Measurements of the atmospheric water vapor on Mars by the Imager for MarsPathfinder

The Imager for Mars Pathfinder (LMP) was the first instrument to measure th e atmospheric water on Mars from its surface. It took the images of the Sun through the Martian atmosphere in five narrowband filters, two in the 0.94 mu m H2O band and three in the continuum around it. The observations were carried out in the mornings and in the evenings when the Sun was between 3 degrees and 8 degrees above the horizon. The absorption due to the atmosphe ric water vapor did not exceed 2%. An average column density of 6+/-4 preci pitated microns (pr mu m) was derived from the IMP data. The dependence of the observed H2O transmittance on Sun elevation tentatively implies that th e water vapor is not uniformly mixed in the atmosphere but is rather confin ed to a layer 1-3 km thick near the surface. IMP observations also indicate a horizontal inhomogeneity of the layer but show no significant morning-to -evening variations of the water vapor amount.