Study On High-resolution SAR Imaging Algorithms Based On Subaperture Processing

Synthetic aperture radar (SAR) is used to generate high-resolution images of radar reflectivity of the scene of interest. It can provide specific information in all day and all weather which optical and infrared sensors can't do. Therefore, it becomes an important remote sensing tool and widely used in both the military and the civil application. High resolution is the most important feature which makes SAR distinguished from traditional radar, and higher resolution is the unremitting pursuit in SAR development. Ultra-high resolution SAR is an important research direction in recent years. Image formation algorithm is the core of ultra-high resolution SAR signal processing. Various SAR imaging algorithms have been presented in literature. The subaperture algorithm is highly regarded because of its unique characters in the imaging performance, motion compensation and processing efficiency. The advanced signal-processing scheme based on the overlapped subaperture algorithm (OSA) has been tested on the foreign airborne SAR system.Chapter 1 is the introduction.The history of SAR technology is firstly outlined. Then, the latest developments of ultra-high resolution SAR in China and abroad are reviewed. At last, the research background and main contents of this thesis are presented.Chapter 2 describes the SAR imaging mode, and basic imaging principle. Then the frequency history of the spotlight SAR echo signal is studied, and the range and azimuthal resolution formulations are derived.Chapter 3 makes comprehensive research into polar format algorithm (PFA). Then the resolution and scene size of this methodology are analyzed.Chapter 4 describes the basic principle of the overlapped subaperture imaging algorithm. The basic concepts of tiered subaperture are introduced with one-dimensional signal. The computer simulation indicates that this methodology is feasible and effective. Then the application of OSA in the spotlight SAR is analyzed. The principle of residual phase errors compensation is describled in detail, and a specific realization method is given. At last, the target simulation and raw data processing results are given.Chapter 5 studies the mosaic imaging algorithm for the stripmap SAR imaging based on OSA. At first, the stripmap mode SAR data is divided into small sub-block after an equivalent data convertion. The sub-block data is then processed with the OSA algorithm. And the sub-block images are finally mosaiced into a continuous image. The live data processing results are given to demonstrate the validity of this algorithm.In the end, the work of the thesis is concluded and the issues to be further studied are pointed out as well.