divergence (0.15 mrad), relatively high repetition rate (30 Hz) and the coaxial UV-VIS-NIR .The present challenges are first a new robust more automatized alignment system and second the integration of more Raman detection channels i.e. Raman H2O water vapor at 407 nm. This system is the base of the ROmanian LIdar NETwork (ROLINET).

Tudose, Ovidiu-Gelu; Cazacu, Marius-Mihai; Timofte, Adrian; Balin, Ioan

2011-10-01

234

Measurements of the Vertical Structure of Aerosols and Clouds Over the Ocean Using Micro-Pulse LIDAR Systems  

NASA Technical Reports Server (NTRS)

The determination of the vertical distribution of aerosols and clouds over the ocean is needed for accurate retrievals of ocean color from satellites observations. The presence of absorbing aerosol layers, especially at altitudes above the boundary layer, has been shown to influence the calculation of ocean color. Also, satellite data must be correctly screened for the presence of clouds, particularly cirrus, in order to measure ocean color. One instrument capable of providing this information is a lidar, which uses pulses of laser light to profile the vertical distribution of aerosol and cloud layers in the atmosphere. However, lidar systems prior to the 1990s were large, expensive, and not eye-safe which made them unsuitable for cruise deployments. During the 1990s the first small, autonomous, and eye-safe lidar system became available: the micro-pulse lidar, or MPL. The MPL is a compact and eye-safe lidar system capable of determining the range of aerosols and clouds by firing a short pulse of laser light (523 nm) and measuring the time-of-flight from pulse transmission to reception of a returned signal. The returned signal is a function of time, converted into range using the speed of light, and is proportional to the amount of light backscattered by atmospheric molecules (Rayleigh scattering), aerosols, and clouds. The MPL achieves ANSI eye-safe standards by sending laser pulses at low energy (micro-J) and expanding the beam to 20.32 cm in diameter. A fast pulse-repetition-frequency (2500 Hz) is used to achieve a good signal-to-noise, despite the low output energy. The MPL has a small field-of-view (< 100 micro-rad) and signals received with the instrument do not contain multiple scattering effects. The MPL has been used successfully at a number of long-term sites and also in several field experiments around the world.

Welton, Ellsworth J.; Spinhirne, James D.; Campbell, James R.; Berkoff, Timothy A.; Bates, David; Starr, David OC. (Technical Monitor)

2001-01-01

235

A joint study of the lower ionosphere by radar, lidar, and spectrometer  

SciTech Connect

The dynamics and associated phenomena occurring in the lower ionospheric-E region, especially the mesopause region between 80 km to 110 km at low latitude, are studied. In particular, incoherent scatter radar (ISR), sodium lidar and airglow spectrometry are used to study the ionospheric structure and neutral sodium structure. The simultaneous study of the ionospheric plasma and neutral atomic sodium is unprecedented in scope and detail. The joint study of the mesopause region reveals that plasma, neutral densities and temperature are interconnected through the same atmospheric dynamics. The theme of the thesis is to explain the formation of the controversial sporadic sodium layer (SSL) events. Strong correlation is established between the average total ion and sodium concentrations, and between sporadic-E and SSL events. The mechanism proposed in the thesis, which invokes temperature fluctuations induced by tides and gravity waves, finds good agreement with observations. Tides and gravity waves can converge ions into thin layers through the windshear mechanisms and can influence the concentration of atomic sodium through temperature fluctuations. Sodium abundance is shown to augment rapidly when the temperature is increased. Gravity wave theory states that the ion convergence node coincides with a temperature maximum for a westward propagating gravity wave, and coincides with a temperature minimum for an eastward propagating wave. Because tidal winds propagate westward, the ion layer coincides with the temperature maximum which consequently induces higher sodium concentration. This can account for the general correlation between sodium and total ion concentration and is supported by the O2(0-1) rotational temperature. Gravity waves and their interaction with tidal winds are believed to be responsible for the close association between sudden sodium layers and sporadic-E layers.

Zhou, Qihou.

1991-01-01

236

Improving 3d LIDAR Point Cloud Registration Using Optimal Neighborhood Knowledge  

NASA Astrophysics Data System (ADS)

Automatic 3D point cloud registration is a main issue in computer vision and photogrammetry. The most commonly adopted solution is the well-known ICP (Iterative Closest Point) algorithm. This standard approach performs a fine registration of two overlapping point clouds by iteratively estimating the transformation parameters, and assuming that good a priori alignment is provided. A large body of literature has proposed many variations of this algorithm in order to improve each step of the process. The aim of this paper is to demonstrate how the knowledge of the optimal neighborhood of each 3D point can improve the speed and the accuracy of each of these steps. We will first present the geometrical features that are the basis of this work. These low-level attributes describe the shape of the neighborhood of each 3D point, computed by combining the eigenvalues of the local structure tensor. Furthermore, they allow to retrieve the optimal size for analyzing the neighborhood as well as the privileged local dimension (linear, planar, or volumetric). Besides, several variations of each step of the ICP process are proposed and analyzed by introducing these features. These variations are then compared on real datasets, as well with the original algorithm in order to retrieve the most efficient algorithm for the whole process. Finally, the method is successfully applied to various 3D lidar point clouds both from airborne, terrestrial and mobile mapping systems.

Gressin, A.; Mallet, C.; David, N.

2012-07-01

237

Characterization of Polar Stratospheric Clouds With Spaceborne Lidar: CALIPSO and the 2006 Antarctic Season  

NASA Technical Reports Server (NTRS)

The role of polar stratospheric clouds in polar ozone loss has been well documented. The CALIPSO satellite mission offers a new opportunity to characterize PSCs on spatial and temporal scales previously unavailable. A PSC detection algorithm based on a single wavelength threshold approach has been developed for CALIPSO. The method appears to accurately detect PSCs of all opacities, including tenuous clouds, with a very low rate of false positives and few missed clouds. We applied the algorithm to CALIPSO data acquired during the 2006 Antarctic winter season from 13 June through 31 October. The spatial and temporal distribution of CALIPSO PSC observations is illustrated with weekly maps of PSC occurrence. The evolution of the 2006 PSC season is depicted by time series of daily PSC frequency as a function of altitude. Comparisons with virtual solar occultation data indicate that CALIPSO provides a different view of the PSC season than attained with previous solar occultation satellites. Measurement-based time series of PSC areal coverage and vertically-integrated PSC volume are computed from the CALIPSO data. The observed area covered with PSCs is significantly smaller than would be inferred from a temperature-based proxy such as TNAT but is similar in magnitude to that inferred from TSTS. The potential of CALIPSO measurements for investigating PSC microphysics is illustrated using combinations of lidar backscatter coefficient and volume depolarization to infer composition for two CALIPSO PSC scenes.

Pitts, Michael C.; Thomason, L. W.; Poole, Lamont R.; Winker, David M.

2007-01-01

238

Buildings classification from airborne LiDAR point clouds through OBIA and ontology driven approach  

NASA Astrophysics Data System (ADS)

In the last years, airborne Light Detection and Ranging (LiDAR) data proved to be a valuable information resource for a vast number of applications ranging from land cover mapping to individual surface feature extraction from complex urban environments. To extract information from LiDAR data, users apply prior knowledge. Unfortunately, there is no consistent initiative for structuring this knowledge into data models that can be shared and reused across different applications and domains. The absence of such models poses great challenges to data interpretation, data fusion and integration as well as information transferability. The intention of this work is to describe the design, development and deployment of an ontology-based system to classify buildings from airborne LiDAR data. The novelty of this approach consists of the development of a domain ontology that specifies explicitly the knowledge used to extract features from airborne LiDAR data. The overall goal of this approach is to investigate the possibility for classification of features of interest from LiDAR data by means of domain ontology. The proposed workflow is applied to the building extraction process for the region of "Biberach an der Riss" in South Germany. Strip-adjusted and georeferenced airborne LiDAR data is processed based on geometrical and radiometric signatures stored within the point cloud. Region-growing segmentation algorithms are applied and segmented regions are exported to the GeoJSON format. Subsequently, the data is imported into the ontology-based reasoning process used to automatically classify exported features of interest. Based on the ontology it becomes possible to define domain concepts, associated properties and relations. As a consequence, the resulting specific body of knowledge restricts possible interpretation variants. Moreover, ontologies are machinable and thus it is possible to run reasoning on top of them. Available reasoners (FACT++, JESS, Pellet) are used to check the consistency of the developed ontologies, and logical reasoning is performed to infer implicit relations between defined concepts. The ontology for the definition of building is specified using the Ontology Web Language (OWL). It is the most widely used ontology language that is based on Description Logics (DL). DL allows the description of internal properties of modelled concepts (roof typology, shape, area, height etc.) and relationships between objects (IS_A, MEMBER_OF/INSTANCE_OF). It captures terminological knowledge (TBox) as well as assertional knowledge (ABox) - that represents facts about concept instances, i.e. the buildings in airborne LiDAR data. To assess the classification accuracy, ground truth data generated by visual interpretation and calculated classification results in terms of precision and recall are used. The advantages of this approach are: (i) flexibility, (ii) transferability, and (iii) extendibility - i.e. ontology can be extended with further concepts, data properties and object properties.

Tomljenovic, Ivan; Belgiu, Mariana; Lampoltshammer, Thomas J.

2013-04-01

239

Dynamical Characteristics of Cirrus Clouds from Aircraft and Radar Measurements.  

National Technical Information Service (NTIS)

Cirrus clouds play an important role in climate and in the development of other types of clouds. Although there are many studies of clouds within the boundary layer, cirrus clouds have been neglected up until the last decade. New tools and in-situ measure...

I. Gultepe D. Starr A. J. Heymsfield M. Poellot T. Uttal

1993-01-01

240

Quantification of waves in lidar observations of noctilucent clouds at scales from seconds to minutes  

NASA Astrophysics Data System (ADS)

We present small-scale structures and waves observed in noctilucent clouds by lidar at an unprecedented temporal resolution of 30 s and less. The measurements were taken with the Rayleigh-/Mie-/Raman-lidar at the ALOMAR observatory in northern Norway (69° N) in the years 2008-2011. We find multiple layer NLC in 7.9% of the time for a brightness threshold of ? ? = 12×10-10 m-1 sr-1. In comparison to 10 min averaged data, the 30 s data set shows considerably more structure. For limited periods, quasi-monochromatic waves in NLC altitude variations are common, in accord with ground-based NLC imagery. For the combined dataset on the other hand, we do not find preferred periods but significant periods at all time scales observed (1 min to 1 h). Typical wave amplitudes in the layer vertical displacements are 0.2 km with maximum amplitudes up to 2.3 km. Average spectral slopes of temporal altitude and brightness variations are -1.84 ± 0.31 for centroid altitude, -1.28 ± 0.29 for peak brightness and -1.62 ± 0.28 for integrated brightness. Evaluating a new single-pulse detection system, we observe altitude variations of 70 s period and spectral slopes down to a scale of 10 s. We evaluate the suitability of NLC parameters as tracers for gravity waves.

Kaifler, N.; Baumgarten, G.; Fiedler, J.; Lübken, F.-J.

2013-03-01

241

Quantification of waves in lidar observations of noctilucent clouds at scales from seconds to minutes  

NASA Astrophysics Data System (ADS)

We present small-scale structures and waves observed in noctilucent clouds (NLC) by lidar at an unprecedented temporal resolution of 30 s or less. The measurements were taken with the Rayleigh/Mie/Raman lidar at the ALOMAR observatory in northern Norway (69° N) in the years 2008-2011. We find multiple layer NLC in 7.9% of the time for a brightness threshold of ? ? = 12 × 10-10 m-1 sr-1. In comparison to 10 min averaged data, the 30 s dataset shows considerably more structure. For limited periods, quasi-monochromatic waves in NLC altitude variations are common, in accord with ground-based NLC imagery. For the combined dataset, on the other hand, we do not find preferred periods but rather significant periods at all timescales observed (1 min to 1 h). Typical wave amplitudes in the layer vertical displacements are 0.2 km with maximum amplitudes up to 2.3 km. Average spectral slopes of temporal altitude and brightness variations are -2.01 ± 0.25 for centroid altitude, -1.41 ± 0.24 for peak brightness and -1.73 ± 0.25 for integrated brightness. Evaluating a new single-pulse detection system, we observe altitude variations of 70 s period and spectral slopes down to a scale of 10 s. We evaluate the suitability of NLC parameters as tracers for gravity waves.

Kaifler, N.; Baumgarten, G.; Fiedler, J.; Lübken, F.-J.

2013-12-01

242

Design and development of micro pulse lidar for cloud and aerosol studies  

NASA Astrophysics Data System (ADS)

A micro pulse lidar (MPL) has been indigenously designed and developed at the National Physical Laboratory, New Delhi using a 532 nm, 500 pico second pulsed laser having average power of 50mW (at 7.5 KHz PRR). Photon counting technique has been incorporated using the conventional optics, multichannel scaler (Stanford Research Systems SR430) and high sensitive photomultiplier tube. The sensitivity, range and bin etc are computer controlled in the present system. The interfacing between MPL and computer has been achieved by serial (RS232) and parallel printer port. The necessary software and graphical user interface has been developed using visual basic. In addition to this the telescope cover status sensing circuit has been incorporated to avoid conflict between dark count and background acquisition. The micro pulse lidar will be used for the aerosol, boundary layer and the cloud studies at a bin resolution of 6 meters. In the present communication the details of the system and preliminary results will be presented.

Dubey, P. K.; Arya, B. C.; Ahammed, Y. Nazeer; Kumar, Arun; Kulkarni, P. S.; Jain, S. L.

2008-12-01

243

Dual-polarization airborne lidar observations of polar stratospheric cloud evolution  

NASA Technical Reports Server (NTRS)

Dual-polarization 0.532 micron lidar data show systematic polar stratospheric cloud (PSC) evolution along a portion of the Airborne Arctic Stratospheric Expedition DC-8 flight of January 31, 1989. This flight leg was roughly aligned with air parcel motion on isentropic surfaces from 400-500 K, where the local adiabatic cooling rate was about 20 K/day. Type 1 PSCs show low depolarization ratios and scattering ratios which approach intermediate limiting values as ambient temperature decreases. These data suggest that Type 1 particles formed by rapid cooling may be nearly spherical and are restricted in size by partitioning of a limited HNO3 vapor supply among many competing growth sites. Type 2 PSCs appear at temperatures below estimated local frost points with increases in depolarization and scattering typical of larger ice crystals.

Poole, L. R.; Mccormick, M. P.; Kent, G. S.; Hunt, W. H.; Osborn, M. T.

1990-01-01

244

High Spectral Resolution Lidar measurements of extinction and particle size in clouds  

NASA Technical Reports Server (NTRS)

The spectral width of light backscattered from molecules is increased due to Doppler shifts caused by the thermal motion of the molecules. The thermal motion of aerosol and cloud particles is much slower and the backscatter spectrum is nearly unchanged. The University of Wiconsin High Spectral Resolution Lidar (RSRL) measures optical properties of the atmosphere by separating the Doppler-broadened molecular backscatter return from the unbroadened aerosol return. The molecular backscatter cross section can be calculated from the molecular density profile. Thus, observing the magnitude of the measured molecular signal relative to the computed profile allows unambiguous measurement of the atmospheric extinction profile. The ratio of the aerosol return to the molecular return along with the computed molecular cross section provides direct measurement of the aerosol backscatter cross section.

Eloranta, E. W.; Piironen, P.

1995-01-01

245

ARM Millimeter Wave Cloud Radars (MMCRs) and the Active Remote Sensing of Clouds (ARSCL) Value Added Product (VAP).  

National Technical Information Service (NTIS)

The Millimeter Wave Cloud Radars (MMCRs) are designed as a remote sensing tool that can accurately detect almost all of the hydrometeors present in the atmosphere. To illustrate the difficulty of this task, the various types of hydrometeors that can occur...

E. E. Clothiaux M. A. Miller R. C. Perez D. D. Turner K. P. Moran

2001-01-01

246

A 94 GHz RF Electronics Subsystem for the CloudSat Cloud Profiling Radar  

NASA Technical Reports Server (NTRS)

The CloudSat spacecraft, scheduled for launch in 2004, will carry the 94 GHz Cloud Profiling Radar (CPR) instrument. The design, assembly and test of the flight Radio Frequency Electronics Subsystem (RFES) for this instrument has been completed and is presented here. The RFES consists of an Upconverter (which includes an Exciter and two Drive Amplifiers (DA's)), a Receiver, and a Transmitter Calibrator assembly. Some key performance parameters of the RFES are as follows: dual 100 mW pulse-modulated drive outputs at 94 GHz, overall Receiver noise figure < 5.0 dB, a highly stable W-band noise source to provide knowledge accuracy of Receiver gain of < 0.4 dB over the 2 year mission life, and a W-band peak power detector to monitor the transmitter output power to within 0.5 dB over life. Some recent monolithic microwave integrated circuit (MMIC) designs were utilized which implement the DA's in 0.1 micron GaAs high electron-mobility transistor (HEMT) technology and the Receiver low-noise amplifier (LNA) in 0.1 micron InP HEMT technology.

LaBelle, Remi C.; Girard, Ralph; Arbery, Graham

2003-01-01

247

Retrieving microphysical properties and air motion of cirrus clouds based on the doppler moments method using cloud radar  

NASA Astrophysics Data System (ADS)

Radar parameters including radar reflectivity, Doppler velocity, and Doppler spectrum width were obtained from Doppler spectrum moments. The Doppler spectrum moment is the convolution of both the particle spectrum and the mean air vertical motion. Unlike strong precipitation, the motion of particles in cirrus clouds is quite close to the air motion around them. In this study, a method of Doppler moments was developed and used to retrieve cirrus cloud microphysical properties such as the mean air vertical velocity, mass-weighted diameter, effective particle size, and ice content. Ice content values were retrieved using both the Doppler spectrum method and classic Z-IWC (radar reflectivity-ice water content) relationships; however, the former is a more reasonable method.

Zhong, Lingzhi; Liu, Liping; Deng, Min; Zhou, Xiuji

2012-05-01

248

Analysis and Calibration of CRF Raman Lidar Cloud Liquid Water Measurements  

SciTech Connect

The Atmospheric Radiation Measurement (ARM) Raman lidar (RL), located at the Southern Great Plains (SGP) Climate Research Facility (CRF), is a unique state-of-the-art active remote sensor that is able to measure profiles of water vapor, aerosol, and cloud properties at high temporal and vertical resolution throughout the diurnal cycle. In October 2005, the capability of the RL was extended by the addition of a new detection channel that is sensitive to the Raman scattering of liquid water. This new channel permits the system, in theory, to measure profiles of liquid water content (LWC) by the RL. To our knowledge, the ARM RL is the only operation lidar with this capability. The liquid water Raman backscattering cross-section is a relatively weak and spectrally broad feature, relative to the water vapor Raman backscatter signal. The wide bandpass required to achieve reasonable signal-to-noise in the liquid water channel essentially eliminates the ability to measure LWC profiles during the daytime in the presence of large solar background, and thus all LWC observations are nighttime only. Additionally, the wide bandpass increases the probability that other undesirable signals, such as fluorescence from aerosols, may contaminate the observation. The liquid water Raman cross-section has a small amount of overlap with the water vapor Raman cross-section, and thus there will be a small amount of ‘cross-talk’ between the two signals, with water vapor contributing a small amount of signal to the LWC observation. And finally, there is significant uncertainty in the actual strength of the liquid water Raman cross-section in the literature. The calibrated LWC profiles, together with the coincident cloud backscatter observations also made by the RL, can be used to derive profiles of cloud droplet effective radius. By combining these profiles of effective radius in the lower portion of the cloud with the aerosol extinction measurements made below the cloud by the RL, the first aerosol indirect effect can be investigated using a single instrument, thereby reducing the uncertainty associated with aligning the different sampling periods and fields of view of multiple instruments. We have applied a “first principles” calibration to the LWC profiles. This approach requires that the relative differences in optical efficiency between the water vapor and liquid water channels be known; this relative difference is easily computed using the efficiency values of the beam splitters and interference filters in the lidar that were provided by the vendors of these components. The first principles approach then transfers the calibration from the water vapor mixing ratio to the LWC using the difference in the optical efficiency and an interpolated value of the liquid water Raman cross section from the literature, and the better established water vapor Raman cross section. After accounting for all known error sources, the vertical integral of LWC was compared against a similar value retrieved from a co-located ground-based infrared radiometer. The RL and infrared radiometer have significantly different fields of view; thus to compare the two sensors the data were averaged to 5 min intervals where only cloudy samples were included in the average of each. While there is fair scatter in the data (r=0.47), there is also a clear indication of a positive correlation between the infrared and the RL values. The value of the slope of the regression is 0.49, which indicates a tendency of the RL measurements to underestimate the total liquid amount with respect to the infrared retrieval. Research continues to investigate the source of the bias, but the most likely candidate is the large uncertainty in the liquid water Raman cross-section as there have been no direct measurements made of this parameter at the lidar’s laser wavelength of 355 nm. The calibrated LWC profile was then used together with the cloud backscatter coefficient profile from the RL to derive profiles of cloud droplet effective radius and cloud droplet number density. These profiles o

Turner, D.D. Whiteman, D.N. Russo, F.

