Concatenation of HRSC colour and OMEGA data for the determination and 3D-parameterization of high-altitude CO2 clouds in the Martian atmosphere

Abstract : We used Mars Express HRSC and OMEGA data to investigate mesospheric cloud features observed in the equatorial belt of Mars from December 2007 until early March 2008. This period corresponds to early northern spring of Martian year 29. The reflection peak at 4.26 µm in OMEGA data identifies the clouds as CO2 ice clouds. HRSC observed the clouds together with OMEGA in five orbits. Cloud features are most prominent in the shortwave HRSC colour channels with wavelength centers at 440 nm and 530 nm, but rarely visible in all other channels. In the period of Ls 0°-36°, OMEGA and HRSC together detected mesospheric CO2 ice clouds in 40 orbits. They occur in a latitude belt of ±20° around the equator and at longitudes between 240°E (Tharsis) in the West and 30°E (Sinus Meridiani) in the East. The clouds were observed between 3 pm and 5 pm local time with mainly ripple-like to filamentary cloud forms. The viewing angles of the HRSC blue and green colour channels differ by 6.6° and the resulting parallax can be used to directly measure cloud heights by means of ray intersection. 17 HRSC data takes were found to exhibit clouds with heights from 66 km to 83 km with an accuracy of 1-2 km. The pushbroom imaging technique also yields a time delay for the two observations in the order of 5 to 15 seconds close to periapsis, and therefore time-related cloud movements can be detected. A method was developed to determine the across-track cloud displacements, which can directly be translated to wind velocities. Zonal cloud movements could be measured in 13 cases and were oriented from East to West. Related wind speeds range between 60-93 m/s with an accuracy of 10-13 m/s.
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https://hal.archives-ouvertes.fr/hal-00477373
Contributeur : Catherine Cardon <>
Soumis le : mercredi 28 avril 2010 - 20:43:54
Dernière modification le : mercredi 21 mars 2018 - 18:57:59

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Frank Scholten, Harald Hoffmann, Anni Määttänen, Franck Montmessin, Brigitte Gondet, et al.. Concatenation of HRSC colour and OMEGA data for the determination and 3D-parameterization of high-altitude CO2 clouds in the Martian atmosphere. Planetary and Space Science, Elsevier, 2010, 58 (10), pp.1207-1214. 〈10.1016/j.pss.2010.04.015〉. 〈hal-00477373〉

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