【摘要】：前視雙基地SAR由于可以對飛行方向正前方區(qū)域進(jìn)行成像,現(xiàn)在越來越受到國內(nèi)外研發(fā)人員的重視。SAR成像中,多普勒中心頻率誤差會導(dǎo)致信噪比下降、圖像平移;多普勒調(diào)頻率不準(zhǔn)確將導(dǎo)致圖像模糊、對比度下降;高階多普勒參數(shù)誤差會造成圖像失真。另外,在實(shí)際的SAR飛行中,載機(jī)平臺很容易受到氣流等影響,從而產(chǎn)生運(yùn)動誤差,進(jìn)而影響SAR圖像的聚焦質(zhì)量。本文針對前視雙基地SAR的多普勒參數(shù)估計(jì)和運(yùn)動補(bǔ)償技術(shù)展開研究,主要研究內(nèi)容包括:1.建立了前視雙基地SAR的幾何模型,給出了點(diǎn)目標(biāo)的回波模型,并分析其距離歷史特性和多普勒特性。研究發(fā)現(xiàn):前視雙基地SAR的多普勒參數(shù)具有質(zhì)心大、調(diào)頻斜率較小、高階多普勒參數(shù)不可忽略等特點(diǎn)。同時(shí),通過對線性調(diào)頻信號的相位誤差進(jìn)行分析,發(fā)現(xiàn)一次相位誤差會導(dǎo)致信號中心頻率發(fā)生偏移,二次相位誤差造成壓縮信號展寬、旁瓣電平升高,高次相位誤差造成主瓣不對稱等。2.研究了基于Radon變換和距離徙動校正函數(shù)的多普勒模糊數(shù)估計(jì)方法。運(yùn)用Radon變換對距離壓縮后的回波信號進(jìn)行角度估計(jì),再利用回波信號的直線斜率與多普勒模糊數(shù)之間的關(guān)系,實(shí)現(xiàn)多普勒模糊數(shù)估計(jì)。通過構(gòu)造距離徙動校正函數(shù)并以最小熵為代價(jià)函數(shù),估計(jì)得到多普勒模糊數(shù)。仿真實(shí)驗(yàn)表明:這兩種方法都可以很準(zhǔn)確估計(jì)多普勒模糊數(shù)。3.提出了一種結(jié)合牛頓迭代和DCFT的前視雙基地SAR多普勒參數(shù)估計(jì)方法。通過互相關(guān)技術(shù)完成距離徙動校正之后,采用DCFT算法估計(jì)多普勒參數(shù)的初始值,再利用牛頓迭代法實(shí)現(xiàn)準(zhǔn)確估計(jì)。仿真實(shí)驗(yàn)表明:與基于幾何的方法和DCFT算法相比,提出的算法能夠獲得更準(zhǔn)確的估計(jì)結(jié)果。4.研究了基于離散多項(xiàng)式相位變換(DPT)的前視雙基地SAR多普勒參數(shù)估計(jì)方法。對回波信號完成距離壓縮和距離徙動校正之后,提取方位向信號,利用DPT從高階到低階依次估計(jì)出多普勒參數(shù)。仿真結(jié)果表明:這種算法不僅可以準(zhǔn)確估計(jì)低階多普勒參數(shù),更可以準(zhǔn)確估計(jì)三階多普勒參數(shù)。5.建立了運(yùn)動誤差在航跡向、偏航向和俯仰向的誤差模型,分析了恒定速度誤差和線性速度誤差對成像造成的影響,仿真驗(yàn)證了理論模型和公式推導(dǎo)的正確性。提出了一種基于多普勒參數(shù)估計(jì)的運(yùn)動補(bǔ)償方法:利用估計(jì)的多普勒參數(shù),構(gòu)造方位向壓縮參考函數(shù),結(jié)合前視雙基地SAR成像算法,實(shí)現(xiàn)了前視雙基地SAR的聚焦成像。最后,通過雙基地SAR實(shí)測數(shù)據(jù)驗(yàn)證了算法的有效性。
[Abstract]:Because the forward bistatic SAR can be used to image the front area of flight direction, more and more researchers at home and abroad pay attention to .SAR imaging. The Doppler center frequency error will lead to the decrease of SNR and the translation of image. The inaccuracy of Doppler frequency will lead to blurred image and lower contrast, and the error of high-order Doppler parameter will cause image distortion. In addition, in the actual SAR flight, the platform is easily affected by the airflow, resulting in motion errors, and then affecting the focusing quality of the SAR image. The Doppler parameter estimation and motion compensation techniques of bistatic forward looking SAR are studied in this paper. The main research contents include: 1. The geometric model of forward looking bistatic SAR is established, the echo model of point target is given, and its range history and Doppler characteristics are analyzed. It is found that the Doppler parameters of bistatic forward looking SAR are characterized by large centroid, low slope of frequency modulation and high order Doppler parameters. At the same time, by analyzing the phase error of the LFM signal, it is found that the first phase error will lead to the deviation of the central frequency of the signal, the secondary phase error will cause the compression signal to widen, and the sidelobe level will rise. The high order phase error results in the asymmetry of the main lobe. The Doppler ambiguity number estimation method based on Radon transform and range migration correction function is studied. The Radon transform is used to estimate the angle of the range compressed echo signal, and then the relationship between the linear slope of the echo signal and the Doppler ambiguity number is used to realize the Doppler fuzzy number estimation. By constructing the range migration correction function and taking the minimum entropy as the cost function, the Doppler ambiguity number is estimated. Simulation results show that both methods can accurately estimate the Doppler ambiguity number. 3. A forward looking bistatic SAR Doppler parameter estimation method combining Newton iteration and DCFT is proposed. After the range migration correction is completed by cross-correlation technique, the initial value of Doppler parameters is estimated by DCFT algorithm, and the accurate estimation is realized by Newton iteration method. The simulation results show that the proposed algorithm can obtain more accurate estimation results than the geometric based method and DCFT algorithm. A method for estimating the Doppler parameters of bistatic SAR based on discrete polynomial phase transform (DPT) is studied. After range compression and range migration correction for the echo signal, the azimuth signal is extracted and the Doppler parameters are estimated by DPT from high order to low order. Simulation results show that this algorithm can not only accurately estimate the low order Doppler parameters, but also accurately estimate the third order Doppler parameters. The error models of motion errors in track, yaw and pitch are established, and the effects of constant velocity error and linear velocity error on imaging are analyzed. The theoretical model and formula derivation are verified by simulation. A motion compensation method based on Doppler parameter estimation is proposed. Using the estimated Doppler parameters, the azimuth compression reference function is constructed and combined with the forward bistatic SAR imaging algorithm, the focusing imaging of the forward looking bistatic SAR is realized. Finally, the effectiveness of the algorithm is verified by bistatic SAR data.
【學(xué)位授予單位】：電子科技大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TN957.52

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本文編號：2180455