2007-10-31

249

Evaluation of gridded scanning ARM cloud radar reflectivity observations and vertical doppler velocity retrievals  

NASA Astrophysics Data System (ADS)

The scanning Atmospheric Radiation Measurement (ARM) cloud radars (SACRs) provide continuous atmospheric observations aspiring to capture the 3-D cloud-scale structure. Sampling clouds in 3-D is challenging due to their temporal-spatial scales, the need to sample the sky at high elevations and cloud radar limitations. Thus, a suggested scan strategy is to repetitively slice the atmosphere from horizon to horizon as clouds advect over the radar (Cross-Wind Range-Height Indicator - CW-RHI). Here, the processing and gridding of the SACR CW-RHI scans are presented. First, the SACR sample observations from the ARM Southern Great Plains and Cape Cod sites are post-processed (detection mask, gaseous attenuation correction, insect filtering and velocity de-aliasing). The resulting radial Doppler moment fields are then mapped to Cartesian coordinates with time as one of the dimensions. Next the Cartesian-gridded Doppler velocity fields are decomposed into the horizontal wind velocity contribution and the vertical Doppler velocity component. For validation purposes, all gridded and retrieved fields are compared to collocated zenith-pointing ARM cloud radar measurements. We consider that the SACR sensitivity loss with range, the cloud type observed and the research purpose should be considered in determining the gridded domain size. Our results also demonstrate that the gridded SACR observations resolve the main features of low and high stratiform clouds. It is established that the CW-RHI observations complemented with processing techniques could lead to robust 3-D cloud dynamical representations up to 25-30 degrees off zenith. The proposed gridded products are expected to advance our understanding of 3-D cloud morphology, dynamics and anisotropy and lead to more realistic 3-D radiative transfer calculations.

Lamer, K.; Tatarevic, A.; Jo, I.; Kollias, P.

2014-04-01

250

Evaluation of gridded Scanning ARM Cloud Radar reflectivity observations and vertical Doppler velocity retrievals  

NASA Astrophysics Data System (ADS)

The Scanning ARM Cloud Radars (SACR's) provide continuous atmospheric observations aspiring to capture the 3-D cloud-scale structure. Sampling clouds in 3-D is challenging due to their temporal-spatial scales, the need to sample the sky at high elevations and cloud radar limitations. Thus, a common scan strategy is to repetitively slice the atmosphere from horizon to horizon as clouds advect over the radar (Cross-Wind Range Height Indicator - CWRHI). Here, the processing and gridding of the SACR CW-RHI scans are presented. First, the SACR sample observations from the ARM Oklahoma (SGP) and Cape-Cod (PVC) sites are post-processed (detection mask, velocity de-aliasing and gaseous attenuation correction). The resulting radial Doppler moment fields are then mapped to Cartesian coordinates with time as one of the dimension. The Cartesian-gridded Doppler velocity fields are next decomposed into the horizontal wind velocity contribution and the vertical Doppler velocity component. For validation purposes, all gridded and retrieved fields are compared to collocated zenith pointing ARM cloud radar measurements. We consider that the SACR sensitivity loss with range, the cloud type observed and the research purpose should be considered in determining the gridded domain size. Our results also demonstrate that the gridded SACR observations resolve the main features of low and high stratiform clouds. It is established that the CW-RHI observations complemented with processing techniques could lead to robust 3-D clouds dynamical representations up to 25-30° off zenith. The proposed gridded products are expected to advance our understanding of 3-D cloud morphology, dynamics, anisotropy and lead to more realistic 3-D radiative transfer calculations.

Lamer, K.; Tatarevic, A.; Jo, I.; Kollias, P.

2013-11-01

251

Global distribution of cirrus clouds from CloudSat\\/Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) measurements  

Microsoft Academic Search

The cirrus clouds of the upper troposphere are globally widespread and are important regulators of the radiative balance, and hence climate, of the Earth-atmosphere system. Despite their wide distribution, however, cirrus are difficult to study from satellite radiance measurements or from scattered ground observing sites because they can occur as part of multilayered cloud systems and are characteristically optically thin.

Kenneth Sassen; Zhien Wang; Dong Liu

2008-01-01

252

Application of the CloudSat and NEXRAD Radars Toward Improvements in High Resolution Operational Forecasts  

NASA Technical Reports Server (NTRS)

As computational power increases, operational forecast models are performing simulations with higher spatial resolution allowing for the transition from sub-grid scale cloud parameterizations to an explicit forecast of cloud characteristics and precipitation through the use of single- or multi-moment bulk water microphysics schemes. investments in space-borne and terrestrial remote sensing have developed the NASA CloudSat Cloud Profiling Radar and the NOAA National Weather Service NEXRAD system, each providing observations related to the bulk properties of clouds and precipitation through measurements of reflectivity. CloudSat and NEXRAD system radars observed light to moderate snowfall in association with a cold-season, midlatitude cyclone traversing the Central United States in February 2007. These systems are responsible for widespread cloud cover and various types of precipitation, are of economic consequence, and pose a challenge to operational forecasters. This event is simulated with the Weather Research and Forecast (WRF) Model, utilizing the NASA Goddard Cumulus Ensemble microphysics scheme. Comparisons are made between WRF-simulated and observed reflectivity available from the CloudSat and NEXRAD systems. The application of CloudSat reflectivity is made possible through the QuickBeam radiative transfer model, with cautious application applied in light of single scattering characteristics and spherical target assumptions. Significant differences are noted within modeled and observed cloud profiles, based upon simulated reflectivity, and modifications to the single-moment scheme are tested through a supplemental WRF forecast that incorporates a temperature dependent snow crystal size distribution.

Molthan, A. L.; Haynes, J. A.; Case, J. L.; Jedlovec, G. L.; Lapenta, W. M.

2008-01-01

253

Retrieving fog liquid water content using a new 94 GHz FMCW cloud radar  

NASA Astrophysics Data System (ADS)

The vertical distribution of the liquid water content (LWC) in fog and low stratus is a critical microphysical parameter since it essentially influences the interaction between these low level clouds and the solar and terrestrial radiation. Despite of this importance there are only few investigations concerning LWC-profiles during fog events, which are mainly restricted to balloon borne measurements and suffer from a low temporal resolution. Therefore, no continuous records covering the whole life cycle of fog events can be provided for climatology studies. A new ground based frequency modulated continuous wave (FMCW) cloud radar has the po-tential to fill this lack of knowledge. Working at a frequency of 94 GHz (wavelength 3 mm) it is ideal for monitoring low level water clouds. The radar can detect clouds at a minimum height range of ~30 m and provides a vertical resolution of 4m: This offers the potential to retrieve detailed vertical structures of fog and low stratus. The reconstruction of the LWC-profile can be accomplished due to the close relationship be-tween the cloud LWC and the detected radar reflectivity. However, this relationship depends strongly on the drop size distribution within the cloud. The strength of the radar reflectivity is related to the sixth power of the drop size distribution and the LWC is related to the latter by the third power. Former studies yielded the existence of different fog evolutionary stages with characteristical drop size distributions. In order to explore the effect of the different drop size distribution on the relationship between the radar reflectivity and the LWC we conducted radiative transfer calculations with characteristical drop size distributions and LWC-profiles taken from the literature. For this purpose we adapted the radiative transfer model (RTM) QuickBeam developed for the Cloudsat satellite to our ground based microwave radar. Beside the adaptation to the verti-cal resolution of the ground based cloud radar, the so-called modified gamma distribution, suitable to describe the drop size distribution in fog and low stratus, was implemented into the RTM. By applying representative coefficients for different fog evolutionary stages to the modified gamma distribution together with typical fog LWC-profiles the resulting radar re-flectivity was calculated. The poster presents the findings of the sensitivity study together with the conception of a new technique to retrieve fog LWC-profiles by means of a novel ground based 94 GHz FMCW cloud radar.

Maier, F.; Thies, B.; Bendix, J.

2010-07-01

254

Combining visible and infrared radiometry and lidar data to test ice clouds optical properties  

NASA Astrophysics Data System (ADS)

Measurements taken during the 2003 Pacific THORPEX Observing System Test (P-TOST) by the MODIS Airborne Simulator (MAS), the Scanning High-resolution Interferometer Sounder (S-HIS) and the Cloud Physics Lidar (CPL) are compared to simulations performed with a line-by-line and multiple scattering modeling methodology (LBLMS). Formerly used for infrared hyper-spectral data analysis, LBLMS has been extended to the visible and near infrared with the inclusion of surface bi-directional reflectance properties. A number of scenes are evaluated: two clear scenes, one with nadir geometry and one cross-track encompassing sun glint, and three cloudy scenes, all with nadir geometry. CPL data is used to estimate the particulate optical depth at 532 nm for the clear and cloudy scenes. Cloud optical depth is also retrieved from S-HIS infrared window radiances, and it agrees with CPL values, to within natural variability. MAS data are simulated convolving high resolution radiances. The paper discusses the results of the comparisons for the clear cases and for the three cloudy cases. LBLMS clear simulations agree with MAS data to within 20% in the shortwave (SW) and near infrared (NIR) spectrum and within 2 K in the infrared (IR) range. It is shown that cloudy sky simulations using cloud parameters retrieved from IR radiances systematically underestimate the measured radiance in the SW and NIR by nearly 50%, although the IR retrieved optical thickness agree with same measured by CPL. MODIS radiances measured from Terra are also compared to LBLMS simulations in cloudy conditions using retrieved cloud optical depth and effective radius from MODIS, to understand the origin for the observed discrepancies. It is shown that the simulations agree, to within natural variability, with measurements in selected MODIS SW bands. The paper dwells on a possible explanation of these contraddictory results, involving the phase function of ice particles in the shortwave.

Bozzo, A.; Maestri, T.; Rizzi, R.

2010-03-01

255

Operation Hardtack. Project 6. 6. X-band radar determination of nuclear-cloud parameters  

SciTech Connect

The general objectives of this project were to make observations with weather Radar Set AN/CPS-9 in order to determine what characteristics and parameters of a nuclear detonation could be detected with X-band radar. The specific objectives were to obtain data that would lead to the determination of the following information relative to the nuclear cloud; rate of rise, rate of horizontal growth, maximum height, maximum diameter, stabilized height, fallout pattern due to the initial cloud formation, and range and azimuth versus time. As a result of this project, it was determined that the AN/CPS-9 radar is well suited for observations of surface or near-surface bursts, as would be expected from a comparison of its performance characteristics with those of other available radar sets.

Bastian, C.W.; Robbiani, R.; Hargrave, J.

1985-09-01

256

Evaluation of the performance of the WRF model to reproduce the cloud cover and clouds features over the Mediterranean area using the CALIPSO lidar observations  

NASA Astrophysics Data System (ADS)

It is widely accepted that clouds play a major role on weather and climate forecast. However, the representation of clouds in models is largely uncertain due (i) to the number of processes and interactions involved in the formation and persistence of a cloud and (ii) the difficulty in obtaining accurate observations of clouds at all altitudes and locations. The evaluation of mesoscale models using recently developed parameterizations in different areas is therefore an essential step towards the improvement of clouds representation in models. The Aqua-Train offers an unprecedented set of observations for the microphysical properties of clouds that is very useful for validation of clouds features in models, especially over the sea where ground based instrumentation can not furnish observations. To avoid any inversion of the observed lidar signal that could induce errors responsible for discrepancies between observations and model, we use a model-to-satellite approach (Chepfer et al., 2008) to diagnose the lidar signal directly from model outputs. We then compare the observed space borne lidar profiles with the simulated ones. In this paper, we choose to evaluate the Thompson et al. (2004, 2008) microphysics scheme within the WRF model over the Mediterranean area. The occurrence of severe weather phenomenons, as well as the probable role of Mediterranean sea on climate change make the understanding and the representation of processes in this area a challenge for the future. A statistical study is carried out over several full months of observations. The first stage of the analysis focuses on the cloud occurrence discrepancy between observations and model for the three classes of clouds (low-level, middle and high clouds). In particular the analysis aims to evaluate how much the absence of aerosols in the simulations may be a cause of discrepancies in this area. Chepfer H., S. Bony, D. Winker, M. Chiriaco, J-L. Dufresne, G. Sèze, 2008: Use of CALIPSO lidar observations to evaluate the cloudiness simulated by a climate model. Geophys. Res. Let., 35, L15704, doi:10.1029/2008GL034207. Thompson G., R. M. Rasmussen, K. Manning, 2004: Explicit forecasts of winter precipitations using an improved bulk microphysics scheme. Part I: description and sensitivity analysis. Mon. Wea. Rev., 132, 519-542. Thompson G., P. Field, R. M. Rasmussen, W. D. Hall, 2008: Explicit forecasts of winter precipitations using an improved bulk microphysics scheme. Part II: Implementation of a new snow parameterization. Mon. Wea. Rev., 136, 5095-5115.

Bastin, S.; Chepfer, H.; Chiriaco, M.; Cesana, G.

2009-12-01

257

Microphysical and Radar Observations of Seeded and Nonseeded Continental Cumulus Clouds.  

NASA Astrophysics Data System (ADS)

Controlled cloud seeding experiments were conducted near Bethlehem, South Africa during the summer of 1984-85. The experimental unit was the semi-isolated cumulus congestus cloud. Microphysical measurements were obtained by three instrumented aircraft flying in stacked formation. Radar observations were made by a 5-cm wavelength radar performing volume scans at 5-min intervals. A three-way balanced randomization scheme was used to seed the clouds near the 8°C level with either dry ice pellets, silver iodide pyrotechnics, or a placebo (no-seed) treatment. Strict cloud selection criteria, based on the measurements made during an initial inspection penetration, assured the treatment of clouds in their developing stages as their tops row up through the 10°C level. A total of 60 clouds were chosen and treated.Using ice crystal measurements, mostly above the seeding level, it was conclusively demonstrated that some cumulus clouds were modified by the injection of either dry ice or silver iodide. High ice concentrations were produced and the evolution of the ice particle size distribution is consistent with a rain enhancement hypothesis involving an artificially induced ice embryo process. However, the liquid water contents decayed rapidly, primarily due to entrainment, and in the majority of the seeded cases precipitation particles formed due to low-density accretion onto aggregates resulting in little or no precipitation at the ground. The dry ice and silver iodide seeded clouds that echoed had significantly higher maximum 1-km average ice concentrations than the placebo clouds, as measured by the research aircraft during the clouds' developing stages.Approximately 67% of the dry ice-treated clouds, 63% of the silver iodide-treated clouds and 45% of the placebo clouds produced radar echoes >10 dBZ. The dry ice-seeded clouds that echoed had significantly higher maximum cell heights than the placebo cells and the silver iodide-seeded cells. When the test cloud data were stratified according to cloud diameter, a positive association existed between seeding and the number of clouds that echoed. Wider clouds responded more favorably to seeding, presumably because they were affected less by entrainment.

Krauss, T. W.; Bruintjes, R. T.; Verlinde, J.

1987-05-01

258

TRMM Radar Observations of Cloud Tops in the Tropical Tropopause Layer  

NASA Technical Reports Server (NTRS)

Air dehydrates to stratospheric abundances in the tropical tropopause layer (TTL). The role of overshooting convection in the dehydration process is not well understood. To study this effect, we use the TRMM (Tropical Rainfall Measuring Mission) precipitation radar (PR) to measure the altitudes of cloud tops forming in the TTL. Because the radar signal is dominated by scatter from large particles, these cloud observations imply the presence of strong convective systems with large updraft. Both winter and summer data from two different years are examined to study both interseasonal and interannual variability. The global distribution of these clouds is in good agreement with those of the surface precipitation rates. In addition, the altitude distributions of these clouds follow an exponential dependence. However, clouds over continental regions typically extend to higher altitudes in the tropics. Almost no cloud tops were observed above 20 km. Comparison between the radar cloud tops and colocated IR brightness temperature measurements reveal a large difference in both the diurnal cycle and intensity between continental and oceanic convection.

Alcala, C. M.; Dessler, A. E.; Bhartia, P. K. (Technical Monitor)

2002-01-01

259

Estimation of cirrus cloud particle fallspeeds from vertically pointing Doppler radar  

NASA Technical Reports Server (NTRS)

The First ISCCP (International Satellite Cloud Climatology Project) Regional Experiment 2 (FIRE 2) was conducted in Coffeyville, Kansas in late 1991 to study the microphysical and radiative properties of cirrus clouds. A variety of active and passive remote sensors were employed, including an 8-mm-wavelength cloud-sensing Doppler radar developed at the Wave Propagation Laboratory (WPL). The radar, having excellent sensitivity to cloud particles (-30 dBZ at 10 km), good spatial resolution (37 m), and velocity precision (.05 ms -1), is an excellent tool for observing cirrus clouds. Having this radar directed toward the zenith for long periods of time during FIRE 2 permitted the reflectivity-weighted particle fallspeed to be related to reflectivity which allowed a separation of ice particle fallspeeds from vertical air motions. Additionally, such relationships proved useful in other multi-sensor techniques for determining vertical profiles of ice particle characteristic size and ice water content in cirrus clouds. The analysis method and the results of applying it to cirrus cloud reflectivity and velocity data collected during FIRE 2 are discussed.

Orr, Brad W.; Kropfli, Robert A.

1993-01-01

260

Dynamical characteristics of cirrus clouds from aircraft and radar measurements  

NASA Technical Reports Server (NTRS)

Cirrus clouds play an important role in climate and in the development of other types of clouds. Although there are many studies of clouds within the boundary layer, cirrus clouds have been neglected up until the last decade. New tools and in-situ measurements of various physical and dynamical parameters permit us to now study cirrus clouds in much greater detail. Physical and dynamical structures of cirrus clouds were studied in detail by Heymsfield using aircraft measurements. He emphasized the importance of interactions among physical and dynamical processes. Cirrus clouds often exhibit complex physical and dynamical structure. Upper tropospheric flows contain not only coherent structures, but also chaotic movements. The coherent structures (organized movements) transfer significant amounts of heat and momentum while their form, size, and intensity depend strongly on environmental instability. Various dynamical structures including cells, waves, and turbulence are studied in order to understand cirrus cloud formation and development.

Gultepe, I.; Starr, David; Heymsfield, A. J.; Poellot, M.; Uttal, T.; Ackerman, T.

1993-01-01

261

Can we estimate precipitation rate during snowfall using a scanning terrestrial LiDAR?  

NASA Astrophysics Data System (ADS)

Accurate snowfall measurements in windy areas have proven difficult. To examine a new approach, we have installed an automatic scanning terrestrial LiDAR at Mammoth Mountain, CA. With this LiDAR, we have demonstrated effective snow depth mapping over a small study area of several hundred m2. The LiDAR also produces dense point clouds by detecting falling and blowing hydrometeors during storms. Daily counts of airborne detections from the LiDAR show excellent agreement with automated and manual snow water equivalent measurements, suggesting that LiDAR observations have the potential to directly estimate precipitation rate. Thus, we suggest LiDAR scanners offer advantages over precipitation radars, which could lead to more accurate precipitation rate estimates. For instance, uncertainties in mass-diameter and mass-fall speed relationships used in precipitation radar, combined with low reflectivity of snow in the microwave spectrum, produce errors of up to 3X in snowfall rates measured by radar. Since snow has more backscatter in the near-infrared wavelengths used by LiDAR compared to the wavelengths used by radar, and the LiDAR detects individual hydrometeors, our approach has more potential for directly estimating precipitation rate. A key uncertainty is hydrometeor mass. At our study site, we have also installed a Multi Angle Snowflake Camera (MASC) to measure size, fallspeed, and mass of individual hydrometeors. By combining simultaneous MASC and LiDAR measurements, we can estimate precipitation density and rate.

LeWinter, A. L.; Bair, E. H.; Davis, R. E.; Finnegan, D. C.; Gutmann, E. D.; Dozier, J.

2012-12-01

262

Long range transport of Asian dust and dust-cloud interaction observed by Raman lidar and CALIPSO measurements  

NASA Astrophysics Data System (ADS)

Interactions of dust aerosols with clouds and pollution are important issues for climate and environment. In this study, we investigated dust properties by using Mie/Raman/Polarization lidar systems at wavelengths 532/355/386/407 nm at Chung-Li (24.6N, 121.1E) and compared our studies with CALIPSO measurements. The occurrence of a dust event on March 14, 2009 in Chungli was clearly observed by ground and space lidar systems. CALIPSO observed the occurrence of dust originated in the Northwest China and transported to the south reaching Taiwan three days later. Our observations involve measuring backscattering, polarization, and Raman scatterings of aerosols and water vapor. By comparing the polarization measurements at 532 nm with Raman measurements at 355/386/407 nm, we can clearly see the modification of dust particles because of interaction with cloud, the later was observed in Raman lidar. Reducing of the depolarization ratio due to changing particle shapes and sizes is observed in polarization lidar measurements. CALIPSO data shows properties of the dust along the path of transport.

