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[54.07] Multiple Scattering Retrieval of the Martian Atmosphere from TES Spectra during the Noachis Dust Storm

D.M. Kass, D. Crisp, F.S. Anderson (Jet Propulsion Laboratory, CalTech), TES Instrument Team

The Thermal Emission Spectrometer (TES) measures the IR radiation from Mars. We use a Smith type retrieval scheme to determine the vertical atmospheric temperature structure, dust and ice opacity based on the TES spectra. We are using the nadir looking profiles and thus are concentrating on the lower ~40 km of the atmosphere. The retrieval scheme uses a spectrum-resolving multiple scattering radiative transfer code (SMART, Meadows and Crisp [1996]). The inclusion of multiple scattering allows for significant confidence in the retrievals when there is a large aerosol load in the atmosphere. Unfortunately it is also computationally quite expensive and thus can only be used on a small number of spectra.

Our initial work focuses on the Noachis dust storm seen by MGS during the aerobraking phase. This period was chosen because the high dust opacities are where multiple scattering is expected to be the most important. There is also considerable interest in understanding the thermal structure of a Martian dust storm. The temperature profile is primarily derived from the 15 micron CO₂ absorption feature, while the dust opacity is derived based on a broad region around 9 micron. In some cases, we have been able to retrieve some details of the vertical distribution of the dust in the storm. In particular, we can determine the pressure of the ``top'' of the dust cloud, although this may be sensitive to our assumed dust radiative properties. We have also compared our retrieval results to those done by Conrath et al. [2000].

This work was supported by the NASA Planetary Atmospheres Program, and conducted at the Jet Propulsion Laboratory, California Institute of Technology.