Facilitating the exploitation of ERTS-1 imagery utilizing snow enhancement techniques

NASA Technical Reports Server (NTRS)

Wobber, F. J. (Principal Investigator); Martin, K. R.; Amato, R. V.

1973-01-01

The author has identified the following significant results. Snow cover in combination with low angle solar illumination has been found to provide increased tonal contrast of surface feature and is useful in the detection of bedrock fractures. Identical fracture systems were not as readily detectable in the fall due to the lack of a contrasting surface medium (snow) and a relatively high sun angle. Low angle solar illumination emphasizes topographic expressions not as apparent on imagery acquired with a higher sun angle. A strong correlation exists between the major fracture-lineament directions interpreted from multi-sensor imagery (including snow-free and snow cover ERTS) and the strike of bedrock joints recorded in the field indicating the structural origin of interpreted fracture-lineaments. A fracture-annotated ERTS-1 photo base map (1:250,000 scale) is being prepared for western Massachusetts. The map will document the utilization of ERTS-1 imagery for geological analysis in comparative snow-free and snow-covered terrain.

Mimicking the Moon

NASA Image and Video Library

2014-11-03

When Galileo first observed Venus displaying a crescent phase, he excitedly wrote to Kepler (in anagram) of Venus mimicking the moon-goddess. He would have been delirious with joy to see Saturn and Titan, seen in this image, doing the same thing. More than just pretty pictures, high-phase observations -- taken looking generally toward the Sun, as in this image -- are very powerful scientifically since the way atmospheres and rings transmit sunlight is often diagnostic of compositions and physical states. In this example, Titan's crescent nearly encircles its disk due to the small haze particles high in its atmosphere refracting the incoming light of the distant Sun. This view looks toward the sunlit side of the rings from about 3 degrees above the ringplane. The image was taken in violet light with the Cassini spacecraft wide-angle camera on Aug. 11, 2013. The view was obtained at a distance of approximately 1.1 million miles (1.7 million kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 154 degrees. Image scale is 64 miles (103 kilometers) per pixel. http://photojournal.jpl.nasa.gov/catalog/PIA18291

The effects of solar incidence angle over digital processing of LANDSAT data

NASA Technical Reports Server (NTRS)

Parada, N. D. J. (Principal Investigator); Novo, E. M. L. M.

1983-01-01

A technique to extract the topography modulation component from digital data is described. The enhancement process is based on the fact that the pixel contains two types of information: (1) reflectance variation due to the target; (2) reflectance variation due to the topography. In order to enhance the signal variation due to topography, the technique recommends the extraction from original LANDSAT data of the component resulting from target reflectance. Considering that the role of topographic modulation over the pixel information will vary with solar incidence angle, the results of this technique of digital processing will differ from one season to another, mainly in highly dissected topography. In this context, the effects of solar incidence angle over the topographic modulation technique were evaluated. Two sets of MSS/LANDSAT data, with solar elevation angles varying from 22 to 41 deg were selected to implement the digital processing at the Image-100 System. A secondary watershed (Rio Bocaina) draining into Rio Paraiba do Sul (Sao Paulo State) was selected as a test site. The results showed that the technique used was more appropriate to MSS data acquired under higher Sun elevation angles. Topographic modulation components applied to low Sun elevation angles lessens rather than enhances topography.

Solar System Portrait - 60 Frame Mosaic

NASA Image and Video Library

1996-09-13

The cameras of Voyager 1 on Feb. 14, 1990, pointed back toward the sun and took a series of pictures of the sun and the planets, making the first ever portrait of our solar system as seen from the outside. In the course of taking this mosaic consisting of a total of 60 frames, Voyager 1 made several images of the inner solar system from a distance of approximately 4 billion miles and about 32 degrees above the ecliptic plane. Thirty-nine wide angle frames link together six of the planets of our solar system in this mosaic. Outermost Neptune is 30 times further from the sun than Earth. Our sun is seen as the bright object in the center of the circle of frames. The wide-angle image of the sun was taken with the camera's darkest filter (a methane absorption band) and the shortest possible exposure (5 thousandths of a second) to avoid saturating the camera's vidicon tube with scattered sunlight. The sun is not large as seen from Voyager, only about one-fortieth of the diameter as seen from Earth, but is still almost 8 million times brighter than the brightest star in Earth's sky, Sirius. The result of this great brightness is an image with multiple reflections from the optics in the camera. Wide-angle images surrounding the sun also show many artifacts attributable to scattered light in the optics. These were taken through the clear filter with one second exposures. The insets show the planets magnified many times. Narrow-angle images of Earth, Venus, Jupiter, Saturn, Uranus and Neptune were acquired as the spacecraft built the wide-angle mosaic. Jupiter is larger than a narrow-angle pixel and is clearly resolved, as is Saturn with its rings. Uranus and Neptune appear larger than they really are because of image smear due to spacecraft motion during the long (15 second) exposures. From Voyager's great distance Earth and Venus are mere points of light, less than the size of a picture element even in the narrow-angle camera. Earth was a crescent only 0.12 pixel in size. Coincidentally, Earth lies right in the center of one of the scattered light rays resulting from taking the image so close to the sun. http://photojournal.jpl.nasa.gov/catalog/PIA00451

Solar System Portrait - 60 Frame Mosaic

NASA Technical Reports Server (NTRS)

1990-01-01

The cameras of Voyager 1 on Feb. 14, 1990, pointed back toward the sun and took a series of pictures of the sun and the planets, making the first ever 'portrait' of our solar system as seen from the outside. In the course of taking this mosaic consisting of a total of 60 frames, Voyager 1 made several images of the inner solar system from a distance of approximately 4 billion miles and about 32 degrees above the ecliptic plane. Thirty-nine wide angle frames link together six of the planets of our solar system in this mosaic. Outermost Neptune is 30 times further from the sun than Earth. Our sun is seen as the bright object in the center of the circle of frames. The wide-angle image of the sun was taken with the camera's darkest filter (a methane absorption band) and the shortest possible exposure (5 thousandths of a second) to avoid saturating the camera's vidicon tube with scattered sunlight. The sun is not large as seen from Voyager, only about one-fortieth of the diameter as seen from Earth, but is still almost 8 million times brighter than the brightest star in Earth's sky, Sirius. The result of this great brightness is an image with multiple reflections from the optics in the camera. Wide-angle images surrounding the sun also show many artifacts attributable to scattered light in the optics. These were taken through the clear filter with one second exposures. The insets show the planets magnified many times. Narrow-angle images of Earth, Venus, Jupiter, Saturn, Uranus and Neptune were acquired as the spacecraft built the wide-angle mosaic. Jupiter is larger than a narrow-angle pixel and is clearly resolved, as is Saturn with its rings. Uranus and Neptune appear larger than they really are because of image smear due to spacecraft motion during the long (15 second) exposures. From Voyager's great distance Earth and Venus are mere points of light, less than the size of a picture element even in the narrow-angle camera. Earth was a crescent only 0.12 pixel in size. Coincidentally, Earth lies right in the center of one of the scattered light rays resulting from taking the image so close to the sun.

Reviving a neglected celestial underwater polarization compass for aquatic animals.

PubMed

Waterman, Talbot H

2006-02-01

Substantial in situ measurements on clear days in a variety of marine environments at depths in the water down to 200 m have demonstrated the ubiquitous daytime presence of sun-related e-vector (=plane of polarization) patterns. In most lines of sight the e-vectors tilt from horizontal towards the sun at angles equal to the apparent underwater refracted zenith angle of the sun. A maximum tilt-angle of approximately 48.5 degrees , is reached in horizontal lines of sight at 90 degrees to the sun's bearing (the plane of incidence). This tilt limit is set by Snell's window, when the sun is on the horizon. The biological literature since the 1980s has been pervaded with assumptions that daytime aquatic e-vectors are mainly horizontal. This review attempts to set the record straight concerning the potential use of underwater e-vectors as a visual compass and to reopen the field to productive research on aquatic animals' orientation and navigation.

Solar System Portrait - View of the Sun, Earth and Venus

NASA Image and Video Library

1996-09-13

This color image of the sun, Earth and Venus was taken by the Voyager 1 spacecraft Feb. 14, 1990, when it was approximately 32 degrees above the plane of the ecliptic and at a slant-range distance of approximately 4 billion miles. It is the first -- and may be the only -- time that we will ever see our solar system from such a vantage point. The image is a portion of a wide-angle image containing the sun and the region of space where the Earth and Venus were at the time with two narrow-angle pictures centered on each planet. The wide-angle was taken with the camera's darkest filter (a methane absorption band), and the shortest possible exposure (5 thousandths of a second) to avoid saturating the camera's vidicon tube with scattered sunlight. The sun is not large in the sky as seen from Voyager's perspective at the edge of the solar system but is still eight million times brighter than the brightest star in Earth's sky, Sirius. The image of the sun you see is far larger than the actual dimension of the solar disk. The result of the brightness is a bright burned out image with multiple reflections from the optics in the camera. The "rays" around the sun are a diffraction pattern of the calibration lamp which is mounted in front of the wide angle lens. The two narrow-angle frames containing the images of the Earth and Venus have been digitally mosaiced into the wide-angle image at the appropriate scale. These images were taken through three color filters and recombined to produce a color image. The violet, green and blue filters were used; exposure times were, for the Earth image, 0.72, 0.48 and 0.72 seconds, and for the Venus frame, 0.36, 0.24 and 0.36, respectively. Although the planetary pictures were taken with the narrow-angle camera (1500 mm focal length) and were not pointed directly at the sun, they show the effects of the glare from the nearby sun, in the form of long linear streaks resulting from the scattering of sunlight off parts of the camera and its sun shade. From Voyager's great distance both Earth and Venus are mere points of light, less than the size of a picture element even in the narrow-angle camera. Earth was a crescent only 0.12 pixel in size. Coincidentally, Earth lies right in the center of one of the scattered light rays resulting from taking the image so close to the sun. Detailed analysis also suggests that Voyager detected the moon as well, but it is too faint to be seen without special processing. Venus was only 0.11 pixel in diameter. The faint colored structure in both planetary frames results from sunlight scattered in the optics. http://photojournal.jpl.nasa.gov/catalog/PIA00450

Solar System Portrait - View of the Sun, Earth and Venus

NASA Technical Reports Server (NTRS)

1990-01-01

This color image of the sun, Earth and Venus was taken by the Voyager 1 spacecraft Feb. 14, 1990, when it was approximately 32 degrees above the plane of the ecliptic and at a slant-range distance of approximately 4 billion miles. It is the first -- and may be the only -- time that we will ever see our solar system from such a vantage point. The image is a portion of a wide-angle image containing the sun and the region of space where the Earth and Venus were at the time with two narrow-angle pictures centered on each planet. The wide-angle was taken with the camera's darkest filter (a methane absorption band), and the shortest possible exposure (5 thousandths of a second) to avoid saturating the camera's vidicon tube with scattered sunlight. The sun is not large in the sky as seen from Voyager's perspective at the edge of the solar system but is still eight million times brighter than the brightest star in Earth's sky, Sirius. The image of the sun you see is far larger than the actual dimension of the solar disk. The result of the brightness is a bright burned out image with multiple reflections from the optics in the camera. The 'rays' around the sun are a diffraction pattern of the calibration lamp which is mounted in front of the wide angle lens. The two narrow-angle frames containing the images of the Earth and Venus have been digitally mosaiced into the wide-angle image at the appropriate scale. These images were taken through three color filters and recombined to produce a color image. The violet, green and blue filters were used; exposure times were, for the Earth image, 0.72, 0.48 and 0.72 seconds, and for the Venus frame, 0.36, 0.24 and 0.36, respectively. Although the planetary pictures were taken with the narrow-angle camera (1500 mm focal length) and were not pointed directly at the sun, they show the effects of the glare from the nearby sun, in the form of long linear streaks resulting from the scattering of sunlight off parts of the camera and its sun shade. From Voyager's great distance both Earth and Venus are mere points of light, less than the size of a picture element even in the narrow-angle camera. Earth was a crescent only 0.12 pixel in size. Coincidentally, Earth lies right in the center of one of the scattered light rays resulting from taking the image so close to the sun. Detailed analysis also suggests that Voyager detected the moon as well, but it is too faint to be seen without special processing. Venus was only 0.11 pixel in diameter. The faint colored structure in both planetary frames results from sunlight scattered in the optics.

Large Area Crop Inventory Experiment (LACIE). Effect of sun angle and haze on generation of LANDSAT imagery. [Houston, Texas

NASA Technical Reports Server (NTRS)

Chesnutwood, C. M.; Kraus, G. L. (Principal Investigator)

1975-01-01

The author has identified the following significant results. When heavy haze was present over a nonvegetated scene, the mean radiance values for all MSS channels were lowered, with the greatest decrease occurring in channels 1 and 2. Over a vegetated scene, any apparent decrease in mean radiance values due to haze may be marked by an increase in mean radiance values which occurred as vegetation increased in vigor during its growth cycle. Mean radiance values for nonvegetated targets (except water) were closely correlated to the changes in sun elevation angle throughout the year. A sun angle correction to a fixed reference data appeared to offer the possibility of compensating for haze covered areas by predicting the mean radiance values which would be closely correlated to the normal sun declination curve.

Sun-Relative Pointing for Dual-Axis Solar Trackers Employing Azimuth and Elevation Rotations

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

Riley, Daniel; Hansen, Clifford W.

Dual axis trackers employing azimuth and elevation rotations are common in the field of photovoltaic (PV) energy generation. Accurate sun-tracking algorithms are widely available. However, a steering algorithm has not been available to accurately point the tracker away from the sun such that a vector projection of the sun beam onto the tracker face falls along a desired path relative to the tracker face. We have developed an algorithm which produces the appropriate azimuth and elevation angles for a dual axis tracker when given the sun position, desired angle of incidence, and the desired projection of the sun beam ontomore » the tracker face. Development of this algorithm was inspired by the need to accurately steer a tracker to desired sun-relative positions in order to better characterize the electro-optical properties of PV and CPV modules.« less

Stationary nonimaging lenses for solar concentration.

PubMed

Kotsidas, Panagiotis; Chatzi, Eleni; Modi, Vijay

2010-09-20

A novel approach for the design of refractive lenses is presented, where the lens is mounted on a stationary aperture and the Sun is tracked by a moving solar cell. The purpose of this work is to design a quasi-stationary concentrator by replacing the two-axis tracking of the Sun with internal motion of the miniaturized solar cell inside the module. Families of lenses are designed with a variation of the simultaneous multiple surface technique in which the sawtooth genetic algorithm is implemented to optimize the geometric variables of the optic in order to produce high fluxes for a range of incidence angles. Finally, we show examples of the technique for lenses with 60° and 30° acceptance half-angles, with low to medium attainable concentrations.

Wide angle sun sensor. [consisting of cylinder, insulation and pair of detectors

NASA Technical Reports Server (NTRS)

Schumacher, L. L. (Inventor)

1975-01-01

A single-axis sun sensor consists of a cylinder of an insulating material on which at least one pair of detectors is deposited on a circumference of the cylinder, was disclosed. At any time only one-half of the cylinder is illuminated so that the total resistance of the two detectors is a constant. Due to the round surface on which the detectors are deposited, the sensor exhibits a linear wide angle of + or - 50 deg to within an accuracy of about 2%. By depositing several pairs of detectors on adjacent circumferences, sufficient redundancy is realized to provide high reliability. A two-axis sensor is provided by depositing detectors on the surface of a sphere along at least two orthogonal great circles.

Freeform solar concentrator with a highly asymmetric acceptance cone

NASA Astrophysics Data System (ADS)

Wheelwright, Brian; Angel, J. Roger P.; Coughenour, Blake; Hammer, Kimberly

2014-10-01

A solar concentrator with a highly asymmetric acceptance cone is investigated. Concentrating photovoltaic systems require dual-axis sun tracking to maintain nominal concentration throughout the day. In addition to collecting direct rays from the solar disk, which subtends ~0.53 degrees, concentrating optics must allow for in-field tracking errors due to mechanical misalignment of the module, wind loading, and control loop biases. The angular range over which the concentrator maintains <90% of on-axis throughput is defined as the optical acceptance angle. Concentrators with substantial rotational symmetry likewise exhibit rotationally symmetric acceptance angles. In the field, this is sometimes a poor match with azimuth-elevation trackers, which have inherently asymmetric tracking performance. Pedestal-mounted trackers with low torsional stiffness about the vertical axis have better elevation tracking than azimuthal tracking. Conversely, trackers which rotate on large-footprint circular tracks are often limited by elevation tracking performance. We show that a line-focus concentrator, composed of a parabolic trough primary reflector and freeform refractive secondary, can be tailored to have a highly asymmetric acceptance angle. The design is suitable for a tracker with excellent tracking accuracy in the elevation direction, and poor accuracy in the azimuthal direction. In the 1000X design given, when trough optical errors (2mrad rms slope deviation) are accounted for, the azimuthal acceptance angle is +/- 1.65°, while the elevation acceptance angle is only +/-0.29°. This acceptance angle does not include the angular width of the sun, which consumes nearly all of the elevation tolerance at this concentration level. By decreasing the average concentration, the elevation acceptance angle can be increased. This is well-suited for a pedestal alt-azimuth tracker with a low cost slew bearing (without anti-backlash features).

Dependence of NOAA-AVHRR recorded radiance on scan angle, atmospheric turbidity and unresolved cloud

NASA Technical Reports Server (NTRS)

Piwinski, D. J.; Schoch, L. B.; Duggin, M. J.; Whitehead, V.; Ryland, E.

1984-01-01

Experimental evidence on the scan angle and sun angle dependence of radiance recorded by the Advanced Very High Resolution Radiometer (AVHRR) devices on the NOAA-6 and NOAA-7 satellites is presented. The effects of atmospheric turbidity at various scan angles is shown, and simulations of angular anisotropy and recorded radiance are compared with the recorded digital data from the AVHRR obtained over the Great Plains area of the US. Evidence is presented on the effects of unresolved cloud on the recorded radiance and vegetative indices from uniform, vegetative targets.

Digital sun sensor multi-spot operation.

PubMed

Rufino, Giancarlo; Grassi, Michele

2012-11-28

The operation and test of a multi-spot digital sun sensor for precise sun-line determination is described. The image forming system consists of an opaque mask with multiple pinhole apertures producing multiple, simultaneous, spot-like images of the sun on the focal plane. The sun-line precision can be improved by averaging multiple simultaneous measures. Nevertheless, the sensor operation on a wide field of view requires acquiring and processing images in which the number of sun spots and the related intensity level are largely variable. To this end, a reliable and robust image acquisition procedure based on a variable shutter time has been considered as well as a calibration function exploiting also the knowledge of the sun-spot array size. Main focus of the present paper is the experimental validation of the wide field of view operation of the sensor by using a sensor prototype and a laboratory test facility. Results demonstrate that it is possible to keep high measurement precision also for large off-boresight angles.

Optical performance effects of the misalignment of nonimaging optics solar collectors

NASA Astrophysics Data System (ADS)

Ferry, Jonathan; Ricketts, Melissa; Winston, Roland

2017-09-01

The use of non-imaging optics in the application of high temperature solar thermal collectors can be extremely advantageous in eliminating the need to track the sun. The stationary nature of non-imaging optics collectors, commonly called compound parabolic concentrators (CPC's), present a unique design challenge when orienting them to collect sunlight. Many facilities throughout the world that adopt CPCs are not situated to orient the collectors in the ideal angle facing the sun. This East-West misalignment can adversely affect the optical and power performance of the CPC collector. To characterize how this misalignment effects CPCs, reverse raytracing simulations are conducted for varying offset angles of the collectors from solar South. Optical performance is analyzed for an ideal East-West oriented CPC with a 40-degree acceptance angle. Direction cosine plots are used to develop a ratio of annual solar collection by the CPC over the total annual solar input. From these simulations, average annual collector performance is given for offset angles ranging from 0 to 90 degrees for different Earth Latitudes in 10 degree increments.

ARC-1990-AC79-7127

NASA Image and Video Library

1990-02-14

Range : 4 billion miles from Earth, at 32 degrees to the ecliptic. P-36057C This color image of the Sun, Earth, and Venus is one of the first, and maybe, only images that show are solar system from such a vantage point. The image is a portion of a wide angle image containing the sun and the region of space where the Earth and Venus were at the time, with narrow angle cameras centered on each planet. The wide angle was taken with the cameras darkest filter, a methane absorption band, and the shortest possible exposure, one two-hundredth of a second, to avoid saturating the camera's vidicon tube with scattered sunlight. The sun is not large in the sky, as seen from Voyager's perpective at the edge of the solar system. Yet, it is still 8xs brighter than the brightest star in Earth's sky, Sirius. The image of the sun you see is far larger than the actual dimension of the solar disk. The result of the brightness is a bright burned out image with multiple reflections from the optics of the camera. The rays around th sun are a diffraction pattern of the calibration lamp which is mounted in front of the wide angle lens. the 2 narrow angle frames containing the images of the Earth and Venus have been digitally mosaicked into the wide angle image at the appropriate scale. These images were taken through three color filters and recombined to produce the color image. The violet, green, and blue filters used , as well as exposure times of .72,.48, and .72 for Earth, and .36, .24, and .36 for Venus.The images also show long linear streaks resulting from scatering of sulight off parts of the camera and its shade.

Earth Shadows and the SEV Angle of MAP's Lissajous Orbit At L2

NASA Technical Reports Server (NTRS)

Edery, Ariel

2002-01-01

The Microwave Anisotropy Probe (MAP) launched successfully on June 30, 2001 and is presently in a Lissajous orbit about the Sun-Earth libration point L2. To avoid Earth shadows at L2, the Sun-Earth-Vehicle (SEV) angle of MAP has to be greater than 0.5 deg for an extended mission of four years. An equation is derived for the SEV angle in terms of the phase angle, frequencies and amplitudes of the Lissajous. The SEV angle is shown to oscillate with a period of 90.4 days within an amplitude envelope of period 13.9 years. A range of phase angles that avoids shadows is identified. MAP'S present phase angle is within this range and will avoid shadows for approximately 5.8 years.

Program For Tracking The Sun From The Moon

NASA Technical Reports Server (NTRS)

Woods, Warren K.; Spires, Dustin S.

1995-01-01

SUNTRACKER program computes azimuth and elevation angles of Sun, as viewed from given position on Moon, during time defined by user. Program gets selenographic (moon-centered) position of Sun at given Julian date, then converts selenographic position of Sun into azimuth and elevation at given position on Moon. Written in FORTRAN 77.

Laser Induced Optical Damage in Solids

DTIC Science & Technology

1991-07-01

the full angle subtended by the object. 1 The sun, which subtends 20 = 0.54’, can be concentrated about 46,000 times. Using nonimaging techniques...cone, these nonimaging techniques can concentrate sunlight to intensities as high as -108 W/m 2, (or 104 W/cm 2 as is more often reported when dealing...REFERENCES 1. P. Gleckman. J. O’Gallagher, and R. Winston , "Approaching the Irradiance of the Sun Through Norimaging Optics ," Optics News 15:33, May 1989

Utilising shade to optimize UV exposure for vitamin D

NASA Astrophysics Data System (ADS)

Turnbull, D. J.; Parisi, A. V.

2008-01-01

Numerous studies have stated that humans need to utilise full sun radiation, at certain times of the day, to assist the body in synthesising the required levels of vitamin D3. The time needed to be spent in the full sun depends on a number of factors, for example, age, skin type, latitude, solar zenith angle. Current Australian guidelines suggest exposure to approximately 1/6 to 1/3 of a minimum erythemal dose (MED), depending on age, would be appropriate to provide adequate vitamin D3 levels. The aim of the study was to determine the exposure times to diffuse solar UV to receive exposures of 1/6 and 1/3 MED for a changing solar zenith angle in order to assess the possible role that diffuse UV (scattered radiation) may play in vitamin D3 effective UV exposures (UVD3). Diffuse and global erythemal UV measurements were conducted at five minute intervals over a twelve month period for a solar zenith angle range of 4° to 80° at a latitude of 27.6° S. For diffuse UV exposures of 1/6 and 1/3 MED, solar zenith angles smaller than 60° and 50° respectively can be utilised for exposure times of less than 10 min. Spectral measurements showed that, for a solar zenith angle of 40°, the UVA (315-400 nm) in the diffuse component of the solar UV is reduced by approximately 62% compared to the UVA in the global UV, whereas UVD3 wavelengths are only reduced by approximately 43%. At certain latitudes, diffuse UV under shade may play an important role in providing the human body with adequate levels of UVD3 (290-330 nm) radiation without experiencing the high levels of damaging UVA observed in full sun.

Utilising shade to optimize UV exposure for vitamin D

NASA Astrophysics Data System (ADS)

Turnbull, D. J.; Parisi, A. V.

2008-06-01

Numerous studies have stated that humans need to utilise full sun radiation, at certain times of the day, to assist the body in synthesising the required levels of vitamin D3. The time needed to be spent in the full sun depends on a number of factors, for example, age, skin type, latitude, solar zenith angle. Current Australian guidelines suggest exposure to approximately 1/6 to 1/3 of a minimum erythemal dose (MED), depending on age, would be appropriate to provide adequate vitamin D3 levels. The aim of the study was to determine the exposure times to diffuse solar UV to receive exposures of 1/6 and 1/3 MED for a changing solar zenith angle in order to assess the possible role that diffuse UV (scattered radiation) may play in vitamin D3 effective UV exposures (UVD3). Diffuse and global erythemal UV measurements were conducted at five minute intervals over a twelve month period for a solar zenith angle range of 4° to 80° at a latitude of 27.6° S. For a diffuse UV exposure of 1/3 MED, solar zenith angles smaller than approximately 50° can be utilised for exposure times of less than 10 min. Spectral measurements showed that, for a solar zenith angle of 40°, the UVA (315-400 nm) in the diffuse component of the solar UV is reduced by approximately 62% compared to the UVA in the global UV, whereas UVD3 wavelengths are only reduced by approximately 43%. At certain latitudes, diffuse UV under shade may play an important role in providing the human body with adequate levels of UVD3 (290-315 nm) radiation without experiencing the high levels of UVA observed in full sun.

Analysis of the flight dynamics of the Solar Maximum Mission (SMM) off-sun scientific pointing

NASA Technical Reports Server (NTRS)

Pitone, D. S.; Klein, J. R.

1989-01-01

Algorithms are presented which were created and implemented by the Goddard Space Flight Center's (GSFC's) Solar Maximum Mission (SMM) attitude operations team to support large-angle spacecraft pointing at scientific objectives. The mission objective of the post-repair SMM satellite was to study solar phenomena. However, because the scientific instruments, such as the Coronagraph/Polarimeter (CP) and the Hard X ray Burst Spectrometer (HXRBS), were able to view objects other than the Sun, attitude operations support for attitude pointing at large angles from the nominal solar-pointing attitudes was required. Subsequently, attitude support for SMM was provided for scientific objectives such as Comet Halley, Supernova 1987A, Cygnus X-1, and the Crab Nebula. In addition, the analysis was extended to include the reverse problem, computing the right ascension and declination of a body given the off-Sun angles. This analysis led to the computation of the orbits of seven new solar comets seen in the field-of-view (FOV) of the CP. The activities necessary to meet these large-angle attitude-pointing sequences, such as slew sequence planning, viewing-period prediction, and tracking-bias computation are described. Analysis is presented for the computation of maneuvers and pointing parameters relative to the SMM-unique, Sun-centered reference frame. Finally, science data and independent attitude solutions are used to evaluate the large-angle pointing performance.

Analysis of the flight dynamics of the Solar Maximum Mission (SMM) off-sun scientific pointing

NASA Technical Reports Server (NTRS)

Pitone, D. S.; Klein, J. R.; Twambly, B. J.

1990-01-01

Algorithms are presented which were created and implemented by the Goddard Space Flight Center's (GSFC's) Solar Maximum Mission (SMM) attitude operations team to support large-angle spacecraft pointing at scientific objectives. The mission objective of the post-repair SMM satellite was to study solar phenomena. However, because the scientific instruments, such as the Coronagraph/Polarimeter (CP) and the Hard X-ray Burst Spectrometer (HXRBS), were able to view objects other than the Sun, attitude operations support for attitude pointing at large angles from the nominal solar-pointing attitudes was required. Subsequently, attitude support for SMM was provided for scientific objectives such as Comet Halley, Supernova 1987A, Cygnus X-1, and the Crab Nebula. In addition, the analysis was extended to include the reverse problem, computing the right ascension and declination of a body given the off-Sun angles. This analysis led to the computation of the orbits of seven new solar comets seen in the field-of-view (FOV) of the CP. The activities necessary to meet these large-angle attitude-pointing sequences, such as slew sequence planning, viewing-period prediction, and tracking-bias computation are described. Analysis is presented for the computation of maneuvers and pointing parameters relative to the SMM-unique, Sun-centered reference frame. Finally, science data and independent attitude solutions are used to evaluate the larg-angle pointing performance.

Modelling the Surface Distribution of Magnetic Activity on Sun-Like Stars

NASA Astrophysics Data System (ADS)

Isik, Emre

2018-04-01

With the advent of high-precision space-borne stellar photometry and prospects for direct imaging, it is timely and essential to improve our understanding of stellar magnetic activity in rotational time scales. We present models for 'younger suns' with rotation and flux emergence rates between 1 and 16 times the solar rate. The models provide latitudinal distributions and tilt angles of bipolar magnetic regions, using flux tube rise simulations. Using these emergence patterns, we model the subsequent surface flux transport, to predict surface distributions of star-spots. Based on these models, we present preliminary results from our further modelling of the observed azimuthal magnetic fields, which strengthen for more rapidly rotating Sun-like stars.

A Novel Multi-Aperture Based Sun Sensor Based on a Fast Multi-Point MEANSHIFT (FMMS) Algorithm

PubMed Central

You, Zheng; Sun, Jian; Xing, Fei; Zhang, Gao-Fei

2011-01-01

With the current increased widespread interest in the development and applications of micro/nanosatellites, it was found that we needed to design a small high accuracy satellite attitude determination system, because the star trackers widely used in large satellites are large and heavy, and therefore not suitable for installation on micro/nanosatellites. A Sun sensor + magnetometer is proven to be a better alternative, but the conventional sun sensor has low accuracy, and cannot meet the requirements of the attitude determination systems of micro/nanosatellites, so the development of a small high accuracy sun sensor with high reliability is very significant. This paper presents a multi-aperture based sun sensor, which is composed of a micro-electro-mechanical system (MEMS) mask with 36 apertures and an active pixels sensor (APS) CMOS placed below the mask at a certain distance. A novel fast multi-point MEANSHIFT (FMMS) algorithm is proposed to improve the accuracy and reliability, the two key performance features, of an APS sun sensor. When the sunlight illuminates the sensor, a sun spot array image is formed on the APS detector. Then the sun angles can be derived by analyzing the aperture image location on the detector via the FMMS algorithm. With this system, the centroid accuracy of the sun image can reach 0.01 pixels, without increasing the weight and power consumption, even when some missing apertures and bad pixels appear on the detector due to aging of the devices and operation in a harsh space environment, while the pointing accuracy of the single-aperture sun sensor using the conventional correlation algorithm is only 0.05 pixels. PMID:22163770

Sun glitter imaging analysis of submarine sand waves in HJ-1A/B satellite CCD images

NASA Astrophysics Data System (ADS)

Zhang, Huaguo; He, Xiekai; Yang, Kang; Fu, Bin; Guan, Weibing

2014-11-01

Submarine sand waves are a widespread bed-form in tidal environment. Submarine sand waves induce current convergence and divergence that affect sea surface roughness thus become visible in sun glitter images. These sun glitter images have been employed for mapping sand wave topography. However, there are lots of effect factors in sun glitter imaging of the submarine sand waves, such as the imaging geometry and dynamic environment condition. In this paper, several sun glitter images from HJ-1A/B in the Taiwan Banks are selected. These satellite sun glitter images are used to discuss sun glitter imaging characteristics in different sensor parameters and dynamic environment condition. To interpret the imaging characteristics, calculating the sun glitter radiance and analyzing its spatial characteristics of the sand wave in different images is the best way. In this study, a simulated model based on sun glitter radiation transmission is adopted to certify the imaging analysis in further. Some results are drawn based on the study. Firstly, the sun glitter radiation is mainly determined by sensor view angle. Second, the current is another key factor for the sun glitter. The opposite current direction will cause exchanging of bright stripes and dark stripes. Third, brightness reversal would happen at the critical angle. Therefore, when using sun glitter image to obtain depth inversion, one is advised to take advantage of image properties of sand waves and to pay attention to key dynamic environment condition and brightness reversal.

The angular distributions of ultraviolet spectral irradiance at different solar elevation angles under clear sky conditions

NASA Astrophysics Data System (ADS)

Liu, Yan; Hu, LiWen; Wang, Fang; Gao, YanYan; Zheng, Yang; Wang, Yu; Liu, Yang

2016-01-01

To investigate the angular distributions of UVA, UVB, and effective UV for erythema and vitamin D (vitD) synthesis, the UV spectral irradiances were measured at ten inclined angles (from 0° to 90°) and seven azimuths (from 0° to 180°) at solar elevation angle (SEA) that ranged from 18.8° to 80° in Shanghai (31.22° N, 121.55° E) under clear sky and the albedo of ground was 0.1. The results demonstrated that in the mean azimuths and with the back to the sun, the UVA, UVB, and erythemally and vitD-weighted irradiances increased with the inclined angles and an increase in SEA. When facing toward the sun at 0°-60° inclined angles, the UVA first increased and then decreased with an increase in SEA; at other inclined angles, the UVA increased with SEA. At 0°-40° inclined angles, the UVB and erythemally and vitD-weighted irradiances first increased and then decreased with an increase in SEA, and their maximums were achieved at SEA 68.7°; at other inclined angles, the above three irradiances increased with an increase in SEA. The maximum UVA, UVB, and erythemally and vitD-weighted irradiances were achieved at an 80° inclined angle at SEA 80° (the highest in our measurements); the cumulative exposure of the half day achieved the maximum at a 60° inclined angle, but not on the horizontal. This study provides support for the assessment of human skin sun exposure.

Suits reflectance models for wheat and cotton - Theoretical and experimental tests

NASA Technical Reports Server (NTRS)

Chance, J. E.; Lemaster, E. W.

1977-01-01

Plant canopy reflectance models developed by Suits are tested for cotton and Penjamo winter wheat. Properties of the models are discussed, and the concept of model depth is developed. The models' predicted exchange symmetry for specular irradiance with respect to sun polar angle and observer polar angle agreed with field data for cotton and wheat. Model calculations and experimental data for wheat reflectance vs sun angle disagreed. Specular reflectance from 0.50 to 1.10 micron shows fair agreement between the model and wheat measurements. An Appendix includes the physical and optical parameters for wheat necessary to apply Suits' models.

Design and research of sun sensor based on technology of optical fiber

NASA Astrophysics Data System (ADS)

Li, Ye; Zhou, Wang; Li, Dan

2010-08-01

A kind of sun sensor is designed based on the optical fiber. This project consists of three parts: optical head, photoelectric sensor and signal processing unit. The innovation of this design lies in the improvement of traditional sun sensor, where multi-fibers, used as a leader, are symmetrically distributed on the surface of a spacecraft. To determine the attitude of a spacecraft, the sun sensor should measure the direction of the sun. Because the fiber length can be adjusted according to the fact, photoelectric sensor can be placed deeply inside a spacecraft to protect the photoelectric sensor against the damage by the high-energy particles from outer space. The processing unit calculates the difference value of sun energy imported by each pair of opposite optical fiber so as to obtain the angle and the orientation between the spacecraft and the sun. This sun sensor can suit multi-field of view, both small and large. It improves the accuracy of small field of view and increases the precision of locating a spacecraft. This paper briefly introduces the design of processing unit. This sun sensor is applicable to detect the attitude of a spacecraft. In addition, it can also be used in solar tracking system of PV technology.

Sun compass integration of skylight cues in migratory monarch butterflies.

PubMed

Heinze, Stanley; Reppert, Steven M

2011-01-27

Migrating monarch butterflies (Danaus plexippus) use a time-compensated sun compass to navigate from eastern North America to their overwintering grounds in central Mexico. Here we describe the neuronal layout of those aspects of the butterfly's central complex likely to establish part of the internal sun compass and find them highly homologous to those of the desert locust. Intracellular recordings from neurons in the monarch sun compass network reveal responses tuned to specific E-vector angles of polarized light, as well as azimuth-dependent responses to unpolarized light, independent of spectral composition. The neural responses to these two stimuli in individual neurons are mediated through different regions of the compound eye. Moreover, these dual responses are integrated to create a consistent representation of skylight cues in the sun compass throughout the day. The results advance our understanding of how ambiguous sensory signals are processed by the brain to elicit a robust behavioral response. © 2011 Elsevier Inc. All rights reserved.

Craters 'Twixt Day and Night

NASA Image and Video Library

2004-12-20

Three sizeable impact craters, including one with a marked central peak, lie along the line that divides day and night on the Saturnian moon, Dione (dee-OH-nee), which is 1,118 kilometers, or 695 miles across. The low angle of the Sun along the terminator, as this dividing line is called, brings details like these craters into sharp relief. This view shows principally the leading hemisphere of Dione. Some of this moon's bright, wispy streaks can be seen curling around its eastern limb. Cassini imaged the wispy terrain at high resolution during its first Dione flyby on Dec. 14, 2004. This image was taken in visible light with the Cassini spacecraft narrow angle camera on Nov. 1, 2004, at a distance of 2.4 million kilometers (1.5 million miles) from Dione and at a Sun-Dione-spacecraft, or phase, angle of 106 degrees. North is up. The image scale is 14 kilometers (8.7 miles) per pixel. The image has been magnified by a factor of two and contrast-enhanced to aid visibility of surface features. http://photojournal.jpl.nasa.gov/catalog/PIA06542

Four-cell solar tracker

NASA Technical Reports Server (NTRS)

Berdahl, C. M.

1981-01-01

Forty cm Sun tracker, consisting of optical telescope and four solar cells, stays pointed at Sun throughout day for maximum energy collection. Each solar cell generates voltage proportional to part of solar image it receives; voltages drive servomotors that keep image centered. Mirrored portion of cylinder extends acquisition angle of device by reflecting Sun image back onto solar cells.

Exceptionally omnidirectional broadband light harvesting scheme for multi-junction concentrator solar cells achieved via ZnO nanoneedles

NASA Astrophysics Data System (ADS)

Yeh, Li-Ko; Tian, Wei-Cheng; Lai, Kun-Yu; He-Hau, Jr.

2016-12-01

GaInP/GaAs/Ge triple-junction concentrator solar cells with significant efficiency enhancement were demonstrated with antireflective ZnO nanoneedles. The novel nanostructure was attained with a Zn(NO3)2-based solution containing vitamin C. Under one sun AM 1.5G solar spectrum, conversion efficiency of the triple-junction device was improved by 23.7% via broadband improvement in short-circuit currents of 3 sub-cells after the coverage by the nanoneedles with a graded refractive index profile. The efficiency enhancement further went up to 45.8% at 100 suns. The performance boost through the nanoneedles also became increasingly pronounced in the conditions of high incident angles and the cloudy weather, e.g. 220.0% of efficiency enhancement was observed at the incident angle of 60°. These results were attributed to the exceptional broadband omnidirectionality of the antireflective nanoneedles.

Wherefore Stoppt Thou Me?

NASA Image and Video Library

2015-03-11

Like the Wedding Guest in the thrall of the Ancient Mariner, we are transfixed by the stunning landscape of today's image and the dramatic story it tells. The large degraded impact crater near the center is Coleridge. It has been pummeled by later impacts, crumpled by the formation of lobate scarps, deeply incised by secondary crater chains, and much of the interior and low-lying portions of the exterior have been infilled by plains volcanism. Samuel Taylor Coleridge (1772-1834) was an English poet, known for The Rime of the Ancient Mariner and Kubla Khan. This image was acquired as part of MDIS's high-incidence-angle base map. The high-incidence-angle base map complements the surface morphology base map of MESSENGER's primary mission that was acquired under generally more moderate incidence angles. High incidence angles, achieved when the Sun is near the horizon, result in long shadows that accentuate the small-scale topography of geologic features. The high-incidence-angle base map was acquired with an average resolution of 200 meters/pixel. http://photojournal.jpl.nasa.gov/catalog/PIA19238

The Use of Sun Elevation Angle for Stereogrammetric Boreal Forest Height in Open Canopies

NASA Technical Reports Server (NTRS)

Montesano, Paul M.; Neigh, Christopher; Sun, Guoqing; Duncanson, Laura Innice; Van Den Hoek, Jamon; Ranson, Kenneth Jon

2017-01-01

Stereogrammetry applied to globally available high resolution spaceborne imagery (HRSI; less than 5 m spatial resolution) yields fine-scaled digital surface models (DSMs) of elevation. These DSMs may represent elevations that range from the ground to the vegetation canopy surface, are produced from stereoscopic image pairs (stereo pairs) that have a variety of acquisition characteristics, and have been coupled with lidar data of forest structure and ground surface elevation to examine forest height. This work explores surface elevations from HRSI DSMs derived from two types of acquisitions in open canopy forests. We (1) apply an automated mass-production stereogrammetry workflow to along-track HRSI stereo pairs, (2) identify multiple spatially coincident DSMs whose stereo pairs were acquired under different solar geometry, (3) vertically co-register these DSMs using coincident spaceborne lidar footprints (from ICESat-GLAS) as reference, and(4) examine differences in surface elevations between the reference lidar and the co-registered HRSI DSMs associated with two general types of acquisitions (DSM types) from different sun elevation angles. We find that these DSM types, distinguished by sun elevation angle at the time of stereo pair acquisition, are associated with different surface elevations estimated from automated stereogrammetry in open canopy forests. For DSM values with corresponding reference ground surface elevation from spaceborne lidar footprints in open canopy northern Siberian Larix forests with slopes less than10, our results show that HRSI DSM acquired with sun elevation angles greater than 35deg and less than 25deg (during snow-free conditions) produced characteristic and consistently distinct distributions of elevation differences from reference lidar. The former include DSMs of near-ground surfaces with root mean square errors less than 0.68 m relative to lidar. The latter, particularly those with angles less than 10deg, show distributions with larger differences from lidar that are associated with open canopy forests whose vegetation surface elevations are captured. Terrain aspect did not have a strong effect on the distribution of vegetation surfaces. Using the two DSM types together, the distribution of DSM-differenced heights in forests (6.0 m, sigma = 1.4 m) was consistent with the distribution of plot-level mean tree heights (6.5m, sigma = 1.2 m). We conclude that the variation in sun elevation angle at time of stereo pair acquisition can create illumination conditions conducive for capturing elevations of surfaces either near the ground or associated with vegetation canopy. Knowledge of HRSI acquisition solar geometry and snow cover can be used to understand and combine stereogrammetric surface elevation estimates to co-register rand difference overlapping DSMs, providing a means to map forest height at fine scales, resolving the vertical structure of groups of trees from spaceborne platforms in open canopy forests.

Skin texture parameters of the dorsal hand in evaluating skin aging in China.

PubMed

Gao, Qian; Hu, Li-Wen; Wang, Yang; Xu, Wen-Ying; Ouyang, Nan-Ning; Dong, Guo-Qing; Shi, Song-Tian; Liu, Yang

2011-11-01

There are various non-invasive methods in skin morphology for assessing skin aging. The use of digital photography will make it easier and more convenient. In this study, we explored some skin texture parameters for evaluating skin aging using digital image processing. Two hundred and twenty-eight subjects who lived in Sanya, China, were involved. Individual sun exposure history and other factors influencing skin aging were collected by a questionnaire. Meanwhile, we took photos of their dorsal hands. Skin images were graded according to the Beagley-Gibson system. These skin images were also processed using image analysis software. Five skin texture parameters, Angle Num., Angle Max., Angle Diff., Distance and Grids, were produced in reference to the Beagley-Gibson system. All texture parameters were significantly associated with the Beagley-Gibson score. Among the parameters, the distance between primary lines (Distance) and the value of angle formed by intersection textures (Angle Max., Angle Diff.) were positively associated with the Beagley-Gibson score. However, there was a negative correlation between the number of grids (Grids), the number of angle (Angle Num.) and the Beagley-Gibson score. These texture parameters were also correlated with factors influencing skin aging such as sun exposure, age, smoking, drinking and body mass index. In multivariate analysis, Grids and Distance were mainly affected by age. But Angle Max. and Angle Diff. were mainly affected by sun exposure. It seemed that the skin surface morphologic parameters presented in our study reflect skin aging changes to some extent and could be used to describe skin aging using digital image processing. © 2011 John Wiley & Sons A/S.

Example of Weathering And Sun Angle

NASA Image and Video Library

1996-12-12

The letter 'B' or perhaps the figure '8' appears to have been etched into the Mars rock at the left edge of this picture taken yesterday by NASA's Viking 1 Lander. It is believed to be an illusion caused by weathering processes and the angle of the sun as it illuminated the scene for the spacecraft camera. The object at lower left is the housing containing the surface sampler scoop. http://photojournal.jpl.nasa.gov/catalog/PIA00386

Solar Geometry

Atmospheric Science Data Center

2014-09-25

Solar Noon (GMT time) The time when the sun is due south in the northern hemisphere or due north in the southern ... The average cosine of the angle between the sun and directly overhead during daylight hours.   Cosine solar ...

Seawifs Technical Report Series. Volume 2: Analysis of Orbit Selection for Seawifs: Ascending Versus Descending Node

NASA Technical Reports Server (NTRS)

Hooker, Stanford B. (Editor); Firestone, Elaine R. (Editor); Gregg, Watson W.

1992-01-01

Due to range safety considerations, the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) ocean color instrument may be required to be launched into a near-noon descending node, as opposed to the ascending node used by the predecessor sensor, the Coastal Zone Color Scanner (CZCS). The relative importance of ascending versus descending near-noon orbits was assessed here to determine if descending node will meet the scientific requirements of SeaWiFS. Analyses focused on ground coverage, local times of coverage, solar and viewing geometries (zenith and azimuth angles), and sun glint. Differences were found in the areas covered by individual orbits, but were not important when taken over a 16 day repeat time. Local time of coverage was also different: for ascending node orbits the Northern Hemisphere was observed in the morning and the Southern Hemisphere in the afternoon, while for descending node orbits the Northern Hemisphere was observed in the afternoon and the Southern in the morning. There were substantial differences in solar azimuth and spacecraft azimuth angles both at equinox and at the Northern Hemisphere summer solstice. Negligible differences in solar and spacecraft zenith angles, relative azimuth angles, and sun glint were obtained at the equinox. However, large differences were found in solar zenith angles, relative azimuths, and sun glint for the solstice. These differences appeared to compensate across the scan, however, an increase in sun glint in descending node over that in ascending node on the western part of the scan was compensated by a decrease on the eastern part of the scan. Thus, no advantage or disadvantage could be conferred upon either ascending node or descending node for noon orbits. Analyses were also performed for ascending and descending node orbits that deviated from a noon equator crossing time. For ascending node, afternoon orbits produced the lowest mean solar zenith angles in the Northern Hemisphere, and morning orbits produced the lowest angles for the Southern Hemisphere. For descending node, morning orbits produced the lowest mean solar zenith angles for the Northern Hemisphere; afternoon orbits produced the lowest angles for the Southern Hemisphere.

Using sky radiances measured by ground based AERONET Sun-Radiometers for cirrus cloud detection

NASA Astrophysics Data System (ADS)

Sinyuk, A.; Holben, B. N.; Eck, T. F.; Slutsker, I.; Lewis, J. R.

2013-12-01

Screening of cirrus clouds using observations of optical depth (OD) only has proven to be a difficult task due mostly to some clouds having temporally and spatially stable OD. On the other hand, the sky radiances measurements which in AERONET protocol are taken throughout the day may contain additional cloud information. In this work the potential of using sky radiances for cirrus cloud detection is investigated. The detection is based on differences in the angular shape of sky radiances due to cirrus clouds and aerosol (see Figure). The range of scattering angles from 3 to 6 degrees was selected due to two primary reasons: high sensitivity to cirrus clouds presence, and close proximity to the Sun. The angular shape of sky radiances was parametrized by its curvature, which is a parameter defined as a combination of the first and second derivatives as a function of scattering angle. We demonstrate that a slope of the logarithm of curvature versus logarithm of scattering angle in this selected range of scattering angles is sensitive to cirrus cloud presence. We also demonstrate that restricting the values of the slope below some threshold value can be used for cirrus cloud screening. The threshold value of the slope was estimated using collocated measurements of AERONET data and MPLNET lidars.

Orbital dynamics of high area-to-mass ratio spacecraft with J2 and solar radiation pressure for novel Earth observation and communication services

NASA Astrophysics Data System (ADS)

Colombo, Camilla; Lücking, Charlotte; McInnes, Colin R.

2012-12-01

This paper investigates the effect of planetary oblateness and solar radiation pressure on the orbits of high area-to-mass spacecraft. A planar Hamiltonian model shows the existence of equilibrium orbits with the orbit apogee pointing towards or away from the Sun. These solutions are numerically continued to non-zero inclinations and considering the obliquity of the ecliptic plane relative to the equator. Quasi-frozen orbits are identified in eccentricity, inclination and the angle between the Sun-line and the orbit perigee. The long-term evolution of these orbits is then verified through numerical integration. A set of 'heliotropic' orbits with apogee pointing in the direction of the Sun is proposed for enhancing imaging and telecommunication on the day side of the Earth. The effects of J2 and solar radiation pressure are exploited to obtain a passive rotation of the apsides line following the Sun; moreover the effect of solar radiation pressure enables such orbits at higher eccentricities with respect to the J2 only case.

Estimating Slopes In Images Of Terrain By Use Of BRDF

NASA Technical Reports Server (NTRS)

Scholl, Marija S.

1995-01-01

Proposed method of estimating slopes of terrain features based on use of bidirectional reflectivity distribution function (BRDF) in analyzing aerial photographs, satellite video images, or other images produced by remote sensors. Estimated slopes integrated along horizontal coordinates to obtain estimated heights; generating three-dimensional terrain maps. Method does not require coregistration of terrain features in pairs of images acquired from slightly different perspectives nor requires Sun or other source of illumination to be low in sky over terrain of interest. On contrary, best when Sun is high. Works at almost all combinations of illumination and viewing angles.

Effect of scene illumination conditions on digital enhancement techniques of multispectral scanner LANDSAT images

NASA Technical Reports Server (NTRS)

Parada, N. D. J.; Novo, E. M. L. M.

1983-01-01

Two sets of MSS/LANDSAT data with solar elevation ranging from 22 deg to 41 deg were used at the Image-100 System to implement the Eliason et alii technique for extracting the topographic modulation component. An unsupervised cluster analysis was used to obtain an average brightness image for each channel. Analysis of the enhanced imaged shows that the technique for extracting topographic modulation component is more appropriated to MSS data obtained under high sun elevation ngles. Low sun elevation increases the variance of each cluster so that the average brightness doesn't represent its albedo proprties. The topographic modulation component applied to low sun elevation angle damages rather than enhance topographic information. Better results were produced for channels 4 and 5 than for channels 6 and 7.

Further tests of plant canopy reflectance models and investigation of non-Lambertian properties of plant canopies

NASA Technical Reports Server (NTRS)

Lemaster, E. W.

1975-01-01

The experimental bidirectional reflectance of cotton is presented and compared to the Suits vegetation model. Some wheat reflectance data are presented for a Mexican dwarf wheat. The general results are that the exchange of source position and detector position gives the same reflectance measurement if the irradiance is purely specular. This agrees with Suites. The reflectance versus sun angle and reflectance versus detector angle do not agree with the Suits predictions. There is qualitative agreement between the Suits model and reflectance versus wavelength, but quantitative agreement has not been observed. Reflectance of a vegetation canopy with detector azimuth shows a change of 10 to 40% for even sun angles near zenith, so it seems advisable to include azimuthal angles into models of vegetation.

HCMM: Soil moisture in relation to geologic structure and lithology, northern California

NASA Technical Reports Server (NTRS)

Rich, E. I. (Principal Investigator)

1979-01-01

The author has identified the following significant results. First-look qualitative geologic evaluation of day- and night-IR images discloses several en echelon linear features extending throughout the central part of the northern coast range in California, across the Mendocino triple junction and into southern Oregon. Preliminary examination of these features with respect to topographic expression, vegetation, sun angle and azimuth, and atmospheric conditions suggests that they may be related to the intracontinental plate boundary (Lake Mountain Fault zone of Herd) of the Humbolt Plate. The linear features, which cut across several climatic zones and differently vegetated regions are not confined to topographic valleys, but cross the ridges and valleys at varying angles. Lithology within the Great Valley Sequence can be detected on a few of the images; however, preliminary evaluation suggests that the thermal banding observed may be a function of sun azimuth or late-day sun angle. Soil moisture, related to lithologic composition cannot be ruled out at this time.

What convention is used for the illumination and view angles?

Atmospheric Science Data Center

2014-12-08

... Azimuth angles are measured clockwise from the direction of travel to local north. For both the Sun and cameras, azimuth describes the ... to the equator, because of its morning equator crossing time. Additionally, the difference in view and solar azimuth angle will be near ...

A simple method for verifying the deployment of the TOMS-EP solar arrays

NASA Technical Reports Server (NTRS)

Koppersmith, James R.; Ketchum, Eleanor

1995-01-01

The Total Ozone Mapping Spectrometer-Earth Probe (TOMS-EP) mission relies upon a successful deployment of the spacecraft's solar arrays. Several methods of verification are being employed to ascertain the solar array deployment status, with each requiring differing amounts of data. This paper describes a robust attitude-independent verification method that utilizes telemetry from the coarse Sun sensors (CSS's) and the three-axis magnetometers (TAM's) to determine the solar array deployment status - and it can do so with only a few, not necessarily contiguous, points of data. The method developed assumes that the solar arrays are deployed. Telemetry data from the CSS and TAM are converted to the Sun and magnetic field vectors in spacecraft body coordinates, and the angle between them is calculated. Deployment is indicated if this angle is within a certain error tolerance of the angle between the reference Sun and magnetic field vectors. Although several other methods can indicate a non-deployed state, with this method there is a 70% confidence level in confirming deployment as well as a nearly 100% certainty in confirming a non-deployed state. In addition, the spacecraft attitude (which is not known during the first orbit after launch) is not needed for this algorithm because the angle between the Sun and magnetic field vectors is independent of the spacecraft attitude. This technique can be applied to any spacecraft with a TAM and with CSS's mounted on the solar array(s).

The effect of photoelectrons on boom-satellite potential differences during electron beam ejection

NASA Technical Reports Server (NTRS)

Lai, Shu T.; Cohen, Herbert A.; Aggson, Thomas L.; Mcneil, William J.

1987-01-01

Data taken on the SCATHA satellite at geosynchronous altitudes during periods of electron beam ejection in sunlight showed that the potential difference between an electrically isolated boom and the satellite main body was a function of beam current, energy, and boom-sun angle. The potential difference decreased as the boom area illuminated by the sun increased; the maximum and minimum potential differences were measured when minimum and maximum boom areas, respectively, were exposed to the sun. It is shown that photoelectrons, created on the boom, could be engulfed in the electrostatic field of the highly charged satellite main body. Theoretical calculations made using a simple current balance model showed that these electrons could provide a substantial discharging current to the main body and cause the observed variations in the potential difference between the main body and the booms.

Leaf angle, tree species, and the functioning of broadleaf deciduous forest ecosystems

NASA Astrophysics Data System (ADS)

McNeil, B. E.; Brzostek, E. R.; Fahey, R. T.; King, C. J.; Flamenco, E. A.; Rescorl, S.; Erazo, D.; Heimerl, T.

2016-12-01

The effects of temperate forests on the global cycles of carbon, water, and energy depends strongly on how individual tree species adjust to the novel environmental conditions of the Anthropocene. Here, we seek to identify and understand ecological variability in one important component of tree canopies, the inclination angles of leaves. Leaf angle has important effects on forest albedo, photosynthesis, and evapotranspiration, but there is relatively little data to constrain the many models that include (or perhaps should include) this essential aspect of canopy architecture. We employ a relatively new technique for using an electronic protractor to measure leaf angles from leveled digital photographs. From a suite of observation platforms (e.g. UAVs, eddy flux towers, old fire towers) in Connecticut, Indiana, Maryland, Michigan, Pennsylvania, and West Virginia, USA, we have measured leaf angles periodically throughout the 2014, 2015, and 2016 growing seasons. Based on over 25,000 measurements taken from 15 tree species, we find highly significant differences in mean leaf angle by canopy position, tree species, location, and observation date. In addition to replicating findings where upper-canopy sun leaves are more vertical than lower-canopy shade leaves, our analysis on sun leaves also finds other ecologically meaningful differences. For instance, we find that the mesic, shade tolerant sugar maple had significantly more horizontal leaf angles than drought-resistant species such as white oak. Species also appear to have unique patterns of leaf angle phenology, with most species tending toward more vertical leaf angles during droughty conditions later in the year. We discuss these empirical results in light of an emerging theoretical framework that positions leaf angle as a functional trait. Like leaf traits such as %N or SLA, we suggest that leaf angle is an essential part of the adaptive resource strategy of each tree species. Finally, by linking our leaf angle data to new observations of spatial and temporal variations in near infrared reflectance measured from UAV, airborne, and satellite sensors, we highlight how species-specific patterns of leaf angle phenology could provide a new mechanism to better constrain model predictions of energy, water, and carbon fluxes from temperate forests.

Roll Angle System (RAS) for the High-Energy Solar Spectroscopic Imager HESSI

NASA Astrophysics Data System (ADS)

Henneck, Reinhold; Bialkowski, Jacek; Burri, F.; Fivian, M.; Hajdas, W.; Mchedlishvili, A.; Ming, P.; Thomsen, Knud; Welte, J.; Zehnder, Alex; Dettwyler, M.; Buerki, F.; Hurford, Gordon J.; Curtis, Dave W.; Pankow, Dave

1999-10-01

The purpose of the HESSI RAS is to provide information on the roll angle of the rotation spacecraft. Precise knowledge of the roll angle is a necessary ingredient for image reconstruction. The RAS is a continuously operating star scanner that points out radially and observes stars at 75 degrees from the Sun direction using a commercial lens and a fast CCD. The passage of a star image over the CCD charges one or several pixels above threshold and the timing of this signal defines the roll angle, once the star has been identified by comparing its pixel position and amplitude with a star map. Roll angles at intermediate times are inferred by assuming uniform rotation. With a limiting star magnitude of mv equals 3 we expect to observe at least 1 star per revolution over 1 year; on the average we will detect about 10 stars/revolution.

Estimation of the remote-sensing reflectance from above-surface measurements.

PubMed

Mobley, C D

1999-12-20

The remote-sensing reflectance R(rs) is not directly measurable, and various methodologies have been employed in its estimation. I review the radiative transfer foundations of several commonly used methods for estimating R(rs), and errors associated with estimating R(rs) by removal of surface-reflected sky radiance are evaluated using the Hydrolight radiative transfer numerical model. The dependence of the sea surface reflectance factor rho, which is not an inherent optical property of the surface, on sky conditions, wind speed, solar zenith angle, and viewing geometry is examined. If rho is not estimated accurately, significant errors can occur in the estimated R(rs) for near-zenith Sun positions and for high wind speeds, both of which can give considerable Sun glitter effects. The numerical simulations suggest that a viewing direction of 40 deg from the nadir and 135 deg from the Sun is a reasonable compromise among conflicting requirements. For this viewing direction, a value of rho approximately 0.028 is acceptable only for wind speeds less than 5 m s(-1). For higher wind speeds, curves are presented for the determination of rho as a function of solar zenith angle and wind speed. If the sky is overcast, a value of rho approximately 0.028 is used at all wind speeds.

The normalized magnetic helicity spectrum as a function of the angle between the local mean magnetic field and the flow direction of the solar wind: First results using high resolution magnetic field data from the Wind spacecraft

NASA Astrophysics Data System (ADS)

Podesta, J. J.

2011-12-01

This year, for the first time, the reduced normalized magnetic helicity spectrum has been analyzed as a function of the angle θ between the local mean magnetic field and the flow direction of the solar wind using wavelet techniques. In fast wind, at scales localized near kρp = 1 and kc/ωpp = 1, where ρp is the thermal proton gyro-radius and c/ωpp is the proton inertial length, the analysis reveals two distinct populations of fluctuations. There is a population of fluctuations at oblique angles, centered about an angle of 90 degrees, which are right hand polarized in the spacecraft frame and are believed to be associated with kinetic Alfven waves although the signal covers a wide range of oblique angles and a satisfactory interpretation of their spectrum through comparison with theory has not yet been obtained. A second population of fluctuations is found at angles near zero degrees which are left-hand polarized in the spacecraft frame. The data indicates that these are parallel propagating electromagnetic waves consisting either of left-hand polarized ion cyclotron waves propagating predominantly away from the sun or right-hand polarized whistler waves propagating predominantly toward the sun along the local mean magnetic field. As a consequence of the Doppler shift, both types of waves have the same polarization in the spacecraft frame. Unfortunately, the wave polarization in the plasma frame is difficult to determine using magnetic field data alone. Whether the observed waves are right- or left hand polarized in the plasma frame is a fundamental problem for future investigations. The analyses of spacecraft data performed so far have assumed that the solar wind velocity is directed radially outward from the sun. However, in the ecliptic plane at 1 AU, the flow direction typically deviates from the radial direction by a few degrees, sometimes more, and this adversely affects measurements of the angular helicity spectrum. To correct this, new measurements obtained using data from the Wind spacecraft use the scale dependent local mean solar wind velocity when computing the angle from the data. The first results from this study are presented here.

Correction for reflected sky radiance in low-altitude coastal hyperspectral images.

PubMed

Kim, Minsu; Park, Joong Yong; Kopilevich, Yuri; Tuell, Grady; Philpot, William

2013-11-10

Low-altitude coastal hyperspectral imagery is sensitive to reflections of sky radiance at the water surface. Even in the absence of sun glint, and for a calm water surface, the wide range of viewing angles may result in pronounced, low-frequency variations of the reflected sky radiance across the scan line depending on the solar position. The variation in reflected sky radiance can be obscured by strong high-spatial-frequency sun glint and at high altitude by path radiance. However, at low altitudes, the low-spatial-frequency sky radiance effect is frequently significant and is not removed effectively by the typical corrections for sun glint. The reflected sky radiance from the water surface observed by a low-altitude sensor can be modeled in the first approximation as the sum of multiple-scattered Rayleigh path radiance and the single-scattered direct-solar-beam radiance by the aerosol in the lower atmosphere. The path radiance from zenith to the half field of view (FOV) of a typical airborne spectroradiometer has relatively minimal variation and its reflected radiance to detector array results in a flat base. Therefore the along-track variation is mostly contributed by the forward single-scattered solar-beam radiance. The scattered solar-beam radiances arrive at the water surface with different incident angles. Thus the reflected radiance received at the detector array corresponds to a certain scattering angle, and its variation is most effectively parameterized using the downward scattering angle (DSA) of the solar beam. Computation of the DSA must account for the roll, pitch, and heading of the platform and the viewing geometry of the sensor along with the solar ephemeris. Once the DSA image is calculated, the near-infrared (NIR) radiance from selected water scan lines are compared, and a relationship between DSA and NIR radiance is derived. We then apply the relationship to the entire DSA image to create an NIR reference image. Using the NIR reference image and an atmospheric spectral reflectance look-up table, the low spatial frequency variation of the water surface-reflected atmospheric contribution is removed.

6. DETAIL OF GUSSET WITH CURVE ANGLE IRON AND TWISTED ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

6. DETAIL OF GUSSET WITH CURVE ANGLE IRON AND TWISTED STRIPS, FORMING SUN RAY PATTERN. LATTICE RAILING AT LOWER RIGHT. - River Road Bridge, Spanning Spring Creek in Spring Creek Township, Hallton, Elk County, PA

14. DETAIL OF GUSSET WITH CURVE ANGLE IRON AND TWISTED ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

14. DETAIL OF GUSSET WITH CURVE ANGLE IRON AND TWISTED STRIPS, FORMING SUN RAY PATTERN. LATTICE RAILING AT LOWER RIGHT. - River Road Bridge, Spanning Spring Creek in Spring Creek Township, Hallton, Elk County, PA

Safety Ellipse Motion with Coarse Sun Angle Optimization

NASA Technical Reports Server (NTRS)

Naasz, Bo

2005-01-01

The Hubble Space Telescope Robotic Servicing and De-orbit Mission (HRSDM) was t o be performed by the unmanned Hubble Robotic Vehicle (HRV) consisting of a Deorbit Module (DM), responsible for the ultimate disposal of Hubble Space Telescope (HST) at the end of science operations, and an Ejection Module (EM), responsible for robotically servicing the HST to extend its useful operational lifetime. HRSDM consisted of eight distinct phases, including: launch, pursuit, proximity operations, capture, servicing, EM jettison and disposal, science operations, and deorbit. The scope of this paper is limited to the Proximity Operations phase of HRSDM. It introduces a relative motion strategy useful for Autonomous Rendezvous and Docking (AR&D) or Formation Flying missions where safe circumnavigation trajectories, or close proximity operations (tens or hundreds of meters) are required for extended periods of time. Parameters and algorithms used to model the relative motion of HRV with respect to HST during the Proximity Operations phase of the HRSDM are described. Specifically, the Safety Ellipse (SE) concept, convenient parameters for describing SE motion, and a concept for initializing SE motion around a target vehicle to coarsely optimize sun and relative navigation sensor angles are presented. The effects of solar incidence angle variations on sun angle optimization, and the effects of orbital perturbations and navigation uncertainty on long term SE motion are discussed.

Earth observations taken by the Expedition 12 crew

NASA Image and Video Library

2005-11-15

ISS012-E-13692 (2 Jan. 2006) --- A Forest Fire in Ouachita National Wildlife Refuge, Louisiana is featured in this image photographed by an Expedition 12 crew member on the International Space Station. Dry conditions and high winds have led to numerous recent fire outbreaks throughout much of the southwestern and south-central USA. This image captures the smoke plume from a fire in the Upper Ouachita National Wildlife Refuge in northeastern Louisiana. Drought conditions have persisted for much of the past year, leading to an increased fuel load comprised of dried grasses, shrubs, and trees. The combination of high amounts of dry fuel and frequent high winds has stoked small point fires into widespread brush fires. The fires generating this minimum 25-kilometer smoke plume started at approximately 13:00 hours local time. This image was acquired approximately 3.5 hours later as the station passed over the Texas/Louisiana border to the southwest. The extent of the plume reflects the strong westerly winds that drove the fire eastwards and damaged an estimated 200-300 acres of the wildlife refuge. The striking illumination of the plume is caused by a very low sun angle (angle between the horizon and the Sun directly below the space station), but this also results in generally low illumination of other scene features such as agricultural fields.

Backward-gazing method for measuring solar concentrators shape errors.

PubMed

Coquand, Mathieu; Henault, François; Caliot, Cyril

2017-03-01

This paper describes a backward-gazing method for measuring the optomechanical errors of solar concentrating surfaces. It makes use of four cameras placed near the solar receiver and simultaneously recording images of the sun reflected by the optical surfaces. Simple data processing then allows reconstructing the slope and shape errors of the surfaces. The originality of the method is enforced by the use of generalized quad-cell formulas and approximate mathematical relations between the slope errors of the mirrors and their reflected wavefront in the case of sun-tracking heliostats at high-incidence angles. Numerical simulations demonstrate that the measurement accuracy is compliant with standard requirements of solar concentrating optics in the presence of noise or calibration errors. The method is suited to fine characterization of the optical and mechanical errors of heliostats and their facets, or to provide better control for real-time sun tracking.

Shadows That Enlighten

ERIC Educational Resources Information Center

Vincent, Dan; Cassel, Darlinda

2011-01-01

This inquiry-based investigation focused on shadow measurement and the apparent movement of the Sun throughout the school year. Students would collect data about their shadows weekly. Toward the end of the year, students would then organize and interpret their data. The authors hoped they would discover that the angle of the Sun changes throughout…

Using the sun analog sensor (SAS) data to investigate solar array yoke motion on the GOES-8 and -9 spacecraft

NASA Astrophysics Data System (ADS)

Phenneger, Milton; Knack, Jennifer L.

1996-10-01

The GOES-8 and -9 Sun analog sensor (SAS) flight data is analyzed to evaluate the attitude motion environment of payloads mounted on the solar array. The work was performed in part to extend analysis in progress to support the solar x-ray imager to be flown on the GOES-M. The SAS is a two axis sensor mounted on the x-ray sensor pointing (XRP) module to measure the east/west error angle between the SUn and the solar array normal and to provide a north south error angle for automatic solar pointing of the x-ray sensor by the XRP. The goal was to search for evidence of solar array vibrational modes in the 2 Hz and 0.5 Hz range and to test the predicted amplitudes. The results show that the solar array rotates at the rate of the mean Sun with unexpected oscillation periods of 5.6 minutes, 90 minutes, and 1440 minutes originating from the two 16.1 gear drive train stages between the solar array drive stepper motor and the solar array yoke. The higher frequency oscillations are detected as random noise at the 1/16 Hz telemetry sampling rate of the SAS. This supports the preflight predictions for the high frequency modes but provide s no detailed measurement of the frequency as expected for this data period. In addition to this the data indicates that the solar array is responding unexpectedly to GOES imager instrument blackbody calibration events.

