星载SAR干涉技术获取DEM及其精度分析

星载合成孔径雷达干涉（InSAR）技术是一种数据覆盖范围广、廉价、高效、方便的数字高程模型（DEM）获取方法,但在地面植被覆盖广、大气水汽含量高的地区其影像相干性随时间基线的增加迅速降低;同时,SAR卫星的轨道误差也影响DEM精度。利用ERS-1/2卫星串行模式SAR数据获取镇江地区DEM,分析了轨道误差对DEM精度的影响;根据干涉相位的统计特性,从理论上给出干涉相位噪声与相干系数和视数之间的关系。实验结果表明就干涉像对的卫星轨道误差和相位噪声而言,在小区域内DEM精度优于3.5 m。     

稀疏轨道条件下SAR几何校正轨道拟合策略

针对SAR影像头文件中提供的轨道矢量分布较为稀疏时,使用低阶多项式拟合轨道参数会存在较大误差,从而导致基于距离-多普勒模型的星载SAR影像几何校正精度较差的问题,提出了一种稀疏轨道条件下实用的轨道拟合策略。通过对轨道拟合误差进行分析,综合考虑距离-多普勒模型的解算与现有几何校正资源,选择使用高阶插值方法生成卫星成像时刻处足够的加密点轨道状态矢量,再对局部的轨道进行二阶多项式拟合,利用拟合的轨道模型系数进行几何校正。利用实测GPS点数据进行了SAR几何校正精度验证,结果表明该策略能够明显改善ALOS2 PALSAR影像几何校正精度,证明了该方法的有效性和良好的适用性。     

稀疏轨道条件下SAR几何校正轨道拟合策略

针对SAR影像头文件中提供的轨道矢量分布较为稀疏时,使用低阶多项式拟合轨道参数会存在较大误差,从而导致基于距离-多普勒模型的星载SAR影像几何校正精度较差的问题,提出了一种稀疏轨道条件下实用的轨道拟合策略。通过对轨道拟合误差进行分析,综合考虑距离-多普勒模型的解算与现有几何校正资源,选择使用高阶插值方法生成卫星成像时刻处足够的加密点轨道状态矢量,再对局部的轨道进行二阶多项式拟合,利用拟合的轨道模型系数进行几何校正。利用实测GPS点数据进行了SAR几何校正精度验证,结果表明该策略能够明显改善ALOS2PALSAR影像几何校正精度,证明了该方法的有效性和良好的适用性。     

分段插值同步算法在数字化变电站中的应用

提出一种分段插值同步算法来实现数字化变电站的过程层同步采样,以降低系统对硬件的要求,并提高系统的可靠性.针对插值同步算法进行了分段设计,根据数据的线性度情况分别采用一阶线性插值法或二次插值法;分析了各算法的最大采样值理论误差;提出了过程层采样插值同步的具体实现方法.最后通过现场插值同步精度试验验证了该算法具有较高的同步精度,符合IEC6044-8标准对0.2S级测量电子式互感器的要求.     

基于ALOS极化干涉SAR数据的DEM提取方法研究

极化干涉理论的发展以及全极化卫星的发射,为极化干涉的研究应用提供了广阔的发展空间,开展极化干涉SAR提取DEM的研究对于解决单极化干涉SAR在植被覆盖区DEM提取精度较低的问题具有重要意义。基于山东泰安地区的一对ALOS PALSAR全极化干涉数据,利用相干性最优方法和最大化相位中心分离的方法获取极化干涉信息,并通过对优化后干涉信息的滤波、解缠、基线精确估计等处理来提取DEM,最后将相干优化的结果与传统HH、HV、VV单极化干涉结果进行对比分析。结果表明:优化方法较单极化干涉方法可以有效降低干涉图的噪声,减少相位解缠的残差点,提高解缠相位的质量,并且不同优化方法之间还存在一定差异,数值半径方法获取的DEM精度要好于其他两种优化方法;通过等值线-Goldstein二级干涉SAR滤波方法可进一步提高单极化和优化干涉图的质量,降低残差点,提高相位质量,在水体覆盖的区域通过滤波窗口的设置可以很好地改善DEM的精度。     

岸基北斗IGSO卫星反射信号相位测高

针对全球导航卫星系统反射信号的特性和我国北斗导航卫星系统反射信号在海面测高应用上的特点,证明了利用北斗倾斜地球同步轨道(IGSO)卫星反射信号对湖面和海平面进行岸基载波相位测高的可行性。实验分湖面和海面2组进行研究,用相位测高结果与实际测量结果对比的均方根误差(RMSE)描述测高结果的精度。在湖面岸基实验中,接收天线到湖面的相对高度为5.2 m,IGSO7和IGSO10卫星相位测高结果的RMSE值达到厘米级,分别为3.23 cm和4.98 cm。在海面岸基实验中,海面的潮位高度差约2 m,利用相位测高结果可以反演海面潮位。IGSO8卫星相位测高结果的RMSE为17.96 cm,IGSO9卫星相位测高结果的RMSE为15.27 cm,IGSO10卫星相位测高结果的RMSE为16.38 cm。通过分析IGSO卫星仰角的变化,发现较大的卫星仰角变化率可以提高相位测高的结果的精度。     

