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Title: Retrieval of water vapor column abundance and aerosol properties from ChemCam passive sky spectroscopy

In this work, we derive water vapor column abundances and aerosol properties from Mars Science Laboratory (MSL) ChemCam passive mode observations of scattered sky light. This paper covers the methodology and initial results for water vapor and also provides preliminary results for aerosols. The data set presented here includes the results of 113 observations spanning from Mars Year 31 L s = 291° (March 30, 2013) to Mars Year 33 L s= 127° (March 24, 2016). Each ChemCam passive sky observation acquires spectra at two different elevation angles. We fit these spectra with a discrete-ordinates multiple scattering radiative transfer model, using the correlated-k approximation for gas absorption bands. The retrieval proceeds by first fitting the continuum of the ratio of the two elevation angles to solve for aerosol properties, and then fitting the continuum-removed ratio to solve for gas abundances. The final step of the retrieval makes use of the observed CO 2 absorptions and the known CO 2 abundance to correct the retrieved water vapor abundance for the effects of the vertical distribution of scattering aerosols and to derive an aerosol scale height parameter. Our water vapor results give water vapor column abundance with a precision of ±0.6 precipitablemore » microns and systematic errors no larger than ±0.3 precipitable microns, assuming uniform vertical mixing. The ChemCam-retrieved water abundances show, with only a few exceptions, the same seasonal behavior and the same timing of seasonal minima and maxima as the TES, CRISM, and REMS-H data sets that we compare them to. However ChemCam-retrieved water abundances are generally lower than zonal and regional scale from-orbit water vapor data, while at the same time being significantly larger than pre-dawn REMS-H abundances. Pending further analysis of REMS-H volume mixing ratio uncertainties, the differences between ChemCam and REMS-H pre-dawn mixing ratios appear to be much too large to be explained by large scale circulations and thus they tend to support the hypothesis of substantial diurnal interactions of water vapor with the surface. Our preliminary aerosol results, meanwhile, show the expected seasonal pattern in dust particle size but also indicate a surprising interannual increase in water–ice cloud opacities.« less
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6] ;  [7] ;  [7] ;  [7] ;  [7] ;  [8] ;  [8] ;  [9] ;  [10] ;  [11] ;  [11] ;  [12] ;  [13]
  1. Univ. of Maryland, College Park, MD (United States). Department of Astronomy; NASA Goddard Space Flight Center, Greenbelt, MD (United States)
  2. NASA Goddard Space Flight Center, Greenbelt, MD (United States)
  3. Space Science Institute, Boulder, CO (United States)
  4. Planetary Science Institute, Tucson, AZ (United States)
  5. Texas A & M Univ., College Station, TX (United States)
  6. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  7. Institut de Recherche en Astrophysique et Planetologie, Toulouse (France)
  8. Finnish Meteorological Institute, Helsinki (Finland)
  9. Finnish Meteorological Institute, Helsinki (Finland) ; Kansas State Univ., Manhattan, KS (United States)
  10. Univ. of Michigan, Ann Arbor, MI (United States). Department of Climate and Space Sciences and Engineering
  11. Jet Propulsion Laboratory, Pasadena, CA (United States)
  12. Johns Hopkins University Applied Physics Laboratory, Laurel, MD (United States)
  13. Arizona State University, Tempe, AZ (United States)
Publication Date:
Report Number(s):
Journal ID: ISSN 0019-1035
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Additional Journal Information:
Journal Volume: 307; Journal ID: ISSN 0019-1035
Research Org:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org:
USDOE; National Aeronautic and Space Administration (NASA)
Country of Publication:
United States
79 ASTRONOMY AND ASTROPHYSICS; Planetary Sciences; Mars; Atmosphere; Spectroscopy; Radiative transfer
OSTI Identifier: