Venus surface data extraction from VIRTIS/VEX measurements

Abstract

The capability of near infrared nightside thermal emission measurements by the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) on Venus Express (VEX) was used to extract surface properties in the northern hemisphere of Venus. The study includes VIRTIS topographic footprint variations from – 2000 m to 6000 m in height. Preliminary radiative transfer calculation techniques were applied to simulate Venus nightside radiation with respect to the cloud opacity and surface elevation. The results were compared to the VIRTIS measurements. Below 1.5 µm conservative scattering is dominating the cloud feature, Therefore, radiance ratios in the 1.0-1.35 µm spectral windows can be used to eliminate cloud interferences. It is shown that the radiance ratios of the 1.10, 1.18, 1.28, and 1.31 µm windows with respect to the radiance in the 1.02 µm window are independent on the cloud influence. At constant cloud opacity the simulations at 1.02, 1.10, and 1.18 µm show a clear dependence of the transmitted nightside radiation on topography. An elevation change of 12 km results in a surface temperature change of 100 K. The measured and simulated window radiance ratios are in excellent agreement. The correlation between the ratios of the surface window radiances and elevations was used to retrieve the surface topography and temperatures near Beta region. VIRTIS and Magellan topographies are largely in agreement to each other but differences are obtained in certain small areas. They will be of special interest for the future separation of surface temperature, emissivity and deep atmosphere dynamic phenomena.