Interpulse phase coding for improving accuracy of polarimetric SAR

Polarimetric measurements made by Synthetic Aperture Radar (SAR) may be in some cases, depending on the polarimetric response of distributed targets to be imaged, severely limited in their accuracy due to the joint effect of range ambiguities and weak crosspolarized signal response. Due to the utilization of alternate transmission of pulses at orthogonal polarizations, each ambiguous swath gives rise to one different kind of interference, depending whether its order is even or odd. Interference arising from even-order ambiguous swaths, differently from that arising from odd-order swaths, is generated by pulses transmitted on the same polarization channel of the pulse soliciting the desired echo signal, that they corrupt. Evidently, interference arising from odd-order swaths and affecting crosspolar measurements is most harmful, together with that arising from zones at low incidence angle, which carries a strong reflectivity contribution to the total interference on the desired signal. The paper discusses the utility of appropriate interpulse phase coding strategies, depending on the SAR geometry, than can be devised and utilized in the polarimetric interleaved-pulse measurement technique, with the task to reduce the interference generated by range ambiguities and affecting those target scattering matrix elements, whose measurement is expected to be most critical.