MINERAL MAPPING OF ALLUVIAL FAN, AEOLIAN AND LACUSTRINE DEPOSITS AROUND THE SALTON SEA, CALIFORNIA USING MICA: A NEW TOOL FOR RAPID CLASSIFICATION OF HYSPIRI VSWIR IMAGERY

The wealth of image data that will be produced during the course of the HyspIRI mission will create the need for new software tools and processing algorithms that can be used to rapidly derive land surface material maps from standardized higher level VSWIR (380 – 2500 nm) data products. One potentially useful processing routine is the Material Identification and Characterization Algorithm (MICA) developed at the USGS as a module within the Processing Routines in IDL for Spectroscopic Measurements (PRISM) software. This program can be used as a simple plug-in for the ENVI (ENvironment for Visualizing Images) image processing system. MICA employs continuum removal and linear regression to compare observed spectral absorption features (e.g. HyspIRI pixels) to those diagnostic of reference materials contained within a spectral library or measured separately in the field or laboratory.

For this study, we compare MICA mineral maps of the Salton Sea basin, using AVIRIS-classic, AVIRIS-next-generation, Hyperion and AVIRIS-classic convolved to both 30-m and 60-m simulated HyspIRI datasets. Examples of minerals mapped successfully using MICA include: calcite and aragonite dominating lacustrine deposits left by the receding Lake Cahuilla; montmorillonite, illite and/or muscovite found as coatings on quartz grains in aeolian deposits; and various minerals on alluvial fans depending on their source bedrock compositions and depositional processes of modification. For example, some alluvial fans are dominated by muscovite, chlorite and/or epidote depending on the abundance of unaltered versus mylonitized granite and schists found in bar-n-swale deposits. Younger and more active fans tend to be dominated by weathering clays such as montmorillionite, which forms abundant soil crusts after major floods. Montmorillonite forms mixtures with kaolinite and muscovite in alluvial fans derived from hydrothermally altered source areas. Older alluvial fans tend to be dominated by desert varnish coatings containing nanocrystalline hematite, mixed with montmorillonite and/or illite. Additional ferric/ferrous iron and serpentine minerals, buddingtonite and gypsum were mapped in other bedrock areas, as well as in ancient and active geothermal deposits.