Scattering properties of the Venusian surface: Preliminary results from Magellan

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Abstract
Radar backscatter functions for incidence angles 0≤ϕ≤4°–10° have been derived from Magellan altimetry radar echoes. The procedure includes constrained solution of a system of simultaneous equations for which the echo spectrum and echo time profile are inputs. An initially practical and workable set of constraints has been applied; optimization and improved results are expected as the analysis matures. The scattering functions yield information on small scale surface structure (tens of centimeters to tens of meters) but averaged over hundreds of square kilometers. RMS surface slopes derived from fits of analytic functions to the results have been converted to map form and show patterns similar to those reported using other techniques. A scattering law of exponential form matches the data better than either the Hagfors or Gaussian form in most areas, but the Hagfors function is generally best at the smoothest sites. Limited study of radar image data indicates that average backscatter cross section, and possibly its derivative with incidence angle, can be derived at oblique angles (17°≤ϕ≤45°). The altimetry results in combination with those derived from the synthetic aperture radar will strongly constrain the form of over the range 0≤ϕ≤45°. Offsets of the echo peak in altimetry spectra from those expected of nadir echoes are surprisingly common and are loosely correlated with Venus topography; to date no specific cause for this phenomenon has been identified.