3种测站布局星载观测数据增强定轨研究

低轨卫星(LEO)星载观测数据可削弱导航星精密定轨时对地面站的依赖性。分析了在全球测站均匀但不均衡、国内区域测站加入我国南北极测站、仅国内区域测站3种测站布局情况下,加入LEO进行联合定轨时LEO对导航星定轨的增强程度。使用双星GRACE和地面实测数据进行了定轨实验分析,并对轨道进行1 d预报。结果表明,3种测站布局加入LEO后定轨精度一维RMS分别提高了6 mm、2.7 cm和2.5 dm,提高程度分别在19.5%、38.2%、63.1%,区域测站提高最为明显,加入我国南北极测站定轨精度提高至5 cm以内;切向、法向、径向均有相应程度的提高,切向稍大;轨道预报精度分别提高了15.3%、28.9%、66.0%,与定轨精度提高程度相一致。     

利用多面函数拟合和欧拉矢量法建立福建省GPS速度场模型

通过处理福建省卫星导航定位基准服务系统(FJCORS)2013-2015年观测资料,获得GPS站实测运动速度值,在此基础上,分别利用多面函数拟合法和欧拉矢量法构建了福建省及周边区域GPS速度场模型.内符合精度方面,多面函数拟合的速度精度南北分量为1.06 mm/a、东西分量为2.00 mm/a;欧拉矢量法得到的速度精度南北分量为1.36 mm/a、东西分量为1.22 mm/a.外符合精度方面,两种方法模拟得到的检核点速度值与实测速度值的较差均在±2.28 mm/a以内.在福建省陆域内,两种方法得到的速度场具有高度的一致性,运动速度均为35 mm/a左右,运动方向为SE-E向.     

地震破裂模型约束的中国阿里地震三维形变场

利用环境卫星（Environmental Satellite,Envisat）的升、降轨数据在地震破裂模型约束下获取2007年阿里地震的高质量同震地表三维形变场。首先,对合成孔径雷达（synthetic aperture radar,SAR）影像进行差分干涉处理,得到地震造成的视线向同震地表形变场;然后,以地震破裂模型为约束条件,采用赫尔默特方差分量估计法来解算阿里地震的高质量地表三维同震形变场。结果表明,震中区域最大下沉达约4.7 cm,东西向位移较小,南北向呈挤压趋势。总体上,三维形变的特征表明阿里地震是一个以正倾滑为主兼少量右旋走滑运动的地震事件。     

At the dawn of geodesy

The first land surveyors were rope stretchers and rope knotters, remembered in ancient documents and tomb paintings and also in some terminology. The L-shaped carpenter’s square, one of the earliest and most versatile basic tools, represents the observed direction of the plumb line versus the water level and appears as the shadow-casting gnomon and also as the geometrical gnomon in magically-restricted enlargements of altars. The related “Pythagorean” theorem was known in antiquity centuries before Pythagoras, with algebraic proofs in Babylonia and China. The spherical shape of the earth, deduced from the observation of circumpolar stars, was part of a complete equatorial astronomical system in ancient China. But although shadow measurements were generally used to establish north-south distances, only the Greeks derived from them the size of the earth. The striking difference between the abstract, geometric approach of Greece and the concrete, algebraic approach of Babylonia and China represents not a difference in talents but a difference in culture-bound interests.     

一种能适应月相变化的月球图像中心提取算法

月球是夜间最亮的天体,测月导航可在云雾天气下有效弥补传统天文导航在夜间只能观测恒星的不足,扩大天文导航的可用范围。为实现测月导航,提出了一种能适应不同月相变化的月球敏感器图像月球中心提取算法。利用Sobel-Zernike矩算子对图像进行边缘检测,利用基于圆形性检测的搜索算法筛选月球边缘点并以此提取月球中心。经半物理仿真实验解算,该算法能够针对不同月相图像有效提取月球中心,中心提取的内符合平均精度为0.16像素,外符合平均精度为2.86″。由于在月球上观测地球也有"地相"变化,该算法同样适用于月球车地球敏感器图像中心提取。     

The establishment of a calibration standard for gravimeters in Eastern Canada and the United States

A program of gravimeter measurements for the establishment of a suitable gravity standard in eastern Canada and United States is described. It is shown that the consistency of nine independent measurements of the gravity differences between stations forming a north-south line from Ottawa to Washington is highly satisfactory and that this line is suitable for calibration purposes. The gravity differences depend fundamentally upon a gravimeter calibration made against values of gravity at Cambridge pendulum stations in Canada. Communication présentée à l'Assemblée Générale de Toronto (1957).     

