Radar measurements of Martian topography and surface properties: The 1971 and 1973 oppositions

The Goldstone radar system was used at a wavelength of 12.6 cm to probe the Martian surface during the 1973 opposition. Measurements of range and reflected power were made at least weekly between July 12 and November 24. Surface cells isolated by the radar system were 8 km E-W × 110 km N-S. Altitudes were calculated from signal time delays measured relative to a triaxial ellipsoid and were combined with altitudes measured during the 1971 opposition. Contours of constant altitude were calculated at 200 m intervals between latitudes ?14° and ?22°. These contours are presented in conjunction with Mars charts derived from Mariner 9 television pictures. Reflected power was measured at angles of incidence between ?5° and +5°. These measurements were combined with those obtained during the 1971 opposition. Predictions of the reflected power versus the angle of incidence were calculated from the exponential surface model of Hagfors. The predictions were fit to the data in a least-squares sense, using a nonlinear iterative procedure, to yield estimates of surface roughness and reflectivity. The smoother regions exhibit a typical reflectivity of 8.2%. A tendency for the reflectivity to decrease with increasing roughness was observed.