【作者】 谷德峰；

【导师】 易东云；

【作者基本信息】 国防科学技术大学 ， 系统分析与集成， 2009， 博士

【摘要】 分布式InSAR卫星系统在近距离编队飞行的小卫星上装载SAR天线,通过小卫星和SAR天线的协同工作,完成干涉SAR任务,是一种具有巨大潜力的新概念新体制雷达系统,其实现在基础理论和技术层面上面临许多挑战。编队空间状态的高精度确定是实现小卫星分布式雷达任务的关键技术之一,是小卫星分布式雷达功能实现的前提和重要保证,也是卫星编队飞行需要解决的共性问题。本文以分布式InSAR卫星系统为背景,阐述了系统与空间状态测量之间的关系,重点针对双频GPS和星间无线电两种不同的测量手段,开展了编队卫星空间状态高精度确定方法的研究。主要工作包括五部分:第一,对分布式InSAR目标三维定位的空间几何关系进行了分析,阐述了系统参数与空间状态测量之间的关系,明确了空间状态测量在分布式InSAR任务中的意义和要求。给出了目标三维定位的闭合形式解及灵敏度分析,给出了目标三维定位精度指标与系统参数精度指标之间关系的解析表达式。给出了干涉基线的定义,将干涉基线分解为空间域干涉基线和时间域干涉基线,其中时间域干涉基线可通过主星的绝对轨道测量获得,空间域干涉基线则通过高精度星间基线测量获得。由测量基线到空间域干涉基线的转换需要进行部位修正和时间对齐,给出了部位修正的精度分析。第二,研究了星载双频GPS观测数据预处理方法,给出了完整的数据预处理方案与流程。研究了一种新的抗差Vondrak滤波方法,在原始信号拟合函数形式未知且被粗差污染的情况下,有效的抑制粗差对信号拟合的影响,对观测数据进行合理的平滑。研究了星载双频GPS观测数据质量评估方法,完善了已有的评估方法。并采用CHAMP卫星在轨数据进行了预处理与质量评估,验证了算法的正确性与可靠性。第三,研究了星载双频GPS原始观测数据降采样处理方法,分析了多项式平滑伪距和载波相位平滑伪距方法的优缺点。研究了星载双频GPS非差运动学定轨方法,结合GPS观测数据质量分析结果,给出了一种合理的伪码和相位观测数据加权策略。研究并实现了星载双频GPS非差动力学定轨方法,将CHAMP卫星定轨结果与GFZ科学轨道进行比对,二者在轨道位置R、T、N分量上差值的均方根为4.8cm,8.2cm,7.5cm,三维误差的均方根为12.2cm,表明本文的非差动力学定轨精度已与GFZ科学轨道相当。研究了SLR检核精密定轨精度方法,提出了一种利用SLR数据校准GPS精密定轨系统误差的新方法,在卫星一次过境的短弧段内,用二阶多项式来参数化表示GPS定轨慢变系统误差,进而利用不同地面激光测站的分时观测数据,估计GPS定轨系统误差。第四,研究了基于双频GPS的高精度星间相对定位技术。建立了星载GPS电离层延迟的单层投影模型,利用单层投影模型仿真分析了差分电离层延迟对分布式SAR编队卫星CDGPS相对定位结果的影响。研究了基于轨道动力学模型的分布式SAR卫星编队CDGPS相对定位方法,在CDGPS技术的基础上,引入轨道动力学模型提供的先验约束信息,对长弧段的观测数据进行解算,有效的抑制测量中的随机误差,提高相对定位精度,并克服运动学逐点解算方法在观测几何较差或观测数据不足情况下无法应用的缺点。分析了星间测距信息对CDGPS相对定位精度的贡献。第五,研究了基于无线电测量的高精度星间相对状态确定方法。介绍星间无线电测量原理,比较分析了几种传统的相对状态估计方法的优缺点。研究了一种基于样条模型的星间相对定位与定姿的新方法。该方法将传统的直接估计状态参数转化为估计样条参数,减少了待估参数的个数,提高了距离变化对姿态参数的敏感性,估计精度更高,估计结构更加稳定。讨论了无线电测量用于分布式SAR星间基线确定存在的问题,包括星间无线电测量信号的覆盖与遮挡和编队构形设计对无线电测量几何的影响。更多还原

