Statistics – Applications
Scientific paper
Jan 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004adspr..34.1673j&link_type=abstract
Advances in Space Research, Volume 34, Issue 8, p. 1673-1676.
Statistics
Applications
1
Scientific paper
Mars Global Reference Atmospheric Model (Mars-GRAM 2001) is an engineering-level Mars atmosphere model widely used for many Mars mission applications. From 0 80 km, it is based on NASA Ames Mars General Circulation Model (MGCM), while above 80 km it is based on University of Arizona Mars Thermospheric General Circulation Model. Mars-GRAM 2001 and MGCM use surface topography from Mars Global Surveyor Mars Orbiter Laser Altimeter (MOLA). Validation studies are described comparing Mars-GRAM with Mars Global Surveyor Radio Science (RS) and Thermal Emission Spectrometer (TES) data. RS data from 2480 profiles were used, covering latitudes 75°S 72°N, surface to ˜40 km, for seasons ranging from areocentric longitude of Sun (Ls) = 70 160° and 265 310°. RS data spanned a range of local times, mostly 0 9 and 18 24 h. For interests in aerocapture and precision landing, comparisons concentrated on atmospheric density. At a fixed height of 20 km, measured RS density varied by about a factor of 2.5 over the range of latitudes and Ls values observed. Evaluated at matching positions and times, average RS/Mars-GRAM density ratios were generally 1 ± 0.05, except at heights above ˜25 km and latitudes above ˜50°N. Average standard deviation (SD) of RS/Mars-GRAM density ratio was 6%. TES data were used covering surface to ˜40 km, over more than a full Mars year (February, 1999 through June, 2001, just before start of a Mars global dust storm). Depending on season, TES data covered latitudes 85°S 85°N. Most TES data were concentrated near local times 2 and 14 h. Observed average TES/Mars-GRAM density ratios were generally 1 ± 0.05, except at high altitudes (15 30 km, depending on season) and high latitudes (>45°N), or at most altitudes in the southern hemisphere at Ls ˜ 90° and 180°. Compared to TES averages for a given latitude and season, TES data had average density SD about the mean of ˜2.5% for all data, or ˜1 4%, depending on time of day and dust optical depth. Average SD of TES/Mars-GRAM density ratio was 8.9% for local time 2 h and 7.1% for local time 14 h. Thus SD of observed TES/Mars-GRAM density ratio, evaluated at matching positions and times, is about three times the SD of TES data about the TES mean value at a given position and season.
Duvall Aleta
Johnson David L.
Justus C. G.
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