Huang, Z.; Nee, J. B.

2012-12-01

263

Distributions and radiative forcings of various cloud types based on active and passive satellite datasets - Part 1: Geographical distributions and overlap of cloud types  

NASA Astrophysics Data System (ADS)

Based on four year' 2B-CLDCLASS-Lidar (Radar-Lidar) cloud classification product from CloudSat, we analyze the geographical distributions of different cloud types and their co-occurrence frequency across different seasons, moreover, utilize the vertical distributions of cloud type to further evaluate the cloud overlap assumptions. The statistical results show that more high clouds, altocumulus, stratocumulus or stratus and cumulus are identified in the Radar-Lidar cloud classification product compared to previous results from Radar-only cloud classification (2B-CLDCLASS product from CloudSat). In particularly, high clouds and cumulus cloud fractions increased by factors 2.5 and 4-7, respectively. The new results are in more reasonable agreement with other datasets (typically the International Satellite Cloud Climatology Project (ISCCP) and surface observer reports). Among the cloud types, altostratus and altocumulus are more popular over the arid/semi-arid land areas of the Northern and Southern Hemispheres, respectively. These features weren't observed by using the ISCCP D1 dataset. For co-occurrence of cloud types, high cloud, altostratus, altocumulus and cumulus are much more likely to co-exist with other cloud types. However, stratus/stratocumulus, nimbostratus and convective clouds are much more likely to exhibit individual features. After considering the co-occurrence of cloud types, the cloud fraction based on the random overlap assumption is underestimated over the vast ocean except in the west-central Pacific Ocean warm pool. Obvious overestimations are mainly occurring over land areas in the tropics and subtropics. The investigation therefore indicates that incorporate co-occurrence information of cloud types based on Radar-Lidar cloud classification into the overlap assumption schemes used in the current GCMs possible be able to provide an better predictions for vertically projected total cloud fraction.

Li, J.; Huang, J.; Stamnes, K.; Wang, T.; Yi, Y.; Ding, X.; Lv, Q.; Jin, H.

2014-04-01

264

Evaluations of Three-Dimensional Building Model Reconstruction from LiDAR Point Clouds and Single-View Perspective Imagery  

NASA Astrophysics Data System (ADS)

This paper briefly presents two approaches for effective three-dimensional (3D) building model reconstruction from terrestrial laser scanning (TLS) data and single perspective view imagery and assesses their applicability to the reconstruction of 3D models of landmark or historical buildings. The collected LiDAR point clouds are registered based on conjugate points identified using a seven-parameter transformation system. Three dimensional models are generated using plan and surface fitting algorithms. The proposed single-view reconstruction (SVR) method is based on vanishing points and single-view metrology. More detailed models can also be generated according to semantic analysis of the façade images. Experimental results presented in this paper demonstrate that both TLS and SVR approaches can successfully produce accurate and detailed 3D building models from LiDAR point clouds or different types of single-view perspective images.

Tsai, F.; Chang, H.

2014-06-01

265

Trajectory-Based Registration of 3d LIDAR Point Clouds Acquired with a Mobile Mapping System  

NASA Astrophysics Data System (ADS)

Thanks to a hybrid georeferencing unit coupling GNSS and IMU sensors, mobile mapping systems (MMS) with lidar sensors provide accurate 3D point clouds of the acquired areas, mainly urban cities. When dealing with several acquisitions of the same area with the same device, differences in the range of several tens of centimeters can be observed. Such degradation of the georeferencing accuracies are due to two main reasons: inertial drift and losses of GNSS signals in urban corridors. The purpose of this paper is therefore to correct these differences with an accurate ICP-based registration algorithm, and then to correct the MMS trajectory using these retrieved local transformation parameters.The trajectory loop information plays a key role for that purpose. We propose a four-step method starting from a 3D point cloud with overlapping parts, and the trajectory of the mobile mapping system. First, a polygonal approximation of the trajectory is computed in order to first divide the whole registration problem in local sub-issues. Secondly, we aim to find all the potential overlapping acquired areas between these segments using simple bounding box intersections. Thirdly, for each pair of overlapping areas, an efficient variant of the ICP algorithm is proposed to (1) prune cases where segments do not share point clouds of the same areas and (2) retrieve the transformation parameters, for real overlapping cases. Finally, all these transformations are linked together, and fed into a global distance compensation problem, allowing to adjust the MMS trajectories for several passages. As a conclusion, this method is successfully applied to data acquired over Paris (France) with the Stereopolis mobile mapping system.

Gressin, A.; Cannelle, B.; Mallet, C.; Papelard, J.-P.

2012-07-01

266

Lidar observations of polar mesospheric clouds at Rothera, Antarctica (67.5°S, 68.0°W)  

Microsoft Academic Search

Polar mesospheric clouds (PMC) were observed by an Fe Boltzmann temperature lidar at Rothera (67.5°S, 68.0°W), Antarctica in the austral summer of 2002–2003. The Rothera PMC are much weaker, less frequent, and not as high as the PMC observed at the South Pole. The mean PMC altitude is 83.74 ± 0.25 km, which is approximately 1.3 km lower than the

Xinzhao Chu; Graeme J. Nott; Patrick J. Espy; Chester S. Gardner; Jan C. Diettrich; Mark A. Clilverd; Martin J. Jarvis

2004-01-01

267

A Lidar and Backscatter Sonde Measurement Campaign at Table Mountain during February-March 1997: Observations of Cirrus Clouds  

Microsoft Academic Search

Results from a measurement campaign performed at Table Mountain Facility\\/Jet Propulsion Laboratory\\/California Institute of Technology (34.38°N, 117.68°W, 2280 m ASL) are presented. Between 19 February and 18 March 1997 more than 400 h worth of lidar data were acquired and four backscatter sondes were launched. About 50% of the observations show the presence of cirrus clouds at altitudes close to

G. Beyerle; M. R. Gross; D. A. Haner; N. T. Kjome; I. S. McDermid; T. J. McGee; J. M. Rosen; H.-J. Schäfer; O. Schrems

2001-01-01

268

A Lidar and Backscatter Sonde Measurement Campaign at Table Mountain during February–March 1997: Observations of Cirrus Clouds  

Microsoft Academic Search

Results from a measurement campaign performed at Table Mountain Facility\\/Jet Propulsion Laboratory\\/ California Institute of Technology (34.388N, 117.688W, 2280 m ASL) are presented. Between 19 February and 18 March 1997 more than 400 h worth of lidar data were acquired and four backscatter sondes were launched. About 50% of the observations show the presence of cirrus clouds at altitudes close

G. Beyerle; M. R. Gross; D. A. Haner; N. T. Kjome; I. S. McDermid; T. J. McGee; J. M. Rosen; H.-J. Schäfer; O. Schrems

2001-01-01

269

Additional development of remote sensing techniques for observing morphology, microphysics, and radiative properties of clouds and tests using a new, robust CO{sub 2} lidar. Final report  

SciTech Connect

A three-year project with a goal of advancing CO{sub 2} lidar technology and measurement techniques for cloud studies was successfully completed. An eyesafe, infrared lidar with good sensitivity and improved Doppler accuracy was designed, constructed, and demonstrated. Dual-wavelength operation was achieved. A major leap forward in robustness was demonstrated. CO{sub 2} lidars were operated as part of two Intensive Operations Periods at the Southern Great Plains CART site. The first used an older lidar and was intended primarily for measurement technique development. The second used the new lidar and was primarily a demonstration and evaluation of its performance. Progress was demonstrated in the development, evaluation, and application of measurement techniques using CO{sub 2} lidar.

Eberhard, W.L.; Brewer, W.A.; Intrieri, J.M.

1998-09-28

270

Augmented reality system using lidar point cloud data for displaying dimensional information of objects on mobile phones  

NASA Astrophysics Data System (ADS)

Mobile augmented reality system is the next generation technology to visualise 3D real world intelligently. The technology is expanding at a fast pace to upgrade the status of a smart phone to an intelligent device. The research problem identified and presented in the current work is to view actual dimensions of various objects that are captured by a smart phone in real time. The methodology proposed first establishes correspondence between LiDAR point cloud, that are stored in a server, and the image t hat is captured by a mobile. This correspondence is established using the exterior and interior orientation parameters of the mobile camera and the coordinates of LiDAR data points which lie in the viewshed of the mobile camera. A pseudo intensity image is generated using LiDAR points and their intensity. Mobile image and pseudo intensity image are then registered using image registration method SIFT thereby generating a pipeline to locate a point in point cloud corresponding to a point (pixel) on the mobile image. The second part of the method uses point cloud data for computing dimensional information corresponding to the pairs of points selected on mobile image and fetch the dimensions on top of the image. This paper describes all steps of the proposed method. The paper uses an experimental setup to mimic the mobile phone and server system and presents some initial but encouraging results

Gupta, S.; Lohani, B.

2014-05-01

271

Polar Stratospheric Clouds from ground-based lidar and CALIPSO observations and Chemistry Climate Models evaluation  

NASA Astrophysics Data System (ADS)

We evaluate the Antarctic PSC observational databases of CALIPSO and the ground-based lidars of NDACC (Network for Detection of Atmospheric Composition Changes) located in McMurdo and Dumont D'Urville stations and provide a process-oriented evaluation of PSC in a subset of CCMVAL-2 chemistry-climate models. Lidar observatories have a decadal coverage, albeit with discontinuities, spanning from 1992 to today hence offering a unique database. A clear issue is the representativeness of ground-based long-term data series of the Antarctic stratosphere conditions that may limit their value in climatological studies and model evaluation. The comparison with the CALIPSO observations with a global coverage is, hence, a key issue. In turn, models can have a biased representation of the stratospheric conditions and of the PSC microphysics leading to large discrepancies in PSC occurrence and composition. CALIPSO observations indicate a large longitudinal variability in PSC formation in the polar atmosphere and ground-based observations are hence representative of different cloud conditions. Point-to-point comparison is difficult due to sparseness of the database (or PSC appearance at the edge of the vortex) and to intrinsic differences in spatial distribution between models and observations. So the use of simple diagnostics that are independent from instrumental coverage is fundamental. Comparison between ground-based and satellite borne-lidar is overall satisfactory and differences may be attributed to differences in coverage. As expected, McMurdo site is dominated by a NAT-type regime that is a clear feature of the eastern part of polar vortex while Dumont D'Urville is largely influenced by the transition at the edge the polar vortex resulting, on average, in a much reduced PSC coverage with a partition between NAT and STS cloud types. Data from the 5 CCMs having provided PSC surface areas on daily basis have been evaluated using the same diagnostic type that may be derived CALIPSO (i.e. frequency of PSC occurrence function of lon-lat, height and temperature) showing large differences that may be explained by the interplay of model temperatures that may show a large bias (negative for 3 models over 5) and the microphysical scheme itself. Two models in fact show an excess of NAT formation relative to ice clouds while two others have an unrealistic dominance of ice. Most of them show a somewhat too efficient PSC production with temperature decrease below NAT formation temperature. Evaluation CCMs with ground-based instruments databases should be done with great care due to the large spatial differences inside the polar vortex that are not fully reproduced by the models. In turn, longer series as provided by NDACC should be used to evaluate interannual variability and trends that is difficult to identify in the shorter CALIPSO database.

Fierli, Federico; Di Liberto, Luca; Cairo, Francesco; Cagnazzo, Chiara; Snels, Marcel; Keckhut, Philippe; Jumelet, Julien; Pitts, Michael C.

2014-05-01

272

Automated Detection of Geomorphic Features in LiDAR Point Clouds of Various Spatial Density  

NASA Astrophysics Data System (ADS)

LiDAR, also referred to as laser scanning, has proved to be an important tool for topographic data acquisition. Terrestrial laser scanning allows for accurate (several millimeter) and high resolution (several centimeter) data acquisition at distances of up to some hundred meters. By contrast, airborne laser scanning allows for acquiring homogeneous data for large areas, albeit with lower accuracy (decimeter) and resolution (some ten points per square meter) compared to terrestrial laser scanning. Hence, terrestrial laser scanning is preferably used for precise data acquisition of limited areas such as landslides or steep structures, while airborne laser scanning is well suited for the acquisition of topographic data of huge areas or even country wide. Laser scanners acquire more or less homogeneously distributed point clouds. These points represent natural objects like terrain and vegetation and artificial objects like buildings, streets or power lines. Typical products derived from such data are geometric models such as digital surface models representing all natural and artificial objects and digital terrain models representing the geomorphic topography only. As the LiDAR technology evolves, the amount of data produced increases almost exponentially even in smaller projects. This means a considerable challenge for the end user of the data: the experimenter has to have enough knowledge, experience and computer capacity in order to manage the acquired dataset and to derive geomorphologically relevant information from the raw or intermediate data products. Additionally, all this information might need to be integrated with other data like orthophotos. In all theses cases, in general, interactive interpretation is necessary to determine geomorphic structures from such models to achieve effective data reduction. There is little support for the automatic determination of characteristic features and their statistical evaluation. From the lessons learnt from automated extraction and modeling of buildings (Dorninger & Pfeifer, 2008) we expected that similar generalizations for geomorphic features can be achieved. Our aim is to recognize as many features as possible from the point cloud in the same processing loop, if they can be geometrically described with appropriate accuracy (e.g., as a plane). For this, we propose to apply a segmentation process allowing determining connected, planar structures within a surface represented by a point cloud. It is based on a robust determination of local tangential planes for all points acquired (Nothegger & Dorninger, 2009). It assumes that for points, belonging to a distinct planar structure, similar tangential planes can be determined. In passing, points acquired at continuous such as vegetation can be identified and eliminated. The plane parameters are used to define a four-dimensional feature space which is used to determine seed-clusters globally for the whole are of interest. Starting from these seeds, all points defining a connected, planar region are assigned to a segment. Due to the design of the algorithm, millions of input points can be processed with acceptable processing time on standard computer systems. This allows for processing geomorphically representative areas at once. For each segment, numerous parameter are derived which can be used for further exploitation. These are, for example, location, area, aspect, slope, and roughness. To prove the applicability of our method for automated geomorphic terrain analysis, we used terrestrial and airborne laser scanning data, acquired at two locations. The data of the Doren landslide located in Vorarlberg, Austria, was acquired by a terrestrial Riegl LS-321 laser scanner in 2008, by a terrestrial Riegl LMS-Z420i laser scanner in 2009, and additionally by three airborne LiDAR measurement campaigns, organized by the Landesvermessungsamt Vorarlberg, Feldkirch, in 2003, 2006, and 2007. The measurement distance of the terrestrial measurements was considerably varying considerably because of the various base points that were neede

Dorninger, Peter; Székely, Balázs; Zámolyi, András.; Nothegger, Clemens

2010-05-01

273

Tropical cirrus clouds near cold point tropopause under ice supersaturated conditions observed by lidar and balloon-borne cryogenic frost point hygrometer  

NASA Astrophysics Data System (ADS)

Simultaneous vertical profiles of cirrus cloud backscattering and frost point temperature were obtained for the first time in the tropopause region over Bandung, Indonesia, (6.9°S, 107.6°E). These profiles were measured by ground-based lidar and by balloon-borne Cryogenic Frost point Hygrometer (CFH) sondes. Supersaturation up to several ten percent was observed by the CFH just below the cold point tropopause at the altitude where a cirrus cloud was observed by lidar. The water vapor mixing ratio decreased slightly at the altitude of the cirrus cloud, suggesting that this decrease was caused by uptake in the cirrus cloud and that the water vapor reduction corresponds to the lower limit of the cloud water content of the observed cirrus cloud. Theoretical calculations of the scattering parameters for the observed cirrus cloud particles and estimations of the time constants for sedimentation and for condensational growth indicate that particles size range is between 4 ?m and 30 ?m.

Shibata, Takashi; VöMel, Holger; Hamdi, Saipul; Kaloka, Sri; Hasebe, Fumio; Fujiwara, Masatomo; Shiotani, Masato

2007-02-01

274

Variability of Cloud Vertical Structure during ASTEX Observed from a Combination of Rawinsonde, Radar, Ceilometer, and Satellite  

Microsoft Academic Search

The macroscale cloud vertical structure (CVS), including cloud-base and -top heights and layer thickness, and characteristics of multilayered clouds, is studied at Porto Santo Island during the Atlantic Stratocumulus Transition Experiment (ASTEX) by using rawinsonde, radar, ceilometer, and satellite data. The comparisons of CVS parameters obtained from four different approaches show that 1) by using the method developed by Wang

Junhong Wang; William B. Rossow; Taneil Uttal; Margaret Rozendaal

1999-01-01

275

DEVELOPMENT OF A PROCEDURE FOR VERTICAL STRUCTURE ANALYSIS AND 3D-SINGLE TREE EXTRACTION WITHIN FORESTS BASED ON LIDAR POINT CLOUD  

Microsoft Academic Search

A procedure for both vertical canopy structure analysis and 3D single tree extraction based on Lidar raw point cloud is presented in this paper. The whole study area is segmented into small study cells by a raster net. For each cell, a normalized point cloud whose point heights represent the absolute heights of the ground objects is generated from the

Yunsheng Wang; Holger Weinacker; Barbara Koch

2007-01-01

276

Assessing lidar-based classification schemes for polar stratospheric clouds based on 16 years of measurements at Esrange, Sweden  

NASA Astrophysics Data System (ADS)

Lidar measurements of polar stratospheric clouds (PSCs) are commonly analyzed in classification schemes that apply the backscatter ratio and the particle depolarization ratio. This similarity of input data suggests comparable results of different classification schemes—despite measurements being performed with a variety of mostly custom-made instruments. Based on a time series of 16 years of lidar measurements at Esrange (68°N, 21°E), Sweden, we show that PSC classification differs substantially depending on the applied scheme. The discrepancies result from varying threshold values of lidar-derived parameters used to define certain PSC types. The resulting inconsistencies could impact the understanding of long-term PSC observations documented in the literature. We identify two out of seven considered classification schemes that are most likely to give reliable results and should be used in future lidar-based studies. Using polarized backscatter ratios gives the advantage of increased contrast for observations of weakly backscattering and weakly depolarizing particles. Improved confidence in PSC classification can be achieved by a more comprehensive consideration of the effect of measurement uncertainties. The particle depolarization ratio is the key to a reliable identification of different PSC types. Hence, detailed information on the calibration of the polarization-sensitive measurement channels should be provided to assess the findings of a study. Presently, most PSC measurements with lidar are performed at 532 nm only. The information from additional polarization-sensitive measurements in the near infrared could lead to an improved PSC classification. Coincident lidar-based temperature measurements at PSC level might provide useful information for an assessment of PSC classification.

Achtert, P.; Tesche, M.

2014-02-01

277

Highly Supercooled Cirrus Cloud Water: Confirmation and Climatic Implications  

Microsoft Academic Search

Liquid cloud droplets supercooled to temperatures approaching -40 degrees C have been detected at the base of a cirrostratus cloud through a combination of ground-based, polarization laser radar (lidar) and in situ aircraft measurements. Solar and thermal infrared radiative budget calculations based on these observations indicate that significant changes in the atmospheric heating distribution and the surface radiative budget may

Kenneth Sassen; Kuo Nan Liou; Stefan Kinne; Michael Griffin

1985-01-01

278

Simulations of radar signals on the basis of cloud model results - deep convection conditions  

NASA Astrophysics Data System (ADS)

Simulation of observed radar returns is one of the tools for validating a new cloud microphysics code by H. Morrison and W.W. Grabowski. The code includes a two-moment bulk warm rain scheme and two-moment ice microphysics scheme with prognostic rime mass fraction. Both the simulator and the cloud model share the following set of assumptions. Three general types of particles are taken into account: cloud droplets, drizzle drops and ice crystals; particles are characterised by modified gamma size distribution (in case of rain drops it becomes exponential); and particles are described in terms of mass and area to dimension relationships. Liquid particles are assumed to be spherical and ice crystals are treated as spheres, dense non-spherical particles, graupel or aggregates, depending on their size and rimed mass fraction. Simulator input consists of particle number concentrations, mixing ratios (for ice crystals separate mixing ratios for mass grown by riming and water vapour deposition are employed), temperature and relative humidity profiles. Pre-calculated look up tables containing particle scattering properties (radar reflectivity and attenuation) as functions of input parameters are used in order to speed up the code. The simulator is applied to deep convection conditions observed during the Tropical Warm Pool International Cloud Experiment, Darwin, Australia, January - February 2006. The simulation results are compared to data collected by the millimeter wavelength cloud radar (MMCR) situated in Darwin, Australia - one of the measurement sites of the Atmospheric Radiation Measurement program.

