【作者】 胡杰民；

【导师】 景宁； 黎湘；

【作者基本信息】 国防科学技术大学 ， 信息与通信工程， 2010， 博士

【摘要】 宽带雷达成像可以获取目标的形状结构信息,是目标识别的主要手段。本文针对复杂运动目标成像的特点和难点,从复杂运动目标对成像影响分析、复杂运动目标高分辨距离成像技术、平动补偿技术以及复杂运动目标高分辨二维成像技术四个方面开展了研究。论文首先阐述了研究背景和意义,回顾了高分辨雷达成像系统的发展历程,详细地比较和分析了国内外在高分辨雷达成像领域的研究工作,指出了已有技术手段在处理复杂运动目标高分辨成像中存在的问题。推导了复杂运动目标的回波相位与运动参数之间的解析关系,给出了其对距离像影响的定量计算公式;分析了匀加速转动、高速旋转、进动等复杂运动目标的多普勒特征,包括多普勒、多普勒率和多普勒展宽。针对复杂运动目标的高分辨距离成像问题,分别针对步进频信号和调频步进信号,提出一种脉冲重复时间的预先设计的方法,消除了由目标速度引入的相位高次项,并提出一种相位对消技术,消除由目标加速度引入的相位高次项。对于在成像时间内可近似为匀加速的目标,该方法无需进行参数估计和运动补偿,通过系列的仿真和实测数据进行了实验验证。针对平动补偿中的包络对齐问题,提出一种综合利用距离像幅度信息和相位信息进行包络对齐的方法,新方法不需要对距离像进行插值,因此可以在计算时间稳定的同时获得较高对齐精度。针对平动补偿中的初相校正问题,分析了基于图像准则方法与初相校正方法的一致性,提出一种新的基于图像衡量准则方法,降低了图像准则方法的聚焦结果与理想初相校正结果不一致的可能性。在转角估计方面,提出一种基于相位对消的转角估计方法,通过相位对消直接消除回波的相位一次项,克服了由于相位一次项的存在导致转角难以估计这一难题,利用加权最小二乘算法对估计结果进行拟合,增强了估计结果的稳定性和准确性。对匀加速转动、高速旋转、进动等复杂运动目标的二维成像方法进行了研究。针对匀加速转动目标回波二次相位系数与一次相位系数的比值为定值这一特点,提出一种基于调频傅立叶变换的ISAR成像方法,通过调频傅立叶变换后搜索最小熵的方法估计该比值,算法无需对散射点进行分离,有效减少了计算量。旋转速度估计是高速旋转目标高分辨二维成像的前提,论文提出一种估计目标旋转速度的新方法,利用较多相干脉冲进行估计以获得较高精度的旋转初速度,用较少的相干脉冲进行旋转速度精确值的搜索以保证搜索过程收敛。因此具有良好的准确性和抗噪性能。进动目标的高分辨二维成像需要先对进动周期进行估计,目标RCS可看作是姿态角余弦通过线性系统得到的响应,通过对输入信号频谱特性和系统频率传输特性的分析,确定了RCS的频谱特征,在此基础上提出一种空间锥体目标进动周期估计的新方法,仿真实验验证了算法的有效性。基于旋转对称目标的散射模型分析,提出了一种基于后向投影变换的高分辨二维成像新方法。通过将目标散射中心分布在距离时间域上的复数信号进行相干累加,转换目标的散射中心分布平面,从而实现了进动目标的高分辨二维成像,利用暗室测量数据进行了实验验证。论文最后总结了全文工作,并指出了下一步要着力开展的研究内容。更多还原

【Abstract】 Wideband radar imaging is a primary technique for target recognition, due to its capability to provide the shape and structure information. Four main subjects have been researched in this dissertation, which are the imaging performance analysis for targets with complex motion, the high resolution range profile (HRRP) imaging, translation compensation, and two dimensional imaging for targets with complex motion.Firstly, the research background and significance is introduced, and the development of high resolution radar system for target imaging is reviewed. Then the work about signal processing technology of radar imaging is compared and analyzed in detail. The problems of high resolution radar imaging of targets with complex motion are pointed out.Secondly, the analytic relationships between the phase of echos and the movement parameters are derived, and the formulas for calculating the effection of HRRP are given. For the targets which are equably accelerative rotating, rapidly spinning or precessing, the Doppler signatures are analyzed respectively, including Doppler, Doppler rate and spread of Doppler.Thirdly, in order to obtain the HRRP of targets with complex motion, a method based on predesigned pulse repetition time (PRT) is presented for stepped frequency signals and frequency-stepped chirp signals, respectively. The target velocity will not cause higher order phase terms for the new signals, and the higher order phase terms caused by the acceleration can be eliminated by phase cancellation technology. For a nearly constant acceleration target in imaging time, the parameters estimation is not required for the new technology. The conclusion is verified by a series of experiments conducted both on the simulated and measured data.Fourthly, in the research of translation compensation and the rotational angle estimation, the dissertation proposed a novel range alignment algorithm, which uses both the phase information and the envelope information. Interpolation is not needed for the new algorithm, as a result, good performance can be achieved without a heavy computation burden. Then the inherent consistency between phase compensation and image auto- focusing method in ISAR imaging is analyzed and a new image auto-focusing method is presented, which has more consistency performance with the ideal result of phase compensation. In order to estimate the rotational angle, a method based on phase cancellation (PC) is proposed. In this method, PC is used to eliminate the linear terms of the phase, which is a disadvantage to the rotational angle estimation. By employing the weighted linear least squares algorithm, the rotation angle can be estimated efficiently and robustly.Fifthly, the dissertation has researched the imaging technology for three typical targets with complex motion, i.e., equably accelerative rotating targets, rapidly spinning targets and precessing targets. For an equably accelerative rotating target, the ratio of the second order terms of the phase to the linear terms is derived, and a novel imaging method based on the chirp-Fourier transform is presented. In the new method, the ratio is estimated by calculating the entropy of all the scattering points in cross-range. The steps of choosing range cell and the separation of the scattering points are not need in the proposed method, so the computation burden is greatly reduced. For a rapidly spinning target, a new spinning-rate estimating method is proposed, which is a precondition for two dimensional imaging. In this method, a primary estimation using many coherent pulses is put forward, and it is refined in specified range by calculating the entropy of the whole image, which uses a few coherent pulses to guarantee the convergence. Simulations results confirm its effectiveness and robustness. For a precession target, the cosine of the aspect angle and the RCS can be treated as the input and the response of a linear system, respectively. Both the frequency characteristic of the input signals and the frequency transmission characteristic of the system are analyzed. Then the frequency characteristic of RCS is achieved and a new method of estimating the precession cycle based on the frequency characteristic is presented. The simulation results show that the algorithm is effective. After that, the scattering model of a target with rotational symmetry is analyzed and a novel imaging method is proposed , which is based on the back prejection transform. The echos of the target in the range-time domain are transformed to the scatterer distribution plane by means of coherent cumulation. The algorithm is verified by the experiment results of both the simulated and anechoic chamber data.Chapter 6 is the summary of the dissertation. It also discusses the future work to be further researched.更多还原