Venus Express bistatic radar: High‐elevation anomalous reflectivity

Abstract

[1] Magellan (MGN) bistatic radar observations in 1994 confirmed earlier Pioneer Venus reports of unusual Venus surface reflectivity and emissivity at elevations above 6054 km radius. They also revealed that the anomalous values of surface dielectric constant e near Cleopatra Patera included a large imaginary component (e % Ài 100) at 13 cm wavelength, consistent with a semiconducting surface material. The MGN observations were conducted using a linearly polarized wave, canted at 45°with respect to the plane of incidence and radiated by the MGN synthetic aperture radar antenna toward the specularly reflecting region of the mean planetary surface. In 2006 similar experiments were conducted using 13 cm circularly polarized transmissions from Venus Express (VEX). The VEX signal-to-noise ratio (SNR) was lower than that of MGN, but elevated jej has been inferred broadly over Maxwell Montes. A quasi-specular echo was detected near Cleopatra but with insufficient SNR to address the question of conductivity. An early failure of the VEX 13 cm radio system precludes further measurements with VEX.

High circular polarization ratios in radar scattering from geologic targets

“…This same study found that the linear polarization ratio, analogous to σ 0 HV / σ 0 HH , has a maximum of about 0.5. As with other regions of Venus above about 6053‐km planetary radius, Maxwell Montes has enhanced surface reflectivity, consistent with a real dielectric constant of 20 or more and a potentially very high imaginary component [e.g., Simpson et al , 2009]. From Section 3, we expect that echoes arising from the dihedral mechanism will exhibit a steady increase in CPR as the real dielectric constant rises.…”

Orbital bistatic radar observations of asteroid Vesta by the Dawn mission

“…Over the past decades, orbital BSR experiments have been used to assess the textural (and in some cases, dielectric) properties of the surfaces of terrestrial bodies such as Mercury 2 , Venus 3 , the Moon 4 – 6 , Mars 7 , 8 , Saturn’s moon Titan 9 , and now comet 67P/CG 10 . In contrast to most orbital BSR experiments, Dawn’s HGA beam intersected Vesta’s surface at grazing angles of incidence near 89° and in a microgravity environment with substantial variability in its gravity field 11 , leading to a low and variable orbital velocity and hence a more challenging detection of the Doppler-shifted surface echo (hereafter simply referred to as the “surface echo”).…”

Venus: A phase equilibria approach to model surface alteration as a function of rock composition, oxygen- and sulfur fugacities

“…Beyond these hints of unusual bulk composition, tesserae in northern latitudes such as Maxwell Montes and other mountain ranges around Ishtar Terra show an abrupt change in radar backscatterabove ~5 km elevation, they have very high backscatter (high reflectivity) and appear in SAR images as if they were covered with "snow" (Masursky et al, 1980;Pettengill et al, 1988;Garvin et al, 1985;Klose et al, 1992a;Pettengill et al, 1992;Simpson et al, 2009;Treiman et al, 2016). The cause and nature of this "snow," and the abrupt change in radar backscatter at a "snow line" in the northern highlands, have been debated vigorously.…”