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United States Department of Agriculture

Agricultural Research Service

Title: Satellite Trend Analysis of Wyoming Rangelands for Impacts of Grazing

Author
item Hunt, Earle

Submitted to: BARC Poster Day
Publication Type: Abstract Only
Publication Acceptance Date: February 24, 2000
Publication Date: April 6, 2000

Technical Abstract: The Landsat Multi Spectral Scanner (MSS) acquired data starting in 1972 and ending in the mid 1990's. The MSS sensor has 4 bands with a pixel size of approximately 60 m by 60 m and a repeat frequency every 16 to 18 days. Images from the 1970's to the 1990's are available from the USGS EROS Data Center as the North American Land Characterization Dataset. Normalized Difference Vegetation Index (NDVI) emphasizes differences between green vegetation and bare soil. Standard change detection techniques using remotely sensed NDVI cannot be used for semiarid regions because of the high year-to-year variability in precipitation which affects the amount of vegetation cover and biomass. I developed a model relating Advanced Very High Resolution Radiometer (AVHRR) NDVI data to the amount and timing of rainfall. I used the meteorological data to adjust MSS NDVI so differences indicate the changes in vegetation biomass and cover over time. This technique was applied to 15 MSS scenes covering most of Wyoming. The vast majority of rangelands in Wyoming have remained unchanged over the 20-year period. Areas that decreased were usually associated with wildfires. Furthermore, we found that riparian zones (defined as a swath 10 pixels around rivers and creeks obtained from vector GIS data) had to be separated from the above analyses; NDVI of most riparian areas either increased or remained the same over the 20-year period. Because NDVI is related to the amount of vegetation cover and biomass, and not the species present, these data cannot be used for assessment of condition and trend as defined by the USDA NRCS. However, decreases in NDVI are related to increases in bare soil, so these data are useful for erosion assessments and for prioritization of areas to check on the ground.

Last Modified: 4/24/2014
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