前视双基地SAR多普勒参数估计与运动补偿研究
发布时间：2018-08-13 08:42
【摘要】：前视双基地SAR由于可以对飞行方向正前方区域进行成像,现在越来越受到国内外研发人员的重视。SAR成像中,多普勒中心频率误差会导致信噪比下降、图像平移;多普勒调频率不准确将导致图像模糊、对比度下降;高阶多普勒参数误差会造成图像失真。另外,在实际的SAR飞行中,载机平台很容易受到气流等影响,从而产生运动误差,进而影响SAR图像的聚焦质量。本文针对前视双基地SAR的多普勒参数估计和运动补偿技术展开研究,主要研究内容包括:1.建立了前视双基地SAR的几何模型,给出了点目标的回波模型,并分析其距离历史特性和多普勒特性。研究发现:前视双基地SAR的多普勒参数具有质心大、调频斜率较小、高阶多普勒参数不可忽略等特点。同时,通过对线性调频信号的相位误差进行分析,发现一次相位误差会导致信号中心频率发生偏移,二次相位误差造成压缩信号展宽、旁瓣电平升高,高次相位误差造成主瓣不对称等。2.研究了基于Radon变换和距离徙动校正函数的多普勒模糊数估计方法。运用Radon变换对距离压缩后的回波信号进行角度估计,再利用回波信号的直线斜率与多普勒模糊数之间的关系,实现多普勒模糊数估计。通过构造距离徙动校正函数并以最小熵为代价函数,估计得到多普勒模糊数。仿真实验表明:这两种方法都可以很准确估计多普勒模糊数。3.提出了一种结合牛顿迭代和DCFT的前视双基地SAR多普勒参数估计方法。通过互相关技术完成距离徙动校正之后,采用DCFT算法估计多普勒参数的初始值,再利用牛顿迭代法实现准确估计。仿真实验表明:与基于几何的方法和DCFT算法相比,提出的算法能够获得更准确的估计结果。4.研究了基于离散多项式相位变换(DPT)的前视双基地SAR多普勒参数估计方法。对回波信号完成距离压缩和距离徙动校正之后,提取方位向信号,利用DPT从高阶到低阶依次估计出多普勒参数。仿真结果表明:这种算法不仅可以准确估计低阶多普勒参数,更可以准确估计三阶多普勒参数。5.建立了运动误差在航迹向、偏航向和俯仰向的误差模型,分析了恒定速度误差和线性速度误差对成像造成的影响,仿真验证了理论模型和公式推导的正确性。提出了一种基于多普勒参数估计的运动补偿方法:利用估计的多普勒参数,构造方位向压缩参考函数,结合前视双基地SAR成像算法,实现了前视双基地SAR的聚焦成像。最后,通过双基地SAR实测数据验证了算法的有效性。
[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.
【学位授予单位】：电子科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN957.52
本文编号：2180455
[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.
【学位授予单位】：电子科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN957.52
【参考文献】
相关硕士学位论文 前1条
1 周峰;机载合成孔径雷达基于数据的运动误差分析及补偿研究[D];西安电子科技大学;2005年
，本文编号：2180455
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