Kardas, A. E.; McFarlane, S. A.; Morrison, H.; Comstock, J. M.; Grabowski, W. W.; Malinowski, S. P.

2009-12-01

279

Precipitating Snow Retrievals from Combined Airborne Cloud Radar and Millimeter-Wave Radiometer Observations  

NASA Technical Reports Server (NTRS)

An algorithm for retrieving snow over oceans from combined cloud radar and millimeter-wave radiometer observations is developed. The algorithm involves the use of physical models to simulate cloud radar and millimeter-wave radiometer observations from basic atmospheric variables such as hydrometeor content, temperature, and relative humidity profiles and is based on an optimal estimation technique to retrieve these variables from actual observations. A high-resolution simulation of a lake-effect snowstorm by a cloud-resolving model is used to test the algorithm. That is, synthetic observations are generated from the output of the cloud numerical model, and the retrieval algorithm is applied to the synthetic data. The algorithm performance is assessed by comparing the retrievals with the reference variables used in synthesizing the observations. The synthetic observation experiment indicates good performance of the retrieval algorithm. The algorithm is also applied to real observations from the Wakasa Bay field experiment that took place over the Sea of Japan in January and February 2003. The application of the retrieval algorithm to data from the field experiment yields snow estimates that are consistent with both the cloud radar and radiometer observations.

Grecu, Mircea; Olson, William S.

2008-01-01

280

Airborne LIDAR Measurements of Water Vapor, Ozone, Clouds, and Aerosols in the Tropics Near Central America During the TC4 Experiment  

NASA Technical Reports Server (NTRS)

Large scale distributions of ozone, water vapor, aerosols, and clouds were measured throughout the troposphere by two NASA Langley lidar systems on board the NASA DC-8 aircraft as part of the Tropical Composition, Cloud, and Climate Coupling Experiment (TC4) over Central and South America and adjacent oceans in the summer of 2007. Special emphasis was placed on the sampling of convective outflow and transport, sub-visible cirrus clouds, boundary layer aerosols, Saharan dust, volcanic emissions, and urban and biomass burning plumes. This paper presents preliminary results from this campaign, and demonstrates the value of coordinated measurements by the two lidar systems.

Kooi, Susan; Fenn, Marta; Ismail, Syed; Ferrare, Richard; Hair, John; Browell, Edward; Notari, Anthony; Butler, Carolyn; Burton, Sharon; Simpson, Steven

2008-01-01

281

Horizontal and vertical structure of the Eyjafjallajökull ash cloud over the UK: a comparison of airborne lidar observations and simulations  

NASA Astrophysics Data System (ADS)

During April and May 2010 the ash cloud from the eruption of the Icelandic volcano Eyjafjallajökull caused widespread disruption to aviation over northern Europe. Because of the location and impact of the eruption a wealth of observations of the ash cloud were obtained and can be used to assess modelling of the long range transport of ash in the troposphere. The UK's BAe-146-301 Atmospheric Research Aircraft overflew the ash cloud on a number of days during May. The aircraft carries a downward looking lidar which detected the ash layer through the backscatter of the laser light. The ash concentrations are estimated from lidar extinction coefficients and in situ measurements of the ash particle size distributions. In this study these estimates of the ash concentrations are compared with simulations of the ash cloud made with NAME (Numerical Atmospheric-dispersion Modelling Environment), a general purpose atmospheric transport and dispersion model. The ash layers seen by the lidar were thin, with typical depths of 550-750 m. The vertical structure of the ash cloud simulated by NAME was generally consistent with the observed ash layers. The layers in the simulated ash clouds that could be identified with observed ash layers are about twice the depth of the observed layers. The structure of the simulated ash clouds were sensitive to the profile of ash emissions that was assumed. In terms of horizontal and vertical structure the best results were mainly obtained by assuming that the emission occurred at the top of the eruption plume, consistent with the observed structure of eruption plumes. However, when the height of the eruption plume was variable and the eruption was weak, then assuming that the emission of ash was uniform with height gave better guidance on the horizontal and vertical structure of the ash cloud. Comparison between the column masses in the simulated and observed ash layers suggests that about 3% of the total mass erupted by the volcano remained in the ash cloud over the United Kingdom. The problems with the interpretation of this estimate of the distal fine ash fraction are discussed.

Grant, A. L. M.; Dacre, H. F.; Thomson, D. J.; Marenco, F.

2012-04-01

282

Extraction of Features from High-resolution 3D LiDaR Point-cloud Data  

NASA Astrophysics Data System (ADS)

Airborne and tripod-based LiDaR scans are capable of producing new insight into geologic features by providing high-quality 3D measurements of the landscape. High-resolution LiDaR is a promising method for studying slip on faults, erosion, and other landscape-altering processes. LiDaR scans can produce up to several billion individual point returns associated with the reflection of a laser from natural and engineered surfaces; these point clouds are typically used to derive a high-resolution digital elevation model (DEM). Currently, there exist only few methods that can support the analysis of the data at full resolution and in the natural 3D perspective in which it was collected by working directly with the points. We are developing new algorithms for extracting features from LiDaR scans, and present method for determining the local curvature of a LiDaR data set, working directly with the individual point returns of a scan. Computing the curvature enables us to rapidly and automatically identify key features such as ridge-lines, stream beds, and edges of terraces. We fit polynomial surface patches via a moving least squares (MLS) approach to local point neighborhoods, determining curvature values for each point. The size of the local point neighborhood is defined by a user. Since both terrestrial and airborne LiDaR scans suffer from high noise, we apply additional pre- and post-processing smoothing steps to eliminate unwanted features. LiDaR data also captures objects like buildings and trees complicating greatly the task of extracting reliable curvature values. Hence, we use a stochastic approach to determine whether a point can be reliably used to estimate curvature or not. Additionally, we have developed a graph-based approach to establish connectivities among points that correspond to regions of high curvature. The result is an explicit description of ridge-lines, for example. We have applied our method to the raw point cloud data collected as part of the GeoEarthScope B-4 project on a section of the San Andreas Fault (Segment SA09). This section provides an excellent test site for our method as it exposes the fault clearly, contains few extraneous structures, and exhibits multiple dry stream-beds that have been off-set by motion on the fault.

Keller, P.; Kreylos, O.; Hamann, B.; Kellogg, L. H.; Cowgill, E. S.; Yikilmaz, M. B.; Hering-Bertram, M.; Hagen, H.

2008-12-01

283

Analysis of Doppler Lidar Wind Measurements.  

National Technical Information Service (NTIS)

Doppler lidar and multiple Doppler radar data were obtained in a convectively mixed planetary boundary layer. The lidar measurements were possible due to scattering from existing aerosols; radar reflecting chaff was released in the atmosphere to make it v...

R. C. ivastava

1986-01-01

284

Simultaneous Observations of Tropical Cirrus Clouds by Lidar and Humidity by CFH Over Bandung and Biak, Indonesia During SOWER Campaigns  

NASA Astrophysics Data System (ADS)

Vertical profiles of cirrus cloud backscattering and of frost point temperature near the tropical tropopause region were observed simultaneously by ground-based lidar and balloon borne Cryogenic Frost point Hygrometer (CFH) over Bandung (7S, 108E) and Biak (1S, 136E), Indonesia. SOWER (Soundings of Ozone and Water in the Equatorial Region) observation campaigns were conducted in December 2003 and 2004 at Bandung, and in January 2006 at Biak. Supersaturation up to several ten percent was observed just below the cold point tropopause at the altitude where a cirrus cloud was observed. The supersaturated water vapor humidity over ice observed over Bandung decreased slightly at the altitude of the cirrus cloud, suggesting that this decrease was caused by uptake in the cirrus cloud, and that the water vapor reduction corresponds to the lower limit of the cloud water content of the observed cirrus cloud. The humidity over Biak showed higher supersaturation at the altitude of cirrus cloud, but the decrease was not observed.

Shibata, T.; Voemel, H.; Hamdi, S.; Kaloka, S.; Hasebe, F.; Fujiwara, M.; Shiotani, M.

2006-12-01

285

A bottom-up approach to segment individual deciduous trees using leaf-off lidar point cloud data  

NASA Astrophysics Data System (ADS)

Light Detection and Ranging (Lidar) can generate three-dimensional (3D) point cloud which can be used to characterize horizontal and vertical forest structure, so it has become a popular tool for forest research. Recently, various methods based on top-down scheme have been developed to segment individual tree from lidar data. Some of these methods, such as the one developed by Li et al. (2012), can obtain the accuracy up to 90% when applied in coniferous forests. However, the accuracy will decrease when they are applied in deciduous forest because the interlacing tree branches can increase the difficulty to determine the tree top. In order to solve challenges of the tree segmentation in deciduous forests, we develop a new bottom-up method based on the intensity and 3D structure of leaf-off lidar point cloud data in this study. We applied our algorithm to segment trees in a forest at the Shavers Creek Watershed in Pennsylvania. Three indices were used to assess the accuracy of our method: recall, precision and F-score. The results show that the algorithm can detect 84% of the tree (recall), 97% of the segmented trees are correct (precision) and the overall F-score is 90%. The result implies that our method has good potential for segmenting individual trees in deciduous broadleaf forest.

Lu, Xingcheng; Guo, Qinghua; Li, Wenkai; Flanagan, Jacob

2014-08-01

286

Combined satellite and radar retrievals of drop concentration and CCN at convective cloud base  

NASA Astrophysics Data System (ADS)

number of activated cloud condensation nuclei (CCN) into cloud drops at the base of convective clouds (Na) is retrieved based on the high-resolution (375 m) satellite retrievals of vertical profiles of convective cloud drop effective radius (re). The maximum cloud base supersaturation (S) is calculated when Na is combined with radar-measured updraft and yields CCN(S), which was validated well against ground-based CCN measurements during the conditions of well-mixed boundary layer over the U.S. Department of Energy's Atmospheric System Research Southern Great Plains site. Satellite retrieving Na is a new capability, which is one essential component of simultaneous measurements of cloud microstructure and CCN from space by using clouds as natural CCN chambers. This has to be complemented by a methodology for satellite estimates of cloud base updraft, which is yet to be developed and demonstrated. In the mean time, the retrieved Na can be used for the assimilation of the combined CCN and updraft effects on clouds in models.

Rosenfeld, Daniel; Fischman, Baruch; Zheng, Youtong; Goren, Tom; Giguzin, David

2014-05-01

287

Evaluation of tropical cloud regimes in observations and a general circulation model  

Microsoft Academic Search

Tropical cloud regimes defined by cluster analysis of International Satellite Cloud Climatology Project (ISCCP) cloud top\\u000a pressure (CTP)–optical thickness distributions and ISCCP-like Goddard Institute for Space Studies (GISS) general circulation\\u000a model (GCM) output are analyzed in this study. The observations are evaluated against radar–lidar cloud-top profiles from\\u000a the atmospheric radiation measurement (ARM) Program active remote sensing of cloud layers (ARSCL)

Yonghua Chen; Anthony D. Del Genio

2009-01-01

288

Development of Spaceborne Radar Simulator by NICT and JAXA using JMA Cloud-resolving Model  

NASA Astrophysics Data System (ADS)

We are developing synthetic spaceborne radar data toward a simulation of the Dual-frequency Precipitation Radar (DPR) aboard the Global Precipitation Measurement (GPM) core-satellite. Our purposes are a production of test-bed data for higher level DPR algorithm developers, in addition to a diagnosis of a cloud resolving model (CRM). To make the synthetic data, we utilize the CRM by the Japan Meteorological Agency (JMA-NHM) (Ikawa and Saito 1991, Saito et al. 2006, 2007), and the spaceborne radar simulation algorithm by the National Institute of Information and Communications Technology (NICT) and the Japan Aerospace Exploration Agency (JAXA) named as the Integrated Satellite Observation Simulator for Radar (ISOSIM-Radar). The ISOSIM-Radar simulates received power data in a field of view of the spaceborne radar with consideration to a scan angle of the radar (Oouchi et al. 2002, Kubota et al. 2009). The received power data are computed with gaseous and hydrometeor attenuations taken into account. The backscattering and extinction coefficients are calculated assuming the Mie approximation for all species. The dielectric constants for solid particles are computed by the Maxwell-Garnett model (Bohren and Battan 1982). Drop size distributions are treated in accordance with those of the JMA-NHM. We assume a spherical sea surface, a Gaussian antenna pattern, and 49 antenna beam directions for scan angles from -17 to 17 deg. in the PR. In this study, we report the diagnosis of the JMA-NHM with reference to the TRMM Precipitation Radar (PR) and CloudSat Cloud Profiling Radar (CPR) using the ISOSIM-Radar from the view of comparisons in cloud microphysics schemes of the JMA-NHM. We tested three kinds of explicit bulk microphysics schemes based on Lin et al. (1983), that is, three-ice 1-moment scheme, three-ice 2-moment scheme (Eito and Aonashi 2009), and newly developed four-ice full 2-moment scheme (Hashimoto 2008). The hydrometeor species considered here are rain, graupel, snow, cloud water, cloud ice and hail (4-ice scheme only). We examined a case of an intersection with the TRMM PR and the CloudSat CPR on 6th April 2008 over sea surface in the south of Kyushu Island of Japan. In this work, observed rainfall systems are simulated with one-way double nested domains having horizontal grid sizes of 5 km (outer) and 2 km (inner). Data used here are from the inner domain only. Results of the PR indicated better performances of 2-moment bulk schemes. It suggests that prognostic number concentrations of frozen hydrometeors are more effective in high altitudes and constant number concentrations can lead to the overestimation of the snow there. For three-ice schemes, simulated received power data overestimated above freezing levels with reference to the observed data. In contrast, the overestimation of frozen particles was heavily reduced for the four-ice scheme.

Kubota, T.; Eito, H.; Aonashi, K.; Hashimoto, A.; Iguchi, T.; Hanado, H.; Shimizu, S.; Yoshida, N.; Oki, R.

2009-12-01

289

The Use of Coincident Synthetic Aperture Radar and Visible Imagery to Aid in the Analysis of Photon-Counting Lidar Data Sets Over Complex Ice/Snow Surfaces  

NASA Astrophysics Data System (ADS)

Qualitative and quantitative analysis of multi-sensor data is becoming increasingly useful as a method of improving our understanding of complex environments, and can be an effective tool in the arsenal to help climate scientists to predict sea level rise due to change in the mass balance of large glaciers in the Arctic and Antarctic. A novel approach to remote sensing of the continuously changing polar environment involves the use of coincident RADARSAT-2 synthetic aperture radar (SAR) imagery and Landsat 7 visible/near-infrared imagery, combined with digital elevation models (DEM) developed from Multiple Altimeter Beam Experimental Lidar (MABEL) data sets. MABEL is a scaled down model of the lidar altimeter that will eventually be flown on ICESat-2, and provides dense along-track and moderate slope (cross-track) elevation data over narrow (~198 m) aircraft transects. Because glacial terrain consists of steep slopes, crevices, glacial lakes, and outflow into the sea, accurate slope information is critical to our understanding of any changes that may be happening in the ice sheets. RADARSAT-2 operates in the C-band, at a wavelength of 5.55 cm, and was chosen partly for its ability to image the Earth under all atmospheric conditions, including clouds. The SAR images not only provide spatial context for the elevation data found using the lidar, but also offer key insights into the consistency of the snow and ice making up the glacier, giving us some idea of mean temperature and surface conditions on the ice sheet. Finally, Landsat 7 images provide us with information on the extent of the glacier, and additional understanding of the state of the glacial surface. To aid in the analysis of the three data sets, proper preparation of each data set must first be performed. For the lidar data, this required the development of a new data reduction technique, based on statistical analysis, to reduce the number of received photons to those representing only the surface return. Accordingly, the raw SAR images require calibration, speckle reduction, and geocorrection, before they can be used. Landsat 7 bands are selected to provide the most contrast between rock, snow, and other surface features, and compiled into a three-band red, green, blue (RGB) image. By qualitatively analyzing images and data taken only a short time apart using multiple imaging modalities, we are able to accurately compare glacial surface features to elevation provided by MABEL, with the goal of increasing our understanding of how the glacier is changing over time. Quantitative analysis performed throughout this thesis has indicated that there is a strong correlation between top-of-the-atmosphere reflectance (Landsat 7), sigma,0-calibrated HH and HV polarized backscatter coefficients (RADARSAT-2), elevation (MABEL), and various surface features and glacial zones on the ice sheet. By comparing data from unknown or mixed surfaces to known quantities scientists can effectively estimate the type of glacial zone the area of interest occurs in. Climate scientists can then use this data, along with long-term digital elevations models, as a measure of predicting climate change.

Horan, Kimberly H.

290

3D Scanning Cloud Radar Observations at Azores during the ARM AMF field campaign: Reconstruction and study of 3D cloud structures and properties  

NASA Astrophysics Data System (ADS)

The U.S. Department of Energy Atmospheric Radiation Measurement (ARM) Mobile Facility (AMF) has been operating at Graciosa Island (Azores) since May 2009. This 21-month field campaign focuses on the study of marine stratus clouds. The ARM/AMF instrumentation and location provides a unique opportunity to observe the cloud properties of marine stratocumulus utilizing a variety of active and passive remote sensors. In addition to the standard profiling instrumentation, the first scanning W-band (94-GHz) ARM Cloud Radar (SWACR) was deployed for a short two-month period (October-November 2009). Several scan strategies were tested during the SWACR deployment. The scan strategies were designed specifically to provide the ability to reconstruct the 3D cloud structure. The raw radar observations are quality controlled with the identification of radar volumes with significant detections, water vapor attenuation and unfolding of the radar Doppler velocity. The observations are also transformed from the original radar coordinate system (spherical) to a Cartesian coordinate system using an adaptive gridding algorithm. The 3D gridding of the radar observables, along with spatial data analysis, allow us to evaluate important issues, specifically spatial variability of cloud and drizzle structures. Column profiles of SWACR observables are used in combination with Liquid Water Path measurements from the collocated Microwave Radiometer (MWR) to develop new relationships to compute Liquid Water Content (LWC). The best possible estimate of the 3D LWC structure is reconstructed by assessing both our relationship and other known relationships between radar reflectivity and LWC. This is required in order to use the 3D cloud observations for radiative transfer modeling. Additional drizzle-identification techniques are also being developed to allow the isolation of 3D cloud-only or liquid-only fields. These types of variables have a key impact on the understanding of the radiative budget of marine stratocumulus. Furthermore, this type of analysis can provide key information for the modeling of such clouds.

Bowley, K.; Jo, I.; Tatarevic, A.; Kollias, P.

2010-12-01

291

A Lidar Point Cloud Based Procedure for Vertical Canopy Structure Analysis And 3D Single Tree Modelling in Forest  

PubMed Central

A procedure for both vertical canopy structure analysis and 3D single tree modelling based on Lidar point cloud is presented in this paper. The whole area of research is segmented into small study cells by a raster net. For each cell, a normalized point cloud whose point heights represent the absolute heights of the ground objects is generated from the original Lidar raw point cloud. The main tree canopy layers and the height ranges of the layers are detected according to a statistical analysis of the height distribution probability of the normalized raw points. For the 3D modelling of individual trees, individual trees are detected and delineated not only from the top canopy layer but also from the sub canopy layer. The normalized points are resampled into a local voxel space. A series of horizontal 2D projection images at the different height levels are then generated respect to the voxel space. Tree crown regions are detected from the projection images. Individual trees are then extracted by means of a pre-order forest traversal process through all the tree crown regions at the different height levels. Finally, 3D tree crown models of the extracted individual trees are reconstructed. With further analyses on the 3D models of individual tree crowns, important parameters such as crown height range, crown volume and crown contours at the different height levels can be derived.

