GPS水准及其在测绘工程中的应用

随着似大地水准面的不断精化,GPS水准有可能代替繁重的几何水准工作,介绍了似大地水准面的确定方法,并基于我国新一代似大地水准面CQG2000,在高山区GPS高程拟合的正常高中误差达到±0.21m。结合GPS实际工程分析,GPS高程拟合精度在平原地区可达到像控点高程精度要求。     

局部大地水准面的精确确定及地球物理解释

大地水准面,定义为地球重力场在平均海水面上的等位面,是陆地地形及海洋高程系统的基准面.局部大地水准面的精确确定对测绘、地球物理以及海洋学都是极为重要的.几何水准是地球表面高程的常用方法,但由于几何水准劳动强度大、费力、费钱,因此,近几十年各国都在研究和开发取代传统水准的方法和技术.如今,全球定位系统 ( GPS ) 相对定位精度达到几厘米 +1～2×10-6D,如果大地水准面精度足够高,GPS大地高就可以转化为几何高程.从而使GPS代替水准成为可能.局部大地水准面的精确确定可以使GPS得到更广泛的应用.     

鄱阳湖湖区似大地水准面精化研究

本文利用环鄱阳湖GPS/水准成果,重点研究了以江西省似大地水准面精化模型为平台、应用移去～恢复技术确定鄱阳湖湖区似大地水准面的方法,并对鄱阳湖湖区似大地水准面的模型和江西省似大地水准面的模型做了比较和分析。     

泉州市大地水准面精化及其应用

本文介绍了在泉州市完成分辨率较高、精度较好的GPS/水准网布测与数据处理的基础上,充分利用泉州市及周边地区陆地重力测量资料、国内外先进的地球重力场模型,采用先进的大地水准面确定理论与方法,应用remove-restore技术完成了泉州市规划区高精度的似大地水准面的确定工作;同时,利用GPS定位技术结合区域性高精度大地水准面成果,探讨解决大比例尺成图像控点高程的测定问题,真正实现利用GPS技术精确确定平面位置的同时,也精确测定了高程,充分发挥GPS测量精度高、快速、灵活的特点与优势,极大地提高了生产效率.     

区域似大地水准面精化算法及成果三维仿真研究

利用GPS水准代替繁重的几何水准测量工作,必须确定高精度、高分辨率的似大地水准面。本文分别介绍了函数模型算法、随机模型算法和综合模型算法,并基于试验区域的GPS水准数据,通过各种算法的分类计算比较,验证了这几种模型算法的有效性和可靠性,结果证明最小二乘配置算法精度较高,并对实验结果进行三维仿真,可视化的分析似大地水准面的变化。     

GPS水准综合模型在局部控制测量中的应用研究

针对无法将GPS测得的大地高转换为正常高,而传统的几何水准测量方法费时、费力且效率低等问题,采用GPS水准综合模型拟合局部地区似大地水准面的方法,根据拟合求取的高程异常对该地区的GPS点进行大地高向正常高的精确转换。结合Matlab软件,利用GPS水准综合模型对局部区域进行高程拟合,与传统的几何水准测量成果对比,在局部控制测量中应用GPS水准综合模型对高程拟合的精度较高,能满足局部地区GPS控制测量的需求,并大大提高工作效率。     

全国及部分省市地区高精度高分辨率似大地水准面的研究和实施

结合我国重力和地形资料及国内外较优的重力场模型,研制适合我国重力场特征的360阶重力场模型WDM94;建立中国新一代分米级似大地水准面CQG2000,包括建立新的以GPS/水准为基础的高程异常控制网、利用海洋卫星测高数据计算海洋大地水准面、陆地重力似大地水准面的研制及陆海似大地水准面的拼接等;研制江苏省、海南省、深圳市、大连市、南京市及"南水北调"西线工程具有厘米级精度的局域似大地水准面模型;结合GPS技术和高精度似大地水准面模型,研制GPS测图软硬件一体化系统.本研究项目获得2004年度国家科技进步二等奖.     

矿区似大地水准面拟合模型适用性分析

为提高GPS/水准数据拟合高程异常的逼近精度,利用某矿区控制网观测的GPS/水准数据,计算控制点高程异常值,分别用加权平均法、Shepard插值、多项式曲面拟合和多面函数法4种方法对矿区似大地水准面进行拟合。对各种拟合模型的原理和拟合精度进行比较分析。在此基础上,根据似大地水准面物理和几何特性,采用组合拟合的方法进一步改善似大地水准面的拟合精度,利用该模型内插高程异常值与实测GPS/水准点的高程异常值比较,其均方根误差不超过0.02 m,结合GPS观测成果可以取代四等及以下几何水准测量。     

