Extraction of Vegetation Biophysical Parameters by Inversion of the PROSPECT + SAIL Models on Sugar Beet Canopy Reflectance Data. Application to TM and AVIRIS Sensors

T h e PROSPECT leaf optical properties and SAIL canopy reflectance models were coupled and inverted using a set of 96 AVIRIS (Airborne Visible~Infrared Imaging Spectrometer) equivalent spectra gathered in afield experiment on sugar beet plots expressing a large range in leaf area index, chlorophyll concentration, and soil color. In a first attempt, the model accurately reproduced the spectral reflectance of vegetation, using six variables: chlorophyll a + b concentration (C~), water depth (Cw), leaf mesophyll structure parameter (N), leaf area index (LAI), mean leaf inclination angle (0 O, and hot-spot size parameter (s). The four structural parameters (N, LAI, 01, and s) were poorly estimated, indicating instability in the inversion process; however, the two biochemical parameters (Cab and Cw) were evaluated reasonably well, except over very bright soils. In a second attempt, three of the four structure variables were assigned a fixed value