同轨双基SAR成像算法研究
发布时间：2018-09-11 12:12
【摘要】：与传统的单基合成孔径雷达不同，双基地合成孔径雷达(Bistatic SyntheticAperture Radar, BiSAR)的接收机和发射机放置在不同的运动平台上，发射机和接收机可以有不同的空间位置和速度。因此双基地SAR在军事应用，资源调查和地壳形变监测等方面具有特殊的优势。在诸多的双基SAR构型中，同轨双基SAR的发射机和接收机以相同的速度沿着相同的航迹匀速直线飞行，这种体制的双基地SAR编队构形相对简单，工程上较容易实现，在地面运动目标检测等方面有着广阔的应用前景。基于此，本文对同轨构型双基SAR目标二维频谱精度和同轨构型不同模式下的成像算法进行了一些研究，主要工作概括如下： 1.理论上LBF(Loffeld’s bistatic formula, LBF)双基SAR目标频谱适用于任意的双基构型，但是在具体的双基构型条件下其谱精度因不同参数配置的影响而有所不同。针对同轨双基地SAR构型，本文通过数学方法将其与一种严格解析的双基目标二维频谱进行对比分析，详细推导出了影响LBF双基谱精度的两个约束条件。即半双基角的余弦值大小以及半基线长度与目标到航线的最近距离的比值是否等于半双基角的正切值。当半双基角的余弦值等于1，半基线长度与目标到航线的最近距离的比值等于半双基角的正切值这两个条件同时得到满足时，LBF谱是完全严格解析的。在这两个影响谱精度的约束条件中，LBF双基谱的谱精度对半双基角的余弦值的大小变化更为敏感，而并不直接受到基线长度和斜视角大小的影响，通过仿真实验详细分析讨论了各种因素对于LBF谱精度的影响。 2.提出一种同轨构型下基于严格解析双基SAR目标二维频谱的线频调变标(Chirp Scaling, CS)成像算法，解决条带模式下双基地SAR包络徙动的空变问题。不同于波数域的成像算法，整个成像过程不需要进行插值运算，在频域聚焦实现快速成像。高精度的双基频谱使得所提算法对基线的长短不再敏感，可以进行大双基角，，长基线情形下的同轨双基SAR数据处理。仿真实验和对比实验验证了所提算法的有效性和优越性。 3.针对大斜视情形下同轨双基SAR目标的距离徙动和二次距离压缩(SecondRange Compression, SRC)的空变性问题，基于严格解析的双基SAR目标二维频谱，提出了一种适用于同轨构型双基SAR的非线性CS(Nonlinear Chirp ScalingAlgorithm, NCSA)成像算法，不同于适用于小斜视角条件的CS成像算法，非线性CS算法不仅考虑了调频率随多普勒频率的变化，而且也考虑了其随距离的线性变化，更好地实现了同轨双基SAR中SRC的精确补偿，取得了满意的聚焦效果。仿真实验验证了所提算法的有效性。 4.对于聚束模式下的同轨双基SAR构型，基于同轨构型下严格解析的半双基角和谱分析方法，提出了一种适用于同轨构型下聚束式双基SAR的频率变标(Frequency Scaling, FS)成像算法。首先，类比单基情形，推导出了双基地情形下的deramp函数，实现方位向的粗聚焦，有效地消除系统方位向的频谱混叠问题。然后基于同轨构型下严格解析的双基SAR目标二维频谱，通过一种适用于聚束式双基地SAR的FS成像算法校正目标的距离徙动，取得理想的成像效果。FS算法通过相位相乘代替插值操作实现目标的距离徙动校正，可以实现快速成像。精确的双基频谱使得所提算法可以进行长基线情形下的数据处理。仿真实验验证了算法的有效性。此外，针对大斜视情形下SRC的空变问题，提出一种基于严格解析双基频谱的改进频率变标成像算法，通过非线性变标操作消除由大斜视导致的随距离变化的二次距离压缩项。仿真实验表明，与常规FS算法相比，改进算法在大斜视情形下可实现目标良好的成像，点目标冲激响应的主副瓣可清晰分辨。
[Abstract]:Different from the traditional monostatic SAR, the receiver and transmitter of Bistatic Synthetic Aperture Radar (BiSAR) are placed on different moving platforms, and the transmitter and receiver can have different spatial positions and velocities. In many bistatic SAR configurations, the transmitter and receiver of the same-orbit bistatic SAR fly along the same track at the same speed in a uniform straight line. The bistatic SAR formation configuration of this system is relatively simple, easy to implement in engineering, and has a broad application prospect in the detection of ground moving targets. Based on this, the two-dimensional spectral accuracy of bistatic SAR targets with homoorbital configuration and the imaging algorithm under different modes of homoorbital configuration are studied in this paper.
