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Abstract

The physics of thermal infrared aerospace measurements is based on Planck’s Radiation law, Wien’s Displacement law, and Kirchoff’s law. The electromagnetic spectrum for thermal infrared aerospace measurements includes measurements beyond the reflected short- (2.5 μm) to the long-wave infrared (14 μm).

Thermal infrared sensors measure thermal emission from the Earth’s surface in single wavelength bands (broadband), tens of bands (multiband), and in hundreds of bands (hyperspectral). Broadband thermal infrared measurement techniques include surface temperature mapping and thermal inertia mapping. Multiband and hyperspectral techniques involve mapping of changes in thermal emission at different wavelengths (emissivity mapping). Today, broadband surface temperature mapping is mostly done with satellite sensors. Thermal inertia mapping is done using broadband measurements taken during the day and night. Emissivity mapping is done using tens to hundreds of bands, and it requires sensors capable of measuring small changes in radiant emittance. Sensor systems discussed in this study include: Thermal Infrared Multispectral Scanner (TIMS), the Moderate Resolution Imaging Spectroradiometer (MODIS), Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Simulator (MASTER), the Spatially Enhanced Broadband Array Spectrograph System (SEBASS) and the ASTER satellite sensor.

Several areas of Nevada, such as Brady’s Hot Springs, Steamboat Springs, Geiger Grade, and Virginia City, were used as sites for demonstrating the geologic applications of thermal infrared remote sensing. Corrected day and night images over Steamboat Springs were acquired by TIMS. These day-night images were combined together to produce a final processed temperature image, in which the temperature effects of albedo, topographic slope, and thermal inertia were minimized to facilitate the detection of geothermal anomalies. Spectral variations in emitted thermal energy were detected over the Geiger Grade and Virginia City areas using the MODIS-ASTER Simulator (MASTER) and (SEBASS). MASTER thermal infrared image data allowed two primary mineralogic units in the Steamboat Springs area to be identified: sinter and/or chalcedony deposits and quartz-alunite alteration, which have spectral emissivity features around 9.0 μm; and clay-rich soil and clay alteration, which have spectral emissivity features around 9.7 μm. The higher spatial and spectral resolution SEBASS data allowed six different alteration assemblages to be identified: quartz, alunite, pyrophyllite, feldspar, kaolinite, and montmorillonite and/or illite.

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