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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Characterization of Venera 15/16 Geologic Units from Pioneer Venus Reflectivity and Roughness Data

Geologic units have been defined for the surface of Venus from Venera 15/16 image data. A characterization of these geologic units is carried out using information on surface properties derived from Pioneer Venus (PV) reflectivity and rms slope data. The geologic context provided by Venera 15/16 units allows additional, more specific interpretations of surface radar properties to be made. Characterization of Venera units results in the definition of four groups of Venera units: (1) smooth rocky units, 2) rough rocky units, (3) rough high dielectric units, and (4) diffusely scattering units. On the basis of correlations of surface morphology to spatial and statistical distributions in rms slope and reflectivity data, we test models for the origin of the surface properties of some units. We conclude that plains and tectonic units can be contrasted in terms of the average roughness of the surface and that tectonic deformation appears to roughen the surface at 0.5- to 10-m and 5- to 50-cm scales. This tectonic weathering process appears to dominate the erosional regime of Venus. Unlike Earth or Mars, production and transport of soils dominates only a small portion (less than or equal to 5%) of the surface. Some of the Venera units display distinctive spatial and statistical distributions of PV radar data. In particular, apparent low reflectivity in the tesserae appears to be caused by small (5-50 cm) rock fragments on the surface which cause diffuse scattering at Pioneer Venus wavelengths. Analysis of models for the formation of these fragments suggests that they are due to the pervasive deformation undergone by the tesserae. Finally, aspects of this study have been used to extend results of Venera image data analysis southward of 30 deg. N lat, resulting in it prediction of the distribution of tessera. Such results can aid in Magellan investigations.

Bindschadler, D. L.↗
NASA NTRS1989

Venus surface properties deduced from radar and radiometry

The brightness of surface features on side looking radar images of Venus is determined by many factors: the angles of incidence and reflection, polarization, surface geometry and composition, and so forth. The contribution from surface properties themselves can only be deduced by combining several types of measurement. For instance, without additional information, it is impossible to distinguish the effects of changes in surface roughness from those in dielectric constant. In common with the Moon and Mars, the surface of Venus appears to scatter radar waves in two ways: small-scale surface inhomogeneities, i.e., those smaller than the incident wavelength, depolarize and scatter the energy over a wide range of angles. The Pioneer Venus radar mapper experiment made three overlapping sets of measurements of the equatorial region of Venus from 15 deg S latitude to 45 deg N; the backscatter cross section at a range of incidence angles, the shape and intensity of radar echoes from the nadir, and the microwave brightness temperature of the surface. These techniques developed during the analysis of Pioneer Venus data will be used during the Magellan mission to extract measurements of surface slopes and dielectric constants over all areas covered by the SAR and altimeter antennae, with a resolution of about 10 km. A knowledge of the mechanisms that govern surface scattering will also be useful in the analysis of higher resolution side looking radar images, particularly in distinguishing the effects of changing roughness from those caused by a long range surface tilt or changing dielectric constant.

Ford, P. G.↗
NASA NTRS2002

Investigation of Venus Surface Properties

Strong localized radar echoes have been observed at decimeter wavelengths from the highlands of Venus since the earliest radar maps were obtained over 30 years ago. These echoes are some five to ten times stronger than those from the presumably basaltic rocks seen at lower altitudes elsewhere on Venus. Observations of thermal emission from the visible disk of Venus at wavelengths corresponding to those used in the radar mapping confirm that the regions of high reflectivity also exhibit low emissivity, as expected from considerations of detailed thermodynamic balance. Two possibilities have been put forward to explain this unexpected aspect of the Venus highlands: 1) surface materials of high effective dielectric constant, probably associated with finite electrical conductivity, and 2) volume scattering associated with multiple scattering from a layer of very-low-loss material containing voids and extending down a few hundred wavelengths beneath the surface. Analogs to these two mechanisms are found elsewhere in the solar system, and each is capable of explaining the basic observations. as of the early 1990's. In 1993, however, it became possible to carry out a bistatic observation of the anomalous highland regions using the Magellan spacecraft, then in orbit about Venus. In this experiment the on-board telemetry transmitter was aimed at the planet's surface with its linear S-band polarization vector oriented at 45 deg to the spacecraft-Venus-Earth scattering plane. The pointing of the transmitting antenna was adjusted so that the spacecraft-to-illuminated-surface incidence angle equalled the Earth-to-Venus-surface incidence angle. In this way, the experiment emphasized the specular scattering component. A full Stokes-Vector analysis of the reflected signal as received on Earth was carried out as the illuminated region scanned across the highland regions of Venus. From the observed position angle of the echo, it was possible to calculate the Fresnel reflectivity of a number of regions on Venus, including the high-altitude Maxwell Montes, and to show unequivocally that the complex dielectric constant of that anomalous area was 100 +/- 50i, as compared to 4.0 (real) for the typical lowland area. Thus this experiment was able to rule out definitively an hypothesis of volume scattering as the explanation for the anomalous scattering in the Venus highlands.

