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