1. Theoretically, the target spectrum of LBF (Loffeld's bistatic formula) bistatic SAR is suitable for any bistatic configuration, but its spectral accuracy varies with different parameter configurations under specific bistatic configuration. For the same-orbit bistatic SAR configuration, this paper uses mathematical method to analyze it with a rigorous bistatic target 2. Two constraints affecting the accuracy of LBF bispectrum are deduced by comparing and analyzing the two-dimensional spectrum, that is, whether the cosine value of the half-bispectrum angle and the ratio of the half-baseline length to the nearest distance from the target to the route are equal to the tangent value of the half-bispectrum angle. The LBF spectra are completely strictly analytic when the ratio of the near distance to the tangent of the half-bistatic angle is satisfied simultaneously. Among the two constraints affecting the spectral accuracy, the spectral accuracy of the LBF bistatic spectrum is more sensitive to the variation of the cosine of the half-bistatic angle, and is not directly affected by the baseline length and the angle of inclination. The influence of various factors on the accuracy of LBF spectrum is discussed in detail through simulation experiments.
2. A chirp scaling (CS) imaging algorithm based on rigorous analysis of two-dimensional spectrum of bistatic SAR targets in the same orbit configuration is proposed to solve the problem of envelope migration of bistatic SAR in strip mode. High-precision bistatic spectrum makes the proposed algorithm insensitive to baseline length and can process homo-orbital bistatic SAR data with large bistatic angle and long baseline. Simulation and contrast experiments show the effectiveness and superiority of the proposed algorithm.
3. Aiming at the range migration and the spatial variability of the second Range Compression (SRC) of the bistatic SAR target in the case of large squint, a nonlinear CS (Nonlinear Chirp Scaling Algorithm, NCSA) imaging algorithm for the bistatic SAR target with the same orbit configuration is proposed based on the strict analysis of the two-dimensional spectrum of the bistatic SAR target. For CS imaging algorithm with small squint angle, the nonlinear CS algorithm not only considers the change of modulation frequency with Doppler frequency, but also considers the linear change of modulation frequency with range. It achieves the accurate compensation of SRC in homo-orbital bistatic SAR, and achieves satisfactory focusing effect.
4. For homo-orbital bistatic SAR configurations in spotlight mode, a new frequency scaling (FS) imaging algorithm for homo-orbital bistatic SAR is proposed based on the rigorous analytical method of semi-bistatic angle and spectrum. Firstly, the deramp function for bi-orbital bistatic SAR is derived by analogizing the single-orbital case. The coarse focusing of azimuth can effectively eliminate the aliasing problem in azimuth direction of the system. Then, based on the two-dimensional spectrum of bistatic SAR target, a FS imaging algorithm suitable for spotlight bistatic SAR is proposed to correct the range migration of the target. FS algorithm uses phase multiplication instead of interpolation. The precise bistatic spectrum enables the proposed algorithm to process data in the case of long baseline. Simulation results show the effectiveness of the proposed algorithm. In addition, an improved frequency based on strictly analytic bistatic spectrum is proposed for the space-variant problem of SRC in the case of large squint. Rate-varying scaling algorithm eliminates the range-varying quadratic range compression term caused by large squint by nonlinear scaling operation. Simulation results show that the improved algorithm can achieve good target imaging and the main and side lobes of point target impulse response can be clearly distinguished compared with the conventional FS algorithm.
【学位授予单位】：西安电子科技大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TN957.52
[Abstract]:Different from the traditional monostatic SAR, the receiver and transmitter of Bistatic Synthetic Aperture Radar (BiSAR) are placed on different moving platforms, and the transmitter and receiver can have different spatial positions and velocities. In many bistatic SAR configurations, the transmitter and receiver of the same-orbit bistatic SAR fly along the same track at the same speed in a uniform straight line. The bistatic SAR formation configuration of this system is relatively simple, easy to implement in engineering, and has a broad application prospect in the detection of ground moving targets. Based on this, the two-dimensional spectral accuracy of bistatic SAR targets with homoorbital configuration and the imaging algorithm under different modes of homoorbital configuration are studied in this paper.
