合成孔径雷达原始回波频域模拟算法研究

发布时间：2018-09-11 14:23

【摘要】：合成孔径雷达(Synthetic Aperture Radar,SAR)成像具有全天时、全天候获取高分辨图像的能力,已广泛的用于军事和民用领域。合成孔径雷达回波模拟技术是一种通过计算机仿真来模拟合成孔径雷达回波的技术,它对于SAR成像算法,SAR图像处理,以及SAR系统参数设计等都具有十分重要的作用,随着合成孔径雷达的观测区域不断增大,SAR回波的频域快速模拟方法越来越受到重视,传统的频域算法都是基于理想条件下推导,而随着合成孔径雷达逐步向高分辨、多平台等方向发展,传统的频域回波模拟算法已经不能满足要求,需要有新的模拟算法保证不同模式下所产生的SAR回波信号的准确性以及高效性。本文系统的研究了SAR回波频域模拟方面的关键问题,分别从变速运动SAR的回波模拟,超宽带SAR的回波模拟以及双站SAR的回波模拟等几个方面展开了研究,并通过计算机仿真对回波模拟算法进行了验证,本论文的主要研究内容包括以下几个方面:1)对于变速运动雷达平台,其二维频域表达式较一般理想的匀速直线SAR更为复杂。针对此问题基于级数反演法提出了一种变速运动SAR回波二维频域模拟快速算法。算法分析了变速运动模式SAR的几何模型,并通过级数反演法,得到了较为准确的信号二维频谱表达式,并分析了变速运动SAR的距离空变性,给出了模拟空变性的函数,保证了大场景SAR回波数据的高相位精度。运算量分析表明,该算法可以大大的提高SAR回波的仿真速度,且仿真场景越大,其效率越高。最后通过仿真证明了该算法的准确性以及高效性。2)针对频域回波模拟算法很难准确的添加运动误差的问题,提出了一种对运动误差进行模拟的大场景SAR回波频域模拟快速算法。算法利用矢量表达式对瞬时斜距重新整理,分析了运动误差对瞬时斜距的影响,明确了小斜视模式下影响回波质量的主要运动误差分量,并采用运动误差两步模拟的方法,首先模拟了不随距离变化的大的运动误差分量,然后模拟了大场景情况下随距离变化的小的运动误差的空变分量,从而完成曲线轨迹SAR回波数据的精确仿真。该算法能够在保证高的相位精度情况下大大的提高仿真速度,仿真结果证明了该算法的有效性。3)针对超宽带(Ultra Wide Band,UWB)SAR工作频段低,发射带宽大,大累积角长孔径,大距离徙动等特点,提出了一种超宽带SAR高效原始回波数据模拟算法。算法研究了UWB-SAR的信号模型,在方位时域模拟了不随距离空变的距离徙动,重新推导了UWB-SAR系统的二维频域传递函数,并对距离空变性进行了研究,实现了超宽带SAR原始回波数据的精确仿真。仿真实验证明了该算法的高效性以及实用性。4)分析了地球、月球以及环月卫星的轨道构型,提出了一种新的双基SAR构形——地星双基合成孔径雷达的概念,给出了地星双基SAR系统模糊函数的定义,推导了其模糊函数的表达式,依据此式,对发射站处于地球不同位置的地星双基SAR进行了计算机仿真。仿真结果表明地星双基SAR的模糊函数不仅由发射信号的带宽和合成孔径时间决定,还与发射站在地球上所处的位置以及双站构型有关。研究了地星双基SAR的几何模型,提出了地星双基合成孔径雷达的原始回波数据二维频域模拟算法,算法分析了地星双基SAR的回波信号模型,结合级数反演法,得到了地星双基SAR回波信号的二维频域表达式,最后利用二维频域表达式仿照单基SAR的频域模拟方法得到了较为准确的地星双基SAR回波数据,仿真结果表明该算法兼顾了仿真效率与精度。
[Abstract]:Synthetic Aperture Radar (SAR) imaging has been widely used in military and civilian fields because of its ability to acquire high-resolution images all-day and all-weather. As the observation area of synthetic aperture radar (SAR) increases, the fast simulation method of SAR echo in frequency domain becomes more and more important. The traditional frequency domain algorithm is based on the derivation under ideal conditions. With the development of synthetic aperture radar (SAR) towards high resolution, multi-platform and so on. The traditional frequency-domain echo simulation algorithm can not meet the requirements, and a new simulation algorithm is needed to ensure the accuracy and efficiency of the SAR echo signal generated in different modes. This paper systematically studies the key issues of the frequency-domain simulation of SAR echo, including the echo simulation of variable-speed SAR and the echo simulation of UWB SAR. The echo simulation algorithm of bistatic SAR is validated by computer simulation. The main research contents of this paper include the following aspects: 1) For the variable-speed moving radar platform, its two-dimensional frequency domain expression is more complex than the ideal uniform linear SAR. A fast algorithm for 2-D frequency domain echo simulation of variable-speed SAR is proposed by series inversion method. The geometric model of variable-speed SAR is analyzed, and a more accurate 2-D spectrum expression of signal is obtained by series inversion method. The range-spatiality of variable-speed SAR is analyzed, and the function of simulated spatiality is given to guarantee the algorithm. The computation analysis shows that the algorithm can greatly improve the simulation speed of SAR echo, and the larger the simulation scene, the higher its efficiency. Finally, the simulation proves the accuracy and efficiency of the algorithm. 