Integration of an On-Axis General Sun-Tracking Formula in the Algorithm of an Open-Loop Sun-Tracking System

PubMed Central

Chong, Kok-Keong; Wong, Chee-Woon; Siaw, Fei-Lu; Yew, Tiong-Keat; Ng, See-Seng; Liang, Meng-Suan; Lim, Yun-Seng; Lau, Sing-Liong

2009-01-01

A novel on-axis general sun-tracking formula has been integrated in the algorithm of an open-loop sun-tracking system in order to track the sun accurately and cost effectively. Sun-tracking errors due to installation defects of the 25 m2 prototype solar concentrator have been analyzed from recorded solar images with the use of a CCD camera. With the recorded data, misaligned angles from ideal azimuth-elevation axes have been determined and corrected by a straightforward changing of the parameters' values in the general formula of the tracking algorithm to improve the tracking accuracy to 2.99 mrad, which falls below the encoder resolution limit of 4.13 mrad. PMID:22408483

Analysis of the Command and Control Segment (CCS) attitude estimation algorithm

NASA Technical Reports Server (NTRS)

Stockwell, Catherine

1993-01-01

This paper categorizes the qualitative behavior of the Command and Control Segment (CCS) differential correction algorithm as applied to attitude estimation using simultaneous spin axis sun angle and Earth cord length measurements. The categories of interest are the domains of convergence, divergence, and their boundaries. Three series of plots are discussed that show the dependence of the estimation algorithm on the vehicle radius, the sun/Earth angle, and the spacecraft attitude. Common qualitative dynamics to all three series are tabulated and discussed. Out-of-limits conditions for the estimation algorithm are identified and discussed.

Seeing Equinoxes and Solstices from Space [hd animation

NASA Image and Video Library

2014-03-19

Images acquired December 21, 2010 - September 20, 2011. To download the high res and learn more go to: earthobservatory.nasa.gov/IOTD/view.php?id=52248 One of the most frequently misunderstood concepts in science is the reason for Earth’s seasons. As we experience the September equinox today—anyone try to balance an egg yet?—we thought we’d offer a space-based view of what’s going on. Around 6 a.m. local time each day, the Sun, Earth, and any geosynchronous satellite form a right angle, affording a nadir (straight down) view of the terminator, where the shadows of nightfall meet the sunlight of dusk and dawn. The shape of this line between night and day varies with the seasons, which means different lengths of days and differing amounts of warming sunshine. (The line is actually a curve because the Earth is round, but satellite images only show it in two-dimensions.) The Spinning Enhanced Visible and Infrared Imager (SEVIRI) on EUMETSAT's Meteosat-9 captured these four views of the day-night terminator on December 21, 2010, and March 20, June 21, and September 20, 2011. Each image was taken at 6:12 a.m. local time. On March 20 and September 20, the terminator is a straight north-south line, and the Sun is said to sit directly above the equator. On December 21, the Sun resides directly over the Tropic of Capricorn when viewed from the ground, and sunlight spreads over more of the Southern Hemisphere. On June 21, the Sun sits above the Tropic of Cancer, spreading more sunlight in the north and turning the tables on the south. The bulge of our spherical Earth blocks sunlight from the far hemisphere at the solstices; that same curvature allows the Sun’s rays to spread over more area near the top and bottom of the globe. Of course, it is not the Sun that is moving north or south through the seasons, but a change in the orientation and angles between the Earth and its nearest star. The axis of the Earth is tilted 23.5 degrees relative to the Sun and the ecliptic plane. The axis is tilted away from the Sun at the December solstice and toward the Sun at the June solstice, spreading more and less light on each hemisphere. At the equinoxes, the tilt is at a right angle to the Sun and the light is spread evenly. The equinox and changing of the seasons occurs on September 23, 2011 at 9:05 a.m. Universal Time. (Our September image above is a few days early.) Equinox means "equal night" in Latin, capturing the idea that daytime and nighttime are equal lengths everywhere on the planet. That is true of the Sun's presence above the horizon, though it does not account for twilight, when the Sun's rays extend from beyond the horizon to illuminate our gas-filled atmosphere. NASA images and animation by Robert Simmon, using data ©2010 EUMETSAT. Caption by Mike Carlowicz. Instrument: Meteosat Credit: NASA Earth Observatory NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Seeing Equinoxes and Solstices from Space

NASA Image and Video Library

2014-03-19

Images acquired December 21, 2010 - September 20, 2011. To view a HD animation of this go to: www.flickr.com/photos/gsfc/6175313242/in/photostream/ To download the high res and learn more go to: earthobservatory.nasa.gov/IOTD/view.php?id=52248 One of the most frequently misunderstood concepts in science is the reason for Earth’s seasons. As we experience the September equinox today—anyone try to balance an egg yet?—we thought we’d offer a space-based view of what’s going on. Around 6 a.m. local time each day, the Sun, Earth, and any geosynchronous satellite form a right angle, affording a nadir (straight down) view of the terminator, where the shadows of nightfall meet the sunlight of dusk and dawn. The shape of this line between night and day varies with the seasons, which means different lengths of days and differing amounts of warming sunshine. (The line is actually a curve because the Earth is round, but satellite images only show it in two-dimensions.) The Spinning Enhanced Visible and Infrared Imager (SEVIRI) on EUMETSAT's Meteosat-9 captured these four views of the day-night terminator on December 21, 2010, and March 20, June 21, and September 20, 2011. Each image was taken at 6:12 a.m. local time. On March 20 and September 20, the terminator is a straight north-south line, and the Sun is said to sit directly above the equator. On December 21, the Sun resides directly over the Tropic of Capricorn when viewed from the ground, and sunlight spreads over more of the Southern Hemisphere. On June 21, the Sun sits above the Tropic of Cancer, spreading more sunlight in the north and turning the tables on the south. The bulge of our spherical Earth blocks sunlight from the far hemisphere at the solstices; that same curvature allows the Sun’s rays to spread over more area near the top and bottom of the globe. Of course, it is not the Sun that is moving north or south through the seasons, but a change in the orientation and angles between the Earth and its nearest star. The axis of the Earth is tilted 23.5 degrees relative to the Sun and the ecliptic plane. The axis is tilted away from the Sun at the December solstice and toward the Sun at the June solstice, spreading more and less light on each hemisphere. At the equinoxes, the tilt is at a right angle to the Sun and the light is spread evenly. The equinox and changing of the seasons occurs on September 23, 2011 at 9:05 a.m. Universal Time. (Our September image above is a few days early.) Equinox means "equal night" in Latin, capturing the idea that daytime and nighttime are equal lengths everywhere on the planet. That is true of the Sun's presence above the horizon, though it does not account for twilight, when the Sun's rays extend from beyond the horizon to illuminate our gas-filled atmosphere. NASA images and animation by Robert Simmon, using data ©2010 EUMETSAT. Caption by Mike Carlowicz. Instrument: Meteosat Credit: NASA Earth Observatory NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Downlink Probability Density Functions for EOS-McMurdo Sound

NASA Technical Reports Server (NTRS)

Christopher, P.; Jackson, A. H.

1996-01-01

The visibility times and communication link dynamics for the Earth Observations Satellite (EOS)-McMurdo Sound direct downlinks have been studied. The 16 day EOS periodicity may be shown with the Goddard Trajectory Determination System (GTDS) and the entire 16 day period should be simulated for representative link statistics. We desire many attributes of the downlink, however, and a faster orbital determination method is desirable. We use the method of osculating elements for speed and accuracy in simulating the EOS orbit. The accuracy of the method of osculating elements is demonstrated by closely reproducing the observed 16 day Landsat periodicity. An autocorrelation function method is used to show the correlation spike at 16 days. The entire 16 day record of passes over McMurdo Sound is then used to generate statistics for innage time, outage time, elevation angle, antenna angle rates, and propagation loss. The levation angle probability density function is compared with 1967 analytic approximation which has been used for medium to high altitude satellites. One practical result of this comparison is seen to be the rare occurrence of zenith passes. The new result is functionally different than the earlier result, with a heavy emphasis on low elevation angles. EOS is one of a large class of sun synchronous satellites which may be downlinked to McMurdo Sound. We examine delay statistics for an entire group of sun synchronous satellites ranging from 400 km to 1000 km altitude. Outage probability density function results are presented three dimensionally.

Sky-radiance gradient measurements at narrow bands in the visible.

PubMed

Winter, E M; Metcalf, T W; Stotts, L B

1995-07-01

Accurate calibrated measurements of the radiance of the daytime sky were made in narrow bands in the visible portion of the spectrum. These measurements were made over several months and were tabulated in a sun-referenced coordinate system. The radiance as a function of wavelength at angles ranging from 5 to 90 deg was plotted. A best-fit inverse power-law fit shows inversely linear behavior of the radiance versus wavelength near the Sun (5 deg) and a slope approaching inverse fourth power far from the Sun (60 deg). This behavior fits a Mie-scattering interpretation near the Sun and a Rayleigh-scattering interpretation away from the Sun. The results are also compared with LOWTRAN models.

Apollo 8 Mission image

NASA Image and Video Library

1968-12-21

Apollo 8,Moon, Latitude 15 degrees South,Longitude 170 degrees West. Camera Tilt Mode: High Oblique. Direction: Southeast. Sun Angle 17 degrees. Original Film Magazine was labeled E. Camera Data: 70mm Hasselblad; F-Stop: F-5.6; Shutter Speed: 1/250 second. Film Type: Kodak SO-3400 Black and White,ASA 40. Other Photographic Coverage: Lunar Orbiter 1 (LO I) S-3. Flight Date: December 21-27,1968.

The role of 1-D and 3-D radiative heating in the organization of shallow cumulus convection and the formation of cloud streets

NASA Astrophysics Data System (ADS)

Jakub, Fabian; Mayer, Bernhard

2017-11-01

The formation of shallow cumulus cloud streets was historically attributed primarily to dynamics. Here, we focus on the interaction between radiatively induced surface heterogeneities and the resulting patterns in the flow. Our results suggest that solar radiative heating has the potential to organize clouds perpendicular to the sun's incidence angle. To quantify the extent of organization, we performed a high-resolution large-eddy simulation (LES) parameter study. We varied the horizontal wind speed, the surface heat capacity, the solar zenith and azimuth angles, and radiative transfer parameterizations (1-D and 3-D). As a quantitative measure we introduce a simple algorithm that provides a scalar quantity for the degree of organization and the alignment. We find that, even in the absence of a horizontal wind, 3-D radiative transfer produces cloud streets perpendicular to the sun's incident direction, whereas the 1-D approximation or constant surface fluxes produce randomly positioned circular clouds. Our reasoning for the enhancement or reduction of organization is the geometric position of the cloud's shadow and its corresponding surface fluxes. Furthermore, when increasing horizontal wind speeds to 5 or 10 m s-1, we observe the development of dynamically induced cloud streets. If, in addition, solar radiation illuminates the surface beneath the cloud, i.e., when the sun is positioned orthogonally to the mean wind field and the solar zenith angle is larger than 20°, the cloud-radiative feedback has the potential to significantly enhance the tendency to organize in cloud streets. In contrast, in the case of the 1-D approximation (or overhead sun), the tendency to organize is weaker or even prohibited because the shadow is cast directly beneath the cloud. In a land-surface-type situation, we find the organization of convection happening on a timescale of half an hour. The radiative feedback, which creates surface heterogeneities, is generally diminished for large surface heat capacities. We therefore expect radiative feedbacks to be strongest over land surfaces and weaker over the ocean. Given the results of this study we expect that simulations including shallow cumulus convection will have difficulties producing cloud streets if they employ 1-D radiative transfer solvers or may need unrealistically high wind speeds to excite cloud street organization.

Analysis of the effect on optical equipment caused by solar position in target flight measure

NASA Astrophysics Data System (ADS)

Zhu, Shun-hua; Hu, Hai-bin

2012-11-01

Optical equipment is widely used to measure flight parameters in target flight performance test, but the equipment is sensitive to the sun's rays. In order to avoid the disadvantage of sun's rays directly shines to the optical equipment camera lens when measuring target flight parameters, the angle between observation direction and the line which connects optical equipment camera lens and the sun should be kept at a big range, The calculation method of the solar azimuth and altitude to the optical equipment at any time and at any place on the earth, the equipment observation direction model and the calculating model of angle between observation direction and the line which connects optical equipment camera lens are introduced in this article. Also, the simulation of the effect on optical equipment caused by solar position at different time, different date, different month and different target flight direction is given in this article.

Effect of heliotropism on the bidirectional reflectance of irrigated cotton

NASA Technical Reports Server (NTRS)

Schutt, J. B.; Kimes, D. S.; Newcomb, W. W.

1985-01-01

The dynamic behavior of cotton leaves is described using gyroscopic coordinates. Angular movements represented as pitching, rolling, and yawing are used to follow the movement of leaf normals and their instantaneous relationships to the sun on an individual basis. A sensitivity analysis establishes that the angle between a leaf normal and the sun is most affected by changes in pitch and roll. Plots of the phase angle gamma averaged by quadrant show the pronounced heliotropic behavior of cotton leaves. Plots of pitch versus roll averaged by quadrant demonstrate the differential behavior of cotton leaves relative to the position of the sun. These results are used to interpret sections taken from bidirectional reflectance curves obtained using 0.57-0.69 micron band in terms of the evolution of gamma from sunrise until noon. The measured and experimental values of gamma are in reasonable agreement. Forescattered and backscattered exitances are observed to have distinct leaf normal directions.

Attitude-Independent Magnetometer Calibration for Spin-Stabilized Spacecraft

NASA Technical Reports Server (NTRS)

Natanson, Gregory

2005-01-01

The paper describes a three-step estimator to calibrate a Three-Axis Magnetometer (TAM) using TAM and slit Sun or star sensor measurements. In the first step, the Calibration Utility forms a loss function from the residuals of the magnitude of the geomagnetic field. This loss function is minimized with respect to biases, scale factors, and nonorthogonality corrections. The second step minimizes residuals of the projection of the geomagnetic field onto the spin axis under the assumption that spacecraft nutation has been suppressed by a nutation damper. Minimization is done with respect to various directions of the body spin axis in the TAM frame. The direction of the spin axis in the inertial coordinate system required for the residual computation is assumed to be unchanged with time. It is either determined independently using other sensors or included in the estimation parameters. In both cases all estimation parameters can be found using simple analytical formulas derived in the paper. The last step is to minimize a third loss function formed by residuals of the dot product between the geomagnetic field and Sun or star vector with respect to the misalignment angle about the body spin axis. The method is illustrated by calibrating TAM for the Fast Auroral Snapshot Explorer (FAST) using in-flight TAM and Sun sensor data. The estimated parameters include magnetic biases, scale factors, and misalignment angles of the spin axis in the TAM frame. Estimation of the misalignment angle about the spin axis was inconclusive since (at least for the selected time interval) the Sun vector was about 15 degrees from the direction of the spin axis; as a result residuals of the dot product between the geomagnetic field and Sun vectors were to a large extent minimized as a by-product of the second step.

Effect of molecular anisotropy on backscattered ultraviolet radiance.

PubMed

Ahmad, Z; Bhartia, P K

1995-12-20

The effect of molecular anisotropy on backscattered UV (BUV) radiances is computed by accounting for it in both Rayleigh optical thickness and the scattering-phase matrix. If the effect of molecular anisotropy is included only in the optical thickness and not in the phase matrix, then for high sun (θ(0) ∼ 0°), the nadir radiance (I(0)) leaving the top of the atmosphere is approximately 1.8% higher than the radiance (I(op)) computed with the effect included in the phase matrix. For very low sun (θ(0) > 80°), I(0) is approximately 2.3% lower than I(op). For off-nadir radiances the relative increase (decrease) depends on both the local zenith angle as well as the azimuth angle. Also, an increase in the surface reflectivity decreases the effect of molecular anisotropy on the upwelling radiances. Exclusion of the anisotropy factor in the Rayleigh-phase matrix has very little effect (<1%) on ozone retrieval from the BUV-type instruments. This is because of the ratio technique used in the retrieval algorithm, which practically cancels out the anisotropy effect.

Automatic grid azimuth by hour angle of the sun, a star or a planet using an electronic theodolite Kern E2

NASA Astrophysics Data System (ADS)

Solaric, Nikola

1991-03-01

The paper describes a procedure for automatic determinations of the grid azimuth of an object on the earth surface by the hour angle of a celestial object (the sun, a star, or a planet), using the electronic theodolite Kern E2. The observation procedure is simple because the electronic calculator is directing the procedure, and the degree of accuracy is immediately determined. With this method, the external rms error of a single set is approximately two times smaller than in the case of the altitude method. The paper includes a flowchart of the program.

Exponential approximation for daily average solar heating or photolysis. [of stratospheric ozone layer

NASA Technical Reports Server (NTRS)

Cogley, A. C.; Borucki, W. J.

1976-01-01

When incorporating formulations of instantaneous solar heating or photolytic rates as functions of altitude and sun angle into long range forecasting models, it may be desirable to replace the time integrals by daily average rates that are simple functions of latitude and season. This replacement is accomplished by approximating the integral over the solar day by a pure exponential. This gives a daily average rate as a multiplication factor times the instantaneous rate evaluated at an appropriate sun angle. The accuracy of the exponential approximation is investigated by a sample calculation using an instantaneous ozone heating formulation available in the literature.

Kansas environmental and resource study: A Great Plains model. Monitoring fresh water resources. [water quality of reservoirs

NASA Technical Reports Server (NTRS)

Yarger, H. L. (Principal Investigator); Mccauley, J. R.

1974-01-01

The author has identified the following significant results. Processing and analysis of CCT's for numerous ground truth supported passes over Kansas reservoirs has demonstrated that sun angle and atmospheric conditions are strong influences on water reflectance levels as detected by ERTS-1 and can suppress the contributions of true water quality factors. Band ratios, on the other hand, exhibit very little dependence on sun angle and sky conditions and thus are more directly related to water quality. Band ratio levels can be used to reliably determine suspended load. Other water quality indicators appear to have little or no affect on reflectance levels.

Corruption of radio metric Doppler due to solar plasma dynamics: S/X dual-frequency Doppler calibration for these effects

NASA Technical Reports Server (NTRS)

Winn, F. B.; Reinbold, S. R.; Yip, K. W.; Koch, R. E.; Lubeley, A.

1975-01-01

Doppler data from Mariner 6, 7, 9, and 10 and Pioneer 10 and 11 were discussed and the rms noise level for various sun-earth-probe angles were shown. The noise levels of both S- and X-band Doppler data for sun-earth-probe angles smaller than 20 deg were observed to be orders of magnitude greater than nominal. Such solar plasma-related Doppler degradation reduced the Mariner 10-Mercury 11 encounter navigation accuracy by nearly a factor of 10. Furthermore, this degradation was shown to be indirectly related to plasma dynamics and not a direct measure of the dynamics.

Light coupling into the Whispering Gallery Modes of a fiber array thin film solar cell for fixed partial Sun tracking

PubMed Central

Mariano, Marina; Rodríguez, Francisco J.; Romero-Gomez, Pablo; Kozyreff, Gregory; Martorell, Jordi

2014-01-01

We propose the use of whispering gallery mode coupling in a novel configuration based on implementing a thin film cell on the backside of an array of parallel fibers. We performed numerical calculations using the parameters of a thin film organic cell which demonstrate that light coupling becomes more effective as the angle for the incident light relative to the fiber array normal increases up to an optimal angle close to 55 deg. At this angle the power conversion efficiency of the fiber array solar cell we propose becomes 30% times larger than the one from an equivalent planar cell configuration. We demonstrate that the micro fiber array solar cell we propose may perform an effective partial tracking of the sun movement for over 100 degrees without any mechanical help. In addition, in the event that such fiber array cell would be installed with the adequate orientation on a vertical façade, an optimal photon-to-charge conversion would be reached for sunlight incident at 55 deg with respect to the horizon line, very close to the yearly average position for the sun at Latitude of 40 deg.

Angular Normalization of Ground and Satellite Observations of Sun-induced Chlorophyll Fluorescence for Assessing Vegetation Productivity

NASA Astrophysics Data System (ADS)

Chen, J. M.; He, L.; Chou, S.; Ju, W.; Zhang, Y.; Joiner, J.; Liu, J.; Mo, G.

2017-12-01

Sun-induced chlorophyll fluorescence (SIF) measured from plant canopies originates mostly from sunlit leaves. Observations of SIF by satellite sensors, such as GOME-2 and GOSAT, are often made over large view zenith angle ranges, causing large changes in the viewed sunlit leaf fraction across the scanning swath. Although observations made by OCO-2 are near nadir, the observed sunlit leaf fraction could still vary greatly due to changes in the solar zenith angle with latitude and time of overpass. To demonstrate the importance of considering the satellite-target-view geometry in using SIF for assessing vegetation productivity, we conducted multi-angle measurements of SIF using a hyperspectral sensor mounted on an automated rotating system over a rice field near Nanjing, China. A method is developed to separate SIF measurements at each angle into sunlit and shaded leaf components, and an angularly normalized canopy-level SIF is obtained as the weighted sum of sunlit and shaded SIF. This normalized SIF is shown to be a much better proxy of GPP of the rice field measured by an eddy covariance system than the unnormalized SIF observations. The same normalization scheme is also applied to the far-red GOME-2 SIF observations on sunny days, and we found that the normalized SIF is better correlated with model-simulated GPP than the original SIF observations. The coefficient of determination (R2) is improved by 0.07±0.04 on global average using the normalization scheme. The most significant improvement in R2 by 0.09±0.04 is found in deciduous broadleaf forests, where the observed sunlit leaf fraction is highly sensitive to solar zenith angle.

Sun, Moon and Earthquakes

NASA Astrophysics Data System (ADS)

Kolvankar, V. G.

2013-12-01

During a study conducted to find the effect of Earth tides on the occurrence of earthquakes, for small areas [typically 1000km X1000km] of high-seismicity regions, it was noticed that the Sun's position in terms of universal time [GMT] shows links to the sum of EMD [longitude of earthquake location - longitude of Moon's foot print on earth] and SEM [Sun-Earth-Moon angle]. This paper provides the details of this relationship after studying earthquake data for over forty high-seismicity regions of the world. It was found that over 98% of the earthquakes for these different regions, examined for the period 1973-2008, show a direct relationship between the Sun's position [GMT] and [EMD+SEM]. As the time changes from 00-24 hours, the factor [EMD+SEM] changes through 360 degree, and plotting these two variables for earthquakes from different small regions reveals a simple 45 degree straight-line relationship between them. This relationship was tested for all earthquakes and earthquake sequences for magnitude 2.0 and above. This study conclusively proves how Sun and the Moon govern all earthquakes. Fig. 12 [A+B]. The left-hand figure provides a 24-hour plot for forty consecutive days including the main event (00:58:23 on 26.12.2004, Lat.+3.30, Long+95.980, Mb 9.0, EQ count 376). The right-hand figure provides an earthquake plot for (EMD+SEM) vs GMT timings for the same data. All the 376 events including the main event faithfully follow the straight-line curve.

Thermal Consideration of SWIFT XRT Radiator At-35C or Colder in Low Earth Orbit

NASA Technical Reports Server (NTRS)

Choi, Michael K.

2000-01-01

The X-Ray Telescope (XRT) is an instrument on the National Aeronautics and Space Administration (NASA) SWIFT spacecraft. The thermoelectric cooler (TEC) for the charge coupled device (CCD) of the XRT requires a radiator temperature of -35 C or colder, and a goal of -55 C to minimize the damage by radiation. The waste heat rejected from the TEC to the radiator is in the 8 W to 20 W range. In the Phase A baseline design, the XRT radiator is mounted to the rear end of the XRT telescope tube and is very close to the bottom closeout of the spacecraft bus. The bottom closeout is multi-layer insulation (MLI) blankets. At sun angles between 90 deg and 180 deg, there is direct solar impingement on the bottom closeout. When the rolls +/- 5 deg, the XRT radiator is exposed to direct solar radiation. The radiator also has a view factor to the solar arrays. The results of thermal analysis showed that the flight temperature prediction of the radiator exceeds the temperature requirement of -35 C substantially at sun angles from 110 deg to 180 deg. A new location on the anti-sun side of the spacecraft is proposed for the radiator. It requires a heat pipe to couple the TEC and the radiator thermally. The results of thermal analysis show that the flight temperature prediction of the proposed radiator meets the temperature requirement at all sun angles.

Generating Land Surface Reflectance for the New Generation of Geostationary Satellite Sensors with the MAIAC Algorithm

NASA Astrophysics Data System (ADS)

Wang, W.; Wang, Y.; Hashimoto, H.; Li, S.; Takenaka, H.; Higuchi, A.; Lyapustin, A.; Nemani, R. R.

2017-12-01

The latest generation of geostationary satellite sensors, including the GOES-16/ABI and the Himawari 8/AHI, provide exciting capability to monitor land surface at very high temporal resolutions (5-15 minute intervals) and with spatial and spectral characteristics that mimic the Earth Observing System flagship MODIS. However, geostationary data feature changing sun angles at constant view geometry, which is almost reciprocal to sun-synchronous observations. Such a challenge needs to be carefully addressed before one can exploit the full potential of the new sources of data. Here we take on this challenge with Multi-Angle Implementation of Atmospheric Correction (MAIAC) algorithm, recently developed for accurate and globally robust applications like the MODIS Collection 6 re-processing. MAIAC first grids the top-of-atmosphere measurements to a fixed grid so that the spectral and physical signatures of each grid cell are stacked ("remembered") over time and used to dramatically improve cloud/shadow/snow detection, which is by far the dominant error source in the remote sensing. It also exploits the changing sun-view geometry of the geostationary sensor to characterize surface BRDF with augmented angular resolution for accurate aerosol retrievals and atmospheric correction. The high temporal resolutions of the geostationary data indeed make the BRDF retrieval much simpler and more robust as compared with sun-synchronous sensors such as MODIS. As a prototype test for the geostationary-data processing pipeline on NASA Earth Exchange (GEONEX), we apply MAIAC to process 18 months of data from Himawari 8/AHI over Australia. We generate a suite of test results, including the input TOA reflectance and the output cloud mask, aerosol optical depth (AOD), and the atmospherically-corrected surface reflectance for a variety of geographic locations, terrain, and land cover types. Comparison with MODIS data indicates a general agreement between the retrieved surface reflectance products. Furthermore, the geostationary results satisfactorily capture the movement of clouds and variations in atmospheric dust/aerosol concentrations, suggesting that high quality land surface and vegetation datasets from the advanced geostationary sensors can help complement and improve the corresponding EOS products.

An experimental test of plant canopy reflectance models on cotton

NASA Technical Reports Server (NTRS)

Lemaster, E. W.

1974-01-01

Extensive data on the plant parameters necessary to evaluate any model are presented for a cotton crop. The variation of the bidirectional reflectance function with observer altitude, observer azimuth, and sun altitude angle is presented for a high density cotton crop having leaf index of 19. A comparison with the quantitative behavior obtained from the Suits model is accomplished in the wavelength region from 400 nm to 1050 nm.

Methods for reducing ghost rays on the Wolter-I focusing figures of the FOXSI rocket payload

NASA Astrophysics Data System (ADS)

Buitrago-Casas, Juan Camilo; Glesener, Lindsay; Christe, Steven; Ramsey, Brian; Elsner, Ronald; Courtade, Sasha; Vievering, Juliana; Subramania, Athiray; Krucker, Sam; Bale, Stuart

2017-08-01

In high energy solar astrophysics, imaging hard X-rays by direct focusing offers higher dynamic range and greater sensitivity compared to past techniques that used indirect imaging. The Focusing Optics X-ray Solar Imager (FOXSI) is a sounding rocket payload which uses seven sets of nested Wolter-I figured mirrors that, together with seven high-sensitive semiconductor detectors, observes the Sun in hard X-rays by direct focusing. The FOXSI rocket has successfully flown twice and is funded to fly a third time in summer 2018.The Wolter-I geometry consists of two consecutive mirrors, one paraboloid, and one hyperboloid, that reflect photons at grazing angles. Correctly focused X-rays reflect twice, once per mirror segment. For extended sources, like the Sun, off-axis photons at certain incident angles can reflect on only one mirror and still reach the focal plane, generating a pattern of single-bounce photons, or ‘ghost rays’ that can limit the sensitivity of the observation of focused X-rays. Understanding and cutting down the ghost rays on the FOXSI optics will maximize the instrument’s sensitivity of the solar faintest sources for future flights. We present an analysis of the FOXSI ghost rays based on ray-tracing simulations, as well as the effectiveness of different physical strategies to reduce them.

Methods for Reducing Singly Reflected Rays on the Wolter-I Focusing Figures of the FOXSI Rocket Experiment

NASA Technical Reports Server (NTRS)

Buitrago-Casas, Juan Camilo; Glesener, Lindsay; Christe, Steven; Elsner, Ronald; Ramsey, Brian; Courtade, Sasha; Ishikawa, Shin-nosuke; Narukage, Noriyuki; Vievering, Juliana; Subramania, Athiray;

Castro Valley High School's Solar Panels

NASA Astrophysics Data System (ADS)

Lew, A.; Ham, S.; Shin, Y.; Yang, W.; Lam, J.

2014-12-01

Solar panels are photovoltaic cells that are designed to convert the sun's kinetic energy to generate usable energy in the form of electricity. Castro Valley High School has tried to offset the cost of electricity by installing solar panels, costing the district approximately 3.29 million dollars, but have been installed incorrectly and are not operating at peak efficency. By using trigonometry we deduced that Castro Valley High School's south facing solar panels were at an incline of 10o and that the east and west facing solar panels are at an incline of 5o. By taking the averages of the optimum angles for the months of September through May, roughly when school is in session, we found that the optimum angle for south facing solar panels should be roughly 46o. This shows that Castro Valley High School has not used it's budget to its full potential due to the fact that the solar panels were haphazardly installed.

Outreach Testing of Ancient Astronomy

NASA Astrophysics Data System (ADS)

Sanmartin, J. R. S.; Blanco, M. B. M.

2015-10-01

This work is an outreach approach to an ubiquitous recent problem in secondary-school education: how to face back the decreasing interest in natural sciences shown by students under 'pressure' of convenient resources in digital devices/applications. The approach rests on two features. First, empowering of teen-age students to understand regular natural events around, as very few educated people they meet could do. Secondly, an understanding that rests on personal capability to test and verify experimental results from the oldest science, astronomy, with simple instruments as used from antiquity down to the Renaissance (a capability restricted to just solar and lunar motions). Because lengths in astronomy and daily life are so disparate, astronomy basically involved observing and registering values of angles (along with times), measurements being of two types, of angles on the ground and of angles in space, from the ground. First, the gnomon, a simple vertical stick introduced in Babylonia and Egypt, and then in Greece, is used to understand solar motion. The gnomon shadow turns around during any given day, varying in length and thus angle between solar ray and vertical as it turns, going through a minimum (noon time, at a meridian direction) while sweeping some angular range from sunrise to sunset. Further, the shadow minimum length varies through the year, with times when shortest and sun closest to vertical, at summer solstice, and times when longest, at winter solstice six months later. The extreme directions at sunset and sunrise correspond to the solstices, swept angular range greatest at summer, over 180 degrees, and the opposite at winter, with less daytime hours; in between, spring and fall equinoxes occur, marked by collinear shadow directions at sunrise and sunset. The gnomon allows students to determine, in addition to latitude (about 40.4° North at Madrid, say), the inclination of earth equator to plane of its orbit around the sun (ecliptic), this fundamental quantity being given by half the difference between solar distances to vertical at winter and summer solstices, with value about 23.5°. Day and year periods greatly differing by about 2 ½ orders of magnitude, 1 day against 365 days, helps students to correctly visualize and interpret the experimental measurements. Since the gnomon serves to observe at night the moon shadow too, students can also determine the inclination of the lunar orbital plane, as about 5 degrees away from the ecliptic, thus explaining why eclipses are infrequent. Independently, earth taking longer between spring and fall equinoxes than from fall to spring (the solar anomaly), as again verified by the students, was explained in ancient Greek science, which posited orbits universally as circles or their combination, by introducing the eccentric circle, with earth placed some distance away from the orbital centre when considering the relative motion of the sun, which would be closer to the earth in winter. In a sense, this can be seen as hint and approximation of the elliptic orbit proposed by Kepler many centuries later. EPSC Abstracts Vol. 10, EPSC2015-40, 2015 European Planetary Science Congress 2015 c Author(s) 2015 EPSC European Planetary Science Congress Secondly, by observing lunar phases and eclipses from the ground, students could also determine, following Aristarchus of Samos in the 3rd century BC, 4 length ratios involving moon and sun distances to earth, and radii of all three, moon, sun, and earth. The angular width of the moon could be first determined with simplest optical devices as about half a degree; this yields the ratio between moon diameter 2RM and distance DM to earth. Next, eclipses of sun prove its angular width, and thus ratio 2RS/DS, similar to the lunar one, though the relatively high lunar orbital eccentricity, 0.055, does result in not quite a full eclipse if at lunar apogee. Further, at a half-moon phase, when the angle sun-moon-earth is a right one, the angle moonearth- sun observed at earth, though also extremely close to 90° and tough to measure, determines the distance ratio DM/DS. Finally, at a lunar eclipse, observation of the shadow-cone width at the moon behind the earth,over 2.6 times the moon diameter, yields the ratio RE/RM. An actual measurement of RE on earth, as crudely carried out by Eratosthenes, again in the 3rd century BC, could then yield all 4 values of moon and sun sizes and distances to earth.

Wild 2 Close Look

NASA Image and Video Library

2004-06-17

This image shows the comet Wild 2, which NASA's Stardust spacecraft flew by on Jan. 2, 2004. This image is the closest short exposure of the comet, taken at an11.4-degree phase angle, the angle between the camera, comet and the Sun. http://photojournal.jpl.nasa.gov/catalog/PIA06285

Internal reflection sensors with high angular resolution

NASA Astrophysics Data System (ADS)

Shavirin, I.; Strelkov, O.; Vetskous, A.; Norton-Wayne, L.; Harwood, R.

1996-07-01

We discuss the use of total internal reflection for the production of sensors with high angular resolution. These sensors are intended for measurement of the angle between a sensor's axis and the direction to a source of radiation or reflecting object. Sensors of this type are used in controlling the position of machine parts in robotics and industry, orienting space vehicles and astronomic devices in relation to the Sun, and as autocollimators for checking angles of deviation. This kind of sensor was used in the Apollo space vehicle some 20 years ago. Using photodetectors with linear and area CCD arrays has opened up new application possibilities for appropriately designed sensors. A generalized methodology is presented applicable to a wide range of tasks. Some modifications that can improve the performance of the basic design are described.

Adaptability of solar energy conversion systems on ships

NASA Astrophysics Data System (ADS)

Visa, I.; Cotorcea, A.; Neagoe, M.; Moldovan, M.

2016-08-01

International trade of goods largely uses maritime/transoceanic ships driven by engines using fossil fuels. This two centuries tradition is technologically mature but significantly adds to the CO2 emissions; therefore, recent trends focus on on-board implementation of systems converting the solar energy into power (photovoltaic systems) or heat (solar-thermal systems). These systems are carbon-emissions free but are still under research and plenty of effort is devoted to fast reach maturity and feasibility. Unlike the systems implemented in a specific continental location, the design of solar energy conversion systems installed on shipboard has to face the problem generated by the system base motion along with the ship travelling on routes at different latitudes: the navigation direction and sense and roll-pitch combined motion with reduced amplitude, but with relatively high frequency. These raise highly interesting challenges in the design and development of mechanical systems that support the maximal output in terms of electricity or heat. The paper addresses the modelling of the relative position of a solar energy conversion surface installed on a ship according to the current position of the sun; the model is based on the navigation trajectory/route, ship motion generated by waves and the relative sun-earth motion. The model describes the incidence angle of the sunray on the conversion surface through five characteristic angles: three used to define the ship orientation and two for the solar angles; based on, their influence on the efficiency in solar energy collection is analyzed by numerical simulations and appropriate recommendations are formulated for increasing the solar energy conversion systems adaptability on ships.

Variable area light reflecting assembly

DOEpatents

Howard, T.C.

1986-12-23

Device is described for tracking daylight and projecting it into a building. The device tracks the sun and automatically adjusts both the orientation and area of the reflecting surface. The device may be mounted in either a wall or roof of a building. Additionally, multiple devices may be employed in a light shaft in a building, providing daylight to several different floors. The preferred embodiment employs a thin reflective film as the reflecting device. One edge of the reflective film is fixed, and the opposite end is attached to a spring-loaded take-up roller. As the sun moves across the sky, the take-up roller automatically adjusts the angle and surface area of the film. Additionally, louvers may be mounted at the light entrance to the device to reflect incoming daylight in an angle perpendicular to the device to provide maximum reflective capability when daylight enters the device at non-perpendicular angles. 9 figs.

Variable area light reflecting assembly

DOEpatents

Howard, Thomas C.

1986-01-01

Device for tracking daylight and projecting it into a building. The device tracks the sun and automatically adjusts both the orientation and area of the reflecting surface. The device may be mounted in either a wall or roof of a building. Additionally, multiple devices may be employed in a light shaft in a building, providing daylight to several different floors. The preferred embodiment employs a thin reflective film as the reflecting device. One edge of the reflective film is fixed, and the opposite end is attached to a spring-loaded take-up roller. As the sun moves across the sky, the take-up roller automatically adjusts the angle and surface area of the film. Additionally, louvers may be mounted at the light entrance to the device to reflect incoming daylight in an angle perpendicular to the device to provide maximum reflective capability when daylight enters the device at non-perpendicular angles.

Psychophysical study of the visual sun location in pictures of cloudy and twilight skies inspired by Viking navigation.

PubMed

Barta, András; Horváth, Gábor; Meyer-Rochow, Victor Benno

2005-06-01

In the late 1960s it was hypothesized that Vikings had been able to navigate the open seas, even when the sun was occluded by clouds or below the sea horizon, by using the angle of polarization of skylight. To detect the direction of skylight polarization, they were thought to have made use of birefringent crystals, called "sun-stones," and a large part of the scientific community still firmly believe that Vikings were capable of polarimetric navigation. However, there are some critics who treat the usefulness of skylight polarization for orientation under partly cloudy or twilight conditions with extreme skepticism. One of their counterarguments has been the assumption that solar positions or solar azimuth directions could be estimated quite accurately by the naked eye, even if the sun was behind clouds or below the sea horizon. Thus under partly cloudy or twilight conditions there might have been no serious need for a polarimetric method to determine the position of the sun. The aim of our study was to test quantitatively the validity of this qualitative counterargument. In our psychophysical laboratory experiments, test subjects were confronted with numerous 180 degrees field-of-view color photographs of partly cloudy skies with the sun occluded by clouds or of twilight skies with the sun below the horizon. The task of the subjects was to guess the position or the azimuth direction of the invisible sun with the naked eye. We calculated means and standard deviations of the estimated solar positions and azimuth angles to characterize the accuracy of the visual sun location. Our data do not support the common belief that the invisible sun can be located quite accurately from the celestial brightness and/or color patterns under cloudy or twilight conditions. Although our results underestimate the accuracy of visual sun location by experienced Viking navigators, the mentioned counterargument cannot be taken seriously as a valid criticism of the theory of the alleged polarimetric Viking navigation. Our results, however, do not bear on the polarimetric theory itself.

Far side Helioseismology with Solar Orbiter

NASA Astrophysics Data System (ADS)

Appourchaux, T.; Birch, A.; Gizon, L. C.; Löptien, B.; Schou, J.; Solanki, S. K.; del Toro Iniesta, J. C.; Gandorfer, A.; Hirzberger, J.; Alvarez-Herrero, A.; Woch, J. G.; Schmidt, W.

2016-12-01

The Solar Orbiter mission, to be launched in October 2018, will carry a suite of remote sensing and in-situ instruments, including the Polarimetric and Helioseismic Imager (PHI). PHI will deliver high-cadence images of the Sun in intensity and Doppler velocity suitable for carrying out novel helioseismic studies. The orbit of the Solar Orbiter spacecraft will reach a solar latitude up to 34 degrees by the end of the extended mission and thus will enable the first local helioseismology studies of the polar regions. The full range of Earth-Sun-spacecraft angles provided by the orbit will enable helioseismology from two vantage points by combining PHI with another instrument: stereoscopic helioseismology will allow the study of the deep solar interior and a better understanding of the physics of solar oscillations in both quiet Sun and sunspots. In this paper we will review the helioseismic objectives achievable with PHI, and will also give a short status report of the development of the Flight Model of PHI.

Survey of Experimental Results in High-Contrast Imaging for Future Exoplanet Missions

NASA Technical Reports Server (NTRS)

Lawson, P. R.; Belikov, R.; Cash, W.; Clampin, M.; Glassman, T.; Guyon, O.; Kasdin, N. J.; Kern, B. D.; Lyon, R.; Mawet, D.;

Miniaturized star tracker for micro spacecraft with high angular rate

NASA Astrophysics Data System (ADS)

Li, Jianhua; Li, Zhifeng; Niu, Zhenhong; Liu, Jiaqi

2017-10-01

There is a clear need for miniaturized, lightweight, accurate and inexpensive star tracker for spacecraft with large anglar rate. To face these new constraints, the Beijing Institute of Space Long March Vehicle has designed, built and flown a low cost miniaturized star tracker that provides autonomous ("Lost in Space") inertial attitude determination, 2 Hz 3-axis star tracking, and digital imaging with embedded compression. Detector with high sensitivity is adopted to meet the dynamic and miniature requirement. A Sun and Moon avoiding method based on the calculation of Sun and Moon's vector by astronomical theory is proposed. The produced prototype weight 0.84kg, and can be used for a spacecraft with 6°/s anglar rate. The average angle measure error is less than 43 arc second. The ground verification and application of the star tracker during the pick-up flight test showed that the capability of the product meet the requirement.

Sizing up skylights

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

Warner, J.L.

1993-11-01

This article discusses various aspects of skylights. Designers, builders, and homeowners who understand the energy aspects of skylights can best select them for comfort as well as appearance. Topics covered include heat loss problems (convection, radiation); the sun and the sun angles; ventilation; skylight ratings for efficiency; pointers about what to look for; comparison of skylight and window U-Factors; ventilation. 3 figs., 1 tab.

A method to calculate Stokes parameters and angle of polarization of skylight from polarized CIMEL sun/sky radiometers

NASA Astrophysics Data System (ADS)

Li, L.; Li, Z.; Li, K.; Blarel, L.; Wendisch, M.

2014-12-01

The polarized CIMEL sun/sky radiometers have been routinely operated within the Sun/sky-radiometer Observation NETwork (SONET) in China and some sites of the AErosol RObotic NETwork (AERONET) around the world. However, the polarization measurements are not yet widely used due to in a certain degree the lack of Stokes parameters derived directly from these polarization measurements. Meanwhile, it have been shown that retrievals of several microphysical properties of aerosol particles can be significantly improved by using degree of linear polarization (DoLP) measurements of polarized CIMEL sun/sky radiometers (CE318-DP). The Stokes parameters Q and U, as well as angle of polarization (AoP) contain additional information about linear polarization and its orientation. A method to calculate Stokes parameters Q, U, and AoP from CE318-DP polarized skylight measurements is introduced in this study. A new polarized almucantar geometry based on CE318-DP is measured to illustrate abundant variation features of these parameters. The polarization parameters calculated in this study are consistent with previous results of DoLP and I, and also comparable to vector radiative transfer simulations.

Experiments out of the solar system ecliptic plane: An introduction to the ecliptic mission

NASA Technical Reports Server (NTRS)

Simpson, J. A.

1976-01-01

Mission planning by NASA and ESA for the 1980 timeframe to observe the sun from an angle other than the solar ecliptic plane is discussed. Such missions will aid in a more thorough understanding of the sun, interplanetary space, and their influence on the earth. Jupiter swing-by techniques (first achieved by Pioneer 10) are proposed as a means of achieving an out-of-the-ecliptic mission for solar studies. Spacecraft trajectories are illustrated for a dual Pioneer spacecraft mission to observe the sun.

Near Earth Inner-Source and Interstellar Pickup Ions Observed with the Hot Plasma Composition Analyzer of the Magnetospheric Multiscale Mission Mms-Hpca

NASA Astrophysics Data System (ADS)

Gomez, R. G.; Fuselier, S. A.; Mukherjee, J.; Gonzalez, C. A.

2017-12-01

Pickup ions found near the earth are generally picked up in the rest frame of the solar wind, and propagate radially outward from their point of origin. While propagating, they simultaneously gyrate about the magnetic field. Pickup ions come in two general populations; interstellar and inner source ions. Interstellar ions originate in the interstellar medium, enter the solar system in a neutral charge state, are gravitationally focused on the side of the sun opposite their arrival direction and, are ionized when they travel near the sun. Inner-source ions originate at a location within the solar system and between the sun and the observation point. Both pickup ion populations share similarities in composition and charge states, so measuring of their dynamics, using their velocity distribution functions, f(v)'s, is absolutely essential to distinguishing them, and to determining their spatial and temporal origins. Presented here will be the results of studies conducted with the four Hot Plasma Composition Analyzers of the Magnetospheric Multiscale Mission (MMS-HPCA). These instruments measure the full sky (4π steradians) distribution functions of near earth plasmas at a 10 second cadence in an energy-to-charge range 0.001-40 keV/e. The instruments are also capable of parsing this combined energy-solid angle phase space with 22.5° resolution polar angle, and 11.25° in azimuthal angle, allowing for clear measurement of the pitch angle scattering of the ions.

Glare on the Window

NASA Image and Video Library

2018-03-05

In this image, NASA's Cassini sees Saturn and its rings through a haze of Sun glare on the camera lens. If you could travel to Saturn in person and look out the window of your spacecraft when the Sun was at a certain angle, you might see a view very similar to this one. Images taken using red, green and blue spectral filters were combined to show the scene in natural color. The images were taken with Cassini's wide-angle camera on June 23, 2013, at a distance of approximately 491,200 miles (790,500 kilometers) from Saturn. The Cassini spacecraft ended its mission on Sept. 15, 2017. https://photojournal.jpl.nasa.gov/catalog/PIA17185

The Focusing Optics X-ray Solar Imager

NASA Astrophysics Data System (ADS)

Glesener, Lindsay; Krucker, S.; Christe, S.; Turin, P.; McBride, S.

2009-01-01

The Focusing Optics X-ray Solar Imager (FOXSI) is a NASA Low Cost Access to Space sounding rocket payload scheduled to fly in late 2010 to observe hard X-ray emission (HXR) from the quiet Sun. Particle acceleration in small "nanoflares" in the quiet Sun is thought to play an important role in the heating of the corona to millions of degrees Kelvin. FOXSI HXR observations of these flares will provide first estimates of the non-thermal energy content in small flares from the quiet Sun. Imaging nanoflares requires high energy sensitivity and a large dynamic range. To date, the most sensitive HXR images are made using a rotating modulating collimator aboard the Reuven Ramaty High Energy Spectroscopic Imager satellite (RHESSI). However, the rotating modulation technique is intrinsically limited in sensitivity and dynamic range. The focusing optics of FOXSI will achieve a sensitivity 100 times better than that of RHESSI at energies around 10 keV. FOXSI uses nested-shell, grazing-angle optics and silicon strip detectors to achieve an angular resolution of 12" (FWHM) and 1 keV energy resolution. FOXSI will observe the quiet Sun in the 4 to 15 keV range for 5 minutes. The focusing optics technique developed by FOXSI will prove useful to future solar HXR observing missions, especially those interested in imaging faint HXR emission from particle acceleration regions in the corona.

Consequences for sun protection factors when solar simulator spectra deviate from the spectrum of the sun.

PubMed

Uhlmann, B; Mann, T; Gers-Barlag, H; Alert, D; Sauermann, G

1996-02-01

Synopsis The sun protection factor (SPF) of two products, one with an expected SPF of 4 and another with an expected SPF of 15 were determined, using two solar simulators: Multiport Solar UV Simulator (xenon, Solar Light, Philadelphia, PA, USA), and Supersun 5000 (metal halide, Mutzhas, Munich, Germany). The mean SPFs using the Multiport were: 4.8 for the low SPF product and 19.4 for the high SPF one. The results using the Supersun were lower: 2.6 for the low SPF product and 7.2 for the high SPF one. Relative emission spectra of the two sources were recorded using a fluorescence spectrophotometer in bioluminescence mode. Efficacy spectra were calculated and compared with the corresponding spectrum of natural sunlight. It was evident that the spectral power of the xenon source is too high in the UVB, leading to overestimation of SPFs, whereas the Supersun irradiator emits too much in the UVA, resulting in too low SPFs. Heat effects and photodegradation of UV filters are discussed as further possible reasons for the discrepancies between the experimentally determined SPFs. Our results confirm a recent publication about theoretical SPFs, calculated with emission spectra of a xenon source and spectra of the sun at different elevation angles, where the authors provide evidence that in natural sunlight the contribution of UVA to total UV radiation is twice as high as in a xenon source. This may contribute to an understanding of why sunscreens tested according to the FDA method (xenon sources) often yield higher SPFs than those obtained from European testing procedures.

Celestial polarization patterns sufficient for Viking navigation with the naked eye: detectability of Haidinger's brushes on the sky versus meteorological conditions

NASA Astrophysics Data System (ADS)

Horváth, Gábor; Takács, Péter; Kretzer, Balázs; Szilasi, Szilvia; Száz, Dénes; Farkas, Alexandra; Barta, András

2017-02-01

If a human looks at the clear blue sky from which light with high enough degree of polarization d originates, an 8-shaped bowtie-like figure, the yellow Haidinger's brush can be perceived, the long axis of which points towards the sun. A band of high d arcs across the sky at 90° from the sun. A person can pick two points on that band, observe the yellow brushes and triangulate the position of the sun based on the orientation of the two observed brushes. This method has been suggested to have been used on the open sea by Viking navigators to determine the position of the invisible sun occluded by cloud or fog. Furthermore, Haidinger's brushes can also be used to locate the sun when it is below the horizon or occluded by objects on the horizon. To determine the position of the sun using the celestial polarization pattern, the d of the portion of the sky used must be greater than the viewer's degree of polarization threshold d* for perception of Haidinger's brushes. We studied under which sky conditions the prerequisite d > d* is satisfied. Using full-sky imaging polarimetry, we measured the d-pattern of skylight in the blue (450 nm) spectral range for 1296 different meteorological conditions with different solar elevation angles θ and per cent cloud cover ρ. From the measured d-patterns of a given sky we determined the proportion P of the sky for which d > d*. We obtained that P is the largest at low solar elevations θ ≈ 0° and under totally or nearly clear skies with cloud coverage ρ = 0%, when the sun's position is already easily determined. If the sun is below the horizon (-5° ≤ θ < 0°) during twilight, P = 76.17 ± 4.18% for dmin∗=23 % under clear sky conditions. Consequently, the sky-polarimetric Viking navigation based on Haidinger's brushes is most useful after sunset and prior to sunrise, when the sun is not visible and large sky regions are bright, clear and polarized enough for perception of Haidinger's brushes.

A daytime measurement of the lunar contribution to the night sky brightness in LSST's ugrizy bands-initial results

NASA Astrophysics Data System (ADS)

Coughlin, Michael; Stubbs, Christopher; Claver, Chuck

2016-06-01

We report measurements from which we determine the spatial structure of the lunar contribution to night sky brightness, taken at the LSST site on Cerro Pachon in Chile. We use an array of six photodiodes with filters that approximate the Large Synoptic Survey Telescope's u, g, r, i, z, and y bands. We use the sun as a proxy for the moon, and measure sky brightness as a function of zenith angle of the point on sky, zenith angle of the sun, and angular distance between the sun and the point on sky. We make a correction for the difference between the illumination spectrum of the sun and the moon. Since scattered sunlight totally dominates the daytime sky brightness, this technique allows us to cleanly determine the contribution to the (cloudless) night sky from backscattered moonlight, without contamination from other sources of night sky brightness. We estimate our uncertainty in the relative lunar night sky brightness vs. zenith and lunar angle to be between 0.3-0.7 mags depending on the passband. This information is useful in planning the optimal execution of the LSST survey, and perhaps for other astronomical observations as well. Although our primary objective is to map out the angular structure and spectrum of the scattered light from the atmosphere and particulates, we also make an estimate of the expected number of scattered lunar photons per pixel per second in LSST, and find values that are in overall agreement with previous estimates.

Radiance distribution over a ruffled sea: contributions from glitter, sky, and ocean.

PubMed

Plass, G N; Kattawar, G W; Guinn, J A

1976-12-01

The upward radiance just above the ocean surface and at the top of the atmosphere is calculated for a realistic model including an ocean surface with waves. The separate contributions of the sun glitter, the reflected sky radiance, and the upwelling photons from the ocean are calculated. The Monte Carlo method takes account of both Rayleigh scattering by the molecules and Mie scattering by the aerosols as well as molecular and aerosol absorption in the atmosphere. Similarly, in the ocean, both Rayleigh scattering by the water molecules and Mie scattering by the hydrosols as well as absorption by the water molecules and hydrosols are considered. Separate single-scattering functions are used for the aerosols and hydrosols calculated from the Mie theory. Both the reflected and refracted rays, as well as the rays that undergo total internal reflection, are followed at the ocean surface. The wave slope is chosen from the Cox-Munk distribution. The upward radiance just above the ocean surface outside of the sun glitter region is dominated by the reflected sky radiation from the horizon to a nadir angle of observation of from 68 degrees to 23 degrees depending on the azimuthal angle and the solar zenith angle; the upwelling photons from the ocean dominate over the remainder of the hemisphere, except in the region of the sun glitter which centers around the mirror image of the sun on a calm ocean. It is possible to answer various questions about the interaction of light with the ocean from the quantitative results presented here.

Two wide-angle imaging neutral-atom spectrometers (TWINS)

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

McComas, D.J.; Blake, B.; Burch, J.

1998-11-01

Two Wide-angle Imaging Neutral-atom Spectrometers (TWINS) is a revolutionary new mission designed to stereoscopically image the magnetosphere in charge exchange neutral atoms for the first time. The authors propose to fly two identical TWINS instruments as a mission of opportunity on two widely-spaced high-altitude, high-inclination US Government spacecraft. Because the spacecraft are funded independently, TWINS can provide a vast quantity of high priority science observations (as identified in an ongoing new missions concept study and the Sun-Earth Connections Roadmap) at a small fraction of the cost of a dedicated mission. Because stereo observations of the near-Earth space environs will providemore » a particularly graphic means for visualizing the magnetosphere in action, and because of the dedication and commitment of the investigator team to the principles of carrying space science to the broader audience, TWINS will also be an outstanding tool for public education and outreach.« less

Psychophysical study of the visual sun location in pictures of cloudy and twilight skies inspired by Viking navigation

NASA Astrophysics Data System (ADS)

Barta, András; Horváth, Gábor; Benno Meyer-Rochow, Victor

2005-06-01

In the late 1960s it was hypothesized that Vikings had been able to navigate the open seas, even when the sun was occluded by clouds or below the sea horizon, by using the angle of polarization of skylight. To detect the direction of skylight polarization, they were thought to have made use of birefringent crystals, called "sunstones," and a large part of the scientific community still firmly believe that Vikings were capable of polarimetric navigation. However, there are some critics who treat the usefulness of skylight polarization for orientation under partly cloudy or twilight conditions with extreme skepticism. One of their counterarguments has been the assumption that solar positions or solar azimuth directions could be estimated quite accurately by the naked eye, even if the sun was behind clouds or below the sea horizon. Thus under partly cloudy or twilight conditions there might have been no serious need for a polarimetric method to determine the position of the sun. The aim of our study was to test quantitatively the validity of this qualitative counterargument. In our psychophysical laboratory experiments, test subjects were confronted with numerous 180° field-of-view color photographs of partly cloudy skies with the sun occluded by clouds or of twilight skies with the sun below the horizon. The task of the subjects was to guess the position or the azimuth direction of the invisible sun with the naked eye. We calculated means and standard deviations of the estimated solar positions and azimuth angles to characterize the accuracy of the visual sun location. Our data do not support the common belief that the invisible sun can be located quite accurately from the celestial brightness and/or color patterns under cloudy or twilight conditions. Although our results underestimate the accuracy of visual sun location by experienced Viking navigators, the mentioned counterargument cannot be taken seriously as a valid criticism of the theory of the alleged polarimetric Viking navigation. Our results, however, do not bear on the polarimetric theory itself.

All About That Basin

NASA Image and Video Library

2015-02-25

This mosaic of Caloris basin is an enhanced-color composite overlain on a monochrome mosaic featured in a previous post. The color mosaic is made up of WAC images obtained when both the spacecraft and the Sun were overhead, conditions best for discerning variations in albedo, or brightness. The monochrome mosaic is made up of WAC and NAC images obtained at off-vertical Sun angles (i.e., high incidence angles) and with visible shadows so as to reveal clearly the topographic form of geologic features. The combination of the two datasets allows the correlation of geologic features with their color properties. In portions of the scene, color differences from image to image are apparent. Ongoing calibration efforts by the MESSENGER team strive to minimize these differences. Caloris basin has been flooded by lavas that appear orange in this mosaic. Post-flooding craters have excavated material from beneath the surface. The larger of these craters have exposed low-reflectance material (blue in this mosaic) from beneath the surface lavas, likely giving a glimpse of the original basin floor material. Analysis of these craters yields an estimate of the thickness of the volcanic layer: 2.5-3.5 km (1.6-2.2 mi.). http://photojournal.jpl.nasa.gov/catalog/PIA19216

Horizontal and sun-normal spectral biologically effective ultraviolet irradiances.

PubMed

Parisi, A V; Kimlin, M G

1999-01-01

The dependence of the spectral biologically effective solar UV irradiance on the orientation of the receiver with respect to the sun has been determined for relatively cloud-free days at a sub-tropical Southern Hemisphere latitude for the solar zenith angle range 35-64 degrees. For the UV and biologically effective irradiances, the sun-normal to horizontal ratio for the total UV ranges from 1.18 +/- 0.05 to 1.27 +/- 0.06. The sun-normal to horizontal ratio for biologically effective irradiance is dependent on the relative effectiveness of the relevant action spectrum in the UV-A waveband. In contrast to the total UV, the diffuse UV and diffuse biologically effective irradiances are reduced in a sun-normal compared with a horizontal orientation by a factor ranging from 0.70 +/- 0.05 to 0.76 +/- 0.03.

Statistical analysis of geomagnetic field intensity differences between ASM and VFM instruments onboard Swarm constellation

NASA Astrophysics Data System (ADS)

De Michelis, Paola; Tozzi, Roberta; Consolini, Giuseppe

2017-02-01

From the very first measurements made by the magnetometers onboard Swarm satellites launched by European Space Agency (ESA) in late 2013, it emerged a discrepancy between scalar and vector measurements. An accurate analysis of this phenomenon brought to build an empirical model of the disturbance, highly correlated with the Sun incidence angle, and to correct vector data accordingly. The empirical model adopted by ESA results in a significant decrease in the amplitude of the disturbance affecting VFM measurements so greatly improving the vector magnetic data quality. This study is focused on the characterization of the difference between magnetic field intensity measured by the absolute scalar magnetometer (ASM) and that reconstructed using the vector field magnetometer (VFM) installed on Swarm constellation. Applying empirical mode decomposition method, we find the intrinsic mode functions (IMFs) associated with ASM-VFM total intensity differences obtained with data both uncorrected and corrected for the disturbance correlated with the Sun incidence angle. Surprisingly, no differences are found in the nature of the IMFs embedded in the analyzed signals, being these IMFs characterized by the same dominant periodicities before and after correction. The effect of correction manifests in the decrease in the energy associated with some IMFs contributing to corrected data. Some IMFs identified by analyzing the ASM-VFM intensity discrepancy are characterized by the same dominant periodicities of those obtained by analyzing the temperature fluctuations of the VFM electronic unit. Thus, the disturbance correlated with the Sun incidence angle could be still present in the corrected magnetic data. Furthermore, the ASM-VFM total intensity difference and the VFM electronic unit temperature display a maximal shared information with a time delay that depends on local time. Taken together, these findings may help to relate the features of the observed VFM-ASM total intensity difference to the physical characteristics of the real disturbance thus contributing to improve the empirical model proposed for the correction of data.[Figure not available: see fulltext.

LANDSAT data preprocessing

NASA Technical Reports Server (NTRS)

Austin, W. W.

1983-01-01

The effect on LANDSAT data of a Sun angle correction, an intersatellite LANDSAT-2 and LANDSAT-3 data range adjustment, and the atmospheric correction algorithm was evaluated. Fourteen 1978 crop year LACIE sites were used as the site data set. The preprocessing techniques were applied to multispectral scanner channel data and transformed data were plotted and used to analyze the effectiveness of the preprocessing techniques. Ratio transformations effectively reduce the need for preprocessing techniques to be applied directly to the data. Subtractive transformations are more sensitive to Sun angle and atmospheric corrections than ratios. Preprocessing techniques, other than those applied at the Goddard Space Flight Center, should only be applied as an option of the user. While performed on LANDSAT data the study results are also applicable to meteorological satellite data.

Validation of multi-angle imaging spectroradiometer aerosol products in China

Treesearch

J. Liu; X. Xia; Z. Li; P. Wang; M. Min; WeiMin Hao; Y. Wang; J. Xin; X. Li; Y. Zheng; Z. Chen

2010-01-01

Based on AErosol RObotic NETwork and Chinese Sun Hazemeter Network data, the Multi-angle Imaging SpectroRadiometer (MISR) level 2 aerosol optical depth (AOD) products are evaluated in China. The MISR retrievals depict well the temporal aerosol trend in China with correlation coefficients exceeding 0.8 except for stations located in northeast China and at the...

Methods for reducing singly reflected rays on the Wolter-I focusing mirrors of the FOXSI rocket experiment

NASA Astrophysics Data System (ADS)

Buitrago-Casas, Juan Camilo; Elsner, Ronald; Glesener, Lindsay; Christe, Steven; Ramsey, Brian; Courtade, Sasha; Ishikawa, Shin-nosuke; Narukage, Noriyuki; Turin, Paul; Vievering, Juliana; Athiray, P. S.; Musset, Sophie; Krucker, Säm.

2017-08-01

In high energy solar astrophysics, imaging hard X-rays by direct focusing offers higher dynamic range and greater sensitivity compared to past techniques that used indirect imaging. The Focusing Optics X-ray Solar Imager (FOXSI) is a sounding rocket payload that uses seven sets of nested Wolter-I figured mirrors together with seven high-sensitivity semiconductor detectors to observe the Sun in hard X-rays through direct focusing. The FOXSI rocket has successfully flown twice and is funded to fly a third time in summer 2018. The Wolter-I geometry consists of two consecutive mirrors, one paraboloid and one hyperboloid, that reflect photons at grazing angles. Correctly focused X-rays reflect once per mirror segment. For extended sources, like the Sun, off-axis photons at certain incident angles can reflect on only one mirror and still reach the focal plane, generating a background pattern of singly reflected rays (i.e., ghost rays) that can limit the sensitivity of the observation to faint, focused sources. Understanding and mitigating the impact of the singly reflected rays on the FOXSI optical modules will maximize the instruments' sensitivity to background-limited sources. We present an analysis of the FOXSI singly reflected rays based on ray-tracing simulations and laboratory measurements, as well as the effectiveness of different physical strategies to reduce them.

Thunderstorm clouds over Western Africa

NASA Technical Reports Server (NTRS)

1989-01-01

The overshooting tops of a series of strong thunderstorms are seen in this late afternoon scene over the African Ivory Coast, exact location unknown. The low sun angle of the setting sun casts long shadows, accentuating the shapes and heights of the clouds. This seasonal thunderstorm is an African Intertropical Front located along the land/sea breeze interface over the West African coastline and is a normal occurance for this time of year.

A star tracker insensitive to stray light generated by radiation sources close to the field of view

NASA Astrophysics Data System (ADS)

Romoli, A.; Gambicorti, L.; Simonetti, F.; Zuccaro Marchi, A.

2017-11-01

Aim of this work is to propose an innovative star tracker, practically insensitive to the radiation coming from the sun or from other strong planetary sources out of (but near) the Field of View. These sources need to be stopped in some way. The classical solution to reject the unwanted radiation is to place a shadow (or baffle) before the star tracker objective. The shadow size depends on the Field of View and on the minimum angle subtended by the source (i.e. the sun) with respect to the optical axis of the star tracker. The lower is this angle the larger is the shadow. Requests for star trackers able to work with the sun as close as possible to the Field of View are increasing, due to the need of maximum mission flexibility. The innovation of this proposed star tracker is conceived by using spatial filtering with a concept complementary to that of coronagraph for sun corona observation, allowing to drastically reduce the size of the shadow. It can also work close to antennas and other part of the platform, which, when illuminated by the sun, become secondary sources capable to blind the star tracker. This kind of accommodation offers three main advantages: no cumbersome shadows (baffle), maximum flexibility in terms of mission profile, less platform location constraints. This new star sensor concept, dated 2007, is now patent pending. Galileo Avionica (now Selex Galileo) is the owner of the patent.

Retrieval of Aerosol Phase Function and Polarized Phase Function from Polarization of Skylight for Different Observation Geometries

NASA Astrophysics Data System (ADS)

Li, L.; Qie, L. L.; Xu, H.; Li, Z. Q.

2018-04-01

The phase function and polarized phase function are important optical parameters, which describe scattering properties of atmospheric aerosol particles. Polarization of skylight induced by the scattering processes is sensitive to the scattering properties of aerosols. The Stokes parameters I, Q, U and the polarized radiance Lp of skylight measured by the CIMEL dual-polar sun-sky radiometer CE318- DP can be use to retrieve the phase function and polarized phase function, respectively. Two different observation geometries (i.e., the principal plane and almucantar) are preformed by the CE318-DP to detect skylight polarization. Polarization of skylight depends on the illumination and observation geometries. For the same solar zenith angle, retrievals of the phase function and the polarized phase function are still affected by the observation geometry. The performance of the retrieval algorithm for the principal plane and almucantar observation geometries was assessed by the numerical experiments at two typical high and low sun's positions (i.e. solar zenith angles are equal to 45° and 65°). Comparing the results for the principal plane and almucantar geometries, it is recommended to utilize the principal plane observations to retrieve the phase function when the solar zenith angle is small. The Stokes parameter U and the polarized radiance Lp from the almucantar observations are suggested to retrieve the polarized phase function, especially for short wavelength channels (e.g., 440 and 500 nm).

Residual Strahls in Solar Wind Electron Dropouts: Signatures of Magnetic Connection to the Sun, Disconnection, or Interchange Reconnection?

NASA Technical Reports Server (NTRS)

Crooker, N. U.; Pagel, C.

2008-01-01

A recent assessment of suprathermal electron heat flux dropouts (HFDs) in the solar wind eliminated 90% as possible signatures of field lines disconnected from the Sun at both ends (Pagel et al., 2005b). The primary reason for elimination was the presence of a residual field-aligned strahl presumably signaling field lines connected to the Sun. Using high-time-resolution data from the Wind spacecraft, this paper tests whether the residual strahls were an artifact of averaging over pitch angle distributions (PADs) with and without strahls. An automated search for PADs without strahls (flat PADs) yields an occurrence rate of only 14% within HFDs, but a detailed case study shows that these flat PADs are imbedded within intervals of nearly flat PADs, that is, PADS with residual strahls that cannot be artifacts of averaging. An attractive alternative is that the residual strahls result from intermixing of originally back-scattered fluxes (haloes) of unequal intensities on field lines that have either disconnected or interchange reconnected at the Sun. A reevaluation of reported streaming of higher-energy electrons in HFDs suggests a similar cause. While the high-time-resolution data show high variability of PAD profiles within HFDs, this paper reopens the possibility that a substantial fraction signal disconnection or interchange reconnection. Estimated occurrence rates of fields having undergone these processes based upon published HFD rates are of the same order of magnitude as the surprisingly low values of 1-5% recently predicted by a model of a balanced heliospheric flux budget (Owens and Crooker, 2007).

Photochemical reflectance ratio for tracking light use efficiency for sunlit leaves in two forest types

NASA Astrophysics Data System (ADS)

Zheng, Ting; Chen, Jing M.

2017-01-01

The estimation of maximum carboxylation rate (Vcmax)-a critical determinant of the terrestrial carbon simulation-over space remains a challenging task. Inverting the Vcmax through the sunlit gross primary productivity (GPP) is a possible solution if the key parameter sunlit light use efficiency (ɛsun) could be acquired through remote sensing approaches. Previous studies have shown that the reflectance centered at 531 nm (R531) is very sensitive to variations of ɛsun and the photochemical reflectance index (PRI, the normalized difference index using R531 and R570) can be used as an indicator of ɛsun at the leaf level though little is known about the PRI-ɛsun relationship at the canopy level due to the mixing of sunlit and shaded leaves. In this study, the photochemical reflectance ratio (PRR, defined as the ratio between R531 and R570) is proposed to enable the sunlit-shaded separation of the canopy reflectance observations acquired from a tower based multi-angular platform. The canopy PRR can be expressed as the algebraic sum of sunlit PRR and shaded PRR weighted by the visible portions of the sunlit canopy and the shaded canopy respectively. The visible portions from different angles were simulated using the 4-Scale model and the sunlit (/shaded) PRR was acquired through solving a set of equations describing the canopy PRR obtained from different angles. The relationships between the sunlit PRR (PRRsun) and ɛsun were studied for a white pine stand (TP39) and a sugar maple stand (HA). At both sites, significant correlations between PRRsun and ɛsun were obtained (R2 = 0.57 (TP39), 0.585 (HA), p < 0.001), showing the ability of PRRsun to track the variation of ɛsun. Nevertheless, differences existed in the expressions of the PRRsun-ɛsun relationship between TP39 and HA, a general expression could not be found. Further studies have shown that introducing the normalized difference vegetation index (NDVI) to correct PRRsun (NDVI × PRRsun) largely removed such differences, suggesting the potential of the NDVI corrected PRRsun in estimating the ɛsun for different biomes.

The determination of interplanetary magnetic field polarities around sector boundaries using E greater than 2 keV electrons

NASA Technical Reports Server (NTRS)

Kahler, S.; Lin, R. P.

