Compact PolInSAR and Ionosphere

摘要

In spaceborne SAR, a single-polarisation on transmit has, over full polarisation, the vast advantage of a doubleswath due to SAR system design issues. Without getting into the technical details deserving by themselves a fullpaper, we can just mention the swath characteristics of ALOS PALSAR, reducing from 70km for dual-pol modeto 30 km for full-polarisation mode. The options chosen up to now for dual-pol system designs (or singlepolarisationon transmit) rely on a linear polarisation on transmit, with two orthogonal polarisations on receive. Inan earlier paper, we proposed a more pertinent alternative for the selection of the transmit polarisation leading toa better characterisation of the scattering mechanisms [1,2]. This mode is called the p/2 CP mode, in reference tothe transmit polarisation being circular. At low frequency, where the ionosphere has a significant effect, the circulartransmit polarisation is the only sensible option as it provides an effective constant polarisation as seen by thescattering surface. This is an essential condition for a meaningful multi-temporal analysisIn this paper, the analysis is pursued in more depth by including the effect of the ionosphere on the wave propagation,exploring both the POLSAR and PolInSAR applications and investigating procedure to estimate the Faradayrotation from the CP data.