Polarimetric calibration for wideband synthetic aperture radar imaging

Multi-channel techniques are introduced to calibrate for effects of antenna shading and crosstalk in wideband, wide-angle full polarisation radar imaging. The system is modelled as a two-dimensional integral operator which includes the transmit pulse function, receive and transmit antenna transfer functions, and response from scattering objects. Existing imaging algorithms provide an approximate inversion of this integral operator, without compensation for the effect of the multi-channel antenna transfer functions. Thus, standard processing yields poor image quality, due to the inherent variation of the antenna response (in magnitude, phase, and polarisation) across the large band of frequencies and wide range of aspect angles. Two techniques are proposed for regularised inversion of the system model. Both techniques require measurements of the antenna transfer function over the look angles and frequency band of interest. The first technique adopts a local approximation to process multi-channel range lines separately and is suitable for imaging small regions. The second technique achieves multi-channel deconvolution of the antenna response in the transform (Doppler) domain and is suitable for large data records. The result is imagery with improved polarisation purity and a more localised point spread function