Key Technologies In On-board Real-time Imaging Processing For Spaceborne SAR

The space-borne SAR, on-board SAR imaging processing has becoming a trend, since the technical advance of imaging and application demanding increased. In space environment, the on-board processing system had some limited conditions which are the hardware size, weight and power requirements, so it blocked to achieving real-time processing for the space-borne SAR imaging algorithm; in addition, these conditions made algorithm very complex and requiring more powerful processing capability. In order to realize Space-borne SAR imaging processing on FPGA structure and build on-board system work flow, this dissertation was focus on studying the real-time imaging algorithm optimization, SAR imaging processing matrix transpose method and the implementation of a variety of transcendental functions in space-borne SAR imaging algorithm. All of main works’ innovations are as follows:1. The first part of research included three aspects which are the space-borne SAR processing algorithms, on-board core processor and system architecture. The FPGA was chose as on-board core processor, and CS algorithm was used to the space-borne kernel algorithm achieving by FPGA structure. Then the dissertation was proposed standardize, modular, scalable on-board real-time SAR imaging processing system architecture.2. Aim at the research problem of huge computing requirement and inefficiencies by achieving CS algorithm in FPGA structure, focused on the Doppler parameter estimation, selection and optimization. By analyzing the influence of phase compensation factor on the real-time processing of CS imaging algorithm, the paper proposed the CS imaging algorithm with area invariant compensation factor. This method as the premise of ensuring imaging quality, and it can decrease the computation complex of compensation factor and improve SAR imaging processing algorithm efficiency.3. Matrix block three-dimensional mapping method and matrix block cross-mapping method are proposed to approach the issue of data access efficiency of the corner turning memory in the SAR imaging processing. These two methods took advantage of timing characteristics of the corner turning memory, and they also can improve the data access efficiency and capability of the real-time SAR imaging processing.4. The studying research was according to implementing the transcendental function which is appears in the space-borne SAR imaging algorithm on FPGA. To calculate the sine, cosine and arctangent function by traditional CORDIC algorithm was optimized in aspects of angle range coverage, hardware resources and accuracy. To calculate the arcsine and arccosine functions, the double iteration algorithm was improved to avoid the computing exceeding the domain of the function. Then a multi-mode CORDIC algorithm was proposed, and it can realize real-time switching between sine/cosine and arcsine/arccosine functions. This method was very effectively and can reduce the hardware resources when the two kinds of function are both needed.5. Finally, this dissertation combines the research result of all chapters, implement all the processing stages of space-borne SAR imaging algorithm, and then build the on-board real-time imaging processing prototype system for space-borne SAR. The research results can be served as foundation for the subsequent development of on-board real-time processing for space-borne SAR.