本文選題：合成孔徑雷達 + 多模式成像��； 參考：《西安電子科技大學(xué)》2014年博士論文

【摘要】：合成孔徑雷達(SAR)具有全天時、全天候、遠作用距離、二維高分辨率及寬場景成像等特點,已在軍事及民事領(lǐng)域得到廣泛的應(yīng)用。不同的應(yīng)用,要求SAR圖像具有不同的分辨率和場景覆蓋范圍,由此SAR發(fā)展出多種不同的工作模式,比如條帶式、聚束式、滑動聚束式及TOPS SAR。同時,SAR靈活的波束指向又使其可以工作于正側(cè)視、前斜視及前視等不同構(gòu)型。由于不同模式不同構(gòu)型的數(shù)據(jù)錄取方式存在較大的差異,回波信號具有各自的特點,導(dǎo)致各種模式的信號處理方法不盡相同。本論文集中于多種SAR工作模式的信號處理,根據(jù)不同模式工作幾何的特點,分析回波信號的特性,提出了合適的成像方法。具體內(nèi)容如下:1.根據(jù)機載TOPS SAR工作模式波束掃描速度快、旋轉(zhuǎn)角度大的特點,研究了一種新穎的全孔徑成像方法。首先根據(jù)TWO-STEP思想進行方位預(yù)濾波,消除由天線方位旋轉(zhuǎn)引起的多普勒頻譜模糊問題,得到信號無模糊的二維頻譜;其次結(jié)合非線性頻調(diào)變標(biāo)(NCS)算法完成距離單元徙動(RCM)校正及距離脈壓;然后采用SPECAN的方法將數(shù)據(jù)聚焦在方位頻域,避免聚焦在時域時出現(xiàn)的圖像混疊問題;最后通過Chirp-Z變換,校正成像結(jié)果的幾何形變。該算法不需要插值操作和坐標(biāo)轉(zhuǎn)換,因此運算量小、效率高。通過對仿真數(shù)據(jù)及某機載試驗SAR系統(tǒng)錄取的實測數(shù)據(jù)的處理,驗證了方法的有效性。2.對廣義極坐標(biāo)格式算法(GPFA)進行了改進,使其可用于斜視TOPS SAR的數(shù)據(jù)處理。改進方法采用先線性距離走動校正后PFA插值的步驟。線性走動校正可以極大地降低距離向與方位向的耦合性,簡化距離單元徙動(RCM)校正過程,并且有別于斜視聚束模式PFA插值常采用的坐標(biāo)旋轉(zhuǎn)思想,線性走動校正之后方位信號采樣間隔依然是均勻的,這給方位向的插值帶來了極大的便利。對于波束掃描及走動校正引起的多普勒調(diào)頻率方位空變問題,采用方位非線性變標(biāo)(NCS)的方法進行統(tǒng)一校正,大大提高了方位向聚焦深度,增加了可聚焦的場景范圍。仿真和實測數(shù)據(jù)處理結(jié)果驗證了所提方法的有效性。3.針對斜視多模式SAR的信號處理,提出了一種基于方位重采樣的成像方法。斜視SAR回波信號由于存在線性走動,其距離向與方位向的耦合要顯著得多。線性走動校正雖然可以極大地緩解這種耦合性,但同時也導(dǎo)致信號的方位空變性,使方位平移不變性不再成立。為了消除信號的方位空變性,我們提出了一種基于方位重采樣的信號頻譜處理方法。線性走動校正后,根據(jù)等效陣列的原理,在二維頻域?qū)π盘栴l譜進行重采樣,將斜視SAR信號的頻譜等效為正側(cè)視SAR。對于斜視波束指向SAR(BS-SAR),也即斜視聚束、斜視滑動聚束及斜視TOPS SAR,將方位重采樣結(jié)合到信號頻譜恢復(fù)的過程中,因此,由線性走動校正引入的方位空變性和由天線波束旋轉(zhuǎn)引起的信號模糊都將被消除。經(jīng)過線性走動校正及方位重采樣后,斜視SAR數(shù)據(jù)就可以采用常規(guī)正側(cè)視SAR成像算法完成聚焦。通過對仿真數(shù)據(jù)及實測數(shù)據(jù)的處理,驗證了所提方法在多模式SAR成像中的有效性。4.將所提基于方位重采樣的成像方法推廣應(yīng)用于斜視聚束式FMCW-SAR的數(shù)據(jù)處理。FMCW-SAR達到毫秒級的信號時寬導(dǎo)致常規(guī)算法推導(dǎo)中常用的“走-停-走”近似模型不再成立。針對此,并根據(jù)FMCW-SAR常采用Dechirp技術(shù)接收信號的特點,結(jié)合所提基于方位重采樣的方法,我們提出了一種合適于斜視聚束式FMCW-SAR的全孔徑成像方法。完成線性走動校正及方位卷積操作后,在距離多普勒域?qū)走_平臺連續(xù)運動引起的多普勒頻移進行補償,避免在距離脈壓結(jié)果中出現(xiàn)剩余的RCM。然后進行方位重采樣,消除線性走動校正引起的方位空變性。最后執(zhí)行RCM校正、二次距離脈壓及方位匹配濾波,完成對數(shù)據(jù)的聚焦。此外,針對寬場景成像中RCM的距離空變問題,提出了一種基于子場景的校正方法。最后通過窄場景及寬場景的仿真實驗對該方法進行了驗證。5.提出一種采用周期性非均采樣實現(xiàn)高分辨率寬測繪帶的SAR成像體制。單通道星載SAR系統(tǒng)由于受最小天線面積的限制,高分辨率與寬測繪帶構(gòu)成一對矛盾。在所提的新體制中,采用發(fā)射正交波形及合適的系統(tǒng)PRF等方式,避免了距離模糊問題。利用非均勻的采樣,并通過對采樣序列的合理設(shè)計,使距離盲區(qū)均勻的分布在回波數(shù)據(jù)內(nèi),避開盲區(qū)的重疊現(xiàn)象;然后利用方位采樣的周期性,構(gòu)造出等效的多通道數(shù)據(jù),并通過多通道解模糊的方法實現(xiàn)方位信號的頻譜恢復(fù)。該體制可以實現(xiàn)星載單通道SAR系統(tǒng)高分辨寬測繪帶成像,且不存在距離盲區(qū)問題。點目標(biāo)的仿真實驗驗證了所提體制及方法的可行性及有效性。6.對多普勒調(diào)頻率估計的平移相關(guān)(SAC)算法進行改進,使其適合用于聚束及滑動聚束SAR的全孔徑成像處理。將距離Keystone變換引入到原始SAC算法中,消除了互相關(guān)峰值位置與目標(biāo)距離間的耦合關(guān)系,從而去除了互相關(guān)函數(shù)幅度疊加時受到的聚焦深度的限制。對于因沒有進行時域補零導(dǎo)致在調(diào)頻率估計過程中出現(xiàn)的模糊問題,采用最小熵準則對模糊次數(shù)進行估計,并對調(diào)頻率計算公式進行修正以得到正確的估計值。通過對仿真數(shù)據(jù)及某機載試驗SAR系統(tǒng)錄取的實測數(shù)據(jù)的處理,充分驗證了改進SAC算法的優(yōu)越性。
[Abstract]:Synthetic aperture radar (SAR) has the characteristics of all-weather, all-weather, far action distance, two-dimensional high resolution and wide scene imaging. It has been widely used in military and civil fields. Different applications require different resolution and scene coverage of SAR images, thus SAR has developed a variety of different working modes, such as strip type, Bunching, sliding cluster and TOPS SAR. simultaneously, the flexible beam direction of SAR enables it to work in different configurations such as Yu Zheng side view, front strabismus and forward view. Due to the large difference in the data admission mode of different modes and different configurations, the echo signal has its own characteristics, which leads to the different methods of signal processing in various modes. The thesis focuses on the signal processing of various SAR