Advanced analysis of differences between C and X bands using SRTM data for mountainous topography

By Interferometric Synthectic Aperture Radar (InSAR), during the Shuttle Radar Topography Mission (SRTM) height models have been generated, covering the earth surface from 56° south to 60.25° north. With the exception of small gaps in steep parts, dry sand deserts and water surfaces, the free available US C-band data cover the earth surface from 56° south to 60.25° north completely while the X-band data, distributed by the DLR (German Aerospace Center), cover it only partially. The C-band and X-band radar cannot penetrate the vegetation because of the short wavelength. Therefore, the height models are not Digital Elevation Models (DEM) representing bare Earth surface without any details, they are Digital Surface Models (DSM) representing the visible surface including vegetation and buildings. In the area of Zonguldak, Turkey, C-band and X-band DSMs are available and have been analysed in cooperation between Zonguldak Karaelmas University (ZKU) and Leibniz University of Hannover. The digitized contour lines from the 1:25,000 scale topographic maps and also a more precise height model derived directly from large scale photogrammetric mapping are used as reference height models. The terrain inclination influences the accuracy strongly, but also the directions of the inclination in relation to the radar view direction, the aspects, are important. Independent from the aspects, the analysed results do have root mean square differences against the reference data fitting very well to the Koppe formula SZ=a+b*tan α. The analyses are made separately for open and forest areas, with clear accuracy differences between both. Also, the analysis of X-band separately for three sub-areas is done and the positive effect of double observation to the accuracy has been clearly determined. The C-band data are only available with a spacing of 3 arcsec, corresponding to 92m × 70m, while the X-band data do have a spacing of 1 arcsec. This is important for the interpolation in the mountainous test area. The accuracy of the height points is approximately the same for the C- and the X-band data. But the C-band data which have three times larger spacing than Xband data, do not include the same morphological information. While C-band data contain very generalised contour lines X-band data have quite more details depending on 1 arcsec point spacing. The differential DEMs have been generated, separately, for displaying the differences between SRTM height models and reference DEMs of the test field.     

GNSS navigation and positioning for the GEOHALO experiment in Italy

GEOHALO is a joint experiment of several German institutes for atmospheric research and earth observation where exploring airborne gravimetry over Italy using the High Altitude and LOng Range (HALO) aircraft data is one of the major goals. The kinematic positioning of the aircraft, on which all remote sensing instruments are located, by Global Navigation Satellite System (GNSS) is affected by the characteristics of long-distance, long-time duration, and high-platform dynamics which are a key factor for the success of the GEOHALO project. We outline the strategy and method of GNSS data processing which takes into account multiple GNSS systems (GPS and GLONASS), multiple static reference stations including stations from the International GNSS Service (IGS) and the EUropean REFerence network (EUREF), multiple GNSS-receiving equipments mounted on the kinematic platform, geometric relations between multiple antennas, and assumptions of similar characteristic of atmospheric effects within a small area above the aircraft. From this precondition, various data processing methods for kinematic positioning have been developed, applied and compared. It is shown that the proposed method based on multiple reference stations and multiple kinematic stations with a common atmospheric delay parameter can effectively improve the reliability and accuracy of GNSS kinematic positioning.     

基于块体模型的青藏高原及邻区地壳三维构造形变分析

2020珠峰高程测量,获得了丰富的青藏高原及邻区的GNSS监测数据。本文收集了陆态网、尼泊尔CORS网GNSS长期观测数据,计算了该地区20多年GNSS三维速度场,利用GRACE模型精化了垂直速度场,通过活动块体模型,从地壳运动、块体运动与应变、块体相对运动等多个方面研究了青藏高原地壳运动与构造形变特征。研究表明,青藏高原地壳形变具有明显的分区特征,南北向收缩主要表现在拉萨块体,东西向伸展主要表现在巴颜喀拉块体,中部羌塘块体没有明显水平挤压,但地壳隆升速率最大,且水平面积有扩大趋势,本文研究能够在一定程度上支持青藏高原地壳增厚学说。     