精化山西区域内大地水准面的思考

本文概述了确定大地水准面的一般方法,并指出精化山西区域的大地水准面现阶段应该采用GPS水准方法,然后从理论上分析了大地水准面精度．地表地形．GPS水准点问距三者之间的关系最后还论述了大地水准面的成果形成以及如何进行质量控制本文听述的GPS水准方法．用于确定高程异常时,与确定大地水准为差距是相同的。     

大区域似大地水准面模型的建立方法研究

在充分研究现有几何方法确定局域似大地水准面的基础上,根据独立网内点间高程异常差的不变性和独立网间大地高起算基准面与WGS84椭球面的平行性,提出通过两步处理,获得大区域连续似大地水准面的思想和方法,即首先统一相邻两个独立GPS网大地高起算基准面,然后再利用几何方法确定大区域似大地水准面.该方法在长江口北岸得到了很好的验证,并取得了比较理想的精度.     

区域性跟踪站地心坐标精化方法及定轨试验分析─中国GIG′91和IGS′92会战数据处理分析

本文介绍了中国GIG’91和Epoch’92二次GPS会战的情况,着重分析了GIG’91和Epoch’92会战数据处理的结果。结果证明,利用1－2星期质量良好的数据（含分布均匀的部分全球跟踪站数据）,解算的未知区域性跟踪站地心坐标的重复性可以达到几个厘米,站间基线分量的重复性可以达到10－8或更好。利用中国国内4个跟踪站的数据,由5天轨道弧解算的卫星星历与全球精密星历之差在1－3米水平,平均差一般小于1米。我们的研究证明,参加GPS国际会战,是迅速提高区域性跟踪站地心坐标精度和建立区域性高精度地心坐标框架的有效途径,利用区域性跟踪站可有效地改进GPS卫星轨道的精度,形成全国范围的大尺度的控制,进一步改进GPS测量的精度。     

Modelling local GPS/levelling geoid undulations using artificial neural networks

The use of GPS for establishing height control in an area where levelling data are available can involve the so-called GPS/levelling technique. Modelling of the GPS/levelling geoid undulations has usually been carried out using polynomial surface fitting, least-squares collocation (LSC) and finite-element methods. Artificial neural networks (ANNs) have recently been used for many investigations, and proven to be effective in solving complex problems represented by noisy and missing data. In this study, a feed-forward ANN structure, learning the characteristics of the training data through the back-propagation algorithm, is employed to model the local GPS/levelling geoid surface. The GPS/levelling geoid undulations for Istanbul, Turkey, were estimated from GPS and precise levelling measurements obtained during a field study in the period 1998–99. The results are compared to those produced by two well-known conventional methods, namely polynomial fitting and LSC, in terms of root mean square error (RMSE) that ranged from 3.97 to 5.73 cm. The results show that ANNs can produce results that are comparable to polynomial fitting and LSC. The main advantage of the ANN-based surfaces seems to be the low deviations from the GPS/levelling data surface, which is particularly important for distorted levelling networks.     

利用轨道参数修正的无控制点星载SAR图像几何校正方法

使用距离多普勒模型进行SAR图像几何校正时,卫星轨道误差、系统成像参数误差和DEM高程的误差会影响几何校正精度。本文提出了一种基于轨道参数修正的星载SAR图像几何校正方法。首先利用多项式对卫星轨道进行参数化,然后使用模拟SAR图像与真实SAR图像进行匹配得到控制点来修正轨道参数,最后利用修正后的参数进行几何精校正,从而提高几何校正精度。该方法无需地面控制点,适用于不易于人工测量获取地面控制点地区的SAR图像几何校正,与基于模拟SAR图像匹配并使用多项式改正的几何校正方法相比,本文方法具有更高的精度。使用Radarsat-2图像进行试验,并使用地面实测GPS控制点验证了本方法的有效性。     

On the combined adjustment of a gravimetrically determined geoid and GPS levelling stations

Summary A new basic geodetic network using the GPS technique is now being set up in France. There will be altogether 1000 benchmarks connected to the French levelling network. Obviously, the GPS levelling points are not dense enough to produce a national levelling reference surface. A gravimetrically determined geoid has therefore been proposed to be used for the interpolation between the GPS levelling points. However, because of long-wavelength errors, we consider that a gravimetric geoid does not have sufficient accuracy. A regression by fitting the gravimetrically determined geoid to the GPS levelling points is generally proposed. Unfortunately, this country-wide geoid fitting work cannot eliminate local deformations in the geoid, which happen in areas where there are errors or shortages of gravity or DTM data. This paper proposes and discusses a combined adjustment method. The principle is to divide up the geoid into small pieces and then to adjust them to the GPS levelling points locally with constraint conditions for the common points of the adjacent pieces. In order to benefit from the advantages of the high resolution and high relative accuracy of the gravimetric geoid, as well as the high absolute accuracy of the GPS levelling points, we establish respectively a relative observation equation for the difference of the gravimetric geoid undulation and an absolute observation equation for the GPS levelling points. Finally, we adjust the observation equations as a whole. Several global and local systematic errors are also taken into account and some special cases, such as adjustment in groups and blunder detection, are also discussed.     