1994-01-01

The determination of the polarities of interplanetary magnetic fields (whether the field direction is outward from or inward toward the sun) has been based on a comparison of observed field directions with the nominal Parker spiral angle. These polarities can be mapped back to the solar source field polarities. This technique fails when field directions deviate substantially from the Parker angle or when fields are substantially kinked. We introduce a simple new technique to determine the polarities of interplanetary fields using E greater than 2 keV interplanetary electrons which stream along field lines away from the sun. Those electrons usually show distinct unidirectional pitch-angle anisotropies either parallel or anti-parallel to the field. Since the electron flow direction is known to be outward from the sun, the anisotropies parallel to the field indicate outward-pointing, positive-polarity fields, and those anti-parallel indicate inward-pointing, negative-polarity fields. We use data from the UC Berkeley electron experiment on the International Sun Earth Explorer 3 (ISSE-3) spacecraft to compare the field polarities deduced from the electron data, Pe (outward or inward), with the polarities inferred from field directions, Pd, around two sector boundaries in 1979. We show examples of large (greater than 100 deg) changes in azimuthal field direction Phi over short (less than 1 hr) time scales, some with and some without reversals in Pe. The latter cases indicate that such large directional changes can occur in unipolar structures. On the other hand, we found an example of a change in Pe during which the rotation in Phi was less than 30 deg, indicating polarity changes in nearly unidirectional structures. The field directions are poor guides to the polarities in these cases.

Hi, Hokusai!

NASA Image and Video Library

2017-12-08

This dramatic image features Hokusai in the foreground, famous for its extensive set of rays, some of which extend for over a thousand kilometers across Mercury's surface. The extensive, bright rays indicate that Hokusai is one of the youngest large craters on Mercury. Check out previously featured images to see high-resolution details of its central peaks, rim and ejecta blanket, and impact melt on its floor. This image was acquired as part of MDIS's high-incidence-angle base map. The high-incidence-angle base map complements the surface morphology base map of MESSENGER's primary mission that was acquired under generally more moderate incidence angles. High incidence angles, achieved when the Sun is near the horizon, result in long shadows that accentuate the small-scale topography of geologic features. The high-incidence-angle base map was acquired with an average resolution of 200 meters/pixel. The MESSENGER spacecraft is the first ever to orbit the planet Mercury, and the spacecraft's seven scientific instruments and radio science investigation are unraveling the history and evolution of the Solar System's innermost planet. During the first two years of orbital operations, MESSENGER acquired over 150,000 images and extensive other data sets. MESSENGER is capable of continuing orbital operations until early 2015. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Angular dependance of spectral reflection for different materials

NASA Astrophysics Data System (ADS)

Kiefer, Pascal M.

2017-10-01

Parameters like the sun angle as well as the measurement angle mostly are not taken into account when simulating because their influence on the reflectivity is weak. Therefore the impact of a changing measurement and illumination angle on the reflectivity is investigated. Furthermore the impact of humidity and chlorophyll in the scenery is studied by analyzing reflectance spectra of different vegetative background areas. It is shown that the measurement as well as the illumination angle has an important influence on the absolute reflection values which raises the importance of measurements of the bidirectional reflectance distribution function (BRDF).

Dark matter at DeepCore and IceCube

NASA Astrophysics Data System (ADS)

Barger, V.; Gao, Y.; Marfatia, D.

2011-03-01

With the augmentation of IceCube by DeepCore, the prospect for detecting dark matter annihilation in the Sun is much improved. To complement this experimental development, we provide a thorough template analysis of the particle physics issues that are necessary to precisely interpret the data. Our study is about nitty-gritty and is intended as a framework for detailed work on a variety of dark matter candidates. To accurately predict the source neutrino spectrum, we account for spin-correlations of the final state particles and the helicity-dependence of their decays, and absorption effects at production. We fully treat the propagation of neutrinos through the Sun, including neutrino oscillations, energy losses and tau regeneration. We simulate the survival probability of muons produced in the Earth by using the Muon Monte Carlo program, reproduce the published IceCube effective area, and update the parameters in the differential equation that approximates muon energy losses. To evaluate the zenith-angle dependent atmospheric background event rate, we track the Sun and determine the time it spends at each zenith-angle. Throughout, we employ neutralino dark matter as our example.

Apollo 8 Mission image,Target of Opportunity (T/O) 10

NASA Image and Video Library

1968-12-21

Apollo 8,Moon,Target of Opportunity (T/O) 10, Various targets. Latitude 18 degrees South,Longitude 163.50 degrees West. Camera Tilt Mode: High Oblique. Direction: South. Sun Angle 12 degrees. Original Film Magazine was labeled E. Camera Data: 70mm Hasselblad; F-Stop: F-5.6; Shutter Speed: 1/250 second. Film Type: Kodak SO-3400 Black and White,ASA 40. Other Photographic Coverage: Lunar Orbiter 1 (LO I) S-3. Flight Date: December 21-27,1968.

Geometrical Model of Solar Radiation Pressure Based on High-Performing Galileo Clocks - First Geometrical Mapping of the Yarkowsky effect

NASA Astrophysics Data System (ADS)

Svehla, Drazen; Rothacher, Markus; Hugentobler, Urs; Steigenberger, Peter; Ziebart, Marek

2014-05-01

Solar radiation pressure is the main source of errors in the precise orbit determination of GNSS satellites. All deficiencies in the modeling of Solar radiation pressure map into estimated terrestrial reference frame parameters as well as into derived gravity field coefficients and altimetry results when LEO orbits are determined using GPS. Here we introduce a new approach to geometrically map radial orbit perturbations of GNSS satellites using highly-performing clocks on board the first Galileo satellites. Only a linear model (time bias and time drift) needs to be removed from the estimated clock parameters and the remaining clock residuals map all radial orbit perturbations along the orbit. With the independent SLR measurements, we show that a Galileo clock is stable enough to map radial orbit perturbations continuously along the orbit with a negative sign in comparison to SLR residuals. Agreement between the SLR residuals and the clock residuals is at the 1 cm RMS for an orbit arc of 24 h. Looking at the clock parameters determined along one orbit revolution over a period of one year, we show that the so-called SLR bias in Galileo and GPS orbits can be explained by the translation of the determined orbit in the orbital plane towards the Sun. This orbit translation is due to thermal re-radiation and not accounting for the Sun elevation in the parameterization of the estimated Solar radiation pressure parameters. SLR ranging to GNSS satellites takes place typically at night, e.g. between 6 pm and 6 am local time when the Sun is in opposition to the satellite. Therefore, SLR observes only one part of the GNSS orbit with a negative radial orbit error that is mapped as an artificial bias in SLR observables. The Galileo clocks clearly show orbit translation for all Sun elevations: the radial orbit error is positive when the Sun is in conjuction (orbit noon) and negative when the Sun is in opposition (orbit midnight). The magnitude of this artificial negative SLR bias depends on the orbit quality and should rather be called GNSS orbit bias instead of SLR bias. When LEO satellite orbits are estimated using GPS, this GPS orbit bias is mapped into the antenna phase center. All LEO satellites, such as CHAMP, GRACE and JASON-1/2, need an adjustment of the radial antenna phase center offset. GNSS orbit translations towards the Sun in the orbital plane do not only propagate into the estimated LEO orbits, but also into derived gravity field and altimetry products. Geometrical mapping of orbit perturbations using an on board GNSS clock is a new technique to monitor orbit perturbations along the orbit and was successfully applied in the modeling of Solar radiation pressure. We show that CODE Solar radiation pressure parameterization lacks dependency with the Sun's elevation, i.e. elongation angle (rotation of Solar arrays), especially at low Sun elevations (eclipses). Parameterisation with the Sun elongation angle is used in the so-called T30 model (ROCK-model) that includes thermal re-radiation. A preliminary version of Solar radiation pressure for the first five Galileo and the GPS-36 satellite is based on 2×180 days of the MGEX Campaign. We show that Galileo clocks map the Yarkowsky effect along the orbit, i.e. the lag between the Sun's illumination and thermal re-radiation. We present the first geometrical mapping of anisotropic thermal emission of absorbed sunlight of an illuminated satellite. In this way, the effects of Solar radiation pressure can be modelled with only two paramaters for all Sun elevations.

Autonomous navigation accuracy using simulated horizon sensor and sun sensor observations

NASA Technical Reports Server (NTRS)

Pease, G. E.; Hendrickson, H. T.

1980-01-01

A relatively simple autonomous system which would use horizon crossing indicators, a sun sensor, a quartz oscillator, and a microprogrammed computer is discussed. The sensor combination is required only to effectively measure the angle between the centers of the Earth and the Sun. Simulations for a particular orbit indicate that 2 km r.m.s. orbit determination uncertainties may be expected from a system with 0.06 deg measurement uncertainty. A key finding is that knowledge of the satellite orbit plane orientation can be maintained to this level because of the annual motion of the Sun and the predictable effects of Earth oblateness. The basic system described can be updated periodically by transits of the Moon through the IR horizon crossing indicator fields of view.

A Detection of the Same Hot Plasma in the Corona: During a CME and Later at Ulysses

NASA Technical Reports Server (NTRS)

Suess, S. T.; Poletto, G.

2004-01-01

We show direct evidence for the same very hot plasma being detected remotely from SOHO in the corona and subsequently, at Ulysses in the solar wind. This is, to our knowledge, the first time that such an unambiguous identification has been made in the case of hot plasma. This detection complements studies correlating other plasma and field properties observed to the properties measured at the source in the corona. This observation takes advantage of a SOHO-Sun-Ulysses quadrature, during which the Sun-Ulysses included angle is $90^\\circ$ and it is possible to observe with Ulysses instruments the same plasma that has previously been remotely observed with SOHO instruments in the corona on the limb of the Sun. The identification builds on an existing base of separate SOHO and interplanetary detections of hot plasma. SOHO/UVCS has found evidence for very hot coronal plasma in current sheets in the aftermath of CMEs in the [Fe XVIII] $\\lambda$ \\AA\\ line, implying a temperature on the order of $6\\times 10(exp 6)$ K. This temperature is unusually high even for active regions, but is compatible with the high temperature predicted in current sheets. In the solar wind, ACE data from early 1998 to middle 2000 revealed high frozen-in Fe charge state in many cases to be present in interplanetary plasma.

Celestial polarization patterns sufficient for Viking navigation with the naked eye: detectability of Haidinger's brushes on the sky versus meteorological conditions

PubMed Central

Takács, Péter; Kretzer, Balázs; Szilasi, Szilvia; Száz, Dénes; Farkas, Alexandra; Barta, András

2017-01-01

If a human looks at the clear blue sky from which light with high enough degree of polarization d originates, an 8-shaped bowtie-like figure, the yellow Haidinger's brush can be perceived, the long axis of which points towards the sun. A band of high d arcs across the sky at 90° from the sun. A person can pick two points on that band, observe the yellow brushes and triangulate the position of the sun based on the orientation of the two observed brushes. This method has been suggested to have been used on the open sea by Viking navigators to determine the position of the invisible sun occluded by cloud or fog. Furthermore, Haidinger's brushes can also be used to locate the sun when it is below the horizon or occluded by objects on the horizon. To determine the position of the sun using the celestial polarization pattern, the d of the portion of the sky used must be greater than the viewer's degree of polarization threshold d* for perception of Haidinger's brushes. We studied under which sky conditions the prerequisite d > d* is satisfied. Using full-sky imaging polarimetry, we measured the d-pattern of skylight in the blue (450 nm) spectral range for 1296 different meteorological conditions with different solar elevation angles θ and per cent cloud cover ρ. From the measured d-patterns of a given sky we determined the proportion P of the sky for which d > d*. We obtained that P is the largest at low solar elevations θ ≈ 0° and under totally or nearly clear skies with cloud coverage ρ = 0%, when the sun's position is already easily determined. If the sun is below the horizon (−5° ≤ θ < 0°) during twilight, P = 76.17 ± 4.18% for dmin∗=23% under clear sky conditions. Consequently, the sky-polarimetric Viking navigation based on Haidinger's brushes is most useful after sunset and prior to sunrise, when the sun is not visible and large sky regions are bright, clear and polarized enough for perception of Haidinger's brushes. PMID:28386426

Celestial polarization patterns sufficient for Viking navigation with the naked eye: detectability of Haidinger's brushes on the sky versus meteorological conditions.

PubMed

Horváth, Gábor; Takács, Péter; Kretzer, Balázs; Szilasi, Szilvia; Száz, Dénes; Farkas, Alexandra; Barta, András

2017-02-01

If a human looks at the clear blue sky from which light with high enough degree of polarization d originates, an 8-shaped bowtie-like figure, the yellow Haidinger's brush can be perceived, the long axis of which points towards the sun. A band of high d arcs across the sky at 90° from the sun. A person can pick two points on that band, observe the yellow brushes and triangulate the position of the sun based on the orientation of the two observed brushes. This method has been suggested to have been used on the open sea by Viking navigators to determine the position of the invisible sun occluded by cloud or fog. Furthermore, Haidinger's brushes can also be used to locate the sun when it is below the horizon or occluded by objects on the horizon. To determine the position of the sun using the celestial polarization pattern, the d of the portion of the sky used must be greater than the viewer's degree of polarization threshold d * for perception of Haidinger's brushes. We studied under which sky conditions the prerequisite d  >  d * is satisfied. Using full-sky imaging polarimetry, we measured the d -pattern of skylight in the blue (450 nm) spectral range for 1296 different meteorological conditions with different solar elevation angles θ and per cent cloud cover ρ . From the measured d -patterns of a given sky we determined the proportion P of the sky for which d  >  d *. We obtained that P is the largest at low solar elevations θ  ≈ 0° and under totally or nearly clear skies with cloud coverage ρ  = 0%, when the sun's position is already easily determined. If the sun is below the horizon (-5° ≤  θ  < 0°) during twilight, P  = 76.17 ± 4.18% for [Formula: see text] under clear sky conditions. Consequently, the sky-polarimetric Viking navigation based on Haidinger's brushes is most useful after sunset and prior to sunrise, when the sun is not visible and large sky regions are bright, clear and polarized enough for perception of Haidinger's brushes.

Two Fixed, Evacuated, Glass, Solar Collectors Using Nonimaging Concentration

NASA Astrophysics Data System (ADS)

Garrison, John D.; Winston, Roland; O'Gallagher, Joseph; Ford, Gary

1984-01-01

Two fixed, evacuated, glass solar thermal collectors have been designed. The incorporation of nonimaging concentration, selective absorption and vacuum insulation into their design is essential for obtaining high efficiency through low heat loss, while operating at high temperatures. Nonimaging, approximately ideal concentration with wide acceptance angle permits solar radiation collection without tracking the sun, and insures collection of much of the diffuse radiation. It also minimizes the area of the absorbing surface, thereby reducing the radiation heat loss. Functional integration, where different parts of these two collectors serve more than one function, is also important in achieving high efficiency, and it reduces cost.

Solar Cycle Variability Induced by Tilt Angle Scatter in a Babcock-Leighton Solar Dynamo Model

NASA Astrophysics Data System (ADS)

Karak, Bidya Binay; Miesch, Mark

2017-09-01

We present results from a three-dimensional Babcock-Leighton (BL) dynamo model that is sustained by the emergence and dispersal of bipolar magnetic regions (BMRs). On average, each BMR has a systematic tilt given by Joy’s law. Randomness and nonlinearity in the BMR emergence of our model produce variable magnetic cycles. However, when we allow for a random scatter in the tilt angle to mimic the observed departures from Joy’s law, we find more variability in the magnetic cycles. We find that the observed standard deviation in Joy’s law of {σ }δ =15^\\circ produces a variability comparable to the observed solar cycle variability of ˜32%, as quantified by the sunspot number maxima between 1755 and 2008. We also find that tilt angle scatter can promote grand minima and grand maxima. The time spent in grand minima for {σ }δ =15^\\circ is somewhat less than that inferred for the Sun from cosmogenic isotopes (about 9% compared to 17%). However, when we double the tilt scatter to {σ }δ =30^\\circ , the simulation statistics are comparable to the Sun (˜18% of the time in grand minima and ˜10% in grand maxima). Though the BL mechanism is the only source of poloidal field, we find that our simulations always maintain magnetic cycles even at large fluctuations in the tilt angle. We also demonstrate that tilt quenching is a viable and efficient mechanism for dynamo saturation; a suppression of the tilt by only 1°-2° is sufficient to limit the dynamo growth. Thus, any potential observational signatures of tilt quenching in the Sun may be subtle.

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

Liu, Ying D.; Luhmann, Janet G.; Moestl, Christian

We investigate how coronal mass ejections (CMEs) propagate through, and interact with, the inner heliosphere between the Sun and Earth, a key question in CME research and space weather forecasting. CME Sun-to-Earth kinematics are constrained by combining wide-angle heliospheric imaging observations, interplanetary radio type II bursts, and in situ measurements from multiple vantage points. We select three events for this study, the 2012 January 19, 23, and March 7 CMEs. Different from previous event studies, this work attempts to create a general picture for CME Sun-to-Earth propagation and compare different techniques for determining CME interplanetary kinematics. Key results are obtainedmore » concerning CME Sun-to-Earth propagation: (1) the Sun-to-Earth propagation of fast CMEs can be approximately formulated into three phases: an impulsive acceleration, then a rapid deceleration, and finally a nearly constant speed propagation (or gradual deceleration); (2) the CMEs studied here are still accelerating even after the flare maximum, so energy must be continuously fed into the CME even after the time of the maximum heating and radiation has elapsed in the corona; (3) the rapid deceleration, presumably due to interactions with the ambient medium, mainly occurs over a relatively short timescale following the acceleration phase; and (4) CME-CME interactions seem a common phenomenon close to solar maximum. Our comparison between different techniques (and data sets) has important implications for CME observations and their interpretations: (1) for the current cases, triangulation assuming a compact CME geometry is more reliable than triangulation assuming a spherical front attached to the Sun for distances below 50-70 solar radii from the Sun, but beyond about 100 solar radii we would trust the latter more; (2) a proper treatment of CME geometry must be performed in determining CME Sun-to-Earth kinematics, especially when the CME propagation direction is far away from the observer; and (3) our approach to comparing wide-angle heliospheric imaging observations with interplanetary radio type II bursts provides a novel tool in investigating CME propagation characteristics. Future CME observations and space weather forecasting are discussed based on these results.« less

Sand dune ridge alignment effects on surface BRF over the Libya-4 CEOS calibration site.

PubMed

Govaerts, Yves M

2015-02-03

The Libya-4 desert area, located in the Great Sand Sea, is one of the most important bright desert CEOS pseudo-invariant calibration sites by its size and radiometric stability. This site is intensively used for radiometer drift monitoring, sensor intercalibration and as an absolute calibration reference based on simulated radiances traceable to the SI standard. The Libya-4 morphology is composed of oriented sand dunes shaped by dominant winds. The effects of sand dune spatial organization on the surface bidirectional reflectance factor is analyzed in this paper using Raytran, a 3D radiative transfer model. The topography is characterized with the 30 m resolution ASTER digital elevation model. Four different regions-of-interest sizes, ranging from 10 km up to 100 km, are analyzed. Results show that sand dunes generate more backscattering than forward scattering at the surface. The mean surface reflectance averaged over different viewing and illumination angles is pretty much independent of the size of the selected area, though the standard deviation differs. Sun azimuth position has an effect on the surface reflectance field, which is more pronounced for high Sun zenith angles. Such 3D azimuthal effects should be taken into account to decrease the simulated radiance uncertainty over Libya-4 below 3% for wavelengths larger than 600 nm.

Tethys the Spy

NASA Image and Video Library

2014-12-15

Tethys appears to be peeking out from behind Rhea, watching the watcher. Scientists believe that Tethys' surprisingly high albedo is due to the water ice jets emerging from its neighbor, Enceladus. The fresh water ice becomes the E ring and can eventually arrive at Tethys, giving it a fresh surface layer of clean ice. Lit terrain seen here is on the anti-Saturn side of Rhea. North on Rhea is up. The image was taken in red light with the Cassini spacecraft narrow-angle camera on April 20, 2012. The view was obtained at a distance of approximately 1.1 million miles (1.8 million kilometers) from Rhea and at a Sun-Rhea-spacecraft, or phase, angle of 59 degrees. Image scale is 7 miles (11 kilometers) per pixel. http://photojournal.jpl.nasa.gov/catalog/PIA18293

Area utilization efficiency of a sloping heliostat system for solar concentration.

PubMed

Wei, L Y

1983-02-15

Area utilization efficiency (AUE) is formulated for a sloping heliostat system facing any direction. The effects of slope shading, incidence factor, sun shading, and tower blocking by the mirrors are all taken into account. Our results show that annually averaged AUEs calculated for heliostat systems (1) increase with tower height at low slope angles but less rapidly at high slopes, (2) increase monotonically with slope angle and saturate at large slopes for systems facing due south, (3) reach a maximum at a certain slope for systems facing other directions than due south, and (4) drop sharply at slopes greater than a certain value for systems facing due east or west due to slope shading effect. The results are useful for solar energy collection on nonflat terrains.

Shadows on Ice

NASA Image and Video Library

2007-01-17

Canyons and mountain peaks snake along the terminator on the crater-covered, icy moon Dione. With the Sun at a low angle on their local horizon, the line of mountain ridges above center casts shadows toward the east

Efficient Solar Concentrators: Affordable Energy from Water and Sunlight

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

None

2010-01-01

Broad Funding Opportunity Announcement Project: Teledyne is developing a liquid prism panel that tracks the position of the sun to help efficiently concentrate its light onto a solar cell to produce power. Typically, solar tracking devices have bulky and expensive mechanical moving parts that require a lot of power and are often unreliable. Teledyne’s liquid prism panel has no bulky and heavy supporting parts—instead it relies on electrowetting. Electrowetting is a process where an electric field is applied to the liquid to control the angle at which it meets the sunlight above and to control the angle of the sunlightmore » to the focusing lensthe more direct the angle to the focusing lens, the more efficiently the light can be concentrated to solar panels and converted into electricity. This allows the prism to be tuned like a radio to track the sun across the sky and steer sunlight into the solar cell without any moving mechanical parts. This process uses very little power and requires no expensive supporting hardware or moving parts, enabling efficient and quiet rooftop operation for integration into buildings.« less

Seasonal skin darkening in Chinese women: the Shanghaiese experience of daily sun protection.

PubMed

Qiu, Huixia; Flament, Frederic; Long, Xiaohui; Wu, Jun; Xu, Mengzhi; Leger, Didier Saint; Meaudre, Helene; Senee, Jerome; Piot, Bertrand; Bazin, Roland

2013-01-01

The facial skin tone of two groups of Chinese women from Shanghai was compared using standard colorimetric space techniques during a 6-month interval between January and July 2011. During the study period, one group of women (n = 40) applied a potent sun-protective cosmetic product daily, while the other group (n = 40) did not use any sun protection. The results, based on images taken using a standardized digital camera coupled to a spectroradiometer, showed that sun protection largely mitigated changes in the components of skin tone, ie, lightness, melanization, and individual typology angle parameters. The skin darkening process appeared to be reduced or prevented in the sun-protected group when compared with the control group. The sun-protected women had participated in an earlier study in 2008, which confirmed that seasonal skin darkening occurs from winter through summer in Shanghaiese women. Comparing the data obtained in the winters of 2008 and 2011, we were able to identify better the impact of 3 years of aging on the components of skin tone. Comparing data between seasons on the same women with (2011 study) and without (2008 study) sun protection highlights the role of the test product in preventing skin darkening.

A Fractured Pole

NASA Image and Video Library

2015-10-15

NASA's Cassini spacecraft zoomed by Saturn's icy moon Enceladus on Oct. 14, 2015, capturing this stunning image of the moon's north pole. A companion view from the wide-angle camera (PIA20010) shows a zoomed out view of the same region for context. Scientists expected the north polar region of Enceladus to be heavily cratered, based on low-resolution images from the Voyager mission, but high-resolution Cassini images show a landscape of stark contrasts. Thin cracks cross over the pole -- the northernmost extent of a global system of such fractures. Before this Cassini flyby, scientists did not know if the fractures extended so far north on Enceladus. North on Enceladus is up. The image was taken in visible green light with the Cassini spacecraft narrow-angle camera. The view was acquired at a distance of approximately 4,000 miles (6,000 kilometers) from Enceladus and at a Sun-Enceladus-spacecraft, or phase, angle of 9 degrees. Image scale is 115 feet (35 meters) per pixel. http://photojournal.jpl.nasa.gov/catalog/PIA19660

Epimetheus Above the Rings

NASA Image and Video Library

2015-11-09

Although Epimetheus appears to be lurking above the rings here, it's actually just an illusion resulting from the viewing angle. In reality, Epimetheus and the rings both orbit in Saturn's equatorial plane. Inner moons and rings orbit very near the equatorial plane of each of the four giant planets in our solar system, but more distant moons can have orbits wildly out of the equatorial plane. It has been theorized that the highly inclined orbits of the outer, distant moons are remnants of the random directions from which they approached the planets they orbit. This view looks toward the unilluminated side of the rings from about -0.3 degrees below the ringplane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on July 26, 2015. The view was obtained at a distance of approximately 500,000 miles (800,000 kilometers) from Epimetheus and at a Sun-Epimetheus-spacecraft, or phase, angle of 62 degrees. Image scale is 3 miles (5 kilometers) per pixel. http://photojournal.jpl.nasa.gov/catalog/PIA18342

Direct computation of orbital sunrise or sunset event parameters

NASA Technical Reports Server (NTRS)

Buglia, J. J.

1986-01-01

An analytical method is developed for determining the geometrical parameters which are needed to describe the viewing angles of the Sun relative to an orbiting spacecraft when the Sun rises or sets with respect to the spacecraft. These equations are rigorous and are frequently used for parametric studies relative to mission planning and for determining instrument parameters. The text is wholly self-contained in that no external reference to ephemerides or other astronomical tables is needed. Equations are presented which allow the computation of Greenwich sidereal time and right ascension and declination of the Sun generally to within a few seconds of arc, or a few tenths of a second in time.

Lissajous Orbit Control for the Deep Space Climate Observatory Sun-Earth L1 Libration Point Mission

NASA Technical Reports Server (NTRS)

Roberts, Craig; Case, Sarah; Reagoso, John

2015-01-01

DSCOVR Lissajous Orbit sized such that orbit track never extends beyond 15 degrees from Earth-Sun line (as seen from Earth). Requiring delta-V maneuvers, control orbit to obey a Solar Exclusion Zone (SEZ) cone of half-angle 4 degrees about the Earth-Sun line. Spacecraft should never be less than 4 degrees from solar center as seen from Earth. Following Lissajous Orbit Insertion (LOI), DSCOVR should be in an opening phase that just skirts the 4-degree SEZ. Maximizes time to the point where a closing Lissajous will require avoidance maneuvers to keep it out of the SEZ. Station keeping maneuvers should take no more than 15 minutes.

Twisting Plasma

NASA Image and Video Library

2016-06-08

A close-up of twisting plasma above the Sun's surface produced a nice display of turbulence by caused combative magnetic forces (June 7-8, 2016) over a day and a half. The plasma does not break away, but just spins and twists the entire period. Images were taken in extreme ultraviolet light. The mass we observed is part of a longer, darkish filament angling down from the upper left of the frame. Filaments are unstable clouds of plasma suspended above the Sun by magnetic forces. http://photojournal.jpl.nasa.gov/catalog/PIA20739

The Solar Twin Planet Search. IV. The Sun as a typical rotator and evidence for a new rotational braking law for Sun-like stars

NASA Astrophysics Data System (ADS)

dos Santos, Leonardo A.; Meléndez, Jorge; do Nascimento, José-Dias; Bedell, Megan; Ramírez, Iván; Bean, Jacob L.; Asplund, Martin; Spina, Lorenzo; Dreizler, Stefan; Alves-Brito, Alan; Casagrande, Luca

2016-08-01

Context. It is still unclear how common the Sun is when compared to other similar stars in regards to some of its physical properties, such as rotation. Considering that gyrochronology relations are widely used today to estimate ages of stars in the main sequence, and that the Sun is used to calibrate it, it is crucial to assess whether these procedures are acceptable. Aims: We analyze the rotational velocities, limited by the unknown rotation axis inclination angle, of an unprecedented large sample of solar twins to study the rotational evolution of Sun-like stars, and assess whether the Sun is a typical rotator. Methods: We used high-resolution (R = 115 000) spectra obtained with the HARPS spectrograph and the 3.6 m telescope at La Silla Observatory. The projected rotational velocities for 81 solar twins were estimated by line profile fitting with synthetic spectra. Macroturbulence velocities were inferred from a prescription that accurately reflects their dependence with effective temperature and luminosity of the stars. Results: Our sample of solar twins include some spectroscopic binaries with enhanced rotational velocities, and we do not find any nonspectroscopic binaries with unusually high rotation velocities. We verified that the Sun does not have a peculiar rotation, but the solar twins exhibit rotational velocities that depart from the Skumanich relation. Conclusions: The Sun is a regular rotator when compared to solar twins with a similar age. Additionally, we obtain a rotational braking law that better describes the stars in our sample (v ∝ t-0.6) in contrast to previous, often-used scalings. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programs 188.C-0265, 183.D-0729, 292.C-5004, 077.C-0364, 072.C-0488, 092.C-0721, 093.C-0409, 183.C-0972, 192.C-0852, 091.C-0936, 089.C-0732, 091.C-0034, 076.C-0155, 185.D-0056, 074.C-0364, 075.C-0332, 089.C-0415, 60.A-9036, 075.C-0202, 192.C-0224, 090.C-0421 and 088.C-0323.Full Table 3 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/592/A156

MESSENGER Reveals Mercury in New Detail

NASA Image and Video Library

2008-01-16

As NASA MESSENGER approached Mercury on January 14, 2008, the spacecraft Narrow-Angle Camera on the Mercury Dual Imaging System MDIS instrument captured this view of the planet rugged, cratered landscape illuminated obliquely by the Sun.

Characterizing a New Surface-Based Shortwave Cloud Retrieval Technique, Based on Transmitted Radiance for Soil and Vegetated Surface Types

NASA Technical Reports Server (NTRS)

Coddington, Odele; Pilewskie, Peter; Schmidt, K. Sebastian; McBride, Patrick J.; Vukicevic, Tomislava

2013-01-01

This paper presents an approach using the GEneralized Nonlinear Retrieval Analysis (GENRA) tool and general inverse theory diagnostics including the maximum likelihood solution and the Shannon information content to investigate the performance of a new spectral technique for the retrieval of cloud optical properties from surface based transmittance measurements. The cumulative retrieval information over broad ranges in cloud optical thickness (tau), droplet effective radius (r(sub e)), and overhead sun angles is quantified under two conditions known to impact transmitted radiation; the variability in land surface albedo and atmospheric water vapor content. Our conclusions are: (1) the retrieved cloud properties are more sensitive to the natural variability in land surface albedo than to water vapor content; (2) the new spectral technique is more accurate (but still imprecise) than a standard approach, in particular for tau between 5 and 60 and r(sub e) less than approximately 20 nm; and (3) the retrieved cloud properties are dependent on sun angle for clouds of tau from 5 to 10 and r(sub e) less than 10 nm, with maximum sensitivity obtained for an overhead sun.

Intra-Minute Cloud Passing Forecasting Based on a Low Cost IoT Sensor-A Solution for Smoothing the Output Power of PV Power Plants.

PubMed

Sukič, Primož; Štumberger, Gorazd

2017-05-13

Clouds moving at a high speed in front of the Sun can cause step changes in the output power of photovoltaic (PV) power plants, which can lead to voltage fluctuations and stability problems in the connected electricity networks. These effects can be reduced effectively by proper short-term cloud passing forecasting and suitable PV power plant output power control. This paper proposes a low-cost Internet of Things (IoT)-based solution for intra-minute cloud passing forecasting. The hardware consists of a Raspberry PI Model B 3 with a WiFi connection and an OmniVision OV5647 sensor with a mounted wide-angle lens, a circular polarizing (CPL) filter and a natural density (ND) filter. The completely new algorithm for cloud passing forecasting uses the green and blue colors in the photo to determine the position of the Sun, to recognize the clouds, and to predict their movement. The image processing is performed in several stages, considering selectively only a small part of the photo relevant to the movement of the clouds in the vicinity of the Sun in the next minute. The proposed algorithm is compact, fast and suitable for implementation on low cost processors with low computation power. The speed of the cloud parts closest to the Sun is used to predict when the clouds will cover the Sun. WiFi communication is used to transmit this data to the PV power plant control system in order to decrease the output power slowly and smoothly.

Intra-Minute Cloud Passing Forecasting Based on a Low Cost IoT Sensor—A Solution for Smoothing the Output Power of PV Power Plants

PubMed Central

Sukič, Primož; Štumberger, Gorazd

2017-01-01

Clouds moving at a high speed in front of the Sun can cause step changes in the output power of photovoltaic (PV) power plants, which can lead to voltage fluctuations and stability problems in the connected electricity networks. These effects can be reduced effectively by proper short-term cloud passing forecasting and suitable PV power plant output power control. This paper proposes a low-cost Internet of Things (IoT)-based solution for intra-minute cloud passing forecasting. The hardware consists of a Raspberry PI Model B 3 with a WiFi connection and an OmniVision OV5647 sensor with a mounted wide-angle lens, a circular polarizing (CPL) filter and a natural density (ND) filter. The completely new algorithm for cloud passing forecasting uses the green and blue colors in the photo to determine the position of the Sun, to recognize the clouds, and to predict their movement. The image processing is performed in several stages, considering selectively only a small part of the photo relevant to the movement of the clouds in the vicinity of the Sun in the next minute. The proposed algorithm is compact, fast and suitable for implementation on low cost processors with low computation power. The speed of the cloud parts closest to the Sun is used to predict when the clouds will cover the Sun. WiFi communication is used to transmit this data to the PV power plant control system in order to decrease the output power slowly and smoothly. PMID:28505078

Modulated solar pressure-based surface shape control of paraboloid space reflectors with an off-axis Sun-line

NASA Astrophysics Data System (ADS)

Liu, Jiafu; McInnes, Colin R.

2018-03-01

This paper considers utilizing solar radiation pressure (SRP) to actively control the surface shape of a reflector consisting of a rigid hoop and slack membrane with embedded reflectivity control devices. The full nonlinear static partial differential governing equations for a reflector with negligible elastic deformations are established for the circumferential, radial and transverse directions respectively, in which the SRP force with ideal/non-perfect models, the centripetal force caused by the rotation of the reflector and the internal stresses are considered. The inverse problem is then formulated by assuming that the required surface shape is known, and then the governing algebraic-differential equations used to determine the required surface reflectivity, together with the internal stresses where are presented accordingly. The validity of the approach is verified by comparing the results in this paper with corresponding published results as benchmarks. The feasible regions of the angular velocity and Sun angle for a paraboloidal reflector with an invariant radius and focal length (case 1), and the achievable focal lengths with a specific angular velocity and Sun angle (case 2) are presented for two SRP models respectively, both by considering the constraints on the reflectivity and internal stresses. It is then found that the feasible region is toward a larger angular velocity and Sun angle when using the non-perfect SRP model, compared with the ideal one in case 1. The angular velocity of the spinning reflector should be within a certain range to make the required reflectivity profiles within a practical range, i.e., [0, 0.88], as indicated from prior NASA solar sail studies. In case 2, it is found that the smallest achievable focal length of the reflector with the non-perfect SRP model is smaller than that with the ideal SRP model. It is also found that the stress level is extremely low for all cases considered and that the typical real material strength available for the reflector is sufficient to withstand these internal stresses.

Sun and Shade leaves, SIF, and Photosynthetic Capacity

NASA Astrophysics Data System (ADS)

Berry, J. A.; Badgley, G.

2016-12-01

Recent advances in retrieval of solar induced chlorophyll fluorescence (SIF) have opened up new possibilities for remote sensing of canopy physiology and structure. To date most of the emphasis has been placed on SIF as an indicator of stress and photosynthetic capacity. However, it is clear that canopy structure can also have an influence. To this point, simulations of SIF in land surface models tend to under predict observed variation in SIF. Also, large, systematic differences in SIF from different canopy types seem to correlate well with the photosynthetic capacity of these canopies. SIF emissions from pampered crops can be several-fold that from evergreen, needle-leaf forests. Yet, these may have similar vegetation indices and absorb a similar fraction of incident PAR. SIF photons produced in a conifer canopy do have a lower probability of escaping its dense, clumped foliage. However, this does not explain the correlated differences in photosynthetic rate and SIF. It is useful, in this regard, to consider the separate contributions of sun and shade leaves to the SIF emitted by a canopy. Sun leaves tend to be displayed to intercept the direct solar beam, and these highly illuminated leaves are often visible from above the canopy. Sun leaves produce more SIF and a large fraction of it escapes. Therefore, the intensity of SIF may be a sensitive indicator of the partitioning of absorbed PAR to sun and shade leaves. Many models account tor the different photosynthetic capacity of sun and shade leaves in calculating canopy responses. However, the fraction of leaves in each category is usually parameterized by an assumed leaf angle distribution (e.g. spherical). In reality, the sun/shade fraction can vary over a wide range, and it has been difficult to measure. SIF and possibly near-IR reflectance of canopies can be used to specify this key parameter with obvious importance to understanding photosynthetic rate.

Chapter 6: CPV Tracking and Trackers

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

Luque-Heredia, Ignacio; Magalhaes, Pedro; Muller, Matthew

2016-04-15

This chapter explains the functional requirements of a concentrator photovoltaic (CPV) sun tracker. It derives the design specifications of a CPV tracker. The chapter presents taxonomy of trackers describing the most common tracking architectures, based on the number of axes, their relative position, and the foundation and placing of tracking drives. It deals with the structural issues related to tracker design, mainly related to structural flexure and its impact on the system's acceptance angle. The chapter analyzes the auto-calibrated sun tracking control, by describing the state of the art and its development background. It explores the sun tracking accuracy measurementmore » with a practical example. The chapter discusses tracker manufacturing and tracker field works. It reviews survey of different types of tracker designs obtained from different manufacturers. Finally, the chapter deals with IEC62817, the technical standard developed for CPV sun trackers.« less

The Effect of atmospheric humidity level to the determination of Islamic Fajr/morning prayer time and twilight appearance

NASA Astrophysics Data System (ADS)

Rohmah, Nihayatur

2016-11-01

Islamic prayer times are based on the astronomical position of the Sun in the sky. One of them is the Fajr prayer. It is marked by some indicators in the morning twilight which is white light spread in the Eastern horizon. However, determining the true time of twilight can be difficult. One of the reasons is the effect of atmospheric humidity to the appearance of morning twilight. The higher the humidity, the redder twilight sky appearance. This paper discusses this effect. It is shown that despite of the same Sun's position, sky color can vary considerably. Observations of various solar dip angle have been made to study this effect. Visibility for different angle can change accordingly. We obtained that the average solar dip for Fajr prayer by morning twilight images was -18°39'29.4".

Detailed real-time infrared radiation simulation applied to the sea surface

NASA Astrophysics Data System (ADS)

Zhang, Xuemin; Wu, Limin; Long, Liang; Zhang, Lisha

2018-01-01

In this paper, the infrared radiation characteristics of sea background have been studied. First, MODTRAN4.0 was used to calculate the transmittance of mid-infrared and far-infrared, and the solar spectral irradiance, the atmospheric and sea surface radiation. Secondly, according to the JONSWAP sea spectrum model, the different sea conditions grid model based on gravity wave theory was generated. The spectral scattering of the sun and the atmospheric background radiation was studied. The total infrared radiation of the sea surface was calculated. Finally, the infrared radiation of a piece of sea surface was mapped to each pixel of the detector, and the infrared radiation is simulated. The conclusion is that solar radiance has a great influence on the infrared radiance. When the detector angle is close to the sun's height angle, there will be bright spots on the sea surface.

Building Shadow Detection from Ghost Imagery

NASA Astrophysics Data System (ADS)

Zhou, G.; Sha, J.; Yue, T.; Wang, Q.; Liu, X.; Huang, S.; Pan, Q.; Wei, J.

2018-05-01

Shadow is one of the basic features of remote sensing image, it expresses a lot of information of the object which is loss or interference, and the removal of shadow is always a difficult problem to remote sensing image processing. In this paper, it is mainly analyzes the characteristics and properties of shadows from the ghost image (traditional orthorectification). The DBM and the interior and exterior orientation elements of the image are used to calculate the zenith angle of sun. Then this paper combines the scope of the architectural shadows which has be determined by the zenith angle of sun with the region growing method to make the detection of architectural shadow areas. This method lays a solid foundation for the shadow of the repair from the ghost image later. It will greatly improve the accuracy of shadow detection from buildings and make it more conducive to solve the problem of urban large-scale aerial imagines.

Diurnal patterns of wheat spectral reflectances and their importance in the assessment of canopy parameters from remotely sensed observations. [Phoenix, Arizona

NASA Technical Reports Server (NTRS)

Pinter, P. J.; Jackson, R. D.; Idso, S. B.; Reginato, R. J. (Principal Investigator)

1982-01-01

Spectral reflectances of Produra wheat were measured at 13 different times of the day at Phoenix, Arizona, during April 1979 using a nadir-oriented hand-held 4-band radiometer which had bandpass characteristics similar to those on LANDSAT satellites. Different Sun altitude and azimuth angles caused significant diurnal changes in radiant return in both visible and near-IR regions of the spectrum and in several vegetation indices derived from them. The magnitude of these changes were related to different canopy architecture, percent cover and green leaf area conditions. Spectral measurements taken at each time period were well correlated with green leaf area index but the nature of the relationship changed significantly with time of day. Thus, a significant bias in the estimation of the green leaf area index from remotely sensed spectral data could occur if sun angles are not properly accounted for.

A Digital Solar Aspect Sensor

NASA Technical Reports Server (NTRS)

Albus, James S.

1961-01-01

The solar aspect sensor described herein performs the analog-to-digital conversion of data optically. To accomplish this, it uses a binary "Gray code" light mask to produce a digital indication, in vehicle-fixed coordinates, of the elevation and azimuth angles of incident light from the sun. This digital solar aspect sensor system, in Explorer X, provided measurements of both elevation and azimuth angles to +/- 2 degrees at a distance of over 140,000 statute miles.

Suggestions for improving the efficiency of ground-based neutron monitors for detecting solar neutrons

NASA Technical Reports Server (NTRS)

Iucci, N.; Parisi, M.; Signorini, C.; Storini, M.; Villoresi, G.

1985-01-01

On the occasion of the June 3, 1982 intense gamma-ray solar flare a significant increase in counting rate due to solar neutrons was observed by the neutron monitors of Junsfraujoch and Lomnicky Stit located at middle latitudes and high altitudes. In spite of a larger detector employed and of the smaller solar zenith angle, the amplitude of the same event observed at Rome was much smaller and the statistical fluctuations of the salactic cosmic ray background higher than the ones registered at the two mountain stations, because of the greater atmospheric depth at which the Rome monitor is located. The effeciency for detecting a solar neutron event by a NM-64 monitor as a function of the Sun zenith angle, atmospheric depth and threshold rigidity of the station was studied.

Sun position calculator (SPC) for Landsat imagery with geodetic latitudes

NASA Astrophysics Data System (ADS)

Seong, Jeong C.

2015-12-01

Landsat imagery comes with sun position information such as azimuth and sun elevation, but they are available only at the center of a scene. To aid in the use of Landsat imagery for various solar radiation applications such as topographic correction, solar power, urban heat island, agriculture, climate and vegetation, it is necessary to calculate the sun position information at every pixel. This research developed a PC application that creates sun position data layers in ArcGIS at every pixel in a Landsat scene. The SPC program is composed of two major routines - converting universal transverse Mercator (UTM) projection coordinates to geographic longitudes and latitudes, and calculating sun position information based on the Meeus' routine. For the latter, an innovative method was also implemented to account for the Earth's flattening on an ellipsoid. The Meeus routine implemented in this research showed about 0.2‧ of mean absolute difference from the National Renewable Energy Laboratory (NREL) Solar Position Algorithm (SPA) routine when solar zenith and azimuth angles were tested with every 30 min data at four city locations (Fairbanks, Atlanta, Sydney and Rio Grande) on June 30, 2014. The Meeus routine was about ten times faster than the SPA routine. Professionals who need the Sun's position information for Landsat imagery will benefit from the SPC application.

Relative Positions of Distant Spacecraft

NASA Image and Video Library

2011-04-29

This graphic shows the relative positions of NASA most distant spacecraft in early 2011, looking at the solar system from the side. Voyager 1 is the most distant spacecraft, 10.9 billion miles away from the sun at a northward angle.

Effect of the atmosphere on the color coordinates of sunlit surfaces

NASA Astrophysics Data System (ADS)

Willers, Cornelius J.; Viljoen, Johan W.

2016-02-01

Aerosol attenuation in the atmosphere has a relatively weak spectral variation compared to molecular absorption. However, the solar spectral irradiance differs considerably for the sun at high zenith angles versus the sun at low zenith angles. The perceived color of a sunlit object depends on the object's spectral reflectivity as well as the irradiance spectrum. The color coordinates of the sunlit object, hence also the color balance in a scene, shift with changes in the solar zenith angle. The work reported here does not claim accurate color measurement. With proper calibration mobile phones may provide reasonably accurate color measurement, but the mobile phones used for taking these pictures and videos are not scientific instruments and were not calibrated. The focus here is on the relative shift of the observed colors, rather than absolute color. The work in this paper entails the theoretical analysis of color coordinates of surfaces and how they change for different colored surfaces. Then follows three separate investigations: (1) Analysis of a number of detailed atmospheric radiative transfer code (Modtran) runs to show from the theory how color coordinates should change. (2) Analysis of a still image showing how the colors of two sample surfaces vary between sunlit and shaded areas. (3) Time lapse video recordings showing how the color coordinates of a few surfaces change as a function of time of day. Both the theoretical and experimental work shows distinct shifts in color as function of atmospheric conditions. The Modtran simulations demonstrate the effect from clear atmospheric conditions (no aerosol) to low visibility conditions (5 km visibility). Even under moderate atmospheric conditions the effect was surprisingly large. The experimental work indicated significant shifts during the diurnal cycle.

Wild 2 Close Look

NASA Technical Reports Server (NTRS)

2004-01-01

[figure removed for brevity, see original site] Figure 1

This image shows the comet Wild 2, which NASA's Stardust spacecraft flew by on Jan. 2, 2004. This image is the closest short exposure of the comet, taken at an11.4-degree phase angle, the angle between the camera, comet and the Sun. The listed names on the diagram (see Figure 1) are those used by the Stardust team to identify features. 'Basin' does not imply an impact origin.

CallFUSE Version 3: A Data Reduction Pipeline for the Far Ultraviolet Spectroscopic Explorer

DTIC Science & Technology

2007-05-01

Earth orbit with an inclination of 25 to the equator and an approximately 100 minute orbital period. Data obtained with the instrument are reduced...throughout the mis- sion reveal that the gratings’ orbital motion depends on three parameters: beta angle (the angle between the target and the anti- Sun ...University, Bal- timore, MD; wvd@pha.jhu.edu. 3 Space Telescope Science Institute, ESS/SSG, Baltimore, MD. 4 Current address: Earth Orientation Department

The hot spot of vegetation canopies

NASA Technical Reports Server (NTRS)

Myneni, Ranga B.; Kanemasu, Edward T.

1988-01-01

A conventional radiometer is used to identify the hot spot (the peak in reflected radiation in the retrosolar direction) of vegetation. A multiwavelength-band radiometer collected radiances on fully grown dense wheat and maize canopies on several clear sunny days. It is noted that the hot spot is difficult to detect in the near IR wavelengths because the shadows are much darker. In general, the retrosolar brightness is found to be higher for smaller sun polar angles than for larger angles.

[The Effect of Observation Geometry on Polarized Skylight Spectrum].

PubMed

Zhang, Ren-bin; Wang, Ling-mei; Gao, Jun; Wang, Chi

2015-03-01

Study on polarized skylight spectral characters while observation geometry changing in different solar zenith angles (SZA), viewing zenith angles (VZA) or relative azimuth angles (RAA). Simulation calculation of cloudless daylight polarimetric spectrum is realized based on the solver, vector discrete ordinate method, of radiative transfer equation. In the Sun's principal and perpendicular plane, the spectral irradiance data, varying at wavelengths in the range between 0.4 and 3 μm, are calculated to extend the atmospheric polarization spectral information under the conditions: the MODTRAN solar reference spectrur is the only illuminant source; the main influencing factors of polarized radiative transfer include underlying surface albedo, aerosol layers and components, and the absorption of trace gases. Simulation analysis results: (1) While the relative azimuth angle is zero, the magnitude of spectrum U/I is lower than 10(-7) and V/I is negligible, the degree of polarization and the spectrum Q/I are shaped like the letter V or mirror-writing U. (2) In twilight, when the Sun is not in FOV of the detector, the polarization of the daytime sky has two maximum near 0.51 and 2.75 μm, and a minimum near 1.5 μm. For arbitrary observation geometry, the spectral signal of V/I may be ignored. According to observation geometry, choosing different spectral bands or polarized signal will be propitious to targets detection.

On the long-period evolution of the sun-synchronous orbits

NASA Astrophysics Data System (ADS)

Kuznetsov, E. D.; Jasim, A. T.

2016-05-01

The dynamic evolution of sun-synchronous orbits at a time interval of 20 years is considered. The numerical motion simulation has been carried out using the Celestial Mechanics software package developed at the Institute of Astronomy of the University of Bern. The dependence of the dynamic evolution on the initial value of the ascending node longitude is examined for two families of sun-synchronous orbits with altitudes of 751 and 1191 km. Variations of the semimajor axis and orbit inclination are obtained depending on the initial value of the ascending node longitude. Recommendations on the selection of orbits, in which spent sun-synchronous satellites can be moved, are formulated. Minimal changes of elements over a time interval of 20 years have been observed for orbits in which at the initial time the angle between the orbit ascending node and the direction of the Sun measured along the equator have been close to 90° or 270°. In this case, the semimajor axis of the orbit is not experiencing secular perturbations arising from the satellite's passage through the Earth's shadow.

Illumination angle and layer thickness influence on the photo current generation in organic solar cells: A combined simulative and experimental study

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

Mescher, Jan, E-mail: jan.mescher@kit.edu; Mertens, Adrian; Egel, Amos

2015-07-15

In most future organic photovoltaic applications, such as fixed roof installations, facade or clothing integration, the solar cells will face the sun under varying angles. By a combined simulative and experimental study, we investigate the mutual interdependencies of the angle of light incidence, the absorber layer thickness and the photon harvesting efficiency within a typical organic photovoltaic device. For thin absorber layers, we find a steady decrease of the effective photocurrent towards increasing angles. For 90-140 nm thick absorber layers, however, we observe an effective photocurrent enhancement, exhibiting a maximum yield at angles of incidence of about 50°. Both effectsmore » mainly originate from the angle-dependent spatial broadening of the optical interference pattern inside the solar cell and a shift of the absorption maximum away from the metal electrode.« less

Illumination angle and layer thickness influence on the photo current generation in organic solar cells: A combined simulative and experimental study

NASA Astrophysics Data System (ADS)

Mescher, Jan; Mertens, Adrian; Egel, Amos; Kettlitz, Siegfried W.; Lemmer, Uli; Colsmann, Alexander

2015-07-01

In most future organic photovoltaic applications, such as fixed roof installations, facade or clothing integration, the solar cells will face the sun under varying angles. By a combined simulative and experimental study, we investigate the mutual interdependencies of the angle of light incidence, the absorber layer thickness and the photon harvesting efficiency within a typical organic photovoltaic device. For thin absorber layers, we find a steady decrease of the effective photocurrent towards increasing angles. For 90-140 nm thick absorber layers, however, we observe an effective photocurrent enhancement, exhibiting a maximum yield at angles of incidence of about 50°. Both effects mainly originate from the angle-dependent spatial broadening of the optical interference pattern inside the solar cell and a shift of the absorption maximum away from the metal electrode.

Navigation by light polarization in clear and turbid waters

PubMed Central

Lerner, Amit; Sabbah, Shai; Erlick, Carynelisa; Shashar, Nadav

2011-01-01

Certain terrestrial animals use sky polarization for navigation. Certain aquatic species have also been shown to orient according to a polarization stimulus, but the correlation between underwater polarization and Sun position and hence the ability to use underwater polarization as a compass for navigation is still under debate. To examine this issue, we use theoretical equations for per cent polarization and electric vector (e-vector) orientation that account for the position of the Sun, refraction at the air–water interface and Rayleigh single scattering. The polarization patterns predicted by these theoretical equations are compared with measurements conducted in clear and semi-turbid coastal sea waters at 2 m and 5 m depth over sea floors of 6 m and 28 m depth. We find that the per cent polarization is correlated with the Sun's elevation only in clear waters. We furthermore find that the maximum value of the e-vector orientation angle equals the angle of refraction only in clear waters, in the horizontal viewing direction, over the deeper sea floor. We conclude that navigation by use of underwater polarization is possible under restricted conditions, i.e. in clear waters, primarily near the horizontal viewing direction, and in locations where the sea floor has limited effects on the light's polarization. PMID:21282170

Aerial photographic water color variations from the James River

NASA Technical Reports Server (NTRS)

Bressette, W. E.

1979-01-01

Photographic flights from 305 meters altitude were made throughout the day of May 17, 1977, over seven water data stations in the James River. The flights resulted in wide-angle, broadband, spectral radiance film exposure data between the wavelengths of 500 to 900 nanometers for sun elevation angles ranging from 37 to 64 deg and variable atmospheric haze conditions. It is shown from densitometer data that: (1) the dominant observed color from James River waters is determined by the optical properties of the total suspended solid load, (2) variability in observed color is produced by a changing solar elevation angle; and (3) the rate at which observed color changes is influenced by both solar elevation angle and atmospheric conditions.

The Sharjah Center for Astronomy and Space Sciences (SCASS 2015): Concept and Resources

NASA Astrophysics Data System (ADS)

Naimiy, Hamid M. K. Al

2015-08-01

The Sharjah Center for Astronomy and Space Sciences (SCASS) was launched this year 2015 at the University of Sharjah in the UAE. The center will serve to enrich research in the fields of astronomy and space sciences, promote these fields at all educational levels, and encourage community involvement in these sciences. SCASS consists of:The Planetarium: Contains a semi-circle display screen (18 meters in diameter) installed at an angle of 10° which displays high-definition images using an advanced digital display system consisting of seven (7) high-performance light-display channels. The Planetarium Theatre offers a 200-seat capacity with seats placed at highly calculated angles. The Planetarium also contains an enormous star display (Star Ball - 10 million stars) located in the heart of the celestial dome theatre.The Sharjah Astronomy Observatory: A small optical observatory consisting of a reflector telescope 45 centimeters in diameter to observe the galaxies, stars and planets. Connected to it is a refractor telescope of 20 centimeters in diameter to observe the sun and moon with highly developed astronomical devices, including a digital camera (CCD) and a high-resolution Echelle Spectrograph with auto-giving and remote calibration ports.Astronomy, space and physics educational displays for various age groups include:An advanced space display that allows for viewing the universe during four (4) different time periods as seen by:1) The naked eye; 2) Galileo; 3) Spectrographic technology; and 4) The space technology of today.A space technology display that includes space discoveries since the launching of the first satellite in 1940s until now.The Design Concept for the Center (450,000 sq. meters) was originated by HH Sheikh Sultan bin Mohammed Al Qasimi, Ruler of Sharjah, and depicts the dome as representing the sun in the middle of the center surrounded by planetary bodies in orbit to form the solar system as seen in the sky.

Geoeffectiveness of interplanetary shocks controlled by impact angles: A review

NASA Astrophysics Data System (ADS)

Oliveira, D. M.; Samsonov, A. A.

2018-01-01

The high variability of the Sun's magnetic field is responsible for the generation of perturbations that propagate throughout the heliosphere. Such disturbances often drive interplanetary shocks in front of their leading regions. Strong shocks transfer momentum and energy into the solar wind ahead of them which in turn enhance the solar wind interaction with magnetic fields in its way. Shocks then eventually strike the Earth's magnetosphere and trigger a myriad of geomagnetic effects observed not only by spacecraft in space, but also by magnetometers on the ground. Recently, it has been revealed that shocks can show different geoeffectiveness depending closely on the angle of impact. Generally, frontal shocks are more geoeffective than inclined shocks, even if the former are comparatively weaker than the latter. This review is focused on results obtained from modeling and experimental efforts in the last 15 years. Some theoretical and observational background are also provided.

Thermospheric O I 844.6-nm emission in twilight

NASA Technical Reports Server (NTRS)

Bahsoun-Hamade, F.; Wiens, R. H.; Shepherd, G. G.; Richards, P. G.

1994-01-01

The thermospheric O I 844.6-nm column emission rate was measured over Toronto, a midlatitude station, in the autumn of 1991 using an imaging Fabry-Perot spectrometer. Twilight decay curves were measured on four clear evenings when the solar zenith angle was between 95 degs and 104 degs, giving corresponding column emission rates between 874 R and 130 R at 20 degs elevation angle in the azimuth of the Sun. The expected decay curves were calculated from the field line interhemisperic plasma model assuming only photoelectron impact excitation as the production mechanism with a cross section appropriate to an optically thin atmosphere. The agreement was good when the solar and geomagnetic activity levels were low to moderate, but the emission rate was overestimated during high activity periods. The comparison indicates that the photoelectron impact mechanism with a thin-atmosphere cross section is sufficient to explain the twilight decay of the thermospheric O I 844.6-nm emission.

A geometric model of a V-slit Sun sensor correcting for spacecraft wobble

NASA Technical Reports Server (NTRS)

Mcmartin, W. P.; Gambhir, S. S.

1994-01-01

A V-Slit sun sensor is body-mounted on a spin-stabilized spacecraft. During injection from a parking or transfer orbit to some final orbit, the spacecraft may not be dynamically balanced. This may result in wobble about the spacecraft spin axis as the spin axis may not be aligned with the spacecraft's axis of symmetry. While the widely used models in Spacecraft Attitude Determination and Control, edited by Wertz, correct for separation, elevation, and azimuthal mounting biases, spacecraft wobble is not taken into consideration. A geometric approach is used to develop a method for measurement of the sun angle which corrects for the magnitude and phase of spacecraft wobble. The algorithm was implemented using a set of standard mathematical routines for spherical geometry on a unit sphere.

The Spiral Arm Segments of the Galaxy within 3 kpc from the Sun: A Statistical Approach

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

Griv, Evgeny; Jiang, Ing-Guey; Hou, Li-Gang, E-mail: griv@bgu.ac.il

As can be reasonably expected, upcoming large-scale APOGEE, GAIA, GALAH, LAMOST, and WEAVE stellar spectroscopic surveys will yield rather noisy Galactic distributions of stars. In view of the possibility of employing these surveys, our aim is to present a statistical method to extract information about the spiral structure of the Galaxy from currently available data, and to demonstrate the effectiveness of this method. The model differs from previous works studying how objects are distributed in space in its calculation of the statistical significance of the hypothesis that some of the objects are actually concentrated in a spiral. A statistical analysismore » of the distribution of cold dust clumps within molecular clouds, H ii regions, Cepheid stars, and open clusters in the nearby Galactic disk within 3 kpc from the Sun is carried out. As an application of the method, we obtain distances between the Sun and the centers of the neighboring Sagittarius arm segment, the Orion arm segment in which the Sun is located, and the Perseus arm segment. Pitch angles of the logarithmic spiral segments and their widths are also estimated. The hypothesis that the collected objects accidentally form spirals is refuted with almost 100% statistical confidence. We show that these four independent distributions of young objects lead to essentially the same results. We also demonstrate that our newly deduced values of the mean distances and pitch angles for the segments are not too far from those found recently by Reid et al. using VLBI-based trigonometric parallaxes of massive star-forming regions.« less

Optimization of nonimaging focusing heliostat in dynamic correction of astigmatism for a wide range of incident angles.

PubMed

Chong, Kok-Keong

2010-05-15

To overcome astigmatism has always been a great challenge in designing a heliostat capable of focusing the sunlight on a small receiver throughout the year. In this Letter, a nonimaging focusing heliostat with a dynamic adjustment of facet mirrors in a group manner has been analyzed for optimizing the astigmatic correction in a wide range of incident angles. This what is to the author's knowledge a new heliostat is not only designed to serve the purpose of concentrating sunlight to several hundreds of suns, but also to significantly reduce the variation of the solar flux distribution with the incident angle.

The Sun lightens and enlightens: high noon shadow measurements

NASA Astrophysics Data System (ADS)

Babović, Vukota; Babović, Miloš

2014-11-01

Contemporary physicists and science experts include Eratosthenes’ measurement of the Earth's circumference as one of the most beautiful experiments ever performed in physics. Upon revisiting this famous event in the history of science, we find that some interesting generalizations are possible. On the basis of a rather simple model of the Earth's insolation, we have managed, using some advanced mathematics, to derive a new formula for determining the length of the year, generalized in such a way that it can be used for all planets with sufficiently small eccentricity of the orbit and for all locations with daily sunrises and sunsets. The practical technique that our formula offers is simple to perform, entirely Eratosthenian in spirit, and only requires the angle of the noonday sun to be found on successive days around an equinox. Our results show that this kind of approach to the problem of the Earth's insolation deserves to be included in university courses, especially those which cover astronomy and environmental physics.

Northern Summer on Titan

NASA Image and Video Library

2017-06-14

NASA's Cassini spacecraft sees bright methane clouds drifting in the summer skies of Saturn's moon Titan, along with dark hydrocarbon lakes and seas clustered around the north pole. Compared to earlier in Cassini's mission, most of the surface in the moon's northern high latitudes is now illuminated by the sun. The image was taken with the Cassini spacecraft narrow-angle camera on June 9, 2017, using a spectral filter that preferentially admits wavelengths of near-infrared light centered at 938 nanometers. Cassini obtained the view at a distance of about 315,000 miles (507,000 kilometers) from Titan. https://photojournal.jpl.nasa.gov/catalog/PIA21615

RELATIVE HUMIDITY DATASETS FOR CALCULATING VISIBILITY IMPAIRMENT

EPA Science Inventory

The EPA's Regional Haze Rule directs that visibility conditions in 156 national parks and wilderness areas should improve during the next sixty years. Since visibility varies with air quality, the contrast between objects, the angle of the sun, and other factors, visibility impa...

Precipitable water vapour content from ESR/SKYNET sun-sky radiometers: validation against GNSS/GPS and AERONET over three different sites in Europe

NASA Astrophysics Data System (ADS)

Campanelli, Monica; Mascitelli, Alessandra; Sanò, Paolo; Diémoz, Henri; Estellés, Victor; Federico, Stefano; Iannarelli, Anna Maria; Fratarcangeli, Francesca; Mazzoni, Augusto; Realini, Eugenio; Crespi, Mattia; Bock, Olivier; Martínez-Lozano, Jose A.; Dietrich, Stefano

2018-01-01

The estimation of the precipitable water vapour content (W) with high temporal and spatial resolution is of great interest to both meteorological and climatological studies. Several methodologies based on remote sensing techniques have been recently developed in order to obtain accurate and frequent measurements of this atmospheric parameter. Among them, the relative low cost and easy deployment of sun-sky radiometers, or sun photometers, operating in several international networks, allowed the development of automatic estimations of W from these instruments with high temporal resolution. However, the great problem of this methodology is the estimation of the sun-photometric calibration parameters. The objective of this paper is to validate a new methodology based on the hypothesis that the calibration parameters characterizing the atmospheric transmittance at 940 nm are dependent on vertical profiles of temperature, air pressure and moisture typical of each measurement site. To obtain the calibration parameters some simultaneously seasonal measurements of W, from independent sources, taken over a large range of solar zenith angle and covering a wide range of W, are needed. In this work yearly GNSS/GPS datasets were used for obtaining a table of photometric calibration constants and the methodology was applied and validated in three European ESR-SKYNET network sites, characterized by different atmospheric and climatic conditions: Rome, Valencia and Aosta. Results were validated against the GNSS/GPS and AErosol RObotic NETwork (AERONET) W estimations. In both the validations the agreement was very high, with a percentage RMSD of about 6, 13 and 8 % in the case of GPS intercomparison at Rome, Aosta and Valencia, respectively, and of 8 % in the case of AERONET comparison in Valencia. Analysing the results by W classes, the present methodology was found to clearly improve W estimation at low W content when compared against AERONET in terms of % bias, bringing the agreement with the GPS (considered the reference one) from a % bias of 5.76 to 0.52.

Maximum-likelihood-based extended-source spatial acquisition and tracking for planetary optical communications

NASA Astrophysics Data System (ADS)

Tsou, Haiping; Yan, Tsun-Yee

1999-04-01

This paper describes an extended-source spatial acquisition and tracking scheme for planetary optical communications. This scheme uses the Sun-lit Earth image as the beacon signal, which can be computed according to the current Sun-Earth-Probe angle from a pre-stored Earth image or a received snapshot taken by other Earth-orbiting satellite. Onboard the spacecraft, the reference image is correlated in the transform domain with the received image obtained from a detector array, which is assumed to have each of its pixels corrupted by an independent additive white Gaussian noise. The coordinate of the ground station is acquired and tracked, respectively, by an open-loop acquisition algorithm and a closed-loop tracking algorithm derived from the maximum likelihood criterion. As shown in the paper, the optimal spatial acquisition requires solving two nonlinear equations, or iteratively solving their linearized variants, to estimate the coordinate when translation in the relative positions of onboard and ground transceivers is considered. Similar assumption of linearization leads to the closed-loop spatial tracking algorithm in which the loop feedback signals can be derived from the weighted transform-domain correlation. Numerical results using a sample Sun-lit Earth image demonstrate that sub-pixel resolutions can be achieved by this scheme in a high disturbance environment.

The Superior Lambert Algorithm

NASA Astrophysics Data System (ADS)

der, G.

2011-09-01

Lambert algorithms are used extensively for initial orbit determination, mission planning, space debris correlation, and missile targeting, just to name a few applications. Due to the significance of the Lambert problem in Astrodynamics, Gauss, Battin, Godal, Lancaster, Gooding, Sun and many others (References 1 to 15) have provided numerous formulations leading to various analytic solutions and iterative methods. Most Lambert algorithms and their computer programs can only work within one revolution, break down or converge slowly when the transfer angle is near zero or 180 degrees, and their multi-revolution limitations are either ignored or barely addressed. Despite claims of robustness, many Lambert algorithms fail without notice, and the users seldom have a clue why. The DerAstrodynamics lambert2 algorithm, which is based on the analytic solution formulated by Sun, works for any number of revolutions and converges rapidly at any transfer angle. It provides significant capability enhancements over every other Lambert algorithm in use today. These include improved speed, accuracy, robustness, and multirevolution capabilities as well as implementation simplicity. Additionally, the lambert2 algorithm provides a powerful tool for solving the angles-only problem without artificial singularities (pointed out by Gooding in Reference 16), which involves 3 lines of sight captured by optical sensors, or systems such as the Air Force Space Surveillance System (AFSSS). The analytic solution is derived from the extended Godal’s time equation by Sun, while the iterative method of solution is that of Laguerre, modified for robustness. The Keplerian solution of a Lambert algorithm can be extended to include the non-Keplerian terms of the Vinti algorithm via a simple targeting technique (References 17 to 19). Accurate analytic non-Keplerian trajectories can be predicted for satellites and ballistic missiles, while performing at least 100 times faster in speed than most numerical integration methods.

sin2 θ W estimate and bounds on nonstandard interactions at source and detector in the solar neutrino low-energy regime

NASA Astrophysics Data System (ADS)

Khan, Amir N.; McKay, Douglas W.

2017-07-01

We explore the implications of the Borexino experiment's real time measurements of the lowest energy part of the neutrino spectrum from the primary pp fusion process up to 0.420 MeV through the 7Be decay at 0.862 MeV to the pep reaction at 1.44 MeV. We exploit the fact that at such low energies, the large mixing angle solution to the Mikheyev-Smirnov-Wolfenstein matter effects in the sun are small for 7Be and pep and negligible for pp. Consequently, the neutrinos produced in the sun change their flavor almost entirely through vacuum oscillations during propagation from the sun's surface and through possible nonstandard interactions acting at the solar source and Borexino detector. We combine the different NSI effects at source and detector in a single framework and use the current Borexino data to bound NSI non-universal and flavor-changing parameters at energies below the reach of reactor neutrino experiments. We also study the implication of the current data for the weak-mixing angle at this "low-energy frontier" data from the Borexino experiment, where it is expected to be slightly larger than its value at the Z mass. We find sin2 θ W = 0.224 ± 0.016, the lowest energy-scale estimate to date. Looking to the future, we use projected sensitivities to solar neutrinos in next generation dedicated solar experiments and direct dark matter detection experiments and find a potential factor five improvement in determination of the weak-mixing angle and up to an order of magnitude improvement in probing the NSI parameters space.

Properties of the smallest solar magnetic elements. I - Facular contrast near sun center

NASA Technical Reports Server (NTRS)

Topka, K. P.; Tarbell, T. D.; Title, A. M.

1992-01-01

Measurements are presented which indicate that the continuum intensity of facular areas in solar active regions, outside sunspots and pores, is less than that of the quiet sun very near disk center. It is shown that the observed continuum intensity of faculae at disk center near 5000 A is nearly 3 percent less than that of the quiet sun. The continuum contrast increases rapidly away from disk center, reaching +2 percent at 45 deg. The zero-crossing point, where the contrast changes sign, occurs at 20-degree heliocentric angle. This is contrary to many earlier observations. The constraint these observations place on the size of flux tubes depends upon the value of the zero-crossing point. It is proposed that most of the flux tubes in solar faculae may be very small, in the range 50-100 km in diameter, and that inclination from local vertical of about 10 deg at the photosphere is common on the sun. Footpoints of opposite polarity tend to tilt toward one another.

