USE OF 2ND DERIVATIVES OF CANOPY REFLECTANCE FOR MONITORING PRAIRIE VEGETATION OVER DIFFERENT SOIL BACKGROUNDS

Spectral derivative indices were compared with the commonly used near-infrared to red reflectance ratio (NIR/red) and the normalized difference (ND) spectral indices. Two ''windows- of second derivatives, rho''0.69 mum, and rho''0.74 mum, exist in the visible and NIR spectral regions, which can be used to estimate vegetation characteristics such as percent cover and leaf area index (LAI). Second derivatives centered on the red and NIR wavebands (MSS Bands 3 and 4) were calculated using broadband radiometer data for grassland sites which had been previously burned or had been left unburned for several years. The second derivative indices minimized the effect of the soil background differences caused by the prior burning treatments, and clearly showed the advantages of the derivative technique over the conventional NIR/red ratio and ND spectral indices.