Venus: global surface radio emissivity.

Observations of thermal radio emission from the surface of Venus, made by the Pioneer Venus radar mapper at a wavelength of 17 centimeters, show variations that are dominated by changes in surface emissivity. The regions of lowest emissivity (0.54 +/- 0.05 for the highland areas of Aphrodite Terra and Theia Mons) correspond closely to regions of high radar reflectivity reported earlier. These results support the inference of inclusions of material with high electrical conductivity in the surface rock of these areas.