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Communication Dans Un Congrès Année : 2018

Spectral albedo of Venus clouds in the UV as measured onboard the VEX orbiter

Résumé

Venus clouds possess high spherical albedo (70-80%) in the visible spectral range, and the planet disk looks very bright and homogeneous. On the other hand, the ultraviolet (UV) albedo is 2-3 times lower and the clouds appear to be very contrasted. The dark spots point out to presence of some cloud components that absorb solar radiation at wavelengths from 250 to 400 nm. One of molecules is sulfur dioxide (SO _{2}), which varies from 0.1 to 1 ppm at the cloud top [1, 2]. Other candidates are also sulfur-bearing species, sulfur S _{x} with different valences [3], OSSO [4], and even FeCl _{3} [5]. So far, there was no published precise measurement of Venus albedo in spectral range 200-400 nm that would allow retrieval the unknown UV absorbers of Venus clouds. In the present work we perform data processing from two spectrometers that measured UV albedo of Venus clouds onboard the Venus Express (VEX) orbiter in 2006-2014. The UV channel of SPICAV operated at 115-320 nm [6], while the UV-VIS channel of VIRTIS covered 300-1000 nm [7]. We have selected a few tens of simultaneous nadir observations with similar pointing that allows us combining the clouds reflectance spectra at 200-400 nm. At the moment, spectral and absolute radiance calibrations are being performed for correct merging of spectra between two spectrometers. J.-L. Bertaux and the co-authors from IKI acknowledge support by the Ministry of Education and Science of Russian Federation grant #14.W03.31.0017. REFERENCES [1] Barker E.S., 1979. Detection of SO _{2} in the UV spectrum of Venus. Geophys. Res. Lett. 6, 117-120. [2] Marcq E. et al., 2013. Variations of sulphur dioxide at the cloud top of Venus's dynamic atmosphere. Nature Geoscience, 6, 25-28. [3] Carlson R. W. et al., 2016. Venus's ultraviolet absorber: Cyclo-octal (S _{8}) and polymeric sulfur (S _{x}) and their latitudinal behavior. International Venus Conference, Oxford, 2016. [4] Frandsen B. N. et al., 2016. Identification of OSSO as a near-UV absorber in the Venusian atmosphere. Geophys. Res. Lett. 43, 11146-11155, doi:10.1002/2016GL070916. [5] Zasova L.V. et al., 1981. Vertical distribution of SO _{2} in upper cloud layer of Venus and origin of UV absorption. Adv. Sp. Science. [6] Bertaux J.-L. et al., 2007. SPICAV on Venus Express: Three spectrometers to study the global structure and composition of the Venus atmosphere. Planet. Space Sci. 55, 1673-1700. [7] Drossart P. et al., 2007. Scientific goals for the observation of Venus by VIRTIS on ESA/Venus express mission. Planet. Space Sci. 55, 1653-1672.
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insu-04437639 , version 1 (04-02-2024)

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Jean-Loup Bertaux, Denis Belyaev, Nikolay Ignatiev, Emmanuel Marcq, Emiliano d'Aversa, et al.. Spectral albedo of Venus clouds in the UV as measured onboard the VEX orbiter. 42nd COSPAR Scientific Assembly, Jul 2018, Pasadena, United States. pp.Abstract id. C3.1-2-18. ⟨insu-04437639⟩
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