Estimation of aerosol opacity and land surface bidirectional reflectance from ATSR-2 dual-angle imagery: Operational method and validation

[1] Imagery from the second Along Track Scanning Radiometer (ATSR-2) is analyzed to reveal that a separation of the atmospheric from the land surface signal is possible given two near-simultaneous images at differing slant paths. The method is based on the inversion of a simple physical model of light scattering by the land surface. The result is an image of the land surface reflectance that is relatively uncontaminated by atmospheric scattering and a separate image of the atmospheric aerosol loading. Unlike single-image satellite methods for aerosol estimation, no assumptions are required about the land surface spectral properties, allowing for quantitative mapping of aerosol over an arbitrary land surface. Validation is performed over boreal forest by comparison with data from a network of Sun photometers. Satellite estimates of aerosol optical depth agree with field measurements to within 0.02 at 550 nm. An important consequence is that measurements can be compared over time, and small changes in land surface reflectance can be separated from atmospheric changes.