Wang, Yunsheng; Weinacker, Holger; Koch, Barbara

2008-01-01

292

Space radar image of Western Pacific rain clouds  

NASA Technical Reports Server (NTRS)

This radar image shows the ocean surface in a portion of the Western Pacific Ocean. Scientists are using images like this to study the occurrence, distribution and activity of tropical rain squalls and to understand the exchange of heat between the atmosphere and ocean and the upper layer mixing in the tropical oceans, which are critical factors for understanding the driving forces which produce the El Nino phenomenon. The white, curved area at the top of the image is a portion of the Ontong Java Atoll, part of the Solomon Islands group. The yellowish green area near the bottom of the image is an intense rain cell. This image is centered near 5.5 degrees South latitude and 159.5 degrees East longitude. The area shown is 50 kilometers by 21 kilometers (31 miles by 13 miles). This image was acquired by the Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR) aboard the space shuttle Endeavour on its 13th orbit on April 10, 1994. The colors in the image are assigned to different frequencies and polarizations of the SIR-C radar as follows: Red is C-band horizontally transmitted and received; green is L-band horizontally transmitted and vertically received and blue is L-band horizontally transmitted and received. The large rain cell is about 15 kilometers by 15 kilometers (9 miles by 9 miles) and contains two dark regions, one circular and one rectangular, inside it. Two smaller reddish cells are visible closer to the atoll. The red areas may be caused by reflection from ice particles in the colder, upper portion of the storm cell and not from the ocean surface at all. This provides direct evidence that it is raining within this storm cell, valuable information which is usually very difficult to measure over more remote regions of the ocean away from coastal-based weather systems. The dark holes in the middle of the cell are thought to be areas of very heavy rainfall which actually smooth out the ocean surface and result in lower radar returns. The surrounding ocean is blue to green plus black. Winds and currents cause the ocean surface to be rough and those variations on the surface affect how the radar signals bounce off the surface. The bright areas on the image correspond to areas where the wind speed is high. The highest winds are seen as the yellow-green region of the large rain cell. The lowest winds are seen inside the atoll as dark areas. Outside the rain cell, the winds are moderately low, which is indicated by the puff-like, blue patterns surrounding the cell and extending into the atoll. The long, thin, dark lines extending across the ocean are surface currents. Here the currents are likely accumulating natural oils caused by small marine biological organisms. The oils cause the small, wind-generated waves to be reduced in size or damped which produces a smooth, dark zone on the radar image.

1995-01-01

293

Performance of a Developed Low-Power and High-Sensitivity Cloud Profiling Millimeter-wave Radar : FALCON-I  

Microsoft Academic Search

We have developed a low-power and high- sensitivity cloud profiling radar, named FALCON-I, transmitting frequency modulated continuous wave (FM-CW) at 95 GHz for ground-based observations. Millimeter wave at 95 GHz is used to realize much higher sensitivity than lower frequencies to small cloud particles. An FM-CW type radar realizes similar sensitivity with much smaller output power to a pulse type

T. Takano; Y. Nakanishi; H. Abe; J. Yamaguchi; S.-I. Yokote; K.-I. Futaba; Y. Kawamura; H. Kumagai; Y. Ohno; T. Takamura; T. Nakajima

2007-01-01

294

Retrieval of stratus cloud microphysical parameters using millimeter-wave radar and visible optical depth in preparation for CloudSat 1. Algorithm formulation  

Microsoft Academic Search

A new retrieval of stratus cloud microphysical parameters is developed based on measurements of millimeter-wave radar reflectivity and visible optical depth. The retrieval assumes a lognormal distribution of cloud droplets with no significant amounts of drizzle. The retrieval is formulated in an estimation theory framework, allowing the inclusion of a priori information. This formulation provides quantitative measures of uncertainty in

Richard T. Austin; Graeme L. Stephens

2001-01-01

295

Effects of Cloud on Goddard Lidar Observatory for Wind (GLOW) Performance and Analysis of Associated Errors  

Microsoft Academic Search

The Goddard Lidar Observatory for Wind (GLOW), a mobile direct detection Doppler LIDAR based on molecular backscattering for measurement of wind in the troposphere and lower stratosphere region of atmosphere is operated and its errors characterized. It was operated at Howard University Beltsville Center for Climate Observation System (BCCOS) side by side with other operating instruments: the NASA\\/Langely Research Center

Tulu Bacha

2011-01-01

296

An intercomparison of radar-based liquid cloud microphysics retrievals and implications for model evaluation studies  

NASA Astrophysics Data System (ADS)

This paper presents a statistical comparison of three cloud retrieval products of the Atmospheric Radiation Measurement (ARM) program at the Southern Great Plains (SGP) site from 1998 to 2006: MICROBASE, University of Utah (UU), and University of North Dakota (UND) products. The probability density functions of the various cloud liquid water content (LWC) retrievals appear to be consistent with each other. While the mean MICROBASE and UU cloud LWC retrievals agree well in the middle of cloud, the discrepancy increases to about 0.03 gm-3 at cloud top and cloud base. Alarmingly large differences are found in the droplet effective radius (re) retrievals. The mean MICROBASE re is more than 6 ?m lower than the UU re, whereas the discrepancy is reduced to within 1 ?m if columns containing raining and/or mixed-phase layers are excluded from the comparison. A suite of stratified comparisons and retrieval experiments reveal that the LWC difference stems primarily from rain contamination, partitioning of total liquid later path (LWP) into warm and supercooled liquid, and the input cloud mask and LWP. The large discrepancy among the re retrievals is mainly due to rain contamination and the presence of mixed-phase layers. Since rain or ice particles are likely to dominate radar backscattering over cloud droplets, the large discrepancy found in this paper can be thought of as a physical limitation of single-frequency radar approaches. It is therefore suggested that data users should use the retrievals with caution when rain and/or mixed-phase layers are present in the column.

Huang, D.; Zhao, C.; Dunn, M.; Dong, X.; Mace, G. G.; Jensen, M. P.; Xie, S.; Liu, Y.

2012-06-01

297

Automatic 3D Building Detection and Modeling from Airborne LiDAR Point Clouds  

NASA Astrophysics Data System (ADS)

Urban reconstruction, with an emphasis on man-made structure modeling, is an active research area with broad impact on several potential applications. Urban reconstruction combines photogrammetry, remote sensing, computer vision, and computer graphics. Even though there is a huge volume of work that has been done, many problems still remain unsolved. Automation is one of the key focus areas in this research. In this work, a fast, completely automated method to create 3D watertight building models from airborne LiDAR (Light Detection and Ranging) point clouds is presented. The developed method analyzes the scene content and produces multi-layer rooftops, with complex rigorous boundaries and vertical walls, that connect rooftops to the ground. The graph cuts algorithm is used to separate vegetative elements from the rest of the scene content, which is based on the local analysis about the properties of the local implicit surface patch. The ground terrain and building rooftop footprints are then extracted, utilizing the developed strategy, a two-step hierarchical Euclidean clustering. The method presented here adopts a "divide-and-conquer" scheme. Once the building footprints are segmented from the terrain and vegetative areas, the whole scene is divided into individual pendent processing units which represent potential points on the rooftop. For each individual building region, significant features on the rooftop are further detected using a specifically designed region-growing algorithm with surface smoothness constraints. The principal orientation of each building rooftop feature is calculated using a minimum bounding box fitting technique, and is used to guide the refinement of shapes and boundaries of the rooftop parts. Boundaries for all of these features are refined for the purpose of producing strict description. Once the description of the rooftops is achieved, polygonal mesh models are generated by creating surface patches with outlines defined by detected vertices to produce triangulated mesh models. These triangulated mesh models are suitable for many applications, such as 3D mapping, urban planning and augmented reality.

Sun, Shaohui

298

Balloon-borne and Raman lidar observations of Asian dust and cirrus cloud properties over Tsukuba, Japan  

NASA Astrophysics Data System (ADS)

vertical distributions of the microphysical and optical properties of tropospheric aerosols and cirrus cloud were measured using an instrumented balloon and a ground-based Raman lidar over Tsukuba, Japan (36°N, 140°E), during the Asian dust events on 9 and 21 May 2007 to investigate the influence of Asian mineral dust on ice cloud formation in the upper troposphere. The instrumented balloon measured the particle size distribution, ice crystal images, dew/frost point, relative humidity, and temperature. The Raman lidar measured the particle backscattering and extinction coefficients and the depolarization ratio at a wavelength of 532 nm. The results of the balloon measurements showed that supermicrometer (0.7 to 2.8 µm in optical-equivalent radius) dust particles and ice crystals (10 to 400 µm in maximum dimension) were present in the upper troposphere (8 to 12 km in altitude), with number concentrations varying from 5 × 10-3 to 0.6 cm-3 for dust and from 5 × 10-3 to 0.15 cm-3 for ice crystals. The Raman lidar measurement indicated that the particle depolarization ratios were 15 to 35% in the altitude range of 6 to 12 km, indicating the predominance of nonspherical particles in the region. The temperature ranged from -33 to -63°C, and the relative humidity with respect to ice (RHi), estimated from the total (vapor plus condensate) water content obtained with the Snow White hygrometer in the cloud, was 130% at maximum on 9 May, which was close to the activation point of Asian mineral dust as ice nuclei to form ice crystals.

Sakai, Tetsu; Orikasa, Narihiro; Nagai, Tomohiro; Murakami, Masataka; Tajiri, Takuya; Saito, Atsushi; Yamashita, Katsuya; Hashimoto, Akihiro

2014-03-01

299

Demonstration of a virtual active hyperspectral LiDAR in automated point cloud classification  

NASA Astrophysics Data System (ADS)

In this paper, a measurement system for the acquisition of a virtual hyperspectral LiDAR dataset is presented. As commercial hyperspectral LiDARs are not yet available, the system provides a novel type of data for the testing and developing of future hyperspectral LiDAR algorithms. The measurement system consists of two parts: first, backscattered reflectance spectra are collected using a spectrometer and a cutting-edge technology, white-light supercontinuum laser source; second, a commercial monochromatic LiDAR system is used for ranging. A virtual hyperspectral LiDAR dataset is produced by data fusion. Such a dataset was collected on a Norway spruce ( Picea abies) sample. The performance of classification was tested using an experimental hyperspectral algorithm based on a novel combination of the Spectral Correlation Mapper and a region growing algorithm. The classifier was able to automatically distinguish between needles, branches and background, in other words, perform a difficult task using only traditional TLS data.

Suomalainen, Juha; Hakala, Teemu; Kaartinen, Harri; Räikkönen, Esa; Kaasalainen, Sanna

2011-09-01

300

Polarimetric Radar Observations of Arctic Clouds: Signal Processing and First Results from the may 2013 Iop  

NASA Astrophysics Data System (ADS)

The ARM Climate Research Facility site at the North Slope of Alaska in Barrow provides polarimetric radar observations of Arctic clouds at X, Ka and W bands. During the May 2013 Scanning radar Intensive Observation Period, raw I and Q data were acquired with the X-SAPR and the Ka-W SACR for the purpose of validating existing, and testing new signal processing procedures specifically tailored for Arctic observations. The raw I and Q datasets were collected on May 3rd 2013 for the case of low-level boundary layer mixed-phase arctic clouds and on May 6th 2013 for the case of a synoptic low moving in from the west. http://www.arm.gov/campaigns/nsa2013nsasr The present paper describes the impact of signal processing procedures on the data, and establishes dual-polarization radar as a valuable tool for the microphysical characterization of ice clouds. In particular, the X-SAPR operates at STSR mode, making available differential reflectivity ZDR, copolar correlation coefficient ?hv, specific differential phase KDP and Degree of Polarization at Simultaneous Transmit DOPS. Low-level boundary layer mixed-phase Arctic clouds are characterized by layers of supercooled liquid water aloft, which present a stark polarimetric contrast with respect to the associated ice precipitation fallout. The ice particles falling from boundary layer Arctic clouds on May 2nd, 3rd and 4th 2013 (winds were very weak or absent) showed the remarkable property of being composed exclusively by large dendrites - fern-like, stellars, twelve-branched - indicating deposition as the main accretion mechanism. http://www.flickr.com/photos/michele_galletti/sets/72157633422079814/ Boundary Layer mixed-phase Arctic clouds provide an exceptional natural laboratory for the exploration of polarimetric signatures in presence of dendritic ice particles. The first-ever X-band analysis of differential reflectivity ZDR of mixed-phase Arctic clouds is presented in [1]. For the May 6th case, ice particle populations associated with frontal systems underwent more significant vertical mixing, and therefore more significant break-up and aggregation, with the overall result that ice particles possessed less geometrical symmetry, and consequently less prominent polarimetric contrast was detected by the radars. [1] Oue, Galletti, Verlinde "Observations of X-band differential reflectivity in Arctic mixed-phase clouds", submitted.

Galletti, M.; Oue, M.; Verlinde, J.

2013-12-01

301

BOREAS AFM-6 NOAA/ETL 35 GHz Cloud/Turbulence Radar GIF Images  

NASA Technical Reports Server (NTRS)

The Boreal Ecosystem-Atmosphere Study (BOREAS) Airborne Fluxes and Meteorology (AFM)-6 team from the National Oceanic and Atmospheric Administration/Environment Technology Laboratory (NOAA/ETL) operated a 35-GHz cloud-sensing radar in the Northern Study Area (NSA) near the Old Jack Pine (OJP) tower from 16 Jul 1994 to 08 Aug 1994. This data set contains a time series of GIF images that show the structure of the lower atmosphere. The NOAA/ETL 35-GHz cloud/turbulence radar GIF images are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The data files are available on a CD-ROM (see document number 20010000884).

Martner, Brooks E.; Newcomer, Jeffrey A. (Editor); Hall, Forrest G.; Smith, David E. (Technical Monitor)

2000-01-01

302

Detection of Tropical Thin Cirrus Clouds Over Dark Water From MISR With Comparisons to Ground-based Lidar  

NASA Astrophysics Data System (ADS)

A detailed tropical cirrus cloud climatology having good temporal and spatial resolution is important because cirrus clouds are known to play important roles in the tropical radiation budget and the global climate system. In addition, undetected, optically thin cirrus can lead to biases in satellite aerosol and surface property retrievals. Inventories of tropical cirrus occurrence have been compiled from limb-sounding instruments, but these instruments are limited in their ability to characterize the horizontal extent and distribution of the clouds. Due to their tenuous nature, thin cirrus can be difficult to detect using higher horizontal resolution, nadir- viewing techniques, particular those that rely on infrared channels. Ground-based lidar observations of tropical thin cirrus clouds at the Atmospheric Radiation Measurement (ARM) sites at Manus and Nauru have provided detailed information about the frequency and properties of the cirrus clouds that occur over these sites. However, these studies only provide sparse spatial sampling. Here we present a unique approach to the problem of tropical thin cirrus detection and characterization that exploits the capabilities of the Multi-angle Imaging SpectroRadiometer (MISR) instrument on NASA's polar- orbiting Terra satellite. Although the lower optical depth limit of typical satellite cloud detection algorithms is no better than 0.1, it has been demonstrated that MISR is sensitive to aerosol optical depths approximately 0.05 and larger. The geometry of MISR's nine cameras increases instrument sensitivity to optically thin layers, since air mass factors as high as three are sampled at the most oblique camera angles. In the tropics, MISR observes scattering angles ranging from about 100 to 160 degrees, which provides sensitivity to particle shape for all but the smallest particles. To test MISR's ability to detect and characterize optically thin tropical cirrus, we compare MISR retrievals with coincident observations from ground-based lidar located at a number of Atmospheric Radiation Measurement (ARM) and Micro-pulse Lidar Network (MPLNET) sites. Preliminary results suggest that MISR is capable of distinguishing cirrus in the presence of other aerosols if the total column aerosol optical depth is greater than 0.2 and cirrus contributes more than approximately 20 percent to this total. This work is the first step toward the larger goal of retrieving cirrus optical depth and ice particle properties using this technique on a global basis over the world's oceans. The work of MJG and RAK is performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

Garay, M. J.; Kahn, R.; Comstock, J.; Welton, E. J.

2006-12-01

303

Cloud Images and Turbulent Spectra Taken by the NRL 94 GHz WARLOC Radar  

Microsoft Academic Search

Gyroklystron development has been reported at APS DPP meetings for years. One of these, a 94 GHz, 100 kW gyroklystron has been incorporated into an NRL radar system called WARLOC, situated on the west shore of Chesapeake Bay. One application of WARLOC has been the study of clouds[1,2]. The added power of the gyroklystron has made possible the rapid resolution

Wallace Manheimer

2003-01-01

304

Combined infrared emission spectra and radar reflectivity studies of cirrus clouds  

Microsoft Academic Search

Thermal-infrared emission spectra from cirrus clouds taken with a unique prism spectrograph are combined with Ka-band radar reflectivity measurements to obtain mass concentration and size information on the cirrus ice crystals. A two-stream radiation transfer model utilizing Mie scattering theory was used to infer the averaged effective ice sphere diameter which, for the cirrus studied, was near 50 ?m

A. Jay Palmer; S. Y. Matrosov; B. E. Martner; T. Uttal; D. K. Lynch; M. A. Chatelain; J. A. Hackwell; R. W. Russell

1993-01-01

305

EarthCARE Simulator: The new Doppler Cloud Profiling Radar module  

NASA Astrophysics Data System (ADS)

The EarthCARE simulator provides end-to-end (forward and inversion) modeling of the instruments on board the European Space Agency Earth Clouds Aerosol Radiation Explorer (EarthCARE) mission. One of the primary instruments on board the EarthCARE mission is the Doppler cloud profiling radar (CPR). The CPR is the first spaceborne Doppler radar and its vertical velocity measurements are expected to provide unique global insights in deep convective motions and ice particles sedimentation rates. Here we describe in detail the instrument and forward models of the EarthCARE CPR simulator. The instrument model includes the satellite platform motion and location parameters, the radar technical specifications and the digital signal processing module. The forward model includes hydrometeor scattering libraries, surface modeling, mirror images, multiple scattering and melting layer modules. Emphasis is given in the detail representation of the parameters that affect the quality (errors and biases) in the Doppler velocity measurements from space. Data produced by a state-of-the-art, high-resolution cloud-resolving model (CRM) serve as the basis for creating `scenes' that will be used as input to various radiative transfer programs and instrument simulation modules. This provides the ability to simulate satellite overpasses and subsequent measurement processes.

Kollias, P.; Battaglia, A.; Tanelli, S.; Tatarevic, A.; Wilker, H.; Acarreta, J. R.

2009-12-01

306

Turbulence as observed by concurrent measurements made at NSSL using weather radar, Doppler radar, Doppler lidar and aircraft  

NASA Technical Reports Server (NTRS)

As air traffic increases and aircraft capability increases in range and operating altitude, the exposure to weather hazards increases. Turbulence and wind shears are two of the most important of these hazards that must be taken into account if safe flight operations are to be accomplished. Beginning in the early 1960's, Project Rough Rider began thunderstorm investigations. Past and present efforts at the National Severe Storm Laboratory (NSSL) to measure these flight safety hazards and to describe the use of Doppler radar to detect and qualify these hazards are summarized. In particular, the evolution of the Doppler-measured radial velocity spectrum width and its applicability to the problem of safe flight is presented.

Lee, Jean T.

1987-01-01

307

Identification of a Debris Cloud from the Nuclear Powered SNAPSHOT Satellite with Haystack Radar Measurements  

NASA Technical Reports Server (NTRS)

Data from the MIT Lincoln Laboratory (MIT/LL) Long Range Imaging Radar (known as the Haystack radar) have been used in the past to examine families of objects from individual satellite breakups or families of orbiting objects that can be isolated in altitude and inclination. This is possible because for some time after a breakup, the debris cloud of particles can remain grouped together in similar orbit planes. This cloud will be visible to the radar, in fixed staring mode, for a short time twice each day, as the orbit plane moves through the field of view. There should be a unique three-dimensional pattern in observation time, range, and range rate which can identify the cloud. Eventually, through slightly differing precession rates of the right ascension of ascending node of the debris cloud, the observation time becomes distributed so that event identification becomes much more difficult. Analyses of the patterns in observation time, range, and range rate have identified good debris candidates released from the polar orbiting SNAPSHOT satellite (International Identifier: 1965-027A). For orbits near 90o inclination, there is essentially no precession of the orbit plane. The SNAPSHOT satellite is a well known nuclear powered satellite launched in 1965 to a near circular 1300 km orbit with an inclination of 90.3o. This satellite began releasing debris in 1979 with new pieces being discovered and cataloged over the years. 51 objects are still being tracked by the United States Space Surveillance Network. An analysis of the Haystack data has identified at least 60 pieces of debris separate from the 51 known tracked debris pieces, where all but 2 of the 60 pieces have a size less than 10cm. The altitude and inclination (derived from range-rate with a circular orbit assumption) are consistent with the SNAPSHOT satellite and its tracked debris cloud.

Stokely, C.; Stansbery, E.

