【作者】 薛国义；

【导师】 何建国； 周智敏；

【作者基本信息】 国防科学技术大学 ， 电子科学与技术， 2008， 博士

【摘要】 机载低频超宽带合成孔径雷达(UWB SAR)具有探测隐蔽在叶簇或浅地表覆盖下的目标,对其高分辨成像的能力,军事应用潜力巨大。然而,载机的非理想运动给UWB SAR回波带来了严重的相位误差,直接影响高分辨成像能力,有效的运动补偿技术对高分辨成像至关重要。本论文以装备预研项目为背景,从以下几个方面对机载UWB SAR运动补偿开展了较深入的研究:首先,研究了在获得了载机运动参数情况下的UWB SAR视线误差补偿方法。论文着重研究了视线误差对UWB SAR成像中的距离迁徙校正影响问题,推导了包含视线误差的点目标二维频谱,并在子孔径视线误差补偿算法的基础上,推导出一种在距离多普勒域、距离迁徙校正前补偿视线误差的新补偿算法,点目标仿真结果验证了该算法在连续大面积实时成像时的优越性。其次,研究了目前国内机载组合导航系统测量精度不高,不能满足UWB SAR高分辨成像需要时的运动补偿方法。针对UWB SAR特点,论文提出了一种结合全球定位系统(GPS)实时信息和改进MD自聚焦的运动补偿方法,并基于实测数据,提出了几点提高改进MD估计精度的措施。两段实测数据处理的结果验证了所提方法的有效性。论文中还深入分析了该补偿方法中的几个问题,给出了UWB SAR中MD子孔径划分应满足的条件。然后,深入研究了适合UWB SAR回波特点、以对比度最大为聚焦准则的自聚焦算法。对已广泛应用的对比度最优自聚焦算法进行改进,使其满足实时运动补偿的需要,实际数据处理结果验证了该改进算法的有效性;借鉴频域PACE算法思路,提出一种在时域提取回波中高次多项式相位误差的TD-PACE算法,实际数据处理结果验证了该算法的有效性:针对PACE算法的不足,提出一种减小计算量的IPACE算法,实际数据处理结果表明,IPACE算法执行效率较PACE大幅提高,而聚焦效果相当。论文中还比较了IPACE和PGA聚焦UWB SAR图像的能力,实测数据处理结果表明,IPACE聚焦效果较PGA更好。最后,结合无人机特点,设计了一种适合无人机UWB SAR高分辨成像要求的低成本运动补偿方案。该方案利用互补滤波器融合GPS接收机输出的速度和单轴加速度计输出的加速度,对UWB SAR回波粗补偿,利用自聚焦进行精补偿。论文中推导了加速度计输出的有用加速度表达式,分析了天线平台稳定精度对加速度计输出的影响,并用仿真数据验证了该补偿方案的有效性。更多还原

【Abstract】 Airborne ultra-wideband synthetic aperture radar (UWB SAR) working in low frequency band can reconnoitre targets concealed by foliage or earth surface, which is very valuable for military purpose. But trajectory deviation of aircraft will introduce troublesome phase errors into radar echoes, which would influence badly SAR images quality without correction, and effective motion compensation method is crucial to UWB SAR with high resolution. Under the support by some National Defense Research Project, this dissertation researched the motion compensation (MoCo) for UWB SAR from the following subjects:Firstly, how to compensate the trajectory deviation error in line of sight (LOS) for UWB SAR was discussed in detail with the help of exact motion track. In this dissertation, the influence of error in LOS to range cell migration correction (RCMC) in UWB SAR imaging was analyzed with emphasis, and the spectrum formulation of a point target comprising the LOS error was derived under some approximation. On the basis of sub-aperture compensation method, a new MoCo method with sub-aperture in azimuth direction and sub-swath in range direction was detailedly derived, and computer simulation results validate the new method.Secondly, how to eliminate effectively errors in UWB SAR echoes was researched when inertial navigation system (INS) on board can not provide exact motion track, which is a universal fact for our country currently. A method combined the real time information from global position system(GPS )receiver with refined map drift(MD) was proposed in the dissertation, and based on the real UWB SAR data, some measurements were added into the refined MD to improve the precision of estimation. The processing results of two data segment validate the proposed method. Some questions in the method were discussed also.Thirdly, some autofocus algorithms for UWB SAR were deeply investigated, which were on the basis of imaging contrast. On the one hand, the widely used contrast optimization autofocus (COA) was mended to satisfy the demand of the real time MoCo onboard, and the real processing results prove the validation of the mended method. On the other hand, based on phase adjustment by Contrast enhancement(PACE), a new algorithm named as phase adjustment by contrast enhancement in time dimension (TD-PACE) was proposed, which can extract polynomial errors with high order from range compressed echoes, and the real results show that the method can get three order polynomial phase errors. Aimed the disadvantage of PACE algorithm with the huge computation load, an interpolated PACE (IPACE) was advanced also. The processing results of real UWB SAR data prove that the IPACE can greatly accelerate the run time of algorithm with the same quality. Furthermore, the images quality focused by IPACE was better than the images by phase gradient autofocus (PGA), which is considered to be standard nonparametric SAR autofocus algorithm.Finally, a low cost MoCo scheme for unmanned aerial vehicle (UAV) was designed. A GPS receiver with high sampling and a one-axis accelerometer mounted directly on the SAR antenna phase center (APC) and aligned in LOS were used to measure the motion of UAV in the scheme, and the information from complementary filter (CF), which was used to fuse the speed from GPS and the acceleration from accelerometer, was used to compensate SAR echoes roughly. The useful acceleration expression for accelerometer was derived, and the influence of SAR antenna platform stabilization’s precision on the output of accelerometer was discussed also. The computer simulation results justify the scheme.更多还原