31st Annual Meeting of the DPS, October 1999
Session 67. Mars Atmosphere: Relation to Surface Features and Poles I
Contributed Oral Parallel Session, Friday, October 15, 1999, 9:40-10:00am, Sala Plenaria

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[67.01] Observations of reflectivity of the Martian surface in the Mars Orbiter Laser Altimeter investigation

A. B. Ivanov, D. O. Muhleman (Caltech)

The Mars Orbiter Laser Altimeter (MOLA) is an instrument on board the Mars Global Surveyor (MGS) spacecraft. The laser operates at the 1.064 micron wavelength. MOLA measures range to the planet's surface, reflectivity and returned pulse width. Reflectivity (R) is a ratio of the returned energy to the emitted energy. It can be interpreted as a product of albedo (A) of the Martian surface and two-way atmospheric transmission ( R = A * e-2 \tau), where \tau is total atmospheric opacity. Attenuation of the MOLA signal in the atmosphere is only due to extinction of photons from the laser beam. There are practically no photons scattered into the laser beam. This allows us a very straightforward calculation of albedo, given the opacity of the atmosphere.

At the same time the MGS Thermal Emission Spectrometer (TES) was performing measurements of opacity at 9 micron wavelength (Smith et al., 1999). We propose to use these opacities to calculate albedo of the Martian surface from MOLA observations. Appropriate scaling should be applied to TES 9 micron opacity to scale it to the 1.064 micron wavelength, where MOLA operates. This scaling depends on the assumed particle size distribution of dust, suspended in the atmosphere. We will investigate the effect of this assumption on our final albedo results.

MOLA has performed measurements of reflectivity during Science Phasing (Ls = 300 - 7) and Mapping (Ls = 103-170) orbits. We will concentrate our albedo calculations on reflectivities obtained by MOLA during the mapping orbit in the darker regions of Mars (Chryse Planitia, North Polar Dune fields). The resulting albedo dataset can then used to estimate the opacity during the Science Phasing Orbit period.


Smith M.D. et al., Mars Global Surveyor Thermal Emission Spectrometer (TES) observations of dust opacity during aerobraking and science phasing, submitted to JGR-Planets, 1999

The author(s) of this abstract have provided an email address for comments about the abstract: anton@gps.caltech.edu

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