Efficient DPCA SAR imaging with fast iterative spectrum reconstruction method

The displaced phase center antenna (DPCA) technique is an effective strategy to achieve wide-swath synthetic aperture radar (SAR) imaging with high azimuth resolution. However, traditionally, it requires strict limitation of the pulse repetition frequency (PRF) to avoid non-uniform sampling. Otherwise, any deviation could bring serious ambiguity if the data are directly processed using a matched filter. To break this limitation, a recently proposed spectrum reconstruction method is capable of recovering the true spectrum from the nonuniform samples. However, the performance is sensitive to the selection of the PRF. Sparse regularization based imaging may provide a way to overcome this sensitivity. The existing time-domain method, however, requires a large-scale observation matrix to be built, which brings a high computational cost. In this paper, we propose a frequency domain method, called the iterative spectrum reconstruction method, through integration of the sparse regularization technique with spectrum analysis of the DPCA signal. By approximately expressing the observation in the frequency domain, which is realized via a series of decoupled linear operations, the method performs SAR imaging which is then not directly based on the observation matrix, which reduces the computational cost from O(N ²) to O(N log N) (where N is the number of range cells), and is therefore more efficient than the time domain method. The sparse regularization scheme, realized via a fast thresholding iteration, has been adopted in this method, which brings the robustness of the imaging process to the PRF selection. We provide a series of simulations and ground based experiments to demonstrate the high efficiency and robustness of the method. The simulations show that the new method is almost as fast as the traditional mono-channel algorithm, and works well almost independently of the PRF selection. Consequently, the suggested method can be accepted as a practical and efficient wide-swath SAR imaging technique.