Geodetic VLBI correlation in software

Correlation algorithms for geodetic very long baseline interferometry (VLBI) can now be effectively implemented on parallel computers of modest size. We have undertaken a detailed comparison of the output from a trusted geodetic correlator, one that has supported global geodetic VLBI observations for many years, with the output of a software correlator implemented on a small parallel computing cluster. We show that the correlator outputs agree closely, within expected error bounds, after accounting for the differences in the adopted geometric delay models, and therefore that use of the software correlator is feasible for geodetic VLBI processing, as a first step toward routine geodetic data processing. Recent developments in software correlation for geodesy are discussed, including the possibility of real-time processing options.     

通导遥一体化深远海PNT基准及服务网络构想

从海底控制网设计、布设、测量、数据处理和海洋声速场构建几个方面介绍了海底控制网建设的现状。结合国家海洋战略需求和海洋大地测量技术发展,分析了现阶段海底控制网建设面临的问题：认为目前的海底网规模小,缺乏信息共享,功能单一;设计与布设原则未与控制网等级关联,多为定性描述,缺乏操作性;声速场精度和分辨率偏低;测量和数据处理仅考虑了海底控制点的定位问题,难以满足大区域、高精度海洋PNT(positioning,navigation,and timing)基准网建设需求。据此,利用海洋声道的远程通讯和测距定位能力,提出了建设联合北斗/GNSS(global navigation satellite system)定位和通信导航功能的通导遥一体化深远海PNT基准及服务网络的构想,针对该网络的功能和布放设计、高精度、高分辨率海洋声速场模型的构建、各类PNT基准点的测量和整体网平差处理、海底PNT基准点的自校准和自维护、覆盖水域的位置增强服务、目标和环境的遥测和感知服务等几个关键技术问题,提出了实施方法和设想,以期解决当前海洋控制网大区域建设面临的缺乏通讯、布网原则和测量方法不完善、功能单一等问题,为...     

联系不同大地参考系的回归模型及RCT软件的应用

为综合应用不同参考坐标系中的测量成果，必须实现不同参考坐标系的统一。本文研究了回归模型在坐标转换中的应用，结合坐标转换实际提出并采用了多项式回归及逐次剔除的回归方法。文中介绍了坐标转换软件ＲＣＴ的主要功能，应用该软件计算了 １９５４年北京坐标系至 １９８０ＮＮＳＳ（ＢＥ）的最优回归转换模型。     

Inertial survey systems in the geodetic arsenal

After reviewing the overall goals of geodesy, the paper focuses on the unique properties of inertial survey systems in the geodetic arsenal: three-dimensionality; ability to determine relative positions and changes in the anomalous components of the earth’s gravity field; and independence of line-of-sight observations and the effects of refraction, both traditional antagonists in geodetic operations. Inertial survey systems, including field and office computational procedures, are briefly reviewed. Their short-comings are pointed out and certain remedies offered. Future possible improvements in hardware and software, as well as the development of hybrid systems (e.g., with gravity gradiometers), are discussed. “Apart from the refinement of existing techniques through the use of computers and the introduction of electromagnetic and optical distance measurement devices, instrumental research and development has been conducted by scientists and engineers outside the geodetic profession. This separateness of geodetic instrument research and development is seen as a deficiency by some, because of the reduced interaction between measurement techniques and the problems to which they apply. However, geodesy does not seem extraordinarily different from other environmentally oriented sciences in this respect and certainly has been quick to adopt new techniques once the benefits become evident.” (NAS 1978, p. 6) From the Keynote Address presented at Second International Symposium on Inertial Technology for Surveying and Geodesy, June 1–5, 1981, Banff, Alberta, Canada.     

中国VLBI网软件相关处理机测地应用精度分析

为支持国际VLBI大地测量数据处理,中国VLBI网(CVN)软件相关处理机完成了功能、性能升级,提高了信噪比,实现了以国际测地通用Mk4格式数据输出结果,可以直接被VLBI通用测地后处理软件用于时延数据解算。本文通过与国外软件相关处理机DiFX的实测数据比对,系统地分析了CVN软件处理机带宽综合残余时延和时延率精度、带宽综合总时延和时延率精度、信噪比和VLBI站坐标解算值。数据显示,CVN软件相关处理机已经达到了测地数据处理的精度要求,可以用于IVS国际联测数据处理。     

A comparative analysis of GPS range,Doppler and interferometric observations for geodetic positioning

Geodetic positioning accuracies obtained from range, integrated Doppler and double differenced interferometric phase observations from a constellation of twenty-four Global Positioning System satellites are presented. It is demonstrated that GPS range and Doppler observations will provide sufficient accuracy for the estimation of geodetic coordinates. However the instability of the receiver atomic oscillator will limit the usefulness of these observations in providing rapid first-order baseline determination. Interferometric phase measurements twice differenced to eliminate clock error appear as an alternate procedure for providing such accuracies.     

