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Motion Parameter Estimation of Doppler-Ambiguous Moving Targets in SAR-GMTI

In an along-track interferometric SAR system, the discrete sampling of 
moving target signals can give rise to two types of ambiguity: Doppler 
ambiguity, and interferometric angle ambiguity. These ambiguities lead to 
ambiguities in target velocity estimation. 
 
Range cell migration of moving targets is unambiguous in target velocity. 
Hence, it can be used for resolving the ambiguities in target velocity 
estimation mentioned above. The wave number domain algorithm as well as 
the chirp scaling algorithm is adapted to moving target signals. In order to 
focus moving target signals with arbitrary velocities both approaches are 
extended to arbitrary Doppler frequency ands. Moving target signals 
distributed over two neighbouring PRF bands are especially difficult to detect 
and analyze because the sgnal splits into two parts. It is shown that the two 
parts appear at different positions in the SAR image and have different ATI 
phases. They show up as two weaker targets since the energy is split 
between them. It is demonstrated how the two targets can be identified as 
possibly the same target, and how they can be properly focussed by 
adaptation of the SAR focussing algorithms.