Retrieving Mars aerosol optical depth from CRISM/MRO imagery

Analysis of near infrared hyperspectral images for the detection, mapping and characterization of surface materials on Mars requires the modeling and the correction of the atmospheric (gas and aerosols) spectral effects on the spectra. The CRISM imaging spectrometer offers unprecedented possibilites in that matter since it performs a sequence of Emission Phase Function measurements accompanying every high resolution nadir image. In this paper we propose an original method to retrieve the optical depth of the Martian aerosols over the targeted scene. The method is based on the dependence of the intensity of the CO2 gas absorption bands that mark the spectra with the amount of aerosols and with the geometry of the acquisition. Retrieving the atmospheric opacity is the first step toward getting surface reflectance.