Study Of Imaging Method On The SAR With Continuous PRF Variation

Synthetic aperture radar(SAR) is a remote sensing technique, capable of providing high-resolution images independent of sunlight illumination and weather condition. However, conventional synthetic aperture radar is short in that a wide swath can only be achieved at the expense of a degraded azimuth resolution. In order to overcome these inherent limitations, researchers proposed an innovative concept, staggered SAR, where multiple swaths can be imaged using digital beam-forming in elevation, and the “blind range” problem in conventional SAR with constant PRI can be solved by continue PRF variation. What’s more, both the hardware complexity and the cost can be significantly reduced if compared to HRWS systems employing multiple azimuth apertures. In a word, it has important significance for the study of the imaging method of staggered SAR.Due to the no uniform sampling in azimuth direction and periodic pulse loss of the echo signal, the data can’t be processed by conventional frequency domain algorithm, which may lead to serious deterioration of imaging quality. The Back Projection can accomplish the focus of the raw data directly in time domain, but this method may take much time. In order to solve those problems, this thesis has done the following work:1. The imaging results of three kinds of PRI changes are studied. Slow PRI changes may lead to continuous signal loss, which bring certain difficulties to signal processing; for PRI fast change and PRI elaborate change, blind range effectively dispersed. The experiment shows that the imaging result is good.2. Three methods of resampling raw data are studied in this thesis. Lagrange interpolation, best linear unbiased interpolation, and multi-channel reconstruction. What’s more, the no uniform fast Fourier transform for staggered SAR is proposed. Through theoretical analysis and simulation results, these methods have different characteristics. Performance of Lagrange interpolation and BLU interpolation is very stable and can effectively deal with a variety of situations of echo signal, however, the amount of calculation is very large; multi-channel reconstruction algorithm which is only applicable to the change of PRI cycle is small, and this algorithm also enhances the influence of azimuth ambiguity and noise; multi-channel reconstruction based on LCMP can weaken the influence of noise on imaging results; NUFFT can complete data resampling and azimuth Fourier transform at the same time, and achieve a good balance between the performance of the algorithm and computational complexity.An asynchronous parallel backward projection algorithm based on CUDA stream is proposed. The method is improved on the basis of parallel image pixels, and makes data transmission and processing carried out simultaneously. In addition, the method of improving the operation efficiency by optimizing the number of CUDA stream is also studied.