Research On SAR/ISAR Imaging Algorithms Of Surface Ship Target With Helicopter Platform

Synthetic Aperture Radar(SAR)and Inverse Synthetic Aperture Radar(ISAR)are important means to monitoring territorial sea and real-time reconnaissance of ships in our country in recent years because of their ability to obtain high resolution images of targets all day and all weather.Compared with the fixed wing aircraft SAR/ISAR imaging platform,because of its advantages of vertical takeoff and landing,flying close to the ground,landing on uneven areas and hovering in the air,helicopter platform has been widely used in civil and national defense fields,and has become an important SAR/ISAR imaging platform,which plays a more and more important role in sea target monitoring and detection.However,the existing SAR/ISAR imaging algorithms based on the helicopter-borne platform are still in their infancy,with problems of low imaging resolution and high computational complexity,and further research on fast and high-resolution imaging algorithms is needed.In view of the above problems,this paper focuses on the research of helicopter-borne SAR/ISAR imaging algorithm,and the main research contents and innovation points are as follows:(1)Aiming at the problems of low azimuth resolution and high computational complexity due to the existing helicopter-borne rotating SAR imaging azimuth resolution depends on the size of reconstruction angle and requires interpolation operation,this paper proposed a fast high-resolution imaging algorithm for helicopter-borne Rotating SAR(Ro SAR)based on two-dimensional Chirp-Z transform.Firstly,the geometric and signal models of helicopter Ro SAR are established,and the two-dimensional frequency domain analytical expression of the echo signal is obtained by using the series inversion method.On this basis,by introducing efficient Chirp-Z transform,the range cell migration and sector distortion caused by azimuth Deramp processing is corrected,and the focused SAR image is obtained.The resolution of Ro SAR system and its influencing factors are analyzed in detail as well.Compared with the existing Ro SAR imaging methods,the proposed method has low computational complexity and high azimuthal resolution because of avoiding interpolation operation and expanding azimuth reconstruction angle size,which lays a foundation for subsequent target detection and recognition.Finally,the effectiveness and correctness of the proposed method are verified by computer simulation.And based on the MATLAB graphical user interface,the integrated application system of helicopter Ro SAR imaging is developed,which has been successfully applied in related projects and achieved good results.(2)In view of the existing helicopter ISAR imaging method need multidimensional search and platform movement leads to the hypothesis of constant imaging plane during the synthetic aperture time fails,which is difficult to get the focused ISAR image quickly.In this paper,a fast helicopter-borne ISAR imaging algorithm based on pseudo-polar coordinates is proposed by referring to the space-invariant characteristics of strip-band SAR imaging mode.Firstly,a new geometric and signal model of helicopter-borne ISAR imaging is established,and the analytical expression of echo signal in range-Doppler domain is obtained by using the principle of stationary phase.On this basis,a new interpolation kernel is designed to correct range migration and remove azimuthal Doppler modulation,then the computational complexity is further reduced by introducing a interpolation-free Stolt mapping.Compared with the existing imaging methods,due to the avoidance of multi-dimensional search and interpolation operations,and utilized the gain of two-dimensional coherent accumulation,the proposed method can achieve fast ISAR imaging under low SNR.Finally,the effectiveness and correctness of the proposed method are verified by computer simulation.