Spectroscopic studies of Venusian atmosphere by BepiColombo's MERTIS instrument during the two Venus flybys
- 1DLR, Institute of Planetary Reaseaech, Berlin, Germany (gabriele.arnold@dlr.de)
- 2Institute of Geoscience, University Potsdam, Karl-Liebknecht-Str. 24-25, 14476 Potsdam
- 3Institute of Planetology, Westfälische Wilhelms-Universität Münster, 48149 Münster, Germany
Introduction
The MErcury Radiometer and Thermal Infrared Spectrometer (MERTIS) onboard BepiColombo is designed to study and map Mercury surface mineralogy and temperatures. It combines an imaging push-broom infrared spectrometer (TIS, 7-14 µm) with a radiometer (TIR, 7-40 µm) that share the same in-flight optics, electronics, and calibration unit [1]. During the two Venus flybys of BepiColombo spacecraft in October 2020 and August 2021, MERTIS-TIS acquired several hundred thousand spectra in the mid-infrared range with spectral resolution down to 90 nm [2, 3, 4]. The MERTIS measurements were the first spectrally resolved observations of Venus in the mid-IR range since the Venera 15 mission in 1983 [8]. We report on the results of MERTIS mid IR measurements and show average brightness temperature spectra. Basing on a multi-channel radiative transfer simulation and retrieval algorithm we extract atmospheric temperature profiles and cloud parameters of Venus’ upper troposphere and mesosphere.
Method
A multi-channel radiative transfer simulation and retrieval algorithm has been adapted to investigate MERTIS-TIS data and to extract atmospheric temperature altitude profiles and cloud mode factors MF1/2 of Venus’ atmosphere. The Radiative Transfer Model (RTM) includes the discrete ordinate package DISORT [5]. It considers absorption, emission, and multiple scattering by gaseous and particulate atmospheric constituents and makes simultaneous use of information from different spectral ranges of an individual spectrum [6,7]. Mesospheric temperature profiles are retrieved using Smith’s relaxation method [8]. It employs initial and measured brightness temperatures in the 15 µm CO2 band. The results of the MERTIS measurements were compared with mid-infrared data recorded by the FS-1/4 spectrometer (PMV) aboard the Venera-15 mission in 1983 [8].
Results
We show that Venusian mesospheric parameters like temperature profiles and cloud properties can reliable determined from MERTIS flyby data (Fig. A). The short-wave edge of the 15-µm CO2 band was used to determine atmospheric temperature profiles in an altitude range of about 58-77 km (Fig. B). The retrieved temperature profiles well agree both with VIRA [9] and corresponding profiles obtained from Venera 15 PMV data.
Atmospheric cloud factors were investigated from MERTIS spectral data around 10 µm. They are also well coinciding with earlier analyses. Still ongoing refinements of calibration will allow the use of data between 7 and 10 μm for the analysis of further atmospheric properties.
Fig. MERTIS-TIS FB2, A: Comparison of measured and simulated MERTIS brightness temperature spectra, B: Comparison of initial and retrieved temperature profiles.
References
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How to cite: Arnold, G., Haus, R., Helbert, J., D'Amore, M., Maturilli, A., and Hiesinger, H.: Spectroscopic studies of Venusian atmosphere by BepiColombo's MERTIS instrument during the two Venus flybys, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-156, https://doi.org/10.5194/epsc2022-156, 2022.
