Vegetation and Cryptobiotic Soils Mapping in Arid Regions

http://speclab.cr.usgs.gov

R.F. Kokaly, R.N. Clark, and G.A. Swayze

From: Spectral Analysis Workshop: The Use of Vegetation as an Indicator of Environmental Contamination, Desert Research Institute, Reno, Nevada, November 9-10, 1994)

On the arid Colorado Plateau, vegetation is sparse, consisting primarily of Pinon Pine, shrubs and grasses. Soils contain microbiotic organisms, and lichens grow on the surfaces of soils and rocks. These all have spectra with diagnostic spectral features which allows us to map them with imaging spectroscopy.

By analyzing only mineral absorptions, it is possible to "see around" the vegetation and cryptobiotics. By selecting green vegetation absorptions, soils are ignored, and by selecting cryptobiotic soils spectral features, vegetation and minerals can be discriminated. By properly modeling the various spectral mixtures of minerals, vegetation and cryptobiotics, accurate abundances of each can be derived. (Note, older methods of vegetation mapping, such as NDVI, using band ratios from broadband instrumentation have significant errors in arid lands.)

The vegetation mapping can be further extended to map communities and species with imaging spectroscopy. The synergistic combination of vegetation species, vegetation cover, mineralogy, and cryptobiotics cover maps provides a unique database for ecosystem studies and more effective land management.

Figure 1: 274K GIF

Figure 1: This image shows an estimate of microbiotic (cryptobiotic) soil coverage (expressed as fractional areal coverage in percent) for an area in Arches National Park. In order to accurately map the distribution and abundance of cryptobiotic soils, AVIRIS remote sensing data were compared to laboratory reference spectra of cryptobiotic soil samples. This image covers an approximately 10.5 km by 17.5km area of Arches National Park from the Colorado river in the south, Wolfe Ranch and Delicate Arch near the center, and Fiery Furnace and the campground area to the north. This image was derived from AVIRIS data collected in 1992 and processed using the USGS Tricorder algorithm. AVIRIS is an imaging spectrometer remote sensing instrument. This instrument, flown on an ER-2 aircraft at 65,000 feet altitude, measures reflectance in visible to near infrared wavelengths in 224 channels (0.4 to 2.5 microns). Pixels are spaced 17m apart. Representative spectra of cryptobiotic soils, vegetation and soil background ("sand, rock or soil") measured in the laboratory were combined mathematically in various mixtures. For each pixel in the image, AVIRIS acquired a reflectance spectra from 0.4-2.5 microns. These remotely sensed spectra were then compared to the synthetic mixtures and the closest match determined. These data were field checked in 1994. Field checking shows that the black lichens on the rocks have the same spectral character as the cryptobiotic soils, so the map here is really a "Cryptobiotic plus Black Lichen Map." Additional AVIRIS data were acquired in 1995. These new data cover all of Arches National Park and a majority of Canyonlands National Park. Preliminary mapping of this new data for mineralogy with the Tricorder algorithm has been completed. Vegetation and cryptobiotic soils maps are currently being processed. Field verification is scheduled for fall of 2000. Updates on this and other USGS projects involving imaging spectroscopy in National Parks and other areas can be obtained from http://speclab.cr.usgs.gov/

U.S. Geological Survey, a bureau of the U.S. Department of the Interior
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This page is maintained by: Dr. Roger N. Clark rclark@speclab.cr.usgs.gov
Last modified November 18, 1998.