Infrared solar occultation sounding of the Martian atmosphere by the Phobos spacecraft

A spectrometer designed at the Space Research Institute, Moscow, for solar occultation measurements of the Martian atmosphere from the Phobos spacecraft has the spectral range 2706–2740 and 5293–5372 cm −1 in the first and second diffraction orders, respectively, with resolving power λ/ Δλ = 1200. Data on the water vapor distribution in the Martian atmosphere were derived from nine occultation profiles at low latitudes and give a mean mixing ratio of 150 ppm below 12 km decreasing to 3 ppm at 40 km. The total amount of the water vapor is 10 μm of precipitable water. Mean scale height of water vapor is 3.8 km between 12 and 45 km. Small-scale variations of the water vapor density, though close to the experimental errors, may be caused by tidal waves with an amplitude of 2 K near 20 km and 5 K at 40 km with a further increase to 15 K at 100 km. The volume extinction coefficients and their spectral slopes at 1.9 and 3.7 μm have been measured to study the properties of aerosols in the Martian atmosphere.