working modes. According to the characteristics of different modes of working geometry, the characteristics of the echo signal are analyzed and the appropriate imaging methods are proposed. The specific contents are as follows: 1. a novel full aperture imaging method is studied according to the characteristics of the fast beam scanning speed and the large angle of rotation in the working mode of the airborne TOPS SAR. Firstly, the azimuth pre filtering is carried out according to the TWO-STEP idea to eliminate the ambiguity of Doppler spectrum caused by the azimuth rotation of the antenna, get the two-dimensional spectrum without ambiguity, and then combine the nonlinear frequency modulation (NCS) algorithm to complete the distance unit migration (RCM) correction and the distance pulse pressure, and then use the SPECAN method to focus the data in the azimuth frequency. Domain, avoiding the problem of image aliasing when focusing on the time domain; finally, the geometric deformation of the imaging results is corrected by Chirp-Z transformation. The algorithm does not need interpolation operation and coordinate conversion, so the computation is small and efficient. The effectiveness of the method is verified by the processing of the simulated data and the measured data accepted by an airborne test SAR system,.2 The generalized polar coordinate format algorithm (GPFA) is improved so that it can be used for the data processing of the strabismus TOPS SAR. The improved method adopts the step of the PFA interpolation after the linear distance movement correction. The linear walk correction can greatly reduce the coupling between the distance to the azimuth, simplify the RCM correction process and be different from the deviation. The idea of coordinate rotation often used in the PFA interpolation of optical beam mode is used, and the sampling interval of azimuth signal is still uniform after linear motion correction, which brings great convenience to the azimuth interpolation. The azimuthal nonlinear scaling (NCS) method is used for the Doppler frequency azimuth change problem caused by beam scanning and moving correction. The unified correction greatly improves the orientation focus depth and increases the range of the focusable scene. The simulation and measured data processing results verify the effectiveness of the proposed method.3.. A method based on azimuth resampling is proposed for the signal processing of the strabismus multi mode SAR. The skew SAR echo signal has a linear motion and its distance due to the existence of a linear motion. The coupling of the off direction and the azimuth is much more significant. Although the linear motion correction can greatly alleviate this coupling, it also leads to the azimuth invariance of the signal, which makes the invariance of the azimuth shift no longer established. In order to eliminate the azimuth denaturation of the signal, we propose a method of signal spectrum processing based on azimuth resampling. After the correction, the signal spectrum is resampling in two-dimensional frequency domain according to the principle of the equivalent array, and the spectrum of the SAR signal is equivalent to the positive side view SAR. for the strabismus beam pointing to SAR (BS-SAR), that is, the strabismus bunching, the strabismus slipping bunching and the squint TOPS SAR, and the azimuth resampling in the process of the signal spectrum recovery. The azimuth denaturation introduced by linear motion correction and the signal blur caused by the antenna beam rotation are eliminated. After linear motion correction and azimuth resampling, the