Orientation angle estimation over forested terrain using P-band POLSAR data

One important secondary objective of the proposed Earth-Explorer Candidate Mission BIOMASS is the retrieval of a digital terrain model (DTM) using satellite-borne P-band SAR data. The interferometric phase acquired in repeat-pass mode may be affected by ionospheric effects leading to corrupted phase estimates and, consequently, to errors in the derived DTM. In contrast, line-of-sight orientation angles induced by azimuth slopes can be estimated using single-pass POLSAR measurements. The orientation angle estimates allow a necessary pre-processing of POLSAR observations and the retrieval of topographic information such as a DTM. In this study, the performance of the circular polarization method for orientation angle estimation is examined over forested areas. To this end, the orientation angles computed from P-band POLSAR data are compared with the results obtained from LIDAR DTMs. In particular, the estimation performance is investigated with respect to the impact of topography and vegetation. POLSAR data at P-band are used that have been acquired by the E-SAR system of DLR over three forested test sites: two boreal forests in Sweden (one over flat terrain located at Remningstorp, the other over terrain with topographic variations at Krycklan) and the tropical forest Mawas in Indonesia over flat terrain.