The importance of instrument pointing accuracy for surface bidirectional reflectance distribution function mapping

Abstract

An investigation into the magnitude of error introduced into bidirectional reflectance distribution functions (BRDFs) due to unqualified attitude perturbations and uncertainties in the pointing accuracy of the sensor is described. For a given perturbation in the sensing geometry the magnitude of the error in the measured BRDF depends on the shape of the BRDF, i.e. on the Sun-target-sensor geometry and on the surface cover type. Using typical BRDF data sets measured in the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) it is shown that an error of 1° in the sensing geometry could result in approximately 1-5 per cent error in the BRDF. It is suggested that these errors could be reduced by sensing multi-angle data from stabilized platforms and/or by incorporating facilities for recording the sensor viewing geometry.