Range Ambiguities For A Polarimetric Spaceborne SAR

Results of modelling are presented of range ambiguities on a spaceborne polarimetric synthetic-aperture radar (SAR). Using 'interleaved-pulse' polarimetry and no additional pulse coding to suppress ambiguities, simulations have been performed of forest and ocean imaging for different numbers of near-range ambiguous swaths. Even neglecting antenna inter-channel crosstalk, which we expect to be serious in the sidelobes of an antenna's gain pattern, cross-polarised measurements become contaminated by ambiguous co-polarised backscatter. For a realistic antenna sidelobe gain of -20 dB, cross-polarised data over forests are expected to be useable (i.e. below -20 dB), while over the ocean they are likely to be overwhelmed by ambiguous responses. This is a consequence of the steep increase in co-polarised ocean backscatter towards nadir and the weakness of cross-polarised backscatter.