Retrieval and study of near-infrared surface emissivity maps of Themis Regio on Venus with VIRTIS-M (Venus Express)

Abstract

Surface emissivity maps of Themis Regio on Venus have been derived from nightside radiance spectra acquired by VIRTIS-M-R aboard Venus Express to explore the region’s geology. The emissivity retrieval bases on a new approach combining a full radiative transfer model to simulate the spectra and a multi- spectrum retrieval algorithm to retrieve parameters that are common to a set of spectra. Assuming geologic activity to be negligible during the observations, the emissivity maps at 1.02 μm, 1.10 μm, and 1.18 μm were retrieved as parameter vector that is common to many spectral image cubes covering Themis Regio. This approach provides the so far most precise semi-quantitative emissivity data at Themis Regio in the near IR range. Resulting emissivity maps display clear spatial variations relative to a referance value. We discuss the relevance of these variations to geologic structures and surficial properties.