31st Annual Meeting of the DPS, October 1999
Session 49. Mars Atmosphere: Structure Posters
Poster Group II, Thursday-Friday, October 14, 1999, , Kursaal Center

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[49.07] ISO Observations of Mars: a Determination of the Water Vapor Vertical Distribution and the Surface Emissivity

M.J. Burgdorf (ESA), Th. Encrenaz, E. Lellouch (DESPA), H. Feuchtgruber (MPIE), G.R. Davis (University of Saskatchewan), B.M. Swinyard (RAL), Th. de Graauw, P.W. Morris (SRON), S.D. Sidher, M.J. Griffin (QMW)

Infrared spectra of Mars were taken in July and August 1997 with the LWS (Long Wavelength Spectrometer) and the SWS (Short Wavelength Spectrometer) onboard the European Space Agency's Infrared Space Observatory, ISO. They covered the wavelength range from 2.3 to 45~\mum with a spectral resolution of about 1500 and from 45 to 180~\mum with a resolution between 150 and 300. In addition, scans of selected H2O lines have been recorded in Fabry-Perot mode, where the spectral resolution is more than an order of magnitude higher.

A multitude of water lines was detected, and their strengths were determined by means of Interactive Analysis tools. Comparisons of the measured lines in the near-infrared with various synthetic spectra allowed us to obtain information about the vertical distribution of water vapor. Assuming atmospheric and surface temperatures derived from the European Martian Climate Database with a slight adjustment to the observed 15~\mum CO2 band, the ISO data indicate an H2O water distribution confined in the lower atmosphere, within the first 10-12~km above the surface, and a total column density of 15+11-7 ppt-\mum.

Once the water vertical distribution was determined, the mean surface emissivity remained as the most important unknown in the model spectra for the far infrared and could therefore be derived from the measured line to continuum ratios in the LWS range. It was found to have an average value of 0.95 ± 0.03 and to be slightly decreasing between 50 and 180~\mum.

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