Spectral Mapping Using CRISM Data in the Northwest Noachis Terra Region

Introduction: Launched in 2005, the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) [1] is an instrument that measures the composition of Mars’s surface and allows scientists to understand climate patterns that relate to the presence of water on the planet. Our effort consisted of assisting in ongoing mapping by validating and compositionally mapping using CRISM images in three unique areas: Northwest Noachis Terra (this work), Terra Sabaea, and Central Valles Marineris. Spectral analysis utilizing image analysis software of each regions of interest were compared with reference spectra in the MICA library [2], a compilation of the best CRISM end member mineral detections, in order to identify and label minerals in the regions of interest. Compositionally, the NW Noachis Terra region revealed large amounts of low calcium and high calcium pyroxene (LCP and HCP, respectively), magnesium smectite, and iron smectite. This concentration of minerals suggests an aqueous past, as smectite phyllosilicates generally form as a result of aqueous alteration. Methodology: CRISM can detect visible and infrared wavelengths ranging from 0.4 4 microns [1] and is sensitive to absorption features due to primary and secondary minerals. For this project we utilize CRISM “tiles”, 5 by 5 degree mosaics of ~200-m/pixel mapping-mode data (Fig. 1 upper). Absorption bands from mineral signatures are parametrized and derived RedGreen-Blue false color composites of these parameters are used to highlight where detectable minerals are present (Fig. 1 lower). A variety of programs were utilized in order to compare these parameter composites to observable surface features. Java Missionplanning and Analysis for Remote Sensing (JMARS) [3], a geospatial information system (GIS), was used to pinpoint areas of interest in the provided tiles by observing different RGB parameter composites. Once areas of interest were pinpointed, the Environment for Visualizing Images (ENVI) [4], a geospatial imaging program, was used to ratio spectra from these areas against other more spectrally-bland regions along the same image strip in the mosaic. These ratios were then plotted with the reference spectra of potential mineral matches from the MICA library for comparison (Fig. 2). By plotting these ratios, the spectrally-dominant component of each area of interest was able to be classified. The location of these mineral outcrops were then compared to the USGS Geologic Map of Mars (Fig. 3) [5], to determine the age of the units the materials formed in. Five tiles were analyzed in NW Noachis Terra (Fig. 1).