ESTIMATING LEAF BIOCHEMISTRY USING THE PROSPECT LEAF OPTICAL-PROPERTIES MODEL

Thc biophysical, biochemical, and optical properties of 63 fresh leave s and 58 dry leaves were measured to investigate the potential of remo te sensing to estimate the leaf biochemistry from space. Almost 2000 h emispherical reflectance and transmittance spectra were acquired from 400 nm to 2500 nm using a laboratory spectrophotometer. The amount of chlorophyll, water protein, cellulose, hemicellulose, lignin, and star ch was determined on these leaves using standard wet chemistry techniq ues. These experimental data were used to improve the PROSPECT model, a simple but effective radiative transfer model that calculates the le af optical properties with a limited number of input parameters: a str ucture parameter and the leaf biochemistry. The new model construction mainly consisted in. providing specific absorption coefficients for t he biochemical constituents; the comparison with absorption spectra of pure materials derived from the literature showed good agreement. In the inversion, however, it was necessary to group some leaf components in order to estimate leaf biochemistry with reasonable accuracy. Pred ictive power varied with the chemistry variable, wavelengths used in a nalysis, and whether leaves were fresh or dry. r(2) ranged from 0.39 t o 0.88 for predictions on dry leaves; on fresh leaves, water and chlor ophyll had high r(2) values, 0.95 and 0.68 respectively, carbon based compounds reasonable r(2), from 0.50 to 0.88, while the estimation of protein is still at issue.