Hyperspectral mixture modeling for quantifying sparse vegetation cover in arid environments

A linear mixture model based on calibrated, atmospherically corrected Probe -1 hyperspectral imagery was compared with three vegetation indices to test its relative ability to measure small differences in percent green vegetat ive cover for areas of sparse vegetation in arid environments. The goal of this research was tp compare multispectral and hyperspectral remote sensing approaches for detecting human disturbances of arid environments. The norm alized difference vegetation index (NDVI) was tested using both narrow and broad band-widths. Broadband NDVI provided results (r(2) = 0.63) similar to NDVI derived from individual hyperspectral channels (r(2) = 0.60). While t he soil-adjusted vegetation index (SAVI) was designed as an improvement to NDVI for sparse vegetation, in this study SAVI performed significantly wors e than NDVI (r(2) = 0.51). The modified soil-adjusted vegetation index (MSA VI) provided an insignificant improvement overt NDVI (r(2) = 0.64). Linear mixture modeling provided significantly better results, r(2) of 0.74. Cross -validation was used to test the significance of differences between the va rious methods and to determine the standard error associated with each meth od. Results suggest that any improvements provided by adjusted vegetation i ndices over NDVI may be strongly dependent on those adjustments being deriv ed from local conditions. The use of a linear mixture model with multiple s oil endmembers appears to provide the best method for quantifying sparse ve getative cover. Though present in small amounts, a single plant species, Kr ameria erecta, was strongly correlated with residuals of the mixture model. Inclusion of a spectral endmember for this species increased the r(2) of t he fit with percent green cover to 0.86. However, it is not clear if the ex plained variation was actually due to K. erecta or a correlated phenomena. Problems were also identified with the use of multiple vegetation endmember s. (C) Elsevier Science Inc., 2000.