SAR data of the strabismus can be focused by the conventional positive side view SAR imaging algorithm. The effectiveness.4. in the SAR imaging makes the image method based on azimuth resampling applied to the data processing of the strabismus cluster FMCW-SAR data processing.FMCW-SAR to millisecond signal time, which leads to the usual "walk stop walk" approximation model, which is commonly used in the conventional algorithm deduction. With the feature of signal receiving, we propose a full aperture imaging method suitable for the strabismus bunching FMCW-SAR. After completing the linear walk correction and azimuth convolution operation, the Doppler shift caused by the continuous motion of the radar platform in the distance Doppler domain is compensated to avoid the distance pulse pressure junction. The remaining RCM. appears in the fruit and then carries out azimuth resampling to eliminate azimuth denaturation caused by linear motion correction. Finally, RCM correction, two distance pulse pressure and azimuth matching filtering are performed to focus on the data. In addition, a correction method based on the subscene based on the sub scene is proposed for the range space change problem of RCM in wide scene imaging. This method is verified by the simulation experiments of narrow scene and wide scene. A SAR imaging system with high resolution and wide swath with periodic non uniform sampling is proposed. The single channel spaceborne SAR system has a contradiction between the high resolution and the wide swath band because of the limitation of the minimum antenna area. In the proposed new system, the SAR system is used in the new system. The transmission of orthogonal waveforms and appropriate system PRF avoids the problem of distance blurring. Using non-uniform sampling and reasonable design of the sampling sequence, the distance blind area is evenly distributed in the echo data to avoid the overlap phenomenon of the blind area, and then the equivalent multi-channel data is constructed by using the periodicity of azimuth sampling, and it is passed. The spectrum recovery of azimuth signals is realized by the method of multichannel ambiguity resolution. The system can realize high resolution wide swath imaging of the satellite borne single channel SAR system with no distance blind area. The simulation experiment of point target verifies the feasibility and effectiveness of the proposed system and method and the translation correlation (SAC) algorithm for the estimation of Doppler frequency modulation rate (.6.). It is improved so that it is suitable for all aperture imaging processing for bunching and sliding cluster SAR. The distance Keystone transform is introduced into the original SAC algorithm to eliminate the coupling relationship between the position of the correlation peak value and the distance of the target, thus removing the limitation of the focus depth when the amplitude superposition of the cross correlation function is removed. For the reason that the time domain is not carried out in time domain. The fuzzy problem in the estimation of frequency modulation rate is caused by zero filling. The minimum entropy criterion is used to estimate the fuzzy number, and the formula of the frequency modulation is corrected to get the correct estimation value. The superiority of the improved SAC algorithm is fully verified by the processing of the simulated data and the measured data accepted by an airborne test SAR system.
【學(xué)位授予單位】：西安電子科技大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2014
【分類號】：TN957.52

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