VLBI技术测月的数学模型探讨

近年各国已纷纷制定测月计划,采用何种技术对月球进行定位,变得尤为重要。本文通过对VLBI技术特点进行分析,VLBI是目前大地测量中精度最高的技术手段,但只适用于深空探测,因为深空射电信号到达地面时,可看作平行信号。本文针对VLBI技术特点及数学模型,对存在不可忽略视差的VLBI测月模型,通过级数展开,解决月面射电信号到达地球时的视差问题,并顾及地球自转得出最终数学模型,通过站间一次差分消除钟差等影响,得出VLBI对近轨天体(月球)表面射电源定位的数学模型。     

以GPS资料研究中国南北地震带深部构造应力场变化特征

本文利用中国南北地震带2004-2007年间观测的239个GPS站数据,对中国南北地震带地壳内15km深处的最大主应力和最大剪应力进行了计算分析,并将计算结果与同期发生在中国南北地震带的地震活动进行了对比分析,结果表明观测同期发生的中强震大都位于应力变化大并且有深大断裂的地区,汶川地震进一步说明,四川地区地壳内的局部应力场变化与最大剪应力变化在空间分布上与强震活动区域存在较好的一致性。     

无人机倾斜摄影铁路轨道线高精度自动重建

针对既有铁路测绘上线难、作业效率低及测量精度不足的问题,本文提出了一种基于无人机多视图几何原理的铁路轨道线高精度重建方法。首先从无人机影像上提取线特征;然后采用像方测度获得候选匹配线,基于物方距离测度进行Powell优化,获得精确的钢轨线匹配结果;最后,将影像钢轨线匹配结果作为观测值,以钢轨线反投影距离作为测度,最小二乘优化物方钢轨直线段坐标。试验结果表明,本文方法实现了影像轨道线自动匹配与高精度平差解算,像方反投影残差优于0.5像素,轨距和高程的内符合精度分别为0.006和0.005 m。解算成果的平面高程绝对定位精度可达到2 cm左右,平差模型收敛性良好,可以满足工程应用的需要。     

优化先验模型参数的矿区多轨InSAR三维形变监测

监测煤矿开采导致的地表三维形变对于矿区地质灾害防控和开采沉陷机理研究至关重要。针对单轨道InSAR和先验模型融合解算矿山三维形变存在精度不高、时间分辨率差的问题,本文提出了一种通过优化先验模型参数的矿区多轨InSAR三维形变解算方法。首先,利用Weibull模型同步4个轨道LOS向形变位移,以此削弱不同轨道之间时间异步对三维形变解算精度的影响,并采用加权最小二乘求解矿区垂直向和东西向形变;然后,根据垂直向和东西向形变优化矿区开采先验模型参数;最后,解算南北向形变位移。利用覆盖大同矿区的TerraSAR-X数据和3个轨道Sentinel-1 InSAR数据集对本文方法进行验证。研究结果表明,与地面GPS监测点相比,本文方法可以获得相对精确的三维形变结果,垂直向RMSE、东西向RMSE和南北向RMSE约为1.1、1.4和2.1 cm。     

南极长城站建立深空测控站的可行性

在深空探测中,测控(跟踪)系统的有效运行是整个探测任务成功完成的重要保证。由于我国测控站都布设在国内,属于局部性分布,影响深空跟踪和测控的连续性和通信质量。本文提出在中国南极长城站建立深空测控站的设想,以当前热点的月球车巡视探测为例,从地-月通信的改善情况、南极长城站建站的地质条件、电磁环境、气候条件、交通运输后勤保障条件等方面分析了建站的可行性。研究表明:①对于国际主流探月国家所选取的月面探测区域月球南极,南极长城测控站的地-月通信受月面地形的影响要小于我国国内测控站,且测控时间与国内测控站可以实现互补,减小由于地球自转的影响;②南极长城站的地质条件、电磁环境和气候条件等适合于测控站的建设和使用;③南极长城站经过了30 a的建设,建站的各方面条件趋于成熟,逐步适合于深空跟踪站的建立。     