2) It is difficult to accurately add motion error to the frequency domain echo simulation algorithm. A fast algorithm for large-scale SAR echo simulation in frequency domain is presented. The algorithm rearranges the instantaneous squint distance by using vector expression, analyzes the influence of motion error on the instantaneous squint distance, and defines the main motion error components that affect the echo quality in small squint mode. The algorithm is simulated by two-step motion error simulation. Methods: Firstly, the large motion error components which do not vary with the distance are simulated, and then the small motion error components which vary with the distance in the large scene are simulated. Thus, the precise simulation of curve trajectory SAR echo data is completed. The validity of the algorithm is proved. 3) Aiming at the characteristics of Ultra-Wide-Band (UWB) SAR, such as low operating frequency, wide transmitting bandwidth, large cumulative angle, long aperture and large range migration, an efficient raw echo data simulation algorithm for UWB-SAR is proposed. The signal model of UWB-SAR is studied. The algorithm simulates the signal in azimuth-time domain and does not vary with the space-distance. In this paper, the two-dimensional frequency-domain transfer function of UWB-SAR system is deduced again, and the range-spatiality variability is studied. The precise simulation of UWB-SAR raw echo data is realized. The simulation results show that the algorithm is efficient and practical. 4) The orbital configurations of earth, moon and lunar satellite are analyzed, and a new type of orbit configuration is proposed. The concept of bistatic SAR configuration-bistatic synthetic aperture radar is presented. The definition of ambiguity function of bistatic SAR system is given. The expression of ambiguity function is derived. According to this expression, the computer simulation of bistatic SAR with different positions on the earth is carried out. The simulation results show that the ambiguity function of bistatic SAR is not only from the ground-satellite ambiguity function. The bandwidth and synthetic aperture time of the transmitted signal depend on the position of the transmitting station on the earth and the configuration of the bistatic SAR. The geometric model of the bistatic SAR is studied, and a two-dimensional frequency-domain simulation algorithm of the original echo data of the bistatic SAR is proposed. The series inversion method is used to obtain the two-dimensional frequency-domain expression of the earth-satellite bistatic SAR echo signal. Finally, the accurate data of the earth-satellite bistatic SAR echo are obtained by using the two-dimensional frequency-domain expression imitating the frequency-domain simulation method of the single-base SAR. The simulation results show that the algorithm takes into account the simulation efficiency and accuracy.
【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】：TN957.51

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