Mars Analogue Field Thermal Emission Spectroscopy: Complications from Downwelling Radiance

Introduction: The 2003 Mars Exploration Rover science strategy is to identify promising targets for the rover using the visible imaging Pancam and thermal infrared imaging Mini-TES. Those targets would then undergo detailed examination using a suite of instruments including an alpha particle x-ray spectrometer, a Mössbauer spectrometer, and a microscopic imager. Team members will select sites using target morphology and color from Pancam, and interpretations of the mineralogy using Mini-TES. This strategy requires high quality, near real-time interpretations of Mini-TES data. [1] Researchers desire to detect and identify smooth rock coatings, if present. Smooth rock coatings, such as desert varnish or cooling rind, may provide information on the environmental conditions [2]. Desert varnish is a blackish or brownish stain of iron and manganese on a rock surface [3]. Exobiologists are particularly interested in desert varnish because it may be biologically mediated [4]. A hyperspectral thermal infrared field study, measured in a manner very similar to the Mini-TES, is needed. In February 2002, Kirkland et al. [5] measured field spectra of test targets in order to study downwelling effects and design systematic field studies. Of the target types studied, non-diffuse was the most difficult. There are no published studies of non-diffuse targets in the field –using an instrument similar to the Mini-TES. So, in July 2002, we measured data of a varnished desert pavement. This dataset provides a systematic field study, particularly of reflected downwelling radiance effects. In analyzing the July 2002 dataset it has become apparent that no technique exists to compensate for the downwelling radiance on non-diffuse targets.