GPS观测数据中的仪器偏差对确定电离层延迟的影响及处理方法

本文通过设计不同的计算方案详细分析了ＧＰＳ观测中的仪器偏差对确定电离层延迟的影响,利用多天实测数据,结合仪器偏差与电离层延迟的分离方法,探讨了仪器偏差的稳定性,并提出了一种静态确定电离层延迟的方案。算例表明它能有效克服仪器偏差影响。     

中低纬度地区连续运行参考站网络电离层扰动修正技术研究

分析了电离层扰动对中长距离连续运行参考站网络(CORS)的工作性能的影响,论证了中小尺度电离层行进式扰动是影响中低纬度地区CORS基线解算和实时定位精度的最主要误差源。本文提出了时相关电离层修正模型,通过在双线性曲面纠正模型上附加中尺度电离层扰动修正信息,实现电离层预报修正技术。在100 km以上长距离参考站网的实验验证了该技术应用于CORS领域减弱电离层强扰动影响方面的有效性。     

GPS/VRS实时网络改正数生成算法研究

为提高厘米级网络GPS/VRS实时动态定位的精度和可靠性,系统地探讨VRS网络实时改正数的生成模型,并提出适用于中长距离参考站网络的电离层、对流层以及卫星轨道改正数计算的改进算法。结合四川GPS参考站网络(SGRSN)以及自主开发的虚拟参考站软件平台VENUS系统,对上述改正数生成算法进行试验验证,结果表明其大气误差改正数精度为2~4 cm,轨道误差的影响可基本消除,满足80 km以上中长距离稀疏参考站网络厘米级实时动态定位服务要求。     

Auto-covariance estimation of variable samples (ACEVS) and its application for monitoring random ionospheric disturbances using GPS

 Ionospheric variation may be considered as a stationary time series under quiet conditions. However, the disturbance of a stationary random process from stationarity results in the bias of corresponding samples from the stationary observations, and in the change of statistical model parameters of the process. From a general mathematical aspect, a new method is presented for monitoring ionospheric variations, based on the characteristic of time-series observation of GPS, and an investigation of the statistical properties of the estimated auto-covariance of the random ionospheric delay when changing the number of samples in the time series is carried out. A preliminary scheme for monitoring ionospheric delays is proposed. Received: 18 August 2000 / Accepted: 12 April 2001     

GPS/VRS 参考站网络的对流层误差建模技术研究

在虚拟参考站(VRS)技术中,参考站与流动站间的高程差异会引起对流层误差改正数中存在系统偏差影响,使对流层改正精度降低。在常规网络内插改正模型的基础上,借助先验对流层模型,提出了一种能自主修正高程偏差的距离相关对流层网络内插模型(MHDIM)。基于四川GPS连续运行参考站网络(Sichuan GPS Reference Station Network-SGRSN)实际测试数据的分析表明,对于地形变化较大的中长距离稀疏GPS/VRS参考站网络(如流动站与参考站间高程差异大于500m),应用MHDIM模型可使对流层延迟误差改正精度提高到2到3cm并实现cm级网络RTK定位结果,适用于GPS/VRS参考站网络cm级实时动态定位要求。     

关于BP神经网络转换GPS高程的若干问题

BP神经网络用于GPS高程转换有着较高的精度,但也存在不少问题,如网络的隐含层和隐含层单元个数选取、参加学习的样本的质量如何影响仿真精度等。结合实例分析上述问题,得出一些结论。     

附加约束法及其在GPS快速定位中的应用

针对在短时间内GPS观测方程的法方程容易形成病态的实际,探讨用附加约束条件来消除其病态性的方法,然后用LAMBDA方法确定其整周模糊度,实际实验证明,对于单频GPS接收机,利用连续几个历元数据,使用该技术即可正确确定整周模糊度,从而实现厘米级定位。     

A Bayesian method for linear, inequality-constrained adjustment and its application to GPS positioning

One of the typical approaches to linear, inequality-constrained adjustment (LICA) is to solve a least-squares (LS) problem subject to the linear inequality constraints. The main disadvantage of this approach is that the statistical properties of the estimate are not easily determined and thus no general conclusions about the superiority of the estimate can be made. A new approach to solving the LICA problem is proposed. The linear inequality constraints are converted into prior information on the parameters with a uniform distribution, and consequently the LICA problem is reformulated into a Bayesian estimation problem. It is shown that the LS estimate of the LICA problem is identical to the Bayesian estimate based on the mode of the posterior distribution. Finally, the Bayesian method is applied to GPS positioning. Results for four field tests show that, when height information is used, the GPS phase ambiguity resolution can be improved significantly and the new approach is feasible.     

