We have analyzed hyperspectral Airborne Visible-Infrared Imaging System (AVIRIS) imagery taken in September of 1992 in Long VaJley Caldera, CA, a geothermally active region expressed surficially by hot springs and fumaroles. Geological and vegetation mapping are attempted through spectral classification of imagery. Particular hot spring areas in the caldera are targeted for analysis. The data is analyzed for unique geobotanical patterns in the vicinity of hot springs as well as gross identification of dominant plant and mineral species. Spectra used for the classifications come from a vegetation spectral library created for plant species found to be associated with geothermal processes. This library takes into account the seasonality of vegetation by including spectra for species on a monthly basis. Geological spectra are taken from JPL and USGS mineral libraries. Preliminary classifications of hot spring areas indicate some success in mineral identification and less successful vegetation species identification. The small spatial extent of individual plants demands either sub-pixel analysis or increased spatial resolution of imagery. Future work will also include preliminary analysis of a hyperspectral thermal imagery dataset and a multitemporal air photo dataset. The combination of these remotely sensed datasets for Long Valley will yield a valuable product for geothermal exploration efforts in other regions.
.O INTRODUCTIONActive geothermal regions can be characterized by a specific suite of minerals and vegetation. Processes occurring in such environments facilitate the unique interaction between the biological and geological world resulting in predictable patterns. In general, geothermal processes include fumarolic activity, increased geothermal gradients, and discharge of hot water both at the surface and at depth. The interaction of these geothermal processes with the in situ geology results in alteration of the rock to characteristic hydrothermal mineral assemblages. The further interaction of both the ongoing and sometimes cyclic geothermal processes and the mineral assemblages with the vegetation results in patterns dictated by a plant's growth threshold. These thresholds are constrained partly by temperature and pH. One way to study these patterns is through the use of hyperspectral imagery such as that provided by the AVIRIS instrument. There has been great success in using hyperspectral data to characterize mineral provinces (F.A.Kruse, 1988(F.A.Kruse, , 1990(F.A.Kruse, , 1993J.W. Boardman and J.F. Huntington, 1996). Less work has been done with vegetation due to the complex nature of delineating different species of plants which are chemically very similar to one another. However, airborne hyperspectral data has also been successfully used to characterize vegetation communities and condition (R. Merton, 1998;S.M. de Jong, 1996, R.N. Clark et al, 1995. We attempt a geobotanical approach aimed at analysis of hyperspectral imagery of a geothermal region in Long Valley Caldera, California. A s...