Search NASA⌕ Search

SEARCH · Search NASA

Results for “VENUS RADAR REFLECTION”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Radar studies of the Martian surface

The acquisition, processing, and interpretation of radar from Mars are reported with emphasis on the facilities of the Arecibo observatory. The project is now essentially complete. Results include scattering law studies in the Syrtis Major, Elysium, and Chryse areas of that planet and reflectivity measurements. Software for general use in the radar program at Arecibo was developed. Participation in acquisition and reduction of data from Venus and Mercury is detailed.

Simpson, R. A.↗
NASA NTRS2000

Radar Reflectivity of the Martian Polar Regions

Radar experiments provide a unique method of probing the surfaces and subsurfaces of planetary bodies. Information on surface and subsurface structures and properties can be extracted from radar data. There is a well developed history of radar investigations of the planet Mars, beginning with the first reports of variations of scattering properties as a function of martian longitude in the mid-1960's. Because of the rapid rotation of Mars, the standard technique of delay-doppler mapping cannot be used as effectively as it is on Mercury and Venus, making it a more difficult radar target. Techniques have been developed to overcome this difficulty, including an inversion technique to combine many doppler-only (CW) experiments from different viewing geometries into a map of surface reflectivity, and new random long-code techniques. These techniques still suffer from ambiguities, however. A third technique which does not suffer from these ambiguities is the combination of the powerful Goldstone transmitter with the VLA as the receiving instrument to create a combined radar imaging instrument. We have used this combined radar instrument to image the surface of Mars in 3.5-cm radar reflectivity during the 1988, 1992/93, and 1999 oppositions. During the 1988 experiments, the residual south polar ice cap (RSPIC) was the brightest radar reflector on the planet - intrinsically brighter than even the Tharsis lava flows. This was quite an unexpected result. In contrast, during the 1992/93 experiments, the residual north polar ice cap (RNPIC) was not nearly so bright, and in fact showed no enhancement at all, This was puzzling, given the 1988 results for the RSPIC. We attributed the lack of a radar reflection enhancement to a combination of three effects: the geometry was different; the season was different; and the intrinsic scattering from the residual ice caps was different. The 1999 experiments provided a chance to test the relative importance of these three effects, since the RNPIC would be visible in a geometry very similar to the RSPIC in 1988, and the season would also be very similar. Preliminary reduction of the data taken in 1999 shows that the RNPIC did in fact show a radar reflectivity enhancement, but that it was still not as bright as the RSPIC in 1988. Details regarding the radar reflectivity of the residual ice caps, as well as the surrounding polar layered terrains (in light of our radar reflectivity data) will be discussed. Additional information is contained in the original extended abstract.

Butler, B. J.↗
NASA NTRS2024

Dielectric Permittivity Measurements of Geologic Samples at Venus Surface Temperatures

Synthetic-aperture radar (SAR) and radar sounding are two powerful remote sensing techniques used to examine the surface and subsurface of planets. Their value is critical in the case of Venus due to this planet’s global and visually opaque cloud layer. The recently selected VERITAS and EnVision orbital missions, slated to study the planet in the early 2030’s, employ radar instruments to image the surface (VERITAS and EnVision) and probe the subsurface (EnVision). For both techniques, the complex dielectric permittivity of the surface and subsurface materials control radar backscatter intensity and penetration depth. Since the 1970’s, many studies have characterized the dielectric permittivity of geologic materials collected both on Earth and on the Moon to constrain the radar reflectivity and transparency at a variety of radar frequencies [e.g., 1]. Two consistent findings from those studies are that complex permittivity depends on both the density (or porosity) and the composition of the material. Denser materials and more metal-rich compositions tend to have higher permittivity values and to incur greater propagation path loss. Water content also elevates permittivity of otherwise dry rocks/soils/regolith [e.g., 2]. However, permittivity is independent of frequency for the 0.5-18 GHz range, within which SAR imaging commonly lies. The one aspect poorly explored thus far is the effect of elevated temperatures on dielectric permittivity. Previous work suggests that increased lattice vibrations and flow of free electrons associated with an increase in temperature elevate both the real (reflectivity) and imaginary (path loss) parts of the complex permittivity. We are currently conducting a 3-year campaign to measure the complex dielectric permittivity of Venusrelevant geologic materials at Venus surface temperatures (380°C - 460°C) and with frequencies relevant to VERITAS, EnVision, and Magellan imaging synthetic aperture radars.