互相关直径测量的相位跟踪采样控制与校正

为了提高互相关法直径测量的精度,需要对工件表面误差信号进行等相位间隔跟踪整周期采样。介绍分频法实现相位跟踪采样控制的原理;对相位间隔准确度的影响进行了讨论,提出固有误差和随机误差的概念,对其产生原因进行了分析;引入附加角测量环节对采样相位间隔进行校正,给出校正算法;结合ARM7LPC2148 MCU嵌入式系统,介绍相位跟踪采样控制、校正测量及同步的具体实现。实验测试表明:转速频率波动大于千分之一,采样控制系统的分频系数即会发生改变,相位跟踪性良好;在3 000转/分以下,采样相位间隔误差控制在0.001 13度以内;证明附加角测量和采样相位间隔校正是必要的。     

粒子滤波在卫星轨道确定中的应用

卫星轨道确定问题中可能存在初始估计信息误差较大、状态及测量误差分布不是高斯分布等问题,为了寻求一个能采用解决这两种问题的方法,本文采用了“采样-重要性-重采样”SIR(Sampling Importance Resampling)粒子滤波算法作为滤波方法,以地磁场矢量为测量量,对低地球轨道卫星的轨道数据进行自主的估计.为了避免该滤波算法中的采样贫乏的问题,采用了一个崎岖化方法来克服采样贫乏问题.最后给出了此方法应用到了卫星轨道确定问题中的数字仿真实例.     

中高度椭圆轨道星座：一种提高多卫星系统成本效益的途径

利用其高度低于地球同步高度的圆轨道座实现地球覆盖,有其先天不足之处,椭圆轨道星座可为所选择的地理区域提供更有效的覆盖。由赤道平面内的椭圆环带及临界倾角分别为ｉ１＝６３．４３５°与ｉ２＝１１６．５６５°的两个椭圆环带组成星座系统,这种设计对经度与纬度抑或白天的覆盖时间可获得重覆盖,选取多卫星系统的轨道平面间隔及相位布局可以产生重复的地面轨迹,就补偿长期项摄动及保持星座完整性所需的周期性修正机动而消耗     

X射线脉冲星导航系统的闭环校正滤波器设计

X射线脉冲星导航(XNAV)系统对脉冲到达时间或相位的在轨测量存在星载钟计时误差问题. 本文提出将钟差与卫星三维位置参数一起作未知量处理, 采用4颗以上脉冲星的观测信息解算出卫星位置; 将该位置信息与轨道动力学预报的位置信息的差值作为量测信息, 结合卫星轨道动力学模型, 设计闭环校正卡尔曼滤波器. 仿真表明, 设计的闭环校正滤波器能够对卫星轨道状态进行最优估计, 解决了XNAV系统中的钟差问题.     

Review Article SAR interferometry—issues,techniques, applications

Data from interferometric synthetic aperture radar (INSAR) can provide three-dimensional information by using the phase as an additional information source derived from the complex radar data. In this paper, the issues, techniques and applications of SAR interferometry are reviewed. After a brief historical review, the geometric implementations of SAR interferometry are described. The general processing techniques are summarized and an introduction to various phase unwrapping techniques is given. Besides the differential use of SAR interferometry, the review focuses on parameters such as baseline, decorrelation and motion compensation which have a limiting influence on the quality of the data. After evaluating the various existing and potential applications using SAR interferometric techniques such as topographic mapping, digital elevation modelling, slope measurement, change detection, classification, ocean currents, polar research, seismic events and volcanic hazards, the paper concludes with some research issues, trends and developments in SAR interferometry. The paper is illustrated by examples of SAR interferometric data and derived products from the ESA ERS-1/ERS-2 and SIR-C/X-SAR satellite mission and from single pass aircraft data. An extensive list of references and bibliography on SAR interferometry is provided at the end of this review paper.     

Effects of residual motion compensation errors on the performance of airborne along-track interferometric SAR

Two approximations, center-beam approximation and reference digital elevation model (DEM) approximation, are used in synthetic aperture radar (SAR) motion compensation procedures. They usually introduce residual motion compensation errors for airborne single-antenna SAR imaging and SAR interferometry. In this paper, we investigate the effects of residual uncompensated motion errors, which are caused by the above two approximations, on the performance of airborne along-track interferometric SAR (ATI-SAR). The residual uncompensated errors caused by center-beam approximation in the absence and in the presence of elevation errors are derived, respectively. Airborne simulation parameters are used to verify the correctness of the analysis and to show the impacts of residual uncompensated errors on the interferometric phase errors for ATI-SAR. It is shown that the interferometric phase errors caused by the center-beam approximation with an accurate DEM could be neglected, while the interferometric phase errors caused by the center-beam approximation with an inaccurate DEM cannot be neglected when the elevation errors exceed a threshold. This research provides theoretical bases for the error source analysis and signal processing of airborne ATI-SAR.     