Ford, Peter G.↗
NASA NTRS1992

Dielectric surface properties of Venus

It has been known for over a decade that certain high-altitude regions on Venus exhibit bizarre radar-scattering and radiothermal-emission behavior. For example, observed values for normal-incidence power reflection coefficients in these areas can exceed 0.5; enhanced back scatter in some mountainous areas in the Magellan SAR images creates a bright surface with the appearance of snow; and reduced thermal emission in the anomalous areas makes the surface there appear hundreds of degrees cooler than the corresponding physical surface temperatures. The inferred radio emissivity in several of these regions falls to 0.3 for horizontal linear polarization at viewing angles in the range 20 deg - 40 deg. Several explanations have been offered for these linked phenomena. One involves single-surface reflection from a sharp discontinuity separating two media that have extremely disparate values of electromagnetic propagation. The mismatch may occur in either or both the real (associated with propagation velocity) or imaginary (associated with absorption) components of the relevant indices of refraction, and the discontinuity must take place over a distance appreciably shorter than a wavelength. An example of such an interaction of Earth would occur at the surface of a body of water. At radio wavelengths, water has an index of refraction of 9 (dielectric permittivity of about 80), and an associated loss factor that varies strongly with the amount of dissolved salts, but is generally significant. Its single-surface radar reflectivity at normal incidence is about 0.65, and the corresponding emissivity (viewed at the same angle) is therefore 0.35. Both these values are similar to the extremes found on Venus, but in the absence of liquid water, the process on Venus requires a different explanation. Two of the present authors (Pettengill and Ford) have suggested that scattering from a single surface possessing a very high effective dielectric permittivity could explain many of the unusual characteristics displayed by the Venus surface. A second explantion relates to the volume scattering that results from successive interactions with one or more interfaces interior to the planetary surface. If the near-surface material has a moderately low index of refraction (to ensure that a substantial fraction of the radiation incident from outside is not reflected, but rather penetrates into the surface), and a very low internal propagation loss, successive internal reflections can eventually redirect much of the energy back through the surface toward the viewer. The necessary conditions for this process to be effective are a low internal propagation loss coupled with efficient internal reflection. At sufficiently low temperatures, fractured water ice displays both the necessary low loss and near-total internal reflection. The possibility that this mechanism might be acting on Venus has recently been put forward.

Pettengill, G. H.↗
NASA NTRS1980

Images of Venus by three-station radar interferometry - 1977 results

During the 1977 inferior conjunction of Venus, radar observations were made using three receiving stations as a multiple interferometer. Maps of surface reflectivity and altimetry were prepared from these observations. The new altimetry maps show considerable improvement in relation to many of the earlier maps made using the two-station interferometer. In particular, there are consistent and explainable correlations between the altimetry and reflectivity maps that did not always exist in the past. The highest-resolution maps (about 8 km) show three isolated mountains having altitudes of approximately 2 km above their environs, a pair of ridges separated by approximately 100 km and extending 800 km, and a few anomalous reflectivity features for which little or no altitude change is observed. Other maps at slightly lower resolution show a bright irregular ringed crater, a few large low-reflectivity regions, a shallow crater 150 km in diameter, a gently sloping mountain, and a short ridge running north-south. Many of the later features have been seen in earlier radar maps and should be useful in refining the spin axis and further characterizing the regolith of certain areas of Venus.

Jurgens, R. F.↗
NASA NTRS1985

Surface Units on Venus Derived from Pioneer-venus Altimetry, Roughness, and Reflectivity Measurements

The nature of the Venusian surface was revealed by Pioneer-Venus (PV) observations to be diverse at scales from tens to hundreds of kilometers. Spatial correlations of elevation, surface roughness, and radar reflectivity were investigated as a means of assessing the degree of homogeneity of surface radar properties within topographic provinces and develop a map of possible geologic boundaries. Correlations were performed in a supervised fashion whereby unit boundaries were selected on the basis of statistical and empirical studies of the individual data sets. Interpretations of these units in terms of geologic characteristics are based on the determination of physical units which are model dependent.