M Barmatz↗
NASA NTRS1988

Diffuse scattering of radar on the surface of Venus - Origin and implications for the distribution of soils

Pioneer Venus (PV) altimeter data have been analyzed in order to study tectonic, volcanic, and degradational processes on Venus. Analysis of a corrected reflectivity data set in combination with the PV data indicates that no more than 5 percent of the Venusian surface is covered by soils more than several to tens of cm in depth. It is suggested that most regions of apparent low reflectivity are due to the presence of small roughness elements on the surface. These regions are correlated with tessera, and models show that the diffuse scatterers in the tessera are rock fragments originating as part of tectonic deformation of the surface.

Bindschadler, D. L.↗
NASA NTRS1991

Venus tectonics - Initial analysis from Magellan

The styles of lithospheric deformation, the inferred mechanical properties of the lithosphere, and their implications for the tectonic history of Venus are discussed on the basis of radar imaging and altimetry data from Magellan. Observations of the planet plains reveal a superposition of different episodes of deformation and volcanism, strain both distributed and concentrated into zones of extension and shortening, and features reflecting a crustal response to mantle dynamic processes. Lithospheric shortening and crustal thickening are represented by ridge belts and mountain belts. The latter show the evidence for extension and collapse both during and following crustal compression. Venus displays quasi-circular coronae and broad rises with linear rift zones, associated with significant volcanism. Large-offset strike-slip faults have not been observed, although horizontal shear is accommodated across broad zones of crustal shortening. On Venus strain is distributed across zones that are one to a few hundred kilometers wide, and separated by stronger and less deformed blocks hundreds of kilometers in width, as in actively deforming continental regions on earth.

Solomon, Sean C.↗
NASA NTRS1992

Microwave scattering and emission properties of large impact craters on the surface of Venus

Many of the impact craters on Venus imaged by the Magellan synthetic aperture radar (SAR) have interior floors with oblique incidence angle backscatter cross sections 2 to 16 times (3 dB to 12 dB) greater than the average scattering properties of the planet's surface. Such high backscatter cross sections are indicative of a high degree of wavelength-scale surface roughness and/or a high intrinsic reflectivity of the material forming the crater floors. Fifty-three of these (radar) bright floored craters are associated with 93 percent of the parabolic-shaped radar-dark features found in the Magellan SAR and emissivity data, features that are thought to be among the youngest on the surface of Venus. It was suggested by Campbell et al. that either the bright floors of the parabolic feature parent craters are indicative of a young impact and the floor properties are modified with time to a lower backscatter cross section or that they result from some property of the surface or subsurface material at the point of impact or from the properties of the impacting object. As a continuation of earlier work we have examined all craters with diameters greater than 30 km (except 6 that were outside the available data) so both the backscatter cross section and emissivity of the crater floors could be estimated from the Magellan data.

Stacy, N. J. S.↗
NASA NTRS1990

Geology of the Venus equatorial region from Pioneer Venus radar imaging

The data collected by Pioneer Venus have been used to map the broad radar characteristics of the equatorial region on the basis of radar brightness and texture. Seven units are defined and are used to assess the geologic character of the equatorial region. The correspondence between features in the 15 deg region of overlap between Pioneer Venus ans Venera 15/16 images is examined and used to extend units mapped in the northern high latitudes into the equatorial region. Using the properties of rms slope, reflectivity, the scattering behavior of the surface, and topographic signature, seven physiographic units are mapped on the basis of the distribution of the radar units in the equatorial region and are identified by increasing complexity as plains, dark halo plains, upland rises, upland plateaus, interhighland tectonic zones, tectonically segmented linear highlands, and tectonic junctions. The distribution of larger circular structures interpreted as coronae is also examined.

