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R.A. Simpson, G.L. Tyler (Stanford Univ.)
During three orbits in May, the Mars Global Surveyor (MGS) high-gain antenna was aimed toward the planet's surface and followed the specular point as it moved from near 85S latitude to the equator. On at least one orbit, the track crossed the target area for the Mars Polar Lander (MPL) and Deep Space 2 (DS2) spacecraft. The ratio of echo powers in orthogonal circular polarizations can be used to infer the dielectric constant of a reflecting surface as a function of incidence angle. In this case, the calibration system which allows absolute determination of power in each channel malfunctioned. Assuming nominal performance, however, we derive a dielectric constant of approximately 2.3 in the MPL/DS2 area -- somewhat lower than 'average' Mars values obtained in experiments with other spacecraft and from Earth but consistent with loosely packed soil, snow, or both. Echo properties are stable over a range of latitudes, indicating that the dielectric constant (and density of the surface material) is relatively uniform. We infer from these results that the MPL/DS2 target area is not anomalous within the larger context of the southern polar layered terrain.