Quasi-Sun-Pointing of Spacecraft Using Radiation Pressure

NASA Technical Reports Server (NTRS)

Spilker, Thomas

2003-01-01

A report proposes a method of utilizing solar-radiation pressure to keep the axis of rotation of a small spin-stabilized spacecraft pointed approximately (typically, within an angle of 10 deg to 20 deg) toward the Sun. Axisymmetry is not required. Simple tilted planar vanes would be attached to the outer surface of the body, so that the resulting spacecraft would vaguely resemble a rotary fan, windmill, or propeller. The vanes would be painted black for absorption of Solar radiation. A theoretical analysis based on principles of geometric optics and mechanics has shown that torques produced by Solar-radiation pressure would cause the axis of rotation to precess toward Sun-pointing. The required vane size would be a function of the angular momentum of the spacecraft and the maximum acceptable angular deviation from Sun-pointing. The analysis also shows that the torques produced by the vanes would slowly despin the spacecraft -- an effect that could be counteracted by adding specularly reflecting "spin-up" vanes.

Dynamics of Space Particles and Spacecrafts Passing by the Atmosphere of the Earth

PubMed Central

Prado, Antonio Fernando Bertachini de Almeida; Golebiewska, Justyna

2013-01-01

The present research studies the motion of a particle or a spacecraft that comes from an orbit around the Sun, which can be elliptic or hyperbolic, and that makes a passage close enough to the Earth such that it crosses its atmosphere. The idea is to measure the Sun-particle two-body energy before and after this passage in order to verify its variation as a function of the periapsis distance, angle of approach, and velocity at the periapsis of the particle. The full system is formed by the Sun, the Earth, and the particle or the spacecraft. The Sun and the Earth are in circular orbits around their center of mass and the motion is planar for all the bodies involved. The equations of motion consider the restricted circular planar three-body problem with the addition of the atmospheric drag. The initial conditions of the particle or spacecraft (position and velocity) are given at the periapsis of its trajectory around the Earth. PMID:24396298

Dynamics of space particles and spacecrafts passing by the atmosphere of the Earth.

PubMed

Gomes, Vivian Martins; Prado, Antonio Fernando Bertachini de Almeida; Golebiewska, Justyna

2013-01-01

The present research studies the motion of a particle or a spacecraft that comes from an orbit around the Sun, which can be elliptic or hyperbolic, and that makes a passage close enough to the Earth such that it crosses its atmosphere. The idea is to measure the Sun-particle two-body energy before and after this passage in order to verify its variation as a function of the periapsis distance, angle of approach, and velocity at the periapsis of the particle. The full system is formed by the Sun, the Earth, and the particle or the spacecraft. The Sun and the Earth are in circular orbits around their center of mass and the motion is planar for all the bodies involved. The equations of motion consider the restricted circular planar three-body problem with the addition of the atmospheric drag. The initial conditions of the particle or spacecraft (position and velocity) are given at the periapsis of its trajectory around the Earth.

High Energy Replicated Optics to Explore the Sun: Hard X-Ray Balloon-Borne Telescope

NASA Technical Reports Server (NTRS)

Gaskin, Jessica; Apple, Jeff; StevensonChavis, Katherine; Dietz, Kurt; Holt, Marlon; Koehler, Heather; Lis, Tomasz; O'Connor, Brian; RodriquezOtero, Miguel; Pryor, Jonathan;

High Energy Replicated Optics to Explore the Sun: Hard X-ray balloon-borne telescope

NASA Astrophysics Data System (ADS)

Gaskin, J.; Apple, J.; Chavis, K. S.; Dietz, K.; Holt, M.; Koehler, H.; Lis, T.; O'Connor, B.; Otero, M. R.; Pryor, J.; Ramsey, B.; Rinehart-Dawson, M.; Smith, L.; Sobey, A.; Wilson-Hodge, C.; Christe, S.; Cramer, A.; Edgerton, M.; Rodriguez, M.; Shih, A.; Gregory, D.; Jasper, J.; Bohon, S.

Set to fly in the Fall of 2013 from Ft. Sumner, NM, the High Energy Replicated Optics to Explore the Sun (HEROES) mission is a collaborative effort between the NASA Marshall Space Flight Center and the Goddard Space Flight Center to upgrade an existing payload, the High Energy Replicated Optics (HERO) balloon-borne telescope, to make unique scientific measurements of the Sun and astrophysical targets during the same flight. The HEROES science payload consists of 8 mirror modules, housing a total of 109 grazing-incidence optics. These modules are mounted on a carbon-fiber - and Aluminum optical bench 6 m from a matching array of high pressure xenon gas scintillation proportional counters, which serve as the focal-plane detectors. The HERO gondola utilizes a differential GPS system (backed by a magnetometer) for coarse pointing in the azimuth and a shaft angle encoder plus inclinometer provides the coarse elevation. The HEROES payload will incorporate a new solar aspect system to supplement the existing star camera, for fine pointing during both the day and night. A mechanical shutter will be added to the star camera to protect it during solar observations. HEROES will also implement two novel alignment monitoring system that will measure the alignment between the optical bench and the star camera and between the optics and detectors for improved pointing and post-flight data reconstruction. The overall payload will also be discussed. This mission is funded by the NASA HOPE (Hands On Project Experience) Training Opportunity awarded by the NASA Academy of Program/Project and Engineering Leadership, in partnership with NASA's Science Mission Directorate, Office of the Chief Engineer and Office of the Chief Technologist.

A conjunct near-surface spectroscopy system for fix-angle and multi-angle continuous measurements of canopy reflectance and sun-induced chlorophyll fluorescence

NASA Astrophysics Data System (ADS)

Zhang, Qian; Fan, Yifeng; Zhang, Yongguang; Chou, Shuren; Ju, Weimin; Chen, Jing M.

2016-09-01

An automated spectroscopy system, which is divided into fix-angle and multi-angle subsystems, for collecting simultaneous, continuous and long-term measurements of canopy hyper-spectra in a crop ecosystem is developed. The fix-angle subsystem equips two spectrometers: one is HR2000+ (OceanOptics) covering the spectral range 200-1100 nm with 1.0 nm spectral resolution, and another one is QE65PRO (OceanOptics) providing 0.1 nm spectral resolution within the 730-780 nm spectral range. Both spectrometers connect a cosine-corrected fiber-optic fixed up-looking to collect the down-welling irradiance and a bare fiber-optic to measure the up-welling radiance from the vegetation. An inline fiber-optic shutter FOS-2x2-TTL (OceanOptics) is used to switch between input fibers to collect the signal from either the canopy or sky at one time. QE65PRO is used to permit estimation of vegetation Sun-Induced Fluorescence (SIF) in the O2-A band. The data collection scheme includes optimization of spectrometer integration time to maximize the signal to noise ratio and measurement of instrument dark currency. The multi-angle subsystem, which can help understanding bidirectional reflectance effects, alternatively use HR4000 (OceanOptics) providing 0.1 nm spectral resolution within the 680-800 nm spectral range to measure multi-angle SIF. This subsystem additionally includes a spectrometer Unispec-DC (PPSystems) featuring both up-welling and down-welling channels with 3 nm spectral resolution covering the 300-1100 nm spectral range. Two down-looking fiber-optics are mounted on a rotating device PTU-D46 (FLIR Systems), which can rotate horizontally and vertically at 10° angular step widths. Observations can be used to calculate canopy reflectance, vegetation indices and SIF for monitoring plant physiological processes.

Feasibility and optical performance of one axis three positions sun-tracking polar-axis aligned CPCs for photovoltaic applications

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

Tang, Runsheng; Yu, Yamei

2010-09-15

A new design concept, called one axis three positions sun-tracking polar-axis aligned CPCs (3P-CPCs, in short), was proposed and theoretically studied in this work for photovoltaic applications. The proposed trough-like CPC is oriented in the polar-axis direction, and the aperture is daily adjusted eastward, southward, and westward in the morning, noon and afternoon, respectively, by rotating the CPC trough, to ensure efficient collection of beam radiation nearly all day. To investigate the optical performance of such CPCs, an analytical mathematical procedure is developed to estimate daily and annual solar gain captured by such CPCs based on extraterrestrial radiation and monthlymore » horizontal radiation. Results show that the acceptance half-angle of 3P-CPCs is a unique parameter to determine their optical performance according to extraterrestrial radiation, and the annual solar gain stays constant if the acceptance half-angle, {theta}{sub a}, is less than one third of {omega}{sub 0,min}, the sunset hour angle in the winter solstice, otherwise decreases with the increase of {theta}{sub a}. For 3P-CPCs used in China, the annual solar gain, depending on the climatic conditions in site, decreased with the acceptance half-angle, but such decrease was slow for the case of {theta}{sub a}{<=}{omega}{sub 0,min}/3, indicating that the acceptance half-angle should be less than one third of {omega}{sub 0,min} for maximizing annual energy collection. Compared to fixed east-west aligned CPCs (EW-CPCs) with a yearly optimal acceptance half-angle, the fixed south-facing polar-axis aligned CPCs (1P-CPCs) with the same acceptance half-angle as the EW-CPCs annually collected about 65-74% of that EW-CPCs did, whereas 3P-CPCs annually collected 1.26-1.45 times of that EW-CPCs collected, indicating that 3P-CPCs were more efficient for concentrating solar radiation onto their coupling solar cells. (author)« less

Comet ISON Approaching the Sun [still

NASA Image and Video Library

2013-11-27

This movie from NASA’s STEREO spacecraft's Heliospheric Imager shows Comet ISON, Mercury, Comet Encke and Earth over a five-day period from Nov. 20 to Nov. 25, 2013. The sun sits right of the field of view of this camera. Comet ISON, which will round the sun on Nov. 28, is what's known as a sungrazing comet, due to its close approach. Foreshortening or the angle at which these images were obtained make Earth appear as if it is closer to the sun than Mercury. If you look closely you will also see a dimmer and smaller comet Encke near comet ISON. A comet’s journey through the solar system is perilous and violent. A giant ejection of solar material from the sun could rip its tail off. Before it reaches Mars -- at some 230 million miles away from the sun -- the radiation of the sun begins to boil its water, the first step toward breaking apart. And, if it survives all this, the intense radiation and pressure as it flies near the surface of the sun could destroy it altogether. Even if the comet does not survive, tracking its journey will help scientists understand what the comet is made of, how it reacts to its environment, and what this explains about the origins of the solar system. Closer to the sun, watching how the comet and its tail interact with the vast solar atmosphere can teach scientists more about the sun itself. Image Credit: NASA/STEREO NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

A high precision dual feedback discrete control system designed for satellite trajectory simulator

NASA Astrophysics Data System (ADS)

Liu, Ximin; Liu, Liren; Sun, Jianfeng; Xu, Nan

2005-08-01

Cooperating with the free-space laser communication terminals, the satellite trajectory simulator is used to test the acquisition, pointing, tracking and communicating performances of the terminals. So the satellite trajectory simulator plays an important role in terminal ground test and verification. Using the double-prism, Sun etc in our group designed a satellite trajectory simulator. In this paper, a high precision dual feedback discrete control system designed for the simulator is given and a digital fabrication of the simulator is made correspondingly. In the dual feedback discrete control system, Proportional- Integral controller is used in velocity feedback loop and Proportional- Integral- Derivative controller is used in position feedback loop. In the controller design, simplex method is introduced and an improvement to the method is made. According to the transfer function of the control system in Z domain, the digital fabrication of the simulator is given when it is exposed to mechanism error and moment disturbance. Typically, when the mechanism error is 100urad, the residual standard error of pitching angle, azimuth angle, x-coordinate position and y-coordinate position are 0.49urad, 6.12urad, 4.56urad, 4.09urad respectively. When the moment disturbance is 0.1rad, the residual standard error of pitching angle, azimuth angle, x-coordinate position and y-coordinate position are 0.26urad, 0.22urad, 0.16urad, 0.15urad respectively. The digital fabrication results demonstrate that the dual feedback discrete control system designed for the simulator can achieve the anticipated high precision performance.

The Amateur Scientist.

ERIC Educational Resources Information Center

Walker, Jearl

1985-01-01

Discusses how the sun's reflection from water offers a means for calculating sloped of waves. Experiments using angles of reflection from a tilted mirror are suggested and explained. A method of counterbalancing dominoes in a stack beyond the edge of a table (using Euler's constant) is also described. (DH)

A Look at the Future of Strategic Effectiveness Through the Lens of Airpower History

DTIC Science & Technology

2016-05-01

America’s Secret Air Wars. Washington D.C.: Smithsonian Institution Press. Tzu , Sun . 1971. The Art of War. Translated by Samuel B. Griffith. Oxford...14 Bibliography ... Bibliography 2016. AP, ACSC. Biddle, Tami D. 2015. "Angle-American Strategic

Bending of light in quantum gravity.

PubMed

Bjerrum-Bohr, N E J; Donoghue, John F; Holstein, Barry R; Planté, Ludovic; Vanhove, Pierre

2015-02-13

We consider the scattering of lightlike matter in the presence of a heavy scalar object (such as the Sun or a Schwarzschild black hole). By treating general relativity as an effective field theory we directly compute the nonanalytic components of the one-loop gravitational amplitude for the scattering of massless scalars or photons from an external massive scalar field. These results allow a semiclassical computation of the bending angle for light rays grazing the Sun, including long-range ℏ contributions. We discuss implications of this computation, in particular, the violation of some classical formulations of the equivalence principle.

Solid-dielectric compound parabolic concentrators: on their use with photovoltaic devices.

PubMed

Goodman, N B; Ignatius, R; Wharton, L; Winston, R

1976-10-01

Prototype solid dielectric compound parabolic concentrators have been made and tested. By means of the geometry and refractive properties of a transparent solid they provide a technique for increasing the power output of silicon solar cells exposed to the sun by an amount nearly equal to the increase in effective collecting area. The response is uniform over a large angle which eliminates the necessity of diurnal tracking of the sun. The technique can be applied to the construction of thin panels and has the potential for significantly reducing, their cost per unit area.

Stereo and Solar Cycle 24

NASA Technical Reports Server (NTRS)

Kaise,r Michael L.

2008-01-01

The twin STEREO spacecrafi, launched in October 2006, are in heliocentric orbits near 4 AU with one spacecraft (Ahead) leading Earth in its orbit around the Sun and the other (Behind) trailing Earth. As viewed from the Sun, the STEREO spacecraft are continually separating from one another at about 45 degrees per year with Earth biseding the angle. At present, th@spaser=raft are a bit more than 45 degrees apart, thus they are able to each 'vie@ ground the limb's of the Sun by about 23 degrees, corresponding to about 1.75 days of solar rotation. Both spameraft contain an identical set of instruments including an extreme ultraviolet imager, two white light coronagraphs, tws all-sky imagers, a wide selection of energetic particle detectors, a magnetometer and a radio burst tracker. A snapshot of the real time data is continually broadcast to NOW-managed ground stations and this small stream of data is immediately sent to the STEREO Science Center and converted into useful space weather data within 5 minutes of ground receipt. The resulting images, particle, magnetometer and radio astronomy plots are available at j g i t , : gAs timqe conting ues ijnto . g solar cycle 24, the separation angle becomes 90 degrees in early 2009 and 180 degrees in early 201 1 as the activity heads toward maximum. By the time of solar maximum, STEREO will provide for the first time a view of the entire Sun with the mronagraphs and e*reme ultraviolet instruments. This view wilt allow us to follow the evolution of active regions continuously and also detect new active regions long before they pose a space weather threat to Earth. The in situ instruments will be able to provide about 7 days advanced notice of co-rotating structures in the solar wind. During this same intewal near solar maximum, the wide-angle imagers on STEREB will both be ;able to view EarlCP-dirsted CMEs in their plane-oPsky. When combined with Eat-lhorbiting assets available at that time, it seems solar cycle 24 will mark a great increase in our ability to understand and predict space weather.

Inter-Comparison of MODIS and VIIRS Vegetation Indices Using One-Year Global Data

NASA Astrophysics Data System (ADS)

Miura, T.; Muratsuchi, J.; Obata, K.; Kato, A.; Vargas, M.; Huete, A. R.

2016-12-01

The Visible Infrared Imaging Radiometer Suite (VIIRS) sensor series of the Joint Polar Satellite System program is slated to continue the highly calibrated data stream initiated with the Earth Observing System Moderate Resolution Imaging Spectroradiometer (MODIS) sensors. A number of geophysical products are being/to be produced from VIIRS data, including the "Top-of-the-Atmosphere (TOA)" Normalized Difference Vegetation Index (NDVI), "Top-of-Canopy (TOC)" Enhanced Vegetation Index (EVI), and TOC NDVI. In this study, we cross-compared vegetation indices (VIs) from the first VIIRS sensor aboard the Suomi National Polar-orbiting Partnership satellite with the Aqua MODIS counterparts using one-year global data. This study was aimed at developing a thorough understanding of radiometric compatibility between the two VI datasets across globe, seasons, a range of viewing angle, and land cover types. VIIRS and MODIS VI data of January-December 2015 were obtained at monthly intervals when their orbital tracks coincided. These data were projected and spatially-aggregated into a .0036-degree grid while screening for cloud and aerosol contaminations using their respective quality flags. VIIRS-MODIS observation pairs with near-identical sun-target-view angles were extracted from each of these monthly image pairs for cross-comparison. The four VIs of TOA NDVI, TOC NDVI, TOC EVI, and TOC EVI2 (a two-band version of the EVI) were analyzed. Between MODIS and VIIRS, TOA NDVI, TOC NDVI, and TOC EVI2 had very small overall mean differences (MD) of .014, .013, and .013 VI units, respectively, whereas TOC EVI had a slightly larger overall MD of 0.023 EVI units attributed to the disparate blue bands of the two sensors. These systematic differences were consistent across the one-year period. With respect to sun-target-viewing geometry, MDs were also consistent across the view zenith angle range, but always lower for forward- than backward-viewing geometry. MDs showed large land cover dependencies for TOA NDVI and TOC NDVI, varying 10 folds from .002 for forests to .02 for sparsely-vegetated areas. They were consistent across land cover types for TOC EVI and TOC EVI2. Future studies should address the impact of sun-target-view geometry on corss-sensor VI comparisons.

Measured daylighting potential of a static optical louver system under real sun and sky conditions

DOE PAGES

Konis, Kyle; Lee, Eleanor S.

2015-05-04

Side-by-side comparisons were made over solstice-to-solstice changes in sun and sky conditions between an optical louver system (OLS) and a conventional Venetian blind set at a horizontal slat angle and located inboard of a south-facing, small-area, clerestory window in a full-scale office testbed. Daylight autonomy (DA), window luminance, and ceiling luminance uniformity were used to assess performance. The performance of both systems was found to have significant seasonal variation, where performance under clear sky conditions improved as maximum solar altitude angles transitioned from solstice to equinox. Although the OLS produced fewer hours per day of DA on average than themore » Venetian blind, the OLS never exceeded the designated 2000 cd/m2 threshold for window glare. In contrast, the Venetian blind was found to exceed the visual discomfort threshold over a large fraction of the day during equinox conditions. Notably, these peak periods of visual discomfort occurred during the best periods of daylighting performance. Luminance uniformity was analyzed using calibrated high dynamic range luminance images. Under clear sky conditions, the OLS was found to increase the luminance of the ceiling as well as produce a more uniform distribution. Furthermore, compared to conventional venetian blinds, the static optical sunlight redirecting system studied has the potential to significantly reduce the annual electrical lighting energy demand of a daylit space and improve the quality from the perspective of building occupants by consistently transmitting useful daylight while eliminating window glare.« less

The squint Moon and the witch ball

NASA Astrophysics Data System (ADS)

Berry, M. V.

2015-06-01

A witch ball is a reflecting sphere of glass. Looking into the disk that it subtends, the whole sky can be seen at one glance. This feature can be exploited to see and photograph the squint Moon illusion, in which the direction normal to the illuminated face of the Moon—its ‘attitude vector’—does not appear to point towards the Sun. The images of the Sun and Moon in the disk, the geodesic connecting them, the Moon’s attitude, and the squint angle (distinct from the tilt), can be calculated and simulated, for all celestial configurations and viewing inclinations. The Moon direction antipodal to the Sun, corresponding to full Moon, is a singularity of the attitude vector field, with index +1. The main features of the witch ball images also occur in other ways of imaging the squint Moon.

Sky camera geometric calibration using solar observations

DOE PAGES

Urquhart, Bryan; Kurtz, Ben; Kleissl, Jan

2016-09-05

A camera model and associated automated calibration procedure for stationary daytime sky imaging cameras is presented. The specific modeling and calibration needs are motivated by remotely deployed cameras used to forecast solar power production where cameras point skyward and use 180° fisheye lenses. Sun position in the sky and on the image plane provides a simple and automated approach to calibration; special equipment or calibration patterns are not required. Sun position in the sky is modeled using a solar position algorithm (requiring latitude, longitude, altitude and time as inputs). Sun position on the image plane is detected using a simple image processing algorithm. Themore » performance evaluation focuses on the calibration of a camera employing a fisheye lens with an equisolid angle projection, but the camera model is general enough to treat most fixed focal length, central, dioptric camera systems with a photo objective lens. Calibration errors scale with the noise level of the sun position measurement in the image plane, but the calibration is robust across a large range of noise in the sun position. In conclusion, calibration performance on clear days ranged from 0.94 to 1.24 pixels root mean square error.« less

Electron Heat Flux in Pressure Balance Structures at Ulysses

NASA Technical Reports Server (NTRS)

Yamauchi, Yohei; Suess, Steven T.; Sakurai, Takashi; Whitaker, Ann F. (Technical Monitor)

2001-01-01

Pressure balance structures (PBSs) are a common feature in the high-latitude solar wind near solar minimum. Rom previous studies, PBSs are believed to be remnants of coronal plumes and be related to network activity such as magnetic reconnection in the photosphere. We investigated the magnetic structures of the PBSs, applying a minimum variance analysis to Ulysses/Magnetometer data. At 2001 AGU Spring meeting, we reported that PBSs have structures like current sheets or plasmoids, and suggested that they are associated with network activity at the base of polar plumes. In this paper, we have analyzed high-energy electron data at Ulysses/SWOOPS to see whether bi-directional electron flow exists and confirm the conclusions more precisely. As a result, although most events show a typical flux directed away from the Sun, we have obtained evidence that some PBSs show bi-directional electron flux and others show an isotropic distribution of electron pitch angles. The evidence shows that plasmoids are flowing away from the Sun, changing their flow direction dynamically in a way not caused by Alfven waves. From this, we have concluded that PBSs are generated due to network activity at the base of polar plumes and their magnetic structures axe current sheets or plasmoids.

Mickey Mouse Spotted on Mercury!

NASA Image and Video Library

2012-06-15

NASA image acquired: June 03, 2012 This scene is to the northwest of the recently named crater Magritte, in Mercury's south. The image is not map projected; the larger crater actually sits to the north of the two smaller ones. The shadowing helps define the striking "Mickey Mouse" resemblance, created by the accumulation of craters over Mercury's long geologic history. This image was acquired as part of MDIS's high-incidence-angle base map. The high-incidence-angle base map is a major mapping activity in MESSENGER's extended mission and complements the surface morphology base map of MESSENGER's primary mission that was acquired under generally more moderate incidence angles. High incidence angles, achieved when the Sun is near the horizon, result in long shadows that accentuate the small-scale topography of geologic features. The high-incidence-angle base map is being acquired with an average resolution of 200 meters/pixel. The MESSENGER spacecraft is the first ever to orbit the planet Mercury, and the spacecraft's seven scientific instruments and radio science investigation are unraveling the history and evolution of the Solar System's innermost planet. Visit the Why Mercury? section of this website to learn more about the key science questions that the MESSENGER mission is addressing. During the one-year primary mission, MESSENGER acquired 88,746 images and extensive other data sets. MESSENGER is now in a yearlong extended mission, during which plans call for the acquisition of more than 80,000 additional images to support MESSENGER's science goals. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Multiple-Cone Sunshade for a Spaceborne Telescope

NASA Technical Reports Server (NTRS)

Cafferty, Terry; Ford, Virginia

2008-01-01

A document describes a sunshade assembly for the spaceborne telescope of the Terrestrial Planet Finder Coronagraph mission. During operation, the telescope is aimed at target stars in the semihemisphere away from the Earth's Sun. The observatory rotates about its pointing axis during a single star observation, resulting in relative movement of the Sun. The sunshade assembly protects the telescope against excessive solar-induced thermal distortions for times long enough to complete observations. The assembly includes a cylindrical baffle immediately surrounding the telescope, and a series of coaxial conical shields at half-cone angle increments of between 3 and 6. The black inner surface of the cylindrical baffle suppresses stray light. The outer surface of the cylindrical baffle and all the surfaces of the conical shields except the outermost one are specular and highly reflective in the infrared. The outer surface of the outer shield is a material with low solar absorptance and high infrared emittance, such as silverized Teflon or white paint. This arrangement strongly radiatively couples each shield layer more effectively to cold space than to adjacent shield layers. The result is that the solar-driven temperature gradients in the cylindrical baffle are nearly negated, and only weakly communicated to the highly-infrared-reflective face of the primary telescope mirror.

Design optimization of ultra-high concentrator photovoltaic system using two-stage non-imaging solar concentrator

NASA Astrophysics Data System (ADS)

Wong, C.-W.; Yew, T.-K.; Chong, K.-K.; Tan, W.-C.; Tan, M.-H.; Lim, B.-H.

2017-11-01

This paper presents a systematic approach for optimizing the design of ultra-high concentrator photovoltaic (UHCPV) system comprised of non-imaging dish concentrator (primary optical element) and crossed compound parabolic concentrator (secondary optical element). The optimization process includes the design of primary and secondary optics by considering the focal distance, spillage losses and rim angle of the dish concentrator. The imperfection factors, i.e. mirror reflectivity of 93%, lens’ optical efficiency of 85%, circumsolar ratio of 0.2 and mirror surface slope error of 2 mrad, were considered in the simulation to avoid the overestimation of output power. The proposed UHCPV system is capable of attaining effective ultra-high solar concentration ratio of 1475 suns and DC system efficiency of 31.8%.

Effective cloud optical depth and enhancement effects for broken liquid water clouds in Valencia (Spain)

NASA Astrophysics Data System (ADS)

Marín, M. J.; Serrano, D.; Utrillas, M. P.; Núñez, M.; Martínez-Lozano, J. A.

2017-10-01

Partly cloudy skies with liquid water clouds have been analysed, founding that it is essential to distinguish data if the Sun is obstructed or not by clouds. Both cases can be separated considering simultaneously the Cloud Modification Factor (CMF) and the clearness index (kt). For partly cloudy skies and the Sun obstructed the effective cloud optical depth (τ) has been obtained by the minimization method for overcast skies. This method was previously developed by the authors but, in this case, taking into account partial cloud cover. This study has been conducted for the years 2011-2015 with the multiple scattering model SBDART and irradiance measurements for the UV Erythemal Radiation (UVER) and the broadband ranges. Afterwards a statistical analysis of τ has shown that the maximum value is much lower than for overcast skies and there is more discrepancy between the two spectral ranges regarding the results for overcast skies. In order to validate these results the effective cloud optical depth has been correlated with several transmission factors, giving similar fit parameters to those obtained for overcast skies except for the clearness index in the UVER range. As our method is not applicable for partly cloudy skies with the visible Sun, the enhancement of radiation caused by clouds when the Sun is visible has been studied. Results show that the average enhancement CMF values are the same for both ranges although enhancement is more frequent for low cloud cover in the UVER and medium-high cloud cover in the broadband range and it does not depend on the solar zenith angle.

Direct normal irradiance related definitions and applications: The circumsolar issue

DOE PAGES

Blanc, P.; Espinar, B.; Geuder, N.; ...

2014-10-21

The direct irradiance received on a plane normal to the sun, called direct normal irradiance (DNI), is of particular relevance to concentrated solar technologies, including concentrating solar thermal plants and concentrated photovoltaic systems. Following various standards from the International Organization for Standardization (ISO), the DNI definition is related to the irradiance from a small solid angle of the sky, centered on the position of the sun. Half-angle apertures of pyrheliometers measuring DNI have varied over time, up to ≈10°. The current recommendation of the World Meteorological Organization (WMO) for this half-angle is 2.5°. Solar concentrating collectors have an angular acceptancemore » function that can be significantly narrower, especially for technologies with high concentration ratios. The disagreement between the various interpretations of DNI, from the theoretical definition used in atmospheric physics and radiative transfer modeling to practical definitions corresponding to specific measurements or conversion technologies is significant, especially in the presence of cirrus clouds or large concentration of aerosols. Under such sky conditions, the circumsolar radiation—i.e. the diffuse radiation coming from the vicinity of the sun—contributes significantly to the DNI ground measurement, although some concentrating collectors cannot utilize the bulk of it. These issues have been identified in the EU-funded projects MACC-II (Monitoring Atmospheric Composition and Climate-Interim Implementation) and SFERA (Solar Facilities for the European Research Area), and have been discussed within a panel of international experts in the framework of the Solar Heating and Cooling (SHC) program of the International Energy Agency’s (IEA’s) Task 46 “ Solar Resource Assessment and Forecasting”. In accordance with these discussions, the terms of reference related to DNI are specified here. The important role of circumsolar radiation is evidenced, and its potential contribution is evaluated for typical atmospheric conditions. Thus, thorough analysis of performance of concentrating solar systems, it is recommended that, in addition to the conventional DNI related to 2.5° half-angle of today’s pyrheliometers, solar resource data sets also report the sunshape, the circumsolar contribution or the circumsolar ratio (CSR).« less

Trajectory Optimization of a Bimodal Nuclear Powered Spacecraft to Mars

DTIC Science & Technology

1990-05-29

velocity M = initial mass of spacecraft o m= ion fuel expulsion rate (constant) 0 = thrust direction angle = gravitational constant of Sun AVto t...total velocity change possible for the impulsive engines AV1 = velocity change for Earth escape AV2 = velocity change for Mars capture AVto t = AV + AV

The Solar Energy Notebook.

ERIC Educational Resources Information Center

Rankins, William H., III; Wilson, David A.

This publication is a handbook for the do-it-yourselfer or anyone else interested in solar space and water heating. Described are methods for calculating sun angles, available energy, heating requirements, and solar heat storage. Also described are collector and system designs with mention of some design problems to avoid. Climatological data for…

Improved Solar-Radiation-Pressure Models for GPS Satellites

NASA Technical Reports Server (NTRS)

Bar-Sever, Yoaz; Kuang, Da

2006-01-01

A report describes a series of computational models conceived as an improvement over prior models for determining effects of solar-radiation pressure on orbits of Global Positioning System (GPS) satellites. These models are based on fitting coefficients of Fourier functions of Sun-spacecraft- Earth angles to observed spacecraft orbital motions.

Orbital construction demonstration study. Volume 2: Technical

NASA Technical Reports Server (NTRS)

1977-01-01

The following items are discussed in reference to OCDA requirements; (1) flight mechanics and control, (2) effects of sun angle, (3) disturbance torques, (4) control system requirements, (5) OCDA orbit decay profile, and (6) aerodynamic drag forces. Structural design requirements are also given as well as basic design definition.

Optical advantages of astigmatic aberration corrected heliostats

NASA Astrophysics Data System (ADS)

van Rooyen, De Wet; Schöttl, Peter; Bern, Gregor; Heimsath, Anna; Nitz, Peter

2016-05-01

Astigmatic aberration corrected heliostats adapt their shape in dependence of the incidence angle of the sun on the heliostat. Simulations show that this optical correction leads to a higher concentration ratio at the target and thus in a decrease in required receiver aperture in particular for smaller heliostat fields.

Application of digital terrain data to quantify and reduce the topographic effect on LANDSAT data

NASA Technical Reports Server (NTRS)

Justice, C. O.; Wharton, S. W.; Holben, B. N. (Principal Investigator)

1980-01-01

Integration of LANDSAT multispectral scanner (MSS) data with 30 m U.S. Geological Survey (USGS) digital terrain data was undertaken to quantify and reduce the topographic effect on imagery of a forested mountain ridge test site in central Pennsylvania. High Sun angle imagery revealed variation of as much as 21 pixel values in data for slopes of different angles and aspects with uniform surface cover. Large topographic effects were apparent in MSS 4 and 5 was due to a combination of high absorption by the forest cover and the MSS quantization. Four methods for reducing the topographic effect were compared. Band ratioing of MSS 6/5 and MSS 7/5 did not eliminate the topographic effect because of the lack of variation in MSS 4 and 5 radiances. The three radiance models examined to reduce the topographic effect required integration of the digital terrain data. Two Lambertian models increased the variation in the LANDSAT radiances. The nonLambertian model considerably reduced (86 per cent) the topographic effect in the LANDSAT data. The study demonstrates that high quality digital terrain data, as provided by the USGS digital elevation model data, can be used to enhance the utility of multispectral satellite data.

The application analysis of the multi-angle polarization technique for ocean color remote sensing

NASA Astrophysics Data System (ADS)

Zhang, Yongchao; Zhu, Jun; Yin, Huan; Zhang, Keli

2017-02-01

The multi-angle polarization technique, which uses the intensity of polarized radiation as the observed quantity, is a new remote sensing means for earth observation. With this method, not only can the multi-angle light intensity data be provided, but also the multi-angle information of polarized radiation can be obtained. So, the technique may solve the problems, those could not be solved with the traditional remote sensing methods. Nowadays, the multi-angle polarization technique has become one of the hot topics in the field of the international quantitative research on remote sensing. In this paper, we firstly introduce the principles of the multi-angle polarization technique, then the situations of basic research and engineering applications are particularly summarized and analysed in 1) the peeled-off method of sun glitter based on polarization, 2) the ocean color remote sensing based on polarization, 3) oil spill detection using polarization technique, 4) the ocean aerosol monitoring based on polarization. Finally, based on the previous work, we briefly present the problems and prospects of the multi-angle polarization technique used in China's ocean color remote sensing.

Autumn Afternoon in Hale Crater

NASA Technical Reports Server (NTRS)

2000-01-01

The seasons on Mars and Earth are anti-correlated at present: days are getting shorter and shadows are getting longer as autumn end sand the beginning of winter draws nearer in the martian southern hemisphere, just as the same is occurring in Earth's northern hemisphere. Long shadows are especially prominent in this high resolution view of mountains forming part of the central peaks of Hale Crater (left), a 136 kilometer-(85 mile)-diameter impact crater at 36oS, 37oW. The two pictures were taken simultaneously by the Mars Global Surveyor Mars Orbiter Camera on November 10, 2000. The sun illuminates the scene from the northwest (upper left)about 22o above the horizon. Knowing the sun angle and the length of the longest shadow (1.6 km; 1.0 mi), the height of the largest peak in the high resolution view (right) is about 630 meters (2,070 ft) above the crater floor. Sand dunes blanket the middle portion of the high resolution view, and small gullies--possibly carved by water--can be seen on the slopes of some of the peaks at the upper left. Winter in the southern hemisphere will begin in mid-December 2000. The high resolution view covers an area 3 km (1.9 mi) wide at a full-resolution scale of 3 meters (9.8 ft) per pixel.

Fixed solar concentrator-collector-satelite receiver and co-generator

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

Meckler, M.

1985-01-01

An insolation and micro wave receiver fixedly installed in alignment with the suns azimuth and within the look angle of a satellite, and comprised of holographic windows recorded according to time related to the suns position as zone plates to concentrate infrared light into a Rankine cycle power generating receiver and to columnate ultraviolet light onto a photo voltaic power generating plane, utilizing a micro wave dish as the substrate support of photo voltaic cells and as a condenser of the Rankine cycle operating an induction generator synchronous with an external alternating current power system, and with the photo voltaicmore » power synchronized therewith by commutation.« less

Study of CP(N-1) theta-vacua by cluster simulation of SU(N) quantum spin ladders.

PubMed

Beard, B B; Pepe, M; Riederer, S; Wiese, U-J

2005-01-14

D-theory provides an alternative lattice regularization of the 2D CP(N-1) quantum field theory in which continuous classical fields emerge from the dimensional reduction of discrete SU(N) quantum spins. Spin ladders consisting of n transversely coupled spin chains lead to a CP(N-1) model with a vacuum angle theta=npi. In D-theory no sign problem arises and an efficient cluster algorithm is used to investigate theta-vacuum effects. At theta=pi there is a first order phase transition with spontaneous breaking of charge conjugation symmetry for CP(N-1) models with N>2.

Early Mission Maneuver Operations for the Deep Space Climate Observatory

NASA Technical Reports Server (NTRS)

Roberts, Craig; Case, Sara; Reagoso, John

2015-01-01

DSCOVR Lissajous Orbit sized such that orbit track never extends beyond 15 degrees from Earth-Sun line (as seen from Earth). Requiring delta-V maneuvers, control orbit to obey a Solar Exclusion Zone (SEZ) cone of half-angle 4 degrees about the Earth-Sun line. Spacecraft should never be less than 4 degrees from solar center as seen from Earth. Following Lissajous Orbit Insertion (LOI), DSCOVR should be in an opening phase that just skirts the 4-degree SEZ. Maximizes time to the point where a closing Lissajous will require avoidance maneuvers to keep it out of the SEZ. Station keeping maneuvers should take no more than 15 minutes

NASA/University Joint Venture in Space Science (JOVE)

NASA Technical Reports Server (NTRS)

Quigley, Robert J.

1996-01-01

The spectra of the Ring Nebula at position angle 124 degrees, covering a spectral range from [O III] 3727 A to [S II] 6723 A is obtained using McDonald Observatory's 82-inch telescope (operated by the University of Texas at Austin). This work was carried out in September of 1991. During the 1992 summer, the analysis of the McDonald spectra were carried out and compared the results with the IUE (UV) spectra of the Ring Nebula. In addition, IRAF was successfully installed on NASA/Jove Sun IPC workstation (polaris) during September 1993 and the installation of three additional Sun workstations (mizar, dubhe, and merak) is about to be completed.

Techniques for plotting shadow patterns

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

Bainbridge, D.A.

1982-02-01

Basic approaches for plotting shadow patterns (summer or winter) are discussed, illustrated, and compared. The solar simulator technique uses floodlights or a moveable table to mimic the sun's path over a model of the building being studied. The drawback is that, for large developments, very small models would have to be built. Graphic solutions (2 types) are described in which: (1) sun angles are used to calculate shadow patterns using trigonometry and (2) drawings are made and shadows are calculated. Examples are given for a house on level ground and on sloping ground. Calculations of shade density are also illustrated.more » 8 references. (MJJ)« less

Steepness of Slopes at the Luna-Glob Landing Sites: Estimating by the Shaded Area Percentage in the LROC NAC Images

NASA Astrophysics Data System (ADS)

Krasilnikov, S. S.; Basilevsky, A. T.; Ivanov, M. A.; Abdrakhimov, A. M.; Kokhanov, A. A.

2018-03-01

The paper presents estimates of the occurrence probability of slopes, whose steep surfaces could be dangerous for the landing of the Luna-Glob descent probe ( Luna-25) given the baseline of the span between the landing pads ( 3.5 m), for five potential landing ellipses. As a rule, digital terrain models built from stereo pairs of high-resolution images (here, the images taken by the Narrow Angle Camera onboard the Lunar Reconnaissance Orbiter (LROC NAC)) are used in such cases. However, the planned landing sites are at high latitudes (67°-74° S), which makes it impossible to build digital terrain models, since the difference in the observation angle of the overlapping images is insufficient at these latitudes. Because of this, to estimate the steepness of slopes, we considered the interrelation between the shaded area percentage in the image and the Sun angle over horizon at the moment of imaging. For five proposed landing ellipses, the LROC NAC images (175 images in total) with a resolution from 0.4 to 1.2 m/pixel were analyzed. From the results of the measurements in each of the ellipses, the dependence of the shaded area percentage on the solar angle were built, which was converted to the occurrence probability of slopes. For this, the data on the Apollo 16 landing region ware used, which is covered by both the LROC NAC images and the digital terrain model with high resolution. As a result, the occurrence probability of slopes with different steepness has been estimated on the baseline of 3.5 m for five landing ellipses according to the steepness categories of <7°, 7°-10°, 10°-15°, 15°-20°, and >20°.

Thermal performance of evacuated tube heat pipe solar collector

NASA Astrophysics Data System (ADS)

Putra, Nandy; Kristian, M. R.; David, R.; Haliansyah, K.; Ariantara, Bambang

2016-06-01

The high fossil energy consumption not only causes the scarcity of energy but also raises problems of global warming. Increasing needs of fossil fuel could be reduced through the utilization of solar energy by using solar collectors. Indonesia has the abundant potential for solar energy, but non-renewable energy sources still dominate energy consumption. With heat pipe as passive heat transfer device, evacuated tube solar collector is expected to heat up water for industrial and home usage without external power supply needed to circulate water inside the solar collector. This research was conducted to determine the performance of heat pipe-based evacuated tube solar collector as solar water heater experimentally. The experiments were carried out using stainless steel screen mesh as a wick material, and water and Al2O3-water 0.1% nanofluid as working fluid, and applying inclination angles of 0°, 15°, 30°, and 45°. To analyze the heat absorbed and transferred by the prototype, water at 30°C was circulated through the condenser. A 150 Watt halogen lamp was used as sun simulator, and the prototype was covered by an insulation box to obtain a steady state condition with a minimum affection of ambient changes. Experimental results show that the usage of Al2O3-water 0.1% nanofluid at 30° inclination angle provides the highest thermal performance, which gives efficiency as high as 0.196 and thermal resistance as low as 5.32 °C/W. The use of nanofluid as working fluid enhances thermal performance due to high thermal conductivity of the working fluid. The increase of the inclination angle plays a role in the drainage of the condensate to the evaporator that leads to higher thermal performance until the optimal inclination angle is reached.

Earth Observations taken during Expedition Four

NASA Image and Video Library

2002-04-21

ISS004-E-10288 (21 April 2002) --- This view featuring the San Francisco Bay Area was photographed by an Expedition 4 crewmember onboard the International Space Station (ISS). The gray urban footprint of San Francisco, Oakland, San Jose, and their surrounding suburbs contrasts strongly with the green hillsides. Of particular note are the Pacific Ocean water patterns that are highlighted in the sun glint. Sets of internal waves traveling east impinge on the coastline south of San Francisco. At the same time, fresher bay water flows out from the bay beneath the Golden Gate Bridge, creating a large plume traveling westward. Tidal current channels suggest the tidal flow deep in the bay. Because the ISS orbits are not synchronous with the sun, station crewmembers view Earth with variable solar illumination angles. This allows them to document phenomena such as the sun reflecting differentially off surface waters in a way that outlines complicated water structures.

Sky brightness and color measurements during the 21 August 2017 total solar eclipse.

PubMed

Bruns, Donald G; Bruns, Ronald D

2018-06-01

The sky brightness was measured during the partial phases and during totality of the 21 August 2017 total solar eclipse. A tracking CCD camera with color filters and a wide-angle lens allowed measurements across a wide field of view, recording images every 10 s. The partially and totally eclipsed Sun was kept behind an occulting disk attached to the camera, allowing direct brightness measurements from 1.5° to 38° from the Sun. During the partial phases, the sky brightness as a function of time closely followed the integrated intensity of the unobscured fraction of the solar disk. A redder sky was measured close to the Sun just before totality, caused by the redder color of the exposed solar limb. During totality, a bluer sky was measured, dimmer than the normal sky by a factor of 10,000. Suggestions for enhanced measurements at future eclipses are offered.

Directional reflectance factor distributions of a cotton row crop

NASA Technical Reports Server (NTRS)

Kimes, D. S.; Newcomb, W. W.; Schutt, J. B.; Pinter, P. J., Jr.; Jackson, R. D.

1984-01-01

The directional reflectance factor distribution spanning the entire exitance hemisphere was measured for a cotton row crop (Gossypium barbadense L.) with 39 percent ground cover. Spectral directional radiances were taken in NOAA satellite 7 AVHRR bands 1 and 2 using a three-band radiometer with restricted 12 deg full angle field of view at half peak power points. Polar co-ordinate system plots of directional reflectance factor distributions and three-dimensional computer graphic plots of scattered flux were used to study the dynamics of the directional reflectance factor distribution as a function of spectral band, geometric structure of the scene, solar zenith and azimuth angles, and optical properties of the leaves and soil. The factor distribution of the incomplete row crops was highly polymodal relative to that for complete vegetation canopies. Besides the enhanced reflectance for the antisolar point, a reflectance minimum was observed towards the forwardscatter direction in the principle plane of the sun. Knowledge of the mechanics of the observed dynamics of the data may be used to provide rigorous validation for two- or three-dimensional radiative transfer models, and is important in interpreting aircraft and satellite data where the solar angle varies widely.

Lighting Condition Analysis for Mars' Moon Phobos

NASA Technical Reports Server (NTRS)

Li, Zu Qun; de Carufel, Guy; Crues, Edwin Z.; Bielski, Paul

2016-01-01

This study used high fidelity computer simulation to investigate the lighting conditions, specifically the solar radiation flux over the surface, on Phobos. Ephemeris data from the Jet Propulsion Laboratory (JPL) DE405 model was used to model the state of the Sun, Earth, Moon, and Mars. An occultation model was developed to simulate Phobos' self-shadowing and its solar eclipses by Mars. The propagated Phobos state was compared with data from JPL's Horizon system to ensure the accuracy of the result. Results for Phobos lighting conditions over one Martian year are presented, which include the duration of solar eclipses, average solar radiation intensity, surface exposure time, available energy per unit area for sun tracking arrays, and available energy per unit area for fixed arrays (constrained by incident angle). The results show that: Phobos' solar eclipse time varies throughout the Martian year, with longer eclipse durations during the Martian spring and fall seasons and no eclipses during the Martian summer and winter seasons; solar radiation intensity is close to minimum at the summer solstice and close to maximum at the winter solstice; exposure time per orbit is relatively constant over the surface during the spring and fall but varies with latitude during the summer and winter; and Sun tracking solar arrays generate more energy than a fixed solar array. A usage example of the result is also present in this paper to demonstrate the utility.

Employee factors associated with interest in improving sun protection in an Australian mining workforce.

PubMed

Street, Tamara D; Thomas, Drew Leighton

2015-04-01

As Australia experiences moderate to extreme levels of ultraviolet radiation from the sun, high participation in sun protection behaviour is required to minimise the risk of developing skin cancer. Understanding factors associated with interest in improving sun protection will enable employers to increase enrolment in sun protection programs. A cross-sectional survey was conducted at mining sites in rural Australia. The survey assessed employee demographics, stages of change and health-belief model variables, sun protection behaviour, and preferences for improving sun protection. Overall, 897 employees participated: 73% were male and 47% were classed as being at high risk of ultraviolet-related illnesses. Although 24% of high-risk participants wanted to increase their sun protection practices, only 6% wanted employer-provided sun protection assistance. Marital status and recent experience of sunburn were associated with desire to improve sun protection. Over 50% of the high-risk participants who did not want to increase their sun protection and did not want assistance were in the pre-contemplative stage of change. Self-efficacy was associated with desire to improve sun protection while susceptibility was associated with desire for assistance. The use of sun protection behaviours among this sample was low. Many employees at high risk of ultraviolet radiation exposure do not believe their approach to sun protection needs changing. SO WHAT?: Workplace health promotion programs need to educate employees about susceptibility to ultraviolet radiation exposure and develop employees' self-efficacy for sun protection behaviours. These findings can inform the content development of sun protection communication strategies targeting employees.

Investigating the Effect of IMF Path Length on Pitch-angle Scattering of Strahl within 1 au

NASA Astrophysics Data System (ADS)

Graham, G. A.; Rae, I. J.; Owen, C. J.; Walsh, A. P.

2018-03-01

Strahl is the strongly field-aligned, beam-like population of electrons in the solar wind. Strahl width is observed to increase with distance from the Sun, and hence strahl electrons must be subject to in-transit scattering effects. Different energy relations have been both observed and modeled for both strahl width and the width increase with radial distance. Thus, there is much debate regarding what mechanism(s) scatter strahl. In this study, we use a novel method to investigate strahl evolution within 1 au by estimating the distance traveled by the strahl along the interplanetary magnetic field (IMF). We do this by implementing methods developed in previous studies, which make use of the onset of solar energetic particles at ∼1 au. Thus, we are able to obtain average strahl broadening in relation to electron energy and distance, while also taking into account the general effect of IMF topology and adiabatic focusing experienced by strahl. We find that average strahl width broadens with distance traveled along the IMF, which suggests that strahl width is related to the path length taken by the strahl from the Sun to 1 au. We also find that strahl pitch-angle width broadening per au along the IMF length increased with strahl energy, which suggests that the dominant strahl pitch-angle scattering mechanism likely has an inherent energy relation. Our pitch-angle broadening results provide a testable energy relation for the upcoming Parker Solar Probe and Solar Orbiter missions, which are both set to provide unprecedented new observations within 1 au.

Comet ISON Approaching the Sun [hd video

NASA Image and Video Library

2013-11-27

This movie from NASA’s STEREO spacecraft's Heliospheric Imager shows Comet ISON, Mercury, Comet Encke and Earth over a five-day period from Nov. 20 to Nov. 25, 2013. The sun sits right of the field of view of this camera. Comet ISON, which will round the sun on Nov. 28, is what's known as a sungrazing comet, due to its close approach. Foreshortening or the angle at which these images were obtained make Earth appear as if it is closer to the sun than Mercury. If you look closely you will also see a dimmer and smaller comet Encke near comet ISON. A comet’s journey through the solar system is perilous and violent. A giant ejection of solar material from the sun could rip its tail off. Before it reaches Mars -- at some 230 million miles away from the sun -- the radiation of the sun begins to boil its water, the first step toward breaking apart. And, if it survives all this, the intense radiation and pressure as it flies near the surface of the sun could destroy it altogether. Even if the comet does not survive, tracking its journey will help scientists understand what the comet is made of, how it reacts to its environment, and what this explains about the origins of the solar system. Closer to the sun, watching how the comet and its tail interact with the vast solar atmosphere can teach scientists more about the sun itself. Image Credit: NASA/STEREO NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Studies of the Solar Radiations' Influence About Geomembranes Used in Ecological Landfill

NASA Astrophysics Data System (ADS)

Vasiluta, Petre; Cofaru, Ileana Ioana; Cofaru, Nicolae Florin; Popa, Dragos Laurentiu

2017-12-01

The study shown in this paper presents the behavior of geomembranes used at the ecological landfills. The influences of the solar radiations has a great importance regarding the correct mounting of the geomembranes. The mathematical model developed for the determination anytime and anywhere in the world for the next values and parameters: apparent solar time, solar declination, solar altitude, solar azimuth and incidence angle, zone angle, angle of sun elevation, solar declination, solar constant, solar flux density, diffuse solar radiation, global radiation, soil albedo, total radiant flux density and relational links of these values. The results of this model was used for creations an AutoCAD subroutines useful for choosing the correct time for correct mounting anywhere of the geomembranes

On the location of the Io plasma torus: Voyager 1 observations

NASA Astrophysics Data System (ADS)

Volwerk, Martin

2018-06-01

The Voyager 1 outbound ultraviolet observations of the Io plasma torus are used to determine the location of the ansae, to obtain a third viewing angle of this structure in the Jovian magnetosphere. At an angle of -114° with respect to the Sun-Jupiter line, or a Jovian local time of 04:30 LT, the Voyager 1 data deliver a distance of 5.74±0.10 RJ for the approaching and 5.83±0.15 RJ for the receding ansa. Various periodicities in the radial distance, brightness and width of the ansae are seen with respect to system III longitude and Io phase angle. The torus ribbon feature does not appear in all ansa scans.

The Onset of Magnetic Reconnection: Tearing Instability in Current Sheets with a Guide Field

NASA Astrophysics Data System (ADS)

Daldorff, L. K. S.; Klimchuk, J. A.; Knizhnik, K. J.

2016-12-01

Magnetic reconnection is fundamental to many solar phenomena, ranging from coronal heating, to jets, to flares and CMEs. A poorly understood yet crucial aspect of reconnection is that it does not occur until magnetic stresses have built to sufficiently high levels for significant energy release. If reconnection were to happen too soon, coronal heating would be weak and flares would be small. As part of our program to study the onset conditions for magnetic reconnection, we have investigated the instability of current sheets to tearing. Surprisingly little work has been done on this problem for sheets that include a guide field, i.e., for which the field rotates by less than 180 degrees. This is the most common situation on the Sun. We present numerical 3D resistive MHD simulations of several sheets and show how the behaviour depends on the shear angle (rotation). We compare our results to the predictions of linear theory and discuss the nonlinear evolution in terms of plasmoid formation and the interaction of different oblique tearing modes. The relevance to the Sun is explained.

New Horizons High-Phase Observations of Distant Kuiper Belt Objects

NASA Astrophysics Data System (ADS)

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

2017-12-01

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

Highlighting Titan's Hazes

NASA Image and Video Library

2017-08-11

NASA's Cassini spacecraft looks toward the night side of Saturn's moon Titan in a view that highlights the extended, hazy nature of the moon's atmosphere. During its long mission at Saturn, Cassini has frequently observed Titan at viewing angles like this, where the atmosphere is backlit by the Sun, in order to make visible the structure of the hazes. Titan's high-altitude haze layer appears blue here, whereas the main atmospheric haze is orange. The difference in color could be due to particle sizes in the haze. The blue haze likely consists of smaller particles than the orange haze. Images taken using red, green and blue spectral filters were combined to create this natural-color view. The image was taken with the Cassini spacecraft narrow-angle camera on May 29, 2017. The view was acquired at a distance of approximately 1.2 million miles (2 million kilometers) from Titan. Image scale is 5 miles (9 kilometers) per pixel. https://photojournal.jpl.nasa.gov/catalog/PIA21625

Estimation of mass of black hole candidate H1743-322 using spectral and timing analysis of 2010 and 2011 outbursts with TCAF and POS models

NASA Astrophysics Data System (ADS)

Molla, Aslam Ali; Debnath, Dipak; Chakrabarti, Sandip Kumar; Mondal, Santanu; Jana, Arghajit; Chatterjee, Debjit

2016-07-01

The black hole X-ray binary H1743-322 has been observed almost during every X-ray mission since the inception of X-ray astronomy. Like other black hole candidates H1743-322 is highly variable. Using a self consistent accretion flow model (TCAF), we study spectral evolution during its 2010 & 2011 outbursts by keeping model normalization fixed to a value (14.5). As model normalization depends only on mass, distance and inclination angle of the black hole so, it should be a constant. This constant allows us to calculate mass of the black hole if we keep it frozen. The only uncertainty in mass and normalization measurements comes from the uncertainty of distance and inclination angle. Here we present spectral analysis of H1743-322 during 2010 and 2011 outburst and conclude that the mass of the black hole is within a range of 9 - 13 M_Sun.

Transient rotation of photospheric vector magnetic fields associated with a solar flare.

PubMed

Xu, Yan; Cao, Wenda; Ahn, Kwangsu; Jing, Ju; Liu, Chang; Chae, Jongchul; Huang, Nengyi; Deng, Na; Gary, Dale E; Wang, Haimin

2018-01-03

As one of the most violent eruptions on the Sun, flares are believed to be powered by magnetic reconnection. The fundamental physics involving the release, transfer, and deposition of energy have been studied extensively. Taking advantage of the unprecedented resolution provided by the 1.6 m Goode Solar Telescope, here, we show a sudden rotation of vector magnetic fields, about 12-20° counterclockwise, associated with a flare. Unlike the permanent changes reported previously, the azimuth-angle change is transient and cospatial/temporal with Hα emission. The measured azimuth angle becomes closer to that in potential fields suggesting untwist of flare loops. The magnetograms were obtained in the near infrared at 1.56 μm, which is minimally affected by flare emission and no intensity profile change was detected. We believe that these transient changes are real and discuss the possible explanations in which the high-energy electron beams or Alfve'n waves play a crucial role.

The use of color infrared aerial photography in determining salt marsh vegetation and delimiting man-made structures of Lynnhaven Bay, Virginia. M.S. Thesis

NASA Technical Reports Server (NTRS)

Holman, R. E., III

1974-01-01

Color infrared aerial photography was found to be superior to color aerial photography in an ecological study of Lynnhaven Bay, Virginia. The research was divided into three phases: (1) Determination of the feasibility of correlating color infrared aerial photography with saline wetland species composition and zonation patterns, (2) determination of the accuracy of the aerial interpretation and problems related to the aerial method used; and (3) comparison of developed with undeveloped areas along Lynnhaven Bay's shoreline. Wetland species composition and plant community zonation bands were compared with aerial infrared photography and resulted in a high degree of correlation. Problems existed with changing physical conditions; time of day, aircraft angle and sun angle, making it necessary to use several different characteristics in wetland species identification. The main characteristics used were known zonation patterns, textural signatures and color tones. Lynnhaven Bay's shoreline was 61.5 percent developed.

Accurate approximation of in-ecliptic trajectories for E-sail with constant pitch angle

NASA Astrophysics Data System (ADS)

Huo, Mingying; Mengali, Giovanni; Quarta, Alessandro A.

2018-05-01

Propellantless continuous-thrust propulsion systems, such as electric solar wind sails, may be successfully used for new space missions, especially those requiring high-energy orbit transfers. When the mass-to-thrust ratio is sufficiently large, the spacecraft trajectory is characterized by long flight times with a number of revolutions around the Sun. The corresponding mission analysis, especially when addressed within an optimal context, requires a significant amount of simulation effort. Analytical trajectories are therefore useful aids in a preliminary phase of mission design, even though exact solution are very difficult to obtain. The aim of this paper is to present an accurate, analytical, approximation of the spacecraft trajectory generated by an electric solar wind sail with a constant pitch angle, using the latest mathematical model of the thrust vector. Assuming a heliocentric circular parking orbit and a two-dimensional scenario, the simulation results show that the proposed equations are able to accurately describe the actual spacecraft trajectory for a long time interval when the propulsive acceleration magnitude is sufficiently small.

Simulating halos and coronas in their atmospheric environment.

PubMed

David Gedzelman, Stanley

2008-12-01

Models are developed that simulate the light and color of the sky and of circular halos and coronas as a function of atmospheric pressure, cloud height, width, and optical depth, solar zenith angle, aerosol concentration and size, and ozone content. Halos, coronas, and skylight are treated as singly scattered sunbeams that are depleted in their passage through the atmosphere and cloud. Multiple scattering is included only for background cloud light. Halos produced by hexagonal crystal prisms and coronas produced by monodisperse droplets are visible for cloud optical depths in the range 0.0003

The Fall 2000 and Fall 2001 SOHO-Ulysses Quadratures

NASA Technical Reports Server (NTRS)

Suess, S. T.; Poletto, G.; Rose, M. Franklin (Technical Monitor)

2001-01-01

SOHO-Ulysses quadrature occurs when the SOHO-Sun-Ulysses included angle is 90 degrees. It is only at such times that the same plasma leaving the Sun in the direction of Ulysses can first be remotely analyzed with SOHO instruments and then later be sampled in situ by Ulysses instruments. The quadratures in December 2000 and 2001 are of special significance because Ulysses will be near the south and north heliographic poles, respectively, and the solar cycle will be near sunspot maximum. Quadrature geometry is sometimes confusing and observations are influenced by solar rotation. The Fall 2000 and 2001 quadratures are more complex than usual because Ulysses is not in a true polar orbit and the orbital speed of Ulysses about the Sun is becoming comparable to the speed of SOHO about the Sun. In 2000 Ulysses will always be slightly behind the pole but will appear to hang over the pole for over two months because it is moving around the Sun in the same direction as SOHO. In 2001 Ulysses will be slightly in front of the pole so that its footpoint will be directly observable. Detailed plots will be shown of the relative positions of SOHO and Ulysses will their relative positions. In neither case is true quadrature actually achieved, but this works to the observers advantage in 2001.

The Fall 2000 and Fall 2001 SOHO-Ulysses Quadratures

NASA Technical Reports Server (NTRS)

Suess, S. T.; Poletto, G.

2000-01-01

SOHO-Ulysses quadrature occurs when the SOHO-Sun-Ulysses included angle is 90 degrees. It is only at such times that the same plasma leaving the Sun in the direction of Ulysses can first be remotely analyzed with SOHO instruments and then later be sampled in situ by Ulysses instruments. The quadratures in December 2000 and 2001 are of special significance because Ulysses will be near the south and north heliographic poles, respectively, and the solar cycle will be near sunspot maximum. Quadrature geometry is sometimes confusing and observations are influenced by solar rotation. The Fall 2000 and 2001 quadratures are more complex than usual because Ulysses is not in a true polar orbit and the orbital speed of Ulysses about the Sun is becoming comparable to the speed of SOHO about the Sun. In 2000 Ulysses will always be slightly behind the pole but will appear to hang over the pole for over two months because it is moving around the Sun in the same direction as SOHO. In 20001, Ulysses will be slightly in front of the pole so that its footpoint will be directly observable. Detailed plots will be shown of the relative positions of SOHO and Ulysses will their relative positions. In neither case is true quadrature actually achieved, but this works to the observers advantage in 2001.

Absorbed photosynthetically active radiation of steppe vegetation and sun-view geometry effects on APAR estimates

NASA Technical Reports Server (NTRS)

Walter-Shea, E. A.; Blad, B. L.; Mesarch, M. A.; Hays, C. J.; Deering, D. W.; Eck, T. F.

1992-01-01

Instantaneous fractions of absorbed photosynthetically active radiation (APAR) were measured at the Streletskaya Steppe Reserve in conjunction with canopy bidirectional-reflected radiation measured at solar zenith angles ranging between 37 and 74 deg during the Kursk experiment (KUREX-91). APAR values were higher for KUREX-91 than those for the first ISLSCP field experiment (FIFE-89) and the amount of APAR of a canopy was a function of solar zenith angle, decreasing as solar zenith angle increased at the resrve. Differences in absorption are attributed to leaf area index (LAI) and leaf angle distribution and subsequently transmitted radiation interactions. LAIs were considerably higher at the reserve than those at the FIFE site. Leaf angle distributions of the reserve approach a uniform distribution while distributions at the FIFE site more closely approximate erectophile distributions. Reflected photosynthetically active radiation (PAR) components at KUREX-91 and FIFE-89 were similar in magnitude and in their response to solar zenith angle. Transmitted PAR increased with increasing solar zenith angle at KUREX-91 and decreased with increasing solar zenith angle at FIFE-89. Transmitted PAR at FIFE-89 was considerably larger than those at KUREX-91.

Saturn Apollo Program

NASA Image and Video Library

1967-08-01

The Apollo Telescope Mount (ATM), designed and developed by the Marshall Space Flight Center, served as the primary scientific instrument unit aboard the Skylab. The ATM contained eight complex astronomical instruments designed to observe the Sun over a wide spectrum from visible light to x-rays. This angle view is of an ATM contamination monitor meter mockup.

Faint F Ring and Prometheus

NASA Image and Video Library

2016-11-21

Surface features are visible on Saturn's moon Prometheus in this view from NASA's Cassini spacecraft. Most of Cassini's images of Prometheus are too distant to resolve individual craters, making views like this a rare treat. Saturn's narrow F ring, which makes a diagonal line beginning at top center, appears bright and bold in some Cassini views, but not here. Since the sun is nearly behind Cassini in this image, most of the light hitting the F ring is being scattered away from the camera, making it appear dim. Light-scattering behavior like this is typical of rings comprised of small particles, such as the F ring. This view looks toward the unilluminated side of the rings from about 14 degrees below the ring plane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Sept. 24, 2016. The view was acquired at a distance of approximately 226,000 miles (364,000 kilometers) from Prometheus and at a sun-Prometheus-spacecraft, or phase, angle of 51 degrees. Image scale is 1.2 miles (2 kilometers) per pixel. http://photojournal.jpl.nasa.gov/catalog/PIA20508

Shadow Below

NASA Image and Video Library

2016-06-20

As Saturn's northern hemisphere summer approaches, the shadows of the rings creep ever southward across the planet. Here, the ring shadows appear to obscure almost the entire southern hemisphere, while the planet's north pole and its six-sided jet stream, known as "the hexagon," are fully illuminated by the sun. When NASA's Cassini spacecraft arrived at Saturn 12 years ago, the shadows of the rings lay far to the north on the planet (see PIA06077). As the mission progressed and seasons turned on the slow-orbiting giant, equinox arrived and the shadows of the rings became a thin line at the equator (see PIA11667). This view looks toward the sunlit side of the rings from about 16 degrees above the ring plane. The image was taken in red light with the Cassini spacecraft wide-angle camera on March 19, 2016. The view was obtained at a distance of approximately 1.7 million miles (2.7 million kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 92 degrees. Image scale is 100 miles (160 kilometers) per pixel. http://photojournal.jpl.nasa.gov/catalog/PIA20486

Ion Plume Damage in Formation Flight Regimes

NASA Astrophysics Data System (ADS)

Young, Jarred Alexander

This effort examines the potential for damage from plume impingement from an electric propulsion system within spacecraft missions that utilize a formation flight architecture. Specifically, the potential erosion of a structural material (Aluminum) and anti-reflective coatings for solar cell coverglass are explored. Sputter yields for the materials of Aluminum, Magnesium Fluoride, and Indium Tin Oxide are experimentally validated using an electrostatic ion source at energies varying from 500-1500 eV. Erosion depths are analyzed using white-light optical profilometry to measure potential depths up to 1 microm. This erosion data was then utilized to create (or augment) Bohdansky and Yamamura theoretical curve fits for multiple incidence angles to look at theoretical sputter effects within formation flight regimes at multiple formation distances from 50-1000 m. The damage from these electric propulsion plumes is explored throughout multiple orbital conditions from LEO, Sun-Synchronous, and GEO. Factors affecting erosion are: plume density, local geomagnetic field environment and incidence angles of target surfaces. Results from this simulated study show significant erosion with GEO with minor erosion in some LEO and all Sun-Synchronous cases.

Some Unsettled Questions in the Problem of Neutrino Oscillations. Experiments

NASA Astrophysics Data System (ADS)

Muchamedovich Beshtoev, Khamidbi

2003-07-01

It is shown that in order to register neutrino oscillations, it is necessary to see second or higher neutrino oscillation modes on experiments. For this purpose we can use the elliptic character of 1the Earth orbit. A special importance for study of the Earth neutrino sources, using big neutrino detectors, is stressed here. The analysis is showing that the SNO experimental results do not confirm the smallest of νe → ντ transition angle mixings, which was obtained from analysis of the CHOOZ experimental data. It is also noted that there is contradiction between SNO, super-Kamiokande, Homestake and the SAGE and GNO (GALLEX) data. 1. Introduction In this article we will consider some unsettled questions in experiments on the problem of neutrino oscillations. 2. experimental Observation of the Neutrino Oscillations At present it supposed that the neutrino oscillations have been observed [1-3], In reality in these experiments there were observed only transitions between (the Sun or atmospheric) neutrinos. Since we presume that the neutrino oscillations do take place; therefore we must observe (Sun) neutrino oscillations in reality. Since the length of neutrino oscillations is great sufficiently, we cannot observe the higher modes in terrestrial experiment. But we have another possibility to observe the Sun neutrino oscillation using the fact that the Earth orbit is the elliptic one with: Earth's perihelion RP = 147.117 ·106k m , Earth's aphelion RA = 152.083 ·106k m, and their difference R is R = 4.866 · 106 k m. Since the Sun neutrinos conclude all energies up to 15M eV , we must divide this energy spectrum into energy regions and observe these neutrino fluxes as a function of energy and the Ears's distances from the Sun. At these conditions we must observe the neutrino oscillations, in order to determine if the length of neutrino oscillation Rosc is bigger than the region where these (high energy)

Bidirectional reflectance of oceanic waters: A comparison of modeled and measured upward radiance fields

NASA Technical Reports Server (NTRS)

Morel, Andre; Voss, Kenneth J.; Gentili, Bernard

1995-01-01

The bidirectional reflectance of oceanic waters is conveniently described in a normalized way by forming the ratio of the upwelling irradiance E(sub u) to any upwelling radiance L(sub u)(theta prime, phi). This ratio, Q (theta prime, theta(sub 0), (phi(sub 0) - phi), where theta prime, phi are the nadir and azimuth angles for the upward radiance and theta(sub 0), phi(sub 0) are the zenith and azimuth angles of the Sun, has been determined from measurements at sea and computed via Monte Carlo simulations using the inherent optical properties measured in the field and appropriate boundary conditions (clear sky, no wind, varying Sun angle). Experimental ad computed Q values are in excellent agreement. This successful comparison confirms the importance of the bidirectional character of ocean reflectance, already pointed out from a purely numerical approach without field validation, and corroborates the extended range of the Q variations. The later point is of importance when interpreting the marine signals detected by an ocean color satellite-borne sensor. The validation is extended by considering the historical data for the radiance distributions in Lake Pend Oreille determined at various depths. The closure issue in ocean optics is examined by solving the direct problem of radiative transfer and through a model-data comparison in terms of radiance field.

Ant mound as an optimal shape in constructal design: solar irradiation and circadian brood/fungi-warming sorties.

PubMed

Kasimova, R G; Tishin, D; Obnosov, Yu V; Dlussky, G M; Baksht, F B; Kacimov, A R

2014-08-21

Sizes, shapes, ambient and in-dome temperature, incoming solar radiation and illumination are measured on a Formica rufa anthill in a mixed forest of the Volga-Kama National Reserve in Russia. These data are used in a conceptual model of insolation of a right conical surface by direct-beam, descending atmospheric and ascending ground-reflected radiation. Unlike a standard calculation of the energy flux intercepted by a solar panel, the anthill is a 3-D structure and double-integration of the cosine of the angle between the solar beams and normal to the surface is carried out for a "cozy trapezium", where the insects expose themselves and the brood to "morning" sunbathing pulses (Jones and Oldroyd, 2007). Several constructal design problems are formulated with the criteria involving either a pure solar energy gained by the dome or this energy, as a mathematical criterion, penalized by additive terms of mechanical energy (potential and friction) lost by the ants in their diurnal forays from a "heartland" of the nest to the sun-basking zone on the surface. The unique and global optima are analytically found, with the optimal tilt angle of the cone explicitly expressed through the zenith angle of the Sun and meteorological constants for the isotropic sky model. Copyright © 2014 Elsevier Ltd. All rights reserved.