2006-01-01

308

The Retrieval of Stratus Cloud Droplet Effective Radius with Cloud Radars  

Microsoft Academic Search

In situ samples of cloud droplets by aircraft in Oklahoma in 1997, the Surface Heat Budget of the Arctic Ocean (SHEBA)\\/First ISCCP Regional Experiment (FIRE)-Arctic Cloud Experiment (ACE) in 1998, and various other locations around the world were used to evaluate a ground-based remote sensing technique for retrieving profiles of cloud droplet effective radius. The technique is based on vertically

Shelby Frisch; Matthew Shupe; Irina Djalalova; Graham Feingold; Michael Poellot

2002-01-01

309

Velocity and acceleration estimation of Doppler weather radar\\/lidar signals in colored noise  

Microsoft Academic Search

The authors are interested in estimating the Doppler shift occurred in weather radar returns, which yields precipitation velocity information. Conventional techniques including the pulse pair processor rely heavily on the assumption that the additive noise is white and hence their performance degrades when the noise color is unknown. Because the data length for a given range gate is usually small,

Weige Chen; Guotong Zhou; G. B. Giannakis

1995-01-01

310

Spatial Variability of alpine snowfall and snow accumulation from radar and lidar data  

NASA Astrophysics Data System (ADS)

A mobile polarimetric X-band radar (MXPol) deployed in the area of Davos (Switzerland) collected valuable and continuous information on small-scale precipitation for the winter seasons of 2009/2010 and 2010/2011. These data are compared to local measurements of the maximum snow accumulation over the season collected with Airborne Laser Scanning (ALS) at the Wannengrat area (Davos, Switzerland). This unique configuration makes the comparison of the variability in snowfall (as seen by the radar) and in snow accumulation (from laser scans) possible over the entire winter seasons. The spatial variability, quantified by means of the variogram (related to autocorrelation), is shown to be larger in snow accumulation than in snowfall. This indicates that other factors (like wind and turbulence taking place close to the ground) induced by small-scale topographic features govern the snow deposition and accumulation at the ground level in mountainous areas. In order to further investigate this question, the domain covered by the radar is divided in two sub-domains over which the radar beam is either close or far from a mountain ridge. The variability in snowfall, as well as the turbulence intensity, appears consistently larger in the vicinity of the ridge than far from the ground, which confirms the influence of small-scale topography on snowfall.adar data snapshot from March 18, 2011 at 00:06:48 UTC. a) Reflectivity. b) Differential reflectivity. c) Doppler spectral width

Scipion, D. E.; Mott, R.; Lehning, M.; Berne, A.

2012-12-01

311

Microphysical properties of the November 26 cirrus cloud retrieved by Doppler radar/IR radiometer technique  

NASA Technical Reports Server (NTRS)

Gaining information about cirrus cloud microphysics requires development of remote sensing techniques. In an earlier paper. Matrosov et al. (1992) proposed a method to estimate ice water path (IWP) (i.e., vertically integrated ice mass content IMC) and characteristic particle size averaged through the cloud from combined groundbased measurements of radar reflectivities and IR brightness temperatures of the downwelling thermal radiation in the transparency region of 10-12 mu m. For some applications, the vertically averaged characteristic particle sizes and IWP could be the appropriate information to use. However, vertical profiles of cloud microphysical parameters can provide a better understanding of cloud structure and development. Here we describe a further development of the previous method by Matrosov et al. (1992) for retrieving vertical profiles of cirrus particle sizes and IMC rather than their vertically averaged values. In addition to measurements of radar reflectivities, the measurements of Doppler velocities are used in the new method. This provides us with two vertical profiles of measurements to infer two vertical profiles of unknowns, i.e., particle characteristic sizes and IMC. Simultaneous measurements of the IR brightness temperatures are still needed to resolve an ambiguity in particle size-fall velocity relationships.

Matrosov, Sergey Y.; Kropfli, Robert A.; Orr, Brad W.; Snider, Jack B.

1993-01-01

312

DC-8 Scanning Lidar Characterization of Aircraft Contrails and Cirrus Clouds.  

National Technical Information Service (NTIS)

A Subsonic Assessment (SASS) element of the overall Atmospheric Effects of Aviation Project (AEAP) was initiated by NASA to assess the atmospheric impact of subsonic aircraft. A scanning mirror pod attached to the DC-8 aircraft provides for scanning lidar...

N. B. Nielsen E. E. Uthe

1996-01-01

313

Cirrus clouds at Thule, Greenland, during swnmer: lidar observations and infiuence on the planetary radiative budget  

Microsoft Academic Search

l. OBSERV ATIONS A lidar system was installed at Thule (76.5°N , 68.9°W), Greenland, in late 1990 to study the polar upper troposphere, stratosphere and mesosphere. The lidar is equipped with a Nd:YAG laser, emit- ting linearly polarized pulses of up to 300 mJ en- ergy at 532 nm, 4 Hz repetition rate. A 0.8 m dia- meter Cassegrain telescope

A. Benedetti; A. di Sarral; C. Fiocco; D. Fuà

314

An intercomparison of radar-based liquid cloud microphysics retrievals and implication for model evaluation studies  

NASA Astrophysics Data System (ADS)

To assess if current radar-based liquid cloud microphysical retrievals of the Atmospheric Radiation Measurement (ARM) program can provide useful constraints for modeling studies, this paper presents intercomparison results of three cloud products at the Southern Great Plains (SGP) site: the ARM MICROBASE, University of Utah (UU), and University of North Dakota (UND) products over the nine-year period from 1998 to 2006. The probability density and spatial autocorrelation functions of the three cloud Liquid Water Content (LWC) retrievals appear to be consistent with each other, while large differences are found in the droplet effective radius retrievals. The differences in the vertical distribution of both cloud LWC and droplet effective radius retrievals are found to be alarmingly large, with the relative difference between nine-year mean cloud LWC retrievals ranging from 20% at low altitudes to 100% at high altitudes. Nevertheless, the spread in LWC retrievals is much smaller than that in cloud simulations by climate and cloud resolving models. The MICROBASE effective radius ranges from 2.0 at high altitudes to 6.0 ?m at low altitudes and the UU and UND droplet effective radius is 6 ?m larger. Further analysis through a suite of retrieval experiments shows that the difference between MICROBASE and UU LWC retrievals stems primarily from the partition total Liquid Water path (LWP) into supercooled and warm liquid, and from the input cloud boundaries and LWP. The large differences between MICROBASE and UU droplet effective radius retrievals are mainly due to rain/drizzle contamination and the assumptions of cloud droplet concentration used in the retrieval algorithms. The large discrepancy between different products suggests caution in model evaluation with these observational products, and calls for improved retrievals in general.

Huang, D.; Zhao, C.; Dunn, M.; Dong, X.; Mace, G. G.; Jensen, M. P.; Xie, S.; Liu, Y.

2011-12-01

315

Toward the characterization of upper tropospheric clouds using Atmospheric Infrared Sounder and Microwave Limb Sounder observations  

Microsoft Academic Search

We estimate the accuracy of cloud top altitude (Z) retrievals from the Atmospheric Infrared Sounder (AIRS) and Advanced Microwave Sounding Unit (AMSU) observing suite (ZA) on board the Earth Observing System Aqua platform. We compare ZA with coincident measurements of Z derived from the micropulse lidar and millimeter wave cloud radar at the Atmospheric Radiation Measurement (ARM) program sites of

Brian H. Kahn; Annmarie Eldering; Amy J. Braverman; Eric J. Fetzer; Jonathan H. Jiang; Evan Fishbein; Dong L. Wu

2007-01-01

316

Active laser radar (lidar) for measurement of corresponding height and reflectance images  

NASA Astrophysics Data System (ADS)

For the survey and inspection of environmental objects, a non-tactile, robust and precise imaging of height and depth is the basis sensor technology. For visual inspection,surface classification, and documentation purposes, however, additional information concerning reflectance of measured objects is necessary. High-speed acquisition of both geometric and visual information is achieved by means of an active laser radar, supporting consistent 3D height and 2D reflectance images. The laser radar is an optical-wavelength system, and is comparable to devices built by ERIM, Odetics, and Perceptron, measuring the range between sensor and target surfaces as well as the reflectance of the target surface, which corresponds to the magnitude of the back scattered laser energy. In contrast to these range sensing devices, the laser radar under consideration is designed for high speed and precise operation in both indoor and outdoor environments, emitting a minimum of near-IR laser energy. It integrates a laser range measurement system and a mechanical deflection system for 3D environmental measurements. This paper reports on design details of the laser radar for surface inspection tasks. It outlines the performance requirements and introduces the measurement principle. The hardware design, including the main modules, such as the laser head, the high frequency unit, the laser beam deflection system, and the digital signal processing unit are discussed.the signal processing unit consists of dedicated signal processors for real-time sensor data preprocessing as well as a sensor computer for high-level image analysis and feature extraction. The paper focuses on performance data of the system, including noise, drift over time, precision, and accuracy with measurements. It discuses the influences of ambient light, surface material of the target, and ambient temperature for range accuracy and range precision. Furthermore, experimental results from inspection of buildings, monuments and industrial environments are presented. The paper concludes by summarizing results achieved in industrial environments and gives a short outlook to future work.

Froehlich, Christoph; Mettenleiter, M.; Haertl, F.

1997-08-01

317

The CloudSat Mission and the A-Train: A Revolutionary Approach to Observing Earth's Atmosphere  

Microsoft Academic Search

On April 28, 2006 a millimeter radar system, designed expressly for the vertical profiling of hydrometeors, was launched from Vandenburg Air Force Base. Both Cloudsat, carrying the cloud profiling radar (CPR), and the lidar satellite CALIPSO, were inserted into nearly identical orbits each approximately one minute behind the NASA Earth Observing System (EOS) Aqua satellite and in formation with the

Deborah Vane; G. L. Stephens

2008-01-01

318

NASA/GSFC Scanning Raman Lidar Measurements of Water Vapor and Clouds during the International H2O Project (IHOP) Field Campaign  

NASA Technical Reports Server (NTRS)

The NASA/GSFC Scanning Raman Lidar (SFL) acquired approximately 200 hours of water vapor, aerosol and cloud measurements during the IHOP field campaign. The detailed water vapor structure of events such as a dryline passage and internal bores were revealed. We discuss the error characteristics of the instrument as well as the water vapor and cirrus cloud structure during the 19-20 June bore event.

Whiteman, David; Demoz, Belay; DiGirolamo, Paolo; Wang, Zhi-En; Evans, Keith; Lin, Ruei-Fong

2003-01-01

319

Cloud Screening and Quality Control Algorithm for Star Photometer Data: Assessment with Lidar Measurements and with All-sky Images  

NASA Technical Reports Server (NTRS)

This paper presents the development and set up of a cloud screening and data quality control algorithm for a star photometer based on CCD camera as detector. These algorithms are necessary for passive remote sensing techniques to retrieve the columnar aerosol optical depth, delta Ae(lambda), and precipitable water vapor content, W, at nighttime. This cloud screening procedure consists of calculating moving averages of delta Ae() and W under different time-windows combined with a procedure for detecting outliers. Additionally, to avoid undesirable Ae(lambda) and W fluctuations caused by the atmospheric turbulence, the data are averaged on 30 min. The algorithm is applied to the star photometer deployed in the city of Granada (37.16 N, 3.60 W, 680 ma.s.l.; South-East of Spain) for the measurements acquired between March 2007 and September 2009. The algorithm is evaluated with correlative measurements registered by a lidar system and also with all-sky images obtained at the sunset and sunrise of the previous and following days. Promising results are obtained detecting cloud-affected data. Additionally, the cloud screening algorithm has been evaluated under different aerosol conditions including Saharan dust intrusion, biomass burning and pollution events.

Ramirez, Daniel Perez; Lyamani, H.; Olmo, F. J.; Whiteman, D. N.; Navas-Guzman, F.; Alados-Arboledas, L.

2012-01-01

320

Remote Sensing of Cloud Properties: Beyond the A-Train  

Microsoft Academic Search

The combination of active and passive sensors on the A-Train satellites provides the best data set to date for studying cloud and aerosol properties from space. Lidar and mm-wavelength radar provide an unprecedented global view of aerosol and cloud vertical structure. Multi-spectral imaging and thermal wavelength interferometry add spatial context and complementary information on cloud properties and atmospheric state. Science

T. P. Ackerman

2007-01-01

321

Gravity Waves and Mesospheric Clouds in the Summer Middle Atmosphere: A Comparison of Lidar Measurements and Ray Modeling of Gravity Waves Over Sondrestrom, Greenland  

NASA Technical Reports Server (NTRS)

We conducted gravity wave ray-tracing experiments within an atmospheric region centered near the ARCLITE lidar system at Sondrestrom, Greenland (67N, 310 deg E), in efforts to understand lidar observations of both upper stratospheric gravity wave activity and mesospheric clouds during August 1996 and the summer of 2001. The ray model was used to trace gravity waves through realistic three-dimensional daily-varying background atmospheres in the region, based on forecasts and analyses in the troposphere and stratosphere and climatologies higher up. Reverse ray tracing based on upper stratospheric lidar observations at Sondrestrom was also used to try to objectively identify wave source regions in the troposphere. A source spectrum specified by reverse ray tracing experiments in early August 1996 (when atmospheric flow patterns produced enhanced transmission of waves into the upper stratosphere) yielded model results throughout the remainder of August 1996 that agreed best with the lidar observations. The model also simulated increased vertical group propagation of waves between 40 km and 80 km due to intensifying mean easterlies, which allowed many of the gravity waves observed at 40 km over Sondrestrom to propagate quasi-vertically from 40-80 km and then interact with any mesospheric clouds at 80 km near Sondrestrom, supporting earlier experimentally-inferred correlations between upper stratospheric gravity wave activity and mesospheric cloud backscatter from Sondrestrom lidar observations. A pilot experiment of real-time runs with the model in 2001 using weather forecast data as a low-level background produced less agreement with lidar observations. We believe this is due to limitations in our specified tropospheric source spectrum, the use of climatological winds and temperatures in the upper stratosphere and mesosphere, and missing lidar data from important time periods.

Gerrard, Andrew J.; Kane, Timothy J.; Eckermann, Stephen D.; Thayer, Jeffrey P.

2004-01-01

322

Microphysical modelling of a mid-latitude polar stratospheric cloud event: Comparisons against multiwavelength ground-based and spaceborne lidar data  

NASA Astrophysics Data System (ADS)

A newly developed high resolution transport model containing a size-resolving microphysical scheme is used to study a large-scale polar stratospheric cloud (most certainly a liquid PSC) case detected by lidar at mid-latitudes between February 17th and 23rd, 2008. The model simulations are validated locally against ground-based lidar (IfT MARTHA lidar, Leipzig, Germany) and globally against spaceborne lidar (CALIOP/CALIPSO) backscatter measurements. The comparison between the spaceborne and ground-based lidar measurements above Leipzig is satisfactory with an average backscatter ratio of 3.1 observed on February 20th. The microphysical-transport model is found to be able to reproduce the lidar measurements when a 1 K cold bias is assumed for the ECMWF temperatures. Assuming a cold bias and equilibrated PSC particles, our model produces time-evolving fields of optical and geometrical parameters such as the total surface area density (A) and volume (V). A, V, and the median radius of the model-calculated PSC size distribution are compared to the corresponding values derived from the ground-based multiwavelength lidar backscatter measurements. Overall, a good agreement is found between the model calculations and the Leipzig lidar-derived size distribution parameters, with A and V around 10 µm2.cm-3 and 1 µm3.cm-3 respectively and a median radius of around 0.3 µm at 21 km. The horizontal extension of the cloud is analysed. Again, our model calculations are found to be in a good agreement with CALIOP/CALIPSO PSC fields. This type of successful validation of PSC parametrisations in chemistry-transport models is a prerequisite for the calculations of ozone depletion potential.

Jumelet, J.; Bekki, S.; Seifert, P.; Pelon, J.

2009-04-01

323

Wide-angle imaging LIDAR (WAIL): a ground-based instrument for monitoring the thickness and density of optically thick clouds.  

SciTech Connect

Traditional lidar provides little information on dense clouds beyond the range to their base (ceilometry), due to their extreme opacity. At most optical wavelengths, however, laser photons are not absorbed but merely scattered out of the beam, and thus eventually escape the cloud via multiple scattering, producing distinctive extended space- and time-dependent patterns which are, in essence, the cloud's radiative Green functions. These Green functions, essentially 'movies' of the time evolution of the spatial distribution of escaping light, are the primary data products of a new type of lidar: Wide Angle Imaging Lidar (WAIL). WAIL data can be used to infer both optical depth and physical thickness of clouds, and hence the cloud liquid water content. The instrumental challenge is to accommodate a radiance field varying over many orders of magnitude and changing over widely varying time-scales. Our implementation uses a high-speed microchannel plate/crossed delay line imaging detector system with a 60-degree full-angle field of view, and a 532 nm doubled Nd:YAG laser. Nighttime field experiments testing various solutions to this problem show excellent agreement with diffusion theory, and retrievals yield plausible values for the optical and geometrical parameters of the observed cloud decks.

Love, Steven P.; Davis, A. B. (Anthony B.); Rohde, C. A. (Charles A.); Ho, Cheng,

2001-01-01

324

UNCERTAINTY ANALYSIS OF DATA FROM THE POLAR ATMOSPHERIC EMITTED RADIANCE INTERFEROMETER (PAERI) DURING THE SOUTH POLE ATMOSPHERIC RADIATION AND CLOUD LIDAR EXPERIMENT (SPARCLE)  

Microsoft Academic Search

An uncertainty analysis for the Polar Atmospheric Emitted Radiance Interferometer (Polar AERI, or PAERI) is presented for its deployment during the South Pole Atmospheric Radiation and Cloud Lidar Experiment (SPARCLE). The uncertainty analysis involves a Taylor series expansion of the AERI calibration equation, and treatment of several biases and systematic uncertainties in the SPARCLE data set. Most of the random

Michael S. Town

325

Combined Microwave Radiometer and Micro Rain Radar Analysis of Cloud Liquid Water  

NASA Astrophysics Data System (ADS)

The cloud liquid water is a parameter of vital interest in both modeling and forecasting weather. In meso- scale models, the magnitude of latent heat effects corresponds to the amount of cloud liquid water, which is important in the development of a certain weather system. The purpose of this study is to obtain the combined cloud liquid water from a 21.8 and 31.4 GHz ground based microwave radiometer (MWR) and the micro rain radar (MRR), because each instrument has the limitation of observation; it is widely known that the measurements of MWR and MRR are not meaningful with and without rainfall, respectively. The cloud liquid water of the two instruments has been measured at the Cloud Physics Observation System (CPOS) site, located at 37.41¢¥ N, 128.45¢¥ E and 842 m from mean sea level. To examine the performance of instruments, the precipitable water vapor (PWV) measured by the MWR was compared with the calculated PWV of nearest radiosonde from December 2003 to July 2008, and MRR was compared with the several accumulated precipitation observed by AWS. The PWV of MWR gives good agreement with that of radiosonde: R-square = 0.82 for spring, 0.78 for summer, 0.83 for fall, but 0.25 for winter. This bad performance in the winter season seems from the heavy snow on the radome, and then the winter data of MWR has been not considered in the combining algorithm. The comparison of MRR and AWS a correlation coefficient: 30min accumulated precipitation was R-square = 0.84. To combine the MRR and MWR cloud liquid water, firstly we estimate the cloud physical thickness from the difference between the MTSAT-1R cloud top height and cloud base height of visual observation of Daegwallyeong weather station, and the cloud liquid water path of MRR is obtained by multiplying the LWC of MRR and the estimated cloud physical thickness. The trend of MWR liquid water path agrees with that of the MRR during small precipitation. We study these characteristics of MRR and MWR for small precipitation to obtain the combined cloud water content of MRR and MWR, constantly operated regardless to the rainfall.

Yang, H.; Chang, K.; Jeong, J.; Lee, S.; Jang, Y.; Lee, M.; Kim, K.

2008-12-01

326

Polarimetric Radar Remote Sensing of Rainfall and Liquid Water in Clouds  

NASA Astrophysics Data System (ADS)

This study focuses on investigation, development and evaluation of dual linear polarization radar techniques for measuring rainfall rates and liquid water content in clouds. The differential reflectivity (Z_ {DR}) technique and two well-known Z-R relationships (Marshall-Palmer and Jones' Thunderstorm) are evaluated through a case study which compares radar and ground-based raingauge measurements utilizing data from the MAYPOLE (1984) experiments conducted in Colorado. The horizontal storm motion and vertical transport of raindrops, as well as the consistency of the spatial and temporal averaging of the radar and raingauge data are taken into account. It is observed that the Z_{DR } technique performs consistently well in the estimation of rainfall rate R when compared with raingauges at two different locations in the storm. A cross correlation technique is proposed and applied to translating radar measurements of rainfall parameters from aloft to their corresponding ground values. Dual polarization radar measurements obtained during the MIST (1986) experiments in Alabama are utilized for this purpose. This technique is also used to estimate the storm motion direction which is necessary for the radar-raingauge comparative studies. One- and two-dimensional correlation lengths of the reflectivity factor, rainfall rate and median volume diameter fields are presented for rainfall events from both MAYPOLE and MIST experiments. Scattering and propagation properties of millimeter waves (94 and 140 GHz) in rainfall are also studied. Power law relationships based on the Marshall-Palmer drop size distribution are derived for rainfall rate R and the propagation parameters such as specific attenuation, specific differential attenuation and phase shift. It is proposed that these parameters at 94 and 140 GHz can be used for estimating path integrated rainfall rates over short propagation paths less than a few kilometers. Raindrop shape models are also shown to significantly affect the interpretation of the Doppler velocity spectrum for vertically pointing radars. A dual polarization bistatic scattering technique is proposed and illustrated for estimating cloud and fog droplet size distributions and their liquid water contents. (Abstract shortened with permission of author.).