1. Theoretically, the target spectrum of LBF (Loffeld's bistatic formula) bistatic SAR is suitable for any bistatic configuration, but its spectral accuracy varies with different parameter configurations under specific bistatic configuration. For the same-orbit bistatic SAR configuration, this paper uses mathematical method to analyze it with a rigorous bistatic target 2. Two constraints affecting the accuracy of LBF bispectrum are deduced by comparing and analyzing the two-dimensional spectrum, that is, whether the cosine value of the half-bispectrum angle and the ratio of the half-baseline length to the nearest distance from the target to the route are equal to the tangent value of the half-bispectrum angle. The LBF spectra are completely strictly analytic when the ratio of the near distance to the tangent of the half-bistatic angle is satisfied simultaneously. Among the two constraints affecting the spectral accuracy, the spectral accuracy of the LBF bistatic spectrum is more sensitive to the variation of the cosine of the half-bistatic angle, and is not directly affected by the baseline length and the angle of inclination. The influence of various factors on the accuracy of LBF spectrum is discussed in detail through simulation experiments.
2. A chirp scaling (CS) imaging algorithm based on rigorous analysis of two-dimensional spectrum of bistatic SAR targets in the same orbit configuration is proposed to solve the problem of envelope migration of bistatic SAR in strip mode. High-precision bistatic spectrum makes the proposed algorithm insensitive to baseline length and can process homo-orbital bistatic SAR data with large bistatic angle and long baseline. Simulation and contrast experiments show the effectiveness and superiority of the proposed algorithm.
3. Aiming at the range migration and the spatial variability of the second Range Compression (SRC) of the bistatic SAR target in the case of large squint, a nonlinear CS (Nonlinear Chirp Scaling Algorithm, NCSA) imaging algorithm for the bistatic SAR target with the same orbit configuration is proposed based on the strict analysis of the two-dimensional spectrum of the bistatic SAR target. For CS imaging algorithm with small squint angle, the nonlinear CS algorithm not only considers the change of modulation frequency with Doppler frequency, but also considers the linear change of modulation frequency with range. It achieves the accurate compensation of SRC in homo-orbital bistatic SAR, and achieves satisfactory focusing effect.
4. For homo-orbital bistatic SAR configurations in spotlight mode, a new frequency scaling (FS) imaging algorithm for homo-orbital bistatic SAR is proposed based on the rigorous analytical method of semi-bistatic angle and spectrum. Firstly, the deramp function for bi-orbital bistatic SAR is derived by analogizing the single-orbital case. The coarse focusing of azimuth can effectively eliminate the aliasing problem in azimuth direction of the system. Then, based on the two-dimensional spectrum of bistatic SAR target, a FS imaging algorithm suitable for spotlight bistatic SAR is proposed to correct the range migration of the target. FS algorithm uses phase multiplication instead of interpolation. The precise bistatic spectrum enables the proposed algorithm to process data in the case of long baseline. Simulation results show the effectiveness of the proposed algorithm. In addition, an improved frequency based on strictly analytic bistatic spectrum is proposed for the space-variant problem of SRC in the case of large squint. Rate-varying scaling algorithm eliminates the range-varying quadratic range compression term caused by large squint by nonlinear scaling operation. Simulation results show that the improved algorithm can achieve good target imaging and the main and side lobes of point target impulse response can be clearly distinguished compared with the conventional FS algorithm.
【学位授予单位】：西安电子科技大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TN957.52
【参考文献】
相关期刊论文 前6条
1 王国栋,周荫清,李春升;高分辨率星载聚束式SAR的Deramp Chirp Scaling成像算法[J];电子学报;2003年12期
2 孙进平;白霞;毛士艺;;双基地合成孔径雷达的扩展ETF成像算法[J];电子学报;2007年12期
3 郭汉伟,王岩,梁甸农,黄晓涛;小波插值在机载超宽带合成孔径雷达成像中的应用[J];航空学报;2003年06期
4 何友;蔡复青;唐小明;关键;;双/多基地SAR发展评述[J];雷达科学与技术;2008年01期
5 郭华东,王长林;全天候全天时三维航天遥感技术——介绍航天飞机雷达地形测图计划[J];遥感信息;2000年01期
6 Otmar Loffeld;Robert Wang;Holger Nies;Ul-Ann Qurat;;Weighted LBF for spaceborne general bistatic SAR processing[J];Progress in Natural Science;2008年10期
相关博士学位论文 前6条
1 杨科锋;移变双基地SAR特性与成像方法研究[D];国防科学技术大学;2009年
2 刘保昌;SAR解多普勒模糊与双基SAR成像算法研究[D];西安电子科技大学;2010年
3 安道祥;高分辨率SAR成像处理技术研究[D];国防科学技术大学;2011年
4 李燕平;单/双基SAR成像和运动补偿研究[D];西安电子科技大学;2008年
5 刘U
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