Estimation of the bidirectional reflectance distribution function of subarctic boreal forest using C-band SAR

Surface albedo is acknowledged as an important variable in climate research. Monitoring of Earth´s surface albedo in a global scale is practical only with satellite observations. However, satellite-based albedo research in the boreal regions is hampered by continual cloud contamination in the optical wavelengths, as well as long periods of low sun elevation. As the surface albedo can be calculated from the Bidirectional Reflectance Distribution Function (BRDF) of an area, new methods to improve the accuracy of BRDF calculation and remove cloud contamination effects are needed to enhance the accuracy of future climate studies. This study explores the possibility of estimating the BRDF of boreal forest using C-band synthetic aperture radar (SAR) data. The principle of the estimation is based on the knowledge that the BRDF of boreal forests depends on structural parameters such as NDVI or LAI, and that similar structural information can be derived from SAR imagery. The results of the study show that the estimation of BRDF from C-band SAR is possible at least under certain conditions, the proposed estimation method yielded a coefficient of determination of 0.68 for the small-scale study area in Northern Finland.