关于GPS高程测量精度的分析比较*

通过对联测了25个四等水准的GPS点,分别用平面拟合模型和曲面拟合模型解算各点的正常高与四等水准结果比较,得出一些有益的结论,对GPS的实际生产具有一定的指导意义.     

A strategy for determining the regional geoid by combining limited ground data with satellite-based global geopotential and topographical models: a case study of Iran

The computation of regional gravimetric geoid models with reasonable accuracy, in developing countries, with sparse data is a difficult task that needs great care. Here we investigate the procedure for gathering, evaluating and combining different data for the determination of a gravimetric geoid model for Iran, where limited ground gravity data are available. Heterogeneous data, including gravity anomalies, the high-resolution Shuttle Radar Topography Mission global digital terrain model and different global geopotential models including recently published Gravity Recovery and Climate Experiment models, are combined through least-squares modification of the Stokes formula. The new gravimetric geoid model, IRG04, agrees considerably better with GPS/levelling than any of the other recent local geoid model in the area. Its RMS fit with GPS/levelling is 0.27 m and 3.8 ppm in the absolute and relative view, respectively. The relative accuracy of IRG04 is four times better than the most recently published global and regional geoid models available in this area. This progress shows the practical potential of the method of least-squares modification of Stokes’s formula in combination with heterogeneous data for regional geoid determination     

A new coarse-time GPS positioning algorithm using combined Doppler and code-phase measurements

A new coarse-time Global Positioning System (GPS) positioning algorithm based on the use of Doppler and code-phase measurements is proposed and described. The proposed method was demonstrated to be essential for reducing the time to first fix and the power consumption in a GPS receiver. Only 1 ms of data is required to obtain a positioning fix with accuracy comparable to that of the traditional GPS navigation algorithm. The algorithm is divided into two parts. In the first part, the Doppler measurement of the GPS signal is used to determine the coarse user position. With proper constraints, the required time accuracy for the Doppler measurements can be relaxed to be as long as 12 h. In the second part of the algorithm, the accurate user position is calculated by means of the 1 ms code-phase data. The traditional tracking process is no longer necessary in the proposed algorithm. Using the acquired 1-ms code-phase measurement, the positioning accuracy was determined to be approximately a few tens of meters in our experimental results. However, if the data length is extended to 10 ms, the positioning accuracy can be improved to within 10–20 m, which is similar to that of the traditional GPS positioning method. Various experiments were conducted to verify the usefulness of the proposed algorithm.     

基于广播星历的单站载波相位授时算法

针对传统单站授时算法的局限性,提出了一种基于广播星历的单站载波相位授时算法。该算法在标准单点定位授时算法仅采用伪距观测量的基础上,增加了载波相位观测量,授时精度得到了显著改善;该算法与精密单点定位授时算法相比,不需要精密轨道和钟差,摆脱了IGS等外部事后精密星历产品的依赖,能够广泛应用于实时授时。并利用IGS站观测数据进行实验分析,结果表明,单站载波相位授时精度明显优于标准单点定位授时算法,授时精度可达1~2 ns。     

基于区域与分区拟合似大地水准面方法研究

与传统测量方式比较,全球定位系统(global positioning system,GPS)测量具有定位精度高、测量时间短、操作简单、全天候作业等优势,利用GPS观测得到的大地高拟合成正常高可以大大提高测绘效率。研究了二次曲面法拟合似大地水准面模型,以豫北某区域为研究区,分别作整体区域二次曲面拟合和分区二次曲面拟合,并进行精度分析,结论如下:通过提高GPS测量的大地高精度和选用高精度的联测水准点,能够有效提高拟合后的高程精度;测区面积较大和测区地形起伏较大时,采用分区拟合高程的精度相对于整体区域拟合的精度会大大提高。     

跨海桥梁GPS高程拟合方法

针对跨海桥梁高程基准传递的技术难题,该文阐述了GPS高程拟合的基本原理,分析了高程拟合中的几个关键技术问题,总结出了GPS高程拟合的技术要点及提高拟合精度的措施。提出了基于二次多项式曲面的跨海桥梁工程GPS高程拟合方法,利用港珠澳大桥工程区域内的21个高精度GPS水准点建立二次多项式曲面拟合模型,并用另外7个点进行检核。结果显示:模型的内符合精度为±8.7mm,外符合精度为±12.4mm,2个海中测量平台控制点的拟合高程达到二等水准测量精度要求。