【Abstract】 The distributed InSAR satellite system equips SAR antennas on close formation flight satellites, and completes SAR interferometry mission through the collaboration of small satellites and SAR antennas. It is a kind of new conceptual radar system with enormous potential, which faces many challenges in basic theory and technology. The high precision determination of the formation spatial states is one of the key technologies, and is the important guarantee for the success of the distributed InSAR mission. It is also a common problem to solve in other satellite formation flight missions. On the background of the distributed InSAR satellite system, this dissertation clarifies the relation between system and spatial state measurement, emphasizing on the two different measurements dual frequency GPS and inter-satellite wireless, and studies the high precision spatial state determination of satellite formation. The main work includes five parts:Firstly, the spatial geometrical relation of distributed InSAR geolocation is analyzed, the relation between system parameters and spatial states measurement is explained, and the significance of spatial states measurement is illustrated through requirement analysis of the distributed InSAR satellite system. Closed-form solution to the geolocation is provided and sensitivity of the solution is analyzed. The formulations of geolocation precision criterion and system parameters precision criterion are proposed. Interferometry baseline is defined. Interferometry baseline is involved with spatial baseline and time baseline. Time baseline is obtained by master satellite absolute orbit determination, and spatial baseline is obtained by high precision inter-satellite relative position determination. The transfer from measured baseline to spatial baseline needs body correction and time synchronization. The precision analysis of body correction is provided.Secondly, the pre-processing method of onboard dual frequency GPS observations is studied, and data pre-processing scheme and algorithm is proposed. A novel robust Vondrak filter is presented, which can ensure that the gross errors are not too influential on the curve fit, and makes the original model robust, when fitting function of the original signals is unknown and they are contaminated by gross errors. The quality evaluation of onboard dual frequency kinematic GPS observations is studied. Computational experiment is carried on to test the correct and validity of the algorithm by pre-processing and evaluating the onboard observations of CHAMP satellite.Thirdly, Desampling method of onboard dual frequency GPS observations is studied. The advantage and disadvantage between polynomial smoothing pseudo-range method and carrier phase smoothing pseudo-range method are analyzed. Zero-differential kinematic orbit determination of onboard dual frequency GPS is studied. Based on quality analysis of GPS observations, a reasonable weighed method of code and phase is presented. Zero-differential dynamic orbit determination of onboard dual frequency GPS is studied. Observations on CHAMP satellite for one week are tested. Zero-differential dynamic orbit determination results are compared with GFZ science orbit. The RMS (root of mean square) in R, T and N component are 4.8cm, 8.2cm and 7.5cm, and the RMS in three-dimension is 12.2cm. Precise orbit evaluation with satellite laser ranging (SLR) data is studied, based on which a new method to calibrate orbit system error is proposed. The new method gets SLR data from several stations in one pass arch, makes orbit error projection at different time, and estimates orbit system error.Fourthly, High precision determination of relative position based on CDGPS is studied. Projection model of single-layer ionosphere path delay for onboard GPS is constructed. Simulation based on the model analyzes how the differential ionosphere delay affects the relative position determination of distributed InSAR satellite formation. A CDGPS relative position method of distributed InSAR satellite formation based on dynamic orbit model is presented. Based on CDGPS measurement and the prior restricted information provided by dynamic orbit model, the observation of long arch is computed, which controls the random errors in the measurement efficiently, improves the relative position determination precision, and comes over the disadvantage that kinematic single point position determination can not be used when observation geometry is bad or observations are not enough. The contribution of inter-satellite distance measurement to CDGPS relative orbit determination precision is analyzed.Finally, High precision relative states determination based on inter-satellite wireless measurement is studied. The principle of inter-satellite wireless measurement is introduced. The advantage and disadvantage of several different traditional relative state estimation methods are compared. A new inter-satellite relative state determination method based on spline model is proposed. The method transfers the direct estimation of state parameters in traditional method into spline parameters, reduces the number of parameters to estimate, improves the sensitivity of distance change to the state parameters, and makes the estimation structure more stable. The signal coverage and shelter of inter-satellite measurement and the geometric effect of formation design to wireless measurement is discussed.更多还原