Analysis of long-range network RTK during a severe ionospheric storm

The network-based GPS technique provides a broad spectrum of corrections to support RTK (real-time kinematic) surveying and geodetic applications. The most important among them are the ionospheric corrections generated in the reference network. The accuracy of these corrections depends upon the ionospheric conditions and may not always be sufficient to support ambiguity resolution (AR), and hence accurate GPS positioning. This paper presents the analyses of the network-derived ionospheric correction accuracy under extremely varying – quiet and stormy – geomagnetic and ionospheric conditions. In addition, the influence of the correction accuracy on the instantaneous (single-epoch) and on-the-fly (OTF) AR in long-range RTK GPS positioning is investigated, and the results, based on post-processed GPS data, are provided. The network used here to generate the ionospheric corrections consists of three permanent stations selected from the Ohio Continuously Operating Reference Stations (CORS) network. The average separation between the reference stations was ∼200 km and the test baseline was 121 km long. The results show that, during the severe ionospheric storm, the correction accuracy deteriorates to the point when the instantaneous AR is no longer possible, and the OTF AR requires much more time to fix the integers. The analyses presented here also outline the importance of the correct selection of the stochastic constraints in the rover solution applied to the network-derived ionospheric corrections.     

基于GPS/GLONASS/BDS组合的单历元单频短基线RTK定位算法研究

随着多个GNSS系统不断建成,天空中的导航卫星越来越多,使得RTK作业时的观测量也越来越多,这对提高单频单历元RTK的可靠性起到了至关重要的作用。本文分析了GLONASS信号频分多址的特点,对GPS/GLONASS/BDS单历元单频RTK定位的算法和模型进行了研究,提出了一种适用于三系统组合条件下短基线单频单历元RTK定位的算法,并采用实测数据对算法进行了验证,结果表明,GPS/GLONASS/BDS单历元单频RTK定位是可行的。     

GPS/VRS 卫星定位服务网络建设与精度评定

虚拟参考站技术是近几年发展起来的,集Internet、无线通讯、计算机网络和GPS于一体的卫星定位技术。成都虚拟参考站卫星定位服务系统的建设,在设计上可满足全天候地向大成都地区用户提供厘米级实时动态定位服务。为了对该系统的实际定位精度进行客观的评价,从2 0 0 4年7月开展,历时两个月,全面完成了成都虚拟参考站卫星定位服务系统的精度评定工作,结果表明:在网内,水平方向上的精度可达2 .5cm ,垂直方向上的精度为4 . 5cm ,精度分布均匀;在网外,未模型化的距离相关误差的残余逐步增大,特别是距离网络中心大于1 2 0km以上时,定位精度开始衰减,为分米级。     

RTK系统、全站仪及CASS软件在地形测绘中的应用探讨

在地形测绘中,单独的全站仪或RTK系统都无法在工作效率和作业精度上同时满足需要。根据实践,本文介绍了RTK系统、全站仪原理及两者的联合应用,并着重叙述了CASS软件制图的细节,指出存在的问题和改进措施。     

GNSS RTK技术下海洋平台桩腿动态变形监测及数据处理

海洋平台及其桩腿在长期使用中存在着波浪、海流、风荷载等环境激励作用下的动态响应。本文以海星达H32全能型GNSS RTK双频接收机为试验仪器,采用GPS+GLONASS+BDS三星系组合系统对位于渤海海域的埕岛油田某平台桩腿进行动态变形监测。结合Ensemble Empirical Mode Decomposition(EEMD)和Butterworth滤波方法的降噪特性,提出一种适用于海洋平台工作环境的新型混合滤波方法 MDB,并用Matlab软件编制的程序对GNSS RTK监测数据进行分析,得到桩腿测点的实时振动位移曲线。结果表明:GNSS RTK结合MDB滤波技术用于海洋平台桩腿动态变形监测是可行的;MDB滤波器能有效去除海洋平台振动信息的随机噪声和多路径误差;从去除多路径误差和随机噪声之后的海洋平台桩腿测点位移云图,可以非常清楚地看出桩腿在环境激励作用下水平方向产生的可逆位移轨迹,这对海洋平台结构健康监测、诊断和评估具有重要意义。     

