Wavelength dependent visible albedo of CO2 ice in residual south polar cap of Mars using MARCI data

Abstract

The visible surface albedo of the martian residual south polar cap is an important parameter with respect to understanding the stability and evolution of the cap, as well as for investigating the interactions between the surface of the cap and the atmosphere. Extraction of the surface albedo from spacecraft images requires the removal of atmospheric effects, caused primarily by dust aerosols. Such an effort requires knowledge of not only the radiative properties of the aerosols but also their spatial distribution. Here, we use MARCI images and interpolated dust optical depth values, determined from CRISM EPF measurements in MY 28–30, in order to extract the intrinsic surface albedos of the polar cap. The CRISM opacities are referenced to a wavelength of 900 nm, whereas MARCI image span five bands ranging from 720 nm to 440 nm. To translate the CRISM values to the MARCI bands, one must prescribe the size distribution of the dust. Use of the nominal aerosol properties (i.e., reff = 1.5 µ) can result in incorrect behavior of the surface albedo at short wavelengths. In MY 28, a year with a major dust storm, the problem can be eliminated by adopting a smaller effective radius, 1.0 µm, for the dust. Additionally, in MY 29 and 30, a layer of water ice clouds capping the dust is necessary. It is therefore possible to relate the incorrect wavelength behavior to aerosol properties as well as a breakdown in the extrapolation of the EPF values to the South Polar Region.