ISO Observations of Mars: An Estimate of the Water Vapor Vertical Distribution and the Surface Emissivity
de Graauw, Th.; Forget, F.; Lellouch, E.; Feuchtgruber, H.; Griffin, M. J.; Morris, P. W.; Swinyard, B. M.; Lim, T. L.; Encrenaz, Th.; Sidher, S. D.; Burgdorf, M. J.; Davis, G. R.
Spain, France, Germany, Canada, United Kingdom, Netherlands
Abstract
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-μm CO 2 band, the ISO data are consistent with an H 2O mixing ratio of (3±1)×10 -4 at the surface, a saturation level at 13±2 km, and a total column density of 12±3.5 pr-μm. The mean disk emissivity is found to be close to 1.0 at 6 μm and 0.92±0.02 at 40 μm. At longer wavelengths the emissivity decreases from a value of 0.97±0.03 at 50μm to 0.92±0.03 at 180 μm.