Opacity of the Martian Atmosphere from the Mars Orbiter Laser Altimeter (MOLA) observations

In this paper we present an analysis of the Mars Orbiter Laser Altimeter (M OLA) reflectivity measurements from the Mars Global Surveyor (MGS) spacecra ft, during period of solar longitudes (L-s) 198 degrees --> 212 degrees. Re flectivity can be interpreted as a product of the surface geometrical albed o and the two-way atmospheric transmission. Relative surface albedos were o btained from the red filter of Viking Color Mars Digital Mosaics (MDIM) to derive opacities at the MOLA wavelength (1.064 mu m). Opacity measurements are interpreted in terms of atmospheric aerosol loading in the canyons. We also observed sudden increase of opacity in the northern regions ( 65 degre es N), which we interpret as condensing ice clouds.