FUNCTIONAL PATTERNS IN AN ANNUAL GRASSLAND DURING AN AVIRIS OVERFLIGHT

This study relates Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) imagery to ground measurements Of vegetation distribution, physiology, and productivity at Stanford University's jasper Ridge Biological Preserve. Primary efforts focused on a 9-ha region of annual grassland where we completed a detailed ground-based study in conjunction with a 15 May 1991 AVIRIS overflight. Spectral mixture analysis and the normalized difference vegetation index (NDVI) calculated from AVIRIS data were used to evaluate spatial patterns Of vegetation type, productivity, and potential physiological activity. Concurrent ground sampling revealed a high degree of correlation between NDVI and estimates Of canopy chemistry, structure, productivity, and CO2 fluX, supporting the use of imaging spectrometry to estimate spatial and temporal trends in vegetation physiology and productivity in this relatively simple grassland ecosystem. Geostatistical analyses of both ground and AVIRIS data supported the conclusion that the AVIRIS pixel size was suitable for describing the influence of major landscape features in this grassland and that spatial detail would be lost at slightly larger pixel sizes typical of other imaging spectrometers. Analysis of fine spectral features in AVIRIS data may provide new ways of assessing physiological activity in evergreen tree and shrub communities where photosynthetic activity was not correlated with green canopy display.