BiSAR Image Autofocus Method Based on Target Scattering Parameters

The Bistatic synthetic aperture radar (BiSAR) transmitter and receiver are separated, the system configuration is flexible compared with traditional SAR, and it has the advantages of realizing forward-looking imaging, day-and-night and weather-independent, etc.. BiSAR is a research hotspot in the field of SAR imaging. The BiSAR imaging algorithm already has a certain research foundation, but in experimental data. Imaging relies on the measurement accuracy of the platform trajectory, and platform trajectory errors often introduce motion errors. Image autofocusing is required to obtain high-precision BiSAR images. Traditional autofocus methods need to be based on evaluation indicators such as isolated strong points or image entropy, which will have greater limitations when applied to extended targets. In order to achieve high-precision image focusing of BiSAR targets, this paper proposes a BiSAR automatic focusing method based on target scattering characteristics. First, a parameterized BiASR motion error echo model is established, in which the target geometric parameters and motion error phase are simultaneously represented in the echo model. Then, the amplitude and phase of the BiSAR echo are separated. Based on the envelope of echo amplitude, a BiSAR target structure parameter estimation model is established. The Iterative Soft Threshold Algorithm (ISTA) is used to estimate the structural parameters of the target, and the reference envelope of the target in the imaging result is generated based on the target parameter estimation results. Finally, based on the reference imaging envelope and combined with the differential evolution algorithm, the motion error phase is estimated and compensated to obtain the self-focusing result. The effectiveness of the method was verified through simulation and measured data verification.