Symposium on Radar and Radiometric Observations of Venus during the 1962 Conjunction: Study of Venus by CW radar
Between 1 October and 17 December 1962, when Venus was closest to the earth, radar observations were made on a nearly daily basis at the NASA,"JPL Deep Space Instrumentation Facility at Goldstone, Cali- fornia. During these observations, several different experiments were performed. One of these was to obtain high-resolution spectra of the reflection from Venus of a CW signal. These spectra show a detail that ap- peared to move slowly from day to day. If the detail is the result of an actual surface feature on Venus, then its motion would be due to the planet's rotation. Assuming this to be the case, the motion of the detail corresponds to an angular velocity of about half of that expected if Venus were rotating synchronously. The angular velocity leads to a sidereal rotation period of either 1200 days forward or 230 days retrograde. Measurements of the base bandwidth of the signal versus date are incompatible with both synchronous and the 1200-day forward rotation. They lead to a retrograde period of 266 days. An analysis of the base bandwidth measurements for both the 1961 and 1962 inferior conjunctions appears to preclude the possi- bility that the axis of Venus lies near the plane of its orbit. It is concluded that the most consistent inter- pretation of the data is that Venus rotates retrograde with a sidereal period of about 250 days and that its axis is approximately perpendicular to its orbit. Estimates of the opacity of Venus' atmosphere to the radar's wavelength (12.5 cm) indicate that the absorption is small. A backscattering function is derived from a CW spectrum that suggests that Venus is significantly smoother than the moon. The reflectivity and di- electric constant were found to be 9.75% and 3.75, respectively, suggesting that Venus has a dry, sandy, or rocky surface. An attempt is made to estimate the rms slope of the surface. The results obtained from an analysis of the backscattering function and the autocorrelation function of the signal suggest that the rms slope is between 4 and 7 deg.