Lure, Yuan-Ming

1990-01-01

327

Mesoscale and microscale structure of cirrus clouds - Three case studies  

NASA Technical Reports Server (NTRS)

The structure and composition of various types of cirrus clouds were examined using coordinated aircraft and on-ground polarization lidar and Doppler radar measurements carried out during three case studies conducted during autumn or spring in Colorado, Wisconsin, and Utah states. A variety of cirrus cloud types observed included a multilayered orographic cirrus, a 6-km-deep cirrostratus overcast, and a group of fibrous cirrus cloud bands associated with tropopause generating cells, representing three basic cirrus-cloud types. The results on the structure and composition of these clouds provide insights into the microphysical processes and characteristic physical scales involved in the generation of cirrus clouds.

Sassen, Kenneth; Starr, David O'C.; Uttal, Taneil

1989-01-01

328

Retrievals of vertical profiles of stratus cloud properties from combined oxygen A-band and radar observations  

NASA Astrophysics Data System (ADS)

A synergetic algorithm of retrieving vertical distribution of cloud drop effective radius (Re), liquid water content (LWC), and optical depth has been developed by combining oxygen A-band spectral measurements with radar reflectivity. The underlying physics is to utilize the photon path length information from oxygen A-band measurements to constrain the retrievals of cloud microphysical properties from radar reflectivity. Through a radiation closure of the rotating shadowband spectrometer (RSS) diffuse-horizontal irradiances in the oxygen A-band (which is sensitive to vertical distribution of the 2nd moment of particle size distribution), vertical distributions of cloud microphysical property (the 3rd moment of particle size distribution) are optimized and retrieved from Millimeter Wave Cloud Radar (MMCR) reflectivity (the 6th moment of particle size distribution). The critical issues in the synergetic cloud retrievals of combining passive and active instruments are discussed and carefully taken into account. Evaluation and validation through case studies show that the retrieved column mean values of cloud optical depth, effective radius, and liquid water path agree well with independent measurements from the microwave radiometer (MWR) and independent retrievals from a combined algorithm of multifilter rotating shadowband radiometer (MFRSR) and MWR and the column physical characterization (CPC) of MMCR. These studies demonstrate that this active-passive synergetic retrieval algorithm is feasible and accurate for retrievals of vertical distribution of cloud Re and LWC for stratus clouds.

Li, Siwei; Min, Qilong

2013-01-01

329

Characterization of rockslide dynamics by the joint analysis of airborne LiDAR and stereo-photogrammetric point clouds.  

NASA Astrophysics Data System (ADS)

The catchment of Sanières is located on the South-facing slope of the Barcelonnette basin (South French Alps). This region is known to be highly prone to gravitational processes including large landslides and debris-flows. In early August 2013, a large rockslide event occurred in the lower part of the catchment. During several days, a large amount of debris have been mobilised along a 300m length cliff. Deposits have reached and filled the torrential channel downslope. Several field observations carried out in the following weeks have shown the progressive opening of fissures along the main scarp. Today, large volumes of unstable debris are still available on the slope. Local stakeholders are now expecting the formation of a debris-dam in the channel which could lead to a debris flow in case of failure. Since the rockslide cannot be stabilized, it is necessary to monitor the site in order to track the evolution of the sliding processes for hazard assessment purposes. This work is focused on the use of remote sensing techniques (terrestrial photogrammetry, LiDAR) to detect and quantify spatial and temporal distribution of materials on the slope. Dataset includes ground-based and aerial optical images acquired through several field surveys together with an airborne LiDAR points clouds. The Structure From Motion (SFM) technique is used to generate multi-date high-resolution digital elevation models (HRDEMs) in order to quantify volumes changes. Images correlation technique is used to estimate displacements at the surface from images acquired continuously by a fixed camera mounted on the opposite slope and facing the rockslide. The analysis of the terrestrial point clouds indicates two types of dynamics: (i) surficial transport of debris (boulders, tree trunks) which can be identified on daily observations, and (ii) a global deformation of the rockslope along several slip surfaces. The progressive development of the main scarp with velocity of a few cm.month-1 is also monitored. The analysis of an airborne LiDAR point cloud allows to characterize the main discontinuities and the possibility of movement of the global deformation. Finally, an indicator of activity of the slope is proposed from the time serie analysis. The possibility of extension of the rockslide is discussed.

Mathieu, Alexandre; Malet, Jean-Philippe; Stumpf, André

2014-05-01

330

Detection of potentially hazardous convective clouds with a dual-polarized C-band radar  

NASA Astrophysics Data System (ADS)

A method for forecasting very short-term rainfall to detect potentially hazardous convective cloud that produces heavy local rainfall was developed using actual volumetric C-band polarimetric radar data. Because the rainfall estimation algorithm used in this method removed the effect of ice particles based on polarimetric measurements, it was immune to the high reflectivity associated with hail. The reliability of the algorithm was confirmed by comparing the rainfall rate estimated from the polarimetric radar measurements at the lowest elevation angle with that obtained from optical disdrometers on the ground. The rainfall rate estimated from polarimetric data agreed well with the results obtained from the disdrometers, and was much more reliable than results derived from reflectivity alone. Two small cumulus cells were analyzed, one of which developed and later produced heavy rainfall, whereas the other did not. Observations made by polarimetric radar with a volumetric scan revealed that a high vertical maximum intensity of rainfall rate and a vertical area of enhanced differential reflectivity extending above the freezing level, often termed a high ZDR column, were clearly formed about 10 min prior to the onset of heavy rainfall on the ground. The onset time of the heavy rainfall could be estimated in advance from the polarimetric data, which agreed fairly well with observations. These polarimetric characteristics were not observed for the cumulus cell that did not produce heavy rainfall. The results suggest that both the vertical maximum intensity of the rainfall rate and a high ZDR column, estimated from polarimetric measurements, can be used to identify potentially hazardous clouds. Furthermore, this study shows that polarimetric radar measurements with high spatial and temporal resolutions are invaluable for disaster reduction.

Adachi, A.; Kobayashi, T.; Yamauchi, H.; Onogi, S.

2013-10-01

331

Detection of potentially hazardous convective clouds with a dual-polarized C-band radar  

NASA Astrophysics Data System (ADS)

A method for forecasting very short-term rainfall to detect potentially hazardous convective cloud that produces heavy local rainfall was developed using actual volumetric C-band polarimetric radar data. Because the rainfall estimation algorithm used in this method removed the effect of ice particles based on polarimetric measurements, it was immune to the high reflectivity associated with hail. The reliability of the algorithm was confirmed by comparing the rainfall rate estimated from the polarimetric radar measurements at the lowest elevation angle with that obtained from an optical disdrometer on the ground. The rainfall rate estimated from polarimetric data agreed well with the results obtained from the disdrometer, and was much more reliable than results derived from reflectivity alone. Two small cumulus cells were analyzed, one of which developed and later produced heavy rainfall, whereas the other did not. Observations made by polarimetric radar with a volumetric scan revealed that a high vertical maximum intensity of rainfall rate and a vertical area of enhanced differential reflectivity extending above the freezing level, often termed a high ZDR column, were clearly formed about 10 min prior to the onset of heavy rainfall on the ground. The onset time of the heavy rainfall could be estimated in advance from the polarimetric data, which agreed fairly well with observations. These polarimetric characteristics were not observed for the cumulus cell that did not produce heavy rainfall. The results suggest that both the vertical maximum intensity of the rainfall rate and a high ZDR column, estimated from polarimetric measurements, can be used to identify potentially hazardous clouds. Furthermore, this study shows that polarimetric radar measurements with high spatial and temporal resolutions are invaluable for disaster reduction.

Adachi, A.; Kobayashi, T.; Yamauchi, H.; Onogi, S.

2013-04-01

332

Internet-Based Software Tools for Analysis and Processing of LIDAR Point Cloud Data via the OpenTopography Portal  

NASA Astrophysics Data System (ADS)

LIDAR is an excellent example of the new generation of powerful remote sensing data now available to Earth science researchers. Capable of producing digital elevation models (DEMs) more than an order of magnitude higher resolution than those currently available, LIDAR data allows earth scientists to study the processes that contribute to landscape evolution at resolutions not previously possible, yet essential for their appropriate representation. Along with these high-resolution datasets comes an increase in the volume and complexity of data that the user must efficiently manage and process in order for it to be scientifically useful. Although there are expensive commercial LIDAR software applications available, processing and analysis of these datasets are typically computationally inefficient on the conventional hardware and software that is currently available to most of the Earth science community. We have designed and implemented an Internet-based system, the OpenTopography Portal, that provides integrated access to high-resolution LIDAR data as well as web-based tools for processing of these datasets. By using remote data storage and high performance compute resources, the OpenTopography Portal attempts to simplify data access and standard LIDAR processing tasks for the Earth Science community. The OpenTopography Portal allows users to access massive amounts of raw point cloud LIDAR data as well as a suite of DEM generation tools to enable users to generate custom digital elevation models to best fit their science applications. The Cyberinfrastructure software tools for processing the data are freely available via the portal and conveniently integrated with the data selection in a single user-friendly interface. The ability to run these tools on powerful Cyberinfrastructure resources instead of their own labs provides a huge advantage in terms of performance and compute power. The system also encourages users to explore data processing methods and the variations in algorithm parameters since all of the processing is done remotely and numerous jobs can be submitted in sequence. The web-based software also eliminates the need for users to deal with the hassles and costs associated with software installation and licensing while providing adequate disk space for storage and personal job archival capability. Although currently limited to data access and DEM generation tasks, the OpenTopography system is modular in design and can be modified to accommodate new processing tools as they become available. We are currently exploring implementation of higher-level DEM analysis tasks in OpenTopography, since such processing is often computationally intensive and thus lends itself to utilization of cyberinfrastructure. Products derived from OpenTopography processing are available in a variety of formats ranging from simple Google Earth visualizations of LIDAR-derived hillshades to various GIS-compatible grid formats. To serve community users less interested in data processing, OpenTopography also hosts 1 km^2 digital elevation model tiles as well as Google Earth image overlays for a synoptic view of the data.

Nandigam, V.; Crosby, C. J.; Baru, C.; Arrowsmith, R.

2009-12-01

333

Automated Detection of Geomorphic Features in LiDAR Point Clouds of Various Spatial Density  

Microsoft Academic Search

LiDAR, also referred to as laser scanning, has proved to be an important tool for topographic data acquisition. Terrestrial laser scanning allows for accurate (several millimeter) and high resolution (several centimeter) data acquisition at distances of up to some hundred meters. By contrast, airborne laser scanning allows for acquiring homogeneous data for large areas, albeit with lower accuracy (decimeter) and

Peter Dorninger; Balázs Székely; András. Zámolyi; Clemens Nothegger

2010-01-01

334

Simulation study for cloud detection with space lidars by use of analog detection photomultiplier tubes  

Microsoft Academic Search

Output signal electrons from photomultiplier tubes (PMTs) have neither a Gaussian nor a Poisson distribution because of changes induced by multiplication when the number of input signal photons and dark electrons is fewer than approx100. Therefore the assumption of a Gaussian distribution of signal electrons cannot be used in simulations for space lidar observations with PMTs, for which the number

Zhaoyan Liu; Nobuo Sugimoto

2002-01-01

335

Observations of tornadoes and wall clouds with a portable FM-CW Doppler radar: 1989--1990 results  

SciTech Connect

The purpose of this paper is to report on our progress using a portable, 1 W,FM (frequency modulated)-CW (continuous wave) Doppler radar developed at the Los Alamos National Laboratory (LANL), to make measurements of the wind field in tornadoes and wall clouds along with simultaneous visual documentation. Results using a CW version of the radar in 1987--1988 are given in Bluestein and Unruh (1989). 18 refs., 2 figs., 1 tab.

Bluestein, H.B. (Oklahoma Univ., Norman, OK (USA). School of Meteorology); Unruh, W.P. (Los Alamos National Lab., NM (USA))

1990-01-01

336

Monitoring of the Polar Stratospheric Clouds formation and evolution in Antarctica in August 2007 during IPY with the MATCH method applied to lidar data  

NASA Astrophysics Data System (ADS)

The project ORACLE-O3 ("Ozone layer and UV RAdiation in a changing CLimate Evaluated during IPY") is one of the coordinated international proposals selected for the International Polar Year (IPY). As part of this global project, LOLITA-PSC ("Lagrangian Observations with Lidar Investigations and Trajectories in Antarctica and Arctic, of PSC") is devoted to Polar Stratospheric Clouds (PSC) studies. Indeed, understanding the formation and evolution of PSC is an important issue to quantify the impact of climate changes on their frequency of formation and, further, on chlorine activation and subsequent ozone depletion. In this framework, three lidar stations performed PSC observations in Antarctica during the 2006, 2007, and 2008 winters: Davis (68.58°S, 77.97°E), McMurdo (77.86°S, 166.48°E) and Dumont D'Urville (66.67°S, 140.01°E). The data are completed with the lidar data from CALIOP ("Cloud-Aerosol Lidar with Orthogonal Polarization") onboard the CALIPSO ("Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation") satellite. Lagrangian trajectory calculations are used to identify air masses with PSCs sounded by several ground-based lidar stations with the same method, called MATCH, applied for the first time in Arctic to study the ozone depletion with radiosoundings. The evolution of the optical properties of the PSCs and thus the type of PSCs formed (supercooled ternary solution, nitric acid trihydrate particles or ice particles) could thus be linked to the thermodynamical evolution of the air mass deduced from the trajectories. A modeling with the microphysical model of the Danish Meteorological Institute allows assessing our ability to predict PSCs for various environmental conditions. Indeed, from pressure and temperature evolution, the model allows retrieving the types of particles formed as well as their mean radii, their concentrations and could also simulate the lidar signals. In a first step, a case in August 2007 around 17-18 km, involving the three ground-based lidar stations and CALIOP has been selected. Trajectories with different models (gscf and ecmwf), grids and initializations have been computed to test the robustness of the MATCH. Then the DMI model has been used with these different trajectories to test its ability to reproduce the observations. For a same case, the temperature differences (~2-3 K) between the trajectories have a strong impact on the number density of the particles formed (factor 1000). This case is presented here in detail and a statistical comparison is planned with the numerous MATCH cases identified during the three winters and which involve most of the time two ground-based lidar stations with CALIOP.

Montoux, Nadege; David, Christine; Klekociuk, Andrew; Pitts, Michael; di Liberto, Luca; Snels, Marcel; Jumelet, Julien; Bekki, Slimane; Larsen, Niels

2010-05-01

337

Lidar observations of Arctic polar stratospheric clouds, 1988 - Signature of small, solid particles above the frost point  

NASA Technical Reports Server (NTRS)

The paper presents recent (January 1988) Arctic airborne lidar data which suggest that Type I polar stratospheric clouds (PSCs) are composed of small solid particles with radii on the order of 0.5 micron. PSCs were observed remotely in the 21-24 km altitude range north of Greenland during a round-trip flight from Andenes, Norway on January 29, 1988, aboard the NASA Wallops Flight Facility P-3 Orion aircraft. Synoptic analyses at the 30-mb level show local temperatures of 191-193 K, which are well above the estimated frost point temperature of 185 K; this suggests that the PSCs were probably of the binary HNO3-H2O (Type I) class.

Poole, L. R.; Osborn, M. T.; Hunt, W. H.

1988-01-01

338

Relationship between cloud base height retrieved from lidar and downward longwave irradiance  

NASA Astrophysics Data System (ADS)

Downward longwave radiation is a key process to understand the climate change, energy budget, and water cycle at the earth's surface. Cloud is a dominant factor to determine the intensity of longwave radiation. It is widely known that cloud cover and cloud base height (CBH) have strong effects on the downward longwave radiation, however there are not so many studies regarding the quantitative evaluation of relationship between cloud properties and downward longwave radiation. The intent of the present study is to quantify the impact of cloud property on the downward longwave irradiance (DLI). We used the data obtained with CGR-4 pyrgeometer at Tateno, Japan for the period from January 2002 to December 2011. Cloud radiative contribution fraction (CRC) is evaluated with a ratio of the difference of DLI between observation under cloudy sky without precipitation and calculation assumed clear-sky condition to the observed DLI. The difference between calculation and observation is -4.60+/-3.00 W/m2, and the calculation method reproduced to observation. Cloud is classified into three types by CBH, low (CBH<2000 m), middle (2000?CBH<5000 m), and high (CBH?5000 m). In the results, CRC is almost proportional and inverse proportional to cloud cover (CC) and CBH in the average, respectively. However, CRC for low cloud shows proportion to CBH because existence of low altitude cloud is related to large precipitable water (PW).

Yamada, Kyohei; Hayasaka, Tadahiro; Sugimoto, Nobuo

2012-11-01

339

A Cloud and Precipitation Radar System Concept for the ACE Mission  

NASA Technical Reports Server (NTRS)

One of the instruments recommended for deployment on the Aerosol/Cloud/Ecosystems (ACE) mission is a new advanced cloud profiling radar. In this paper, we describe such a radar design, called ACERAD, which has 35- and 94-GHz channels, each having Doppler and dual-polarization capabilities. ACERAD will scan at Ka-band and will be nadir-looking at W-band. To get a swath of 25-30 km, considered the minimum useful for Ka-band, ACERAD needs to scan at least 2 degrees off nadir; this is at least 20 beamwidths, which is quite large for a typical parabolic reflector. This problem is being solved with a Dragonian design; a scaled prototype of the antenna is being fabricated and will be tested on an antenna range. ACERAD also uses a quasi-optical transmission line at W-band to connect the transmitter to the antenna and antenna to the receiver. A design for this has been completed and is being laboratory tested. This paper describes the current ACERAD design and status.

Durden, S. L.; Tanelli, S.; Epp, L.; Jamnejad, V.; Perez, R.; Prata, A.; Samoska, L.; Long, E; Fang, H.; Esteban-Fernandez, D.; Lee, C.

2011-01-01

340

Intercomparison of Vertical Structure of Storms Revealed by Ground-Based (NMQ) and Spaceborne Radars (CloudSat-CPR and TRMM-PR)  

PubMed Central

Spaceborne radars provide great opportunities to investigate the vertical structure of clouds and precipitation. Two typical spaceborne radars for such a study are the W-band Cloud Profiling Radar (CPR) and Ku-band Precipitation Radar (PR), which are onboard NASA's CloudSat and TRMM satellites, respectively. Compared to S-band ground-based radars, they have distinct scattering characteristics for different hydrometeors in clouds and precipitation. The combination of spaceborne and ground-based radar observations can help in the identification of hydrometeors and improve the radar-based quantitative precipitation estimation (QPE). This study analyzes the vertical structure of the 18 January, 2009 storm using data from the CloudSat CPR, TRMM PR, and a NEXRAD-based National Mosaic and Multisensor QPE (NMQ) system. Microphysics above, within, and below the melting layer are studied through an intercomparison of multifrequency measurements. Hydrometeors' type and their radar scattering characteristics are analyzed. Additionally, the study of the vertical profile of reflectivity (VPR) reveals the brightband properties in the cold-season precipitation and its effect on the radar-based QPE. In all, the joint analysis of spaceborne and ground-based radar data increases the understanding of the vertical structure of storm systems and provides a good insight into the microphysical modeling for weather forecasts.

Fall, Veronica M.; Hong, Yang

2013-01-01

341

Active optical remote sensing of dense clouds with diffusing light : Early results, present implementations, and the challenges ahead  

SciTech Connect

We survey the rapid progress of 'off-beam' cloud lidar, from inception to validation via laboratory-scale simulations. Cloud observations from ground, aircraft and even space are covered. Finally, we describe future work in this instrument development effort born out of pure theory in the mid-1990s. We foresee a bright future for off-beam lidar which is, in essence, an atmospheric application of the general principles of optical diffuse-light tomography. The physical cloud-boundary information it delivers is, in principle, the same as given from ground or space (upcoming CloudSat mission) obtained by mm-radar. And mm-radar gives some information about internal variability. However, radar reflectivities quite often disagree with optical estimates of cloud base and optical thickness for well-understood reasons. So optical and microwave cloud probes are now considered as complimentary rather then competitive in our efforts to better understand cloud radiative properties in the context of climate research. We are confident that off-beam lidar will be a valuable and, ultimately, cost-effective source of information about cloud processes. In this, we include direct insight into the present issues in large-scale short-wave absorption based on unambiguous geometrical pathlength statistics, a unique capability of off-beam cloud lidar.

Davis, A. B. (Anthony B.); Cahalan, R. F. (Robert F.); Winker, D. M. (David M.)