GPS非差相位精密单点定位技术探讨

探讨了精密单点定位的基本原理，处理方法，所涉及的误差改正及数据处理中的一些关键技术；采用直接内插IGS卫星精密星历的方法代替利用IGS跟踪站进行轨道精化方法计算卫星轨道参数，对现有精密单点定位计算方法进行了简化，使之更具有实用性。最后利用自主研发的精密非差单点定位软件计算和分析了实测数据。计算结果表明，经过大约15min的初始化后，非差相位单历元的定位结果精确度在X，Y，Z方向上均优于20cm。     

Differential geodetic stereo SAR with TerraSAR-X by exploiting small multi-directional radar reflectors

In this paper, we report on the direct positioning of small multi-directional radar reflectors, so-called octahedrons, with the synthetic aperture radar (SAR) satellite TerraSAR-X. Its highest resolution imaging mode termed staring spotlight enables the use of such octahedron reflectors with a dimension of only half a meter, but still providing backscatter equivalent to 1–2 cm observation error. Four octahedrons were deployed at Wettzell geodetic observatory, and observed by TerraSAR-X with 12 acquisitions in three different geometries. By applying our least squares stereo SAR algorithm already tested with common trihedral corner reflectors (CRs), and introducing a novel differential extension using one octahedron as reference point, the coordinates of the remaining octahedrons were directly retrieved in the International Terrestrial Reference Frame (ITRF). Contrary to our standard processing, the differential approach does not require external corrections for the atmospheric path delays and the geodynamic displacements, rendering it particularly useful for joint geodetic networks employing SAR and GNSS. In this paper, we present and discuss both methods based on results when applying them to the aforementioned Wettzell data set of the octahedrons. The comparison with the independently determined reference coordinates confirms the positioning accuracy with 2–5 cm for the standard approach, and 2–3 cm for the differential processing. Moreover, we present statistical uncertainty estimates of the observations and the positioning solutions, which are additionally provided by our parameter estimation algorithms. The results also include our 1.5 m CR available at Wettzell, and the outcomes clearly demonstrate the advantage of the multi-directional octahedrons over conventional CRs for global positioning applications with SAR.     

GPS非差相位精密单点定位方法与实现

探讨了精密单点定位的基本原理、处理方法、所涉及的误差改正及数据处理中的一些关键技术;采用直接内插IGS卫星精密星历的方法代替利用IGS跟踪站进行轨道精化方法计算卫星轨道参数,对现有精密单点定位计算方法进行了简化,使之更具有实用性。最后利用自主研发的精密非差单点定位软件计算和分析了实测数据。计算结果表明,经过大约15 min的初始化后,非差相位单历元的定位结果精确度在X,Y,Z方向上均优于20 cm。     

Local datum definition and geodetic network positioning using global navigation satellite systems

The problem of datum definition as applied to local-area geodetic networks is investigated using data collected from global navigation satellite systems (GNSS). It is shown that the process of double differencing makes the model more sensitive to computational errors that reduce the ability of the satellites alone to control the translation component of the datum definition, and as a result additional regularization is required. Traditionally, datum definition has been accomplished by constraining one station to set coordinates. Alternative regularization strategies are analysed in terms of their effects on positioning and ambiguity resolution. In doing so, processing strategies are developed which can improve the quality of global positioning system (GPS)-based position solutions in geodetic network applications of limited spatial extent, such as high-precision engineering and deformation monitoring networks.     

解混合边值问题直接计算位系数的变分原理

本文提出了利用变分法解混合边值问题直接计算位系数的原理。根据这一原理可解第一、第二和第三边值问题的混合边值问题直接求得位系数。利用这一原理可较简单地联合利用经典重力测量(即重力点的平面位置由天文或三角测量确定,高程由水准或三角高程确定)、卫星重力测量(即利用卫星定位技术确定重力点的平面位置和大地高)以及卫星测高数据研究地球的重力场。     

3S技术在土地利用动态监测中的应用

准确把握土地使用状况是依法实施土地资源管理的基础。3S（GPS、RS、GIS）技术因具有快速、准确、实时、大范围的对地观测能力及强大的空间信息加工、处理和分析能力,而成为土地使用动态监测的首要技术手段。详细介绍了3S技术在土地使用信息的判读、提取、坎西恩、分析和处理等环节中的作用和具体应用。     

Mobile Wireless GRASS GIS for Handheld Computers Running GNU/Linux

Recent developments of the communication technologies in the last years opened a new dimension to Geographical Information Systems and Geoinformation Techno‐logies. This new dimension is mobility. It is simplifying data gathering, processing and presentation independent from the area of application. A new branch, Mobile Geoinformation Technologies, is based on wireless communication systems, mobile personal computers, positioning systems and GIS. There are some proprietary GIS software solutions for mobile or handheld devices available on the market, but they are more focused on data logging tasks than providing full powered GIS support or data processing functions. In this paper, we propose a mobile implementation of the free and easily expandable GRASS GIS software in combination with the GNU/Linux operating system run on handheld devices. This approach supports real time in the field computations, data processing and cooperation of several active mobile clients using wireless networking.     

