Polar water ice clouds and dust aerosols seasonal mapping using CRISM EPF data

Grant #: NNX11AN41G
Senior Scientist: Adrian Brown

We propose to use Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) emission phase function (EPF) measurements in the Martian poles (regions poleward of 55° latitude) to map dust and water ice aerosols and surface albedos as a function of season using CRISM data. 

To interpret the CRISM EPF data and derive water ice and dust optical depths, we will use a DISORT based radiative transfer model of the Martian atmosphere (called DISORT_multi) to iteratively fit the multi-angle EPF measurements. Under the assumption of fixed aerosol properties (i.e. grain size distributions and refractive indices) we use two specific wavelengths, 0.44 and 0.7 microns to retrieve three key parameters: 1.) the optical depth of dust 2.) optical depth of water ice and 3.) the surface albedo/reflectance. 

The derived water ice and dust optical depth will be used to explore the seasonal atmospheric conditions in the Martian polar regions and address several important polar science questions: 

* What are the rise times and decay times for polar column dust opacity during global dust events? 

* How are surface CO2 and water ice albedos affected by dust events? 

* What are column water ice opacities for water clouds in the polar region? 

The derived seasonal polar dust and water ice opacities and surface albedos will be critical for refinements to standard polar atmospheric conditions for Global Circulation Models such as the NASA Ames and LMD GCMs.