2002-01-01

342

Investigation of polar stratospheric clouds in January 2008 by means of ground-based and spaceborne lidar measurements and microphysical box model simulations  

NASA Astrophysics Data System (ADS)

Polar stratospheric clouds (PSCs) play a key role in heterogeneous chemistry and ozone depletion in the lower stratosphere. The type of PSC as well as their temporal and spatial extent are important for the occurrence of heterogeneous reactions and, thus, ozone depletion. In this study a combination of ground-based and spaceborne lidar measurements were used together with microphysical box model simulations along back trajectories to investigate the formation and alteration of Arctic PSCs. The measurements were made by the Rayleigh/Mie/Raman lidar system at Esrange and by the Cloud-Aerosol Lidar with Orthogonal Polarization aboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite. Between 20 and 23 January 2008 PSCs composed of liquid particles were observed by CALIPSO between Greenland and the western side of the Scandinavian Mountains. Between 21 and 23 January 2008 the Esrange lidar observed a PSC composed of distinct layers of liquid and solid particles on the eastern side of the mountain range. Microphysical box model simulations along air parcel back trajectories indicate that liquid particles had formed at least 40 h before the observation at Esrange. Furthermore, the model indicates a high HNO3 uptake into the liquid layer between 10 and 20 h before the observation. The PSC was formed when the air mass was over Greenland. On two occasions during these 20 h, CALIPSO observed PSCs when its measurement tracks crossed the air parcel back trajectory ending at the location of the Esrange lidar. Backscatter ratios calculated from the output of the box model simulation indicate good agreement with the values observed with the Esrange lidar and by CALIPSO. The box model simulations along the back trajectories from Esrange to the CALIPSO ground track and beyond provide us with the unique opportunity to relate ground-based and spaceborne lidar measurements that were not performed at the same spatial location and time. Furthermore, possible differences in the observations from ground and space can be traced to temporal and/or geographically induced changes in particle microphysics within the measured PSCs.

Achtert, P.; Khosrawi, F.; Blum, U.; Fricke, K. H.

2011-04-01

343

Comparison of Cloud Properties from CALIPSO-CloudSat and Geostationary Satellite Data  

NASA Technical Reports Server (NTRS)

Cloud properties are being derived in near-real time from geostationary satellite imager data for a variety of weather and climate applications and research. Assessment of the uncertainties in each of the derived cloud parameters is essential for confident use of the products. Determination of cloud amount, cloud top height, and cloud layering is especially important for using these real -time products for applications such as aircraft icing condition diagnosis and numerical weather prediction model assimilation. Furthermore, the distribution of clouds as a function of altitude has become a central component of efforts to evaluate climate model cloud simulations. Validation of those parameters has been difficult except over limited areas where ground-based active sensors, such as cloud radars or lidars, have been available on a regular basis. Retrievals of cloud properties are sensitive to the surface background, time of day, and the clouds themselves. Thus, it is essential to assess the geostationary satellite retrievals over a variety of locations. The availability of cloud radar data from CloudSat and lidar data from CALIPSO make it possible to perform those assessments over each geostationary domain at 0130 and 1330 LT. In this paper, CloudSat and CALIPSO data are matched with contemporaneous Geostationary Operational Environmental Satellite (GOES), Multi-functional Transport Satellite (MTSAT), and Meteosat-8 data. Unlike comparisons with cloud products derived from A-Train imagers, this study considers comparisons of nadir active sensor data with off-nadir retrievals. These matched data are used to determine the uncertainties in cloud-top heights and cloud amounts derived from the geostationary satellite data using the Clouds and the Earth s Radiant Energy System (CERES) cloud retrieval algorithms. The CERES multi-layer cloud detection method is also evaluated to determine its accuracy and limitations in the off-nadir mode. The results will be useful for constraining the use of the passive retrieval data in models and for improving the accuracy of the retrievals.

Nguyen, L.; Minnis, P.; Chang, F.; Winker, D.; Sun-Mack, S.; Spangenberg, D.; Austin, R.

2007-01-01

344

Relationship between oceanic boundary layer clouds and lower tropospheric stability observed by AIRS, CloudSat and CALIOP  

NASA Astrophysics Data System (ADS)

Over a year of matched temperature and water vapor profiles from the Atmospheric Infrared Sounder (AIRS), and cloud profiles from the CloudSat and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) instruments, are investigated to quantify aspects of maritime boundary layer clouds and their thermodynamic environment. The AIRS retrieval yield over the oceans between 40S-40N within CloudSat identified Sc clouds is between 61-71% globally, and is greater than 80-90% throughout most of the subtropics. The lower tropospheric stability (LTS) and estimated inversion strength (EIS) are derived from AIRS temperature and water vapor profiles. Temperature inversions are detected about 2-6% of the time, while positive values of EIS occur about 68.5% of the time within scenes identified as Sc by CloudSat. The relative magnitudes and seasonality of LTS and EIS in the subtropical stratocumulus regions are very similar to reanalysis and surface cloud observations, but differences are found in the mid-latitude regions where AIRS yield is low. Low cloud fraction obtained from AIRS, the radar, and a combination of the radar+lidar is somewhat more correlated with EIS than with LTS. Furthermore, correlations improve with cloud fraction from the radar+lidar compared to the radar-only version, demonstrating the importance of CALIOP to detect shallow low clouds over the oceans. This multi-sensor investigation establishes a basis for using A-train observations to quantitatively address elements of the low cloud-climate feedback problem.

Yue, Q.; Kahn, B. H.; Fetzer, E.; Teixeira, J.

2010-12-01

345

Retrieval of Cloud Water and Water Vapor Contents from Doppler Radar Data in a Tropical Squall Line  

Microsoft Academic Search

This paper describes the retrieval of cloud water and water vapor contents from Doppler radar data. The convective part of a tropical squall line (22 June 1981) observed during the COPT 81 (Convection Profonde Tropicale 1981) West African experiment, was chosen for developing a two-dimensional and steady state model for the retrieval of these parameters. The model is based upon

Danièle Hauser; Paul Amayenc

1986-01-01

346

Continuous Lidar Monitoring of Polar Stratospheric Clouds at the South Pole.  

National Technical Information Service (NTIS)

Polar stratospheric clouds (PSC) play a primary role in the formation of annual 'ozone holes' over Antarctica during the austral sunrise. Meridional temperature gradients in the lower stratosphere and upper troposphere, caused by strong radiative cooling,...

E. J. Welton J. D. Spinhirne J. R. Campbell

2009-01-01

347

Small Orbital Planetary Lidar the Measurement of Water Vapor, Cloud and Aerosol Profiles.  

National Technical Information Service (NTIS)

The Martian atmosphere is surprisingly dynamic, with a highly variable water vapor distribution and an unusual amount of atmospheric dust and clouds. The dynamics, and forcing functions of the many Martian atmospheric features, particularly the global pro...

G. R. Allan M. A. Krainka A. E. Andrews A. M. Gates

2004-01-01

348

Cloud Impact on Surface Altimetry From a Spaceborne 532-nm Micropulse Photon-Counting Lidar: System Modeling for Cloudy and Clear Atmospheres  

Microsoft Academic Search

This paper establishes a framework that simulates the behavior of a spaceborne 532-nm micropulse photon-counting lidar in cloudy and clear atmospheres in support of the ICESat-2 mission. Adopted by the current mission design, the photon- counting system will be used to obtain surface altimetry for ICESat-2. To investigate how clouds affect surface elevation re- trievals, a 3-D Monte Carlo radiative

Yuekui Yang; Alexander Marshak; Stephen P. Palm; Tamás Varnai; Warren J. Wiscombe

2011-01-01

349

Cloud Physics Lidar Optical Measurements During the SAFARI-2000 Field Campaign  

NASA Technical Reports Server (NTRS)

In this presentation, we will show new optical data processing results from the Cloud Physics War during SAFARI-2000. Retrieved products include aerosol and cloud layer location and identification, layer optical depths, vertical extinction profiles, and extinction-to-backscatter (S) ratios for 532 and 1064 nm. The retrievals will focus on the persistent and smoky planetary boundary layer and occasional elevated aerosol layers found in southern Africa during August and September 2000.

Hlavka, Dennis L.; McGill, Matt; Hart, William D.; Spinhirne, James D.; Starr, David OC. (Technical Monitor)

2002-01-01

350

Cloud and Aerosol Lidar Channel Design and Performance of the Geoscience Laser Altimeter System on the ICESat Mission.  

National Technical Information Service (NTIS)

The design of the 532 and 1064nm wavelength atmosphere lidar channels of the Geoscience Laser Altimeter System on the ICESat spacecraft is described. The lidar channel performance per on orbit measurements data will be presented.

X. Sun J. B. Abshire M. A. Krainak J. D. Spinhirne S. S. Palm

2004-01-01

351

Cloud and Aerosol Lidar Channel Design and Performance of the Geoscience Laser Altimeter System on the ICESat Mission  

NASA Technical Reports Server (NTRS)

The design of the 532 and 1064nm wavelength atmosphere lidar channels of the Geoscience Laser Altimeter System on the ICESat spacecraft is described. The lidar channel performance per on orbit measurements data will be presented.

Sun, Xiaoli; Abshire, James B.; Krainak, Michael A.; Spinhirne, James D.; Palm, Steve S.; Lancaster, Redgie S.; Allan, Graham R.

2004-01-01

352

Combining visible and infrared radiometry and lidar data to test simulations in clear and ice cloud conditions  

NASA Astrophysics Data System (ADS)

Measurements taken during the 2003 Pacific THORPEX Observing System Test (P-TOST) by the MODIS Airborne Simulator (MAS), the Scanning High-resolution Interferometer Sounder (S-HIS) and the Cloud Physics Lidar (CPL) are compared to simulations performed with a line-by-line and multiple scattering modeling methodology (LBLMS). Formerly used for infrared hyper-spectral data analysis, LBLMS has been extended to the visible and near infrared with the inclusion of surface bi-directional reflectance properties. A number of scenes are evaluated: two clear scenes, one with nadir geometry and one cross-track encompassing sun glint, and three cloudy scenes, all with nadir geometry. CPL data is used to estimate the particulate optical depth at 532 nm for the clear and cloudy scenes and cloud upper and lower boundaries. Cloud optical depth is retrieved from S-HIS infrared window radiances, and it agrees with CPL values, to within natural variability. MAS data are simulated convolving high resolution radiances. The paper discusses the results of the comparisons for the clear and cloudy cases. LBLMS clear simulations agree with MAS data to within 20% in the shortwave (SW) and near infrared (NIR) spectrum and within 2 K in the infrared (IR) range. It is shown that cloudy sky simulations using cloud parameters retrieved from IR radiances systematically underestimate the measured radiance in the SW and NIR by nearly 50%, although the IR retrieved optical thickness agree with same measured by CPL. MODIS radiances measured from Terra are also compared to LBLMS simulations in cloudy conditions, using retrieved cloud optical depth and effective radius from MODIS, to understand the origin for the observed discrepancies. It is shown that the simulations agree, to within natural variability, with measurements in selected MODIS SW bands. The impact of the assumed particles size distribution and vertical profile of ice content on results is evaluated. Sensitivity is much smaller than differences between measured and simulated radiances in the SW and NIR. The paper dwells on a possible explanation of these contradictory results, involving the phase function of ice particles in the shortwave.

Bozzo, A.; Maestri, T.; Rizzi, R.

2010-08-01

353

Evaluation of Cloud Microphysics in JMA-NHM Simulations Using Bin or Bulk Microphysical Schemes through Comparison with Cloud Radar Observations  

NASA Technical Reports Server (NTRS)

Numerical weather prediction (NWP) simulations using the Japan Meteorological Agency NonhydrostaticModel (JMA-NHM) are conducted for three precipitation events observed by shipborne or spaceborneW-band cloud radars. Spectral bin and single-moment bulk cloud microphysics schemes are employed separatelyfor an intercomparative study. A radar product simulator that is compatible with both microphysicsschemes is developed to enable a direct comparison between simulation and observation with respect to theequivalent radar reflectivity factor Ze, Doppler velocity (DV), and path-integrated attenuation (PIA). Ingeneral, the bin model simulation shows better agreement with the observed data than the bulk modelsimulation. The correction of the terminal fall velocities of snowflakes using those of hail further improves theresult of the bin model simulation. The results indicate that there are substantial uncertainties in the masssizeand sizeterminal fall velocity relations of snowflakes or in the calculation of terminal fall velocity of snowaloft. For the bulk microphysics, the overestimation of Ze is observed as a result of a significant predominanceof snow over cloud ice due to substantial deposition growth directly to snow. The DV comparison shows thata correction for the fall velocity of hydrometeors considering a change of particle size should be introducedeven in single-moment bulk cloud microphysics.

Iguchi, Takamichi; Nakajima, Teruyuki; Khain, Alexander P.; Saito, Kazuo; Takemura, Toshihiko; Okamoto, Hajime; Nishizawa, Tomoaki; Tao, Wei-Kuo

2012-01-01

354

Augmenting the micropulse lidar concept  

Microsoft Academic Search

In the early nineties, James Spinhirne reported a revolutionary lidar concept: the Micro Pulse Lidar (MPL). His approach combined a large diameter, low pulse energy, high pulse repetition frequency transmitter with a narrow field, narrow optical bandwidth receiver to create an eye-safe visible lidar for cloud and aerosol studies. MPL systems present challenges because a significant amount of their operating

David W. Roberts; Gary G. Gimmestad

2003-01-01

355

RAMSES: German Meteorological Service autonomous Raman lidar for water vapor, temperature, aerosol, and cloud measurements.  

PubMed

The Raman lidar for atmospheric moisture sensing (RAMSES) for unattended, continuous multiparameter atmospheric profiling is presented. A seeded frequency-tripled Nd:YAG laser serves as the light source. A nine-channel polychromator, nonfiber coupled to the main telescope (790 mm diameter), is used for far-range measurements. Near-range observations are performed with a three-channel polychromator, fiber coupled to a secondary telescope (200 mm diameter). Measurement parameters are water-vapor mixing ratio (MR), temperature, and the optical particle parameters, which are extinction coefficient, backscatter coefficient, lidar ratio, and depolarization ratio at 355 nm. Profiles of water-vapor MR are measured from close to the surface up to 14 km at night and 5 km during the day under favorable atmospheric conditions in 20 min. Temperature profiles of the troposphere and lower stratosphere are determined with the rotational-Raman technique. For the detection of the rotational Raman signals, a new beamsplitter/interference-filter experimental setup is implemented that is compact, robust, and easy to align. Furthermore, the polychromator design allows two independent methods for calibrating measurements of depolarization ratio. RAMSES optical design concept and experimental setup are detailed, and a description of the operational near-real-time data evaluation software is given. A multiday observation is discussed to illustrate the measurement capabilities of RAMSES. PMID:23207381

Reichardt, Jens; Wandinger, Ulla; Klein, Volker; Mattis, Ina; Hilber, Bernhard; Begbie, Robert

2012-12-01

356

Effects of spatially variable snow cover on thermal regime and hydrology of an Arctic ice wedge polygon landscape identified using ground penetrating radar and LIDAR datasets  

NASA Astrophysics Data System (ADS)

Ice wedge polygons are common in Arctic terrains underlain by permafrost. Permafrost degradation could transform low- into high centered polygons, causing profound changes in the hydrologic regime of Arctic lands, which in turn, could affect the energy balance and subsurface biodegradation of organic carbon responsible for greenhouse gas production. Understanding the linkages between microtopography, snow cover, thermal properties, and thaw depth is critical for developing a predictive understanding of terrestrial ecosystems and their feedbacks to climate. In this study, we use high frequency (500-1000 MHz) ground penetrating radar (GPR) data acquired in spring 2012 within the Next Generation Ecosystem Experiment (NGEE) study site in Barrow, AK to characterize the spatial variability of snow distribution. We compare it's distribution to microtopography, estimated using LIDAR data, and thaw depth, also estimated using ground penetrating radar collected at different times during the year and simulated over time using mechanistic thermal-hydrologic modeling. The high spatial resolution offered by LIDAR and ground penetrating radar permit detailed investigations of the control of microtopography on snow and thaw layer depth. Results suggest that microtopographical variations are responsible for substantial differences in snow accumulation. In low centered polygons, snow depth can be up to four times greater in the troughs than on the rims. Both modeling and observations suggest that the microtopography-governed snow thickness affects the thermal properties of the subsurface and thus the thaw layer thickness; regions with thicker snowpack generally correspond to regions of greater thaw depth. We conclude that a transition from low- to high centered polygons will not only impact watershed runoff but, since snow accumulation is sensitive to the microtopography, it will also impact snow distribution. In turn, snow distribution affects thaw depth thickness, and the propensity for microbial degradation of organic carbon and production of greenhouse gasses.

Gusmeroli, A.; Liljedahl, A. K.; Peterson, J. E.; Hubbard, S. S.; Hinzman, L. D.

2012-12-01

357

Doppler-radar observation of the evolution of downdrafts in convective clouds  

NASA Technical Reports Server (NTRS)

A detailed analysis of the 20 July 1977 thunderstorm complex which formed and evolve over the South Park region in Central Colorado is presented. The storm was extensively analyzed using multiple Doppler radar and surface mesonet data, developed within an environment having very weak wind shear. The storm owed its intensification to the strength of the downdraft, which was nearly coincident with the region where the cloud had grown. The noteworthy features of this storm were its motion to the right of the cloud-level winds, its multicellular nature and discrete propagation, its north-south orientation, and its relatively large storm size and high reflectivity factor (55 dBZ). This scenario accounts for the observed mesoscale and cloud-scale event. A line of convergence was generated at the interface between the easterly upslope winds and westerly winds. During stage II, the convergence line subsequently propagated down the slopes of the Mosquito Range, and was the main forcing mechanism for the development of updraft on the west flank of the storm. The formation of downdraft on the eastern side of updraft blacked surface inflow, and created a detectable gust front. As the original downdraft intensified, the accumulation of evaporatively-chilled air caused the intensification of the mesohigh, which likely destroyed the earlier convergence line and created a stronger convergence line to the east, which forced up-lifting of the moist, westerly inflow and caused the formation of updraft to the east. An organized downdraft circulation, apparently maintained by precipitation drag and evaporational cooling, was responsible in sustaining a well-defined gust front. The storm attained its highest intensity as a consequence of merging with a neighboring cloud. The interaction of downdrafts or gust fronts from two intense cells appeared to be the primary mechanism of this merging process as suggested by Simpson et al. (1980). The merging process coincided with more rain than occurred in unmerged echoes.

Motallebi, N.

1982-01-01

358

Fast, Space Qualified 3000 V Modulator for a Cloud Profiling Radar  

NASA Technical Reports Server (NTRS)

Cloudsat's Cloud Profiling Radar (CPR) delivers a 2 kW of RF pulse using an extended Interaction Klystron (EIK). 'To drive such an EIK, it was necessary to develop a -16.3 kV High Voltage Power Supply (HVPS) and a Focus Electrode Modulator (FEM), floating at Cathode potential to turn the EIK's Beam on and off -45V to -3kV with respect to the Cathode. This paper describes the design approach for the FEM and its performance at EM and Flight Configuration. In author's opinion it a simple but universal approach which allow designer to achieve greater flexibility and freedom in designing high swinging space qualifiable FEM.

Haque, Inam U.; Harvey, Wayne; Duong, Johnny; Packard, Roy; Ispirian, Julie

2005-01-01

359

Relationships between layer-mean radar reflectivity and columnar effective radius of warm cloud: Numerical study using a cloud microphysical bin model  

NASA Astrophysics Data System (ADS)

relationship between the layer-mean radar reflectivity, Ze, and the columnar effective particle radius, Re, in evolving shallow warm clouds was investigated by numerical experiments using a hybrid cloud microphysical model and a forward simulator of satellite measurements. Changes in the cloud/rain droplet size distributions were traced in a kinematically driven warm cloud for various values of number concentration of cloud condensation nuclei (CCN) and maximum updraft velocity. In contrast to previous interpretations of the observed data, we found four paths for the relationships between Ze and Re during the lifetime of a warm cloud. In the first path, both Ze and Re increase with an approximate sixth-power dependency, indicating a stage of condensational growth of droplets without raindrops in the cloud. In the second path, only Ze increases rapidly, while Re remains almost constant (Resecond), indicating a stage in which few raindrops emerge in the cloud before appreciable precipitation occurs at the surface. This second path was newly identified in this study. In the third path, Re increases rapidly while Ze does not change greatly, indicating a stage of coalescence of droplets. Precipitation reaches the surface at the end of the third path. In the fourth path, both Ze and Re decrease, indicating a greater contribution of raindrop evaporation and weakening or termination of precipitation. The maximum values of Ze and Re and the constant value of Resecond for the second stage depend on the CCN number concentration and the updraft velocity.

Kuba, Naomi; Hashino, Tempei; Satoh, Masaki; Suzuki, Kentaroh

2014-03-01

360