Senske, D. A.↗
NASA NTRS1992

Venus radar mapping from the Venera 15 and 16 spacecrafts: Results and restrictions

A description of the results of the Venus northern hemisphere radar survey in 1983-1984 from the Venera 15 and 16 spacecrafts is presented. In addition, we discuss some peculiarities in the function of the radar equipment that defined the technology of SAR data processing. Among these peculiarities are insufficient calibration of SAR and radar altimeter and erroneous automatic gain control data transmission from the spacecrafts. As a result, the procedure of image synthesis and mosaicking contained multistage image brightness corrections. This led to the fact that the average image brightness in a spot 100 km in diameter was constant everywhere in the mosaics. Twenty-seven radar mosaics in the Lambert-Hauss conic projection with 1-2 km spatial resolution covering 25 percent of the surface of Venus have been produced. A Venus surface roughness map was constructed by joint processing of SAR and altimeter data. The mutual calibration of the SAR and altimeter was made in the special radar session when the SAR and altimeter were declined from the local vertical at the same angle. The possibility of estimating relative variations in surface reflection properties over a tens-of-kilometers interval from Venera images is still being considered. Joint analysis of the coordinates of small features of the Venera and Magellan images is one more approach being used to refine the period of rotation for Venus.

Akim, E. L.↗
NASA NTRS1995

Wind-Related Features and Processes on Venus Summary of Magellan Results

A search of Magellan synthetic aperture radar images covering about 98% of the venusian surface shows that aeolian features occur at all longitudes and latitudes. A global data base for wind streaks, the most common type of aeolian feature, was developed. For each of the 5970 streaks in the data base, information was compiled on location, streak type, radar backscatter, dimensions, azimuth, orientation with respect to local slope, and type of landform with which it is associated. In addition, streaks occurring in association with parabolic ejecta deposits were designated type P streaks, which constitute about 31% of the data base. Wind streak azimuths were analyzed to assess wind patterns at the time of their formation. Both hemispheres show strong westward and equatorward trends in azimuths, consistent with Hadley circulation and inferred upper atmospheric westward zonal winds. When type P streaks (those considered to result from transient impact events) were removed, the westward component was greatly reduced, suggesting that the upper zonal winds do not extend to the surface. The presence of equator-oriented streaks at high latitudes suggests that Hadley circulation extends to the poles. A field of possible yardangs found southwest of Mead Crater strikes NE-SW and occupies plains situated in a shallow topographic depression. Analysis of non-type P streaks in the area suggests that equatorward winds are funneled through the depression and are responsible for the erosion of the terrain to form the yardangs. Dune deposits are limited on Venus. Two dune fields were identified (Aglonice and Fortuna-Meshkenet) which total in area about 18,300 square km. Microdunes are proposed for some southern hemisphere areas which show distinctive radar reflectivities. Bragg scattering and/or subpixel reflections from the leeward faces of microdune bedforms could account for the unusual radar backscatter cross sections.