西龙池上水库GPS变形监测系统研究及实现

为了实现对西龙池上水库变形的连续、自动化监测,研制了GPS变形监测软件DDMS,建立了西龙池上水库连续运行监测系统。1a的运行表明,系统具有较高的稳定性,DDMS在观测数据无缺失的情况下,提供有效解的概率高于98%。该软件2h时段解在N、E、U方向的重复性分别为1.2mm、0.9mm、2.2mm,4h时段解算N、E、U方向的重复性为0.8mm、0.7mm、1.5mm。利用本文实现的GPS监测系统可进行高效率的实时、自动化、高精度大坝变形监测。     

垂线偏差测量的固体潮和海潮改正

垂线偏差是大地测量学和地球物理学的基础数据。固体潮和海潮是影响高精度垂线偏差测量的重要因素,固体潮改正主要表现为天体引潮位对垂线偏差的直接影响及造成地球形变而产生的附加位对其的间接影响。本文基于引力场球谐展开理论,推导了垂线偏差测量中固体潮和海潮的改正公式。利用JPL DE421星历和EOT11A海潮模型,计算全球19 570个GNSS测站处垂线偏差的潮汐改正值,分析了垂线偏差潮汐改正的时空变化规律。通过实例给出了日、月引潮位及附加位、海潮对垂线偏差子午和卯酉分量的改正。现有高精度垂线偏差测量精度已达到0.1″,而固体潮和海潮对垂线偏差的改正总量级可达我国一等天文规定精度(0.3″)的17%,因此在高精度的垂线偏差应用中需要顾及潮汐改正。     

地球定向参数测量发展现状和展望

随着我国空间探测工程的快速发展,对地球定向参数(EOP)的精度需求越来越高. 通过对地球定向参数的测量原理进行介绍,以现有的经典光学观测手段、甚长基线干涉测量(VLBI)、全球卫星导航系统(GNSS)、多里斯系统(DORIS)、激光测月(LLR)和卫星激光测距(SLR)等为代表的现代空间大地测量手段对地球定向参数测量原理及特点进行全面的阐述,对地球定向参数的自主测量与服务进行展望,为我国建设自主的地球定向参数测量系统提供理论基础和参考.      

VLBI在探月卫星定位中的应用分析

中国实施的"嫦娥"探月工程中,探月卫星的定轨测控系统由我国现有的S频段航天测控网(USB)和甚长基线干涉测量(VLBI)系统组成。系统中,VLBI技术主要为绕月卫星定轨提供卫星的角位置。本文分析了在探月项目中,VLBI单点定位的必要性。探讨了VLBI技术用于探月卫星单点定位的基本原理及其实现方法。通过算例对模拟数据进行处理,检验了方法的正确性。对结果进行分析,得出一些结论。     

Ultra-high degree spherical harmonic analysis and synthesis using extended-range arithmetic

We present software for spherical harmonic analysis (SHA) and spherical harmonic synthesis (SHS), which can be used for essentially arbitrary degrees and all co-latitudes in the interval (0°, 180°). The routines use extended-range floating-point arithmetic, in particular for the computation of the associated Legendre functions. The price to be paid is an increased computation time; for degree 3,000, the extended-range arithmetic SHS program takes 49 times longer than its standard arithmetic counterpart. The extended-range SHS and SHA routines allow us to test existing routines for SHA and SHS. A comparison with the publicly available SHS routine GEOGFG18 by Wenzel and HARMONIC SYNTH by Holmes and Pavlis confirms what is known about the stability of these programs. GEOGFG18 gives errors <1 mm for latitudes [-89°57.5′, 89°57.5′] and maximum degree 1,800. Higher degrees significantly limit the range of acceptable latitudes for a given accuracy. HARMONIC SYNTH gives good results up to degree 2,700 for almost the whole latitude range. The errors increase towards the North pole and exceed 1 mm at latitude 82° for degree 2,700. For a maximum degree 3,000, HARMONIC SYNTH produces errors exceeding 1 mm at latitudes of about 60°, whereas GEOGFG18 is limited to latitudes below 45°. Further extending the latitudinal band towards the poles may produce errors of several metres for both programs. A SHA of a uniform random signal on the sphere shows significant errors beyond degree 1,700 for the SHA program SHA by Heck and Seitz.