Vegetation and Cryptobiotic Soils Mapping in Arid Regions
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
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
This page URL= http://speclab.cr.usgs.gov/PAPERS.arches.crypto.94/arches.crypto.dri.html
This page is maintained by: Dr. Roger N. Clark email@example.com
Last modified November 18, 1998.