Reaserch On Imaging Algorithm And Motion Compensation Of Squint SAR In Near Space

Squint airborne synthetic aperture radar SAR is a hot research field in recent years, because of the mobility and flexibility of beam pointing and imaging range. It can not only image the front of the target, but also on the rear of the target again, thus the security and invisibility can be greatly improved. So the squint mode has a distinct advantage over the positive mode. The studies on near space have not currently been expanded on large-scale, and the research of squint SAR imaging algorithm and motion compensation technology is not complete by now, so the study of near space squint SAR imaging system has a certain theoretical and practical value. This paper studies on near space squint SAR system characteristics, squint SAR imaging algorithm and motion compensation in-depth. The main point of this research and innovation are:(1)Established an imaging model of near space squint SAR platform. Studied the system characteristics of the near space squint SAR in-depth and discussed the basic imaging principles of squint SAR and the echo signal features such as two-dimensional coupling. Compared the SRC algorithm under with squint mode with the RDA algorithm under the positive side mode. The innovation of this section is to discuss the imaging process.of airborne squint SAR while considering the effect of the near space.(2)Proposed the subaperture secondary range compression algorithm. On the basis of secondary range compression algorithm under the squint mode, and considering the new near space environment characteristic like the big squint angles and the long synthetic aperture, this paper proposed an improved SRC algorithm using the subaperture techniques. The key step is to use the subaperture approach in the SRC algorithm. First, the original signals are divided into subapertures in the azimuth direction of the time domain to image independently, and then the sub-bands of the frequency domain are combined to form the final SAR image. The method reduces coupling in the range and azimuth direction of the echo signal under the squint imaging mode, and addresses the. problems of squint SAR in near space including overlong synthetic aperture and motion error. Simulation through point targets demonstrates the improvement in azimuth resolution, ISLR and PSLR, which verifies the effectiveness of this proposed SSRC algorithm in near space squint SAR imaging.(3)Studied the motion compensation technology of near space squint SAR. Firstly, elaborated and analyzed the widely used. motion compensation algorithm and the phase gradient autofocus algorithm which is based on the chirp rate estimates in detail. Then applied the PGA algorithm which is used for spotlight mode SAR to the squint strip mode SAR, in this way can realize the PGA processing of the strip mode SAR. The specific process is:Firstly process the strip mode SAR data in blocks on the basis of the previous subaperture algorithm. Finally the sub-bands of the frequency domain are combined to form the final SAR image.