Detection of Venus surface anomalies in the Northern hemisphere by VIRTIS/VEX and discussion of retrieved results

Venus nightside emission measurements by the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) aboard Venus Express (VEX) are used to extract information about surface features in the Northern hemisphere of the planet. A radiative transfer calculation technique is applied to simulate Venus nightside radiation as a function of surface, atmospheric and instrumental parameters. A radiance ratio based quick-look extraction of topographic information is compared to Magellan radar data. Some discrepancies are identified. These anomalies are examined in detail using a new multi-spectral retrieval algorithm. The anomalies are discussed in terms of possible surface emissivity variations. Radiance spectrum retrievals along several complete Northern hemisphere orbits indicate an emissivity decrease in the highlands in accordance with increased Magellan radar reflectivities