直升机载旋转式SAR与双基SAR大斜视成像算法研究

发布时间：2018-06-21 02:42

本文选题：旋转式合成孔径雷达 + 双基合成孔径雷达　；参考：《西安电子科技大学》2014年博士论文

【摘要】：合成孔径雷达(Synthetic Aperture Radar, SAR)成像是一种全天时、全天候的微波遥感技术；在地球观测、环境监测、军事侦察及飞行器安全飞行和降落等方面具有重要意义。为提高SAR系统性能，扩展其应用平台，国内外开展了新型SAR技术研究。直升机载旋转式SAR利用雷达天线的旋转来合成方位向孔径，从而得到高分辨二维SAR图像。它具有高时空分辨率、短重访周期、前视成像能力、结构简单硬件成本低等优点，且二维成像时不需要直升机平台做任何运动。另外，结合直升机平台运动和天线旋转可合成虚拟二维面阵天线，同时融合距离脉冲压缩技术可实现对观测区域的三维成像。双基SAR是指发射机和接收机位于不同平台上的新型SAR模式。与单基SAR相比，双基SAR具有可获得目标非后向散射特征、系统设计灵活及便于接收机隐身设计等优点。特别地，大斜视双基SAR可以不需要飞越某一地区而能对该区域的目标进行探测；即也具有对前方目标成像能力。因此，作为对具有前方目标成像能力的新型SAR模式，直升机载旋转式SAR和双基SAR具有广泛的军事和民用前景。本文在国家自然科学基金和国家973项目支撑下，围绕直升机载旋转式SAR和双基SAR原理和成像算法展开研究，主要创新点如下： 1、针对直升机载旋转式SAR方位分辨率依赖于方位重构角的大小，传统的划分子孔径的方法使得方位分辨率低的问题。在详细分析其成像几何模型基础上，使用高阶逼近原理近似构造直升机载旋转式SAR的回波信号模型，然后借助级数反演法求得其精确的二维频谱表达式。在此基础上，提出了一种高分辨直升机载旋转式SAR成像算法，给出算法的完整推导过程和各补偿因子的表达式；并详细分析了系统参数选择对直升机载旋转式SAR分辨率的影响。 2、针对直升机载旋转式SAR雷达天线旋转成像时平台存在运动的问题。提出一种融合直升机平台运动补偿的改进Chirp Scaling算法。该算法首先建立了存在平台运动时直升机载旋转式SAR成像的几何模型。在此基础上，详细分析平台运动引起的目标斜距误差在单个孔径时间内随目标位置的变化关系，得到了平台运动误差的空变性大小并给出误差补偿方法。然后，分析了直升机载旋转式SAR几何构型带来的速度随目标位置变化特性对成像质量的影响，并把其影响补偿融入到Chirp Scaling算法的距离徙动空变性校正和方位压缩中。整个算法只包含快速傅立叶变换和复数乘操作，不涉及插值，易于工程实现。最后，计算机仿真结果表明，该算法能够对直升机平台运动时大场景进行成像并具有良好的成像效果。 3、提出了一种基于调频连续波(Frequency Modulated Continuous Wave, FMCW)的直升机载旋转式SAR新的成像模式并给出了相应的成像算法。该方法首先利用等效相位中心原理，将收发分置天线系统的回波信号等效为“自发自收”单基系统。在此基础上，求得了其精确的二维频谱同时分析了雷达天线连续运动的影响--产生多普勒频移，并给出补偿方法；然后运用高效的逆Chirp-Z变换校正了距离徙动空变性。详细分析了速度近似误差对成像区域大小的影响，并把其影响补偿融合到成像算法中。整个算法只包含快速傅立叶变换和复乘操作，不涉及插值，易于工程实现。最后，，仿真结果验证了分析结论的正确性和算法的有效性。 4、结合直升机平台的运动和安装在旋翼末端的雷达天线的旋转，直升机旋转式SAR能实现对载机前方目标的三维成像。本文根据直升机载旋转式SAR几何构型和回波信号特性，提出一种新的直升机载旋转式SAR前视三维成像算法。该算法首先将雷达天线旋转得到回波数据采用改进Chirp Scaling算法处理获得单幅SAR图像；然后把沿每个方位向对应的斜距-沿航向平面的切片数据看成前下视成像模式的回波数据，利用融合子场景划分技术的Omega-k成像算法沿方位依次进行成像处理，最后获得直升机平台前方目标的三维图像。仿真结果验证了该算法的有效性和正确性。该模式仅仅利用了一根天线就能获得载机平台前方目标的三维SAR图像，具有结构简单、成本低等优势。 5、在大斜视方位时变双基SAR模式下，一方面，距离走动校正引入的距离偏移外，方位时变的几何构型也引入一个距离偏移。尤其是在接收和发射平台航线夹角较大时，几何构型引入的空变性变得更剧烈。另一方面，随着斜视角的增大，方位调频率高次项和三次相位的空变性已经不能忽略。针对该问题，提出一种改进的方位非线性调频变标算法。该方法首先在距离频率-方位时域完成距离走动和多普勒中心校正，然后在二维频域通过一致二次距离压缩校正剩余的距离单元徙动和距离-方位高次耦合。在分析方位时变双基SAR几何构型引入的方位空变性、方位调频率高次项和三次相位空变特性的基础上，推导出变标函数的系数。相比传统的非线性调频变标算法，该算法没有增加任何多余处理步骤。该算法可以有效的提高双基SAR成像性能，极大的扩展方位向聚焦深度。
[Abstract]:Synthetic Aperture Radar (SAR) imaging is a all-weather, all-weather microwave remote sensing technology. It is of great significance in the aspects of earth observation, environmental monitoring, military reconnaissance and aircraft safety flight and landing. In order to improve the performance of the SAR system and expand its application platform, a new study of the new SAR technology has been carried out at home and abroad. The airborne rotating SAR uses the rotation of the radar antenna to synthesize the azimuth aperture, thus obtaining the high resolution two-dimensional SAR image. It has the advantages of high spatial resolution, short revisit period, forward-looking imaging ability, simple hardware cost and so on, and does not need any motion in the helicopter platform during two-dimensional imaging. In addition, it is combined with the helicopter platform. The virtual two-dimensional array antenna can be synthesized by the motion and the antenna rotation, and the 3D imaging of the observed area can be realized by the fusion of the distance pulse compression technology. The dual base SAR is a new SAR mode on the transmitter and receiver on different platforms. Compared with the single base SAR, the dual base SAR can obtain the non backscattering characteristics of the target, and the system is flexible and convenient for the system design. In particular, the large strabismus dual base SAR can detect the target in the region without flying over a certain area; that is, it also has the ability to imaging the target in front of the target. Therefore, as a new SAR model for the imaging capability of the front target, the airborne rotary SAR and double base SAR are widely military. And the future of civilian use.
Based on the support of the National Natural Science Fund and the national 973 project, the helicopter rotary SAR and bistatic SAR imaging algorithm and principle research, the main innovations are as follows:
1, in view of the size of azimuth resolution in the azimuth resolution of the helicopter loaded rotating SAR, the traditional method of dividing the sub aperture makes the azimuth resolution low. On the basis of the detailed analysis of its imaging geometry model, the high order approximation principle is used to approximate the echo signal model of the helicopter loaded rotating SAR, and then the series inverse is used. On this basis, a high resolution helicopter rotating SAR imaging algorithm is proposed, the complete derivation process of the algorithm and the expression of the compensation factors are given, and the influence of the selection of the system parameters on the helicopter's rotating SAR resolution is analyzed in detail.