Characterization of the oceanic light field within the photic zone: Fluctuations of downward irradiance and asymmetry of horizontal radiance

NASA Astrophysics Data System (ADS)

Gassmann, Ewa

Two distinctive features of underwater light field in the upper ocean were examined: the wave-induced high-frequency light fluctuations within the near-surface layer under sunny skies, and the asymmetry of horizontal radiance within the photic layer of the ocean. To characterize the spatiotemporal statistical properties of the wave-induced light fluctuations, measurements of downward plane irradiance were made with novel instrumentation within the top 10 m layer of the ocean at depths as shallow as 10 cm under sunny skies, different solar zenith angles, and weak to moderate wind speeds. It was found that the maximum intensity of light fluctuations occurs at depths as shallow as 20 cm under the most favorable conditions for wave focusing, which correspond to high sun in a clear sky with weak wind. The strong frequency dependence of light fluctuations at shallow near-surface depths indicates dominant frequency range of 1 -- 3 Hz under favorable conditions that shifts toward lower frequencies with increasing depth. The light fluctuations were found to be spatially correlated over horizontal distances varying from few up to 10 -- 20 cm at temporal scales of 0.3 -- 1 sec (at the dominant frequency of 1 -- 3 Hz). The distance of correlation showed a tendency to increase with increasing depth, solar zenith angle, and wind speed. The observed variations in spatiotemporal statistical properties of underwater light fluctuations with depth and environmental conditions are driven largely by weakening of sunlight focusing which is associated with light scattering within the water column, in the atmosphere and at the air-sea interface. To investigate the underwater horizontal radiance field, measurements of horizontal spectral radiance in two opposite directions (solar and anti-solar azimuths) within the solar principal plane were made within the photic layer of the open ocean. The ratio of these two horizontal radiances represents the asymmetry of horizontal radiance field. In addition to measurements, the radiative transfer simulations were also conducted to examine variations in the asymmetry of horizontal radiance at different light wavelengths as a function of solar zenith angle at different depths within the water column down to 200 m. It was demonstrated that the asymmetry of horizontal radiance increases with increasing solar zenith angle, reaching a maximum at angles of 60° -- 80° under clear skies at shallow depths (1 -- 10 m). At larger depths the maximum of asymmetry occurs at smaller solar zenith angles. The asymmetry was also found to increase with increasing light wavelength. The results from radiative transfer simulations provided evidence that variations in the asymmetry with solar zenith angle are driven largely by the diffuseness of light incident upon the sea surface and the geometry of illumination of the sea surface, both associated with changing position of the sun. In addition to contributions to the field of ocean optics, the findings of this dissertation have relevance for oceanic animal camouflage and vision as well as photosynthesis and other photochemical processes.

Project Neil Bone: a great success!

NASA Astrophysics Data System (ADS)

Miles, R.

2010-08-01

Last October, the ARPS initiated a new observing project to make photometric observations of asteroids which reach a phase angle of 0.2° or less at opposition. The stimulus for this followed the naming last year of asteroid (7102) in honour of Neil Bone, our former Meteor Section Director, who sadly died last year. It turned out that (7102) would reach opposition on January 18 this year at an unusually low phase angle - just 0.03°. This is so small an angle that if you were standing on the asteroid on this date, you would be able to see the Earth transiting across the face of the Sun! The probability that (7102) would attain such a low phase angle is about once in several hundred years. So our project was set up with a view to observing its namesake along with a selection of thirteen other asteroids, which also happened to pass through very low phase angle at their opposition during the period 2009 October-2010 March.

A Dark Bend

NASA Image and Video Library

2016-09-05

Saturn's rings appear to bend as they pass behind the planet's darkened limb due to refraction by Saturn's upper atmosphere. The effect is the same as that seen in an earlier Cassini view (see PIA20491), except this view looks toward the unlit face of the rings, while the earlier image viewed the rings' sunlit side. The difference in illumination brings out some noticeable differences. The A ring is much darker here, on the rings' unlit face, since its larger particles primarily reflect light back toward the sun (and away from Cassini's cameras in this view). The narrow F ring (at bottom), which was faint in the earlier image, appears brighter than all of the other rings here, thanks to the microscopic dust that is prevalent within that ring. Small dust tends to scatter light forward (meaning close to its original direction of travel), making it appear bright when backlit. (A similar effect has plagued many a driver with a dusty windshield when driving toward the sun.) This view looks toward the unilluminated side of the rings from about 19 degrees below the ring plane. The image was taken in red light with the Cassini spacecraft narrow-angle camera on July 24, 2016. The view was acquired at a distance of approximately 527,000 miles (848,000 kilometers) from Saturn and at a sun-Saturn-spacecraft, or phase, angle of 169 degrees. Image scale is 3 miles (5 kilometers) per pixel. http://photojournal.jpl.nasa.gov/catalog/PIA20497

Twilight observation by the naked eye of the dawn sincere at Hail and other areas in Saudi Arabia

NASA Astrophysics Data System (ADS)

Khalifa, N. S.; Hassan, A. H.; Taha, A. I.

2018-06-01

Naked eye observations of morning twilight phenomenon at Hail and other areas of Saudi Arabia are recorded. During the interval from 2014 to 2015, about 80 morning twilight observations were carried out in Hail at longitude λ = 41°42‧E and latitude φ = 27°31‧N for a desert background. The phenomena was followed over azimuth angles ranged from 0° to 20° of solar vertical direction and from 0° to 10° along the altitudinal range. By selecting 32 days with a very good visibility, it was found that Sun depression, Do, lies in a range between 13.48° and 14.69° with an average of 14.014° ±0.317. The difference between our obtained value and that one which is currently applicable in Saudi Arabia is about 4°. The results indicate that dawn (white thread browser) occurs at a sun vertical depression angle Do = 14.66° (mean + 2SD) according to the normal eye estimations. The results at different areas in the deep desert in KSA showed that the beginning of morning twilight and true dawn is at sun vertical depression Do = 14.88° (mean + 1SD). The current study shows significant results, which are comparable with both naked eye observations and photoelectric measurements of true dawn in both Egypt and Libya for desert background.

Visual imaging control systems of the Mariner to Jupiter and Saturn spacecraft

NASA Technical Reports Server (NTRS)

Larks, L.

1979-01-01

Design and fabrication of optical systems for the Mariner Jupiter Saturn (Voyager) mission is described. Because of the long distances of these planets from the sun, the spacecraft was designed without solar panels with the electricity generated on-board by radio-isotope thermal generators (RTG). The presence of RTG's and Jupiter radiation environment required that the optical systems be fabricated out of radiation stabilized materials. A narrow angle and a wide angle camera are located on the spacecraft scan platform, with the narrow angle lens a modification of the Mariner 10 lens. The optical system is described, noting that the lens was modified by moving the aperture correctors forward and placing a spider mounted secondary mirror in the original back surface of the second aperture corrector. The wide angle lens was made out of cerium doped, radiation stabilized optical glass with greatest blue transmittance, which would be resistant to RTG and Jupiter radiation.

Highlights from 4STAR Sky-Scanning Retrievals of Aerosol Intensive Optical Properties from Multiple Field Campaigns with Detailed Comparisons of SSA Reported During SEAC4RS

NASA Technical Reports Server (NTRS)

Dunagan, Stephen E.

2016-01-01

The 4STAR (Spectrometer for Sky-Scanning, Sun-Tracking Atmospheric Research) instrument combines airborne sun tracking capabilities of the Ames Airborne Tracking Sun Photometer (AATS-14) with AERONET (Aerosol Robotic Network)-like sky-scanning capability and adds state-of-the-art fiber-coupled grating spectrometry to yield hyperspectral measurements of direct solar irradiance and angularly resolved sky radiance. The combination of sun-tracking and sky-scanning capability enables retrievals of wavelength-dependent aerosol optical depth (AOD), mode-resolved aerosol size distribution (SD), asphericity, and complex refractive index, and thus also the scattering phase function, asymmetry parameter, single-scattering albedo (SSA), and absorption aerosol optical thickness (AAOT). From 2012 to 2014 4STAR participated in four major field campaigns: the U.S. Dept. of Energy's TCAP (Two-Column Aerosol Project) I & II campaigns, and NASA's SEAC4RS (Studies of Emissions, Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys) and ARISE (Arctic Radiation - IceBridge Sea & Ice Experiment) campaigns. Establishing a strong performance record, 4STAR operated successfully on all flights conducted during each of these campaigns. Sky radiance spectra from scans in either constant azimuth (principal plane) or constant zenith angle (almucantar) were interspersed with direct beam measurements during level legs. During SEAC4RS and ARISE, 4STAR airborne measurements were augmented with flight-level albedo from the collocated Shortwave Spectral Flux Radiometer (SSFR) providing improved specification of below-aircraft radiative conditions for the retrieval. Calibrated radiances and retrieved products will be presented with particular emphasis on detailed comparisons of ambient SSA retrievals and measurements during SEAC4RS from 4STAR, AERONET, HSRL2 (High Spectral Resolution Lidar), and from in situ measurements.

Measurements of Nitrogen Dioxide Total Column Amounts using a Brewer Double Spectrophotometer in Direct Sun Mode

NASA Technical Reports Server (NTRS)

Cede, Alexander; Herman, Jay; Richter, Andreas; Krotkov, Nickolay; Burrows, John

2006-01-01

NO2 column amounts were measured for the past 2 years at Goddard Space Flight Center, Greenbelt, Maryland, using a Brewer spectrometer in direct Sun mode. A new bootstrap method to calibrate the instrument is introduced and described. This technique selects the cleanest days from the database to obtain the solar reference spectrum. The main advantage for direct Sun measurements is that the conversion uncertainty from slant column to vertical column is negligible compared to the standard scattered light observations where it is typically on the order of 100% (2sigma) at polluted sites. The total 2sigma errors of the direct Sun retrieved column amounts decrease with solar zenith angle and are estimated at 0.2 to 0.6 Dobson units (DU, 1 DU approx. equal to 2.7 10(exp 16) molecules cm(exp -2)), which is more accurate than scattered light measurements for high NO2 amounts. Measured NO2 column amounts, ranging from 0 to 3 DU with a mean of 0.7 DU, show a pronounced daily course and a strong variability from day to day. The NO2 concentration typically increases from sunrise to noon. In the afternoon it decreases in summer and stays constant in winter. As expected from the anthropogenic nature of its source, NO2 amounts on weekends are significantly reduced. The measurements were compared to satellite retrievals from Scanning Image Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY). Satellite data give the same average NO2 column and show a seasonal cycle that is similar to the ground data in the afternoon. We show that NO2 must be considered when retrieving aerosol absorption properties, especially for situations with low aerosol optical depth.

Tidal Friction in the Earth-Moon System and Laplace Planes: Darwin Redux

NASA Technical Reports Server (NTRS)

Rubincam, David P.

2015-01-01

The dynamical evolution of the Earth-Moon system due to tidal friction is treated here. George H. Darwin used Laplace planes (also called proper planes) in his study of tidal evolution. The Laplace plane approach is adapted here to the formalisms of W.M. Kaula and P. Goldreich. Like Darwin, the approach assumes a three-body problem: Earth, Moon, and Sun, where the Moon and Sun are point-masses. The tidal potential is written in terms of the Laplace plane angles. The resulting secular equations of motion can be easily integrated numerically assuming the Moon is in a circular orbit about the Earth and the Earth is in a circular orbit about the Sun. For Earth-Moon distances greater than 10 Earth radii, the Earth's approximate tidal response can be characterized with a single parameter, which is a ratio: a Love number times the sine of a lag angle divided by another such product. For low parameter values it can be shown that Darwin's low-viscosity molten Earth, M. Ross's and G. Schubert's model of an Earth near melting, and Goldreich's equal tidal lag angles must all give similar histories. For higher parameter values, as perhaps has been the case at times with the ocean tides, the Earth's obliquity may have decreased slightly instead of increased once the Moon's orbit evolved further than 50 Earth radii from the Earth, with possible implications for climate. This is contrast to the other tidal friction models mentioned, which have the obliquity always increasing with time. As for the Moon, its orbit is presently tilted to its Laplace plane by 5.2deg. The equations do not allow the Moon to evolve out of its Laplace plane by tidal friction alone, so that if it was originally in its Laplace plane, the tilt arose with the addition of other mechanisms, such as resonance passages.

Time behavior of solar flare particles to 5 AU

NASA Technical Reports Server (NTRS)

Haffner, J. W.

1972-01-01

A simple model of solar flare radiation event particle transport is developed to permit the calculation of fluxes and related quantities as a function of distance from the sun (R). This model assumes the particles spiral around the solar magnetic field lines with a constant pitch angle. The particle angular distributions and onset plus arrival times as functions of energy at 1 AU agree with observations if the pitch angle distribution peaks near 90 deg. As a consequence the time dependence factor is essentially proportional to R/1.7, (R in AU), and the event flux is proportional to R/2.

Rhea and Her Craters

NASA Image and Video Library

2005-01-17

This Cassini image shows predominantly the impact-scarred leading hemisphere of Saturn's icy moon Rhea (1,528 kilometers, or 949 miles across). The image was taken in visible light with the Cassini spacecraft narrow angle camera on Dec. 12, 2004, at a distance of 2 million kilometers (1.2 million miles) from Rhea and at a Sun-Rhea-spacecraft, or phase, angle of 30 degrees. The image scale is about 12 kilometers (7.5 miles) per pixel. The image has been magnified by a factor of two and contrast enhanced to aid visibility. http://photojournal.jpl.nasa.gov/catalog/PIA06564

Late Afternoon Sun

NASA Technical Reports Server (NTRS)

2002-01-01

[figure removed for brevity, see original site]

This image of the northern plains of Mars shows a surface texture of hundreds of small mounds and numerous small impact craters. The THEMIS imaging team is taking advantage of the late afternoon sun illumination to image places like this where the surface may contain small scale features that are 'washed-out' by higher illumination angles. As the sun dips towards the horizon (to the left side of the image), shadows are cast. The length of the shadows can be used to estimate the height of the feature casting them - or the depth of the crater that contains the shadow. In this image the craters - even very small ones - are now partially filled by shadow making it very easy to identify them. The small bumps are not casting shadows yet, but are easily seen. These small bumps were not easily identified when the sun angle was higher (earlier in the afternoon). As this image shows, late afternoon sun illumination is wonderful for making small scale morphologic features visible.

Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

Meteorological Support of the Helios World Record High Altitude Flight to 96,863 Feet

NASA Technical Reports Server (NTRS)

Teets, Edward H., Jr.; Donohue, Casey J.; Wright, Patrick T.; DelFrate, John (Technical Monitor)

2002-01-01

In characterizing and understanding atmospheric behavior when conducting high altitude solar powered flight research flight planning engineers and meteorologists are able to maximize the use of available airspace and coordinate aircraft maneuvers with pilots to make the best use of changing sun elevation angles. The result of this cooperative research produced a new world record for absolute altitude of a non-rocket powered aircraft of 96,863 ft (29,531.4 m). The Helios prototype solar powered aircraft, with a wingspan of 247 ft (75.0m), reached this altitude on August 13, 2001, off the coast of Kauai, Hawaii. The analyses of the weather characterization, the planning efforts, and the weather-of-the-day summary that led to at record flight are described in this paper.

Estimation and experimental evaluation of the shortfall of photovoltaic plants in Tunisia: case study of the use of titled surfaces

NASA Astrophysics Data System (ADS)

Belkilani, Kaouther; Ben Othman, Afef; Besbes, Mongi

2018-02-01

To maximize the production of electrical energy in photovoltaic plants, the best solution is to use sun tracking systems whose panels are permanently exposed to solar radiation to ensure the best angle of inclination. These systems are expensive, their implementation is difficult, and their maintenance is complicated. The fixed inclination of the solar panels is easy to implement but its profitability is minimal. To solve this dilemma, the researchers propose to shift the panel's angle of inclination over predetermined periods. In many countries, weather data measurements are either unavailable or lacking. So to fill this gap, we propose in this paper the development of mathematical models to calculate the best angle of inclination and the period of poise of this angle (month, season or other duration). The theoretical results obtained are validated by experimental tests and are conducted in three regions of Tunisia (North, Center and South). The objective is to determine, for each region, the optimal angle and the duration needed before switching to the next angle depending on the installation of fixed PV panels shortfalls.

Multi-layer Clouds Over the South Indian Ocean

NASA Technical Reports Server (NTRS)

2003-01-01

The complex structure and beauty of polar clouds are highlighted by these images acquired by the Multi-angle Imaging SpectroRadiometer (MISR) on April 23, 2003. These clouds occur at multiple altitudes and exhibit a noticeable cyclonic circulation over the Southern Indian Ocean, to the north of Enderbyland, East Antarctica.

The image at left was created by overlying a natural-color view from MISR's downward-pointing (nadir) camera with a color-coded stereo height field. MISR retrieves heights by a pattern recognition algorithm that utilizes multiple view angles to derive cloud height and motion. The opacity of the height field was then reduced until the field appears as a translucent wash over the natural-color image. The resulting purple, cyan and green hues of this aesthetic display indicate low, medium or high altitudes, respectively, with heights ranging from less than 2 kilometers (purple) to about 8 kilometers (green). In the lower right corner, the edge of the Antarctic coastline and some sea ice can be seen through some thin, high cirrus clouds.

The right-hand panel is a natural-color image from MISR's 70-degree backward viewing camera. This camera looks backwards along the path of Terra's flight, and in the southern hemisphere the Sun is in front of this camera. This perspective causes the cloud-tops to be brightly outlined by the sun behind them, and enhances the shadows cast by clouds with significant vertical structure. An oblique observation angle also enhances the reflection of light by atmospheric particles, and accentuates the appearance of polar clouds. The dark ocean and sea ice that were apparent through the cirrus clouds at the bottom right corner of the nadir image are overwhelmed by the brightness of these clouds at the oblique view.

The Multi-angle Imaging SpectroRadiometer observes the daylit Earth continuously from pole to pole, and every 9 days views the entire globe between 82 degrees north and 82 degrees south latitude. These data products were generated from a portion of the imagery acquired during Terra orbit 17794. The panels cover an area of 335 kilometers x 605 kilometers, and utilize data from blocks 142 to 145 within World Reference System-2 path 155.

MISR was built and is managed by NASA's Jet Propulsion Laboratory, Pasadena, CA, for NASA's Office of Earth Science, Washington, DC. The Terra satellite is managed by NASA's Goddard Space Flight Center, Greenbelt, MD. JPL is a division of the California Institute of Technology.

MISR Global Images See the Light of Day

NASA Technical Reports Server (NTRS)

2002-01-01

As of July 31, 2002, global multi-angle, multi-spectral radiance products are available from the MISR instrument aboard the Terra satellite. Measuring the radiative properties of different types of surfaces, clouds and atmospheric particulates is an important step toward understanding the Earth's climate system. These images are among the first planet-wide summary views to be publicly released from the Multi-angle Imaging SpectroRadiometer experiment. Data for these images were collected during the month of March 2002, and each pixel represents monthly-averaged daylight radiances from an area measuring 1/2 degree in latitude by 1/2 degree in longitude.

The top panel is from MISR's nadir (vertical-viewing) camera and combines data from the red, green and blue spectral bands to create a natural color image. The central view combines near-infrared, red, and green spectral data to create a false-color rendition that enhances highly vegetated terrain. It takes 9 days for MISR to view the entire globe, and only areas within 8 degrees of latitude of the north and south poles are not observed due to the Terra orbit inclination. Because a single pole-to-pole swath of MISR data is just 400 kilometers wide, multiple swaths must be mosaiced to create these global views. Discontinuities appear in some cloud patterns as a consequence of changes in cloud cover from one day to another.

The lower panel is a composite in which red, green, and blue radiances from MISR's 70-degree forward-viewing camera are displayed in the northern hemisphere, and radiances from the 70-degree backward-viewing camera are displayed in the southern hemisphere. At the March equinox (spring in the northern hemisphere, autumn in the southern hemisphere), the Sun is near the equator. Therefore, both oblique angles are observing the Earth in 'forward scattering', particularly at high latitudes. Forward scattering occurs when you (or MISR) observe an object with the Sun at a point in the sky that is in front of you. Relative to the nadir view, this geometry accentuates the appearance of polar clouds, and can even reveal clouds that are invisible in the nadir direction. In relatively clear ocean areas, the oblique-angle composite is generally brighter than its nadir counterpart due to enhanced reflection of light by atmospheric particulates.

MISR was built and is managed by NASA's Jet Propulsion Laboratory, Pasadena, CA, for NASA's Office of Earth Science, Washington, DC. The Terra satellite is managed by NASA's Goddard Space Flight Center, Greenbelt, MD. JPL is a division of the California Institute of Technology.

Development of a digital mobile solar tracker

NASA Astrophysics Data System (ADS)

Baidar, S.; Kille, N.; Ortega, I.; Sinreich, R.; Thomson, D.; Hannigan, J.; Volkamer, R.

2015-11-01

We have constructed and deployed a fast digital solar tracker aboard a moving ground-based platform. The tracker consists of two rotating mirrors, a lens, an imaging camera, and a motion compensation system that provides the Euler angles of the mobile platform in real time. The tracker can be simultaneously coupled to UV-Vis and FTIR spectrometers making it a versatile tool to measure the absorption of trace gases using solar incoming radiation. The integrated system allows the tracker to operate autonomously while the mobile laboratory is in motion. Mobile direct sun Differential Optical Absorption Spectroscopy (mobile DS-DOAS) observations using this tracker were conducted during summer 2014 as part of the Front Range Photochemistry and Pollution Experiment (FRAPPE) in Colorado, USA. We demonstrate an angular precision of 0.052° (about 1/10 of the solar disk diameter) during research drives, and verify this tracking precision from measurements of the center to limb darkening (CLD, the changing appearance of Fraunhofer lines) in the mobile DS-DOAS spectra. The high photon flux from direct sun observation enables measurements of nitrogen dioxide (NO2) slant columns with high temporal resolution, and reveals spatial detail in the variations of NO2 vertical column densities (VCDs). The NO2 VCD from DS-DOAS is compared with a co-located MAX-DOAS instrument. Overall good agreement is observed amid a highly heterogeneous air mass.

Development of a digital mobile solar tracker

NASA Astrophysics Data System (ADS)

Baidar, Sunil; Kille, Natalie; Ortega, Ivan; Sinreich, Roman; Thomson, David; Hannigan, James; Volkamer, Rainer

2016-03-01

We have constructed and deployed a fast digital solar tracker aboard a moving ground-based platform. The tracker consists of two rotating mirrors, a lens, an imaging camera, and a motion compensation system that provides the Euler angles of the mobile platform in real time. The tracker can be simultaneously coupled to UV-Vis and Fourier transform infrared spectrometers, making it a versatile tool to measure the absorption of trace gases using solar incoming radiation. The integrated system allows the tracker to operate autonomously while the mobile laboratory is in motion. Mobile direct sun differential optical absorption spectroscopy (mobile DS-DOAS) observations using this tracker were conducted during summer 2014 as part of the Front Range Air Pollution and Photochemistry Experiment (FRAPPE) in Colorado, USA. We demonstrate an angular precision of 0.052° (about 1/10 of the solar disk diameter) during research drives and verify this tracking precision from measurements of the center to limb darkening (CLD, the changing appearance of Fraunhofer lines) in the mobile DS-DOAS spectra. The high photon flux from direct sun observation enables measurements of nitrogen dioxide (NO2) slant columns with high temporal resolution and reveals spatial detail in the variations of NO2 vertical column densities (VCDs). The NO2 VCD from DS-DOAS is compared with a co-located MAX-DOAS instrument. Overall good agreement is observed amid a highly heterogeneous air mass.

The influence of IMF cone angle on invariant latitudes of polar region footprints of FACs in the magnetotail: Cluster observatio

NASA Astrophysics Data System (ADS)

Cheng, Z.; Shi, J.; Zhang, J.; Kistler, L. M.

2017-12-01

The influence of the interplanetary magnetic field (IMF) cone angle θ (the angle between the IMF direction and the Sun-Earth line) on the invariant latitudes (ILATs) of the footprints of the field-aligned currents (FACs) in the magnetotail has been investigated. We performed a statistic study of 542 FAC cases observed by the four Cluster spacecraft in the northern hemisphere. The results show that the large FAC (>10 nA/m2) cases occur at the low ILATs (<71 º) and mainly occur when the IMF cone angle θ>60º, which implies the footprints of the large FACs mainly expand equatorward with large IMF cone angle. The equatorward boundary of the FAC footprints in the polar region decreases with the IMF cone angle especially when IMF Bz is positive. There is almost no correlation or a weak positive correlation of the poleward boundary and IMF cone angle no matter IMF is northward or southward. The equatorward boundary is more responsive to the IMF cone angle. Compared to the equatorward boundary, the center of the FAC projected location changes very little. This is the first time a correlation between FAC projected location and IMF cone angle has been determined.

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

NASA Technical Reports Server (NTRS)

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

1988-01-01

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

Implementation of the Sun Position Calculation in the PDC-1 Control Microprocessor

NASA Technical Reports Server (NTRS)

Stallkamp, J. A.

1984-01-01

The several computational approaches to providing the local azimuth and elevation angles of the Sun as a function of local time and then the utilization of the most appropriate method in the PDC-1 microprocessor are presented. The full algorithm, the FORTRAN form, is felt to be very useful in any kind or size of computer. It was used in the PDC-1 unit to generate efficient code for the microprocessor with its floating point arithmetic chip. The balance of the presentation consists of a brief discussion of the tracking requirements for PPDC-1, the planetary motion equations from the first to the final version, and the local azimuth-elevation geometry.

Sublimation rates of carbon monoxide and carbon dioxide from comet nuclei at large distances from the Sun

NASA Technical Reports Server (NTRS)

Sekanina, Zdenek

1991-01-01

One of the more attractive among the plausible scenarios for the major emission event recently observed on Comet Halley at a heliocentric distance of 14.3 AU is activation of a source of ejecta driven by an icy substance much more volatile than water. As prerequisite for the forthcoming detailed analysis of the imaging observations of this event, a simple model is proposed that yields the sublimation rate versus time at any location on the surface of a rotating cometary nucleus for two candidate ices: carbon monoxide and carbon dioxide. The model's variable parameters are the comet's heliocentric distance r and the Sun's instantaneous zenith angle z.

Hyperspectral Sun Photometer for Atmospheric Characterization and Vicarious Calibrations

NASA Technical Reports Server (NTRS)

Pagnutti, Mary; Ryan, Robert; Holekamp, Kara

2008-01-01

A hyperspectral sun photometer and associated methods have been developed and demonstrated. Accurate sun photometer calibration is critical to properly measure the solar irradiance and characterize the atmosphere. Traditional sun photometer calibration requires solar observations over several hours. In contrast, the procedures for operating this photometer entail less data acquisition time and embody a more direct approach to calibration. The scientific value of the measurement data produced by this instrument is not adversely affected by atmospheric instability. In addition, this instrument yields hyperspectral data covering a large spectral range (350-2,500 nm) not available from most traditional sun photometers. The hyperspectral sun photometer components include (1) a commercially available spectroradiometer that has been laboratory-calibrated and (2) a commercially available reflectance standard panel that exhibits nearly Lambertian 99% reflectance. The spectroradiometer is positioned above, and aimed downward at, the panel. The procedure for operating this instrument calls for a series of measurements: one in which the panel is fully illuminated by the sun, one in which a shade is positioned between the panel and the sun, and two in which the shade is positioned to cast a shadow to either side of the panel. The total sequence of measurements can be performed in less than a minute. From these measurements, the total radiance, the diffuse radiance, and the direct solar radiance are calculated. The direct solar irradiance is calculated from the direct solar radiance and the known reflectance factor of the panel as a function of the solar zenith angle. Atmospheric characteristics are estimated from the optical depth at various wavelengths calculated from (1) the direct solar irradiance obtained as described above, (2) the air mass along a column from the measurement position to the Sun, and (3) the top-of-atmosphere solar irradiance. The instrumentation used to implement the sun photometer is the same as that used to characterize targets used in radiometric vicarious calibrations. Utilizing this type of sun photometer thus reduces the amount of instrumentation and labor required to perform these studies.

Inferring total canopy APAR from PAR bidirectional reflectances and vegetation indices in tallgrass prairie. [Absorbed Photosynthetically Active Radiation

NASA Technical Reports Server (NTRS)

Middleton, Elizabeth M.

1992-01-01

The fraction of photosynthetically active radiation (PAR) absorbed by a vegetated canopy (APARc) or landscape (APARs) is a critical parameter in climate processes. A grassland study examined: 1) whether APARs can be estimated from PAR bidirectional exitance fractions; and 2) whether APARs is correlated with spectral vegetation indices (SVIs). Data were acquired with a high resolution continuous spectroradiometer at 4 sun angles on grassland sites. APARs was computed from the scattered surface PAR exitance fractions. The nadir APARs value was the most variable diurnally; it provided a good estimate of the average surface APARs at 95 percent. APARc was best represented by exitance factors between 30-60* forward.

Need for expanded environmental measurement capabilities in geosynchronous Earth orbit

NASA Technical Reports Server (NTRS)

Mercanti, Enrico P.

1991-01-01

The proliferation of environmental satellites in low altitude earth orbit (LEO) has demonstrated the usefulness of earth remote sensing from space. As use of the technology grows, the limitations of LEO missions become more apparent. Many inadequacies can be met by remote sensing from geosynchronous earth orbits (GEO) that can provide high temporal resolution, consistent viewing of specific earth targets, long sensing dwell times with varying sun angles, stereoscopic coverage, and correlative measurements with ground and LEO observations. An environmental platform in GEO is being studied by NASA. Small research satellite missions in GEO were studied (1990) at GSFC. Some recent independent assessments of NASA Earth Science Programs recommend accelerating the earlier deployment of smaller missions.

Monitoring the Vernal Advancement and Retrogradation (Green Wave Effect) of Natural Vegetation. [Great Plains Corridor

NASA Technical Reports Server (NTRS)

Rouse, J. W., Jr. (Principal Investigator); Haas, R. H.; Deering, D. W.; Schell, J. A.; Harlan, J. C.

1974-01-01

The author has identified the following significant results. The Great Plains Corridor rangeland project successfully utilized natural vegetation systems as phenological indicators of seasonal development and climatic effects upon regional growth conditions. An effective method was developed for quantitative measurement of vegetation conditions, including green biomass estimates, recorded in bands 5 and 6, corrected for sun angle, were used to compute a ratio parameter (TV16) which is shown to be highly correlated with green biomass and vegatation moisture content. Analyses results of ERTS-1 digital data and correlated ground data are summarized. Attention was given to analyzing weather influences and test site variables on vegetation condition measurements with ERTS-1 data.

The intercrater plains of Mercury and the Moon: Their nature, origin and role in terrestrial planet evolution. Areal measurement of Mercury's first quadrant. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Leake, M. A.

1982-01-01

Various linear and areal measurements of Mercury's first quadrant which were used in geological map preparation, map analysis, and statistical surveys of crater densities are discussed. Accuracy of each method rests on the determination of the scale of the photograph, i.e., the conversion factor between distances on the planet (in km) and distances on the photograph (in cm). Measurement errors arise due to uncertainty in Mercury's radius, poor resolution, poor coverage, high Sun angle illumination in the limb regions, planetary curvature, limited precision in measuring instruments, and inaccuracies in the printed map scales. Estimates are given for these errors.

Sun Protection Practices and Sun Exposure among Children with a Parental History of Melanoma

PubMed Central

Glenn, Beth A.; Lin, Tiffany; Chang, L. Cindy; Okada, Ashley; Wong, Weng Kee; Glanz, Karen; Bastani, Roshan

2014-01-01

Background First-degree relatives of melanoma survivors have a substantially higher lifetime risk for melanoma than individuals with no family history. Exposure to ultraviolet radiation is the primary modifiable risk factor for the disease. Reducing UV exposure through sun protection may be particularly important for children with a parental history of melanoma. Nonetheless, limited prior research has investigated sun protection practices and sun exposure among these children. Methods The California Cancer Registry was used to identify melanoma survivors eligible to participate in a survey to assess their children's sun protection practices and sun exposure. The survey was administered by mail, telephone, or web to Latino and non-Latino white melanoma survivors with at least one child (0–17 years; N = 324). Results Sun exposure was high and the rate of sunburn was equivalent to or higher than estimates from average risk populations. Use of sun protection was suboptimal. Latino children were less likely to wear sunscreen and hats and more likely to wear sunglasses, although these differences disappeared in adjusted analyses. Increasing age of the child was associated with lower sun protection and higher risk for sunburn whereas higher objective risk for melanoma predicted improved sun protection and a higher risk for sunburns. Perception of high barriers to sun protection was the strongest modifiable correlate of sun protection. Conclusions Interventions to improve sun protection and reduce sun exposure and sunburns in high risk children are needed. Impact Intervening in high risk populations may help reduce the burden of melanoma in the U.S. PMID:25587110

Sun Shading Diagrams for School Buildings. Educational Building Report 2.

ERIC Educational Resources Information Center

Mooij, D.

This publication provides data on the angles governing the design of sunshading devices for educational buildings in the countries of the Asian region and gives examples of the ways in which these data can be used. Different methods of excluding direct sunlight from teaching spaces are illustrated in a series of diagrams that show exclusion by…

Apollo 8 Mission image,Farside of Moon

NASA Image and Video Library

1968-12-21

Apollo 8,Farside of Moon. Image taken on Revolution 4. Camera Tilt Mode: Vertical Stereo. Sun Angle: 13. Original Film Magazine was labeled D. Camera Data: 70mm Hasselblad. Lens: 80mm; F-Stop: F/2.8; Shutter Speed: 1/250 second. Film Type: Kodak SO-3400 Black and White,ASA 40. Flight Date: December 21-27,1968.

Central portion of Florida, Gulf of Mexico seen from Gemini 11

NASA Image and Video Library

1966-09-14

S66-54565 (14 Sept. 1966) --- Central portion of Florida, Gulf of Mexico to Atlantic Ocean, Cape Kennedy is at left center of photo, as seen from the Gemini-11 spacecraft during its 29th revolution of Earth. Photo lacks detail due to low sun angle. Sunglint on lakes is visible. Photo credit: NASA

Diurnal movements of cotton leaves expressed as thermodynamic work and entropy changes

NASA Technical Reports Server (NTRS)

Schutt, J. B.; Kimes, D. S.; Newcomb, W. W.

1985-01-01

It is pointed out that some important agricultural crops show heliotropic leaf movements. In these species, the proclivity of leaves to orient either perpendicularly or parallel or in some combination of these positions with respect to the sun is controlled by the leaf turgor and the availability of water. Such an orientational response is particularly noticeable for cotton. Schutt et al. (1985) have detailed leaf trajectories using three angles. The present investigation applies the three-angle representation to leaf trajectory mapping and to the calculation of the phase angle 'gamma' between the individual leaf normals and the solar direction. Using gamma, the thermodynamic work and entropy functions are evaluated and used to distinguish between the behavior of water-stressed and well watered cotton canopies.

Contingency maneuver strategies for the Total Ozone Mapping Spectrometer-Earth Probe (TOMS-EP)

NASA Technical Reports Server (NTRS)

Kestler, James; Walls, Donna

1995-01-01

The Total Ozone Mapping Spectrometer-Earth Probe (TOMS-EP) is a polar-orbiting spacecraft designed to measure total ozone levels in the Earth's atmosphere. The nominal mission orbit is a 955-kilometer circular Sun-synchronous orbit with an ascending node mean local crossing time (MLT) between 11:02 a.m. and 11:25 a.m. These two mean local ascending node times constitute the boundaries of the MLT box for this mission. The MLT boundaries were chosen to maintain the Sun-to-Earth-to-vehicle orbit-normal (SVN) angle within a preselected set of seasonally independent boundaries. Because the SVN angle is seasonally dependent, but the MLT is not, contingency options for correcting the MLT of orbital states that fall outside of the required MLT range become time dependent. This paper focuses on contingency orbit adjustment strategies developed at the Goddard Space Flight Center (GSFC) Flight Dynamics Division (FDD) during the mission planning phase of TOMS-EP. Time-dependent delta-V strategies are presented for correcting mission orbit states lying outside of the MLT range. Typically, passive control of the MLT drift rate can be used to restore the orbit state to the required MLT before a seasonal violation of SVN angle constraints can occur. Passive control of the MLT drift rate is obtained through adjustment of the semimajor axis and/or the inclination. The time between initial arrival on orbit at an 'out-of-the box' MLT state and violation of the SVN angle constraints is always less than or equal to 1 year. The choice of which parameter(s) to adjust is dictated by the duration of this time period, the desired mission lifetime, the delta-V cost, and operational constraints.

Artificial phototropism based on a photo-thermo-responsive hydrogel

NASA Astrophysics Data System (ADS)

Gopalakrishna, Hamsini

Solar energy is leading in renewable energy sources and the aspects surrounding the efforts to harvest light are gaining importance. One such aspect is increasing the light absorption, where heliotropism comes into play. Heliotropism, the ability to track the sun across the sky, can be integrated with solar cells for more efficient photon collection and other optoelectronic systems. Inspired by plants, which optimize incident sunlight in nature, several researchers have made artificial heliotropic and phototropic systems. This project aims to design, synthesize and characterize a material system and evaluate its application in a phototropic system. A gold nanoparticle (Au NP) incorporated poly(N-isopropylacrylamide) (PNIPAAm) hydrogel was synthesized as a photo-thermo-responsive material in our phototropic system. The Au NPs generate heat from the incident via plasmonic resonance to induce a volume phase change of the thermo-responsive hydrogel PNIPAAm. PNIPAAm shrinks or swells at temperature above or below 32°C. Upon irradiation, the Au NP-PNIPAAm micropillar actuates, specifically bending toward the incident light and precisely following the varying incident angle. Swelling ratio tests, bending angle tests with a static incident light and bending tests with varying angles were carried out on hydrogel samples with varying Au NP concentrations. Swelling ratios ranging from 1.45 to 2.9 were recorded for pure hydrogel samples and samples with very low Au NP concentrations. Swelling ratios of 2.41 and 3.37 were calculated for samples with low and high concentrations of Au NPs, respectively. A bending of up to 88° was observed in Au NP-hydrogel pillars with a low Au NP concentration with a 90° incident angle. The light tracking performance was assessed by the slope of the pillar Bending angle (response angle) vs. Incident light angle plot. A slope of 1 indicates ideal tracking with top of the pillar being normal to the incident light, maximizing the photon absorption. Slopes of 0.82 and 0.56 were observed for the low and high Au NP concentration samples. The rapid and precise incident light tracking of our system has shown the promise in phototropic applications.

Digital Astronaut Photography: A Discovery Dataset for Archaeology

NASA Technical Reports Server (NTRS)

Stefanov, William L.

2010-01-01

Astronaut photography acquired from the International Space Station (ISS) using commercial off-the-shelf cameras offers a freely-accessible source for high to very high resolution (4-20 m/pixel) visible-wavelength digital data of Earth. Since ISS Expedition 1 in 2000, over 373,000 images of the Earth-Moon system (including land surface, ocean, atmospheric, and lunar images) have been added to the Gateway to Astronaut Photography of Earth online database (http://eol.jsc.nasa.gov ). Handheld astronaut photographs vary in look angle, time of acquisition, solar illumination, and spatial resolution. These attributes of digital astronaut photography result from a unique combination of ISS orbital dynamics, mission operations, camera systems, and the individual skills of the astronaut. The variable nature of astronaut photography makes the dataset uniquely useful for archaeological applications in comparison with more traditional nadir-viewing multispectral datasets acquired from unmanned orbital platforms. For example, surface features such as trenches, walls, ruins, urban patterns, and vegetation clearing and regrowth patterns may be accentuated by low sun angles and oblique viewing conditions (Fig. 1). High spatial resolution digital astronaut photographs can also be used with sophisticated land cover classification and spatial analysis approaches like Object Based Image Analysis, increasing the potential for use in archaeological characterization of landscapes and specific sites.

MAGNETIC UNTWISTING IN SOLAR JETS THAT GO INTO THE OUTER CORONA IN POLAR CORONAL HOLES

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

Moore, Ronald L.; Sterling, Alphonse C.; Falconer, David A., E-mail: ron.moore@nasa.gov

We study 14 large solar jets observed in polar coronal holes. In EUV movies from the Solar Dynamics Observatory/Atmospheric Imaging Assembly (AIA), each jet appears similar to most X-ray jets and EUV jets that erupt in coronal holes; but each is exceptional in that it goes higher than most, so high that it is observed in the outer corona beyond 2.2 R{sub Sun} in images from the Solar and Heliospheric Observatory/Large Angle Spectroscopic Coronagraph (LASCO)/C2 coronagraph. From AIA He ii 304 Å movies and LASCO/C2 running-difference images of these high-reaching jets, we find: (1) the front of the jet transitsmore » the corona below 2.2 R{sub Sun} at a speed typically several times the sound speed; (2) each jet displays an exceptionally large amount of spin as it erupts; (3) in the outer corona, most of the jets display measureable swaying and bending of a few degrees in amplitude; in three jets the swaying is discernibly oscillatory with a period of order 1 hr. These characteristics suggest that the driver in these jets is a magnetic-untwisting wave that is basically a large-amplitude (i.e., nonlinear) torsional Alfvén wave that is put into the reconnected open field in the jet by interchange reconnection as the jet erupts. From the measured spinning and swaying, we estimate that the magnetic-untwisting wave loses most of its energy in the inner corona below 2.2 R{sub Sun}. We point out that the torsional waves observed in Type-II spicules might dissipate in the corona in the same way as the magnetic-untwisting waves in our big jets, and thereby power much of the coronal heating in coronal holes.« less

Solar Wind Characteristics from SOHO-Sun-Ulysses Quadrature Observations

NASA Technical Reports Server (NTRS)

Poletto, Giannina; Suess, Steve T.; Six, N. Frank (Technical Monitor)

2002-01-01

Over the past few years, we have been running SOHO (Solar and Heliospheric Observatory)-Sun-Ulysses quadrature campaigns, aimed at comparing the plasma properties at coronal altitudes with plasma properties at interplanetary distances. Coronal plasma has been observed by SOHO experiments: mainly, we used LASCO (Large Angle and Spectrometric Coronagraph Experiment) data to understand the overall coronal configuration at the time of quadratures and analyzed SUMER (Solar Ultraviolet Measurements of Emitted Radiation), CDS (Coronal Diagnostic Spectrometer) and UVCS (Ultraviolet Coronagraph Spectrometer) data to derive its physical characteristics. At interplanetary distances, SWICS (Solar Wind Ion Composition Spectrometer) and SWOOPS (Solar Wind Observation over the Poles of the Sun) aboard Ulysses provided us with interplanetary plasma data. Here we report on results from some of the campaigns. We notice that, depending on the geometry of the quadrature, i.e. on whether the radial to Ulysses traverses the corona at high or low latitudes, we are able to study different kinds of solar wind. In particular, a comparison between low-latitude and high-latitude wind, allowed us to provide evidence for differences in the acceleration of polar, fast plasma and equatorial, slow plasma: the latter occurring at higher levels and through a more extended region than fast wind. These properties are shared by both the proton and heavy ions outflows. Quadrature observations may provide useful information also on coronal vs. in situ elemental composition. To this end, we analyzed spectra taken in the corona, at altitudes ranging between approx. 1.02 and 2.2 solar radii, and derived the abundances of a number of ions, including oxygen and iron. Values of the O/Fe ratio, at coronal levels, have been compared with measurements of this ratio made by SWICS at interplanetary distances. Our results are compared with previous findings and predictions from modeling efforts.

NASA Solar Array Demonstrates Commercial Potential

NASA Technical Reports Server (NTRS)

Creech, Gray

2006-01-01

A state-of-the-art solar-panel array demonstration site at NASA's Dryden Flight Research Center provides a unique opportunity for studying the latest in high-efficiency solar photovoltaic cells. This five-kilowatt solar-array site (see Figure 1) is a technology-transfer and commercialization success for NASA. Among the solar cells at this site are cells of a type that was developed in Dryden Flight Research Center s Environmental Research Aircraft and Sensor Technology (ERAST) program for use in NASA s Helios solar-powered airplane. This cell type, now denoted as A-300, has since been transferred to SunPower Corporation of Sunnyvale, California, enabling mass production of the cells for the commercial market. High efficiency separates these advanced cells from typical previously commercially available solar cells: Whereas typical previously commercially available cells are 12 to 15 percent efficient at converting sunlight to electricity, these advanced cells exhibit efficiencies approaching 23 percent. The increase in efficiency is due largely to the routing of electrical connections behind the cells (see Figure 2). This approach to increasing efficiency originated as a solution to the problem of maximizing the degree of utilization of the limited space available atop the wing of the Helios airplane. In retrospect, the solar cells in use at this site could be used on Helios, but the best cells otherwise commercially available could not be so used, because of their lower efficiencies. Historically, solar cells have been fabricated by use of methods that are common in the semiconductor industry. One of these methods includes the use of photolithography to define the rear electrical-contact features - diffusions, contact openings, and fingers. SunPower uses these methods to produce the advanced cells. To reduce fabrication costs, SunPower continues to explore new methods to define the rear electrical-contact features. The equipment at the demonstration site includes two fixed-angle solar arrays and one single-axis Sun-tracking array. One of the fixed arrays contains typical less-efficient commercial solar cells and is being used as a baseline for comparison of the other fixed array, which contains the advanced cells. The Sun-tracking array tilts to follow the Sun, using an advanced, real-time tracking device rather than customary pre-programmed mechanisms. Part of the purpose served by the demonstration is to enable determination of any potential advantage of a tracking array over a fixed array. The arrays are monitored remotely on a computer that displays pertinent information regarding the functioning of the arrays.

Characterization of sun and sky glint from wind ruffled sea surfaces for improved estimation of polarized remote sensing reflectance

NASA Astrophysics Data System (ADS)

Foster, Robert; Ibrahim, Amir; Gilerson, Alex; El-Habashi, Ahmed; Carrizo, Carlos; Ahmed, Sam

2015-09-01

During two cruises in 2014, the polarized radiance of the ocean and the sky were continuously acquired using a HyperSAS-POL system. The system consists of seven hyperspectral radiometric sensors, three of which (one unpolarized and two polarized) look at the water and similarly three at the sky. The system autonomously tracks the Sun position and the heading of the research vessel to which it is attached in order to maintain a fixed relative azimuth angle with respect to the Sun (i.e. 90°) and therefore avoid the specular reflection of the sunlight. For the duration of both cruises, (NASA Ship Aircraft Bio-Optical Research (SABOR), and NOAA VIIRS Validation/Calibration), in situ inherent optical properties (IOPs) were continuously acquired using a set of instrument packages modified for underway measurement, and hyperspectral radiometric measurements were taken manually at all stations. During SABOR, an underwater polarimeter was deployed when conditions permitted. All measurements were combined in an effort to first develop a glint (sky + Sun) correction scheme for the upwelling polarized signal from a wind driven ocean surface and compare with one assuming that the ocean surface is flat.

Dissemination of go sun smart in outdoor recreation: effect of program exposure on sun protection of guests at high-altitude ski areas.

PubMed

Walkosz, Barbara J; Buller, David B; Andersen, Peter A; Scott, Michael D; Dignan, Mark B; Cutter, Gary R; Liu, Xia; Maloy, Julie A

2014-09-01

Go Sun Smart is a theory-based health communication program designed to influence sun-protection behaviors of employees and guests at high-altitude ski areas to reduce skin cancer risk. The effects of Go Sun Smart, in a Phase IV dissemination randomized posttest-only trial, on sun-protection behaviors of ski area guests are reported. Program use was assessed by on-site observation and guest message exposure, and sun protection was measured in intercept surveys at ski areas. Dissemination strategy-enhanced versus basic-was not significantly related to sun safety practices. Additional analyses examined the relation between message exposure and guests' sun safety practices. Ski areas displaying at least 6 Go Sun Smart materials in guest-only areas and 9 Go Sun Smart materials throughout the area increased guests' message exposure. Higher message exposure within the high-use ski areas was associated with improved sun protection by guests but not within the low-use ski areas. The authors underscore the importance of program implementation and message exposure on the success of evidence-based health communication efforts applied industrywide.

Ring Around the Sun

NASA Technical Reports Server (NTRS)

2007-01-01

Our 'constant' sun is really more like a spherical sea of incredibly hot plasma, changing all the time. Astronomers like to keep a good eye on it, so no dramatic change goes by unnoticed. One amazing occurrence happened on Dec 7, 2007 and was seen by one of the two STEREO satellites. STEREO, as you recall, consists of a pair of satellites which observe the sun from different angles and allow astronomers to get a ŗ-D' view of the solar atmosphere and solar outflows. On December 7 one of the STEREO satellites captured a view (in the extreme ultraviolet part of the electromagnetic spectrum) of a Coronal Mass Ejection that released a huge amount of energy into the solar atmosphere, and a huge amount of matter into interplanetary space. A sort of atmospheric 'sunquake'. One result of this 'sunquake' was the production of a giant wave rippling through almost the entire solar atmosphere. The image above shows a snapshot of this unbelievable wave, slightly enhanced for viewability. Don't miss the movie. What damps the wave?

Sun glint requirement for the remote detection of surface oil films

NASA Astrophysics Data System (ADS)

Sun, Shaojie; Hu, Chuanmin

2016-01-01

Natural oil slicks in the western Gulf of Mexico are used to determine the sun glint threshold required for optical remote sensing of oil films. The threshold is determined using the same-day image pairs collected by Moderate Resolution Imaging Spectroradiometer (MODIS) Terra (MODIST), MODIS Aqua (MODISA), and Visible Infrared Imaging Radiometer Suite (VIIRS) (N = 2297 images) over the same oil slick locations where at least one of the sensors captures the oil slicks. For each sensor, statistics of sun glint strengths, represented by the normalized glint reflectance (LGN, sr-1), when oil slicks can and cannot be observed are generated. The LGN threshold for oil film detections is determined to be 10-5-10-6 sr-1 for MODIST and MODISA, and 10-6-10-7 sr-1 for VIIRS. Below these thresholds, no oil films can be detected, while above these thresholds, oil films can always be detected except near the critical-angle zone where oil slicks reverse their contrast against the background water.

Self-tracking solar concentrator with an acceptance angle of 32°.

PubMed

Zagolla, Volker; Dominé, Didier; Tremblay, Eric; Moser, Christophe

2014-12-15

Solar concentration has the potential to decrease the cost associated with solar cells by replacing the receiving surface aperture with cheaper optics that concentrate light onto a smaller cell aperture. However a mechanical tracker has to be added to the system to keep the concentrated light on the size reduced solar cell at all times. The tracking device itself uses energy to follow the sun's position during the day. We have previously shown a mechanism for self-tracking that works by making use of the infrared energy of the solar spectrum, to activate a phase change material. In this paper, we show an implementation of a working 53 x 53 mm(2) self-tracking system with an acceptance angle of 32° ( ± 16°). This paper describes the design optimizations and upscaling process to extend the proof-of-principle self-tracking mechanism to a working demonstration device including the incorporation of custom photodiodes for system characterization. The current version demonstrates an effective concentration of 3.5x (compared to 8x theoretical) over 80% of the desired acceptance angle. Further improvements are expected to increase the efficiency of the system and open the possibility to expand the device to concentrations as high as 200x (C(geo) = 400x, η = 50%, for a solar cell matched spectrum).

High precision dual-axis tracking solar wireless charging system based on the four quadrant photoelectric sensor

NASA Astrophysics Data System (ADS)

Liu, Zhilong; Wang, Biao; Tong, Weichao

2015-08-01

This paper designs a solar automatic tracking wireless charging system based on the four quadrant photoelectric sensor. The system track the sun's rays automatically in real time to received the maximum energy and wireless charging to the load through electromagnetic coupling. Four quadrant photoelectric sensor responsive to the solar spectrum, the system could get the current azimuth and elevation angle of the light by calculating the solar energy incident on the sensor profile. System driver the solar panels by the biaxial movement mechanism to rotate and tilt movement until the battery plate and light perpendicular to each other. Maximize the use of solar energy, and does not require external power supply to achieve energy self-sufficiency. Solar energy can be collected for portable devices and load wireless charging by close electromagnetic field coupling. Experimental data show that: Four quadrant photoelectric sensor more sensitive to light angle measurement. when track positioning solar light, Azimuth deviation is less than 0.8°, Elevation angle deviation is less than 0.6°. Use efficiency of a conventional solar cell is only 10% -20%.The system uses a Four quadrant dual-axis tracking to raise the utilization rate of 25% -35%.Wireless charging electromagnetic coupling efficiency reached 60%.

Near-Earth asteroids orbits using Gaia and ground-based observations

NASA Astrophysics Data System (ADS)

Bancelin, D.; Hestroffer, D.; Thuillot, W.

2011-05-01

Potentially Hazardous Asteroids (PHAs) are Near-Earth Asteroids caraterised by a Minimum Orbital Intersection Distance (MOID) with Earth less to 0.05 A.U and an absolute magnitude H<22. Those objects have sometimes a so significant close approach with Earth that they can be put on a chaotic orbit. This kind of orbit is very sensitive for exemple to the initial conditions, to the planetary theory used (for instance JPL's model versus IMCCE's model) or even to the numerical integrator used (Lie Series, Bulirsch-Stoer or Radau). New observations (optical, radar, flyby or satellite mission) can improve those orbits and reduce the uncertainties on the Keplerian elements.The Gaia mission is an astrometric mission that will be launched in 2012 and will observe a large number of Solar System Objects down to magnitude V≤20. During the 5-year mission, Gaia will continuously scan the sky with a specific strategy: objects will be observed from two lines of sight separated with a constant basic angle. Five constants already fixed determinate the nominal scanning law of Gaia: The inertial spin rate (1°/min) that describe the rotation of the spacecraft around an axis perpendicular to those of the two fields of view, the solar-aspect angle (45°) that is the angle between the Sun and the spacecraft rotation axis, the precession period (63.12 days) which is the precession of the spin axis around the Sun-Earth direction. Two other constants are still free parameters: the initial spin phase, and the initial precession angle that will be fixed at the start of the nominal science operations. These latter are constraint by scientific outcome (e.g. possibility of performing test of fundamental physics) together with operational requirements (downlink to Earth windows). Several sets of observations of specific NEOs will hence be provided according to the initial precession angle. The purpose here is to study the statistical impact of the initial precession angle on the error propagation and on the collision probability, especially for PHAs. We will also analyse the advantage of combining space-based to ground-based observation over long term, as well as in short term from observations in alert.

Near-Earth Asteroids Astrometry with Gaia

NASA Astrophysics Data System (ADS)

Bancelin, D.; Hestroffer, D.; Thuillot, W.

2011-05-01

Potentially Hazardous Asteroids (PHAs) are Near-Earth Asteroids caraterised by a Minimum Orbital Intersection Distance (MOID) with Earth less to 0.05 A.U and an absolute magnitude H<22. Those objects have sometimes a so significant close approach with Earth that they can be put on a chaotic orbit. This kind of orbit is very sensitive for exemple to the initial conditions, to the planetary theory used (for instance JPL's model versus IMCCE's model) or even to the numerical integrator used (Lie Series, Bulirsch-Stoer or Radau). New observations (optical, radar, flyby or satellite mission) can improve those orbits and reduce the uncertainties on the Keplerian elements.The Gaia mission is an astrometric mission that will be launched in 2012 and will observe a large number of Solar System Objects down to magnitude V≤20. During the 5-year mission, Gaia will continuously scan the sky with a specific strategy: objects will be observed from two lines of sight separated with a constant basic angle. Five constants already fixed determinate the nominal scanning law of Gaia: The inertial spin rate (1°/min) that describe the rotation of the spacecraft around an axis perpendicular to those of the two fields of view, the solar-aspect angle (45°) that is the angle between the Sun and the spacecraft rotation axis, the precession period (63.12 days) which is the precession of the spin axis around the Sun-Earth direction. Two other constants are still free parameters: the initial spin phase, and the initial precession angle that will be fixed at the start of the nominal science operations. These latter are constraint by scientific outcome (e.g. possibility of performing test of fundamental physics) together with operational requirements (downlink to Earth windows). Several sets of observations of specific NEOs will hence be provided according to the initial precession angle. The purpose here is to study the statistical impact of the initial precession angle on the error propagation and on the collision probability, especially for PHAs. We will also analyse the advantage of combining space-based to ground-based observation over long term, as well as in short term from observations in alert.

Volume-holographic memory for laser threat discrimination

NASA Astrophysics Data System (ADS)

Delong, Mark L.; Duncan, Bradley D.; Parker, Jack H., Jr.

1996-10-01

Using conventional volume-holographic angle multiplexing in an Fe:LiNbO3 crystal, we have developed a compact laser threat discriminator, intended for aircraft integration, that optically detects laser spatial coherence and angle of arrival while simultaneously rejecting incoherent background sources, such as the Sun. The device is intended for a specific type of psychophysical laser attack against U.S. Air Force pilots, namely, third-world-country exploitation of inexpensive and powerful cw Ar-ion or doubled Nd:YAG lasers in the visible spectrum to blind or disorient U.S. pilots. The component does not solve the general tactical laser weapon situation, which includes identifying precision-guided munitions, range finders, and lidar systems that use pulsed infrared lasers. These are fundamentally different threats requiring different detector solutions. The device incorporates a sequence of highly redundant, simple black-and-white warning patterns that are keyed to be reconstructed as the incident laser threat, playing the role of an uncooperative probe beam, changes angle with respect to the crystal. The device tracks both azimuth and elevation, using a nonconventional hologram viewing system. Recording and playback conditions are simplified because nonzero cross talk is a desirable feature of this discriminator, inasmuch as our application requires a nonzero probability of detection for arbitrary directions of arrival within the sensor's field of view. The device can exploit phase-matched grating trade-off with probe-beam wavelength, accommodating wavelength-tunable threats, while still maintaining high direction-of-arrival tracking accuracy. .

The Laser Astrometric Test of Relativity (LATOR) Mission

NASA Technical Reports Server (NTRS)

Turyshev, Slava G.; Shao, Michael; Nordtvedt, Kenneth, Jr.

2003-01-01

This paper discusses new fundamental physics experiment that will test relativistic gravity at the accuracy better than the effects of the second order in the gravitational field strength, proportional to G(sup 2). The Laser Astrometric Test Of Relativity (LATOR) mission uses laser interferometry between two micro-spacecraft whose lines of sight pass close by the Sun to accurately measure deflection of light in the solar gravity. The key element of the experimental design is a redundant geometry optical truss provided by a long-baseline (100 m) multi-channel stellar optical interferometer placed on the International Space Station (ISS). The spatial interferometer is used for measuring the angles between the two spacecraft and for orbit determination purposes. In Euclidean geometry, determination of a triangle s three sides determines any angle therein; with gravity changing the optical lengths of sides passing close by the Sun and deflecting the light, the Euclidean relationships are overthrown. The geometric redundancy enables LATOR to measure the departure from Euclidean geometry caused by the solar gravity field to a very high accuracy. LATOR will not only improve the value of the parameterized post-Newtonian (PPN) gamma to unprecedented levels of accuracy of 1 part in 10(exp 8), it will also reach ability to measure effects of the next post-Newtonian order (c(sup -4)) of light deflection resulting from gravity s intrinsic non-linearity. The solar quadrupole moment parameter, J(sub 2), will be measured with high precision, as well as a variety of other relativistic effects including Lense-Thirring precession. LATOR will lead to very robust advances in the tests of Fundamental physics: this mission could discover a violation or extension of general relativity, or reveal the presence of an additional long range interaction in the physical law. There are no analogs to the LATOR experiment; it is unique and is a natural culmination of solar system gravity experiments.

Wide and Narrow CMEs and Their Source Explosions Observed at the Spring 2003 SOHO-Sun-Ulysses Quadrature

NASA Technical Reports Server (NTRS)

Suess, Steven; Corti, G.; Poletto, G.; Sterling, A.; Moore, R.

2006-01-01

At the time of the spring 2003 Ulysses-SOHO-Sun quadrature, Ulysses was off the East limb of the Sun at 14.5 degrees north latitude and 4.91 AU. LASCO/C2 images show small transient events that originated from near the limb on May 25, 26 and 27 in the north-east quadrant, along with a large Coronal Mass Ejection (CME) that originated from an active region near disk center on May 26. Ulysses data bear clear signatures of the large CME, specifically including an enhanced abundance of highly ionized Fe. SOHO/UVCS spectra at 1.75 solar radii, near the radial direction to Ulysses, give no evidence of emission from high temperature lines, even for the large CME: instead, for the small events, occasional transient high emission in cool lines was observed, such as the CIII 977 Angstrom line usually absent at coronal levels. Each of these events lasted ca. 1 hour or less and never affected lines from ions forming above ca. 106K. Compact eruptions in Helium 304 Angstrom EIT images, related to the small UVCS transients, were observed at the limb of the Sun over the same period. At least one of these surge events produced a narrow CME observed in LASCO/C2. Most probably all these events are compact magnetic explosions (surges/jets, from around a small island of included polarity) which ejected cool material from lower levels. Ulysses data have been analyzed to find evidence of the cool, narrow CME events, but none or little was found. This puzzling scenario, where events seen by UVCS have no in situ counterparts and vice versa, can be partially explained once the region where the large CME originated is recognized as being at the center of the solar disk so that the CME material was actually much further from the Sun than the 1.7 Rsun height of the UVCS slit off the limb. Conversely, the narrow events may simply have missed Ulysses or been too brief for reliable signatures in composition and ionization state. A basic feature demonstrated by these observations is that large magnetic explosions produce wide-angle CMEs whereas compact magnetic explosions produce narrow CMEs. The results show that quadrature observations need some luck to be successfull: that is, events must be in the plane of the sky to allow SOHO/UVCS and Ulysses to sample the same plasma. This will most easily occur in winter 2007 and winter 2008, when the quadrature geometry will allow for prolonged observations.

Optical image of a cometary nucleus: 1980 flyby of Comet Encke

NASA Technical Reports Server (NTRS)

Wells, W. C.; Benson, R. S.; Anderson, A. D.; Gal, G.

1974-01-01

The feasibility was investigated of obtaining optical images of a cometary nucleus via a flyby of Comet Encke. A physical model of the dust cloud surrounding the nucleus was developed by using available physical data and theoretical knowledge of cometary physics. Using this model and a Mie scattering code, calculations were made of the absolute surface brightness of the dust in the line of sight of the on-board camera and the relative surface brightness of the dust compared to the nucleus. The brightness was calculated as a function of heliocentric distance and for different phase angles (sun-comet-spacecraft angle).

Solar Tracking Error Analysis of Fresnel Reflector

PubMed Central

Zheng, Jiantao; Yan, Junjie; Pei, Jie; Liu, Guanjie

2014-01-01

Depending on the rotational structure of Fresnel reflector, the rotation angle of the mirror was deduced under the eccentric condition. By analyzing the influence of the sun tracking rotation angle error caused by main factors, the change rule and extent of the influence were revealed. It is concluded that the tracking errors caused by the difference between the rotation axis and true north meridian, at noon, were maximum under certain conditions and reduced at morning and afternoon gradually. The tracking error caused by other deviations such as rotating eccentric, latitude, and solar altitude was positive at morning, negative at afternoon, and zero at a certain moment of noon. PMID:24895664

Orbit and geometry constraints on the design and operation of a long-life SIRTF mission. [Shuttle Infrared Telescope Facility

NASA Technical Reports Server (NTRS)

Jackson, R. W.

1984-01-01

For a long-life SIRTF mission, the ability of the telescope to observe targets everywhere in the sky is an important requirement. For low-inclination orbits, a telescope aperture shade must be designed for Sun and Earth Limb avoidance angles of 50 deg to 60 deg to prevent unwanted radiation from entering the telescope. The minimum orbit inclination depends on the Earth Limb avoidance angle. About 30 percent of the sky will be prohibited for observations during any day in orbit, with about 100 days in orbit required to observe the entire sky.

Measurement of surface physical properties and radiation balance for KUREX-91 study

NASA Technical Reports Server (NTRS)

Walter-Shea, Elizabeth A.; Blad, Blaine L.; Mesarch, Mark A.; Hays, Cynthia J.

1992-01-01

Biophysical properties and radiation balance components were measured at the Streletskaya Steppe Reserve of the Russian Republic in July 1991. Steppe vegetation parameters characterized include leaf area index (LAI), leaf angle distribution, mean tilt angle, canopy height, leaf spectral properties, leaf water potential, fraction of absorbed photosynthetically active radiation (APAR), and incoming and outgoing shortwave and longwave radiation. Research results, biophysical parameters, radiation balance estimates, and sun-view geometry effects on estimating APAR are discussed. Incoming and outgoing radiation streams are estimated using bidirectional spectral reflectances and bidirectional thermal emittances. Good agreement between measured and modeled estimates of the radiation balance were obtained.

Piloting a Global Collaborative Experiment to Determine your Place on the Planet and the Circumference of the Earth

NASA Astrophysics Data System (ADS)

Solie, D. J.; Paniwozik, R. L.; Wallace, P.

2012-12-01

As part of the laboratory component in Bush Physics for the 21st Century, a distance delivered physics course geared toward rural and Indigenous students in Alaska, students determine their village location on earth from simple sun angle measurements at local-noon during the spring equinox. Students measure the length of the sun shadow cast by a rod mounted on a horizontal surface, over short time intervals on or near the spring equinox during mid-day. Local-noon occurs when the sun is the highest and its corresponding shadow the shortest. Local noon, when expressed in Universal Time, can be directly converted to the local longitude in degrees. Local latitude in degrees, is obtained from the local-noon shadow length on the spring equinox and simple trigonometry. As an added bonus, using data from different sites, students can collaborate to approximate the circumference of the earth from their measurements. In the spirit of Eratosthenes, students envision an earth-sized pie wedge cut from a polar great-circle where the curve of the wedge on the earth's surface is the North-South distance between two often road-less sites (determined using Google Earth, a map or a globe), and the angle of the wedge is the difference between the site latitudes. The earth's circumference is calculated from this wedge. In 2012 with the aim of including Indigenous groups from other regions of the planet, we expanded this experiment to include teams from Japan, Puerto Rico, American Samoa, and New Zealand. We present our results from this pilot year.

Mapping magnetic field lines between the Sun and Earth

NASA Astrophysics Data System (ADS)

Li, B.; Cairns, Iver H.; Gosling, J. T.; Steward, G.; Francis, M.; Neudegg, D.; Schulte in den Bäumen, H.; Player, P. R.; Milne, A. R.

2016-02-01

Magnetic field topologies between the Sun and Earth are important for the connectivity to Earth of solar suprathermal particles, e.g., solar energetic particles and beam electrons in type III solar radio bursts. An approach is developed for mapping large-scale magnetic field lines near the solar equatorial plane, using near-Earth observations and a solar wind model with nonzero azimuthal magnetic field at the source surface. Unlike Parker's spiral model, which restricts the in-ecliptic angle ΦB in the Geocentric Solar Ecliptic coordinates to (90°-180°, 270°-360°) and so is unable to predict field configurations for the other ΦB values frequently observed in the solar wind, our approach can account for all the observed ΦB values. A set of predicted maps shows that near both minimal and maximal solar activity the field lines are typically open and that loops with both ends either connected to or disconnected from the Sun are relatively rare. The open field lines, nonetheless, often do not closely follow the Parker spiral, being less or more tightly wound, or strongly azimuthally or radially oriented, or inverted. The time-varying classes, e.g., bidirectional electrons, of suprathermal electron pitch angle distributions (PADs) at 1 AU are predicted from the mapped field line configurations and compared with Wind observations for two solar rotations, one each near solar minimum and solar maximum. PAD predictions by our approach agree quantitatively (≈90%) with the PAD observations and outperform (by ≈20%) PAD predictions using Parker's model.

Solar System Portrait - Views of 6 Planets

NASA Image and Video Library

1996-09-13

These six narrow-angle color images were made from the first ever portrait of the solar system taken by NASA’s Voyager 1, which was more than 4 billion miles from Earth and about 32 degrees above the ecliptic. The spacecraft acquired a total of 60 frames for a mosaic of the solar system which shows six of the planets. Mercury is too close to the sun to be seen. Mars was not detectable by the Voyager cameras due to scattered sunlight in the optics, and Pluto was not included in the mosaic because of its small size and distance from the sun. These blown-up images, left to right and top to bottom are Venus, Earth, Jupiter, and Saturn, Uranus, Neptune. The background features in the images are artifacts resulting from the magnification. The images were taken through three color filters -- violet, blue and green -- and recombined to produce the color images. Jupiter and Saturn were resolved by the camera but Uranus and Neptune appear larger than they really are because of image smear due to spacecraft motion during the long (15 second) exposure times. Earth appears to be in a band of light because it coincidentally lies right in the center of the scattered light rays resulting from taking the image so close to the sun. Earth was a crescent only 0.12 pixels in size. Venus was 0.11 pixel in diameter. The planetary images were taken with the narrow-angle camera (1500 mm focal length). http://photojournal.jpl.nasa.gov/catalog/PIA00453

Global Precipitation Measurement: GPM Microwave Imager (GMI) Algorithm Development Approach

NASA Technical Reports Server (NTRS)

Stocker, Erich Franz

2009-01-01

This slide presentation reviews the approach to the development of the Global Precipitation Measurement algorithm. This presentation includes information about the responsibilities for the development of the algorithm, and the calibration. Also included is information about the orbit, and the sun angle. The test of the algorithm code will be done with synthetic data generated from the Precipitation Processing System (PPS).

Electric Fields in Earth Orbital Space.