A comparison of atmospheric phase delay estimated by ASAR and MERIS over the Campania area

Propagation delay through the atmosphere is a key problem in coherent processing of synthetic aperture radar (SAR) data. Modern multitemporal interferometric techniques compensate the atmospheric phase delay contribution by analysing a stack of data. However, assessment of the achieved accuracy of the retrieved atmospheric component is still an open issue. In this work we report the results of an experiment carried out over a wide area aimed at comparing the zenith delay (ZD) estimated by radar and multispectral sensors. In particular, we refer to the instruments onboard the Envisat satellite and specifically to the Advanced Synthetic Aperture Radar (ASAR) and Multispectral Medium Resolution Imaging Spectrometer (MERIS) sensors that simultaneously acquire data along the same orbit. The study is preliminary to the possible exploitation of the MERIS water vapour product for compensating the atmospheric phase delay signals in a long series of acquisitions used in the multipass differential interferometric synthetic aperture radar (DInSAR) techniques to achieve higher accuracy and/or to extend the applicability of the technique to emergency situations, as well as to the possible use of SAR interferometry in meteorological applications.     

空间曲线几何Hermite插值的B样条方法

在给定的GC2插值条件,利用de Boor的构造平面曲线的GC2-Hermite插值方法,构造了一条具有两个自由度的三次B样条插值曲线,并证明插值曲线是局部存在的且具有4阶精度.     

Formation flying orbit design for the distributed synthetic aperture radar satellite

Formation flying orbit design is one of the key technologies for system design and performance analysis of the distributed SAR satellites. The approximately analytic solution of the passive stable formation flying orbit elements is explored based on the expansion form of Kepler's equation. A new method of orbital parameters design for three-dimensional formation flying SAR satellites is presented, and the precision of the orbital elements is analyzed. Formation flying orbit elements are calculated for the L-Band distributed SAR satellites using the formulas deduced in this paper. The accuracy of the orbital elements is validated by the computer simulation results presented in this paper.     

平面隐式曲线的Hermite 插值逼近

隐式曲线在医学图像处理、地理信息系统、数值场可视化等领域中有着重要应用。 在分析点采样和曲线逼近理论的基础上,提出一种运用Hermite 插值方法逼近平面隐式曲线的 算法。首先将曲线绘制区域网格化,在网格单元各边中通过线性插值计算曲线采样点;其次通 过计算采样点精简前后构成的曲线段之间产生的误差优化采样点;最后通过Hermite 插值法逼 近隐函数曲线。实验表明,通过该算法绘制出的曲线在采样点数量较少的情况下,其光滑度和 准确度仍较高。     

The influence of input parameters on SAR interferometric processing and its implication on the calibration of SAR interferometric data

Synthetic Aperture Radar (SAR) interferometry is a field of rapid development. The processing of SAR interferometric data is complex and influenced, in particular, by the input parameters. A sensitivity study of these input parameters and issues relating to the calibration of SAR interferometric data is presented. The pulse repetition frequency has been identified as a critical parameter during the SAR interferometric processing which, in case of inconsistencies in the CEOS standard data format, leads to erroneous results.     

四次Hermite曲线的构造及其特性

在Hermite曲线插值理论基础上,针对工程应用中的特殊要求,提出了四次Hermite捅值曲线的概念．所构造的四次Hermite曲线满足给定点位置矢量和一阶导数矢量的条件,保证构造曲线处于给定锥面上,达到准双曲面齿轮轮廓曲线的插值精度要求．     

干涉雷达永久散射体识别方法的对比分析

基于永久散射体的干涉测量技术可以克服卫星合成孔径雷达应用于区域地表形变探测所面临的时空失相关和大气影响.永久散射体的有效识别是干涉系统中的一个关键环节.本文对永久散射体的两种识别方法, 即相关系数阈值法和振幅离差指数阈值法进行了理论上的分析和实验上的对比.以上海市局部地区作为研究对象, 采用26幅欧洲空间局的ERS-1/2卫星C波段SAR影像为源数据, 使用两种识别方法分别进行了永久散射体的提取, 结果表明, 振幅离差指数方法具有更为稳健的抗噪能力.     

基于Hermite曲线的机器人足球射门算法

机器人足球比赛是关于人工智能的新兴研究领域,它集数学算法、多智能体、机械设计、控制理论等多个学科于一体,是先进科学技术的发展代表。在机器人足球比赛中,射门和传球是两个最基本的动作。提高动作的速度以及准确性、连贯性是提高动作效率的关键。本文提出一种基于Hermite插值曲线的机器人足球射门算法。利用Hermite插值曲线的数学特性,可以使机器人在满足一定速度的基础上,连续、准确地完成射门或传球动作,并且能大幅度地提高射门或传球的效率。本文以FIRA5：5仿真平台为背景,结合试验证明,利用此方法可以较好地提高射门的成功率。