Retrieval of land surface bidirectional reflectance and aerosol opacity from ATSR-2 multiangle imagery

New satellite instruments that sample top-of-atmosphere radiance at a numbe r of view angles offer the potential For improved retrieval of atmospheric aerosol opacity, land surface bidirectional reflectance, and biophysical pa rameters. This paper presents a method for simultaneous retrieval of aeroso l opacity and land surface bidirectional reflectance, which utilizes the du al view capability of the second Along-Track Scanning Radiometer (ATSR-2), Analysis of a physically based model of light scattering results in two sim ple equations defining possible spectral variation of land surface bidirect ional reflectance distribution function (BRDF). These are used as constrain ts to allow inversion of a model of atmospheric scattering to simultaneousl y retrieve atmospheric aerosol opacity and bidirectional reflectance from t op-of-atmosphere radiance, The inversion assumes no a priori knowledge of t he land surface cover. Sensitivity is evaluated using both simulated and he ld-measured data to reproduce expected ATSR-2 observations. Where an atmosp here of known aerosol scattering properties, but of unknown optical depth, is available, results show mean absolute error in retrieval of aerosol opac ity of the greater of 0.02 or 15% relative error and bidirectional reflecta nce retrieval at 55 nm to an accuracy of <0.01, Where a number of candidate aerosol models ave available, results show discrimination of dominant aero sol type is possible in 95% of cases considered. The methods perform best o ver dark surfaces, such as vegetation, but show accurate retrieval over soi l and pixels containing a number of cover types.