Comparing MODIS and AVHRR Vegetation Indices across Montana

The Normalized Difference Vegetation Index (NDVI) derived from the Advanced Very High Resolution Radiometer (AVHRR) is currently used to monitor spatial and temporal changes in live vegetation condition and to assess fire potential across landscapes through a suite of Wildland Fire Assessment System (WFAS) "greenness" products. Recent vegetation index (VI) research has focused on development of products that minimize the confounding effects of clouds and atmosphere, canopy background, and varying sun-target-sensor geometry on vegetation characterization. These efforts have been incorporated into the development of MODIS vegetation indices (MVIs), which are anticipated to improve upon existing NDVI-based assessments of vegetation condition. The MODIS NDVI is intended as a "continuity index" that will allow extension of the existing AVHRR NDVI archive for long-term VI analyses. Preliminary investigation indicates that MVI is more sensitive to vegetation changes in high biomass areas and under light cloud or smoke conditions. An improved compositing algorithm combined with the higher radiometric and spectral resolution of the MODIS sensor may be responsible for these results. This project explores relationships between MODIS NDVI and AVHRR NDVI across several biophysical settings in Montana (as determined by land cover and climate zone stratification) for three composite periods during the summer of 2000. Results of the analysis elucidate differences in spatio-temporal VI patterns and have implications about the extent to which the MODIS NDVI functions as a "continuity index" to the AVHRR NDVI across Montana landscapes.

Principal investigator: Eva Karau