Sensitivity of Spectral Vegetative Indices to Crop Biomass

Abstract

ABSTRACT THE sensitivity of three commonly used spectral vegetative indicesratio (R43), normalized difference (ND43), and greenness (GR43); to plant canopy variables was compared for four row crops. An exponential equation was fitted to nontransformed spectral and canopy variable values and a linear equation was applied to normalized data values to describe the spectral vegetative index (VI)canopy variable relations. R43 asymptotic values for the exponential relationship were highest; however, ND43 and GR43 were more highly correlated with LAI and ground cover over the complete range of values. Relative rates of change (normalized derivatives) of the exponential equations relating the VI to LAI were smallest for ND43. The normalized linear equations indicated that R43 had greater sensitivity to biomass and LAI than GR43 and ND43. The sensitivity of all VI was highest to ground cover, but the sensitivity of ND43 was lower than that of R43 and GR43. Overall R43 is more sensitive to high levels of biomass and LAI, but when crops are small ND43 and GR43 may be the best estimators of LAI and ground cover.