Validation of Bidirectional Reflectance Models Using the First Scene Acquired by the CHRIS Sensor over the Jornada Experimental Range

Multi-angular reflectance data over desert grasslands and shrublands in the USDA, ARS Jornada Experimental Range near Las Cruces, New Mexico, were obtained by the Compact High Resolution Imaging Spectrometer flown on the PROBA satellite on August 5, 2002. An experimental satellite-borne sensor, the CHRIS, is one of the few sources of consistent multi-angular reflectance data on kilometer scales, providing up to five looks at a given target within the space of a few minutes. Two images acquired at different sun-target-sensor geometries were used to examine the validity of a simplified geometric-optical model (SGM) of bidirectional reflectance which incorporates a priori, empirical knowledge of the scattering properties of the underlying soil. The model is based on principles of geometric-optics while providing a mechanism for encapsulating volume scattering effects. It has been subjected to sensitivity studies and tested using a radiosity-based method, with simulations driven by detailed plant maps and measurements of the optical properties of plants and soils. However, up to this point it has only been tested against multi-angular data acquired from the air by tilting a digital multispectral camera; work here using data from the CHRIS sensor extends and corroborates the results presented in the previous studies.