Greeley, Ronald↗
NASA NTRS1995

Wind-Related Features and Processes on Venus: Summary of Magellan Results

A search of Magellan synthetic aperture radar images covering approximately 98% of the venusian surface shows that aeolian features occur at all longitudes and latitudes. A global data base for wind streaks, the most common type of aeolian feature, was developed. For each of the 5970 streaks in the data base, information was compiled on location, streak type, radar backscatter, dimensions, azimuth, orientation with respect to local slope, and type of landform with which it is associated. In addition, streaks occurring in association with parabolic ejecta deposits were designated type P streaks, which constitute about 31% of the data base. Wind streak azimuths were analyzed to assess wind patterns at the time of their formation. Both hemispheres show strong westward and equatorward trends in azimuths, consistent with Hadley circulation and inferred upper atmospheric westward zonal winds. When type P streaks (those considered to result from transient impact events) were removed, the westward component was greatly reduced, suggesting that the upper zonal winds do not extend to the surface. The presence of equator-oriented streaks at high latitudes suggests that Hadley circulation extends to the poles. A field of possible yardangs found southwest of Mead Crater strikes NE-SW and occupies plains situated in a shallow topographic depression. Analysis of non-type P streaks in the area suggests that equatorward winds are funneled through the depression and are responsible for the erosion of the terrain to form the yardangs. Dune deposits are limited on Venus. Two dune fields were identified (Aglonice and Fortuna-Meshkenet) which total in area about 18,300 sq km. Microdunes are proposed for some southern hemisphere areas which show distinctive radar reflectivities. Bragg scattering and/or subpixel reflections from the leeward faces of microdune bedforms could account for the unusual radar backscatter cross sections.

Greeley, Ronald↗
NASA NTRS1988

Radar observations of the inner solar system

Concurrent objectives involve dynamical information: maintenance of Mars ephemeris accuracy, Mercury closure-point ranging for relativity theory testing, and refinement of spin-vector estimates for Venus and Mercury. This task has been renamed to reflect accurately the research it supports. The backlog of unprocessed Venus data has been sharply reduced; most images from the 1980 to 1982 conjunctions, and half of those from 1986, are essentially finished. Suitably formatted data have been distributed to (non-JPL) scientific collaborators for geologic analysis, and to the Magellan project.

Jurgens, Raymond F.↗
NASA NTRS1992

Reflection and emission properties on Venus - Alpha Regio

Procedures developed from Hagfors' (1964) scattering model have been used with success to extract various properties (reflectivity, emissivity, slope, etc.) from both Pioneer Venus and Magellan data. However, under certain circumstances, such as physically rough areas or areas of nonhomogeneous composition, Hagfors' model may lead to serious errors in the interpretation of radar and radiometry data. The Magellan-derived surface properties are examined for some areas of below average emissivity in Alpha Regio and in an area to the east of Alpha, Crater Stuart, in order to determine if Hagfors' model is applicable. Methods of classical multiple scattering theory are also applied to show that enhanced radar backscattering and depressed thermal emission can be expected with a matrix of silicic or mafic rocks embedded in low loss soils.

Tryka, Kimberly A.↗
NASA NTRS1985

Mapping and Geological Analysis of Mercury and Venus Radar Ranging Data

Although many radar profiles and images of the areas within 20 deg of Mercury's equator had been obtained from 1971, at both Goldstone and Arecibo radar facilities, surprisingly little geological analysis had been done with these data until recently. Topographic profiles and radar roughness reflectivity images which can be derived from these data will be crucial in completing the geological mapping of Mercury now underway at the U.S. Geological Survey. Earth based radar observations of Mercury and the other terrestrial planets as well are a potentially very valuable tool in the determination of the physical nature of their surfaces. Processing of available radar data must be completed to establish any systematic relationship between raar reflectivities and roughness, density, dielectric constant, and other related geological parameters.

Clark, P. E.↗
NASA NTRS1983

Venus - Global surface radio emissivity

Observations of thermal radio emission from the surface of Venus, made by the Pioneer Venus radar mapper at a wavelength of 17 cm, show variations that are dominated by changes in surface emissivity. The regions of lowest emissivity (0.54 + or - 0.05 for the highland areas of Aphrodite Terra and Theia Mons) correspond closely to regions of high radar reflectivity reported earlier. These results support the inference of inclusions of material with high electrical conductivity in the surface rock of these areas.

Ford, P. G.↗
NASA NTRS1981

SAR squint analysis of directional extended targets

Results are presented for multisquint processing of L-band like-polarized (HH) SAR data. Images of agricultural fields were generated by Doppler filtering of SAR signal film, with an angular width and step size of 0.8 deg. The results indicate that field reflectivities may vary by more than 10 dB over a range of less than 1 deg. Implications of observing extremely narrow-beamwidth targets are discussed for platform-pointing and antenna-stability requirements. It is suggested that a multiazimuth Venus-orbiting imaging radar could provide a significant amount of information at a relatively low weight penalty.