2, an improved Chirp Scaling algorithm is proposed for the motion compensation of helicopter carrier rotating SAR radar antenna during rotation imaging. This algorithm first establishes a geometric model of helicopter rotating SAR imaging in the presence of platform motion. On this basis, the platform motion is analyzed in detail. The spatial variability of the motion error of the platform is obtained and the error compensation method is given. Then, the effect of the velocity of the helicopter's rotating SAR geometry on the image quality is analyzed, and the compensation is incorporated into the C. Hirp Scaling algorithm is used for distance migration and azimuth compression. The whole algorithm only contains fast Fu Liye transform and complex multiplying operation, which does not involve interpolation and is easy to implement. Finally, the computer simulation results show that the algorithm can image the large field scene in the motion of the helicopter platform and have good imaging effect.
3, a new imaging mode of helicopter borne rotating SAR based on Frequency Modulated Continuous Wave (FMCW) is proposed and the corresponding imaging algorithm is given. The method first uses the principle of the equivalent phase center to equip the echo signal of the receiving and receiving antenna system as a "spontaneous self receiving" single base system. At the same time, the exact two-dimensional spectrum is obtained and the influence of the continuous motion of the radar antenna is analyzed at the same time - the Doppler shift is produced and the compensation method is produced. Then the high efficient inverse Chirp-Z transform is used to correct the distance migration. The influence of the velocity approximation error on the size of the imaging region is analyzed in detail, and the compensation is fused. Imaging algorithm. The algorithm contains only the fast Fu Liye transform and complex multiplication operation, does not involve interpolation, easy to realize. Finally, the simulation results verify the correctness and validity of algorithm analysis.
4, combined with the motion of the helicopter platform and the rotation of the radar antenna installed at the end of the rotor, the helicopter rotating SAR can realize the three-dimensional imaging of the target in front of the carrier. In this paper, a new helicopter borne rotating SAR forward vision 3D imaging algorithm is proposed based on the helicopter's rotating SAR geometry and echo signal. First, the radar antenna is rotated to get the echo data, and the single SAR image is obtained by the improved Chirp Scaling algorithm. Then the slice data of the corresponding oblique distance and direction plane are regarded as the echo data of the front and down view imaging mode, and the Omega-k imaging algorithm using the fusion sub scene division technique is sequentially performed along the azimuth. A three-dimensional image processing, finally get the helicopter platform in front of the goal. The simulation results verify the validity and correctness of the algorithm. The 3D SAR image mode using just one antenna can obtain the aircraft platform in front of the goal, has the advantages of simple structure, low cost advantages.
5, in the dual base SAR mode in the azimuth of large strabismus, on the one hand, the geometric configuration of azimuthal time shift is also introduced by the distance migration from the distance shift correction introduced by the distance moving correction. Especially, the space variability introduced by the geometric configuration becomes more violent when the angle of the route of the receiving and launching platforms is large. On the other hand, with the increase of the angle of view, the azimuth is increased. An improved azimuthal nonlinear frequency modulation (NLFM) scaling algorithm is proposed for the high frequency modulation rate and the three phase. This method first completes the distance travel and the Doppler center correction in the range frequency azimuth time domain, and then corrects the remaining distance units through a two distance compression in the two-dimensional frequency domain. On the basis of azimuthal space variability, azimuth frequency high order and three phase space variation, the coefficient of the variable function is derived on the basis of the analysis of azimuth SAR geometric configuration introduced in the azimuth time-varying dual base geometry. This algorithm does not increase any redundant processing steps compared to the traditional Nonlinear FM scaling algorithm. This algorithm is available. In order to effectively improve the imaging performance of bistatic SAR, the azimuth focusing depth is greatly expanded.
【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

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