Improved Polar Format Algorithm for Maritime Ship Target Imaging in Spaceborne-Maneuvering Platform Bistatic SAR

Spaceborne-maneuvering platform bistatic SAR (BiSAR) can not only make the high-speed maneuvering platform have the advantages of electromagnetic silence and anti-jamming, but also have the ability of high-resolution imaging of the ship targets in front of the flight, which has an important civil and military value. Due to the characteristics of non-cooperation of the movement of ship target, the imaging of ship target will have serious defocusing problem, and the degree of defocusing of the spaceborne-maneuvering platform bistatic SAR are not the same for ship target under different sea conditions. To solve the problem of defocusing, in this paper, the improved polar format algorithm is proposed for different sea conditions. Firstly, the defocusing problem of moving ship target under different sea conditions are analysed. And, the envelope alignment and particular point method are used to compensate the signal for translational motion. Secondly, when the ship target is in a low sea condition, the polar format algorithm can used for imaging directly, and it can focus well. While in high sea conditions, the defocusing problem will become serious. Thus, this paper process the resulting signal in the wave number domain, and fits the two-dimensional wave number as a third-order polynomial, then extracts the higher-order polynomial that affects the focusing to get the space-variant phase. Then the particle swarm optimization (PSO) is adopted to search for these space-variant phase parameters. Finally, compensating for the space-variant phase by the estimated parameters, and then obtain the focusing image of ship target. The effectiveness of the proposed Algorithm is verified through simulation data.