A NOVEL ATMOSPHERIC REMOVAL TECHNIQUE FOR TES SPECTRA APPLIED TO ROCKS IN THE NILI FOSSAE REGION, MARS

Spectra from the Mars Global Surveyor Thermal Emission Spectrometer (TES) display a combination of features attributable to surface and atmospheric components. In order to fully recognize and interpret surface spectral features, the atmospheric spectral features must be removed through some form of surface-atmosphere separation (SAS). Multiple SAS techniques are available representing a range of complexity and accuracy. A ratio between spectra from a region of interest and a relatively spectrally bland, dusty location is an effective SAS technique, but the resulting ratio spectrum contains spectral features of surface dust from the dusty location. We exploited the uniform spectral character of surface dust across Mars to produce dust-removed ratio spectra (DRRS)(Ruff and Hamilton, 2021). The dust spectrum used here is a composite of one obtained by Bandfield and Smith (2003) and an average obtained from rover-based measurements in Gusev crater.

This simple and robust technique allows TES spectra to be compared directly to laboratory spectra and to Mini-TES spectra from the Mars Exploration Rovers. Although previous SAS techniques yield atmospherically corrected spectra that can serve this purpose, they are more challenging to implement, retain fewer data points, and are less accurate in some cases. The DRRS technique provides an option that is well suited to both quick-look assessments of TES spectra and in-depth analyses using follow-on spectral modeling techniques. We found that DRRS of olivine -rich bedrock in the Nili Fossae region display spectral features that match olivine with a composition ranging from ~Fo₅₀ to Fo₇₅ and that match olivine-rich Algonquin-class rocks in the Columbia Hills of Gusev crater, which show characteristics of ignimbrite deposits.

Bandfield, J. L., and M. D. Smith (2003), Multiple emission angle surface–atmosphere separations of Thermal Emission Spectrometer data, Icarus, 161, 47-65.

Ruff, S. W., and V. E. Hamilton (2021), A Novel Atmospheric Removal Technique for TES Spectra Applied to Olivine and Carbonate-rich Bedrock in the Nili Fossae Region, Journal of Geophysical Research: Planets, e2021JE006822, doi:https://doi.org/10.1029/2021JE006822.