Multi-angle data from CHRIS/Proba for determination of canopy structure in desert rangelands

Multi-angle spectral radiance images from the Compact High Resolution Imaging Spectrometer (CHRIS) on the European Space Agency's Proba satellite were acquired over desert grasslands in the USDA, ARS Jornada Experimental Range near Las Cruces, New Mexico, USA. The data were used to obtain multi-angle ratio images and to effect spatial bidirectional reflectance distribution function (BRDF) model inversions. The results show that there is canopy 3-D structure information observable in ratio images but physical interpretation is difficult. Inversion of a simple non-linear model for three canopy parameters resulted in low root-mean-square error values. The difficulty of decomposing the effects of brightness and reflectance anisotropy (BRDF shape) in complex desert shrub landscapes with varying soil-understory characteristics was overcome by allowing linear scaling of the parameters of the soil-understory sub-model as a function of near-nadir 631 nm reflectance. The retrieved parameter maps show a high spatial correlation between width and height but a different distribution for density. Examination of high resolution panchromatic and multi-spectral imagery shows that there are strong relationships between the retrieved parameters and canopy characteristics although further validation is required