两种不同方式智能手机伪距平滑分析

针对智能手机受导航芯片和天线接收器限制、伪距观测值精度不高、粗差较多等问题,本文提出利用各观测量进行历元间求双差,以探测观测值中的粗差并予以剔除,再结合多普勒观测值和载波相位观测值平滑伪距,从数据质量和伪距平滑两方面分析影响智能手机定位精度的原因,说明智能手机载波相位观测值和多普勒观测值平滑伪距的可用性.试验结果表明:...     

Linear homotopy solution of nonlinear systems of equations in geodesy

A fundamental task in geodesy is solving systems of equations. Many geodetic problems are represented as systems of multivariate polynomials. A common problem in solving such systems is improper initial starting values for iterative methods, leading to convergence to solutions with no physical meaning, or to convergence that requires global methods. Though symbolic methods such as Groebner bases or resultants have been shown to be very efficient, i.e., providing solutions for determined systems such as 3-point problem of 3D affine transformation, the symbolic algebra can be very time consuming, even with special Computer Algebra Systems (CAS). This study proposes the Linear Homotopy method that can be implemented easily in high-level computer languages like C++ and Fortran that are faster than CAS by at least two orders of magnitude. Using Mathematica, the power of Homotopy is demonstrated in solving three nonlinear geodetic problems: resection, GPS positioning, and affine transformation. The method enlarging the domain of convergence is found to be efficient, less sensitive to rounding of numbers, and has lower complexity compared to other local methods like Newton–Raphson.     

Treatment of rotation errors in the final adjustment of GPS baseline components

Summary The significant coordinate difference changes of the same baselines, measured in different observing sessions, may be interpreted as the rotation around the station held fixed during the differenced processing, if the length changes of these baselines show random behavior. These rotation errors can significantly bias the final network adjustment based on redundant observing sessions and a relative approach. The Gauss-Helmert model with the estimation of the stochastic properties of the rotation errors is the most effective investigated approach. The standard deviation of the baseline length differences between those derived from a precise geodetic network and derived by Trimvec relative positioning software improved by a factor 2.4 after the final network adjustment using the introduced Gauss-Helmert model.     

Resourcesat (IRS-P6) value added data products

Remote sensing data products need to meet stringent geodetic and geometric accuracy specifications irrespective of intended user applications. Georeferencing is the basic processing step towards achieving this goal. Having known the imaging geometry and mechanism, the mathematical models built with the use of orbit and attitude information of the spacecraft can correct the remote sensing data for its geometric degradations only up to system level accuracy (IRS-P6 DP Team, 2000). The uncertainties in the orbit and attitude information will not allow the geometric correction model to generate products of accuracy that can meet user requirements unless Ground Control Points (GCP) are used as reference geo-location landmarks. IRS-P6 data processing team has been entrusted with developing a software system to generate data products that will have desired geodetic and geometric accuracies with known limitations. The intended software system is called the Value Added Data Products System (VADS). Precision corrected, Template Registered, Merged and Ortho Rectified products are the value added products planned with VADS.     

广阔范围内GPS网坐标系统转换模型的建立及精度分析

全球定位系统(GPS)技术己经在许多领域得到广泛的应用,由于GPS定位得到的观测成果通常是世界大地坐标系统WGS-84中的坐标或坐标差,但在实际应用中上需要的往往是地面点在国家坐标系或地方独立坐标系中的坐标.确立坐标系统转换模型并分析此模型的精度,根据至少3个公共点的两套大地坐标利用最小二乘法原理求出转换参数.本文以W...     

图件更新北京54和西安80坐标系转换方法研究

本文结合国土资源调查图件更新北京54和西安80坐标系转换的具体特点,对各种坐标转换模型进行了分析,研究了一种实用的坐标转换模型。在此基础上编制了适用于国土资源调查中图件更新北京54和西安80坐标系转换特定用途的坐标转换软件,利用实际资料对软件进行了测试分析,测试结果表明,这种实用的坐标转换方法可以满足国土资源调查对坐标转换精度的要求。     

GPS大地水准面拟合模型研究

在调兵山地区,选择已用GPS定位技术求得大地高的76个已知点作为原始数据的基础上,采用两种数学模型建立大地水准面,模型包括二次曲面法和最小二乘配置法,这两种模型是在不分区拟合和分区拟合两种情况下进行的。通过实例发现,拟合点的选取及位置对拟合模型有很大影响,在平坦地区,采用不分区拟合时,二次曲面法和最小二乘配置法的模型所求的检验点高程异常的精度要好于分区拟合时的情况,二次曲面法比最小二乘配置法在求高程异常时精度要高,而在分区拟合和不分区拟合时都能满足精度要求。