Assessment of regional biomass-soil relationships using vegetation indexes

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Abstract
Data from the NOAA-10 Advanced Very High Resolution Radiometer (AVHRR) were collected over the midwestern United States for the 1987 and 1988 growing seasons. A Normalized Difference Vegetation Index (NDVI) transformation was performed using the two optical bands of the sensor (0.58-0.68-mu-m and 0.72-1.10-mu-m). The NDVI is related to the amount of active photosynthetic biomass present on the ground. Samples of NDVI values over 45 fields representing 8 soil associations throughout the State of Indiana were collected to assess the effect of soil conditions and acquisition date on the spectral response of the vegetation, as shown by the NDVI's. Statistical analysis of results indicate that land-cover types (forest, forest/pasture, and crops), soil texture, and soil water-holding capacity have an important effect on vegetation biomass changes as measured by AVHRR data. Acquisition dates should be selected with consideration of the phenological stages of vegetation. Sampling of AVHRR data over extended areas should be stratified according to physiographic units rather than man-made boundaries; this will provide more homogeneous samples for statistical analysis.