On the design of spaceborne polarimetric SARs

To date, spaceborne polarimetric SARs have predominantly been implemented as experimental add-on modes to existing designs for single-pol or dual-pol systems. As a result, current and planned spaceborne SARs have polarimetric (or quad-pol) modes that are severely limited in swath width, are restricted in the range of look angles, suffer from low SNR and ambiguity problems, and are difficult to calibrate. The consequence of this is that the high potential science return expected from polarimetric SAR data has not and will not be realized. In this paper, the design of polarimetric SAR systems is revisited. Design principles are established, and recent advances will be described that allow wider swath polarimetry over a wide range of incidence angles, and simplified calibration of the final data product.