Daily, M. I.↗
NASA NTRS1992

Comparison of Goldstone and Magellan radar data in the equatorial plains of Venus

Goldstone radar observations of the equatorial plains of Venus provide complementary information to that obtained by Magellan. Different radar scattering mechanisms dominate each system, leading to sampling of different surface properties. Comparison of image data and derived parameters indicate that: (1) relatively high dielectric constants on impact-related parabolic features are detected in Goldstone backscatter, Magellan reflectivity, and Magellan emissivity data; the dielectric effects are overwhelmed by roughness-related signatures in Magellan synthetic aperture radar (SAR) data; (2) lava flows in Navka Planitia show dielectric variations both among and within flows; higher dielectric constants on the perimeter of some flows may by due to a decrease in vesicularity; (3) some volcanic domes are relatively smooth at the wavelength scale and probably consist of low-density deposits; (4) comparisons of Magellan SAR data with rough surface scattering models and SAR data of terrestrial surfaces indicate that the roughness characteristics of the equatorial plains surfaces are comparable to modified terrestrial lava flows; and (5) scattering properties of an equatorial 'ridge belt' structure suggest highly weathered or soil-dominated surfaces.

Plaut, Jeffrey J.↗
NASA NTRS1997

Surface Properties of the Moon, Venus and Small Bodies from Radar Observations

Studies of the moon during the period of the grant revolved around the issues of the possible presence of ice at the lunar poles and the determination of the electrical properties of the maria regoliths. The search for ice at the poles was conducted using measurements of the radar backscatter cross sections and circular polarization ratios measured from 125 m resolution Arecibo radar imagery at 13 cm wavelength obtained by Nicholas Stacy. No clear indication of the presence of ice was found in areas thought to be in permanent shadow from solar radiation. Then Cornell graduate student Greg Black modeled the radar backscattering behavior of the icy Galilean satellites using three wavelength measurements of their radar backscattering properties obtained with the Arecibo and Goldstone radars. The radar scattering properties of Europa, Ganymede, and Callisto are unlike those of any other object observed with planetary radars. They are strongly backscattering with specific radar cross sections that can exceed unity. Polarization ratios are also high, approx. 1.5, indicative of multiple scattering, and the echos follow a diffuse scattering law at all incident angles with no indication of quasi-specular reflections. 3) Most of our effort on small bodies went into developing and investigating methods for long baseline radar synthesis imaging of near-earth asteroids and comets. At X-band, the width of the synthesized beam of the Very Long Baseline Array (VLBA) is approximately 15 m at 0.03AU, a typical close approach distance for near-earth asteroids. A small amount of work was done analyzing Venus data from Arecibo and the Magellan mission.

Campbell, Donald B.↗
NASA NTRS1987

Multifrequency and multipolarization radar scatterometry of sand dunes and comparison with spaceborne and airborne radar images

Airborne radar scatterometer data on sand dunes, acquired at multiple frequencies and polarizations, are reported. Radar backscatter from sand dunes is very sensitive to the imaging geometry. At small incidence angles the radar return is mainly due to quasi-specular reflection from dune slopes favorably oriented toward the radar. A peak return usually occurs at the incidence angle equal to the angle of repose for the dunes. The peak angle is the same at all frequencies as computed from specular reflection theory. At larger angles the return is significantly weaker. The scatterometer measurements verified observations made with airborne and spaceborne radar images acquired over a number of dune fields in the U.S., central Africa, and the Arabian peninsula. The imaging geometry constraints indicate that possible dunes on other planets, such as Venus, will probably not be detected in radar images unless the incidence angle is less than the angles of repose of such dunes and the radar look direction is approximately orthogonal to the dune trends.

Blom, Ronald↗