DTIC Science & Technology

1984-09-01

region. Further work on propagation of these fields within the magneto- sphere and on a quantitative examination of their oblique incidence on the...9 1.6 Technical Summary ................................... 13 2 FUTURE WORK .............................................. 16 2.1 Oblique Incidence...ambient or sector structure field normally lies in the ecliptic plane and either points away or toward the sun at the classic "garden hose, angle. It has

Barely Bisected Rings

NASA Image and Video Library

2016-09-12

Saturn's shadow stretched beyond the edge of its rings for many years after Cassini first arrived at Saturn, casting an ever-lengthening shadow that reached its maximum extent at the planet's 2009 equinox. This image captured the moment in 2015 when the shrinking shadow just barely reached across the entire main ring system. The shadow will continue to shrink until the planet's northern summer solstice, at which point it will once again start lengthening across the rings, reaching across them in 2019. Like Earth, Saturn is tilted on its axis. And, just as on Earth, as the sun climbs higher in the sky, shadows get shorter. The projection of the planet's shadow onto the rings shrinks and grows over the course of its 29-year-long orbit, as the angle of the sun changes with respect to Saturn's equator. This view looks toward the sunlit side of the rings from about 11 degrees above the ring plane. The image was taken in visible light with the Cassini spacecraft wide-angle camera on Jan. 16, 2015. The view was obtained at a distance of approximately 1.6 million miles (2.5 million kilometers) from Saturn. Image scale is about 90 miles (150 kilometers) per pixel. http://photojournal.jpl.nasa.gov/catalog/PIA20498

Naked eye determination of the dawn for Sinai and Assiut of Egypt

NASA Astrophysics Data System (ADS)

Hassan, A. H.; Issa, I. A.; Mousa, M.; Abdel-Hadi, Yasser A.

2016-06-01

Twilight observations were carried out by naked eye in the period (2010-2012) for north Sinai (Lat. 31°4‧N, Long. 32°52‧E) where the background is desert, and for Assiut (Lat. 27°10‧N, Long. 31°10‧E) in the period (2012-2014) where the background is agricultural land. The purpose of these observations is to calculate the depression of the sun below the horizon at which the normal eye can discriminate the dawn (morning white thread) for two sites. The results indicated that this discrimination takes place at vertical sun depression angles, Do = 14.61° and 13.665° at Sinai and Assiut respectively.

New uses of shadow enhancement. [interpretation of geologic structures from photographic or scanner imagery of Colorado

NASA Technical Reports Server (NTRS)

Lee, K. (Principal Investigator); Sawatzky, D. L.

1974-01-01

The author has identified the following significant results. Shadow enhancement of topographic linears in photographic or scanner images is a valuable tool for interpretation of geologic structures. Whether linears will be enhanced or subdued depends on sun angle and azimuth. The relationship of the sun's attitude to topographic slopes determines which trends are available for interpretation in existing imagery, and it can be used to select the time of day, surface properties, and film and filter characteristics in planning aircraft flights or satellite orbital passes. The technique of selective shadow enhancement can be applied to all photographic or imaging experiments, but its best for snow-covered scenes, side-looking radar images, and painted relief models.

Rough and Tumble Hyperion Movie

NASA Image and Video Library

2006-02-03

The tumbling and irregularly shaped moon Hyperion rotates away from the Cassini spacecraft in this movie taken during a distant encounter in Dec. 2005. A shadow closes over the large crater at bottom as the movie progresses. Hyperion (280 kilometers, or 174 miles across) is covered with closely packed and deeply etched pits. The warming action of the Sun on water ice lying beneath a darkened layer of surface material apparently has deepened and exaggerated the depressions already created by impacts. Cassini scientists now think that Hyperion’s unusual appearance can be attributed to the fact that it has an unusually low density for such a large object, giving it weak surface gravity and high porosity. These characteristics help preserve the original shapes of Hyperion’s craters by limiting the amount of impact ejecta coating the moon’s surface. Impactors tend to make craters by compressing the surface material, rather than blasting it out. Further, Hyperion’s weak gravity, and correspondingly low escape velocity, means that what little ejecta is produced has a good chance of escaping the moon altogether. The images were taken in visible light with the Cassini spacecraft narrow-angle camera on Dec. 23, 2005 at distances ranging from 228,000 kilometers (142,000 miles) to 238,000 kilometers (148,000 miles) from Hyperion and at a Sun-Hyperion-spacecraft, or phase, angle ranging from 77 to 86 degrees. Resolution in the original images was about 1.4 kilometers (0.9 mile) per pixel. The images have been magnified by a factor of two and contrast-enhanced to aid visibility. An animation is available at http://photojournal.jpl.nasa.gov/catalog/PIA07683

Retrieval of Macro- and Micro-Physical Properties of Oceanic Hydrosols from Polarimetric Observations

NASA Technical Reports Server (NTRS)

Ibrahim, Amir; Gilerson, Alexander; Chowdhary, Jacek; Ahmed, Samir

2016-01-01

Remote sensing has mainly relied on measurements of scalar radiance and its spectral and angular features to retrieve micro- and macro-physical properties of aerosols/hydrosols. However, it is recognized that measurements that include the polarimetric characteristics of light provide more intrinsic information about particulate scattering. To take advantage of this, we used vector radiative transfer (VRT) simulations and developed an analytical relationship to retrieve the macro and micro-physical properties of the oceanic hydrosols. Specifically, we investigated the relationship between the observed degree of linear polarization (DoLP) and the ratio of attenuation-to- absorption coefficients (c/a) in water, from which the scattering coefficient can be readily computed (b equals c minus a), after retrieving a. This relationship was parameterized for various scattering geometries, including sensor zenith/azimuth angles relative to the Sun's principal plane, and for varying Sun zenith angles. An inversion method was also developed for the retrieval of the microphysical properties of hydrosols, such as the bulk refractive index and the particle size distribution. The DoLP vs c/a relationship was tested and validated against in-situ measurements of underwater light polarization obtained by a custom-built polarimeter and measurements of the coefficients a and c, obtained using an in-water WET (Western Environmental Technologies) Labs ac-s (attenuation coefficients In-Situ Spectrophotometer) instrument package. These measurements confirmed the validity of the approach, with retrievals of attenuation coefficients showing a high coefficient of determination depending on the wavelength. We also performed a sensitivity analysis of the DoLP at the Top of Atmosphere (TOA) over coastal waters showing the possibility of polarimetric remote sensing application for ocean color.

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

Xue, Yuxin; Suto, Yasushi; Taruya, Atsushi

The angle between the stellar spin and the planetary orbit axes (the spin-orbit angle) is supposed to carry valuable information concerning the initial condition of planetary formation and subsequent migration history. Indeed, current observations of the Rossiter-McLaughlin effect have revealed a wide range of spin-orbit misalignments for transiting exoplanets. We examine in detail the tidal evolution of a simple system comprising a Sun-like star and a hot Jupiter adopting the equilibrium tide and the inertial wave dissipation effects simultaneously. We find that the combined tidal model works as a very efficient realignment mechanism; it predicts three distinct states of themore » spin-orbit angle (i.e., parallel, polar, and antiparallel orbits) for a while, but the latter two states eventually approach the parallel spin-orbit configuration. The intermediate spin-orbit angles as measured in recent observations are difficult to obtain. Therefore the current model cannot reproduce the observed broad distribution of the spin-orbit angles, at least in its simple form. This indicates that the observed diversity of the spin-orbit angles may emerge from more complicated interactions with outer planets and/or may be the consequence of the primordial misalignment between the protoplanetary disk and the stellar spin, which requires future detailed studies.« less

A Study of TRMM Static Earth Sensor Performance Using On-Orbit Sensor Data

NASA Technical Reports Server (NTRS)

Natanson, Gregory; Glickman, Jonathan

2000-01-01

This paper presents the results of a study of the Barnes static Earth sensor assembly (ESA) using on-orbit data collected from the Tropical Rainfall Measuring Mission (TRMM) spacecraft. It is shown that there exist strong correlations between the large penetration angle residuals and the voltages produced by the Offset Radiation Source (ORS). It is conjectured that at certain times in the TRMM orbit the ORS is operating out of its calibrated range, and consequently corrupts the penetration angle information observed and processed by the ESA. The observed yaw drift between Digital Sun Sensor (DSS) observations is shown to be consistent with predictions by a simple roll-yaw coupling computation. This would explain the large drifts seen on TRMM, where the propagation of the yaw angle between DSS updates does not take into account the possibility of a non-zero roll angle error. Finally, the accuracy of the onboard algorithm used when only three of the four quadrants supply valid penetration angles is assessed. In terms of procedures used to perform this study, the analysis of ESA penetration angle residuals is discovered to be a very useful and insightful tool for assessing, the health and functionality of the ESA.

Solar axion search technique with correlated signals from multiple detectors

DOE PAGES

Xu, Wenqin; Elliott, Steven R.

2017-01-25

The coherent Bragg scattering of photons converted from solar axions inside crystals would boost the signal for axion-photon coupling enhancing experimental sensitivity for these hypothetical particles. Knowledge of the scattering angle of solar axions with respect to the crystal lattice is required to make theoretical predications of signal strength. Hence, both the lattice axis angle within a crystal and the absolute angle between the crystal and the Sun must be known. In this paper, we examine how the experimental sensitivity changes with respect to various experimental parameters. We also demonstrate that, in a multiple-crystal setup, knowledge of the relative axismore » orientation between multiple crystals can improve the experimental sensitivity, or equivalently, relax the precision on the absolute solar angle measurement. However, if absolute angles of all crystal axes are measured, we find that a precision of 2°–4° will suffice for an energy resolution of σ E = 0.04E and a flat background. Lastly, we also show that, given a minimum number of detectors, a signal model averaged over angles can substitute for precise crystal angular measurements, with some loss of sensitivity.« less

Imaging Dot Patterns for Measuring Gossamer Space Structures

NASA Technical Reports Server (NTRS)

Dorrington, A. A.; Danehy, P. M.; Jones, T. W.; Pappa, R. S.; Connell, J. W.

2005-01-01

A paper describes a photogrammetric method for measuring the changing shape of a gossamer (membrane) structure deployed in outer space. Such a structure is typified by a solar sail comprising a transparent polymeric membrane aluminized on its Sun-facing side and coated black on the opposite side. Unlike some prior photogrammetric methods, this method does not require an artificial light source or the attachment of retroreflectors to the gossamer structure. In a basic version of the method, the membrane contains a fluorescent dye, and the front and back coats are removed in matching patterns of dots. The dye in the dots absorbs some sunlight and fluoresces at a longer wavelength in all directions, thereby enabling acquisition of high-contrast images from almost any viewing angle. The fluorescent dots are observed by one or more electronic camera(s) on the Sun side, the shade side, or both sides. Filters that pass the fluorescent light and suppress most of the solar spectrum are placed in front of the camera(s) to increase the contrast of the dots against the background. The dot image(s) in the camera(s) are digitized, then processed by use of commercially available photogrammetric software.

Prevalence of sun protection behaviors in Hispanic youth residing in a high ultraviolet light environment.

PubMed

Altieri, Lisa; Miller, Kimberly A; Huh, Jimi; Peng, David H; Unger, Jennifer B; Richardson, Jean L; Allen, Martin W; Cockburn, Myles

2018-01-01

Although rates of late-stage melanoma are rising in Hispanics, particularly those living in high ultraviolet light environments, little is known about the prevalence of sun protective behaviors in Hispanic children. We analyzed baseline data including frequency of sunburn, sun protective behaviors, level of U.S. acculturation, and skin phototype from a cross-sectional survey of 2003 Hispanic elementary school children in Los Angeles, California, who participated in a skin cancer prevention intervention. Although the Hispanic children reported frequently engaging in some sun protective behaviors, they also had a high rate of sunburn (59%) that exceeded previous national estimates for non-Hispanic white children (43%). Fewer U.S.-acculturated children reported more frequent shade-seeking at home (P = .02), along with less shade-seeking at school (P = .001) and more sunscreen use at school (P = .02). The surprisingly high rate of sunburn in Hispanic children suggests that the way in which they are practicing sun protection is not preventing sunburns. Sun safety interventions should be targeted toward Hispanic youth to provide them with practical methods of effective sun protection, in addition to education on the risks of high sun exposure. © 2017 Wiley Periodicals, Inc.

Field experiment of 800× off-axis XR-Köhler concentrator module on a carousel tracker

NASA Astrophysics Data System (ADS)

Yamada, Noboru; Okamoto, Kazuya; Ijiro, Toshikazu; Suzuki, Takao; Maemura, Toshihiko; Kawaguchi, Takashi; Takahashi, Hiroshi; Sato, Takashi; Hernandez, Maikel; Benitez, Pablo; Chaves, Julio; Cvetkovic, Aleksandra; Vilaplana, Juan; Mohedano, Ruben; Mendes-Lopes, Joao; Miñano, Juan Carlos

2013-09-01

This paper presents the design and preliminary experimental results of a concentrator-type photovoltaic module based on a free-form off-axis 800×XR-Köhler concentrator. The off-axis XR-Köhler concentrator is one of the advanced concentrators that perform high concentration with a large acceptance angle and excellent irradiance uniformity on a solar cell. As a result of on-sun characterization of the unglazed single-cell unit test rig, the temperature-corrected DC module efficiency was 32.2% at 25 °C without an anti-reflective (AR) coating on the secondary optics, and the acceptance angle was more than ±1.0°. In addition, the non-corrected DC efficiency of an individual cell in a glazed 8-cell unit module mounted on a carousel tracking system was measured. The individual efficiency deviated in the range of 24.3-27.4%, owing to the mirror shape and alignment errors. The resultant series-connected efficiency was approximately 25% at direct normal irradiation (DNI) of 770 W/m2.

Influence of age, gender, educational level and self-estimation of skin type on sun exposure habits and readiness to increase sun protection.

PubMed

Falk, M; Anderson, C D

2013-04-01

Sun exposure habits and the propensity to undertake sun protection differ between individuals. Not least in primary prevention of skin cancer, aiming at reducing ultraviolet (UV) exposure, knowledge about these factors may be of importance. The aim of the present study was to investigate, in a primary health care (PHC) population, the relationship between sun exposure habits/sun protection behaviour/readiness to increase sun protection and gender, age, educational level and skin UV-sensitivity. The baseline data from a previously performed RCT on skin cancer prevention was used. 415 patients, aged > 18 years, visiting a PHC centre in southern Sweden, filled-out a questionnaire mapping sun exposure, readiness to increase sun protection according to the Transtheoretical Model of Behaviour Change (TTM), and the above mentioned factors. Female gender was associated with more frequent suntanning (p < 0.001) and sunbed use (p < 0.05), but also with more extensive sunscreen use (p < 0.001). High age was in general associated with low level of sun exposure and high level of protection. Subjects with low educational level reported less frequent sunscreen use than those with higher educational level, and also chose lower SPF (p < 0.001). For almost all parameters, high skin UV-sensitivity was associated with markedly lower sun exposure (p < 0.001) and more pronounced readiness to increase sun protection. Females and subjects with high educational level reported higher readiness to increase sunscreen use than males and subjects with lower educational level (p < 0.001). Gender, age, educational level and skin type appear to be important factors affecting sun exposure habits and sun protection behaviour, which supports the idea of appropriate mapping of these factors in patients in order to individualise sun protection advice according to the individual patient situation and capabilities. Copyright © 2013 Elsevier Ltd. All rights reserved.

A Survey of Geosynchronous Satellite Glints

NASA Astrophysics Data System (ADS)

Vrba, F.; Hutter, D.; Shankland, P.; Armstrong, J.; Schmitt, H.; Hindsley, R.; Divittorio, M.; Benson, J.

Artificial satellites have characteristic diffuse reflected-light signatures as they are illuminated at varying phase angles by the Sun and are viewed at differing orientations by an observer. At times of favorable alignment between the satellite, observer and Sun, specular reflection off of relatively flat surfaces, such as solar panels, can cause brief increases in reflected light of several hundred times that of the nominal diffuse signature. Such events are commonly referred to as "glints". In the case of geosynchronous satellites, favorable glint alignments are due to changes in the Sun-Vehicle-Observer angle which are primarily due to the apparent motion of the Sun as the observer-satellite vector remains nearly stationary. These occur near in time to the vernal and autumnal equinoxes. While the most favorable geosynchronous satellite glint alignments are precluded by the fact that the satellites are at that time most likely to be in Earth shadow, observations of several glints have been reported in the literature. While such studies note the peak brightnesses, durations, and phase angles of individual glints, to our knowledge, no extended study of geosynchronous glint characteristics exists. Beginning with the autumnal equinox glint season of 2007 we have built on our earlier studies using the U.S. Naval Observatory, Flagstaff Station 40-inch Ritchey telescope to provide near-real-time astrometric and photometric information for use by the Navy Prototype Optical Interferometer (NPOI) team in its efforts to obtain interferometric fringes of geosynchronous satellites during a glint episode. The combined observations culminated in successful fringe measurements of DirecTV-9S during the vernal equinox 2008 and 2009 seasons (see Armstrong, et al. 2009, this conference). For our 40-inch telescope observations we used an LN2-cooled 2048x2048 CCD with standard R-band and H-alpha photometric filters, covering an area of the sky of approximately 22x22 arcmin with each integration. Observations typically were initiated well before a predicted potential glint and continued through the glint occurrence (if any) for our secondary goal of estimating peak glint brightnesses. As we were using photometric equipment, took care to obtain photometric calibrations, and were fortunate to have observed on several photometric nights, we have calibrated, time-resolved observations of numerous glint episodes, dominated by the GE2/GE4/DTV4S/DTV9S constellation. In particular, we will discuss systematic differences between glints from different satellites, comparison of glints from the same satellite during different epochs, and the time evolution of glints from DirecTV-9S during the 2009 vernal equinox observing season.

Suction Blister Epidermal Grafting for Vitiligo Involving Angles of Lip: Experience of 112 Patients

PubMed Central

Kar, Bikash R.; Raj, Chinmoy

2018-01-01

Background: Lip vitiligo is usually resistant to medical modalities of treatment, and in all these cases, surgery offers a hope. Suction blister grafting (SBG) has been tried since long for lip vitiligo with high rate of success. There have been no long-term follow-up studies of patients with SBG at a difficult-to-treat site like angles of lip, which prompted us to conduct this study. Aims and Objectives: To assess the pigmentation rate and patient satisfaction of SBG on vitiligo involving angles of lip. Materials and Methods: This is a prospective study conducted on 112 patients with stable vitiligo involving angles of lip. SBG was carried out in all the patients using the standard procedure. Patients were advised to apply topical psoralen followed by sun exposure (PUVASOL) for 8–12 weeks after operation. The patients were followed up at 3, 6, 12, 18, and 24 months for assessment of pigmentation and overall satisfaction. Results: We found a pigmentation success rate of 83.7%, 84.9%, 85.7%, 78.3%, and 77.8% in the patients who were followed up at 3, 6, 12, 18, and 24 months, respectively. A total of 77.8% of patients who came for follow-up at the end of 24 months were very happy with the treatment. Discussion: Our data show clearance of vitiligo and persistence of pigmentation gained through SBG in 77.8% of cases at the end of 2 years as well as excellent patient satisfaction in the cohort of patients who followed up with us. Conclusion: SBG is an easy and cost-effective way of repigmentation of vitiligo involving angles of lip. PMID:29731587

Astronomical function and date of the Taosi observatory

NASA Astrophysics Data System (ADS)

Wu, Jiabi; Chen, Meidong; Liu, Ciyuan

2009-01-01

The Taosi site in Xiangfen County, Shanxi Province, may be the capital of the King Yao. Archeologists recently discovered a large semi-circular stamped-earth platform, II FJT1, which has a clear and definite pounded-earth central core together with a curved wall perforated by twelve gaps. The platform is said to be an ancient observatory used to determine the seasons by watching the sunrise. Each feature of II FJT1 was precisely measured and the data are reproduced in this paper. An astronomical analysis of slots E2 and E12 was carried out using the azimuths of the slots’ centerlines and the vertical angle of the mountain ridge opposite, above which the sun rises. The results show that at present the sun is close to the two slots but does not exactly enter them at summer and winter solstice sunrise. Using 14C analysis archeologists dated the site to about 2100 BC. Because of the secular change in the obliquity of the ecliptic, at that date on the summer solstice the half-risen sun would have appeared inside slot E12 just to the right of the centerline, and on the winter solstice the sun would have been exactly on the centerline of slot E2. This result provides compelling proof that II FJT1 is an ancient observatory.

Ground-based solar astrometric measurements during the PICARD mission

NASA Astrophysics Data System (ADS)

Irbah, A.; Meftah, M.; Corbard, T.; Ikhlef, R.; Morand, F.; Assus, P.; Fodil, M.; Lin, M.; Ducourt, E.; Lesueur, P.; Poiet, G.; Renaud, C.; Rouze, M.

2011-11-01

PICARD is a space mission developed mainly to study the geometry of the Sun. The satellite was launched in June 2010. The PICARD mission has a ground program which is based at the Calern Observatory (Observatoire de la C^ote d'Azur). It will allow recording simultaneous solar images from ground. Astrometric observations of the Sun using ground-based telescopes need however an accurate modelling of optical e®ects induced by atmospheric turbulence. Previous works have revealed a dependence of the Sun radius measurements with the observation conditions (Fried's parameter, atmospheric correlation time(s) ...). The ground instruments consist mainly in SODISM II, replica of the PICARD space instrument and MISOLFA, a generalized daytime seeing monitor. They are complemented by standard sun-photometers and a pyranometer for estimating a global sky quality index. MISOLFA is founded on the observation of Angle-of-Arrival (AA) °uctuations and allows us to analyze atmospheric turbulence optical e®ects on measurements performed by SODISM II. It gives estimations of the coherence parameters characterizing wave-fronts degraded by the atmospheric turbulence (Fried's parameter, size of the isoplanatic patch, the spatial coherence outer scale and atmospheric correlation times). This paper presents an overview of the ground based instruments of PICARD and some results obtained from observations performed at Calern observatory in 2011.

Analysis of LANDSAT-4 TM Data for Lithologic and Image Mapping Purpose

NASA Technical Reports Server (NTRS)

Podwysocki, M. H.; Salisbury, J. W.; Bender, L. V.; Jones, O. D.; Mimms, D. L.

1984-01-01

Lithologic mapping techniques using the near infrared bands of the Thematic Mapper onboard the LANDSAT 4 satellite are investigated. These methods are coupled with digital masking to test the capability of mapping geologic materials. Data are examined under medium to low Sun angle illumination conditions to determine the detection limits of materials with absorption features. Several detection anomalies are observed and explained.

Aerobraking strategies for the sample of comet coma earth return mission

NASA Astrophysics Data System (ADS)

Abe, Takashi; Kawaguchi, Jun'ichiro; Uesugi, Kuninori; Yen, Chen-Wan L.

The results of a study to the validate the applicability of the aerobraking concept to the SOCCER (sample of comet coma earth return) mission using a six-DOF computer simulation of the aerobraking process are presented. The SOCCER spacecraft and the aerobraking scenario and power supply problem are briefly described. Results are presented for the spin effect, payload exposure problem, and sun angle effect.

Aerobraking strategies for the sample of comet coma earth return mission

NASA Technical Reports Server (NTRS)

Abe, Takashi; Kawaguchi, Jun'ichiro; Uesugi, Kuninori; Yen, Chen-Wan L.

1990-01-01

The results of a study to the validate the applicability of the aerobraking concept to the SOCCER (sample of comet coma earth return) mission using a six-DOF computer simulation of the aerobraking process are presented. The SOCCER spacecraft and the aerobraking scenario and power supply problem are briefly described. Results are presented for the spin effect, payload exposure problem, and sun angle effect.

Evaluation of factors affecting resolution of shallow water bottom features

NASA Technical Reports Server (NTRS)

Mason, C. C.; Norris, D. R.; Browne, I. D.

1972-01-01

To ensure good aerial photography, the effects that factors such as submergence depth, sun angle, film and filter type, exposure, aircraft altitude, and polarization have on the photographic resolution of an underwater object must be determined. Various subjects were photographed, such as the deck of a small submersible, colored and gray scale panels, and natural bottom features. No underwater resolution target was used.

Re-examining the effect of particle phase functions on the remote-sensing reflectance.

PubMed

Xiong, Yuanheng; Zhang, Xiaodong; He, Shuangyan; Gray, Deric J

2017-08-20

Even though it is well known that both the magnitude and detailed angular shape of scattering (phase function, PF), particularly in the backward angles, affect the color of the ocean, the current remote-sensing reflectance (R rs ) models typically account for the effect of its magnitude only through the backscattering coefficient (b b ). Using 116 volume scattering function (VSF) measurements previously collected in three coastal waters around the U.S. and in the water of the North Atlantic Ocean, we re-examined the effect of particle PF on R rs in four scenarios. In each scenario, the magnitude of particle backscattering (i.e., b bp ) is known, but the knowledge on the angular shape of particle backscattering is assumed to increase from knowing nothing about the shape of particle PFs to partially knowing the particle backscattering ratio (B p ), the exact backscattering shape as defined by β˜ p (γ≥90°) (particle VSF normalized by the particle total scattering coefficient), and the exact backscattering shape as defined by the χ p factor (particle VSF normalized by the particle backscattering coefficient). At sun zenith angle=30°, the nadir-viewed R rs would vary up to 65%, 35%, 20%, and 10%, respectively, as the constraints on the shape of particle backscattering become increasingly stringent from scenarios 1 to 4. In all four scenarios, the R rs variations increase with both viewing and sun angles and are most prominent in the direction opposite the sun. Our results show a greater impact of the measured particle PFs on R rs than previously found, mainly because our VSF data show a much greater variability in B p , β˜ p (γ≥90°), and χ p than previously known. Among the uncertainties in R rs due to the particle PFs, about 97% can be explained by χ p , 90% by β˜ p (γ≥90°), and 27% by B p . The results indicate that the uncertainty in ocean color remote sensing can be significantly constrained by accounting for χ p of the VSFs.

Correlates of sun protection behaviors among Hispanic children residing in a high UVR environment.

PubMed

Miller, Kimberly A; Huh, Jimi; Unger, Jennifer B; Richardson, Jean L; Allen, Martin W; Peng, David H; Cockburn, Myles G

2017-03-01

Rates of melanoma are rising in Hispanics in the United States. Excessive sun exposure in childhood increases the risk of melanoma in adulthood, and little is known about the factors motivating sun protection behaviors among Hispanic youth. Correlates of sun protection were examined among Hispanic children residing in Los Angeles, California (N = 1891). Associations between multiple constructs (psychosocial, familial, and cultural) and sun protection outcomes (use of sunscreen, protective clothing, and shade seeking/sun avoidance) were examined. Family variables were associated with more frequent sun protection among Hispanic children across outcomes, as were perceived peer norms, perceived self-efficacy, and fewer sun protection barriers. Skin cancer risk factors such as lighter skin and sunburn experience, and level of acculturation were not associated with greater sun protection. Family sun protection habits are instrumental to Hispanic children's sun safe behaviors, and interventions that engage the family may be most effective. Increasing risk communication to high-risk subgroups of Hispanic children (those with lighter, more sun reactive skin) is important when developing intervention strategies. However, there is overlap between Hispanic children's sun protection correlates and those observed among non-Hispanic white children, suggesting that interventions to improve sun protection may generalize across cultural contexts. © 2016 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Mitochondrial DNA deletion percentage in sun exposed and non sun exposed skin.

PubMed

Powers, Julia M; Murphy, Gillian; Ralph, Nikki; O'Gorman, Susan M; Murphy, James E J

2016-12-01

The percentages of mitochondrial genomes carrying the mtDNA 3895 and the mtDNA 4977 (common) deletion were quantified in sun exposed and non sun exposed skin biopsies, for five cohorts of patients varying either in sun exposure profile, age or skin cancer status. Non-melanoma skin cancer diagnoses are rising in Ireland and worldwide [12] but most risk prediction is based on subjective visual estimations of sun exposure history. A quantitative objective test for pre-neoplastic markers may result in better adherence to sun protective behaviours. Mitochondrial DNA (mtDNA) is known to be subject to the loss of a significant proportion of specific sections of genetic code due to exposure to ultraviolet light in sunlight. Although one such deletion has been deemed more sensitive, another, called the mtDNA 4977 or common deletion, has proved to be a more useful indicator of possible risk in this study. Quantitative molecular analysis was carried out to determine the percentage of genomes carrying the deletion using non sun exposed and sun exposed skin biopsies in cohorts of patients with high or low sun exposure profiles and two high exposure groups undergoing treatment for NMSC. Results indicate that mtDNA deletions correlate to sun exposure; in groups with high sun exposure habits a significant increase in deletion number in exposed over non sun exposed skin occurred. An increase in deletion percentage was also seen in older cohorts compared to the younger group. The mtDNA 3895 deletion was detected in small amounts in exposed skin of many patients, the mtDNA 4977 common deletion, although present to some extent in non sun exposed skin, is suggested to be the more reliable and easily detected marker. In all cohorts except the younger group with relatively lower sun exposure, the mtDNA 4977 deletion was more frequent in sun exposed skin samples compared to non-sun exposed skin. Copyright © 2016 Elsevier B.V. All rights reserved.

Sunlight Transmission through Desert Dust and Marine Aerosols: Diffuse Light Corrections to Sun Photometry and Pyrheliometry

NASA Technical Reports Server (NTRS)

Russell, P. B.; Livingston, J. M.; Dubovik, O.; Ramirez, S. A.; Wang, J.; Redemann, J.; Schmid, B.; Box, M.; Holben, B. N.

2003-01-01

Desert dust and marine aerosols are receiving increased scientific attention because of their prevalence on intercontinental scales and their potentially large effects on Earth radiation and climate, as well as on other aerosols, clouds, and precipitation. The relatively large size of desert dust and marine aerosols produces scattering phase functions that are strongly forward- peaked. Hence, Sun photometry and pyrheliometry of these aerosols are more subject to diffuse-light errors than is the case for smaller aerosols. Here we quantify these diffuse-light effects for common Sun photometer and pyrheliometer fields of view (FOV), using a data base on dust and marine aerosols derived from (1) AERONET measurements of sky radiance and solar beam transmission and (2) in situ measurements of aerosol layer size distribution and chemical composition. Accounting for particle non-sphericity is important when deriving dust size distribution from both AERONET and in situ aerodynamic measurements. We express our results in terms of correction factors that can be applied to Sun photometer and pyrheliometer measurements of aerosol optical depth (AOD). We find that the corrections are negligible (less than approximately 1% of AOD) for Sun photometers with narrow FOV (half-angle eta less than degree), but that they can be as large as 10% of AOD at 354 nm wavelength for Sun photometers with eta = 1.85 degrees. For pyrheliometers (which can have eta up to approximately 2.8 degrees), corrections can be as large as 16% at 354 nm. We find that AOD correction factors are well correlated with AOD wavelength dependence (hence Angstrom exponent). We provide best-fit equations for determining correction factors from Angstrom exponents of uncorrected AOD spectra, and we demonstrate their application to vertical profiles of multiwavelength AOD.

Properties of the Circumsolar Dust Distribution Determined from STEREO/SECCHI and Implications for PSP and SolO

NASA Astrophysics Data System (ADS)

Howard, R.; Stenborg, G.

2017-12-01

We have performed an analysis of the HI-1A instrument in the STEREO/SECCHI suite to determine the inclination and longitude of the ascending node of the plane of symmetry of the F-corona. The F-corona arises from sunlight scattered by the dust in orbit about the Sun. We find that the inclination and ascending node are not constant in the field of view of the HI-1A (4° to 24° elongation), but are functions of the elongation angle i.e. the distance to the Sun and are slightly different from the parameters determined from the Helios mission. These parameters are reflecting the gravitational influences of Jupiter, Venus and the Sun as well as Lorentz and Poynting-Robinson forces on the dust orbits. The center of symmetry is not the center of the Sun, but is offset by 0.5 Rsun from the center in the direction of the average position of Jupiter during the epoch studied: from 2007-2012. We also observe a slight difference in the inclination when it is north or south of the ecliptic. We suggest this may be due to remnant dust in the orbit of the Kreutz sun-grazing comets which occur at an average rate of one every 2-3 days. Finally, as the dust particles evaporate we expect to see the F-coronal brightness correspondingly decrease. The detectability of the decrease will depend on the amount of dust evaporating, but a 10% change in the density is easily detectable. If a dust free zone surrounding the Sun exists, it will affect the F-coronal intensities observed by PSP and SolO by an observable amount.

Derivation of Coefficients for the Bidirectional Reflection Distribution Function from AVHRR-data over Europe, under Consideration of the Helmholtz Reciprocity Law

NASA Astrophysics Data System (ADS)

Billing, H.; Koslowsky, D.

In the AVHRR data of the polar orbiting NOAA Satellites, directional reflectance under a certain view from satellite and a certain illumination by the sun is measured. Due to the nearly sunsynchroneous orbit of the NOAA satellite, each area is seen under different viewing angles in successive days. Only after approximately 9 days, the conditions are again similar. Areas, seen in specular direction, may appear only half as bright, as if seen in antispecular direction. This deviation from a Lambertian reflector is a function of the surface roughness and the degree of coverage with vegetation. The NOAA afternoon satellites drift by half an hour from year to year. Thus even data from the same season, but different years, are seen under different illumination conditions. To derive the bidirectional reflection distribution function in dependence on satellite viewing angle and solar illumination becomes a very complicated procedure. Using the Helmholtz reciprocity principle (HRP), i.e. the symetrie in viewing and illumination, reduces the problem by one dimension. For different bidimensional reflection laws it will be tested, whether they can be formulated to fullfill the HRP. Via regression, the parameters will be deduced for time series of AVHRR data of 10 years from NOAA 11,14,16 and 17. Brdfunctions, suggested by Rao as well as a law, suggested by Ba seem to become unstable for low sun resp. large viewing zenit angles. Only brdfs with 4 coefficients can fit the observed distributions. A nonlinear temporal angular model (NTAM), suggested by Latifovic,Cihlar and Chen, seems to be suitable to describe even the hot spot and the dependence on plant growth. The coefficients of these brdf-function will be derived via regression for monthly series of cloud free data for the European area, where AVHRR data in full resolution are received in Berlin. Using these coefficients, monthly maps of surface roughness are produced for the above area for the time since 1985. Ba, M.B., Deschamps, P.-Y.,Frouin, R. 1995. Error reduction in NOAA satellite monitoring of the land surface vegetation during FIFE. J. Geophys. Res., 100: 25537-25548. Rao, C.R.N., Chen, J., 1994. Post-launch calibration of the visible and near infrared channels of the advanced very high resolution radiometer on NOAA-7,- 9, and -11 spacecraft. NOAA Technical Report NESDIS 78. Latifovic, R., Chilar, J., Chen, J., 2003. A Comparison of BRDF Models for the Normalisation of Satellite Optical Data to a Standard Sun-Target- Sensor Geometry. IEEE Transactions on Geoscience and Remote Sensing, Vol.41, No.8, 1889 - 1898.

Efficiency of geometric designs of flexible solar panels: mathematical simulation

NASA Astrophysics Data System (ADS)

Marciniak, Malgorzata; Hassebo, Yasser; Enriquez-Torres, Delfino; Serey-Roman, Maria Ignacia

2017-09-01

The purpose of this study is to analyze various surfaces of flexible solar panels and compare them to the traditional at panels mathematically. We evaluated the efficiency based on the integral formulas that involve flux. We performed calculations for flat panels with different positions, a cylindrical panel, conical panels with various opening angles and segments of a spherical panel. Our results indicate that the best efficiency per unit area belongs to particular segments of spherically-shaped panels. In addition, we calculated the optimal opening angle of a cone-shaped panel that maximizes the annual accumulation of the sun radiation per unit area. The considered shapes are presented below with a suggestion for connections of the cells.

A Vectorial Model to Compute Terrain Parameters, Local and Remote Sheltering, Scattering and Albedo using TIN Domains for Hydrologic Modeling.

NASA Astrophysics Data System (ADS)

Moreno, H. A.; Ogden, F. L.; Steinke, R. C.; Alvarez, L. V.

2015-12-01

Triangulated Irregular Networks (TINs) are increasingly popular for terrain representation in high performance surface and hydrologic modeling by their skill to capture significant changes in surface forms such as topographical summits, slope breaks, ridges, valley floors, pits and cols. This work presents a methodology for estimating slope, aspect and the components of the incoming solar radiation by using a vectorial approach within a topocentric coordinate system by establishing geometric relations between groups of TIN elements and the sun position. A normal vector to the surface of each TIN element describes slope and aspect while spherical trigonometry allows computing a unit vector defining the position of the sun at each hour and DOY. Thus, a dot product determines the radiation flux at each TIN element. Remote shading is computed by scanning the projection of groups of TIN elements in the direction of the closest perpendicular plane to the sun vector. Sky view fractions are computed by a simplified scanning algorithm in prescribed directions and are useful to determine diffuse radiation. Finally, remote radiation scattering is computed from the sky view factor complementary functions for prescribed albedo values of the surrounding terrain only for significant angles above the horizon. This methodology represents an improvement on the current algorithms to compute terrain and radiation parameters on TINs in an efficient manner. All terrain features (e.g. slope, aspect, sky view factors and remote sheltering) can be pre-computed and stored for easy access for a subsequent ground surface or hydrologic simulation.

Validation of OMI Measured Radiances Over Ice

NASA Astrophysics Data System (ADS)

Jaross, G.; Cebula, R. P.; Warner, J.

2005-12-01

The Ozone Monitoring Instrument (OMI) was launched aboard the EOS Aura satellite on 15 July, 2004 and has since performed quite well. Calibrated radiances in the form of Level 1 data products are produced regularly every orbit with minimal data loss. A total of 12 atmospheric constituent data products are currently planned for the OMI science data processing. All rely, to varying degrees, on the sun-normalized radiances of the OMI sensor. Retrievals of atmospheric trace constituents, such as NO{}_2, BrO, OCLO, and HCHO, rely upon spectroscopy and tend to be insensitive to errors in the absolute radiance levels. But column O{}_3 amount, aerosol properties, cloud heights, and UV surface radiation have significant sensitivities to changes in the sun-normalized radiances. In this presentation we discuss our evaluation of the OMI sun-normalized radiances between 330 nm and 500 nm. This covers most of the OMI spectral range where ozone absorption is small. Our technique involves a comparison of normalized radiances measured by OMI over the Antarctic continent with top-of-the-atmosphere (TOA) values computed with a radiative transfer model. In our model we assume a Rayleigh-scattering, aerosol-free, cloud-free atmosphere, and a mean surface reflectance derived from measurements on the ground. TOA radiances are sensitive to the bi-directional distribution of surface reflectance, especially at high solar zenith angles. We have developed a surface reflectance model to help correct these effects, but it still remains the largest source of uncertainty. We estimate the residual uncertainty at all wavelengths to be 2%.

A computer program to determine the possible daily release window for sky target experiments

NASA Technical Reports Server (NTRS)

Michaud, N. H.

1973-01-01

A computer program is presented which is designed to determine the daily release window for sky target experiments. Factors considered in the program include: (1) target illumination by the sun at release time and during the tracking period; (2) look angle elevation above local horizon from each tracking station to the target; (3) solar depression angle from the local horizon of each tracking station during the experimental period after target release; (4) lunar depression angle from the local horizon of each tracking station during the experimental period after target release; and (5) total sky background brightness as seen from each tracking station while viewing the target. Program output is produced in both graphic and data form. Output data can be plotted for a single calendar month or year. The numerical values used to generate the plots are furnished to permit a more detailed review of the computed daily release windows.

Propagation of low energy solar electrons

NASA Technical Reports Server (NTRS)

Anderson, K. A.; Mcfadden, J. P.; Lin, R. P.

1981-01-01

Two events are reported in which 2-10 keV electrons of solar energy have undergone significant adiabatic mirroring and pitch angle scattering in large scale magnetic structures in the interplanetary medium within a distance of about 0.5 AU from the earth. Electrons of 3 keV, typical of the energies measured, have a speed of about one-tenth of the speed of light, so that their travel time from the sun at 0 deg pitch angle would be about 100 minutes. Their cyclotron radius is about 20 km for a pitch angle of 30 deg, and a field of magnitude of 5 nT, and the cyclotron period is about 7.1 milliseconds. The electrons are scattered by spatial variations in the interplanetary magnetic field. When the spatial variations are convected past a stationary spacecraft by a 500 km/sec solar wind, they are seen as temporal fluctuations at a frequency of about 3 Hz.

Variation in spectral response of soybeans with respect to illumination, view, and canopy geometry

NASA Technical Reports Server (NTRS)

Ranson, K. J.; Biehl, L. L.; Bauer, M. E.

1984-01-01

Comparisons of the spectral response for incomplete (well-defined row structure) and complete (overlapping row structure) canopies of soybeans indicated a greater dependence on Sun and view geometry for the incomplete canopies. Red and near-IR reflectance for the incomplete canopy decreased as solar zenith angle increased for a nadir view angle until the soil between the plant rows was completely shaded. Thereafter for increasing solar zenith angle, the red reflectance leveled off and the near-IR reflectance increased. A 'hot spot' effect was evident for the red and near-IR reflectance factors. The 'hot spot' effect was more pronounced for the red band based on relative reflectance value changes. The ratios of off-nadir to nadir acquired data reveal that off-nadir red band reflectance factors more closely approximated straightdown measurements for time periods away from solar noon. Normalized difference generally approximated straightdown measurements during the middle portion of the day.

The registered distance of the celestial sphere: some historical cross-cultural data.

PubMed

Plug, C

1989-02-01

Estimates of the diameters of the sun and moon expressed in centimetres have been reported by several authors in the past. These estimates imply that the sizes of the sun and moon are perceived as if these bodies are only some tens of metres distant. In this study five units of length that were used by ancient astronomers to estimate arcs on the celestial sphere were investigated. The purpose was to determine whether the lengths and angles represented by these units imply a specific registered distance of the star sphere. The sizes of the Babylonian cubit, Arab fitr and shibr, Greek eclipse digit, and Chinese chang support the conclusion that the registered distance of the stars was about 10 to 40 metres in these four cultures over the last two millennia.

A nonlinear estimator for reconstructing the angular velocity of a spacecraft without rate gyros

NASA Technical Reports Server (NTRS)

Polites, M. E.; Lightsey, W. D.

1991-01-01

A scheme for estimating the angular velocity of a spacecraft without rate gyros is presented. It is based upon a nonlinear estimator whose inputs are measured inertial vectors and their calculated time derivatives relative to vehicle axes. It works for all spacecraft attitudes and requires no knowledge of attitude. It can use measurements from a variety of onboard sensors like Sun sensors, star trackers, or magnetometers, and in concert. It can also use look angle measurements from onboard tracking antennas for tracking and data relay satellites or global positioning system satellites. In this paper, it is applied to a Sun point scheme on the Hubble Space Telescope assuming all or most of its onboard rate gyros have failed. Simulation results are presented for verification.

Wide-angle planar microtracking for quasi-static microcell concentrating photovoltaics

NASA Astrophysics Data System (ADS)

Price, Jared S.; Sheng, Xing; Meulblok, Bram M.; Rogers, John A.; Giebink, Noel C.

2015-02-01

Concentrating photovoltaics offer a way to lower the cost of solar power. However, the existing paradigm based on precise orientation of large-area concentrator modules towards the Sun limits their deployment to large, open land areas. Here, we explore an alternate approach using high-efficiency microcell photovoltaics embedded between a pair of plastic lenslet arrays to demonstrate quasi-static concentrating photovoltaic panels <1 cm thick that accomplish full-day tracking with >200x flux concentration ratio through small (<1 cm) lateral translation at fixed latitude tilt. Per unit of installed land area, cosine projection loss for fixed microtracking concentrating photovoltaic panels is ultimately offset by improved ground coverage relative to their conventional dual-axis counterparts, enabling a ~1.9x increase in daily energy output that may open up a new opportunity for compact, high-efficiency concentrating photovoltaics to be installed on rooftops and other limited-space urban environments.

Wide-angle planar microtracking for quasi-static microcell concentrating photovoltaics.

PubMed

Price, Jared S; Sheng, Xing; Meulblok, Bram M; Rogers, John A; Giebink, Noel C

2015-02-05

Concentrating photovoltaics offer a way to lower the cost of solar power. However, the existing paradigm based on precise orientation of large-area concentrator modules towards the Sun limits their deployment to large, open land areas. Here, we explore an alternate approach using high-efficiency microcell photovoltaics embedded between a pair of plastic lenslet arrays to demonstrate quasi-static concentrating photovoltaic panels <1 cm thick that accomplish full-day tracking with >200x flux concentration ratio through small (<1 cm) lateral translation at fixed latitude tilt. Per unit of installed land area, cosine projection loss for fixed microtracking concentrating photovoltaic panels is ultimately offset by improved ground coverage relative to their conventional dual-axis counterparts, enabling a ~1.9x increase in daily energy output that may open up a new opportunity for compact, high-efficiency concentrating photovoltaics to be installed on rooftops and other limited-space urban environments.

Fluxes of MeV particles at Earth's orbit and their relationship with the global structure of the solar corona: Observations from SOHO

NASA Technical Reports Server (NTRS)

Posner, A.; Bothmer, V.; Kunow, H.; Heber, B.; Mueller-Mellin, R.; Delaboudiniere, J.-P.; Thompson, B. J.; Brueckner, G. E.; Howard, R. A.; Michels, D. J.

1997-01-01

The SOHO satellite, launched on 2 December 1995, combines a unique set of instruments which allow comparative studies of the interior of the sun, the outer corona and solar to be carried out. In its halo orbit around the L1 Lagrangian point of the sun-earth system, SOHO's comprehensive suprathermal and energetic particle analyzer (COSTEP) measures in situ energetic particles in the energy range of 44 keV/particle to greater than 53 MeV/n. The MeV proton, electron and helium nuclei measurements from the COSTEP electron proton helium instrument (EPHIN) were used to investigate the relationships of intensity increases of these particle species with the large-scale structures of the solar corona and heliosphere, including temporal variations. Coronal observatons are provided by the large angle spectroscopic coronagraph (LASCO) and the extreme ultraviolet imaging telescope (EIT). It was found that during times of minimum solar activity, intensity increases of the particles have two well defined sources: corotating interaction regions (CIRs) in the heliosphere related to coronal holes at the sun and coronal mass ejections.

[UV-radiation--sources, wavelength, environment].

PubMed

Hölzle, Erhard; Hönigsmann, Herbert

2005-09-01

The UV-radiation in our environment is part of the electromagnetic radiation, which emanates from the sun. It is designated as optical radiation and reaches from 290-4,000 nm on the earth's surface. According to international definitions UV irradiation is divided into short-wave UVC (200-280 nm), medium-wave UVB (280-320 nm), and long-wave UVA (320-400 nm). Solar radiation which reaches the surface of the globe at a defined geographical site and a defined time point is called global radiation. It is modified quantitatively and qualitatively while penetrating the atmosphere. Besides atmospheric conditions, like ozone layer and air pollution, geographic latitude, elevation, time of the season, time of the day, cloudiness and the influence of indirect radiation resulting from stray effects in the atmosphere and reflection from the underground play a role in modifying global radiation, which finally represents the biologically effective radiation. The radiation's distribution on the body surface varies according to sun angle and body posture. The cumulative UV exposure is mainly influenced by outdoor profession and recreational activities. The use of sun beds and phototherapeutic measures additionally may contribute to the cumulative UV dose.

A Raster Based Approach To Solar Pressure Modeling

NASA Technical Reports Server (NTRS)

Wright, Theodore

2014-01-01

The impact of photons upon a spacecraft introduces small forces and moments. The magnitude and direction of the forces depend on the material properties of the spacecraft components being illuminated. Which components are being lit depends on the orientation of the craft with respect to the Sun as well as the gimbal angles for any significant moving external parts (solar arrays, typically). Some components may shield others from the Sun.To determine solar pressure in the presence overlapping components, a 3D model can be used to determine which components are illuminated. A view (image) of the model as seen from the Sun shows the only contributors to solar pressure. This image can be decomposed into pixels, each of which can be treated as a non-overlapping flat plate as far as solar pressure calculations are concerned. The sums of the pressures and moments on these plates approximate the solar pressure and moments on the entire vehicle.The image rasterization technique can also be used to compute other spacecraft attributes that are dependent on attitude and geometry, including solar array power generation capability and free molecular flow drag.

Improving Pixel Level Cloud Optical Property Retrieval using Monte Carlo Simulations

NASA Technical Reports Server (NTRS)

Oreopoulos, Lazaros; Marshak, Alexander; Cahalan, Robert F.

1999-01-01

The accurate pixel-by-pixel retrieval of cloud optical properties from space is influenced by radiative smoothing due to high order photon scattering and radiative roughening due to low order scattering events. Both are caused by cloud heterogeneity and the three-dimensional nature of radiative transfer and can be studied with the aid of computer simulations. We use Monte Carlo simulations on variable 1-D and 2-D model cloud fields to seek for dependencies of smoothing and roughening phenomena on single scattering albedo, solar zenith angle, and cloud characteristics. The results are discussed in the context of high resolution satellite (such as Landsat) retrieval applications. The current work extends the investigation on the inverse NIPA (Non-local Independent Pixel Approximation) as a tool for removing smoothing and improving retrievals of cloud optical depth. This is accomplished by: (1) Delineating the limits of NIPA applicability; (2) Exploring NIPA parameter dependences on cloud macrostructural features, such as mean cloud optical depth and geometrical thickness, degree of extinction and cloud top height variability. We also compare parameter values from empirical and theoretical considerations; (3) Examining the differences between applying NIPA on radiation quantities vs direct application on optical properties; (4) Studying the radiation budget importance of the NIPA corrections as a function of scale. Finally, we discuss fundamental adjustments that need to be considered for successful radiance inversion at non-conservative wavelengths and oblique Sun angles. These adjustments are necessary to remove roughening signatures which become more prominent with increasing absorption and solar zenith angle.

Flying Fast and High: Operational Flight Planning for Maximum Data Return for Airborne Snow Observatory Mountain Surveys

NASA Astrophysics Data System (ADS)

Berisford, D. F.; Painter, T. H.; Richardson, M.; Wallach, A.; Deems, J. S.; Bormann, K. J.

2017-12-01

The Airborne Snow Observatory (ASO - http://aso.jpl.nasa.gov) uses an airborne laser scanner to map snow depth, and imaging spectroscopy to map snow albedo in order to estimate snow water equivalent and melt rate over mountainous, hydrologic basin-scale areas. Optimization of planned flight lines requires the balancing of many competing factors, including flying altitude and speed, bank angle limitation, laser pulse rate and power level, flightline orientation relative to terrain, surface optical properties, and data output requirements. These variables generally distill down to cost vs. higher resolution data. The large terrain elevation variation encountered in mountainous terrain introduces the challenge of narrow swath widths over the ridgetops, which drive tight flightline spacing and possible dropouts over the valleys due to maximum laser range. Many of the basins flown by ASO exceed 3,000m of elevation relief, exacerbating this problem. Additionally, sun angle may drive flightline orientations for higher-quality spectrometer data, which may change depending on time of day. Here we present data from several ASO missions, both operational and experimental, showing the lidar performance and accuracy limitations for a variety of operating parameters. We also discuss flightline planning strategies to maximize data density return per dollar, and a brief analysis on the effect of short turn times/steep bank angles on GPS position accuracy.

Title: Accelerator Test of an Angle Detecting Inclined Sensor (ADIS) Prototype with Beams of 48Ca and Fragments

NASA Astrophysics Data System (ADS)

Connell, J. J.; Lopate, C.; McKibben, R. B.; Enman, A.

2006-12-01

The measurement and identification of high energy ions (> few MeV/n) from events originating on the Sun is of direct interest to the Living With a Star Program. These ions are a major source of Single Event Effects (SEE) in space-based electronics. Measurements of these ions also help in understanding phenomena such as Solar particle events and coronal mass ejections. These disturbances can directly affect the Earth and the near-Earth space environment, and thus human technology. The resource constraints on spacecraft generally mean that instruments that measure cosmic rays and Solar energetic particles must have low mass (a few kg) and power (a few W), be robust and reliable yet highly capable. Such instruments should identify ionic species (at least by element, preferably by isotope) from protons through the iron group. The charge and mass resolution of heavy ion instrument in space depends upon determining ions' angles of incidence. The Angle Detecting Inclined Sensor (ADIS) system is a highly innovative and uniquely simple detector configuration used to determine the angle of incidence of heavy ions in space instruments. ADIS replaces complex position sensing detectors (PSDs) with a system of simple, reliable and robust Si detectors inclined at an angle to the instrument axis. In August 2004 we tested ADIS prototypes with a 48Ca beam at the National Superconducting Cyclotron Laboratory's (NSCL) Coupled Cyclotron Facility (CCF). We demonstrate that our prototype charged particle instrument design with an ADIS system has a charge resolution of better than 0.25 e. An ADIS based system is being incorporated into the Energetic Heavy Ion Sensor (EHIS), one of the instruments in the Space Environment In-Situ Suite (SEISS) on the next generation of Geostationary Operational Environmental Satellite (GOES-R) System. An ADIS based system was also selected for the High Energy Particle Sensor (HEPS), one of the instruments in the Space Environment Sensor Suite (SESS) on the National Polar-orbiting Operational Environmental Satellite System (NPOESS). SESS is presently de-scoped from NPOESS. The ADIS instrument development project was 95% funded by NASA under the Living With a Star (LWS) Targeted Research and Technology program (grant NAG5-12493).

Perspectives for Distributed Observations of Near-Earth Space Using a Russian-Cuban Observatory

NASA Astrophysics Data System (ADS)

Bisikalo, D. V.; Savanov, I. S.; Naroenkov, S. A.; Nalivkin, M. A.; Shugarov, A. S.; Bakhtigaraev, N. S.; Levkina, P. A.; Ibragimov, M. A.; Kil'pio, E. Yu.; Sachkov, M. E.; Kartashova, A. P.; Fateeva, A. M.; Uratsuka, Marta R. Rodriguez; Estrada, Ramses Zaldivar; Diaz, Antonio Alonsa; Rodríguez, Omar Pons; Figuera, Fidel Hernandes; Garcia, Maritza Garcia

2018-06-01

The creation of a specialized network of large, wide-angle telescopes for distributed observations of near-Earth space using a Russian-Cuban Observatory is considered. An extremely important goal of routine monitoring of near-Earth and near-Sun space is warding off threats with both natural and technogenic origins. Natural threats are associated with asteroids or comets, and technogenic threats with man-made debris in near-Earth space. A modern network of ground-based optical instruments designed to ward off such threats must: (a) have a global and, if possible, uniform geographic distribution, (b) be suitable for wide-angle, high-accuracy precision survey observations, and (c) be created and operated within a single network-oriented framework. Experience at the Institute of Astronomy on the development of one-meter-class wide-angle telescopes and elements of a super-wide-angle telescope cluster is applied to determine preferences for the composition of each node of such a network. The efficiency of distributed observations in attaining maximally accurate predictions of the motions of potentially dangerous celestial bodies as they approach the Earth and in observations of space debris and man-made satellites is estimated. The first estimates of astroclimatic conditions at the proposed site of the future Russian-Cuban Observatory in the mountains of the Sierra del Rosario Biosphere Reserve are obtained. Special attention is given to the possible use of the network to carry out a wide range of astrophysical studies, including optical support for the localization of gravitational waves and other transient events.

Energy Landscapes for the Self-Assembly of Supramolecular Polyhedra

NASA Astrophysics Data System (ADS)

Russell, Emily R.; Menon, Govind

2016-06-01

We develop a mathematical model for the energy landscape of polyhedral supramolecular cages recently synthesized by self-assembly (Sun et al. in Science 328:1144-1147, 2010). Our model includes two essential features of the experiment: (1) geometry of the organic ligands and metallic ions; and (2) combinatorics. The molecular geometry is used to introduce an energy that favors square-planar vertices (modeling {Pd}^{2+} ions) and bent edges with one of two preferred opening angles (modeling boomerang-shaped ligands of two types). The combinatorics of the model involve two-colorings of edges of polyhedra with four-valent vertices. The set of such two-colorings, quotiented by the octahedral symmetry group, has a natural graph structure and is called the combinatorial configuration space. The energy landscape of our model is the energy of each state in the combinatorial configuration space. The challenge in the computation of the energy landscape is a combinatorial explosion in the number of two-colorings of edges. We describe sampling methods based on the symmetries of the configurations and connectivity of the configuration graph. When the two preferred opening angles encompass the geometrically ideal angle, the energy landscape exhibits a very low-energy minimum for the most symmetric configuration at equal mixing of the two angles, even when the average opening angle does not match the ideal angle.

SU-F-T-322: A Comparison of Two Si Detectors for in Vivo Dosimetry

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

Talarico, O; Krylova, T; Lebedenko, I

Purpose: To compare two types of semiconductor detectors for in vivo dosimetry by their dependence from various parameters in different conditions. Methods: QED yellow (Sun Nuclear) and EDP (Scanditronix) Si detectors were radiated by a Varian Clinac 2300 ix with 6 and 18 MV energies. 10 cm thickness water equivalent phantom consisted of 30×30 cm{sup 2} squared plates was used for experiments. Dose dependencies for different beam angles (0 – 180°), field size (3–40 cm), dose (50 – 300 MU), and dose rates (50 – 300 MU/min) were obtained and calibrated with Standard Farmer chamber (PTW). Results: Reproducibility, linearity, dosemore » rate, angular dependence, and field size dependence were obtained for QED and EDP. They show no dose-rate dependence in available clinical dose rate range (100–600 MU/min). Both diodes have linear dependence with increasing the dose. Therefore even in case of high radiation therapy (including total body irradiation) it is not necessary to apply an additional correction during in vivo dosimetry. The diodes have different behavior for angular and field size dependencies. QED diode showed that dose value is stable for beam angles from 0 to 60°, for 60–180° correction factor has to be applied for each beam angle during in vivo measurements. For EDP diode dose value is sensitive to beam angle in whole range of angles. Conclusion: The study shows that QED diode is more suitable for in vivo dosimetry due to dose value independence from incident beam angle in the range 0–60°. There is no need in correction factors for increasing of dose and dose rate for both diodes. The next step will be to carry out measurements in non-standard conditions of total body irradiation. After this modeling of these experiments with Monte Carlo simulation for comparison calculated and obtained data is planned.« less

A fast radiative transfer method for the simulation of visible satellite imagery

NASA Astrophysics Data System (ADS)

Scheck, Leonhard; Frèrebeau, Pascal; Buras-Schnell, Robert; Mayer, Bernhard

2016-05-01

A computationally efficient radiative transfer method for the simulation of visible satellite images is presented. The top of atmosphere reflectance is approximated by a function depending on vertically integrated optical depths and effective particle sizes for water and ice clouds, the surface albedo, the sun and satellite zenith angles and the scattering angle. A look-up table (LUT) for this reflectance function is generated by means of the discrete ordinate method (DISORT). For a constant scattering angle the reflectance is a relatively smooth and symmetric function of the two zenith angles, which can be well approximated by the lowest-order terms of a 2D Fourier series. By storing only the lowest Fourier coefficients and adopting a non-equidistant grid for the scattering angle, the LUT is reduced to a size of 21 MB per satellite channel. The computation of the top of atmosphere reflectance requires only the calculation of the cloud parameters from the model state and the evaluation and interpolation of the reflectance function using the compressed LUT and is thus orders of magnitude faster than DISORT. The accuracy of the method is tested by generating synthetic satellite images for the 0.6 μm and 0.8 μm channels of the SEVIRI instrument for operational COSMO-DE model forecasts from the German Weather Service (DWD) and comparing them to DISORT results. For a test period in June the root mean squared absolute reflectance error is about 10-2 and the mean relative reflectance error is less than 2% for both channels. For scattering angles larger than 170 ° the rapid variation of reflectance with the particle size related to the backscatter glory reduces the accuracy and the errors increase by a factor of 3-4. Speed and accuracy of the new method are sufficient for operational data assimilation and high-resolution model verification applications.

Oceanographic Analysis of Sun Glint Images Taken on Space Shuttle Mission STS 41-G.

DTIC Science & Technology

1986-03-01

10. SOURCE OF FUNDING NUMBERS PROGRAM PROJECT TASK WORK UNIT ELEMENT NO. NO. NO. ACCESSION NO. ?I TITLE (Include Security Ciassification) OCEANOGRAPHIC...CONTENTS le INTRJODUCTION --- ---. m.--- --..-- --.-- -- -- -- --- -- ---.-. II. WESTERN MEDITERRANEAN OCEANOGRAPHIC OVERVIEV - --------------- 10. A...By computing the arc tangent of 128 n.m./125 n.m. a tilt angle of 45.7’ was approximated for the camera lens. Two simplifications were made. Earth

An Alternative to EPA Method 9 -- Field Validation of the Digital Opacity Compliance System (DOCS)

DTIC Science & Technology

2005-03-15

at the completion of the Phase I and Phase II DOCS field demonstration. These included the following 1) anemometer, 2) sling psychrometer , 3) Abney...anemometer (Eastern Technical Associates, Inc.) Sky conditions Visual observation Relative Humidity Sling Psychrometer (Eastern Technical Associates...least have access to a range of climatic monitoring equipment including the following 1) anemometer, 2) sling psychrometer , 3) Abney Level (sun angle

An Analysis of the Accessibility of Earth-Approaching Asteroids.

DTIC Science & Technology

1985-12-01

coordinate system. Outputs are the X,Y,Z coordinates of the sun in the geocentric-equatorial coordinate system. The obliquity of the ecliptic is a variable...All positions and velocities are calculated in heliocentric- ecliptic coordinates thus requiring no transformations into unusual frames of reference...tion vectors of the departure and arrival planets in the heliocentric- ecliptic reference frame. ,\\. , V I(W() - / n (16) %: ~22% .b The angle between

Exergy Analyses of Fabricated Compound Parabolic Solar Collector with Evacuated Tubes at Different Operating Conditions: Indore (India)

NASA Astrophysics Data System (ADS)

Geete, Ankur; Dubey, Akash; Sharma, Ankush; Dubey, Anshul

2018-05-01

In this research work, compound parabolic solar collector (CPC) with evacuated tubes is fabricated. Main benefit of CPC is that there is no requirement of solar tracking system. With fabricated CPC; outlet temperatures of flowing fluid, instantaneous efficiencies, useful heat gain rates and inlet exergies (with and without considering Sun's cone angle) are experimentally found. Observations are taken at different time intervals (1200, 1230, 1300, 1330 and 1400 h), mass flow rates (1.15, 0.78, 0.76, 0.86 and 0.89 g/s), ambient temperatures and with various dimensions of solar collector. This research work is concluded as; maximum instantaneous efficiency is 69.87% which was obtained with 0.76 g/s flow rate of water at 1300 h and 42°C is the maximum temperature difference which was also found at same time. Maximum inlet exergies are 139.733 and 139.532 kW with and without considering Sun's cone angle at 1300 h, respectively. Best thermal performance from the fabricated CPC with evacuated tubes is found at 1300 h. Maximum inlet exergy is 141.365 kW which was found at 1300 h with 0.31 m aperture width and 1.72 m absorber pipe length.

Optical Polarization of Light from a Sorghum Canopy Measured Under Both a Clear and an Overcast Sky

NASA Technical Reports Server (NTRS)

Vanderbilt, Vern; Daughtry, Craig; Biehl, Larry; Dahlgren, Robert

2014-01-01

Introduction: We tested the hypothesis that the optical polarization of the light reflected by a sorghum canopy is due to a Fresnel-type redirection, by sorghum leaf surfaces, of light from an unpolarized light source, the sun or overcast sky, toward the measuring sensor. If it can be shown that the source of the polarization of the light scattered by the sorghum canopy is a first surface, Fresnel-type reflection, then removing this surface reflected light from measurements of canopy reflectance presumably would allow better insight into the biochemical processes such as photosynthesis and metabolism that occur in the interiors of sorghum canopy leaves. Methods: We constructed a tower 5.9m tall in the center of a homogenous sorghum field. We equipped two Barnes MMR radiometers with polarization analyzers on the number 1, 3 and 7 Landsat TM wavelength bands. Positioning the radiometers atop the tower, we collected radiance data in 44 view directions on two days, one day with an overcast sky and the other, clear and sunlit. From the radiance data we calculated the linear polarization of the reflected light for each radiometer wavelength channel and view direction. Results and Discussion: Our experimental results support our hypothesis, showing that the amplitude of the linearly polarized portion of the light reflected by the sorghum canopy varied dramatically with view azimuth direction under a point source, the sun, but the amplitude varied little with view azimuth direction under the hemispherical source, the overcast sky. Under the clear sky, the angle of polarization depended upon the angle of incidence of the sunlight on the leaf, while under the overcast sky the angle of polarization depended upon the zenith view angle. These results support a polarized radiation transport model of the canopy that is based upon a first surface, Fresnel reflection from leaves in the sorghum canopy.

Influence of the IMF Cone Angle on Invariant Latitudes of Polar Region Footprints of FACs in the Magnetotail: Cluster Observation

NASA Astrophysics Data System (ADS)

Cheng, Z. W.; Shi, J. K.; Zhang, J. C.; Torkar, K.; Kistler, L. M.; Dunlop, M.; Carr, C.; Rème, H.; Dandouras, I.; Fazakerley, A.

2018-04-01

The influence of the interplanetary magnetic field (IMF) cone angle θ (the angle between the IMF direction and the Sun-Earth line) on the invariant latitudes of the footprints of the field-aligned currents (FACs) in the magnetotail has been investigated. We performed a statistical study of 542 FAC cases observed by the four Cluster spacecraft in the Northern Hemisphere. The results show that there are almost no FACs when the IMF cone angle is less than 10°, and there are indications of the FACs in the plasma sheet boundary layers being weak under the radial IMF conditions. The footprints of the large FAC (>10 nA/m2) cases are within invariant latitudes <71° and mainly within IMF cone angles θ > 60°, which implies that the footprints of the large FACs mainly expand equatorward with large IMF cone angle. The equatorward boundary of the FAC footprints in the polar region decreases with increasing IMF cone angle (and has a better correlation for northward IMF), which shows that the IMF cone angle plays an important controlling role in FAC distributions in the magnetosphere-ionosphere coupling system. There is almost no correlation between the poleward boundary and the IMF cone angle for both northward and southward IMF. This is because the poleward boundary movement is limited by an enhanced lobe magnetic flux. This is the first time a correlation between FAC footprints in the polar region and IMF cone angles has been determined.

Impact of basic angle variations on the parallax zero point for a scanning astrometric satellite

NASA Astrophysics Data System (ADS)

Butkevich, Alexey G.; Klioner, Sergei A.; Lindegren, Lennart; Hobbs, David; van Leeuwen, Floor

2017-07-01

Context. Determination of absolute parallaxes by means of a scanning astrometric satellite such as Hipparcos or Gaia relies on the short-term stability of the so-called basic angle between the two viewing directions. Uncalibrated variations of the basic angle may produce systematic errors in the computed parallaxes. Aims: We examine the coupling between a global parallax shift and specific variations of the basic angle, namely those related to the satellite attitude with respect to the Sun. Methods: The changes in observables produced by small perturbations of the basic angle, attitude, and parallaxes were calculated analytically. We then looked for a combination of perturbations that had no net effect on the observables. Results: In the approximation of infinitely small fields of view, it is shown that certain perturbations of the basic angle are observationally indistinguishable from a global shift of the parallaxes. If these kinds of perturbations exist, they cannot be calibrated from the astrometric observations but will produce a global parallax bias. Numerical simulations of the astrometric solution, using both direct and iterative methods, confirm this theoretical result. For a given amplitude of the basic angle perturbation, the parallax bias is smaller for a larger basic angle and a larger solar aspect angle. In both these respects Gaia has a more favourable geometry than Hipparcos. In the case of Gaia, internal metrology is used to monitor basic angle variations. Additionally, Gaia has the advantage of detecting numerous quasars, which can be used to verify the parallax zero point.

Predictors of sun protection in northern Australian men with a history of nonmelanoma skin cancer.

PubMed

Woolley, Torres; Buettner, Petra G; Lowe, John

2004-08-01

It is important to understand what predicts regular use of sun protection in men susceptible to skin cancer. A questionnaire survey of men with previous nonmelanoma skin cancer (n = 300) was conducted. Participants who typically used sunscreen tended to be younger, have fewer excised skin lesions, work indoors, and have spent most of their life in the tropics. Predictors of wearing a long-sleeved shirt with a wide-brimmed hat were not enjoying sun exposure, not having barriers to using sun protection, having more skin lesions previously excised, working for a company with a mandatory policy of sun protection, attitudes that the benefits of a suntan do not outweigh the risks and that skin cancers cannot be easily treated, and age over 50. Men who adequately protect themselves from the sun and who have better attitudes to sun exposure were more often those with a high level of negative experience with skin cancer. Therefore, the sun protection attitudes and behaviors of some men may only improve after significant sun damage. This study recommends that the use of appropriate sun protective clothing should be made mandatory for all who work outdoors in high-sun-exposure occupations.

Factors associated with risky sun exposure behaviors among operating engineers.

PubMed

Duffy, Sonia A; Choi, Seung Hee; Hollern, Rachael; Ronis, David L

2012-09-01

The objective of this study was to determine the factors associated with sun exposure behaviors among Operating Engineers (heavy equipment operators). Operating Engineers (N = 498) were asked to complete a cross-sectional survey. Linear and logistic regression analyses were used to determine health behavioral, perceptional, and demographic factors associated with sun exposure behavior (sun burns, blistering, use of sunscreen, and interest in sun protection services). Almost half reported two or more sunburns/summer and the median times blistering was 2 with a range of 0-100. About one-third never used sun block, while just over one-third rarely used sun block. Almost one-quarter were interested in sun protection guidance. Multivariate analyses showed that perceptions of skin type, alcohol problems, fruit intake, BMI, sleep quality, age, sex, and race were significantly associated with at least one of the outcome variables (P < 0.05). Operating Engineers are at high risk for skin cancer due to high rates of exposure to ultraviolet light and low rates of sun block use. Subgroups of Operating Engineers are particularly at risk for sun damage. Interventions are needed to decrease sun exposure among Operating Engineers. Copyright © 2012 Wiley Periodicals, Inc.

