Effect of polarization orientation angle shift on X-band TDM SAR COSSC Product of TerraSAR-X and TanDEM-X

摘要

Polarization orientation angle (POA) shift in the backscattered SAR wave induced, due to irregularity of the target surface. Polarimetric signatures of the backscatter SAR wave gets affected by the POA shift, causes error in the decomposition modelling as shift in POA makes coherency matrix asymmetric. POA shift compensation is very necessary to avoid misinterpretation of decomposition modelling results. POA shift effect has been observed using coherency matrix and decomposition model results. This study is conducted over Dudhwa National Park in the state of Uttar Pradesh, using high resolution, TDM SAR COSSC Product of TerraSAR-X and TanDEM-X in Bistatic mode. Present study mainly focused on the comparative analysis of resultant scattering component of decomposition model before and after POA shift compensation. Shift in POA is investigated using circular polarization technique. Yamaguchi four component decomposition model is used to express total backscatter information in terms of volume, double bounce, surface and helix scattering. Volume scattering is overestimated however double bounce and surface scattering is under estimated in decomposition model due to POA shift present in the backscatter SAR wave. Different scattering mechanisms resulted after POA compensation were analyzed using 100 random points taken from forest structure. The results obtained by TerraSAR-X and TanDEM-X shows an overall increase in double bounce scattering and decrease in volume scattering component after POA shift compensation. It is observed that there is negligible effect of POA shift on surface scattering. POA shift compensation necessarily required to improve the accuracy of decomposition models used in the forest parameter retrieval applications.