Viking bistatic radar experiment: Summary of first-order results emphasizing north polar data |
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| Authors: | Richard A Simpson G Leonard Tyler |
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| Institution: | Center for Radar Astronomy, Stanford University, Stanford, California 94305, USA |
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| Abstract: | Bistatic radar observations of Mars' north polar region during 1977–1978 showed surface rms slope σβ ranging from 1 to 6°; these values apply to horizontal scales of 1–100 m. Values of roughness tend to decrease with increasing latitude (especially over 65–80°N), but there are many exceptions. The smoothest surfaces (σβ≤1°) appear to be inclusions within generally rougher (σβ～3°) terrain, rather than broad expanses of very smooth material. The permanent north polar cap is relatively uniform with 2.5?σβ?3.0°. Considerable structure has been found in echo spectra, indicating a heterogeneous and perhaps anisotropic scattering surface. Echo spectra obtained from the same region, but several months apart (1°<LS<62°), show no significant differences in inferred roughness. Estimates of reflectivity and dielectric constant are systematically low in the polar region. This may indicate that surface material north of 65°N is less dense than that near the equator, but more study of these data is needed. Estimates of surface roughness and dielectric constant in the equatorial region are consistent with results from Earth-based measurements to the accuracy of our analysis. |
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