Factors Involved in Estimating Green Biomass by Canopy Spectroreflectance Measurements

Abstract

Factors involved in estimating dry green biomass (DGB) by canopy spectral reflectance were evaluated at six dates during the 1976 growing season. In situ measurements were taken in the Mixed Prairie of western South Dakota on replicated pastures in different range condition classes using a modified hand-held biometer. Canopy reflectance and calibration panel reflectance were determined at 0.675 μm and 0.800 μm. Factors considered in estimating DGB via stepwise multiple regression were the canopy reflectances, calibration panel reflectances, time of day, and coefficient of variability among vegetation samples in a pasture. Canopy reflectance readings were included as both a ratio of the two wave lengths and as two separate variables in two sets of analyses. Canopy reflectance readings alone were not acceptable estimates of DGB (R2=.029 for the ratio and .042 for the linear combination). The coefficient of variability of samples within a pasture improved the association (R2=.233 and .231) while further inclusion of both calibration readings resulted in a marked improvement in estimation of DGB (R2=.633$ and .899). These calibration readings corrected for sun angle and diffuse cloud cover so that time of day of measurement was not an important variable.