Derivation of equivalent water thickness and an index of biochemical component abundance in vegetation from AVIRIS data

Remote sensing of water status and biochemical components of vegetation can have important applications in the fields of agriculture and forestry. Reflectance of fresh, green vegetation in the 1.0 - 2.5 micrometers region is dominated by liquid water absorption and also weakly affected by absorption due to biochemical components, such as lignin and cellulose. We have developed both the nonlinear and linear least squares spectrum- matching techniques for deriving equivalent water thickness (EWT) of vegetation from AVIRIS data in the 1.0 and 1.6 micrometers regions. Seasonal variations of EWTs over an agricultural area in Greeley, Colorado are determined. EWTs from 1.0 micrometers region are generally greater than those from 1.6 micrometers region because of the deeper light penetration into the canopy. After fitting the AVIRIS data with water spectrum alone, a weak lignin-cellulose absorption feature centered at 1.72 micrometers is seen in the residual spectra. We map the depth of the 1.72-micrometers feature, which can be considered as an index of component abundance in the canopy.

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