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Monitoring Changes in Vegetation and Land Surfaces by Remote Sensing

Vegetation and land surfaces on the Colorado Plateau

Identifying Surface Minerals and Vegetation using Imaging Spectroscopy
Remote sensing data collected by the Airborne Visible and InfraRed Imaging Spectrometer (AVIRIS) are being analyzed to reveal the mineral content of rocks and soils and to characterize the status of vegetation cover (for example, green plant cover and species composition) in Canyonlands National Park. AVIRIS data were collected on June 19, 1995. These data were analyzed with the USGS Tetracorder system to produce thematic maps that reveal the distributions of: 1) vegetation cover, 2) iron-bearing minerals, and 3) clay, carbonate and mica minerals. The mineral maps are being analyzed in relation to field and laboratory measurements of soil and plant samples in order to determine whether they can be used to delineate areas in which soil composition may control plant species composition. A relation between the distribution of cheatgrass and the abundance of carbonate minerals is being examined.

Detecting Infestations of Cheatgrass on the Colorado Plateau
Satellite remote sensing data collected by the Landsat-7 Enhanced Thematic Mapper (ETM) sensor is being used to detect potential infestations of the invasive plant cheatgrass (Bromus tectorum) in the Needles District of Canyonlands National Park. Cheatgrass greens up earlier than other native plants on the Colorado Plateau, in normal growing seasons. By mid-summer, cheatgrass has reached a state of senescence (chlorophyll has been removed from the leaves). As a result, cheatgrass is greener than most plants in spring and non-green in the summer. Data from Landsat-7 ETM is being used to calculate Normalized Difference Vegetation Index (NDVI) maps, which reveal the relative greenness of vegetation. High NDVI values indicate high chlorophyll abundance (related to the greenness of the vegetation and the biomass of green leaves). Low NDVI values indicate a low fraction or absence of green plants on the surface. NDVI is being calculated from Landsat data from April 2001 to detect areas of high chlorophyll abundance that may indicate cheatgrass infestations. NDVI calculated from Landsat data from July 2001 will be subtracted from the April NDVI calculations:

As a result, high values will indicate areas that are covered by plants that were green in April and non-green in July (i.e., areas with a vegetation growth cycle like that of cheatgrass). The accuracy of the map in detecting cheatgrass will be evaluated relative to field observations of cheatgrass occurrence.

1993 and 2001 maps of cheatgrass infestations, shown in red (View a larger image: 300K JPEG image or 24 Mb PDF)