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Keywords:

  • Mars;
  • atmosphere;
  • Composition;
  • CRISM

[1] The Compact Reconnaissance Imaging Spectrometer for Mars on the Mars Reconnaissance Orbiter spacecraft has been collecting spectra in the visible to near-infrared wavelength range for over 5 years (approximately 3 Martian years). Observations consist of image cubes, with two main selections of spectral sampling (74 and 545 spectral channels) and two main selections of spatial sampling (approximately 20 and 200  m/pixel). Retrievals of gas abundances, specifically CO2, H2O, and CO, are performed from spectra collected in all observation modes. The retrievals are efficiently performed using a look-up table, where the strength of gas absorption features are precalculated for an N-dimensional discrete grid of known input parameters (season, location, environment, viewing geometry, etc.) and the one unknown parameter to be retrieved (gas abundance). A reverse interpolation in the look-up table is used to match the observed strength of the gas absorption to the gas abundance. This algorithm is extremely fast compared to traditional radiative transfer computations that seek to recursively fit calculated results to an observed spectral feature, and can therefore be applied on a pixel-by-pixel basis to the tens of thousands of Compact Reconnaissance Imaging Spectrometer for Mars images, to examine cross-scene structure as well as to produce climatological averages.