Spectral Observations of Venus Near 1-CENTIMETER Wavelength

During June and July, 1964, measurements of Venus were made with a five-channel microwave radiometer operating at wavelengths of 0.93, 1.02, 1.18, 1.28, and 1.37 cm simultaneously. A single- channel radiometer at 1 A2-cm wavelength was used separately. The antenna was a 28-foot paraboloid located at Lincoln Laboratory, Massachusetts Institute of Technology. The spectrum of Venus was determined by comparison with the Moon. The antenna patterns measured at each frequency were used to relate the observations of the Moon and Venus. The absorption in the terrestrial atmosphere was determined by solar extinction measurements and by measurements of ground4evel humidity. The average observed brightness temperatures and relative rms uncertainties for thirteen separate experiments were: 430 i 24 K 463 + 32 K 428 + 20 K 450 + 23 K, 404 + 28 K and 572 + 82 K, in order of increasing wavelength. The results suggest that near 1.3-cm wavelength there was a resonant absorption feature that was most prominent within a few weeks of inferior conjunction, and that disappeared approximately five weeks after conjunction. This time variation is consistent with the results of other observers. The suggested feature is near the wavelength of a strong water-vapor resonance.