An Overview of the Electron-Proton and High Energy Telescopes for Solar Orbiter

NASA Astrophysics Data System (ADS)

Boden, Sebastian; Kulkarni, Shrinivasrao R.; Tammen, Jan; Steinhagen, Jan; Martin, César; Wimmer-Schweingruber, Robert F.; Böttcher, Stephan I.; Seimetz, Lars; Ravanbakhsh, Ali; Elftmann, Robert; Rodriguez-Pacheco, Javier; Prieto Mateo, Manuel; Gomez Herrero, Rául

2014-05-01

The Energetic Particle Detector (EPD) suite for ESA's Solar Orbiter will provide key measurements to address particle acceleration at and near the Sun. The EPD suite consists of four sensors (STEP, SIS, EPT, and HET). The University of Kiel in Germany is responsible for the design, development, and building of STEP, EPT and HET. This poster will focus on the last two. The Electron Proton Telescope (EPT) is designed to cleanly separate and measure electrons in the energy range from 20 - 400 keV and protons from 20 - 7000 keV. To separate electrons and protons EPT relies on the magnet/foil-technique. EPT is intended to close the gap between the supra-thermal particles measured by STEP and the high energy range covered by HET. The High-Energy Telescope (HET) will measure electrons from 300 keV up to about 30 MeV, protons from 10 to 100 MeV, and heavy ions from ~20 to 200 MeV/nuc. To achieve this performance HET consists of a series of silicon detectors in a telescope configuration with a scintillator calorimeter to stop high energy protons and ions. It uses the dE/dx vs. total E technique . In this way HET covers an energy range which is of interest for studies of the space radiation environment and will perform measurements needed to understand the origin of high-energy particle events at the Sun. EPT and HET share a common Electronics Box, there are two EPT-HET sensors on Solar Orbiter to allow rudimentary pitch-angle coverage. Here we present the current development status of EPT-HET units and calibration results of demonstration models as well as plans for future activities.

Complex-shaped solar sails: A study of the coupled attitude and trajectory dynamics

NASA Astrophysics Data System (ADS)

van de Kolk, Christel Brigitte

The concept of solar sailing is to reflect sunlight of a large surface in space to generate a low thrust, but constantly present, force. By varying the angle between sail normal and incident sunlight, a solar sail can fly inward (to the sun) and outward. The lifetime of a solar sail is not limited by the amount of fuel it can carry, since its fuel is sunlight. Degradation of the reflective surface, due to micrometeorite impact, etc, is the main limiting factor for the lifetime, but it is safe to say that the lifetime of a solar sail will be decades. This extensive lifetime and the possibility of inward and outward travel within the solar system, make solar sails good candidates for cargo missions within our solar system. They are less useful for manned flight, due to the long flight times of solar sail propelled vehicles. For example, the flight time from Earth to Mars is about a year. The solar sails studied previously were flat, single surfaces. The required stiffness and rigidity are provided by either a supporting structure or by spinning the sail. What both concepts have in common is that it was assumed that the attitude dynamics and trajectory dynamics were uncoupled. This assumption eliminates an entire family of promising flight modes in which the coupled motion provides automatic passive attitude dynamics and control. The research presented here will focus on the development of a full 3 dimensional model for the coupled attitude/trajectory dynamics problem of a complex shaped solar sail. This model will then be used to investigate the possible trajectory types and the stability of the attitude dynamics. It will be shown that it is possible to fly either inward to the Sun or out away from the Sun, depending on the dimensions of the individual sail planes and the angle between the two sail planes. However, passive attitude stability for all three axes will not be possible. The roll motion about the sail-sun line is unstable and some form of active control will be needed here.

Sun Shines in High-Energy X-rays

NASA Image and Video Library

2014-12-22

X-rays stream off the sun in this first picture of the sun, overlaid on a picture taken by NASA Solar Dynamics Observatory SDO, taken by NASA NuSTAR. The field of view covers the west limb of the sun.

Aquarius Instrument and Salinity Retrieval

NASA Technical Reports Server (NTRS)

Le Vine, D. M.

2011-01-01

Aquarius has been designed to map the surface salinity field of the global ocean from space a parameter important for understanding ocean circulation and its relationship to climate and the global water cycle. Salinity is measured remotely from space by measuring the thermal emission from the ocean surface. This is done at the low frequency end of the microwave spectrum (e.g. 1.4 GHz) where the emission is sufficiently sensitive to changes in salinity to be detected with sophisticated radiometers. The goal is to monitor the seasonal and interannual variation of the large scale features of the surface salinity field in the open ocean by providing maps on a monthly basis with a spatial resolution of 150 km and an accuracy of 0.2 psu. These are challenging requirements that have led to some unique features of the instrument. These include: a) The addition of a co-located scatterometer to help provide a correction for roughness; b) The addition of a polarimetric channel (third Stokes parameter) to the radiometer to help correct for Faraday rotation; c) Asun-synchronous orbit with a 6 pm ascending equatorial crossing to minimize Faraday rotation and with the antennas looking away from the sun toward the nighttime side to minimize contamination by radiation from the sun; and d) An antenna designed to limit side lobes in the direction of rays from the sun. In addition, achieving the accuracy goal of 0.2 psu requires averaging over one month and to do this requires a highly stable radiometer. Aquarius has three separate radiometers that image in pushbroom fashion with the three antenna beams looking across track. The antenna is a 2.5-m diameter, offset parabolic reflector with three feed horns and the three beams are arranged to image with the boresight aligned to look across track, roughly perpendicular to the spacecraft heading and pointing away from the Sun. The three beams point at angles of theta = 25.8 deg., 33.8 deg. and 40.3 deg. with respect to the spacecraft nadir which correspond to local incidence angles at the surface of 28.7 deg., 37.8 deg. and 45.6 deg., respectively. The resolution of the three radiometer beams (axes of the 3dB ellipse) is: 76 x 94 km for the inner beam, 84 x 120 km for the middle beam to 96 x 156 km for the outer beam. Together they cover a swath of about 390 km. Aquarius will map the global ice-free ocean every 7-days from which monthly average composites will be derived. This will provide a snapshot of the mean field, as well as resolving the seasonal to interannual variations over the three-year baseline of the mission.

Within-twig leaf distribution patterns differ among plant life-forms in a subtropical Chinese forest.

PubMed

Meng, Fengqun; Cao, Rui; Yang, Dongmei; Niklas, Karl J; Sun, Shucun

2013-07-01

In theory, plants can alter the distribution of leaves along the lengths of their twigs (i.e., within-twig leaf distribution patterns) to optimize light interception in the context of the architectures of their leaves, branches and canopies. We hypothesized that (i) among canopy tree species sharing similar light environments, deciduous trees will have more evenly spaced within-twig leaf distribution patterns compared with evergreen trees (because deciduous species tend to higher metabolic demands than evergreen species and hence require more light), and that (ii) shade-adapted evergreen species will have more evenly spaced patterns compared with sun-adapted evergreen ones (because shade-adapted species are generally light-limited). We tested these hypotheses by measuring morphological traits (i.e., internode length, leaf area, lamina mass per area, LMA; and leaf and twig inclination angles to the horizontal) and physiological traits (i.e., light-saturated net photosynthetic rates, Amax; light saturation points, LSP; and light compensation points, LCP), and calculated the 'evenness' of within-twig leaf distribution patterns as the coefficient of variation (CV; the higher the CV, the less evenly spaced leaves) of within-twig internode length for 9 deciduous canopy tree species, 15 evergreen canopy tree species, 8 shade-adapted evergreen shrub species and 12 sun-adapted evergreen shrub species in a subtropical broad-leaved rainforest in eastern China. Coefficient of variation was positively correlated with large LMA and large leaf and twig inclination angles, which collectively specify a typical trait combination adaptive to low light interception, as indicated by both ordinary regression and phylogenetic generalized least squares analyses. These relationships were also valid within the evergreen tree species group (which had the largest sample size). Consistent with our hypothesis, in the canopy layer, deciduous species (which were characterized by high LCP, LSP and Amax) had more even leaf distribution patterns than evergreen species (which had low LCP, LSP and Amax); shade-adapted evergreen species had more even leaf distribution patterns than sun-adapted evergreen species. We propose that the leaf distribution pattern (i.e., 'evenness' CV, which is an easily measured functional trait) can be used to distinguish among life-forms in communities similar to the one examined in this study.

Sun Tracking Systems: A Review

PubMed Central

Lee, Chia-Yen; Chou, Po-Cheng; Chiang, Che-Ming; Lin, Chiu-Feng

2009-01-01

The output power produced by high-concentration solar thermal and photovoltaic systems is directly related to the amount of solar energy acquired by the system, and it is therefore necessary to track the sun's position with a high degree of accuracy. Many systems have been proposed to facilitate this task over the past 20 years. Accordingly, this paper commences by providing a high level overview of the sun tracking system field and then describes some of the more significant proposals for closed-loop and open-loop types of sun tracking systems. PMID:22412341

Ceres Topographic Globe Animation

NASA Image and Video Library

2015-07-28

This frame from an animation shows a color-coded map from NASA Dawn mission revealing the highs and lows of topography on the surface of dwarf planet Ceres. The color scale extends 3.7 miles (6 kilometers) below the surface in purple to 3.7 miles (6 kilometers) above the surface in brown. The brightest features (those appearing nearly white) -- including the well-known bright spots within a crater in the northern hemisphere -- are simply reflective areas, and do not represent elevation. The topographic map was constructed from analyzing images from Dawn's framing camera taken from varying sun and viewing angles. The map was combined with an image mosaic of Ceres and projected onto a 3-D shape model of the dwarf planet to create the animation. http://photojournal.jpl.nasa.gov/catalog/PIA19605

Steepened magnetosonic waves in the high beta plasma surrounding Comet Giacobini-Zinner

NASA Technical Reports Server (NTRS)

Tsurutani, B. T.; Smith, E. J.; Thorne, R. M.; Gosling, J. T.; Matsumoto, H.

1986-01-01

Studies of intense hydromagnetic waves at Giacobini-Zinner are extended to investigate the mode and direction of wave propagation. Simultaneous high-resolution measurements of electron density fluctuations demonstrate that long period waves propagate in the magnetosonic mode. Principal axis analyses of the long period waves and accompanying partial rotations show that the sum of the wave phase rotations is 360 deg, indicating that both are parts of the same wave oscillation. The time sequence of the steepened waveforms observed by ICE shows that the waves must propagate towards the Sun with Cph less than Vsw. Observations are consistent with wave generation by resonant ion ring or ion beam instability which predicts right-hand polarized waves propagating in the ion beam (solar) direction. The large amplitudes and small scale sizes of the cometary waves suggest that rapid pitch-angle scattering and energy transfer with energetic ions should occur. Since the waves are highly compressive, first-order Fermi acceleration is forecast.

Suns-VOC characteristics of high performance kesterite solar cells

NASA Astrophysics Data System (ADS)

Gunawan, Oki; Gokmen, Tayfun; Mitzi, David B.

2014-08-01

Low open circuit voltage (VOC) has been recognized as the number one problem in the current generation of Cu2ZnSn(Se,S)4 (CZTSSe) solar cells. We report high light intensity and low temperature Suns-VOC measurement in high performance CZTSSe devices. The Suns-VOC curves exhibit bending at high light intensity, which points to several prospective VOC limiting mechanisms that could impact the VOC, even at 1 sun for lower performing samples. These VOC limiting mechanisms include low bulk conductivity (because of low hole density or low mobility), bulk or interface defects, including tail states, and a non-ohmic back contact for low carrier density CZTSSe. The non-ohmic back contact problem can be detected by Suns-VOC measurements with different monochromatic illuminations. These limiting factors may also contribute to an artificially lower JSC-VOC diode ideality factor.

All-Sky Imaging of Skylight Polarization With Wildfire Smoke

NASA Astrophysics Data System (ADS)

Shaw, J. A.; Pust, N.; Forbes, E.; Dahl, L.

2014-12-01

We developed an all-sky imaging system for measuring skylight polarization in the visible and near-infrared spectral range. This instrument is used together with a multi-channel solar radiometer, an aerosol/cloud dual-polarization lidar, in-situ aerosol sensors, and a wide-angle thermal infrared cloud imager to study skylight polarization and its variation with changing aerosols, clouds, and underlying surface reflectance. All of these instruments except the lidar operate continuously outdoors. During August 2012, the continuously deployed instruments recorded the transition from relatively clean air to thick wildfire smoke. This presentation will summarize the temporal evolution of the aerosols and the resulting skylight polarization change as the smoke plume expanded and dissipated. During this event, the 500-nm zenith aerosol optical depth determined along the path to the Sun increased from 0.05 to 0.8 and the ground-level aerosol extinction coefficient at 530 nm wavelength increased from near 10 Mm-1 to 490 Mm-1. During the same time period, the maximum skylight polarization at 450 nm wavelength decreased from 0.7 to near 0.2. The skylight degree of linear polarization in an arc 90-degrees from the Sun was observed to transition from a nearly constant value across the arc to a highly spatially variable pattern because of the spatially nonuniform smoke plume.

Effect of ephemeris errors on the accuracy of the computation of the tangent point altitude of a solar scanning ray as measured by the SAGE 1 and 2 instruments

NASA Technical Reports Server (NTRS)

Buglia, James J.

1989-01-01

An analysis was made of the error in the minimum altitude of a geometric ray from an orbiting spacecraft to the Sun. The sunrise and sunset errors are highly correlated and are opposite in sign. With the ephemeris generated for the SAGE 1 instrument data reduction, these errors can be as large as 200 to 350 meters (1 sigma) after 7 days of orbit propagation. The bulk of this error results from errors in the position of the orbiting spacecraft rather than errors in computing the position of the Sun. These errors, in turn, result from the discontinuities in the ephemeris tapes resulting from the orbital determination process. Data taken from the end of the definitive ephemeris tape are used to generate the predict data for the time interval covered by the next arc of the orbit determination process. The predicted data are then updated by using the tracking data. The growth of these errors is very nearly linear, with a slight nonlinearity caused by the beta angle. An approximate analytic method is given, which predicts the magnitude of the errors and their growth in time with reasonable fidelity.

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

Johnson, John Asher; Morton, T. D.; Winn, J. N.

We report the discovery of HAT-P-30b, a transiting exoplanet orbiting the V = 10.419 dwarf star GSC 0208-00722. The planet has a period P = 2.810595 {+-} 0.000005 days, transit epoch T{sub c} = 2455456.46561 {+-} 0.00037 (BJD), and transit duration 0.0887 {+-} 0.0015 days. The host star has a mass of 1.24 {+-} 0.04 M{sub sun}, radius of 1.21 {+-} 0.05 R{sub sun}, effective temperature of 6304 {+-} 88 K, and metallicity [Fe/H] = +0.13 {+-} 0.08. The planetary companion has a mass of 0.711 {+-} 0.028 M{sub J} and radius of 1.340 {+-} 0.065 R{sub J} yielding amore » mean density of 0.37 {+-} 0.05 g cm{sup -3}. We also present radial velocity measurements that were obtained throughout a transit that exhibit the Rossiter-McLaughlin effect. By modeling this effect, we measure an angle of {lambda} = 73.{sup 0}5 {+-} 9.{sup 0}0 between the sky projections of the planet's orbit normal and the star's spin axis. HAT-P-30b represents another example of a close-in planet on a highly tilted orbit, and conforms to the previously noted pattern that tilted orbits are more common around stars with T{sub eff*} {approx}> 6250 K.« less

Characterization of dust aggregates in the vicinity of the Rosetta spacecraft

NASA Astrophysics Data System (ADS)

Güttler, C.; Hasselmann, P. H.; Li, Y.; Fulle, M.; Tubiana, C.; Kovacs, G.; Agarwal, J.; Sierks, H.; Fornasier, S.; Hofmann, M.; Gutiérrez Marqués, P.; Ott, T.; Drolshagen, E.; Bertini, I.; Osiris Team

2017-09-01

In a Rosetta/OSIRIS imaging activity in June 2015, we have observed the dynamic motion of particles close to the spacecraft. Due to the focal setting of the OSIRIS Wide Angle Camera (WAC), these particles were blurred, which can be used to measure their distances to the spacecraft. We detected 108 dust aggregates over a 130 minutes long sequence, and find that their sizes are around a millimetre and their distances cluster between 2 m and 40 m from the spacecraft. Their number densities are about a factor 10 higher than expected for the overall coma and highly fluctuating. Their velocities are small compared to the spacecraft orbital motion and directed away from the spacecraft, towards the comet. From this we conclude that they have interacted with the spacecraft and assess three possible scenarios. We prefer a scenario where centimeter-sized aggregates collide with the spacecraft and we would observe the fragments. Ablation of a dust layer on the spacecraft's z panel when rotated towards the sun is a reasonable alternative. We could also measure an acceleration for a subset of 18 aggregates, which is directed away from the sun and can be explain by a rocket effect, which requires a minimum ice fraction in the order of 0.1%

Characterization of dust aggregates in the vicinity of the Rosetta spacecraft

NASA Astrophysics Data System (ADS)

Güttler, C.; Hasselmann, P. H.; Li, Y.; Fulle, M.; Tubiana, C.; Kovacs, G.; Agarwal, J.; Sierks, H.; Fornasier, S.; Hofmann, M.; Gutiérrez Marqués, P.; Ott, T.; Drolshagen, E.; Bertini, I.; Barbieri, C.; Lamy, P. L.; Rodrigo, R.; Koschny, D.; Rickman, H.; A'Hearn, M. F.; Barucci, M. A.; Bodewits, D.; Bertaux, J.-L.; Boudreault, S.; Cremonese, G.; Da Deppo, V.; Davidsson, B.; Debei, S.; De Cecco, M.; Deller, J.; Geiger, B.; Groussin, O.; Gutiérrez, P. J.; Hviid, S. F.; Ip, W.-H.; Jorda, L.; Keller, H. U.; Knollenberg, J.; Kramm, J. R.; Kührt, E.; Küppers, M.; Lara, L. M.; Lazzarin, M.; López-Moreno, J. J.; Marzari, F.; Mottola, S.; Naletto, G.; Oklay, N.; Pajola, M.; Shi, X.; Thomas, N.; Vincent, J.-B.

2017-07-01

In a Rosetta/OSIRIS imaging activity in 2015 June, we have observed the dynamic motion of particles close to the spacecraft. Due to the focal setting of the OSIRIS wide angle camera, these particles were blurred, which can be used to measure their distances to the spacecraft. We detected 109 dust aggregates over a 130 min long sequence, and find that their sizes are around a millimetre and their distances cluster between 2 and 40 m from the spacecraft. Their number densities are about a factor 10 higher than expected for the overall coma and highly fluctuating. Their velocities are small compared to the spacecraft orbital motion and directed away from the spacecraft, towards the comet. From this we conclude that they have interacted with the spacecraft and assess three possible scenarios. In the likeliest of the three scenarios, centimetre-sized aggregates collide with the spacecraft and we would observe the fragments. Ablation of a dust layer on the spacecraft's z panel (remote instrument viewing direction) when rotated towards the Sun is a reasonable alternative. We could also measure an acceleration for a subset of 18 aggregates, which is directed away from the Sun and can be explain by a rocket effect, which requires a minimum ice fraction of the order of 0.1 per cent.

Development of the Optical Communications Telescope Laboratory: A Laser Communications Relay Demonstration Ground Station

NASA Technical Reports Server (NTRS)

Wilson, K. E.; Antsos, D.; Roberts, L. C. Jr.,; Piazzolla, S.; Clare, L. P.; Croonquist, A. P.

2012-01-01

The Laser Communications Relay Demonstration (LCRD) project will demonstrate high bandwidth space to ground bi-directional optical communications links between a geosynchronous satellite and two LCRD optical ground stations located in the southwestern United States. The project plans to operate for two years with a possible extension to five. Objectives of the demonstration include the development of operational strategies to prototype optical link and relay services for the next generation tracking and data relay satellites. Key technologies to be demonstrated include adaptive optics to correct for clear air turbulence-induced wave front aberrations on the downlink, and advanced networking concepts for assured and automated data delivery. Expanded link availability will be demonstrated by supporting operations at small sun-Earth-probe angles. Planned optical modulation formats support future concepts of near-Earth satellite user services to a maximum of 1.244 Gb/s differential phase shift keying modulation and pulse position modulations formats for deep space links at data rates up to 311 Mb/s. Atmospheric monitoring instruments that will characterize the optical channel during the link include a sun photometer to measure atmospheric transmittance, a solar scintillometer, and a cloud camera to measure the line of sight cloud cover. This paper describes the planned development of the JPL optical ground station.

The Concise Knowledge Astronomy

NASA Astrophysics Data System (ADS)

Clerke, Agnes Mary; Fowler, Alfred; Ellard Gore, John

2011-01-01

Preface; Section I. History Agnes M. Clerke: 1. From Hipparchus to Laplace; 2. A century of progress; Section II. Geometrical Astronomy and Astronomical Instruments A. Fowler: 1. The Earth and its rotation; 2. The Earth's revolution round the Sun; 3. How the positions of the heavenly bodies are defined; 4. The Earth's orbit; 5. Mean solar time; 6. The movements of the Moon; 7. Movements of planets, satellites, and comets; 8. Eclipses and occultations; 9. How to find our situation on the Earth; 10. The exact size and shape of the earth; 11. The distances and dimensions of the heavenly bodies; 12. The masses of celestial bodies; 13. Gravitational effects of Sun and moon upon the Earth; 14. Instrumental measurement of angles and time; 15. Telescopes; 16. Instruments of precision; 17. Astrophysical instruments; Section III. The Solar System Agnes M. Clerke: 1. The solar system as a whole; 2. The Sun; 3. The Sun's surroundings; 4. The interior planets; 5. The Earth and Moon; 6. The planet Mars; 7. The asteroids; 8. The planet Jupiter; 9. The Saturnian system; 10. Uranus and Neptune; 11. Famous comets; 12. Nature and origin of comets; 13. Meteorites and shooting stars; Section IV. The Sidereal Heavens J.E. Gore: 1. The stars and constellations; 2. Double, multiple, and coloured stars; 3. The distances and motions of the stars; 4. Binary stars; 5. Variable and temporary stars; 6. Clusters and nebulae; 7. The construction of the heavens; Index.

Uncertainties of atmospheric polarimetric measurements with sun-sky radiometers induced by errors of relative orientations of polarizers

NASA Astrophysics Data System (ADS)

Li, Li; Li, Zhengqiang; Li, Kaitao; Sun, Bin; Wu, Yanke; Xu, Hua; Xie, Yisong; Goloub, Philippe; Wendisch, Manfred

2018-04-01

In this study errors of the relative orientations of polarizers in the Cimel polarized sun-sky radiometers are measured and introduced into the Mueller matrix of the instrument. The linearly polarized light with different polarization directions from 0° to 180° (or 360°) is generated by using a rotating linear polarizer in front of an integrating sphere. Through measuring the referential linearly polarized light, the errors of relative orientations of polarizers are determined. The efficiencies of the polarizers are obtained simultaneously. By taking the error of relative orientation into consideration in the Mueller matrix, the accuracies of the calculated Stokes parameters, the degree of linear polarization, and the angle of polarization are remarkably improved. The method may also apply to other polarization instruments of similar types.

Low-Latitude Solar Wind During the Fall 1998 SOHO-Ulysses Quadrature

NASA Technical Reports Server (NTRS)

Poletto, G.; Suess, S. T.; Biesecker, D. A.; Esser, R.; Gloeckler, G.; Ko, Y.-K.; Zurbuchen, T. H.

2002-01-01

Solar and Heliospheric Observatory (SOH0)-Ulysses quadratures occur when the SOHO-Sun-Ulysses-included angle is 90 deg. These offer the opportunity to directly compare properties of plasma parcels, observed by SOHO [Dorningo et al.] in the low corona, with properties of the same parcels measured, in due time, in situ, by Ulysses [ Wenzel et al]. We refer the reader to Suess et al. for an extended discussion of SOHO-Ulysses quadrature geometry. Here it suffices to recall that there are two quadratures per year, as SOHO makes its one-year revolution around the Sun. This, because SOHO is at the L1 Lagrangian point, in essentially the same place as the Earth, while Ulysses is in a near-polar -5-year solar orbit with a perihelion of 1.34 AU and aphelion of 5.4 AU.

Preliminary design of the thermal protection system for solar probe

NASA Technical Reports Server (NTRS)

Dirling, R. B., Jr.; Loomis, W. C.; Heightland, C. N.

1982-01-01

A preliminary design of the thermal protection system for the NASA Solar Probe spacecraft is presented. As presently conceived, the spacecraft will be launched by the Space Shuttle on a Jovian swing-by trajectory and at perihelion approach to three solar radii of the surface of the Earth's sun. The system design satisfies maximum envelope, structural integrity, equipotential, and mass loss/contamination requirements by employing lightweight carbon-carbon emissive shields. The primary shield is a thin shell, 15.5-deg half-angle cone which absorbs direct solar flux at up to 10-deg off-nadir spacecraft pointing angles. Secondary shields of sandwich construction and low thickness-direction thermal conductivity are used to reduce the primary shield infrared radiation to the spacecraft payload.

Scintillating C Ring

NASA Image and Video Library

2007-01-16

Both luminous and translucent, the C ring sweeps out of the darkness of Saturn's shadow and obscures the planet at lower left. The ring is characterized by broad, isolated bright areas, or "plateaus," surrounded by fainter material. This view looks toward the unlit side of the rings from about 19 degrees above the ringplane. North on Saturn is up. The dark, inner B ring is seen at lower right. The image was taken in visible light with the Cassini spacecraft wide-angle camera on Dec. 15, 2006 at a distance of approximately 632,000 kilometers (393,000 miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 56 degrees. Image scale is 34 kilometers (21 miles) per pixel. http://photojournal.jpl.nasa.gov/catalog/PIA08855

Performance comparison of single axis tracking and 40° solar panels for sunny weather

NASA Astrophysics Data System (ADS)

Chua, Yaw Long; Yong, Yoon Kuang; Koh, Yit Yan

2017-09-01

The rapid increment in human population and economy growth had led to the rise of the energy demand globally. With the rapid diminishing fossil fuels based energy sources, renewable energy sources had been introduced due to its unlimited availability especially solar energy which is a sustainable and reliable energy. This research was conducted to study and compare the efficiency of the single axis tracking solar panel with a 40° inclined angle solar panel in sunny weather condition. The results indicated that the output generated by the solar panel was directly affected by the angle which the solar panel facing the sun. In terms of performance the single axis tracking solar panel emerged to be more efficient with greater energy generated.

Siblings for SETI

NASA Astrophysics Data System (ADS)

Frisch, D.; Melia, F.

1983-09-01

The SAO Catalog of about 260,000 stars was studied to arrive at a sample of 'sibling', sun-like G-stars whose possible planetary systems' intelligent beings might feel drawn to single out each other for directional listening and broadcasting. A set of mostly untabulated sibling candidate stars can be defined, given a direction and a small solid angle that are mutually interesting to members of that set, so that overlapping broadcast/receiving cones can be selected on the basis of commonality. It is suggested that the double cone about the direction of the galactic center, whose half angle is 1/137 radian, is an almost inevitable choice in which sending and receiving with current technology can reach to about 1 kpsc, yielding an estimated 1000 G-star sibling candidates.

SunSmart: evaluation of a pilot school-based sun protection intervention in Hispanic early adolescents

PubMed Central

Miller, K. A.; Langholz, B. M.; Ly, T.; Harris, S. C.; Richardson, J. L.; Peng, D. H.; Cockburn, M. G.

2015-01-01

The incidence of melanoma is rising among Hispanic populations in the United States. The purpose of this study is to evaluate the impact of a pilot sun safety educational intervention conducted from 2006 to 2012 on Hispanic early adolescents in a high ultraviolet environment. Nineteen schools with high Hispanic enrollment were recruited from urban neighborhoods in Los Angeles. The analytic sample was restricted to students identifying as Hispanic or Latino (n = 777). A mixed effects linear model was used to test mean changes from pre- to posttest on students’ sun protection knowledge, attitudes and behaviors. Significant improvements were observed across several cognitive outcomes related to sun protection, including knowledge of and attitudes toward sun protection and self-efficacy to wear sunscreen. However, changes in sun protective behaviors were not achieved. Although some improvements were observed, future studies should identify the factors that motivate sun protection in this population and develop tailored prevention strategies, as improving the sun safe behaviors of Hispanic youths may aid in reducing the risk of melanoma in adulthood in this population. PMID:25801103

A general-purpose balloon-borne pointing system for solar scientific instruments

NASA Technical Reports Server (NTRS)

Polites, M. E.

1990-01-01

A general purpose balloonborne pointing system for accommodating a wide variety of solar scientific instruments is described. It is designed for precise pointing, low cost, and quick launch. It offers the option of three-axis control, pitch-yaw-roll, or two-axis control, pitch-yaw, depending on the needs of the solar instrument. Simulation results are presented that indicate good pointing capability at Sun elevation angles ranging from 10 to 80 deg.

Power Management System Design for Solar-Powered UAS

DTIC Science & Technology

2015-12-01

PV cells would have their own MPPT modules, which would enable two major advantages. The first can be considered more important to land-based solar ...The efficiency of the PV array is represented by ηpv. R represents the solar irradiance, and θ represents the angle between the array and the sun...SYSTEM DESIGN FOR SOLAR -POWERED UAS by Robert T. Fauci III December 2015 Thesis Advisor: Alejandro Hernandez Co-Advisor: Kevin Jones

Near-terminator and earthshine photography. [special lunar photography obtained during Apollo 17 flight

NASA Technical Reports Server (NTRS)

Head, J. W.; Lloyd, D.

1973-01-01

Photographic results obtained during the Apollo 17 flight for the near terminator and earthshine conditions are discussed. Lunar surface photographs taken in the vicinity of the sunshine terminator provide important information that is not obtained on photographs taken at higher sun evaluation angles. Earthshine photography also provides data on low relief, crater morphology, and small scale structures. Examples of photographs of the lunar surface taken under both conditions are provided.

Searching the Allais effect during the total sun eclipse of 11 July 2010

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

Salva, Horacio R.

2011-03-15

I have measured the precession change of the oscillation plane with an automated Foucault pendulum and found no evidence (within the measurement error) of the Allais effect. The precession speed was registered and, due the variations involved, if the precession speed would changed 0.3 degree per hour (increasing or decreasing the angle of the normal precession speed) during the all eclipse, it would be notice in this measurement.

New light-shielding technique for shortening the baffle length of a star sensor

NASA Astrophysics Data System (ADS)

Kawano, Hiroyuki; Sato, Yukio; Mitani, Kenji; Kanai, Hiroshi; Hama, Kazumori

2002-10-01

We have developed a star sensor with a short baffle of 140 mm. Our baffle provides a Sun rejection angle of 35 degrees with stray light attenuation less than the intensity level of a visual magnitude of Mv = +5 for a wide field of view lens of 13x13 degrees. The application of a new light shielding technique taking advantage of total internal reflection phenomena enables us to reduce the baffle length to about three fourths that of the conventional two-stage baffle. We have introduced two ideas to make the baffle length shorter. The one is the application of a nearly half sphere convex lens as the first focusing lens. The bottom surface reflects the scattering rays with high incident angles of over 50 degrees by using the total internal reflection phenomena. The other is the painting of the surface of the baffle with not frosted but gloss black paint. The gloss black paint enables most of the specular reflection rays to go back to outer space without scattering. We confirm the baffle performance mentioned above by scattering ray tracing simulation and a light attenuation experiment in a darkroom on the ground.

Experimental characterization of Fresnel-Köhler concentrators

NASA Astrophysics Data System (ADS)

Zamora, Pablo; Benítez, Pablo; Mohedano, Rubén; Cvetković, Aleksandra; Vilaplana, Juan; Li, Yang; Hernández, Maikel; Chaves, Julio; Miñano, Juan C.

2012-01-01

Most cost-effective concentrated photovoltaics (CPV) systems are based on an optical train comprising two stages, the first being a Fresnel lens. Among them, the Fresnel-Köhler (FK) concentrator stands out owing to both performance and practical reasons. We describe the experimental measurements procedure for FK concentrator modules. This procedure includes three main types of measurements: electrical efficiency, acceptance angle, and irradiance uniformity at the solar cell plane. We have collected here the performance features of two different FK prototypes (ranging different f-numbers, concentration ratios, and cell sizes). The electrical efficiencies measured in both prototypes are high and fit well with the models, achieving values up to 32.7% (temperature corrected, and with no antireflective coating on SOE or POE surfaces) in the best case. The measured angular transmission curves show large acceptance angles, again perfectly matching the expected values [measured concentration acceptance product (CAP) values over 0.56]. The irradiance pattern on the cell (obtained with a digital camera) shows an almost perfectly uniform distribution, as predicted by raytrace simulations. All these excellent on-sun results confirm the FK concentrator as a potentially cost-effective solution for the CPV market.

A New Technique for Retrieval of Tropospheric and Stratospheric Ozone Profiles using Sky Radiance Measurements at Multiple View Angles: Application to a Brewer Spectrometer

NASA Technical Reports Server (NTRS)

Tzortziou, Maria; Krotkov, Nickolay A.; Cede, Alexander; Herman, Jay R.; Vasilkov, Alexander

2008-01-01

This paper describes and applies a new technique for retrieving diurnal variability in tropospheric ozone vertical distribution using ground-based measurements of ultraviolet sky radiances. The measured radiances are obtained by a polarization-insensitive modified Brewer double spectrometer located at Goddard Space Flight Center, in Greenbelt, Maryland, USA. Results demonstrate that the Brewer angular (0-72deg viewing zenith angle) and spectral (303-320 nm) measurements of sky radiance in the solar principal plane provide sufficient information to derive tropospheric ozone diurnal variability. In addition, the Brewer measurements provide stratospheric ozone vertical distributions at least twice per day near sunrise and sunset. Frequent measurements of total column ozone amounts from direct-sun observations are used as constraints in the retrieval. The vertical ozone profile resolution is shown in terms of averaging kernels to yield at least four points in the troposphere-low stratosphere, including good information in Umkehr layer 0 (0-5 km). The focus of this paper is on the derivation of stratospheric and tropospheric ozone profiles using both simulated and measured radiances. We briefly discuss the necessary modifications of the Brewer spectrometer that were used to eliminate instrumental polarization sensitivity so that accurate sky radiances can be obtained in the presence of strong Rayleigh scattering and aerosols. The results demonstrate that including a site-specific and time-dependent aerosol correction, based on Brewer direct-sun observations of aerosol optical thickness, is critical to minimize the sky radiance residuals as a function of observing angle in the optimal estimation inversion algorithm and improve the accuracy of the retrieved ozone profile.

VSOP Monitoring of the Quasar 1928+738

NASA Technical Reports Server (NTRS)

Murphy, D. W.

1999-01-01

One limitation of the VSOP (VLBI Space Observatory Program) mission is that several famous superluminal sources such as 3C273 cannot be monitored with good uv-coverage throughout the lifetime of the VSOP Mission at regular intervals that are spaced closely enough to follow the evolution in the fine-scale source-structure. The reason for this is that the HALCA spacecraft cannot#observe sources outside certain restricted ranges of sun angle, defined to be the time variable angle between the source and the sun. However sources that lie within 10 degrees of the ecliptic poles can be observed throughout the year and observations are not restricted to narrow temporal windows. Furthermore, the best ground-based uv-coverages are obtained for circumpolar sources and consequently these will be the sources for which the maximum amount of space VLBI data will be obtained with a given ground array. We have began a VSOP monitoring campaign at 5 GHz on the relatively low redshift (z=0.3) superluminal quasar 1928+738 which is both a circumpolar source and lies 10 degrees away from the ecliptic pole. 1928+738 is in the S5 polar cap sample and has been well studied both on the arsecond-scale and mas-scale. 22 GHz observations have shown that the motion of the VLBI components in 1928+738 is inconsistent with simple linear expansion along a fixed position angle (PA) for all components. Indeed, 1928+738 was one of the first sources for which helical jet motion was proposed and it has been further proposed that a massive binary black hole (MBBH) system is responsible for the sinusoidal jet ridge line observed at 22 GHz over a S year period. our VSOP observations are designed to check this proposal.

High Precision, Absolute Total Column Ozone Measurements from the Pandora Spectrometer System: Comparisons with Data from a Brewer Double Monochromator and Aura OMI

NASA Technical Reports Server (NTRS)

Tzortziou, Maria A.; Herman, Jay R.; Cede, Alexander; Abuhassan, Nader

2012-01-01

We present new, high precision, high temporal resolution measurements of total column ozone (TCO) amounts derived from ground-based direct-sun irradiance measurements using our recently deployed Pandora single-grating spectrometers. Pandora's small size and portability allow deployment at multiple sites within an urban air-shed and development of a ground-based monitoring network for studying small-scale atmospheric dynamics, spatial heterogeneities in trace gas distribution, local pollution conditions, photochemical processes and interdependencies of ozone and its major precursors. Results are shown for four mid- to high-latitude sites where different Pandora instruments were used. Comparisons with a well calibrated double-grating Brewer spectrometer over a period of more than a year in Greenbelt MD showed excellent agreement and a small bias of approximately 2 DU (or, 0.6%). This was constant with slant column ozone amount over the full range of observed solar zenith angles (15-80), indicating adequate Pandora stray light correction. A small (1-2%) seasonal difference was found, consistent with sensitivity studies showing that the Pandora spectral fitting TCO retrieval has a temperature dependence of 1% per 3K, with an underestimation in temperature (e.g., during summer) resulting in an underestimation of TCO. Pandora agreed well with Aura-OMI (Ozone Measuring Instrument) satellite data, with average residuals of <1% at the different sites when the OMI view was within 50 km from the Pandora location and OMI-measured cloud fraction was <0.2. The frequent and continuous measurements by Pandora revealed significant short-term (hourly) temporal changes in TCO, not possible to capture by sun-synchronous satellites, such as OMI, alone.

Sky radiance at a coastline and effects of land and ocean reflectivities

NASA Astrophysics Data System (ADS)

Kreuter, Axel; Blumthaler, Mario; Tiefengraber, Martin; Kift, Richard; Webb, Ann R.

2017-12-01

We present a unique case study of the spectral sky radiance distribution above a coastline. Results are shown from a measurement campaign in Italy involving three diode array spectroradiometers which are compared to 3-D model simulations from the Monte Carlo model MYSTIC. On the coast, the surrounding is split into two regions, a diffusely reflecting land surface and a water surface which features a highly anisotropic reflectance function. The reflectivities and hence the resulting radiances are a nontrivial function of solar zenith and azimuth angle and wavelength. We show that for low solar zenith angles (SZAs) around noon, the higher land albedo causes the sky radiance at 20° above the horizon to increase by 50 % in the near infrared at 850 nm for viewing directions towards the land with respect to the ocean. Comparing morning and afternoon radiances highlights the effect of the ocean's sun glint at high SZA, which contributes around 10 % to the measured radiance ratios. The model simulations generally agree with the measurements to better than 10 %. We investigate the individual effects of model input parameters representing land and ocean albedo and aerosols. Different land and ocean bi-directional reflectance functions (BRDFs) do not generally improve the model agreement. However, consideration of the uncertainties in the diurnal variation of aerosol optical depth can explain the remaining discrepancies between measurements and model. We further investigate the anisotropy effect of the ocean BRDF which is featured in the zenith radiances. Again, the uncertainty of the aerosol loading is dominant and obscures the modelled sun glint effect of 7 % at 650 nm. Finally, we show that the effect on the zenith radiance is restricted to a few kilometres from the coastline by model simulations along a perpendicular transect and by comparing the radiances at the coast to those measured at a site 15 km inland. Our findings are relevant to, for example, ground-based remote sensing of aerosol characteristics, since a common technique is based on sky radiance measurements along the solar almucantar.

Solar Power for Near Sun, High-Temperature Missions

NASA Technical Reports Server (NTRS)

Landis, Geoffrey A.

2008-01-01

Existing solar cells lose performance at the high temperatures encountered in Mercury orbit and inward toward the sun. For future missions designed to probe environments close to the sun, it is desirable to develop array technologies for high temperature and high light intensity. Approaches to solar array design for near-sun missions include modifying the terms governing temperature of the cell and the efficiency at elevated temperature, or use of techniques to reduce the incident solar energy to limit operating temperature. An additional problem is found in missions that involve a range of intensities, such as the Solar Probe + mission, which ranges from a starting distance of 1 AU from the sun to a minimum distance of 9.5 solar radii, or 0.044 AU. During the mission, the solar intensity ranges from one to about 500 times AM0. This requires a power system to operate over nearly three orders of magnitude of incident intensity.

Cloud and Sun-Glint Statistics Derived from GOES and MODIS Observations Over the Intra-Americas Sea for GEO-CAPE Mission Planning

NASA Technical Reports Server (NTRS)

Feng, Lian; Hu, Chuanmin; Barnes, Brian B.; Mannino, Antonio; Heidinger, Andrew K.; Strabala, Kathleen; Iraci, Laura T.

2017-01-01

Knowledge of cloud cover, frequency, and duration is not only important to study cloud dynamics, but also critical in determining when and where to take ocean measurements from geostationary orbits such as the Geostationary Coastal and Air Pollution Events (GEO-CAPE) mission due to the challenges in achieving complete hemispheric coverage of coastal oceans, estuaries, and inland waters at hourly frequency. Using GOES hourly measurements at 4 km nadir resolution between 2006 and 2011, the number of cloud-free hourly observations per day (N(sub cf)) for solar zenith angle Theta(sub 0) less than 80 degrees was estimated for each 0.1 degree location of the Intra-Americas Sea. The number of Sun-glint-affected hourly observations per day [Ns(sub sg)] was also calculated based on the planned GEO-CAPE observation geometry and realistic wind speed. High-latitude and equatorial oceans showed the lowest N(sub cf) (less than 2.4) in all climatological months, and highest N(sub cf) was observed in the Gulf of Mexico (GoM) and Caribbean (greater than 4.5). Different regions showed differences in seasonality of cloud-free conditions and also showed differences in the hour of a day at which the satellite observations would have the maximal cloud-free and glint-free probability (Temperature maximum). Cloud cover from Moderate Resolution Imaging Spectroradiometer (MODIS) 1 km measurements are greater than 10 degrees higher than those from the MODIS 250 m measurements, supporting ocean color missions at subkilometer resolutions to enhance both spatial coverage and temporal frequency. These findings provide valuable information for GEO-CAPE mission planning to maximize its science value through minimizing the impacts of clouds and Sun glint.

Cloud and Sun-glint statistics derived from GOES and MODIS observations over the Intra-Americas Sea for GEO-CAPE mission planning

NASA Astrophysics Data System (ADS)

Feng, Lian; Hu, Chuanmin; Barnes, Brian B.; Mannino, Antonio; Heidinger, Andrew K.; Strabala, Kathleen; Iraci, Laura T.

2017-02-01

Knowledge of cloud cover, frequency, and duration is not only important to study cloud dynamics, but also critical in determining when and where to take ocean measurements from geostationary orbits such as the Geostationary Coastal and Air Pollution Events (GEO-CAPE) mission due to the challenges in achieving complete hemispheric coverage of coastal oceans, estuaries, and inland waters at hourly frequency. Using GOES hourly measurements at 4 km nadir resolution between 2006 and 2011, the number of cloud-free hourly observations per day (Ncf) for solar zenith angle θo < 80° was estimated for each 0.1° location of the Intra-Americas Sea. The number of Sun-glint-affected hourly observations per day (Nsg) was also calculated based on the planned GEO-CAPE observation geometry and realistic wind speed. High-latitude and equatorial oceans showed the lowest Ncf (<2.4) in all climatological months, and highest Ncf was observed in the Gulf of Mexico (GoM) and Caribbean (>4.5). Different regions showed differences in seasonality of cloud-free conditions and also showed differences in the hour of a day at which the satellite observations would have the maximal cloud-free and glint-free probability (Tmax). Cloud cover from Moderate Resolution Imaging Spectroradiometer (MODIS) 1 km measurements are >10% higher than those from the MODIS 250 m measurements, supporting ocean color missions at subkilometer resolutions to enhance both spatial coverage and temporal frequency. These findings provide valuable information for GEO-CAPE mission planning to maximize its science value through minimizing the impacts of clouds and Sun glint.

A Model fot the Sources of the Slow Solar Wind

NASA Technical Reports Server (NTRS)

Antiochos, S. K.; Mikic, Z.; Titov, V. S.; Lionello, R.; Linker, J. A.

2011-01-01

Models for the origin of the slow solar wind must account for two seemingly contradictory observations: the slow wind has the composition of the closed-field corona, implying that it originates from the continuous opening and closing of flux at the boundary between open and closed field. On the other hand, the slow wind also has large angular width, up to approx.60deg, suggesting that its source extends far from the open-closed boundary. We propose a model that can explain both observations. The key idea is that the source of the slow wind at the Sun is a network of narrow (possibly singular) open-field corridors that map to a web of separatrices and quasi-separatrix layers in the heliosphere. We compute analytically the topology of an open-field corridor and show that it produces a quasi-separatrix layer in the heliosphere that extends to angles far from the heliospheric current sheet. We then use an MHD code and MDI/SOHO observations of the photospheric magnetic field to calculate numerically, with high spatial resolution, the quasi-steady solar wind, and magnetic field for a time period preceding the 2008 August 1 total solar eclipse. Our numerical results imply that, at least for this time period, a web of separatrices (which we term an S-web) forms with sufficient density and extent in the heliosphere to account for the observed properties of the slow wind. We discuss the implications of our S-web model for the structure and dynamics of the corona and heliosphere and propose further tests of the model. Key words: solar wind - Sun: corona - Sun: magnetic topology

How to Improve Adolescents' Sun Protection Behavior? Age and Gender Issues

ERIC Educational Resources Information Center

Paul, Christine; Tzelepis, Flora; Parfitt, Nicholas; Girgis, Afaf

2008-01-01

Objective: To explore adolescents' self-reported reasons for sun protection, as adolescents as a group continue to have poor sun protection practices. Methods: Seventeen age- and gender-segregated focus groups were conducted in Australian high schools. Results: Reasons for using sun protection included personal comfort, appearance, policies, fear…

21 CFR 352.3 - Definitions.

Code of Federal Regulations, 2013 CFR

2013-04-01

...) and desired response to ultraviolet (UV) radiation. (1) Minimal sun protection product. A sunscreen product that provides a sun protection factor (SPF) value of 2 to under 12. (2) Moderate sun protection product. A sunscreen product that provides an SPF value of 12 to under 30. (3) High sun protection product...

21 CFR 352.3 - Definitions.

Code of Federal Regulations, 2011 CFR

2011-04-01

...) and desired response to ultraviolet (UV) radiation. (1) Minimal sun protection product. A sunscreen product that provides a sun protection factor (SPF) value of 2 to under 12. (2) Moderate sun protection product. A sunscreen product that provides an SPF value of 12 to under 30. (3) High sun protection product...

21 CFR 352.3 - Definitions.

Code of Federal Regulations, 2012 CFR

2012-04-01

...) and desired response to ultraviolet (UV) radiation. (1) Minimal sun protection product. A sunscreen product that provides a sun protection factor (SPF) value of 2 to under 12. (2) Moderate sun protection product. A sunscreen product that provides an SPF value of 12 to under 30. (3) High sun protection product...

21 CFR 352.3 - Definitions.

Code of Federal Regulations, 2014 CFR

2014-04-01

...) and desired response to ultraviolet (UV) radiation. (1) Minimal sun protection product. A sunscreen product that provides a sun protection factor (SPF) value of 2 to under 12. (2) Moderate sun protection product. A sunscreen product that provides an SPF value of 12 to under 30. (3) High sun protection product...

Distribution of Facial Exposure to Non-melanoma Biologically Effective UV Irradiance Changes by Rotation Angles.

PubMed

Wang, Fang; Yu, Jia Ming; Yang, De Qi; Gao, Qian; Hua, Hui; Liu, Yang

2017-02-01

To show the distribution of facial exposure to non-melanoma biologically effective UV irradiance changes by rotation angles. This study selected the cheek, nose, and forehead as representative facial sites for UV irradiance measurements, which were performed using a rotating manikin and a spectroradiometer. The measured UV irradiance was weighted using action spectra to calculate the biologically effective UV irradiances that cause non-melanoma (UVBEnon-mel) skin cancer. The biologically effective UV radiant exposure (HBEnon-mel) was calculated by summing the UVBEnon-mel data collected over the exposure period. This study revealed the following: (1) the maximum cheek, nose and forehead exposure UVA and UVB irradiance times and solar elevation angles (SEA) differed from those of the ambient UV irradiance and were influenced by the rotation angles; (2) the UV irradiance exposure increased in the following order: cheek < nose < forehead; (3) the distribution of UVBEnon-mel irradiance differed from that of unweighted UV radiation (UVR) and was influenced by the rotation angles and exposure times; and (4) the maximum percentage decreases in the UVBEnon-mel radiant exposure for the cheek, nose and forehead from 0°to 180°were 48.41%, 69.48% and 71.71%, respectively. Rotation angles relative to the sun influence the face's exposure to non-melanoma biologically effective UV. Copyright © 2017 The Editorial Board of Biomedical and Environmental Sciences. Published by China CDC. All rights reserved.

Polarized Line Formation in Arbitrary Strength Magnetic Fields Angle-averaged and Angle-dependent Partial Frequency Redistribution

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

Sampoorna, M.; Nagendra, K. N.; Stenflo, J. O., E-mail: sampoorna@iiap.res.in, E-mail: knn@iiap.res.in, E-mail: stenflo@astro.phys.ethz.ch

Magnetic fields in the solar atmosphere leave their fingerprints in the polarized spectrum of the Sun via the Hanle and Zeeman effects. While the Hanle and Zeeman effects dominate, respectively, in the weak and strong field regimes, both these effects jointly operate in the intermediate field strength regime. Therefore, it is necessary to solve the polarized line transfer equation, including the combined influence of Hanle and Zeeman effects. Furthermore, it is required to take into account the effects of partial frequency redistribution (PRD) in scattering when dealing with strong chromospheric lines with broad damping wings. In this paper, we presentmore » a numerical method to solve the problem of polarized PRD line formation in magnetic fields of arbitrary strength and orientation. This numerical method is based on the concept of operator perturbation. For our studies, we consider a two-level atom model without hyperfine structure and lower-level polarization. We compare the PRD idealization of angle-averaged Hanle–Zeeman redistribution matrices with the full treatment of angle-dependent PRD, to indicate when the idealized treatment is inadequate and what kind of polarization effects are specific to angle-dependent PRD. Because the angle-dependent treatment is presently computationally prohibitive when applied to realistic model atmospheres, we present the computed emergent Stokes profiles for a range of magnetic fields, with the assumption of an isothermal one-dimensional medium.« less

The effect of random matter density perturbations on the large mixing angle solution to the solar neutrino problem

NASA Astrophysics Data System (ADS)

Guzzo, M. M.; Holanda, P. C.; Reggiani, N.

2003-08-01

The neutrino energy spectrum observed in KamLAND is compatible with the predictions based on the Large Mixing Angle realization of the MSW (Mikheyev-Smirnov-Wolfenstein) mechanism, which provides the best solution to the solar neutrino anomaly. From the agreement between solar neutrino data and KamLAND observations, we can obtain the best fit values of the mixing angle and square difference mass. When doing the fitting of the MSW predictions to the solar neutrino data, it is assumed the solar matter do not have any kind of perturbations, that is, it is assumed the the matter density monothonically decays from the center to the surface of the Sun. There are reasons to believe, nevertheless, that the solar matter density fluctuates around the equilibrium profile. In this work, we analysed the effect on the Large Mixing Angle parameters when the density matter randomically fluctuates around the equilibrium profile, solving the evolution equation in this case. We find that, in the presence of these density perturbations, the best fit values of the mixing angle and the square difference mass assume smaller values, compared with the values obtained for the standard Large Mixing Angle Solution without noise. Considering this effect of the random perturbations, the lowest island of allowed region for KamLAND spectral data in the parameter space must be considered and we call it very-low region.

SunSmart: evaluation of a pilot school-based sun protection intervention in Hispanic early adolescents.

PubMed

Miller, K A; Langholz, B M; Ly, T; Harris, S C; Richardson, J L; Peng, D H; Cockburn, M G

2015-06-01

The incidence of melanoma is rising among Hispanic populations in the United States. The purpose of this study is to evaluate the impact of a pilot sun safety educational intervention conducted from 2006 to 2012 on Hispanic early adolescents in a high ultraviolet environment. Nineteen schools with high Hispanic enrollment were recruited from urban neighborhoods in Los Angeles. The analytic sample was restricted to students identifying as Hispanic or Latino (n = 777). A mixed effects linear model was used to test mean changes from pre- to posttest on students' sun protection knowledge, attitudes and behaviors. Significant improvements were observed across several cognitive outcomes related to sun protection, including knowledge of and attitudes toward sun protection and self-efficacy to wear sunscreen. However, changes in sun protective behaviors were not achieved. Although some improvements were observed, future studies should identify the factors that motivate sun protection in this population and develop tailored prevention strategies, as improving the sun safe behaviors of Hispanic youths may aid in reducing the risk of melanoma in adulthood in this population. © The Author 2015. Published by Oxford University Press. All rights reserved. For permissions, please email: journals.permissions@oup.com.

NASA's Solar Eclipse Composite Image July 11, 2010

NASA Image and Video Library

2017-12-08

Eclipse 2010 Composite A solar eclipse photo (gray and white) from the Williams College Expedition to Easter Island in the South Pacific (July 11, 2010) was embedded with an image of the Sun’s outer corona taken by the Large Angle Spectrometric Coronagraph (LASCO) on the SOHO spacecraft and shown in red false color. LASCO uses a disk to blot out the bright sun and the inner corona so that the faint outer corona can be monitored and studied. Further, the dark silhouette of the moon was covered with an image of the Sun taken in extreme ultraviolet light at about the same time by the Atmospheric Imaging Assembly on Solar Dynamics Observatory (SDO). The composite brings out the correlation of structures in the inner and outer corona. Credits: Williams College Eclipse Expedition -- Jay M. Pasachoff, Muzhou Lu, and Craig Malamut; SOHO’s LASCO image courtesy of NASA/ESA; solar disk image from NASA’s SDO; compositing by Steele Hill, NASA Goddard Space Flight Center. NASA Goddard Space Flight Center is home to the nation's largest organization of combined scientists, engineers and technologists that build spacecraft, instruments and new technology to study the Earth, the sun, our solar system, and the universe.

Recovery from Maunder-like Grand Minima in a Babcock–Leighton Solar Dynamo Model

NASA Astrophysics Data System (ADS)

Karak, Bidya Binay; Miesch, Mark

2018-06-01

The Sun occasionally goes through Maunder-like extended grand minima when its magnetic activity drops considerably from the normal activity level for several decades. Many possible theories have been proposed to explain the origin of these minima. However, how the Sun managed to recover from such inactive phases every time is even more enigmatic. The Babcock–Leighton type dynamos, which are successful in explaining many features of the solar cycle remarkably well, are not expected to operate during grand minima due to the lack of a sufficient number of sunspots. In this Letter, we explore the question of how the Sun could recover from grand minima through the Babcock–Leighton dynamo. In our three-dimensional dynamo model, grand minima are produced spontaneously as a result of random variations in the tilt angle of emerging active regions. We find that the Babcock–Leighton process can still operate during grand minima with only a minimal number of sunspots, and that the model can emerge from such phases without the need for an additional generation mechanism for the poloidal field. The essential ingredient in our model is a downward magnetic pumping, which inhibits the diffusion of the magnetic flux across the solar surface.

Design of a device for sky light polarization measurements.

PubMed

Wang, Yujie; Hu, Xiaoping; Lian, Junxiang; Zhang, Lilian; Xian, Zhiwen; Ma, Tao

2014-08-14

Sky polarization patterns can be used both as indicators of atmospheric turbidity and as a sun compass for navigation. The objective of this study is to improve the precision of sky light polarization measurements by optimal design of the device used. The central part of the system is composed of a Charge Coupled Device (CCD) camera; a fish-eye lens and a linear polarizer. Algorithms for estimating parameters of the polarized light based on three images are derived and the optimal alignments of the polarizer are analyzed. The least-squares estimation is introduced for sky light polarization pattern measurement. The polarization patterns of sky light are obtained using the designed system and they follow almost the same patterns of the single-scattering Rayleigh model. Deviations of polarization angles between observation and the theory are analyzed. The largest deviations occur near the sun and anti-sun directions. Ninety percent of the deviations are less than 5° and 40% percent of them are less than 1°. The deviations decrease evidently as the degree of polarization increases. It also shows that the polarization pattern of the cloudy sky is almost identical as in the blue sky.

Design of a Device for Sky Light Polarization Measurements

PubMed Central

Wang, Yujie; Hu, Xiaoping; Lian, Junxiang; Zhang, Lilian; Xian, Zhiwen; Ma, Tao

2014-01-01

Sky polarization patterns can be used both as indicators of atmospheric turbidity and as a sun compass for navigation. The objective of this study is to improve the precision of sky light polarization measurements by optimal design of the device used. The central part of the system is composed of a Charge Coupled Device (CCD) camera; a fish-eye lens and a linear polarizer. Algorithms for estimating parameters of the polarized light based on three images are derived and the optimal alignments of the polarizer are analyzed. The least-squares estimation is introduced for sky light polarization pattern measurement. The polarization patterns of sky light are obtained using the designed system and they follow almost the same patterns of the single-scattering Rayleigh model. Deviations of polarization angles between observation and the theory are analyzed. The largest deviations occur near the sun and anti-sun directions. Ninety percent of the deviations are less than 5° and 40% percent of them are less than 1°. The deviations decrease evidently as the degree of polarization increases. It also shows that the polarization pattern of the cloudy sky is almost identical as in the blue sky. PMID:25196003

Stellar background observation during Total Solar Eclipse March 9th 2016

NASA Astrophysics Data System (ADS)

Mumtahana, Farahhati; Timur Jaelani, Anton; Muhamad, Johan; Sutastio, Heri

2016-11-01

We report observation and an early analysis of stellar background from total solar eclipse in Ternate, Indonesia. The eclipse phenomena which occurred on March, 9th 2016 was observed with certain portable instruments in order to obtain the stars behind the Sun in particular field of view and resolution. From our observation site in Ternate city, solar eclipse occurred in the late morning when the weather was unfortunately cloudy. However, during the darkness of totality, we obtained several point source objects between the gaps of the moving clouds and we suspected them as very faint stars due to their appearance in several frames. Those so called stars have been identified and measured with respect to their positions toward the center of the Sun. The main purpose of this research is to revisit strong lensing calculation of the Sun during total solar eclipse by measuring the deflection angle of the background stars as it had been calculated by Einstein and proved by Eddington at a total solar eclipse in 1919. To accomplish this aim, we need to conduct another observation to measure position of the same stars in the next period when those stars appear in the night sky.

The Days Dwindle Down to a Precious Few

NASA Image and Video Library

2015-04-27

This image is located just inside the southern rim of Chong Chol crater and was obtained on April 25, 2015, the day following NASA MESSENGER final orbital correction maneuver. The spacecraft fuel tanks are now completely empty, and there is no means to prevent the Sun's gravity from pulling MESSENGER's orbit closer and closer to the surface of Mercury. Impact is expected to occur on April 30, 2015. The image is located just inside the southern rim of Chong Chol crater, named for a Korean poet of the 1500s. It is challenging to obtain good images when the spacecraft is very low above the planet, because of the high speed at which the camera's field of view is moving across the surface. Very short exposure times are used to limit smear, and this image was binned from its original size of 1024 x 1024 pixels to 512 x 512 to improve the image quality. The title of today's image is a line from "September Song" (composed by Kurt Weill, with lyrics by Maxwell Anderson. The song was subsequently covered by artists including Ian McCulloch of Echo & the Bunnymen, Lou Reed, and Bryan Ferry). Date acquired: April 25, 2015 Image Mission Elapsed Time (MET): 72264694 Image ID: 8392292 Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS) Center Latitude: 45.43° N Center Longitude: 298.62° E Resolution: 2.1 meters/pixel Scale: The scene is about 2.1 km (1.3 miles) across. This image has not been map projected. Incidence Angle: 69.9° Emission Angle: 20.1° Phase Angle: 90.0° http://photojournal.jpl.nasa.gov/catalog/PIA19436

Looking Up to the Giant

NASA Image and Video Library

2015-08-03

Thanks to the illumination angle, Mimas (right) and Dione (left) appear to be staring up at a giant Saturn looming in the background. Although certainly large enough to be noticeable, moons like Mimas (246 miles or 396 kilometers across) and Dione (698 miles or 1123 kilometers across) are tiny compared to Saturn (75,400 miles or 120,700 kilometers across). Even the enormous moon Titan (3,200 miles or 5,150 kilometers across) is dwarfed by the giant planet. This view looks toward the unilluminated side of the rings from about one degree of the ring plane. The image was taken with the Cassini spacecraft wide-angle camera on May 27, 2015 using a spectral filter which preferentially admits wavelengths of near-infrared light centered at 728 nanometers. The view was obtained at a distance of approximately 634,000 miles (one million kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 85 degrees. Image scale is 38 miles (61 kilometers) per pixel. http://photojournal.jpl.nasa.gov/catalog/PIA18331

Improving Photovoltaic Energy Production with Fiber-Optic Distributed Temperature Sensing

NASA Astrophysics Data System (ADS)

Hausner, M. B.; Berli, M.

2014-12-01

The efficiency of solar photovoltaic (PV) generators declines sharply with increased temperatures. Peak solar exposure often occurs at the same time as peak temperatures, but solar PV installations are typically designed based on solar angle. In temperate areas, the peak temperatures may not be high enough to induce significant efficiency losses. In some of the areas with the greatest potential for solar development, however, summer air temperatures regularly reach 45 °C and PV panel temperatures exceed the air temperatures. Here we present a preliminary model of a PV array intended to optimize solar production in a hot and arid environment. The model begins with the diurnal and seasonal cycles in the angle and elevation of the sun, but also includes a meteorology-driven energy balance to project the temperatures of the PV panels and supporting structure. The model will be calibrated and parameterized using a solar array at the Desert Research Institute's (DRI) Renewable Energy Deployment and Display (REDD) facility in Reno, Nevada, and validated with a similar array at DRI's Las Vegas campus. Optical fibers will be installed on the PV panels and structural supports and interrogated by a distributed temperature sensor (DTS) to record the spatial and temporal variations in temperature. Combining the simulated panel temperatures, the efficiency-temperature relationship for the panels, and the known solar cycles at a site will allow us to optimize the design of future PV collectors (i.e., the aspect and angle of panels) for given production goals.

VUV Spectroscopy of the Sun as a Star

NASA Astrophysics Data System (ADS)

Kankelborg, Charles; Philip, Judge; Winebarger, Amy R.; Kobayashi, Ken; Smart, Roy

2017-08-01

We describe a new sounding rocket mission to obtain the first high resolution, high quality VUV (100-200 nm) spectrum of the Sun-as-a-star. Our immediate science goal is to understand better the processes of chromospheric and coronal heating. HST data exist for a dozen or so Sun-like stars of a quality already beyond our ability to construct a comparable sun-as-a-star UV spectrum. The solar spectrum we obtain will enable us to understand the nature of magnetic energy dissipation as a Sun-like star evolves, and the dependence of magnetic activity on stellar mass and metallicity. This poster presents the instrument design, scientific prospects, and broader impacts of the proposed mission.

How could the Viking Sun compass be used with sunstones before and after sunset? Twilight board as a new interpretation of the Uunartoq artefact fragment

PubMed Central

Bernáth, Balázs; Farkas, Alexandra; Száz, Dénes; Blahó, Miklós; Egri, Ádám; Barta, András; Åkesson, Susanne; Horváth, Gábor

2014-01-01

Vikings routinely crossed the North Atlantic without a magnetic compass and left their mark on lands as far away as Greenland, Newfoundland and Baffin Island. Based on an eleventh-century dial fragment artefact, found at Uunartoq in Greenland, it is widely accepted that they sailed along chosen latitudes using primitive Sun compasses. Such instruments were tested on sea and proved to be efficient hand-held navigation tools, but the dimensions and incisions of the Uunartoq find are far from optimal in this role. On the basis of the sagas mentioning sunstones, incompatible hypotheses were formed for Viking solar navigation procedures and primitive skylight polarimetry with dichroic or birefringent crystals. We describe here a previously unconceived method of navigation based on the Uunartoq artefact functioning as a ‘twilight board’, which is a combination of a horizon board and a Sun compass optimized for use when the Sun is close to the horizon. We deduced an appropriate solar navigation procedure using a twilight board, a shadow-stick and birefringent crystals, which bring together earlier suggested methods in harmony and provide a true skylight compass function. This could have allowed Vikings to navigate around the clock, to use the artefact dial as a Sun compass during long parts of the day and to use skylight polarization patterns in the twilight period. In field tests, we found that true north could be appointed with such a medieval skylight compass with an error of about ±4° when the artificially occluded Sun had elevation angles between +10° and −8° relative to the horizon. Our interpretation allows us to assign exact dates to the gnomonic lines on the artefact and outlines the schedule of the merchant ships that sustained the Viking colony in Greenland a millennium ago. PMID:24910520

How could the Viking Sun compass be used with sunstones before and after sunset? Twilight board as a new interpretation of the Uunartoq artefact fragment.

PubMed

Bernáth, Balázs; Farkas, Alexandra; Száz, Dénes; Blahó, Miklós; Egri, Adám; Barta, András; Akesson, Susanne; Horváth, Gábor

2014-06-08

Vikings routinely crossed the North Atlantic without a magnetic compass and left their mark on lands as far away as Greenland, Newfoundland and Baffin Island. Based on an eleventh-century dial fragment artefact, found at Uunartoq in Greenland, it is widely accepted that they sailed along chosen latitudes using primitive Sun compasses. Such instruments were tested on sea and proved to be efficient hand-held navigation tools, but the dimensions and incisions of the Uunartoq find are far from optimal in this role. On the basis of the sagas mentioning sunstones, incompatible hypotheses were formed for Viking solar navigation procedures and primitive skylight polarimetry with dichroic or birefringent crystals. We describe here a previously unconceived method of navigation based on the Uunartoq artefact functioning as a 'twilight board', which is a combination of a horizon board and a Sun compass optimized for use when the Sun is close to the horizon. We deduced an appropriate solar navigation procedure using a twilight board, a shadow-stick and birefringent crystals, which bring together earlier suggested methods in harmony and provide a true skylight compass function. This could have allowed Vikings to navigate around the clock, to use the artefact dial as a Sun compass during long parts of the day and to use skylight polarization patterns in the twilight period. In field tests, we found that true north could be appointed with such a medieval skylight compass with an error of about ±4° when the artificially occluded Sun had elevation angles between +10° and -8° relative to the horizon. Our interpretation allows us to assign exact dates to the gnomonic lines on the artefact and outlines the schedule of the merchant ships that sustained the Viking colony in Greenland a millennium ago.

Ultraviolet damage to the eye revisited: eye-sun protection factor (E-SPF®), a new ultraviolet protection label for eyewear.

PubMed

Behar-Cohen, Francine; Baillet, Gilles; de Ayguavives, Tito; Garcia, Paula Ortega; Krutmann, Jean; Peña-García, Pablo; Reme, Charlotte; Wolffsohn, James S

2014-01-01

Ultraviolet (UV) radiation potentially damages the skin, the immune system, and structures of the eye. A useful UV sun protection for the skin has been established. Since a remarkable body of evidence shows an association between UV radiation and damage to structures of the eye, eye protection is important, but a reliable and practical tool to assess and compare the UV-protective properties of lenses has been lacking. Among the general lay public, misconceptions on eye-sun protection have been identified. For example, sun protection is mainly ascribed to sunglasses, but less so to clear lenses. Skin malignancies in the periorbital region are frequent, but usual topical skin protection does not include the lids. Recent research utilized exact dosimetry and demonstrated relevant differences in UV burden to the eye and skin at a given ambient irradiation. Chronic UV effects on the cornea and lens are cumulative, so effective UV protection of the eyes is important for all age groups and should be used systematically. Protection of children's eyes is especially important, because UV transmittance is higher at a very young age, allowing higher levels of UV radiation to reach the crystalline lens and even the retina. Sunglasses as well as clear lenses (plano and prescription) effectively reduce transmittance of UV radiation. However, an important share of the UV burden to the eye is explained by back reflection of radiation from lenses to the eye. UV radiation incident from an angle of 135°-150° behind a lens wearer is reflected from the back side of lenses. The usual antireflective coatings considerably increase reflection of UV radiation. To provide reliable labeling of the protective potential of lenses, an eye-sun protection factor (E-SPF®) has been developed. It integrates UV transmission as well as UV reflectance of lenses. The E-SPF® compares well with established skin-sun protection factors and provides clear messages to eye health care providers and to lay consumers.

The STEREO Mission: A New Approach to Space Weather Research

NASA Technical Reports Server (NTRS)

Kaiser, michael L.