Ocean tide loading (OTL) displacements from global and local grids: comparisons to GPS estimates over the shelf of Brittany, France

In this paper we examine OTL displacements detected by GPS stations of a dedicated campaign and validate ocean tide models. Our area of study is the continental shelf of Brittany and Cotentin in France. Brittany is one of the few places in the world where tides provoke loading displacements of ∼10–12 cm vertically and a few cm horizontally. Ocean tide models suffer from important discrepancies in this region. Seven global and regional ocean tide models were tested: FES2004 corrected for K2, TPXO.7.0, TPXO.6.2, GOT00.2, CSR4.0, NAO.99b and the most recent regional grids of the North East Atlantic (NEA2004). These gridded amplitudes and phases of ocean tides were convolved in order to get the predicted OTL displacements using two different algorithms. Data over a period of 3.5 months of 8 GPS campaign stations located on the north coast of Brittany are used, in order to evaluate the geographical distribution of the OTL effect. We have modified and implemented new algorithms in our GPS software, GINS 7.1. GPS OTL constituents are estimated based on 1-day batch solutions. We compare the observed GPS OTL constituents of M₂, S₂, N₂ and K₁ waves with the selected ocean tide models on global and regional grids. Large phase-lag and amplitude discrepancies over 20° and 1.5 cm in the vertical direction in the semi-diurnal band of M₂ between predictions and GPS/models are detected in the Bay of Mont St-Michel. From a least squares spectral analysis of the GPS time-series, significant harmonic peaks in the integer multiples of the orbital periods of the GPS satellites are observed, indicating the existence of multipath effects in the GPS OTL constituents. The GPS OTL observations agree best with FES2004, NEA2004, GOT00.2 and CSR4.0 tide models.     

Implementation and testing of the gridded Vienna Mapping Function 1 (VMF1)

The new gridded Vienna Mapping Function (VMF1) was implemented and compared to the well-established site-dependent VMF1, directly and by using precise point positioning (PPP) with International GNSS Service (IGS) Final orbits/clocks for a 1.5-year GPS data set of 11 globally distributed IGS stations. The gridded VMF1 data can be interpolated for any location and for any time after 1994, whereas the site-dependent VMF1 data are only available at selected IGS stations and only after 2004. Both gridded and site-dependent VMF1 PPP solutions agree within 1 and 2 mm for the horizontal and vertical position components, respectively, provided that respective VMF1 hydrostatic zenith path delays (ZPD) are used for hydrostatic ZPD mapping to slant delays. The total ZPD of the gridded and site-dependent VMF1 data agree with PPP ZPD solutions with RMS of 1.5 and 1.8 cm, respectively. Such precise total ZPDs could provide useful initial a priori ZPD estimates for kinematic PPP and regional static GPS solutions. The hydrostatic ZPDs of the gridded VMF1 compare with the site-dependent VMF1 ZPDs with RMS of 0.3 cm, subject to some biases and discontinuities of up to 4 cm, which are likely due to different strategies used in the generation of the site-dependent VMF1 data. The precision of gridded hydrostatic ZPD should be sufficient for accurate a priori hydrostatic ZPD mapping in all precise GPS and very long baseline interferometry (VLBI) solutions. Conversely, precise and globally distributed geodetic solutions of total ZPDs, which need to be linked to VLBI to control biases and stability, should also provide a consistent and stable reference frame for long-term and state-of-the-art numerical weather modeling.     

利用SOFM对鸡西盆地城子河组储层综合评价

通过对已有的储层评价方法优势与不足的分析,提出了在空间数据库基础上应用自组织特征映射神经网络进行油气储层评价。通过对鸡西盆地城子河组表征储层性能参数的分析,建立储层评价参数标准,并按照建立空间数据库-网格化-文件转换-文件合成-神经网络评价-类别评价-图形绘制的评价流程,生成鸡西盆地城子河组储层综合评价图。评价结果显示:Ⅰ级储集层主要发育于鸡东坳陷中央即鸡D6井东侧呈东西向条带状分布和鸡D6井西侧不规则分布;梨树镇坳陷西部:梨树镇周缘即鸡D2、鸡1、鸡3井周缘呈块状分布;Ⅱ级储集层区块主要发育于鸡东坳陷中部;Ⅲ级储集层区块最大;Ⅳ级在鸡西盆地零星分布。     

高层建筑物(群)深基坑工程变形监测与信息化施工

城市高层建筑物(群)的地基处理一般采用深基坑开挖技术,随着高层建筑的不断增多,施工难度及要求越来越高,周边建筑物及深基坑施工安全也显得越来越重要。采用适宜的变形监测技术,并对获得的系列资料进行变形分析,进而为信息化施工奠定基础。通过多个深基坑开挖地基处理的工程应用,工程变形监测与信息化施工正显示和发挥着极大的社会效益和经济效益。文章就工程实践为例,对该系统方法及其运用效果进行阐述。     

都江堰震后土地利用/覆被变化信息提取方法研究

快速和精确评估"5·12"汶川地震后的土地利用/覆被变化对科学减灾、灾后重建及生态环境恢复具有重要意义。常规方法从遥感图像上提取土地利用/覆被变化信息时,多以研究区整体为处理对象,直接对全图像进行分类提取,容易忽略地形地貌和地质构造等背景因素对分类结果的影响。本文以都江堰为试验区,根据地质构造展布特征及地形地貌发育形态将其分成平原区(Ⅰ区)、低山区(Ⅱ区)、中高山区(Ⅲ区)和高山区(Ⅳ区)。对Ⅰ区采用ISODATA方法进行非监督分类;对Ⅱ区和Ⅲ区分别采用最大似然(ML)分类法进行监督分类;对Ⅳ区采用人机交互解译方法进行分类。试验结果表明,基于地理地质环境的分块分类方法是高效、精确的。