本文關鍵詞： SAR 自聚焦算法 多子孔徑自聚焦 兩維自聚焦 FPGA 實時處理　出處：《南京航空航天大學》2014年碩士論文　論文類型：學位論文

【摘要】：自聚焦算法是SAR（SyntheticAperture Radar，合成孔徑雷達）成像處理中的一個重要步驟，，它研究的是估計經(jīng)運動補償后的殘留相位誤差并進行補償以提高SAR圖像的質量，是對運動測量單元的補充。因此，本文對自聚焦算法及其FPGA實現(xiàn)進行了一系列的探究。 第一章介紹了本文研究的背景及意義，對自聚焦算法的發(fā)展及其基于FPGA（FieldProgrammable Gate Array，可編程邏輯門陣列）的硬件實現(xiàn)進行了回顧與總結，比較了常用的各種自聚焦算法的優(yōu)缺點。 第二章詳細分析了幾種估計一維方位相位誤差的自聚焦算法。在這一章里，首先給出了PGA算法的處理流程，分析了估計的性能；針對PGA算法收斂速度慢的缺陷，介紹了QPGA（QualityPGA）算法的原理。然后以PGA算法為基礎，討論了處理長CPI（Coherent Processing Interval，相干處理間隔）圖像的幾種算法：PCA（Phase CurvatureAutofocus，相位曲率自聚焦），PGA-LS，PGA-MD，給出了算法的推導過程，算法性能分析及實測數(shù)據(jù)的處理。處理結果表明，全孔徑PGA與PCA算法處理長CPI散焦問題時是失敗的，PGA-LS和PGA-MD能夠有效的改善原始SAR圖像散焦效果。進一步，我們對PGA-LS與PGA-MD算法進行了比較，分析結果表明PGA-MD算法性能優(yōu)于PGA-LS。最后介紹了基于PAST（Projection Approximation SubspaceTracking，投影近似子孔徑跟蹤技術）的自聚焦算法。該算法克服了基于特征分解方法的自聚焦算法計算量大的問題，且估計的精度高魯棒性好。 在第三章中我們介紹了一種基于先驗知識的兩維自聚焦算法。這一方法克服了第二章中幾種算法對相位誤差直接進行估計而忽略究竟采用何種算法得到SAR圖像的缺陷，充分利用了先驗的信息，獲得了在PFA（Polar Format Algorithm，極坐標格式算法）框架下兩維相位誤差與一維方位向相位誤差的解析關系。因此，只需估計出方位向的相位誤差即可完成兩維相位誤差的估計。我們給出了這種解析關系的詳細推導，并作了仿真驗證及實測數(shù)據(jù)的處理，處理的結果表明了本算法的有效性。 第四章討論了利用Xilinx公司KC705開發(fā)板（Kintex7系列FPGA）實現(xiàn)PGA與PAST兩種自聚焦算法。由于FPGA需要頻繁的從DDR3讀取數(shù)據(jù)，為更方便的訪問DDR3中的二維SAR數(shù)組，設計了一種訪問DDR3的四種工作（轉置讀寫）模式的狀態(tài)機，簡化了接口的使用。分別設計了兩種算法的狀態(tài)機及PGA算法的一次迭代處理流程圖，兩種算法在200MHz的系統(tǒng)時鐘下以0.5s左右的時間處理了一幅2048*2048大小的SAR圖像，并對FPGA處理結果進行了詳細的分析，分析結果表明FPGA實現(xiàn)自聚焦算法的可行性和有效性。這為今后將自聚焦算法與基本成像算法結合起來形成一個完整的SAR實時處理系統(tǒng)奠定了基礎。 第五章對本文的兩大部分內容，即SAR自聚焦算法研究與FPGA的硬件實現(xiàn)作了一個總結。本章還討論了今后的工作安排與展望，指出了未來的任務有兩個：一方面將繼續(xù)探討其他的自聚焦算法，尤其是在除PFA外的其他成像算法下的兩維自聚焦算法，為SAR成像處理提供更好的理論依據(jù)；二是將利用FPGA芯片間的相互通信實現(xiàn)數(shù)據(jù)量更大的聚焦處理并將自聚焦算法與基本成像算法結合起來以實現(xiàn)一個完整的SAR成像處理系統(tǒng)。
[Abstract]:Autofocus algorithm is SAR (SyntheticAperture Radar, synthetic aperture radar) is an important step in image processing, it is estimated by the residual phase error after motion compensation and compensation to improve the quality of SAR images, is a supplement to the motion measurement unit. Therefore, this paper explores a series of implementation autofocus algorithm and FPGA.
The first chapter introduces the background and significance of this paper, reviews the development of self focusing algorithm and its hardware implementation based on FPGA (FieldProgrammable Gate Array, programmable logic gate array), and compares the advantages and disadvantages of various self focusing algorithms.
The second chapter analyzes several estimation autofocus algorithm for one-dimensional azimuth phase errors. In this chapter, firstly, the process of PGA algorithm, the estimation performance is analyzed; according to the defects of PGA algorithm with slow convergence, introduces QPGA (QualityPGA) algorithm principle. Then based on the PGA algorithm, is discussed the length of CPI (Coherent Processing Interval, coherent processing interval) several algorithms of image: PCA (Phase CurvatureAutofocus, PGA-LS, phase curvature autofocus), PGA-MD, derivation of the algorithm is given, processing algorithm and performance analysis of the measured data. The results show that the full aperture PGA and PCA algorithm for defocus length CPI the problem