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具有移变特性的星机联合双基地SAR成像处理算法的研究
【作者】 左子瑾；
【导师】 张晓玲；
【作者基本信息】 电子科技大学 ， 信号与信息处理， 2010， 硕士
【摘要】 星机联合双基地SAR(Spaceborne Airborne Bistatic SAR,SA-BiSAR)系统,是由卫星和飞机组成的一种新型双基地SAR(BiSAR)系统,不仅继承了BiSAR的诸多优点,还在扩大目标照射范围、节约数据获取成本等方面显示了独特的优势。作为一种典型的移变BiSAR系统,SA-BiSAR已经成为雷达成像应用的一个新的研究热点。本文针对SA-BiSAR系统的特点着重研究了适用于该系统的成像算法,做了如下研究工作及创新:1、研究了SA-BiSAR系统的成像机理。首先分析了任意飞行模式的SA-BiSAR系统的几何模型,然后基于系统收发平台速度差高度差很大、卫星过顶时间短的特点建立了近似距离历史模型。最后借助模糊函数的分析手段,研究了系统的空间分辨率。2、提出一种基于降维处理的SA-BiSAR系统成像方法。首先根据近似距离历史模型得到适用于SA-BiSAR系统的多普勒参数,再利用降维处理来实现二维聚焦。然后根据二维聚焦表达式得到目标的畸变位置与实际位置的对应关系,利用反演投影法对聚焦图像中的畸变进行校正,从而恢复出原始场景。3、针对降维处理后的图像畸变提出了几何校正法。首先分析了聚焦图像中畸变的成因,然后引入畸变倾角并推导其表达式,从而得出畸变坐标与真实坐标的几何对应关系,最后由畸变倾角以及畸变坐标得到目标的真实坐标,完成非线性的几何校正。该方法弥补了反演投影法处理速度慢的缺点。4、研究了目前最具代表性的求解二维频谱的模型:LBF模型和ELBF模型。由于这两种模型十分繁琐,且LBF模型不适用于SA-BiSAR系统,ELBF模型也仅限于星机速度夹角较小的情况。于是本文提出一种SA-BiSAR系统二维频谱的求解方法。该方法利用该系统的近似距离历史表达式,求得驻定相位点,从而推导出二维频谱的近似表达式。最后基于传统ωk成像算法思路对SA-BiSAR系统进行了MATLAB仿真,验证了该频域算法的有效性。
【Abstract】 Spaceborne-Airborne Bistatic SAR (SA-BiSAR), which is a new Bistatic SAR composed by the spacecraft and aircraft, not only inherit many advantages of BiSAR, but also demonstrate some unique advantages, such as expanding the scope of target scene, saving the costs of data acquisition, and so on. As being a typical translational variant BiSAR, SA-BiSAR has become a new hotspot in radar imaging application research. In this dissertation, basing on the characteristics of SA-BiSAR, the imaging algorithm of the system has been focused on, and the main research and contributions are as follows:1. The SA-BiSAR system is studied: Establish the general geometry and signal models of SA-BiSAR firstly, and base on these, the range history and the range cell migration (RCM) are disgussed. Then based on the characteristics of the System model, the range history has been approximated sensibly. At last, the spatial resolutions of bistatic SAR have been derived from the ambiguity function.2. An imaging algorithm for SA-BiSAR with any flight mode is proposed. First, use the range history approximated of SA-BiSAR to derivate the Doppler parameter suitably for SA-BiSAR system, which is the key point to the focus of the imaging algorithm basing on the Dimension-reduction Focus. Then use the Inverse-Projection method to correct distortion basing on the formula of final focus expression.3. Analysis the causes of the distortion, which appears after the Dimension-reduction Focus. Thus a geometric correction method for correction distortion is proposed. This method can quickly complete the distortion correction and compensate for the slower processing speed weaknesses of the Inverse-Projection method.4. The LBF model and ELBF model have been detailedly studied. Being the most representative methods of solving two-dimensional spectrum for translational variant BiSAR currently, they are combined with 2-D ISFFT imaging algorithm in this dissertation, and have been compared the imaging results by MATLAB simulation. Basing on the reasonable approximation of range history, an imaging algorithm in two-dimensional frequency-domain is proposed for SA-BiSAR system. The key point of this algorithm is getting the two-dimensional spectrum basing on the inherent characteristics of SA-BiSAR system and the Expression of the range history. Then combined with the reference function multiplication (RFM), and the stolt interpolation to complete imaging method.