ISO observations of Mars: An estimate of the water vapor vertical distribution and the surface emissivity

Infrared spectra of Mars were taken with the two complementary spectrometers onboard the European Space Agency's Infrared Space Observatory (ISO), in both moderate- and high-resolution mode. From the strengths of the observed water lines we derived information about the vertical distribution of water vapor and on the emissivity of the dust/surface system in the infrared. Assuming atmospheric and surface temperatures derived from the European Martian Climate Database with a slight adjustment to the observed 15-mu m CO2 band, the ISO data are consistent with an H2O mixing ratio of (3 +/- 1) x 10(-4) at the surface, a saturation level at 13 +/- 2 km, and a total column density of 12 +/- 3.5 pr-mu m. The mean disk emissivity is found to be close to 1.0 at 6 mu m and 0.92 +/- 0.02 at 40 mu m. At longer wavelengths the emissivity decreases from a value of 0.97 +/- 0.03 at 50 mu m to 0.92 +/- 0.03 at 180 mu m. (C) 2000 Academic Press.