A Radar Image of Venus

Radar scans of Venus, performed at the Jet Propulsion Laboratory's Goldstone Tracking Station, have yielded a brightness map (attached) of a large portion of the surface. The bright area in the south (α) and the twin such areas in the north (β and δ) were dirst discovered by spectral analysis of radar echos. When range-gating is also applied, their shapes are revealed, and they are seen to be roundish and about 1000 km across. Although radar brightness can be the result of either intrinsic reflectivity or surficial roughness, polarization studies show these features to be rough (to the scale of the wavelength, 12.5 cm). Dark, circular areas can also be seen, many with bright central spots. The dark areas are probably smooth. The blurring of the equatorial strip is an artifact of the range-Doppler geometry; all resolution disappears at the equator. Another artifact of the method is the "ghost," in the south, of the images of β and δ. Such ghosts appear only at the eastern and western extremes of the map. Data for this radar map were taken during the close approaches of spring, 1969, and fall, 1970. Another opportunity occurs in June of 1972. Venus will present the same aspect then, except that the spin axis will be inclined slightly toward Earth. We hope to take advantage of this opportunity to fill in the blurred equatorial zone and to remove the ghost images.