Retrieving forest background reflectance in a boreal region from Multi-angle Imaging SpectroRadiometer (MISR) data

Abstract

Studies of the bidirectional behavior of forest canopy have shown that the total reflectance of a forest canopy is the combination of illuminated and shaded components of the tree crown as well as the background. In this study, we estimate the background portion from the bidirectional reflection observed by Multi-angle Imaging SpectroRadiometer (MISR) instrument which scans the earth in nine different view angles in an oblique plane relative to the sun. The nadir and 60° forward directions of the MISR images were used to derive the reflectivity of the forest background based on the probabilities of viewing the illuminated tree crown and background on those view angles. The probabilities were estimated using the Four-Scale model. In the study, background reflectivity mosaic images in red and NIR wavelengths covering the BOREAS region during winter and spring seasons were obtained. The mosaic images of winter show high background reflectivity in both wavelengths, and in most of the areas the reflectivity was more than 0.3. In mosaic images of spring the spatial variations in the background reflectivity were considerable. The seasonal changes in the background reflectivity were also studied with multi temporal MISR data, and a similarity in the temporal pattern was found between the retrieved forest background reflectivity and grass land reflectance. These spatial and temporal patterns of the background component retrieved from MISR would be critically important in retrieving the biophysical parameters of vegetation and in ecosystem modeling.