The electrical characteristics of the atmosphere and surface of Venus from radar observations

Abstract

Radar observations of Venus were made at wavelengths of 12.5 cm and 68 cm during several months around the 1961 inferior conjunction. These observations have been quantitatively compared for possible dispersion effects caused by the atmosphere of Venus and the interplanetary medium. A possible effect of the plasma has been observed at 68 cm through correlations of the radar echo characteristics with solar activity. On the assumption that this correlation was real, a crude model for the ionosphere of Venus has been developed. The model yields a maximum electron density at Venus of order 10 7 cm −3 corresponding to a plasma frequency of about 27 Mcs. The absence of relative dispersion and absorption effects between the two propagation frequencies is interpreted to indicate that all plasma phenomena were small, however. In particular, the proposed “ionospheric” model as the source of the Venusian radio spectrum is shown to be inconsistent with the radar observations. An analysis of the observed echo power indicates the average dielectric constant of the Venusian surface material to be less than 7 but greater than 3 with no large upward variations during the observations. This low value of the dielectric constant and the absence of measurable variations in the echo power (and consequently, in the dielectric constant) is interpreted to indicate that there are no large bodies of water on the Venusian surface.