Evaluation of NDVI for monitoring live moisture in three vegetation types of the western US

The Normalized Difference Vegetation Index (NDVI) is evaluated for monitori ng seasonal changes in live vegetation moisture. NDVI values for scenes of meadow grass, sagebrush, and an open-conifer stand were calculated using 0. 5-m resolution multispectral images acquired from a fixed-wing aircraft fou r times from May to October, and live vegetation moisture was sampled simul taneously with each flight. Changes in sampled live vegetation moisture wer e compared with changes in the NDVI, and the proportion of seasonal change in NDVI attributable to changes in the understory vegetation rather than th e conifer canopy was examined. Seasonal changes in vegetation moisture for all sites were statistically significant (p < 0.05). Time-series profiles o f the NDVI were functionally related to changes in vegetation moisture only for the grass and forest understory vegetation. No significant relationshi ps were observed for either the shrub or coniferous forest canopy vegetatio n. This field experiment will improve our interpretation of seasonal NDVI d ata with respect to fire potential.