is a failure, PGA-LS and PGA-MD can effectively improve the original SAR image defocusing effect. Further, we compare PGA-LS with PGA-MD algorithm, and the results show that the PGA-MD algorithm is of better performance At the end of PGA-LS., a self focusing algorithm based on PAST (Projection Approximation SubspaceTracking, projection approximation subaperture tracking technology) is introduced. The algorithm overcomes the problem of large computation based on eigendecomposition algorithm, and has high accuracy and robustness.
In the third chapter, we introduce a two dimensional autofocus algorithm based on prior knowledge. This method overcomes several algorithms in chapter second of the phase error to be estimated directly and ignore what exactly SAR image defects which kind of algorithm, make full use of the prior information obtained in PFA (Polar Format Algorithm, a the algorithm) under the framework of two dimensional phase error and one-dimensional azimuth analytical relationship of phase error. Therefore, only need to estimate the phase error estimation of azimuth can be completed two dimensional phase error is derived in detail. We give the analytic relationship, and makes the processing simulation and measured data, processing the results showed that this algorithm is effective.
The fourth chapter discusses the use of Xilinx KC705 development board (Kintex7 series FPGA) PGA and PAST two kinds of autofocus algorithm. Because FPGA requires frequent read data from DDR3, two-dimensional SAR array is more convenient access to the DDR3, designed four kinds of a DDR3 access (read and write to the state) machine mode, simplify the use of the interface are designed. The state machine of PGA algorithm and two algorithms of an iterative processing flow chart, two kinds of algorithm in the 200MHz system clock to 0.5s around the time of processing SAR images of 2048*2048 and FPGA on the size of the processing results are analyzed in detail the results show that the FPGA, the feasibility and effectiveness of the autofocus algorithm. This is the future of the autofocus algorithm with basic imaging algorithm are combined to form a complete SAR real-time processing system of the foundation.
The fifth chapter two most of the contents of this article, namely SAR and FPGA study on self focusing algorithm hardware implementation has made a summary. This chapter also discusses the future work arrangements and prospects, and points out that the future has two tasks: on the one hand will continue to explore other autofocus algorithm, especially in the other two dimensions in addition to PFA imaging algorithm under the autofocus algorithm, provides a better theoretical basis for SAR imaging; two is the use of mutual communication between the FPGA chips to realize data volume focusing more and the autofocus algorithm with basic imaging algorithms are combined to achieve a complete SAR imaging system.

【學位授予單位】：南京航空航天大學
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：TN957.52

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相關期刊論文 前1條

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