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Theodore Roosevelt NP Vegetation Map Advanced Remote Sensing Research for Mapping Invasive Leafy Spurge
(Ralph Root, USGS/BRD, enter for Biological Informatics, Denver, CO)
The recently completed (March, 2000) USGS-NPS vegetation map
at Theodore Roosevelt National Park (THRO), produced via contract with the
Bureau of Reclamation Remote Sensing and GIS Applications Group, is being used
in support of an ongoing project that is demonstrating the use of NASA AVIRIS
(Airborne Visible and Infrared Imaging Spectrometer) imagery for detecting and
mapping invasive leafy spurge in the park and its immediate surroundings. Leafy
spurge is a highly aggressive and difficult to control herbaceous exotic plant.
It was first introduced at the park's western boundary in 1966 and now
occupies approximately 10 percent of the total area of the South Unit. It grows
in extensive, dense monocultures, often occupying entire sections of stream
floodplains or smaller drainages.
Although the plants grow in dense stands, openings in the canopy can expose
litter and soil, adding to the challenge of mapping via remote sensing.
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| A team of scientists from the NPS, USGS, and the University of California, Davis
have been analyzing AVIRIS data collected over the park on July 6, 1999 to
examine the feasibility of detecting and mapping leafy spurge via imaging
spectroscopy. The recently completed USGS-NPS Vegetation Mapping Program map at
THRO has proven to be a valuable aid in this research because leafy spurge was
one of the vegetation types included in the mapping process. Because the
vegetation mapping products were in digital form, the leafy spurge class was
rapidly and easily extracted from the overall vegetation database for comparison
and overlay with the AVIRIS data.
Although the leafy spurge in the new USGS-NPS vegetation map was interpreted from
1996 aerial photographs, it was recent enough to be of great value to the remote
sensing research team for locating probable leafy spurge spectra directly from a
georeferenced version of the AVIRIS data. The only other source of information was
a 1993 map of leafy spurge, produced by the park in earlier efforts to generate
baseline data to be used in control efforts. The more recent USGS-NPS THRO
vegetation map represented a significant update to this original baseline map.
The leafy spurge class as represented in the more recent USGS-NPS vegetation map
also proved to be a useful resource for the leafy spurge research team because
it served as a basis for setting thresholds on AVIRIS classification "rule" images
that portray probabilities of leafy spurge occurrence. By comparing the probability
image with leafy spurge polygons from the vegetation map, thresholds can be
determined and set for the probability images, taking the "guesswork" out of this
process. |
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| In the image to the left, the black areas are classified AVIRIS spectra with a
threshold applied to approximate the red polygons that represent leafy spurge stands
from the new NPS vegetation map.
Direct overlay of the two totally independent data sets have also produced some
additional side benefits. Because of an ongoing program at the park to control
leafy spurge populations some polygons on the 1996 map do not correlate with the
AVIRIS classification, adding an additional variable to the verification process.
Assuming that the AVIRIS classification is accurate, areas that do not correlate
may represent locations where control efforts were successful. On the other hand,
areas on the AVIRIS classification showing leafy spurge that are not represented
on the 1996 map probably represent locations of spread during the past 3 years,
with allowances for some errors in classification.
Comparing the georeferenced AVIRIS data and the USGS-NPS vegetation map also
provided some valuable information on the ground referencing accuracy of each of
these products. By checking the vegetation map polygons against recently produced
Digital Orthophoto Quarter Quads (DOQQ’s), it was determined that most of the
locational error was in the AVIRIS data, and not the USGS-NPS vegetation map.
Armed with this knowledge, some allowances can be made when comparing the two data
sets during the process of selecting spectra within the AVIRIS data for further
classification refinements. This process also has demonstrated the need for using
localized "rubber sheeting" algorithms for better georeferencing of the AVIRIS data. |
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Biological Informatics Program 
U.S. Department of the Interior |
U.S. Geological Survey
