Measurements of the Ka Band opacity of sulfuric acid vapor with application towards radio occultations of Venus

Abstract Radio occultation experiments are capable of providing insight into the properties of the Venus atmosphere at the boundary between the upper and lower atmosphere. To retrieve vertical profiles of atmospheric gases from Venus radio occultation experiments, accurate models for the absorption of these gases are necessary. New laboratory measurements have been made of the microwave opacity of H2SO4 vapor at Ka Band (30–45 GHz, 6.5–10 mm) in mixtures containing up to 3 bars of CO2 at temperatures ranging from 550 to 585 K, simulating the conditions of the lower atmosphere of Venus. The results of these measurements and prior microwave and millimeter-wavelength laboratory studies have been used to derive a model for H2SO4 vapor opacity valid from 1 to 150 GHz. This model is incorporated into a microwave radiative transfer model of the Venus atmosphere, which has been used to predict the penetration depth of a radio occultation signal at 32 GHz and determine the contributions of atmospheric gases to 32 GHz opacity. These results can be used to interpret signal attenuation profiles for future Ka Band radio occultations of Venus.