Peterfreund, A. R.↗
NASA NTRS1985

Unsupervised Classification of Global Radar Units on Venus

Characterization of the Venusian surface in terms of its radar properties was accomplished by application of an unsupervised, linear discriminant algorithm to two Pioneer-Venus (PV) Orbiter radar data sets: the RMS-slope (surface roughness) and reflectivity. Both databases were spatially filtered to the same effective resolution of 100 km prior to classification. A recent supervised classification study using these data was based on presupposed morphologic significance of selected data ranges. The knowledge of both Venusian geology and the geologic significance of the radar data is so limited that the data warrant a more unsupervised approach; for this study a linear discriminant classifier was chosen. This approach is purely statistical, thereby removing any observer bias. Statistical significance of the resulting clusters was evaluated by an ancillary program in which an F test utilizing the Mahalanobis' distance.

Kozak, R. C.↗
NASA NTRS1988

Venus - Surface electromagnetic properties

Pioneer Venus high-angle radar imaging data are used here to correct values of the specular power reflection coefficient for the effects of diffusely scattering small-scale surface roughness. A value of 5.0 + or - 0.9 is found for the average dielectric permittivity of the rolling plains and lowlands, suggesting that most of the Venus surface is overlain by at most only a few cm of soil or dust. The unexpectedly high values of power reflection coefficient are confirmed by observations of correspondingly low values of radiothermal emission. Thus there can be little doubt that most of the highlands contain significant amounts of a conducting mineral near the surface.

Pettengill, Gordon H.↗
NASA NTRS1990

Western Eisila Regio, Venus - Radar properties of volcanic deposits

The 1988 Arecibo Observatory dual-polarization radar images are presented for Western Eisila Regio, Venus. The polarization information and Pioneer-Venus Orbiter reflectivity and altimetry data are analyzed for volcanic deposits on two 400-500 km radius constructs, Sif and Gula Montes. Many of the large effusive deposits studied appear to require superposed flows or multiple vents to explain the observed progression of roughness along their length. High Fresnel reflectivity material may be present along the summit region of Gula Mons and in an embayed tessera-like region to the N. Radar-dark units on the flanks of Sif Mons are inferred to be pyroclastic deposits, but radar-dark features near the summits of both edifices are more consistent with very smooth lava flows. Higher spatial resolution Magellan data will be useful in testing these predictions.

Campbell, Bruce A.↗
NASA NTRS2002

Four Station Interferometric Radar Observations of Mars

Planetary targets have been observed with radar since the late 1950s when it was first used for ranging experiments with the Moon. As telescope size and power increased, it became possible to observe more distant targets (Venus, Mars, and the outer satellites). Inherent to radar observations is the uncertainty as to the source of the reflection, there being two points where range and Doppler rings intersect on a sphere. The use of interferometric methods, first used on the moon with two stations and later on Venus and Mars, solved this problem. We extend the method through the addition of a fourth receiving telescope (thus doubling the number of projected baselines) and integration of the newly available Mars Orbiter Laser Altimeter (MOLA) topographic datasets.

Larsen, K. W.↗
NASA NTRS1991

Magellan

The Magellan Mission consists of a single spacecraft to be placed in an elliptical orbit around Venus. The main objective of the mission is to perform radar imaging, altimetry, and reflectivity of 90 percent of the planet for one Venusian year (243 days). A flight profile is given, and information is presented in tabular form on the following topics: Deep Space Network support, frequency assignments, telemetry, command, and tracking support responsibilities.

Scott, J.↗
NASA NTRS1977

Probable distribution of large impact basins on Venus - Comparison with Mercury and the moon

The reported study is based on the 12.5 cm wavelength data of Rumsey et al. (1974). The considered low resolution (80 km) radar image covers an area equivalent to 19% of the surface of Venus. The study had the objective to map potential large impact structures and relate their size frequency distribution to those of Mercury and the moon. The Venus radar map was analyzed using a color television film density slicer system for enhancement of subtle changes and gross patterns of contrasting radar reflectivity. Analysis by this technique permitted the recognition of 12 possible basins with diameters exceeding 600 km on about 8% of the total surface area of the planet. The preliminary basin size frequency distribution determined for Venus from these low resolution data suggests that the cloud-covered planet could be more cratered per unit area by basins than either the moon or Mercury.

