APPLICATION OF HIGH-RESOLUTION THERMAL INFRARED SENSORS FOR GEOTHERMAL EXPLORATION AT THE SALTON SEA, CALIFORNIA

The Salton Sea geothermal field straddles the southeast margin of the Salton Sea in California. This field includes approximately 20km² of mud volcanoes and mud pots and is centered on the Mullet Island thermal anomaly. The field itself is relatively un-vegetated, which provides for unobstructed detection of the surface mineralogy, radiant heat, and emitted gases using ground-, air- and space-based thermal infrared (TIR) sensors. On March 26, 2009, the airborne Spatially Enhanced Broadband Array Spectrograph System (SEBASS) sensor was flown over the area collecting high spectral (128 bands) and spatial resolution (1m/pixel) TIR data in the 7.5-14.5 micron spectral region. A large portion of the Calipatria Fault, was imaged during this flight, several thermal/mineralogical anomalies were also noted. The orbital Advanced Spaceborne Thermal Emission Reflection Radiometer (ASTER) has only 5 spectral bands at 90m/pixel resolution, but has acquired dozens of visible and TIR datasets over the region in the 10-year history of the instrument. The thermal-temporal trend of this dataset has been analyzed, and studied in detail for comparison to the SEBASS data. The land-leaving TIR radiance data were separated into brightness temperature and surface emissivity, which is unique to each mineral. A spectral library was used to determine the presence of each mineral surrounding the most active geothermal features. In some cases spectra were identified that did not match any known spectrum within the library. Laboratory-based TIR emission spectra and X-Ray diffraction (XRD) were acquired to identify these unknown minerals. The higher spectral/spatial resolution SEBASS data were also used to validate the lower spectral/spatial resolution ASTER data (as well as the higher resolution laboratory TIR data). By using this approach of progressively higher spatial and spectral resolution sensors, the temperature and mineral anomalies commonly associated with geothermal activity were more easily identified and related to the geothermal processes. This approach enables an innovative exploration methodology for future exploration of geothermal locations using TIR remote sensing.