2006-01-01

With the launch of the twin STEREO spacecraft in July 2006, a new capability will exist for both real-time space weather predictions and for advances in space weather research. Whereas previous spacecraft monitors of the sun such as ACE and SOH0 have been essentially on the sun-Earth line, the STEREO spacecraft will be in 1 AU orbits around the sun on either side of Earth and will be viewing the solar activity from distinctly different vantage points. As seen from the sun, the two spacecraft will separate at a rate of 45 degrees per year, with Earth bisecting the angle. The instrument complement on the two spacecraft will consist of a package of optical instruments capable of imaging the sun in the visible and ultraviolet from essentially the surface to 1 AU and beyond, a radio burst receiver capable of tracking solar eruptive events from an altitude of 2-3 Rs to 1 AU, and a comprehensive set of fields and particles instruments capable of measuring in situ solar events such as interplanetary magnetic clouds. In addition to normal daily recorded data transmissions, each spacecraft is equipped with a real-time beacon that will provide 1 to 5 minute snapshots or averages of the data from the various instruments. This beacon data will be received by NOAA and NASA tracking stations and then relayed to the STEREO Science Center located at Goddard Space Flight Center in Maryland where the data will be processed and made available within a goal of 5 minutes of receipt on the ground. With STEREO's instrumentation and unique view geometry, we believe considerable improvement can be made in space weather prediction capability as well as improved understanding of the three dimensional structure of solar transient events.

Association of 25-hydroxyvitamin D3)levels in adult New Zealanders with ethnicity, skin color and self-reported skin sensitivity to sun exposure.

PubMed

Nessvi, Sofia; Johansson, Lisa; Jopson, Jan; Stewart, Alistair; Reeder, Anthony; McKenzie, Richard; Scragg, Robert K

2011-01-01

The study aim was to determine the contribution of ethnicity, objectively measured skin color and skin reaction-to-sun exposure to variations in 25-hydroxyvitamin D(3) [25(OH)D(3) ]. A multiethnic sample (European, Maori, Pacific and Asian) of 503 adult volunteers aged 18-85 years, recruited from Auckland and Dunedin in New Zealand, answered a questionnaire on sun exposure and self-defined ethnicity. Skin color was measured using a spectrophotometer and the Individual Typology Angle (ITA) calculated. A blood sample was collected 4 weeks later to measure 25(OH)D(3). 25(OH)D(3) was associated with ethnicity, but not self-reported skin reaction-to-sun exposure. Amongst the ethnic groups, Asians had the lowest mean 25(OH)D level (37.0 nmol L(-1)) and Europeans with lighter colored skin had the highest (57.9 nmol L(-1)). An association also was seen between 25(OH)D(3) and skin color, with an increase of 2-3 nmol L(-1) per 10° increase in ITA value, indicating higher 25(OH)D(3) with lighter skin color; but much of this association disappeared after adjusting for ethnicity. In contrast, ethnicity remained associated with 25(OH)D(3) after adjusting for ITA skin color and skin reaction-to-sun exposure. These results indicate that self-defined ethnicity was a major determinant of variations in serum 25(OH)D(3), while objective measures of skin color explained relatively little additional variation. © 2011 The Authors. Photochemistry and Photobiology © 2011 The American Society of Photobiology.

A Balloon-Borne Telescope System for Planetary Atmosphere and Plasma Studies

NASA Astrophysics Data System (ADS)

Taguchi, M.; Yoshida, K.; Sakamoto, Y.; Kanazawa, T.; Shoji, Y.; Sawakami, T.; Takahashi, Y.; Hoshino, N.; Sato, T.; Sakanoi, T.

2007-12-01

A telescope floating in the polar stratosphere can continuously monitor planets for more than 24 hours. Thin, clear and stable air of the stratosphere makes it possible to observe planets in a condition free from cloud with fine seeing and high atmospheric transmittance. Moreover, a balloon-borne telescope system is less expensive compared with a huge terrestrial telescope or a direct planetary probe mission. Targets of a balloon-borne telescope system will extend over various atmospheric and plasma phenomena on almost all the planets, i.e., a sodium tail of Mercury, lightning, airglow and aurora in the atmospheres of Venus, Jupiter and Saturn, escaping atmospheres of the Earth-type planets, satellite-induced luminous events in the Jovian atmosphere, etc. The first target is global dynamics of the Venusian atmosphere by detecting cloud motion in UV and NIR imagery. A decoupling mechanism and a pair of control moment gyros (CMGs) are mounted at the top of the gondola. The decoupling mechanism isolates the gondola from a balloon and also transfers an excess angular momentum of the CMGs to the balloon. The attitude of the gondola is stabilized at a constant sun azimuthal angle so that a solar cell panel faces to the sun. A 300 mm F30 Schmidt-Cassegrain telescope is installed at the bottom of the gondola. DC/DC converters, a PC, a high voltage power supply for a piezo-electrically moving mirror and digital video recorders are contained in a sealed cell. The azimuthal angle is detected by a sun-sensor. A PC processes sensor output to control DC motors used in the decoupling mechanism and CMGs with an accuracy in azimuthal attitude of about 0.5 deg. The two-axis gimbal mount of the telescope is controlled by the same PC, guiding an object within a field-of-view of a guide telescope. Residual tracking error is detected by a position sensitive photomultiplier tube and corrected by the two-axis moving mirror installed in the optical system. The optical path is divided into three paths with different colors: the first one with wavelengths less than 450 nm, the second one with 550-630 nm, and the last one more than 750 nm. The first and last paths are utilized for imagery of UV and NIR with bandpass filters and analog and digital CCD video cameras, respectively. The second path is for tracking error detection. The first experiment was scheduled in June, 2007 at Sanriku Balloon Center (SBC), Japan, but it was postponed until late August because of delay in final testing of the system. As of submission of this abstract the gondola has been ready for launch but has not yet been launched. The result of experiment will be presented.

Analyses of solar viewing time, beta angle, and doppler shift for solar observations from the space shuttle

NASA Technical Reports Server (NTRS)

Brandon, J. P.

1972-01-01

Studies of solar physics phenomena are aided by the ability to observe the sun from earth orbit without periodic occultation. Charts are presented for the selection of suitable orbits about the earth at which a spacecraft is continuously illuminated through a period of a few days. Selection of the orbits considers the reduction of Doppler shift and wavefront attenuation due to relative orbital velocity and residual earth atmosphere.

The intercrater plains of Mercury and the Moon: Their nature, origin and role in terrestrial planet evolution. Measurement and errors of crater statistics. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Leake, M. A.

1982-01-01

Planetary imagery techniques, errors in measurement or degradation assignment, and statistical formulas are presented with respect to cratering data. Base map photograph preparation, measurement of crater diameters and sampled area, and instruments used are discussed. Possible uncertainties, such as Sun angle, scale factors, degradation classification, and biases in crater recognition are discussed. The mathematical formulas used in crater statistics are presented.

Interpretation of Hydrographic Features Using Landsat Images,

DTIC Science & Technology

1981-06-01

photograph, Western Atlantic Ocean Figure B-2. Apollo 7, Oblique 146 photograph, Gulf of California (October 13, 1968) Figure B-3. Solar elevation 147 angle...of Land,,it imagery uises the the Hotine Oblique Mercator (HOM) map low-gain Linear setting where signals projection. on all four Iiainnels 1lave...Inclination to ecliptic =23.44 ° eliminate sunglint and enhance the A = Sun’s apparent position (00 at water color is to subtract an IR vernal equinox

Solar powered aircraft

NASA Technical Reports Server (NTRS)

Phillips, W. H. (Inventor)

1983-01-01

A cruciform wing structure for a solar powered aircraft is disclosed. Solar cells are mounted on horizontal wing surfaces. Wing surfaces with spanwise axis perpendicular to surfaces maintain these surfaces normal to the Sun's rays by allowing aircraft to be flown in a controlled pattern at a large bank angle. The solar airplane may be of conventional design with respect to fuselage, propeller and tail, or may be constructed around a core and driven by propeller mechanisms attached near the tips of the airfoils.

CLARREO Pathfinder Mission to ISS: Demonstrating Greatly Increased Accuracy for Reflected Solar Space Based Observations: Calibration and Intercalibration

NASA Astrophysics Data System (ADS)

Wielicki, B. A.

2016-12-01

The CLARREO (Climate Absolute Radiance and Refractivity) Pathfinder mission is a new mission started by NASA in 2016. CLARREO Pathfinder will fly a new generation of high accuracy reflected solar spectrometer in orbit on the Inernational Space Station (ISS) to demonstrate the ability to increase accuracy of reflected solar observations from space by a factor of 3 to 20. The spectrometer will use the sun and moon as calibration sources with a baseline objective of 0.3% (1 sigma) reflectance calibration uncertainty for the contiguous spectrum from 350nm to 2300nm, covering over 95% of the Earth's reflected solar spectrum. Spectral sampling is 3nm with resolution of 6nm. The spectrometer is mounted on a 2-axis gimbal enabling a new ability to use the same optical path to view the sun, moon, and Earth. Planned launch is 2020 with at least 1 year on orbit to demonstrate the new capability. The mission will also demonstrate the ability to use the new spectrometer as a reference transfer spectrometer in orbit to achieve intercalibration of reflected solar instruments to within 0.3% (1 sigma) using space, time, spectral, and angle matched observations across the full scan width of remote sensing instruments. Intercalibration to 0.3% will be demonstrated across the full scan width of the NASA CERES broadband radiometer and the NOAA VIIRS imager reflected solar spectral channels. This mission will demonstrate reflected solar intercalibration across the full swath width as opposed to current nadir only intercalibration used by GSICS (Global Space Based InterCalibration System). Intercalibration will include a new capability to determine scan angle dependence of polarization sensitivity of instruments like VIIRS. The high accuracy goals of this mission are driven primarily by the accuracy required to more rapidly and accurately observe climate change signals such as cloud feedback (see Wielicki et al. 2013 Bulletin of the American Meteorological Society). The new high accuracy and intercalibration capability will also be very useful for serving as a reference calibrator for constellations of operational instruments in Geostationary or Low Earth Orbit (e.g. land resource imagers, ocean color, cloud imagers). The higher accuracy will enable operational sensors to more effectively serve as climate change sensors.

Comparison of Skylab and LANDSAT images for geologic mapping in Northern Arizona. [Shivwits Plateau, Verde Valley, Coconino Plateau, and Red Lake in Arizona

NASA Technical Reports Server (NTRS)

Goetz, A. F. H. (Principal Investigator); Abrams, M. J.; Gillespie, A. R.; Siegal, B. S.; Elston, D. P.; Lucchitta, I.; Wu, S. S. C.; Sanchez, A.; Dipaola, W. D.; Schafer, F. J.

1976-01-01

The author has identified the following significant results. It was found that based on resolution, the Skylab S190A products were superior to LANDSAT images. Based on measurements of shoreline features in Lake Mead S190A images had 1.5 - 3 times greater resolution than LANDSAT. In general, the higher resolution of the Skylab data yielded better discrimination among rock units, but in the case of structural features, lower sun angle LANDSAT images (50 deg) were superior to higher sun angle Skylab images (77 deg). The most valuable advantage of the Skylab over the LANDSAT image products is the capability of producing stereo images. Field spectral reflectance measurements on the Coconino Plateau were made in an effort to determine the best spectral band for discrimination of the six geologic units in question, and these bands were 1.3, 1.2, 1.0, and 0.5 microns. The EREP multispectral scanner yielded data with a low signal to noise ratio which limited its usefulness for image enhancement work. Sites that were studied in Arizona were Shivwits Plateau, Verde Valley, Coconino Plateau, and Red Lake. Thematic maps produced by the three classification algorithms analyzed were not as accurate as the maps produced by photointerpretation of composites of enhanced images.

Evaluation of CLM4 Solar Radiation Partitioning Scheme Using Remote Sensing and Site Level FPAR Datasets

DOE PAGES

Wang, Kai; Mao, Jiafu; Dickinson, Robert; ...

2013-06-05

This paper examines a land surface solar radiation partitioning scheme, i.e., that of the Community Land Model version 4 (CLM4) with coupled carbon and nitrogen cycles. Taking advantage of a unique 30-year fraction of absorbed photosynthetically active radiation (FPAR) dataset derived from the Global Inventory Modeling and Mapping Studies (GIMMS) normalized difference vegetation index (NDVI) data set, multiple other remote sensing datasets, and site level observations, we evaluated the CLM4 FPAR ’s seasonal cycle, diurnal cycle, long-term trends and spatial patterns. These findings show that the model generally agrees with observations in the seasonal cycle, long-term trends, and spatial patterns,more » but does not reproduce the diurnal cycle. Discrepancies also exist in seasonality magnitudes, peak value months, and spatial heterogeneity. Here, we identify the discrepancy in the diurnal cycle as, due to, the absence of dependence on sun angle in the model. Implementation of sun angle dependence in a one-dimensional (1-D) model is proposed. The need for better relating of vegetation to climate in the model, indicated by long-term trends, is also noted. Evaluation of the CLM4 land surface solar radiation partitioning scheme using remote sensing and site level FPAR datasets provides targets for future development in its representation of this naturally complicated process.« less

Location and size of flux ropes in Titan's ionosphere

NASA Astrophysics Data System (ADS)

Martin, C.; Arridge, C. S.; Badman, S. V.; Dieval, C.

2017-12-01

Cassini magnetometer data was surveyed during Titan flybys to find 73 instances of flux rope signatures. A force free flux rope model was utilised to obtain the radii, maximum magnetic field and flux content of flux ropes that adhere to the force-free assumptions. We find that flux ropes at Titan are similar in size in km and flux content to the giant flux ropes identified at Venus, with a median radii of 280 km and an inter-quartile range of 270 km, a median maximum magnetic field of 8 nT with an inter-quartile range of 7 nT and a median flux content of 76 Wb with a large inter-quartile range of 250 Wb. We additionally investigate the occurrence of flux ropes with respect to the Sun-lit facing hemisphere (zenith angle) and the ram-side of Titan within Saturn's corotating magnetosphere (angle of attack of the incoming plasma flow). We find that flux ropes are more commonly detected in Sun-lit areas of Titan's ionosphere, as well as the ram-side of Titan. We see a statistically-significant absence of flux ropes in all SLT sectors in the night side of Titan and the anti-ram side of Titan. We also comment on the physical mechanisms associated with the production of these flux ropes, with particular attention on the variability of Titan's environment in Saturn's magnetosphere.

Crew Earth Observations (CEO) taken during Expedition 8

NASA Image and Video Library

2003-12-03

ISS008-E-09603 (20 December 2003) --- The village of Argudan near the north slopes of the Greater Caucasus Mountains in Russia is featured in this photo taken by an Expedition 8 crewmember onboard the International Space Station (ISS). The striking land use pattern, seen through a high magnification lens and highlighted by winter snow and low sun angles, produces this unique view. This rural, agricultural community sits astride the main highway about 15 kilometers east-southeast of the city of Nalchik. Shadows from a line of trees planted as a windbreak near the highway give the road a ragged appearance. A small stream flowing northeastward exits heavily forested foothills through the village and fields of intensely cultivated croplands on the plains. Snow falls through the vegetation, making the woodlands appear extremely dark compared to the snow-covered fields.

Earth observation

NASA Image and Video Library

2014-09-06

ISS040-E-124198 (6 Sept. 2014) --- Puget Sound is partly reflecting the sun in this detailed image taken by an Expedition 40 crew member on the International Space Station. Patterns of boat wakes are prominent in the sun’s partial reflection zone. The difference between the boat wakes in this view relates to the speed of the boat and the particular patterns (of several) that happen to be captured in the specific light reflection angles at the time the image was taken. The land areas show parts of Seattle. The darkest areas with rectangular grids are suburbs richly covered with trees. The broadly gray zones of the central city (bottom center) are brighter where structures are lower, as in the harbor zone (Harbor Island), and darker where the shadows of high-rise buildings downtown cast black shadows. Interstate Highway 5 bisects downtown.

SUN: A fully automated interferometric test bench aimed at measuring photolithographic grade lenses with a sub nanometer accuracy

NASA Astrophysics Data System (ADS)

Bourgois, R.; Hamy, A. L.; Pourcelot, P.

2017-10-01

SUN is a test bench developed by Safran Reosc to measure spherical or aspherical surface errors of litho-grade lenses with sub-nanometer accuracy. SUN provides full aperture high resolution interferometric measurements. Measurements are performed at the center of curvature using high precision transmission sphere (TS), and Computer Generated Holograms (CGH) for aspheres, in order to light the surface at normal incidence. SUN can measure lenses with diameter up to 350mm and a radius of curvature varying from 60 to 3000 mm.

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NASA Astrophysics Data System (ADS)

2012-01-01

WE RECOMMEND Air swimmers Helium balloon swims like a fish Their Arrows will Darken the Sun: The Evolution and Science of Ballistics Ballistics book hits the spot Physics Experiments for your Bag Handy experiments for your lessons Quantum Physics for Poets Book shows the economic importance of physics SEP colour wheel kit Wheels investigate colour theory SEP colour mixing kit Cheap colour mixing kit uses red, green and blue LEDs iHandy Level iPhone app superbly measures angles Photonics Explorer kit Free optics kit given to schools WORTH A LOOK DrDAQ DrDAQ software gets an upgrade WEB WATCH Websites show range of physics

A search for the coronal origins of fast solar wind streams during the whole sun month period

NASA Technical Reports Server (NTRS)

Lazarus, A. J.; Steinberg, J. T.; Biesecker, D. A.; Forsyth, R. J.; Galvin, A. B.; Ipavich, F. M.; Gibson, S. E.; Lecinski, A.; Hassler, D. M.; Hoeksema, J. T.;

"Driverless" Shocks in the Interplanetary Medium

NASA Technical Reports Server (NTRS)

Gopalswamy, N.; Kaiser, M. L.; Lara, A.

1999-01-01

Many interplanetary shocks have been detected without an obvious driver behind them. These shocks have been thought to be either blast waves from solar flares or shocks due to sudden increase in solar wind speed caused by interactions between large scale open and closed field lines of the Sun. We investigated this problem using a set of interplanetary shock detected {\\it in situ} by the Wind space craft and tracing their solar origins using low frequency radio data obtained by the Wind/WAVES experiment. For each of these "driverless shocks" we could find a unique coronal mass ejections (CME) event observed by the SOHO (Solar and Heliospheric Observatory) coronagraphs. We also found that these CMEs were ejected at large angles from the Sun-Earth line. It appears that the "driverless shocks" are actually driver shocks, but the drivers were not intercepted by the spacecraft. We conclude that the interplanetary shocks are much more extended than the driving CMEs.

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

NASA Technical Reports Server (NTRS)

Brunk, W. E.

1972-01-01

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

A Possible Astronomically Aligned Monolith at Gardom's Edge

NASA Astrophysics Data System (ADS)

Brown, Daniel; Alder, Andy; Bemand, Elizabeth

2015-05-01

A unique triangular shaped monolith located within the Peak District National Park at Gardom's Edge could be intentionally astronomically aligned. It is set within a landscape rich in late Neolithic and Bronze Age remains. We show that the stone is most likely in its original orientation owing to its clear signs of erosion and associated to the time period of the late Neolithic. It is tilted towards south and its north side slopes at an angle equal to the maximum altitude of the Sun at mid-summer. This alignment emphasizes the changing declinations of the Sun during the seasons as well as giving an indication of mid-summers day. This functionality is achieved by an impressive display of light and shadow on the north facing side of the monolith. Together with other monuments in the close vicinity the monolith would have represented an ideal marker or social arena for seasonal gatherings for the otherwise dispersed small communities.

A Tracking Sun Photometer Without Moving Parts

NASA Technical Reports Server (NTRS)

Strawa, Anthony W.

2012-01-01

This innovation is small, lightweight, and consumes very little electricity as it measures the solar energy attenuated by gases and aerosol particles in the atmosphere. A Sun photometer is commonly used on the Earth's surface, as well as on aircraft, to determine the solar energy attenuated by aerosol particles in the atmosphere and their distribution of sizes. This information is used to determine the spatial and temporal distribution of gases and aerosols in the atmosphere, as well as their distribution sizes. The design for this Sun photometer uses a combination of unique optics and a charge coupled device (CCD) array to eliminate moving parts and make the instrument more reliable. It could be selfcalibrating throughout the year. Data products would be down-welling flux, the direct-diffuse flux ratio, column abundance of gas phase constituents, aerosol optical depth at multiple-wavelengths, phase functions, cloud statistics, and an estimate of the representative size of atmospheric particles. These measurements can be used to obtain an estimate of aerosol size distribution, refractive index, and particle shape. Incident light is received at a light-reflecting (inner) surface, which is a truncated paraboloid. Light arriving from a hemispheric field of view (solid angle 2 steradians) enters the reflecting optic at an entrance aperture at, or adjacent to, the focus of the paraboloid, and is captured by the optic. Most of this light is reflected from an inner surface. The light proceeds substantially parallel to the paraboloid axis, and is detected by an array detector located near an exit aperture. Each of the entrance and exit apertures is formed by the intersection of the paraboloid with a plane substantially perpendicular to the paraboloid axis. Incident (non-reflected) light from a source of limited extent (the Sun) illuminates a limited area on the detector array. Both direct and diffuse illumination may be reflected, or not reflected, before being received on the detector array. As the Sun traverses a path in the sky over some time interval, the track of the Sun can be traced on the detector array. A suitably modified Sun photometer might be used to study the dynamics of an environment on another planet or satellite with an atmosphere.

Dreamy Swirls on Saturn

NASA Image and Video Library

2017-09-12

NASA's Cassini spacecraft gazed toward the northern hemisphere of Saturn to spy subtle, multi-hued bands in the clouds there. This view looks toward the terminator -- the dividing line between night and day -- at lower left. The sun shines at low angles along this boundary, in places highlighting vertical structure in the clouds. Some vertical relief is apparent in this view, with higher clouds casting shadows over those at lower altitude. Images taken with the Cassini spacecraft narrow-angle camera using red, green and blue spectral filters were combined to create this natural-color view. The images were acquired on Aug. 31, 2017, at a distance of approximately 700,000 miles (1.1 million kilometers) from Saturn. Image scale is about 4 miles (6 kilometers) per pixel. https://photojournal.jpl.nasa.gov/catalog/PIA21888

Advanced Receiver tracking of Voyager 2 near solar conjunction

NASA Technical Reports Server (NTRS)

Brown, D. H.; Hurd, W. J.; Vilnrotter, V. A.; Wiggins, J. D.

1988-01-01

The Advanced Receiver (ARX) was used to track the Voyager 2 spacecraft at low Sun-Earth-Probe (SEP) angles near solar conjunction in December of 1987. The received carrier signal exhibited strong fluctuations in both phase and amplitude. The ARX used spectral estimation and mathematical modeling of the phase and receiver noise processes to set an optimum carrier tracking bandwidth. This minimized the mean square phase error in tracking carrier phase and thus minimized the loss in the telemetry signal-to-noise ratio due to the carrier loop. Recovered symbol SNRs and errors in decoded engineering data for the ARX are compared with those for the current Block 3 telemetry stream. Optimum bandwidths are plotted against SEP angle. Measurements of the power spectral density of the solar phase and amplitude fluctuations are also given.

A Glimpse of Atlas

NASA Technical Reports Server (NTRS)

2005-01-01

Saturn's little moon Atlas orbits Saturn between the outer edge of the A ring and the fascinating, twisted F ring. This image just barely resolves the disk of Atlas, and also shows some of the knotted structure for which the F ring is known. Atlas is 32 kilometers (20 miles) across.

The bright outer edge of the A ring is overexposed here, but farther down the image several bright ring features can be seen.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on April 25, 2005, at a distance of approximately 2.4 million kilometers (1.5 million miles) from Atlas and at a Sun-Atlas-spacecraft, or phase, angle of 60 degrees. Resolution in the original image was 14 kilometers (9 miles) per pixel.

Star scanner. [with a reticle with a pair of slits having differing separation

NASA Technical Reports Server (NTRS)

Gutshall, R. L.; Mcconaughey, R. T.; Volpe, F. A. (Inventor)

1974-01-01

A star scanner on a spin stabilized spacecraft is described which includes a reticle with a pair of slits having different separations as a function of the spacecraft vertical plane, to form a V slit. The time between a star image crossing one of the slits relative to a reference telemetry time provides an indication of azimuth angle. The time between the image crossing the two slits provides an indication of elevation angle of the star. If a star cluster is detected such that two stars pass the slits in less time than normally required for a single star to cross the two slits, an indication of the cluster occurrence is derived. Means are provided to prevent effective detection of large celestial bodies, such as the sun or moon.

Using Lunar Module Shadows To Scale the Effects of Rocket Exhaust Plumes

NASA Technical Reports Server (NTRS)

2008-01-01

Excavating granular materials beneath a vertical jet of gas involves several physical mechanisms. These occur, for example, beneath the exhaust plume of a rocket landing on the soil of the Moon or Mars. We performed a series of experiments and simulations (Figure 1) to provide a detailed view of the complex gas-soil interactions. Measurements taken from the Apollo lunar landing videos (Figure 2) and from photographs of the resulting terrain helped demonstrate how the interactions extrapolate into the lunar environment. It is important to understand these processes at a fundamental level to support the ongoing design of higher fidelity numerical simulations and larger-scale experiments. These are needed to enable future lunar exploration wherein multiple hardware assets will be placed on the Moon within short distances of one another. The high-velocity spray of soil from the landing spacecraft must be accurately predicted and controlled or it could erode the surfaces of nearby hardware. This analysis indicated that the lunar dust is ejected at an angle of less than 3 degrees above the surface, the results of which can be mitigated by a modest berm of lunar soil. These results assume that future lunar landers will use a single engine. The analysis would need to be adjusted for a multiengine lander. Figure 3 is a detailed schematic of the Lunar Module camera calibration math model. In this chart, formulas relating the known quantities, such as sun angle and Lunar Module dimensions, to the unknown quantities are depicted. The camera angle PSI is determined by measurement of the imaged aspect ratio of a crater, where the crater is assumed to be circular. The final solution is the determination of the camera calibration factor, alpha. Figure 4 is a detailed schematic of the dust angle math model, which again relates known to unknown parameters. The known parameters now include the camera calibration factor and Lunar Module dimensions. The final computation is the ejected dust angle, as a function of Lunar Module altitude.

SunSmart: Evaluation of a Pilot School-Based Sun Protection Intervention in Hispanic Early Adolescents

ERIC Educational Resources Information Center

Miller, K. A.; Langholz, B. M.; Ly, T.; Harris, S. C.; Richardson, J. L.; Peng, D. H.; Cockburn, M. G.

2015-01-01

The incidence of melanoma is rising among Hispanic populations in the United States. The purpose of this study is to evaluate the impact of a pilot sun safety educational intervention conducted from 2006 to 2012 on Hispanic early adolescents in a high ultraviolet environment. Nineteen schools with high Hispanic enrollment were recruited from urban…

MODIS Solar Diffuser On-Orbit Degradation Characterization Using Improved SDSM Screen Modeling

NASA Technical Reports Server (NTRS)

Chen, H.; Xiong, Xiaoxiong; Angal, Amit Avinash; Wang, Z.; Wu, A.

2016-01-01

The Solar Diffuser (SD) is used for the MODIS reflective solar bands (RSB) calibration. An on-board Solar Diffuser Stability Monitor (SDSM) tracks the degradation of its on-orbit bi-directional reflectance factor (BRF). To best match the SDSM detector signals from its Sun view and SD view, a fixed attenuation screen is placed in its Sun view path, where the responses show ripples up to 10%, much larger than design expectation. Algorithms have been developed since the mission beginning to mitigate the impacts of these ripples. In recent years, a look-up-table (LUT) based approach has been implemented to account for these ripples. The LUT modeling of the elevation and azimuth angles is constructed from the detector 9 (D9) of SDSM observations in the MODIS early mission. The response of other detectors is normalized to D9 to reduce the ripples observed in the sun-view data. The accuracy of all detectors degradation estimation depends on how well the D9 approximated. After multiple years of operation (Terra: 16 years; Aqua: 14 years), degradation behavior of all detectors can be monitored by their own. This paper revisits the LUT modeling and proposes a dynamic scheme to build a LUT independently for each detector. Further refinement in the Sun view screen characterization will be highlighted to ensure the degradation estimation accuracy. Results of both Terra and Aqua SD on-orbit degradation are derived from the improved modeling and curve fitting strategy.

THE UBV(RI){sub C} COLORS OF THE SUN

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

Ramirez, I.; Michel, R.; Schuster, W. J.

2012-06-10

Photometric data in the UBV(RI){sub C} system have been acquired for 80 solar analog stars for which we have previously derived highly precise atmospheric parameters T{sub eff}, log g, and [Fe/H] using high-resolution, high signal-to-noise ratio spectra. UBV and (RI){sub C} data for 46 and 76 of these stars, respectively, are published for the first time. Combining our data with those from the literature, colors in the UBV(RI){sub C} system, with {approx_equal} 0.01 mag precision, are now available for 112 solar analogs. Multiple linear regression is used to derive the solar colors from these photometric data and the spectroscopically derivedmore » T{sub eff}, log g, and [Fe/H] values. To minimize the impact of systematic errors in the model-dependent atmospheric parameters, we use only the data for the 10 stars that most closely resemble our Sun, i.e., the solar twins, and derive the following solar colors: (B - V){sub Sun} = 0.653 {+-} 0.005, (U - B){sub Sun} = 0.166 {+-} 0.022, (V - R){sub Sun} = 0.352 {+-} 0.007, and (V - I){sub Sun} = 0.702 {+-} 0.010. These colors are consistent, within the 1{sigma} errors, with those derived using the entire sample of 112 solar analogs. We also derive the solar colors using the relation between spectral-line-depth ratios and observed stellar colors, i.e., with a completely model-independent approach, and without restricting the analysis to solar twins. We find (B - V){sub Sun} = 0.653 {+-} 0.003, (U - B){sub Sun} = 0.158 {+-} 0.009, (V - R){sub Sun} = 0.356 {+-} 0.003, and (V - I){sub Sun} = 0.701 {+-} 0.003, in excellent agreement with the model-dependent analysis.« less

Sun burn incidence and knowledge of greek elementary and high school children about sun protection.

PubMed

Saridi, Maria Ioannis; Toska, Aikaterini George; Rekleiti, Maria Dimitrios; Tsironi, Maria; Geitona, Maria; Souliotis, Kyriakos

2015-01-01

Overexposure to sun radiation and particularly its accumulation during childhood and adolescence is a significant risk factor for skin cancer development. The sun burn is particularly important. To estimate sun burn incidence in young pupils in a coastal area of Greece. Two surveys were conducted in a school population in the same district in Greece, over different periods of time, in young people 9 to 18 years old (n=2 977). Anonymous questionnaires were completed. Levels of significance were two- tailed and statistical significance was set at p=0.05. SPSS 17.0 software was used for statistical analysis. From the individual characteristics of the participants it was shown that the majority of them had dark hair and fair skin, whereas a significant percentage reported the existence of moles on face and their body (83.4% vs 68.1%). The sun burn incidence was high in adolescents and the younger pupils (41.9% vs 55.6%). The younger aged children who were living in an urban area had significantly higher rates of sun burn than those living in semi-urban areas (33.8% vs 24.8%, p=0.020). As far as the knowledge of pupils about the risks of sun radiation it was shown that the elementary school pupils had better knowledge than those at high school. Finally, those with better knowledge had the fewer sun burns (Mean 2.83 SD 0.87, p<0.001). The contribution of knowledge to the decrease of sun burn incidence is important as long as this is continuous. Therefore, the education should concern not only children but also teachers and parents in the context of continuous and systematic programs of health education.

Determinants of Sunburn and Sun Protection of Agricultural Workers During Occupational and Recreational Activities.

PubMed

Backes, Claudine; Milon, Antoine; Koechlin, Alice; Vernez, David; Bulliard, Jean-Luc

2017-11-01

The aim of this study was to identify determinants of occupational sunburn in agricultural workers and assess their occupational and recreational sun protection habits. Specific surveys of agricultural workers in Switzerland and France were conducted (N = 1538). Multivariate logistic regressions identified occupational sunburn determinants. Occupational and recreational sun protection habits were estimated and correlated. One-year occupational and recreational sunburn prevalences were 19.8% and 11.5%, respectively. Occupational sunburn increased with having a recent recreational sunburn, highly sensitive skin, young age, high perceived skin cancer risk, using sunscreen, and not wearing a hat. Correlation between protection habits during work and leisure was substantial (rs 0.5 to 0.7). Skin health knowledge was high and pro-tanning attitude moderate. Potentially modifiable sunburn determinants and suboptimal recreational and occupational sun protection practices were identified in agricultural workers. Refining and tailoring sun protection messages targeting the agricultural sector are needed.

Relationship factors and couples' engagement in sun protection.

PubMed

Manne, S L; Coups, E J; Kashy, D A

2016-08-01

Individuals may be more motivated to adopt health practices if they consider the benefits of these behaviors for their close relationships. The goal of this study was to examine couple concordance with sun protection and use the interdependence and communal coping theory to evaluate the role of relationship factors in sun protection. One hundred and eighty-four married couples aged 50 years and older completed measures of objective skin cancer risk, perceived risk, sun protection benefits, relationship-centered motivations for sun protection, discussions about sun protection, and sun protection. A mediational model was evaluated. Results indicated a high level of couple concordance. Partners who adopted a relationship-centered motivation for sun protection were more likely to discuss sun protection with one another, and partners who discussed sun protection together were more likely to engage in sun protection. One partner's attitude about personal risk and sun protection benefits was associated with the other partner's sun protection. Wives had higher relationship-centered motivation and discussed sun protection more with their husbands. Behavioral interventions may benefit from encouraging couples to discuss sun protection and encouraging married individuals to consider the benefits of sun protection for their relationship and for their spouse's health. © The Author 2016. Published by Oxford University Press. All rights reserved. For permissions, please email: journals.permissions@oup.com.

The relieving effects of shelter modes on physiological stress of traffic police in summer

NASA Astrophysics Data System (ADS)

Zheng, G. Z.; Wang, Y. J.; Bu, W. T.; Lu, Y. Z.; Li, Ke; Li, Z. H.

2018-03-01

In summer, high temperature and strong sun radiation last for a long time. However, traffic police still stick to their positions to ensure normal traffic order. Therefore, the health and safety of traffic police are challenged by the high temperature weather. To protect the safety of the traffic police in the outdoor high temperature environment, some shelter modes, such as sun hat and sun umbrella are selected for duty traffic police. The relieving effects on the physiological stress of the shelter modes are analyzed by comparison of the physiological parameters in these shelter modes. The results show that sun umbrella has a good effect on relieving physiological stress. And sun hat has no effect on relieving physiological stress, although it avoids the direct sunlight on the face. However, it causes the increase of the thermal sensation. This study can provide important methods for health protecting of traffic police in the outdoor high temperature environment. It also provides a theoretical support for the revision of the outdoor high temperature labour protection standard.

Exposure to mass media health information, skin cancer beliefs, and sun protection behaviors in a United States probability sample.

PubMed

Hay, Jennifer; Coups, Elliot J; Ford, Jennifer; DiBonaventura, Marco

2009-11-01

The mass media is increasingly important in shaping a range of health beliefs and behaviors. We examined the association among mass media health information exposure (general health, cancer, sun protection information), skin cancer beliefs, and sun protection behaviors. We used a general population national probability sample comprised of 1633 individuals with no skin cancer history (Health Information National Trends Survey, 2005, National Cancer Institute) and examined univariate and multivariate associations among family history of skin cancer, mass media exposure, skin cancer beliefs, and sun protection (use of sunscreen, shade seeking, and use of sun-protective clothing). Mass media exposure was higher in younger individuals, and among those who were white and more highly educated. More accurate skin cancer beliefs and more adherent sun protection practices were reported by older individuals, and among those who were white and more highly educated. Recent Internet searches for health or sun protection information were associated with sunscreen use. Study limitations include the self-report nature of sun protection behaviors and cross-sectional study design. We identify demographic differences in mass media health exposure, skin cancer beliefs, and sun protection behaviors that will contribute to planning skin cancer awareness and prevention messaging across diverse population subgroups.

Visibility Analysis of Domestic Satellites on Proposed Ground Sites for Optical Surveillance

NASA Astrophysics Data System (ADS)

Kim, Jae-Hyuk; Jo, Jung Hyun; Choi, Jin; Moon, Hong-Kyu; Choi, Young-Jun; Yim, Hong-Suh; Park, Jang-Hyun; Park, Eun-Seo; Park, Jong-Uk

2011-12-01

The objectives of this study are to analyze the satellite visibility at the randomly established ground sites, to determine the five optimal ground sites to perform the optical surveillance and tracking of domestic satellites, and to verify the acquisition of the optical observation time sufficient to maintain the precise ephemeris at optimal ground sites that have been already determined. In order to accomplish these objectives, we analyzed the visibility for sun-synchronous orbit satellites, low earth orbit satellites, middle earth orbit satellites and domestic satellites as well as the continuous visibility along with the fictitious satellite ground track, and calculate the effective visibility. For the analysis, we carried out a series of repetitive process using the satellite tool kit simulation software developed by Analytical Graphics Incorporated. The lighting states of the penumbra and direct sun were set as the key constraints of the optical observation. The minimum of the observation satellite elevation angle was set to be 20 degree, whereas the maximum of the sun elevation angle was set to be -10 degree which is within the range of the nautical twilight. To select the candidates for the optimal optical observation, the entire globe was divided into 84 sectors in a constant interval, the visibility characteristics of the individual sectors were analyzed, and 17 ground sites were arbitrarily selected and analyzed further. Finally, five optimal ground sites (Khurel Togoot Observatory, Assy-Turgen Observatory, Tubitak National Observatory, Bisdee Tier Optical Astronomy Observatory, and South Africa Astronomical Observatory) were determined. The total observation period was decided as one year. To examine the seasonal variation, the simulation was performed for the period of three days or less with respect to spring, summer, fall and winter. In conclusion, we decided the optimal ground sites to perform the optical surveillance and tracking of domestic satellites and verified that optical observ! ation ti me sufficient to maintain the precise ephemeris could be acquired at the determined observatories.

Exploring Extreme Retro-reflection by Asteroids Using Las Cumbres Observatory Robotic Telescope Observations

NASA Astrophysics Data System (ADS)

Goguen, Jay D.; Bauer, James M.

2017-10-01

The reflectivity of solar system surfaces ‘spikes’ sharply when the Sun is less than 1 degree from directly behind the observer. The Galileo spacecraft measured the reflectivity of part of Europa’s surface to increase by as much as a factor of 8 as the observer moves from 5 degrees to the exact backscattering direction! One mechanism explains this spike as coherent light scattering that occurs only close to this unique retro-reflection geometry. Due to the tight linear alignment of the target, observer and Sun required to measure the peak brightness of the spike, accurate and complete measurements of the amplitude and decay of the spike exist for only a few targets. We used the unique capabilities of the automated Las Cumbres Observatory global telescope network (LCO) to systematically measure this extreme opposition surge for 60+ asteroids sampling a variety of taxonomic classes in the Bus/DeMeo taxonomy.Each asteroid was observed in the SDSS r’ and g’ filters during the ~8 hour interval when it passes within ~0.1 deg of the point opposite the Sun on the sky. Supporting observations of each asteroid with LCO collected over ~50 days measure asteroid rotation and phase angle brightness changes to enable accurate characterization of the retro-reflection spike. This data set vastly increases the number and variety of the surfaces characterized at such small phase angles compared to existing asteroid data. We examine how the spike characteristics vary with surface composition, albedo, and wavelength providing new constraints on physical models of this ubiquitous yet poorly understood phenomenon.Analysis and modeling of these measurements will advance our understanding of the physical mechanism responsible for this enhanced retro-reflection thereby improving our ability to characterize these surfaces from remote observations. The ability to infer surface physical properties from remote sensing data is a key capability for future asteroid missions, manned exploration, impact hazard assessment, and fundamental asteroid science.

Predicting Ground Illuminance

NASA Astrophysics Data System (ADS)

Lesniak, Michael V.

2014-01-01

Our Sun outputs 3.85 × 1026 W of radiation, of which ≈37% is in the visible band. It is directly responsible for nearly all natural illuminance experienced on Earth's surface, either in the form of direct/refracted sunlight or in reflected light bouncing off the surfaces and/or atmospheres of our Moon and the visible planets. Ground illuminance, defined as the amount of visible light intercepting a unit area of surface (from all incident angles), varies over 7 orders of magnitude from day to night. It is highly dependent on well-modeled factors such as the relative positions of the Sun, Earth, and Moon. It is also dependent on less predictable factors such as local atmospheric conditions and weather. Several models have been proposed to predict ground illuminance, including Brown (1952) and Shapiro (1982, 1987). The Brown model is a set of empirical data collected from observation points around the world that has been reduced to a smooth fit of illuminance against a single variable, solar altitude. It provides limited applicability to the Moon and for cloudy conditions via multiplicative reduction factors. The Shapiro model is a theoretical model that treats the atmosphere as a three layer system of light reflectance and transmittance. It has different sets of reflectance and transmittance coefficients for various cloud types. Ground illuminance data from an observing run at the White Sands missile range were obtained from the United Kingdom Meteorology Office. Based on available weather reports, five days of clear sky observations were selected. These data are compared to the predictions of the two models. We find that neither of the models provide an accurate treatment during twilight conditions when the Sun is at or a few degrees below the horizon. When the Sun is above the horizon, the Shapiro model straddles the observed data, ranging between 90% and 120% of the recorded illuminance. During the same times, the Brown model is between 70% and 90% of the observed value. While the results are preliminary, the Shapiro model appears to have better predictive power than does the Brown model.

How to improve adolescents' sun protection behavior? Age and gender issues.

PubMed

Paul, Christine; Tzelepis, Flora; Parfitt, Nicholas; Girgis, Afaf

2008-01-01

To explore adolescents' self-reported reasons for sun protection, as adolescents as a group continue to have poor sun protection practices. Seventeen age- and gender-segregated focus groups were conducted in Australian high schools. Reasons for using sun protection included personal comfort, appearance, policies, fear of skin cancer, expectations of authority figures, peer actions, and habit. Reasons for not using sun protection included desire for a tan, inconvenience, low perceived risk, and fashion. Age and gender effects were found. Avenues for intervention with adolescents include authority figures, peer advocacy, the fashion industry, and improved sun protection products.

Analysis of Opportunities for Intercalibration Between Two Spacecraft. Chapter 1

NASA Technical Reports Server (NTRS)

Roithmayr, Carlos M.; Speth, Paul W.

2012-01-01

There is currently a strong interest in obtaining highly accurate measurements of solar radiation reflected by Earth. For example, the Traceable Radiometry Underpinning Terrestrial- and Helio- Studies (TRUTHS) satellite mission has been under consideration in Europe for several years, and planning is now under way for the Climate Absolute Radiance and Refractivity Observatory (CLARREO) spacecraft in the United States. Such spacecraft will provide measurements whose high accuracy is traceable to SI standards; these measurements will be useful as a reference for calibrating similar instruments on board other spacecraft. Hence, analysis of opportunities for intercalibration between two spacecraft plays an important role in the planning of future missions. In order for intercalibration to take place, the measurements obtained from two spacecraft must have similar viewing geometry and be taken within a few minutes of one another. Viewing geometry is characterized in terms of viewing zenith angle, solar zenith angle, and relative azimuth angle. Opportunities for intercalibration are greater in number and longer in duration if the sensor with high accuracy can be aimed at points on the surface of the Earth other than the nadir or sub-satellite point. Analysis of intercalibration over long periods is rendered tractable by making several simplifying assumptions regarding orbital motions of the two spacecraft about Earth, as well as Earth s orbit about the Sun. The shape of the Earth is also considered. A geometric construction called a tent is introduced to facilitate analysis. It is helpful to think of an intercalibration opportunity as the passage of one spacecraft through a tent that has a fixed shape and moves with the spacecraft whose measurements are to be calibrated. Selection of points on Earth s surface as targets for measurement is discussed, as is aiming the boresight of a steerable instrument. Analysis results for a pair of spacecraft in typical low Earth orbits are provided.

Sun Exposure, Sun-Related Symptoms, and Sun Protection Practices in an African Informal Traditional Medicines Market.

PubMed

Wright, Caradee Y; Reddy, Tarylee; Mathee, Angela; Street, Renée A

2017-09-28

Informal workers in African market trade have little formal protection against sun exposure. We aimed to examine sun exposure, sun-related symptoms, and sun protection practices in an informal occupational setting. Trained fieldworkers asked 236 workers in the Warwick Junction market about their workplace, skin and eye sensitivity and skin colour, symptoms faced at work during the summer due to heat, and preventive measures. Data were analyzed using univariate logistic regression to assess the effect of gender and the risk of experiencing symptoms to sun exposure in relation to pre-existing diseases and perception of sun exposure as a hazard. Of the 236 participants, 234 were Black African and 141 (59.7%) were female. Portable shade was the most commonly used form of sun protection (69.9%). Glare from the sun (59.7%) and excessive sweating (57.6%) were commonly reported sun-related health symptoms. The use of protective clothing was more prevalent among those who perceived sun exposure as a hazard ( p = 0.003). In an informal occupational setting, sun exposure was high. Protective clothing and portable shade to eliminate heat and bright light were self-implemented. Action by local authorities to protect informal workers should consider sun exposure to support workers in their efforts to cope in hot weather.

PROCAMS - A second generation multispectral-multitemporal data processing system for agricultural mensuration

NASA Technical Reports Server (NTRS)

Erickson, J. D.; Nalepka, R. F.

1976-01-01

PROCAMS (Prototype Classification and Mensuration System) has been designed for the classification and mensuration of agricultural crops (specifically small grains including wheat, rye, oats, and barley) through the use of data provided by Landsat. The system includes signature extension as a major feature and incorporates multitemporal as well as early season unitemporal approaches for using multiple training sites. Also addressed are partial cloud cover and cloud shadows, bad data points and lines, as well as changing sun angle and atmospheric state variations.

Methods of extending crop signatures from one area to another

NASA Technical Reports Server (NTRS)

Minter, T. C. (Principal Investigator)

1979-01-01

Efforts to develop a technology for signature extension during LACIE phases 1 and 2 are described. A number of haze and Sun angle correction procedures were developed and tested. These included the ROOSTER and OSCAR cluster-matching algorithms and their modifications, the MLEST and UHMLE maximum likelihood estimation procedures, and the ATCOR procedure. All these algorithms were tested on simulated data and consecutive-day LANDSAT imagery. The ATCOR, OSCAR, and MLEST algorithms were also tested for their capability to geographically extend signatures using LANDSAT imagery.

Mathematical model of the solar radiation force and torques acting on the components of a spacecraft

NASA Technical Reports Server (NTRS)

Georgevic, R. M.

1971-01-01

General expressions for the solar radiation force and torques are derived in the vectorial form for any given reflecting surface, provided that the reflecting characteristics of the surface, as well as the value of the solar constant, are known. An appropriate choice of a spacecraft-fixed frame of reference leads to relatively simple expressions for the solar radiation forces and torques in terms of the functions of the sun-spacecraft-earth angle.

Invariant Tori in the Secular Motions of the Three-body Planetary Systems

NASA Astrophysics Data System (ADS)

Locatelli, Ugo; Giorgilli, Antonio

We consider the problem of the applicability of KAM theorem to a realistic problem of three bodies. In the framework of the averaged dynamics over the fast angles for the Sun-Jupiter-Saturn system we can prove the perpetual stability of the orbit. The proof is based on semi-numerical algorithms requiring both explicit algebraic manipulations of series and analytical estimates. The proof is made rigorous by using interval arithmetics in order to control the numerical errors.

Aerodynamic Characterizations of Asymmetric and Maneuvering 105-, 120-, and 155-mm Fin-Stabilized Projectiles Derived from Telemetry Experiments

DTIC Science & Technology

2011-04-01

roll rates are estimates of projectile roll rates with respect to the sun and the local geomagnetic field respectively. The solar aspect angle is the...vector and a vector originating at the CG and parallel to the local geomagnetic field. Methodologies employed to obtain these and other airframe states...and an independent approach (POINTER) and relative magnitude information about the side moments was obtained. VAPP-24 underwent a reversal in coning

LDEF grappled by remote manipulator system (RMS) during STS-32 retrieval

NASA Image and Video Library

1990-01-20

This view taken through overhead window W7 on Columbia's, Orbiter Vehicle (OV) 102's, aft flight deck shows the Long Duration Exposure Facility (LDEF) in the grasp of the remote manipulator system (RMS) during STS-32 retrieval activities. Other cameras at eye level were documenting the bus-sized spacecraft at various angles as the RMS manipulated LDEF for a lengthy photo survey. The glaring celestial body in the upper left is the sun with the Earth's surface visible below.

A Stealth CME Bracketed between Slow and Fast Wind Producing Unexpected Geoeffectiveness

NASA Astrophysics Data System (ADS)

He, Wen; Liu, Ying D.; Hu, Huidong; Wang, Rui; Zhao, Xiaowei

2018-06-01

We investigate how a weak coronal mass ejection (CME) launched on 2016 October 8 without obvious signatures in the low corona produced a relatively intense geomagnetic storm. Remote sensing observations from SDO, STEREO, and SOHO and in situ measurements from Wind are employed to track the CME from the Sun to the Earth. Using a graduated cylindrical shell model, we estimate the propagation direction and the morphology of the CME near the Sun. CME kinematics are determined from the wide-angle imaging observations of STEREO A and are used to predict the CME arrival time and speed at the Earth. We compare ENLIL MHD simulation results with in situ measurements to illustrate the background solar wind where the CME was propagating. We also apply a Grad–Shafranov technique to reconstruct the flux-rope structure from in situ measurements in order to understand the geoeffectiveness associated with the CME magnetic field structure. Key results are obtained concerning how a weak CME can generate a relatively intense geomagnetic storm: (1) there were coronal holes at low latitudes, which could produce high speed streams (HSSs) to interact with the CME in interplanetary space; (2) the CME was bracketed between a slow wind ahead and an HSS behind, which enhanced the southward magnetic field inside the CME and gave rise to the unexpected geomagnetic storm.

Sandmeier model based topographic correction to lunar spectral profiler (SP) data from KAGUYA satellite.

PubMed

Chen, Sheng-Bo; Wang, Jing-Ran; Guo, Peng-Ju; Wang, Ming-Chang

2014-09-01

The Moon may be considered as the frontier base for the deep space exploration. The spectral analysis is one of the key techniques to determine the lunar surface rock and mineral compositions. But the lunar topographic relief is more remarkable than that of the Earth. It is necessary to conduct the topographic correction for lunar spectral data before they are used to retrieve the compositions. In the present paper, a lunar Sandmeier model was proposed by considering the radiance effect from the macro and ambient topographic relief. And the reflectance correction model was also reduced based on the Sandmeier model. The Spectral Profile (SP) data from KAGUYA satellite in the Sinus Iridum quadrangle was taken as an example. And the digital elevation data from Lunar Orbiter Laser Altimeter are used to calculate the slope, aspect, incidence and emergence angles, and terrain-viewing factor for the topographic correction Thus, the lunar surface reflectance from the SP data was corrected by the proposed model after the direct component of irradiance on a horizontal surface was derived. As a result, the high spectral reflectance facing the sun is decreased and low spectral reflectance back to the sun is compensated. The statistical histogram of reflectance-corrected pixel numbers presents Gaussian distribution Therefore, the model is robust to correct lunar topographic effect and estimate lunar surface reflectance.

New Moon

NASA Image and Video Library

2017-12-08

New Moon. By the modern definition, New Moon occurs when the Moon and Sun are at the same geocentric ecliptic longitude. The part of the Moon facing us is completely in shadow then. Pictured here is the traditional New Moon, the earliest visible waxing crescent, which signals the start of a new month in many lunar and lunisolar calendars. This marks the first time that accurate shadows at this level of detail are possible in such a computer simulation. The shadows are based on the global elevation map being developed from measurements by the Lunar Orbiter Laser Altimeter (LOLA) aboard the Lunar Reconnaissance Orbiter (LRO). LOLA has already taken more than 10 times as many elevation measurements as all previous missions combined. The Moon always keeps the same face to us, but not exactly the same face. Because of the tilt and shape of its orbit, we see the Moon from slightly different angles over the course of a month. When a month is compressed into 12 seconds, as it is in this animation, our changing view of the Moon makes it look like it's wobbling. This wobble is called libration. The word comes from the Latin for "balance scale" (as does the name of the zodiac constellation Libra) and refers to the way such a scale tips up and down on alternating sides. The sub-Earth point gives the amount of libration in longitude and latitude. The sub-Earth point is also the apparent center of the Moon's disk and the location on the Moon where the Earth is directly overhead. The Moon is subject to other motions as well. It appears to roll back and forth around the sub-Earth point. The roll angle is given by the position angle of the axis, which is the angle of the Moon's north pole relative to celestial north. The Moon also approaches and recedes from us, appearing to grow and shrink. The two extremes, called perigee (near) and apogee (far), differ by more than 10%. The most noticed monthly variation in the Moon's appearance is the cycle of phases, caused by the changing angle of the Sun as the Moon orbits the Earth. The cycle begins with the waxing (growing) crescent Moon visible in the west just after sunset. By first quarter, the Moon is high in the sky at sunset and sets around midnight. The full Moon rises at sunset and is high in the sky at midnight. The third quarter Moon is often surprisingly conspicuous in the daylit western sky long after sunrise. Celestial north is up in these images, corresponding to the view from the northern hemisphere. The descriptions of the print resolution stills also assume a northern hemisphere orientation. To adjust for southern hemisphere views, rotate the images 180 degrees, and substitute "north" for "south" in the descriptions. Credit: NASA/Goddard Space Flight Center Scientific Visualization Studio NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Join us on Facebook Find us on Instagram

A highly accurate wireless digital sun sensor based on profile detecting and detector multiplexing technologies

NASA Astrophysics Data System (ADS)

Wei, Minsong; Xing, Fei; You, Zheng

2017-01-01

The advancing growth of micro- and nano-satellites requires miniaturized sun sensors which could be conveniently applied in the attitude determination subsystem. In this work, a profile detecting technology based high accurate wireless digital sun sensor was proposed, which could transform a two-dimensional image into two-linear profile output so that it can realize a high update rate under a very low power consumption. A multiple spots recovery approach with an asymmetric mask pattern design principle was introduced to fit the multiplexing image detector method for accuracy improvement of the sun sensor within a large Field of View (FOV). A FOV determination principle based on the concept of FOV region was also proposed to facilitate both sub-FOV analysis and the whole FOV determination. A RF MCU, together with solar cells, was utilized to achieve the wireless and self-powered functionality. The prototype of the sun sensor is approximately 10 times lower in size and weight compared with the conventional digital sun sensor (DSS). Test results indicated that the accuracy of the prototype was 0.01° within a cone FOV of 100°. Such an autonomous DSS could be equipped flexibly on a micro- or nano-satellite, especially for highly accurate remote sensing applications.

Effect of an Intervention on Observed Sun Protection by Vacationers in a Randomized Controlled Trial at North American Resorts

PubMed Central

Buller, David B.; Andersen, Peter A.; Walkosz, Barbara J.; Scott, Michael D.; Beck, Larry; Cutter, Gary R.

2017-01-01

During vacations, many individuals receive high-risk sun exposure that is associated with skin cancer. Vacationers in outdoor recreation venues (pretest n=4,347; posttest n=3,986) at warm-weather destination resorts in North America (n=41) were enrolled in a pair-matched, group-randomized pretest-posttest controlled quasi-experimental design in 2012-14. Print, audiovisual, and online messages based on Transportation Theory and Diffusion of Innovation Theory and promoting advanced sun protection (e.g., use of clothing, hats, shade and pre-application/reapplication of sunscreen and reliable cues to high UV) were delivered through resort channels. Vacationers' sun protection practices observed by trained research staff (i.e., body coverage and shade use analyzed individually and in combined scores) did not differ by experimental condition (p>0.05) or intervention implementation (p>0.05). However, recreation venue moderated intervention impact. The intervention improved sun protection at waterside recreation venues (z-score composite: intervention pre=-22.74, post=-15.77; control pre=-27.24, post=-23.24) but not non-waterside venues (z-score composite: intervention pre=20.43, post=20.53; control pre=22.94, post=18.03, p<0.01). An additional analysis showed that resorts with greater program implementation showed more improvements in sun protection by vacationers at waterside (z=score composite: high implementation pre=-25.45, post=-14.05; low implementation pre=-24.70, post=-21.40) compared to non-waterside (z-score composite: high implementation pre=14.51, post=19.98; low implementation pre=24.03, post=18.98, p<0.01) recreation venues. The intervention appeared effective with the vacationers in recreation venues with the highest-risk for sun exposure, waterside venues. However, it was not effective throughout all the resort venues, possibly because of the sun-seeking desires of vacationers, information overload at the resorts, and constraints on clothing styles and sun protection by recreation activity. PMID:28189810

Effect of an intervention on observed sun protection by vacationers in a randomized controlled trial at North American resorts.

PubMed

Buller, David B; Andersen, Peter A; Walkosz, Barbara J; Scott, Michael D; Beck, Larry; Cutter, Gary R

2017-06-01

During vacations, many individuals receive high-risk sun exposure that is associated with skin cancer. Vacationers in outdoor recreation venues (pretest n=4347; posttest n=3986) at warm-weather destination resorts in North America (n=41) were enrolled in a pair-matched, group-randomized pretest-posttest controlled quasi-experimental design in 2012-14. Print, audiovisual, and online messages based on Transportation Theory and Diffusion of Innovation Theory and promoting advanced sun protection (e.g., use of clothing, hats, shade and pre-application/reapplication of sunscreen and reliable cues to high UV) were delivered through resort channels. Vacationers' sun protection practices observed by trained research staff (i.e., body coverage and shade use analyzed individually and in combined scores) did not differ by experimental condition (p>0.05) or intervention implementation (p>0.05). However, recreation venue moderated intervention impact. The intervention improved sun protection at waterside recreation venues (z-score composite: intervention pre=-22.74, post=-15.77; control pre=-27.24, post=-23.24) but not non-waterside venues (z-score composite: intervention pre=20.43, post=20.53; control pre=22.94, post=18.03, p<0.01). An additional analysis showed that resorts with greater program implementation showed more improvements in sun protection by vacationers at waterside (z=score composite: high implementation pre=-25.45, post=-14.05; low implementation pre=-24.70, post=-21.40) compared to non-waterside (z-score composite: high implementation pre=14.51, post=19.98; low implementation pre=24.03, post=18.98, p<0.01) recreation venues. The intervention appeared effective with the vacationers in recreation venues with the highest-risk for sun exposure, waterside venues. However, it was not effective throughout all the resort venues, possibly because of the sun-seeking desires of vacationers, information overload at the resorts, and constraints on clothing styles and sun protection by recreation activity. Copyright © 2017 Elsevier Inc. All rights reserved.

View angle dependence of cloud optical thicknesses retrieved by MODIS

NASA Technical Reports Server (NTRS)

Marshak, Alexander; Varnai, Tamas

2005-01-01

This study examines whether cloud inhomogeneity influences the view angle dependence of MODIS cloud optical thickness (tau) retrieval results. The degree of cloud inhomogeneity is characterized through the local gradient in 11 microns brightness temperature. The analysis of liquid phase clouds in a one year long global dataset of Collection 4 MODIS data reveals that while optical thickness retrievals give remarkably consistent results for all view directions if clouds are homogeneous, they give much higher tau-values for oblique views than for overhead views if clouds are inhomogeneous and the sun is fairly oblique. For solar zenith angles larger than 55deg, the mean optical thickness retrieved for the most inhomogeneous third of cloudy pixels is more than 30% higher for oblique views than for overhead views. After considering a variety of possible scenarios, the paper concludes that the most likely reason for the increase lies in three-dimensional radiative interactions that are not considered in current, one-dimensional retrieval algorithms. Namely, the radiative effect of cloud sides viewed at oblique angles seems to contribute most to the enhanced tau-values. The results presented here will help understand cloud retrieval uncertainties related to cloud inhomogeneity. They complement the uncertainty estimates that will start accompanying MODIS cloud products in Collection 5 and may eventually help correct for the observed view angle dependent biases.

Cometary jets in interaction with the solar wind: a hybrid simulation study

NASA Astrophysics Data System (ADS)

Wiehle, Stefan; Motschmann, Uwe; Gortsas, Nikolaos; Mueller, Joachim; Kriegel, Hendrik; Koenders, Christoph; Glassmeier, Karl-Heinz

The effect of a cometary jet on the solar wind interaction is studied using comet 67P/Churyumov-Gerasimenko as case study. This comet is the target of the Rosetta-mission which will arrive in 2014. Observations suggest that cometary outgassing is confined to only a few percent of the cometary surface; thus, the measurement of jets is expected. Most former comet simulations did not attend to this fact and used an isotropic outgassing scheme or simplified outgassing patterns. Here, a single sun-facing jet is set to be the only source of cometary gas produc-tion. Using an analytic profile, this outgassing jet was implemented in a hybrid simulation code which treats protons and cometary heavy ions as particles and electrons as massless fluid. In a simulation series, the geometric parameters of the jet were varied to study the effect of different opening angles while the integrated outgassing rate remained constant. It was shown that the resulting solar wind interaction is highly dependent on the geometry of the jet. The plasma-structures like the solar wind pile-up found in the situation with isotropic outgassing are moved more and more sunward as the opening angle of the jet decreases. Furthermore, the cometary ion tail shows some kind of splitting which is not known from isotropic models.

Coherent Doppler lidar for automated space vehicle rendezvous, stationkeeping and capture

NASA Technical Reports Server (NTRS)

Bilbro, James A.

1991-01-01

The inherent spatial resolution of laser radar makes ladar or lidar an attractive candidate for Automated Rendezvous and Capture application. Previous applications were based on incoherent lidar techniques, requiring retro-reflectors on the target vehicle. Technology improvements (reduced size, no cryogenic cooling requirement) have greatly enhanced the construction of coherent lidar systems. Coherent lidar permits the acquisition of non-cooperative targets at ranges that are limited by the detection capability rather than by the signal-to-noise ratio (SNR) requirements. The sensor can provide translational state information (range, velocity, and angle) by direct measurement and, when used with any array detector, also can provide attitude information by Doppler imaging techniques. Identification of the target is accomplished by scanning with a high pulse repetition frequency (dependent on the SNR). The system performance is independent of range and should not be constrained by sun angle. An initial effort to characterize a multi-element detection system has resulted in a system that is expected to work to a minimum range of 1 meter. The system size, weight and power requirements are dependent on the operating range; 10 km range requires a diameter of 3 centimeters with overall size at 3 x 3 x 15 to 30 cm, while 100 km range requires a 30 cm diameter.

An Algorithm for Converting Static Earth Sensor Measurements into Earth Observation Vectors

NASA Technical Reports Server (NTRS)

Harman, R.; Hashmall, Joseph A.; Sedlak, Joseph

2004-01-01

An algorithm has been developed that converts penetration angles reported by Static Earth Sensors (SESs) into Earth observation vectors. This algorithm allows compensation for variation in the horizon height including that caused by Earth oblateness. It also allows pitch and roll to be computed using any number (greater than 1) of simultaneous sensor penetration angles simplifying processing during periods of Sun and Moon interference. The algorithm computes body frame unit vectors through each SES cluster. It also computes GCI vectors from the spacecraft to the position on the Earth's limb where each cluster detects the Earth's limb. These body frame vectors are used as sensor observation vectors and the GCI vectors are used as reference vectors in an attitude solution. The attitude, with the unobservable yaw discarded, is iteratively refined to provide the Earth observation vector solution.

Crescent Mimas

NASA Image and Video Library

2014-09-15

A thin sliver of Mimas is illuminated, the long shadows showing off its many craters, indicators of the moon's violent history. The most famous evidence of a collision on Mimas (246 miles, or 396 kilometers across) is the crater Herschel that gives Mimas its Death Star-like appearance. See PIA12568 for more on Herschel. This view looks toward the anti-Saturn hemisphere of Mimas. North on Mimas is up and rotated 40 degrees to the right. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on May 20, 2013. The view was acquired at a distance of approximately 100,000 miles (200,000 kilometers) from Mimas and at a Sun-Mimas-spacecraft, or phase, angle of 130 degrees. Image scale is 4,000 feet (1 kilometer) per pixel. http://photojournal.jpl.nasa.gov/catalog/PIA18285

An Inexpensive High-Temporal Resolution Electronic Sun Journal for Monitoring Personal Day to Day Sun Exposure Patterns

PubMed Central

Downs, Nathan J.; Parisi, Alfio V.; Butler, Harry; Rawlings, Alex; Elrahoumi, Raja Salem

2017-01-01

Exposure to natural sunlight, specifically solar ultraviolet (UV) radiation contributes to lifetime risks of skin cancer, eye disease, and diseases associated with vitamin D insufficiency. Improved knowledge of personal sun exposure patterns can inform public health policy; and help target high-risk population groups. Subsequently, an extensive number of studies have been conducted to measure personal solar UV exposure in a variety of settings. Many of these studies, however, use digital or paper-based journals (self-reported volunteer recall), or employ cost prohibitive electronic UV dosimeters (that limit the size of sample populations), to estimate periods of exposure. A cost effective personal electronic sun journal (ESJ) built from readily available infrared photodiodes is presented in this research. The ESJ can be used to complement traditional UV dosimeters that measure total biologically effective exposure by providing a time-stamped sun exposure record. The ESJ can be easily attached to clothing and data logged to personal devices (including fitness monitors or smartphones). The ESJ improves upon self-reported exposure recording and is a cost effective high-temporal resolution option for monitoring personal sun exposure behavior in large population studies. PMID:29201865

Prevention of skin cancer in primary healthcare: an evaluation of three different prevention effort levels and the applicability of a phototest.

PubMed

Falk, Magnus; Anderson, Chris

2008-01-01

The high skin cancer incidence in western society, and its known association with sun exposure habits, makes the area an important target for prevention. We investigated, in a primary healthcare setting, differentiated levels of prevention efforts directed at the propensity of the patient to change his/her sun habits, sun protection behaviour, and attitudes, after information intervention. Additionally, the impact of the performance of a phototest to determine individual sun sensitivity was evaluated. 308 patients visiting a primary healthcare centre in southern Sweden completed a questionnaire concerning sun habits, sun protection behaviour, and attitudes, and were randomized into one of three groups, representing increasing levels of prevention effort in terms of resources. Feedback on their questionnaire and general preventive sun protection advice was given, in the first group by means of a letter, and in the second and third groups by a doctor's consultation. Group 3 also underwent a phototest, with a self-reading assessment and a written follow-up of the phototest result. Change of sun habits, behaviour, and attitudes, based on the Transtheoretical Model of Behaviour Change and on Likert scale scorings, was evaluated after 6 months, by a repeated questionnaire. Prevention mediated by a doctor's consultation had a clearly better impact on the subjects. The addition of a phototest did not further reinforce this effect in the group as a whole, but it did for a subgroup of individuals with high ultraviolet (UV) sensitivity, as determined by the phototest itself, suggesting that this might actually be a tool to improve outcome in this high-risk group. A personal doctor's consultation is a valuable tool in the effective delivery of preventive information in the general practice setting. In individuals with high UV-sensitivity and thus high risk for skin cancer the performance of a photo-test reinforces a positive outcome in habits, behaviour and attitudes.

A study to explore the use of orbital remote sensing to determine native arid plant distribution. [Arizona

NASA Technical Reports Server (NTRS)

Mcginnies, W. G. (Principal Investigator); Conn, J. S.; Haase, E. F.; Lepley, L. K.; Musick, H. B.; Foster, K. E.

1975-01-01

The author has identified the following significant results. Research results include a method for determining the reflectivities of natural areas from ERTS data taking into account sun angle and atmospheric effects on the radiance seen by the satellite sensor. Ground truth spectral signature data for various types of scenes, including ground with and without annuals, and various shrubs were collected. Large areas of varnished desert pavement are visible and mappable on ERTS and high altitude aircraft imagery. A large scale and a small scale vegetation pattern were found to be correlated with presence of desert pavement. A comparison of radiometric data with video recordings shows quantitatively that for most areas of desert vegetation, soils are the most influential factor in determining the signature of a scene. Additive and subtractive image processing techniques were applied in the dark room to enhance vegetational aspects of ERTS.

Analysis of substrate and plant spectral features of semi-arid shrub communities in the Owens Valley, California

NASA Technical Reports Server (NTRS)

Ustin, S. L.; Rock, B. N.; Woodward, R. A.

1986-01-01

Airborne Imaging Spectrometer (AIS) data were analyzed to deduce plant density and species composition in three semi-arid shrub-dominated communities of Owens Valley, CA, occurring on either a sand, granite alluvium, or basalt substrate. The high-spectral resolution AIS data were related to spectra obtained with field portable spectrometers, which in turn were related to plant and soil characteristics of the communities. Many of the dominant species have unique spectral features which permit their identification in AIS pixel images. The canopy-induced shadow may be a major factor influencing substrate spectral properties during fall and winter, because of low sun angles. Moreover, changes in spectral signatures following dormancy and leaf senescence tend to decrease contrasts between the plant community and the geologic substrate, also suggesting that fall and winter are a difficult time of year for spectral analyses.

Marsh canopy leaf area and orientation calculated for improved marsh structure mapping

USGS Publications Warehouse

Ramsey, Elijah W.; Rangoonwala, Amina; Jones, Cathleen E.; Bannister, Terri

2015-01-01

An approach is presented for producing the spatiotemporal estimation of leaf area index (LAI) of a highly heterogeneous coastal marsh without reliance on user estimates of marsh leaf-stem orientation. The canopy LAI profile derivation used three years of field measured photosynthetically active radiation (PAR) vertical profiles at seven S. alterniflora marsh sites and iterative transform of those PAR attenuation profiles to best-fit light extinction coefficients (KM). KM sun zenith dependency was removed obtaining the leaf angle distribution (LAD) representing the average marsh orientation and the LAD used to calculate the LAI canopy profile. LAI and LAD reproduced measured PAR profiles with 99% accuracy and corresponded to field documented structures. LAI and LAD better reflect marsh structure and results substantiate the need to account for marsh orientation. The structure indexes are directly amenable to remote sensing spatiotemporal mapping and offer a more meaningful representation of wetland systems promoting biophysical function understanding.