Spectral Observations of Venus in the Frequency Interval 18.5-24.0 GHz: 1964 and 1967-68

During July 1964, Venus was observed with a tunable radiometer at eight frequencies in the interval 20.6-24.0 GHz and again at six frequencies in the interval 18.5-24.0 GHz during an eight-month period beginning approximately one month after the inferior conjunction of 1967. Microwave spectra for these frequency intervals were computed using the results from Mariner 5 and Veneras 4-7 and compared to these data. One block of data suggests a lower percentage of H2O than that reported by the Venera probes, while other blocks may be consistent with the probe data. These data therefore suggest that the distribution of water vapor down to atmospheric levels probed at these frequencies may vary with time or else the Venera probes may have detected localized enhancements in water vapor.