Refinements in the data analysis of VIRTIS-M-IR Venus nightside spectra

Abstract

The successful long-duration radiation measurements performed by the VIRTIS instrument aboard ESA’s Venus Express spacecraft have provided an excellent collection of atmospheric and surface data that stand out due to their high temporal and spatial coverage of the planet and due to a high diversity of measurement and environmental conditions.A detailed investigation of the VIRTIS-M-IR data archive is described and possible improvements in the analysis of Venus night and dayside spectra are discussed. These improvements are both based on the application of new retrieval algorithms and on some calibration and data preprocessing refinements including a detector sensitivity investigation, an advanced straylight removal technique, and the allocation of a revised surface topography model customized to the intended surface and deep atmosphere parameter retrieval. Different data binning schemes are investigated and recommendations for their use, based on scientific objectives, are given.While the precise impacts on the retrieved parameters are difficult to summarize in a few numbers due to the sophisticated relations between the measurement space and the high dimensional parameter space, some general or exemplary trends are presented. Compared to retrieval results from spectra based on the earlier calibration and preprocessing pipeline, for instance CO and SO2 can display a column density change in the order of 10%, and the surface emissivity at 1.02μm can exhibit changes in the order of 0.2 and up to 0.36 in an example. Such changes can lead to different interpretations concerning atmospheric and geologic properties of Venus.The proposed refinements and the corresponding mathematical tools exploit the limits of what can be achieved with the available data. They enhance the retrieval reliability of atmospheric and surface parameters of Venus.Some of the tools described in the paper are not only very useful for VIRTIS data analyses, but should also provide interesting suggestions for a handling of data from other spaceborne experiments.