Rotation Rate of Venus measured by Radar Observations, 1964

Abstract

DUBING the June 19, 1964, close approach of Venus, radar observations at 410.25 Mc/s were made using the 250-ft. Mark I radio telescope at Jodrell Bank. Echoes were first obtained at full strength on June 5 and continued at intervals until July 26. The equipment¹ was basically that used in 1962: a C.W. radar system in which the quantities measured were the doppler shift and the frequency spectrum of the returned signal. Modifications to the receiver, including the use of a parametric amplifier, improved the signal-to-noise ratio to give a radio frequency signal to noise at closest approach of about 0.5. Again the spectral analysis was made with a multi-channel real-time integration system, having eleven channels in frequency each approximately 1 c/s wide spaced 1 c/s apart. As in 1962, the spectrum was very narrow, most of the energy being in one channel. Owing to the improved signal-to-noise ratio, however, significant rises were obtained in at least two channels on each side of the centre. Examples of the channel readings for June 17 and July 14 are shown in Fig. 1. These have been corrected for a 10 per cent bias by integrations of noise to determine correction factors.