Long-term Vegetation Assessment in Wyoming using Landsat Multi Spectral Scanner (MSS) Data

Images and change in NDVI are in georeferenced TIFF format. Changes corrected for precipitation variability will be available in the future. What the dataset was used for: to estimate the change in vegetation amount over time in Wyoming.

We used three Landsat Multi Spectral Scanner (MSS) images, one from the early-to-mid 1970s, one from the mid 1980s, and one from the early 1990s. Vegetation amount is determined from the Normalized Difference Vegetation Index, defined as (Band 4 - Band 2)/(Band 4 + Band 2), where Band 4 covers near-infrared (NIR) wavelengths from 0.8 to 1.1 Fm and Band 2 covers red wavelengths from 0.6 to 0.7 Fm. NDVI saturates with one-sided leaf area indices (LAI) of 4 and higher; however, this is not a problem for Wyoming grasslands and shrublands have low LAI.

NDVI varies from -1 to 1, and are converted into digital numbers (DN) by: 100 (NDVI+1), so the DN varies from 0 to 200. Change detection is estimated as the NDVI(1990) - 0.5[NDVI(1980) - NDVI(1970)] for each image, except for areas covered with snow, clouds, and shadows caused by clouds. If two dates were available for these areas, we subtracted the NDVI of the earlier date from the NDVI of the later date.

The dates of acquisition were usually collected towards the end of the growing season, and usually during years of drought (for example: 1992, 1985, 1972). We have developed an algorithm using the Advanced Very High Resolution Radiometer (AVHRR) data from the EROS Data Center to adjust NDVIs to average precipitation amounts, but these corrections were not applied to this dataset.