Evaluation of a Canopy Reflectance Model for LAI Estimation through Its Inversion

A technique described earlier for estimating leaf area index (LAI) from bidirectional canopy reflectance (CR) data is applied and evaluated for three plant canopies-a naturally growing healthy soybean canopy and two orchardgrass canopies-one homogenous and the other spatially clumped or "tufted." This technique employs the inversion of a CR model which is chosen to be the SAIL model. The CR data were collected using a new ilstrument called the PARABOLA which is capable of acquiring the complete sky-and-ground looking hemisphere radiances in only 11 s. The model fit and LAI estimations for the soybean and uniform orchardgrass canopies are quite good. For the inhomogenous tufted orchardgrass canopy the LAI estimation is poor unless the maximum view zenith angle is restricted to 500. These results indicate that the biophysical parameter estimation from CR measurements may be applied with considerable confidence to homogenous herbaceous vegetation types but better CR models are needed to adequately represent discontinuous plant canopies.