Schaber, G. G.↗
NASA NTRS1993

Spacecraft studies of planetary surfaces using bistatic radar

Spaceborne transmitters have been used in bistatic geometries for a number of planetary surface studies including inference of topography, Fresnel reflectivity, and rms surface slopes on the moon, Mars, and Venus. For the moon and Mars in particular, the bistatic geometry has enabled remote probing in regions and under conditions not obtainable with Earth-based radar systems, yielding information about surface characteristics and properties on scales of centimeters to hundreds of meters that complements monostatic radar observations. A new generation of planetary spacecraft now provides opportunities for further experiments, including more nearly complete definition of the surface scattering function and, possibly, imaging. Targets of interest include the polar regions of Venus (by Magellan) and Mars (by Mars Observer), the enigmatic icy Galilean satellites of Jupiter (by Galileo), and Saturn's largest moon Titan (by Cassini).

Simpson, Richard A.↗
NASA NTRS1984

Volcanism and rift formation in Beta Regio, Venus: New radar results

A high-resolution (approximately 2 km) image of Beta Regio, Venus, obtained with the Arecibo radar system, reveals additional details of its structure which seem to confirm past suggestions that this region consists of a rift system and associated volcanism. Numerous long linear features approximately parallel to the north-south trending trough discovered by the Pioneer-Venus Orbiter are interpreted as being indicative of extensive faulting and the detail for the radar reflectivity anomaly coincident with Theia Mons suggests that it is a major volcano situated on what would be the western bounding fault of the rift system.

Campbell, D. B.↗
NASA NTRS1985

Volcanism and Rift Formation in Beta Regio, Venus: New Radar Results

A high resolution (approximately 2 km) image of Beta Regio, Venus, obtained with the Arecibo radar system, reveals additional details of structure which seem to confirm past suggestions that this region consists of a rift system and associated volcanism. Numerous long linear features approximately parallel to the north-south trending trough discovered by the Pioneer-Venus Orbiter are interpreted as being indicative of extensive faulting and the detail for the radar reflectivity anomaly coincident with Theia Mons suggests that it is a major volcano situated on what would be the western bounding fault of the rift system.

Campbell, D. B.↗
NASA NTRS1974

Radar studies of the planets

The radar measurements phase of the lunar studies involving reflectivity and topographic mapping of the visible lunar surface was ended in December 1972, but studies of the data and production of maps have continued. This work was supported by Manned Spacecraft Center, Houston. Topographic mapping of the equatorial regions of Mars has been carried out during the period of each opposition since that of 1967. The method comprised extended precise traveling time measurements to a small area centered on the subradar point. As measurements continued, planetary motions caused this point to sweep out extensive areas in both latitude and longitude permitting the development of a fairly extensive topographical map in the equatorial region. Radar observations of Mercury and Venus have also been made over the past few years. Refinements of planetary motions, reflectivity maps and determinations of rotation rates have resulted.

Ingalls, R. P.↗
NASA NTRS1990

Distribution of tessera terrain on Venus - Prediction for Magellan

Tessera terrain is the dominant tectonic unit in the northern hemisphere of Venus and is characterized by complex sets of intersecting structural trends and distinctive radar properties due to a high degree of meter and sub-meter scale (5 cm to 10 m) roughness. Based on these distinctive radar properties, a prediction of the global distribution of tessera can be made using Pioneer Venus (PV) reflectivity and roughness data. Where available, Benera 15/16 and Arecibo images and PV diffuse scattering data were used to evaluate the prediction. From this assessment, it is concluded that most of the regions with prediction values greater than 0.6 (out of 1) are likely to be tessera, and are almost certain to be techonically deformed.

Bindschadler, D. L.↗
NASA NTRS1988

Aercibo S-band radar program

The high powered 12.6 cm wavelength radar on the 1000-ft Arecibo reflector is utilized for a number of solar system studies. Chief among these are: (1) surface reflectivity mapping of Venus, Mercury and the Moon. Resolutions achievable on Venus are less than 1.5 km over some areas, for Mercury about 30 km and for the Moon 200 m at present, (2) high time resolution ranging measurements to the surfaces of the terrestrial planets. These measurements are used to obtain profiles and scattering parameters in the equatorial region. They can also be used to test relativistic and gravitational theories by monitoring the rate of advance of the perihelion of the orbit of Mercury and placing limits on the stability of the gravitational constant, (3) measurements of the orbital parameters, figure, spin vector and surface properties of asteroids and comets, and (4) observations of the Galilean Satellites of Jupiter and the satellites of Mars, Phobos and Deimos. The Galilean Satellites of Jupiter were re-observed with the 12.6 cm radar for the first time since 1981. Much more accurate measurements of the scattering properties of the three icy satellites were obtained that generally confirmed previous observations. Unambiguous measurements of the cross section and circular polarizations ratio of Io were also obtained for the first time. The radar scattering properties of four mainbelt asteroids and one near-earth asteroid were studied.

Campbell, Donald B.↗