A Novel Focus Approach for Squint Mode Multi-Channel in Azimuth High-Resolution and Wide-Swath SAR Imaging Processing

An imaging processing for the squint mode multi-channel in azimuth high-resolution and wide-swath (MC-HRWS) synthetic aperture radar (SAR) system is presented in this paper. First, the linear range cell migration correction (RCMC) is employed to correct the skew Doppler spectrum for each channel echo. Then, a robust Doppler spectrum reconstruction method is proposed, which is based on the robust Capon beamforming and multi-Doppler-direction restriction technique. After the reconstruction, a two-step focus approach is utilized to focus the image, where the first step is utilized to deal with the azimuth-invariance components and the second addresses the azimuth-variance component introduced by the linear RCMC. Since the Doppler centroid estimation is crucial to squint mode SAR imaging, this paper also presents a robust entropy-based Doppler centroid estimation algorithm for an MC-HRWS SAR system, where the correlation function approach is employed to estimate the baseband Doppler centroid. More importantly, an entropy-based Doppler ambiguity number resolving approach is proposed and the bisection algorithm is utilized to accelerate the searching process. Some simulation experiments are conducted to verify our proposal. Besides, the results of some real MC-HRWS SAR data also show that the proposed method works well.