Submitted to: Geoscience and Remote Sensing Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/18/2008
Publication Date: 1/14/2009
Citation: Balick, L., Gillespie, A., French, A.N., Danilina, I., Allard, J., Mushkin, A. 2009. LONGWAVE THERMAL INFRARED SPECTRAL VARIABILITY IN INDIVIDUAL ROCKS. Geoscience and Remote Sensing Letters. 6:1, 52-56. Interpretive Summary: Remote sensing of the land surface over thermal infrared wavelengths has the potential to resolve textural, geometrical and compositional variations that are difficult to retrieve any other way. Knowing these land surface properties greatly improves our ability to monitor features such as landcover change, water energy balance, and health of agricultural lands. Using a newly available hyperspectral imaging camera, FIRST 1, an experiment was conducted at a USDA Maricopa, Arizona site to observe various rock types at sub-centimeter scales. The results showed large spectral variations within and between rock samples that would otherwise be undetectable using conventional thermal radiometry. The outcome from this experiment will be important for remote sensing scientists investigating the benefits of hyperspectral thermal infrared imaging for land surface studies. 1 Mention of trade names or proprietary products does not constitute a guarantee or warranty of the product by USDA and does not imply its approval to the exclusion of other products that may also be suitable.
Technical Abstract: A hyperspectral imaging spectrometer measuring in the longwave thermal infrared (7.6 - 11.6 µm) with a spatial resolution less than 5 mm at a range of 10 m was used in the field to observe the variability of emissivity spectra of individual rock surfaces. The rocks were obtained commercially, were on the order of 20 cm in size and were selected to have distinct spectral features: they include alabaster (gypsum), soapstone (steatite with talc), obsidian (volcanic glass), norite (plagioclase and orthopyroxene), and “jasper” (silica with iron oxides). The advantages of using an imaging spectrometer to characterize these rocks spectrally are apparent. Large spectral variations were observed within individual rocks that may be attributed to roughness, surface geometry, and compositional variation. Non-imaging spectrometers would normally miss these variations as would small samples used in laboratory measurements, spatially averaged spectra can miss the optimum spectra for identification of materials and spatially localized components of the rock can be obscured.