M S Ramsey (Dept. of Geology, Arizona State Univ., Box 871404, Tempe, AZ 85287-1404; ph. 602-965-1790; email: ramsey@elwood.la.asu.edu)

The Kelso Dune field is located in the eastern Mojave Desert, California at the terminus of a moderate-length sand transport path that begins at the Afton Canyon alluvial fan 50 km to the west. Previous investigations have studied the dunes in detail, reporting on their mineralogy and sources for the majority of material that comprises the field. However, processing of 1984 airborne Thermal Infrared Multispectral Scanner (TIMS) data showed significant spectral variations within the active dunes that indicated mineralogic heterogeneities. These apparent differences prompted the collection of a suite 48 sand samples in 1990, and new TIR multispectral data to be acquired in 1995. The sand samples were analyzed by standard petrographic techniques to determine mineralogy, grain size, and shape. This analysis reveled that the dunes did contain mineralogic variations and were more immature (quartz content ~ 42%) than previously reported. To confirm these results, the newly acquired 1994 TIMS data were used to test the linear spectral retrieval algorithm with a mineral library approach for endmember selection. Remote sensing of actively saltating dunes is an ideal test locale since complications such as vegetation, particle size variations, and thermal shadowing are minimized.

Deconvolution of the emissivity data produced mineral endmember images containing marked variations within the dunes and results that agreed with the point count data to within an average of 5.3% for the TIMS data and 3.1% for laboratory spectra. High concentrations of several of the endmember minerals on the surrounding alluvial fans indicate a potential near source for some percentage of the Kelso sand. There is a significant input source of potassium feldspar from a granite-dominated fan emanating from the Providence Mountains east of the dunes. This input is previously unidentified and not visible with other remote sensing techniques. Much of the quartz and some plagioclase, on the other hand, appear to be being transported from a source to the west. Considering the 6 year time difference between sample collection and remote data acquisition, the general agreement between the petrographic and spectral analyses indicate relatively little net movement has occurred recently at Kelso. Studies such as this using linear deconvolution of TIR data provide the geologist with a synoptic look at an entire eolian system, allowing an inference of past activity and the monitoring of current climate changes. Drought-prone areas near these sand transport pathways are susceptible to dune encroachment and possible desertification and will benefit from repetitive monitoring programs using the upcoming spaceborne ASTER instrument.

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Presented at: First JPL Workshop on Remote Sensing of Land Surface Emissivity
Date: 1997