The interrelationship of atmospheric correction of reflectances and surface BRDF retrieval: a sensitivity study

This paper systematically studies the interrelationship between surface bidirectional reflectance distribution function (BRDF) retrieval and atmospheric correction. The study uses the atmospheric correction scheme of the Moderate Resolution Imaging Spectroradiometer (MODIS) and angular sampling expected for MODIS and the Multiangle Imaging SpectroRadiometer (MISR) for different land cover types and optical depths of aerosols. The results show the following two points. 1) Even for a nonturbid atmosphere, the assumption of a Lambertian surface in atmospheric correction causes relative errors in the retrieved surface reflectances that average from 2 to 7% in the red and near-infrared bands, with worst cases showing errors of up to about 15% for turbid conditions. Consequently, it is necessary for improved accuracy to consider surface anisotropy in atmospheric correction. 2) Surface BRDF retrieval and atmospheric correction can be coupled in a converging iteration loop that improves the quality of atmospheric correction and subsequent BRDF retrievals. For example, performing two steps of the iteration loop is already sufficient to obtain mean relative errors of less than 1% in the retrieved surface reflectances even for an atmospheric aerosol optical depth of 0.4. As BRDF retrieval accuracies improve, so do bihemispherical albedo retrieval accuracies, with mean relative errors being 1-5% when using a Lambertian assumption and less than 1% after two iteration steps.