A comparison between analytical aerial photogrammetry,laser scanning,total station and global positioning system surveys for generation of digital terrain model

The present paper compares between four data sources for creating digital terrain models (DTMs), based on analytical aerial photogrammetry, laser scanning, total station (TS) and global positioning system surveys. The case study presents the comparative results obtained using the methods listed above. After obtaining the ground coordinates of points using each method, DTMs were created using Surfer Software to establish comparison consistency. To check accuracy of each method used, a series of 100 independent points were collected at random positions over the case study area using the TS for horizontal position and a digital level for elevation. The comparison of the results of the methods was performed based on accuracy and efficiency aspects. The results have shown that TS and terrestrial laser scanners (TLSs) could represent precise, effective and rapid solutions to produce economical and accurate DTMs. Also, using TLSs allow more various possibilities of data representation.     

我国天文大地网与GPS2000网联合平差单区平差处理方法研究

我国天文大地网与GPS2000网联合平差是一项大规模的测量数据处理工程,解算的未知数众多,为了便于检查原始观测数据粗差以及验证地面网与空间网的权匹配关系,需要进行单区平差数据处理研究和计算。本文主要讨论单区平差数据处理中的主要模型、大规模稀疏矩阵有效的解算方法并用软件加以实现,用此软件对5000点的实验区数据进行平差计算,得到了有益的结论。     

GPS城市地壳变形监测网的数据处理及精度分析

应用GPS定位技术进行城市或区域地壳变形监测,研究了GPS监测的数据处理和精度分析的理论和方法.使用高精度的定位分析软件GAMIT,对某城市地壳变形监测网的试验观测数据进行数据处理,并对解算得到的基线向量和坐标分别进行精度分析,结果表明:在100km范围内,GPS基线重复率在平面上比例误差可以达到10-8,垂直方向比例误差可以达到10-7;GPS监测点的三维坐标重复率精度可达到3mm左右,能满足城市或区域地壳变形监测的精度要求.     

Crop classification accuracy as influenced by training strategy,data transformation and spatial resolution of data

The possibility of improving classification accuracies using different training strategies and data transformations within the framework of a supervised maximum likelihood classification scheme was explored in this study. The effect of spatial resolution of data on the accuracy of classification was also studied Single-pixel training strategy resulted in improved classification accuracy over the block-training method. Data transformations gave no significant improvements in accuracy over untransformed data. There was a reduction in classification accuracy as resolution of data improved from 72 m (LISS I) to 36 m (LISS II) while other sensor characteristics remained same.     

On the sensitivity of the location, size and shape of the GPS ambiguity search space to certain changes in the stochastic model

In this contribution we analyse in a qualitative sense for the geometry-free model the dependency of the location, the size and the shape of the ambiguity search space on different factors of the stochastic model. For this purpose a rather general stochastic model is used. It includes time-correlation, cross-correlation, satellite elevation dependency and the use of an a priori weighted ionospheric model, having the ionosphere-fixed model and the ionosphere-float model as special cases. It is shown that the location is invariant for changes in the cofactor matrix of the phase observables. This also holds true for the cofactor matrix of the code observables in the ionosphere-float case. As for time-correlation and satellite elevation dependency, it is shown that they only affect the size of the search space, but not its shape and orientation. It is also shown that the least-squares ambiguities, their variance matrix and its determinant, for, respectively, the ionosphere-fixed model, the ionosphere-float model and the ionosphere-weighted model, are all related through the same scalar weighted mean, the weight of which is governed by the variance ratio of the ionospheric delays and the code observables. A closed-form expression is given for the area of the search space in which all contributing factors are easily recognized. From it one can infer by how much the area gets blown up when the ionospheric spatial decorrelation increases. This multiplication factor is largest when one switches from the ionosphere-fixed model to the ionosphere-float model, in which case it is approximately equal to the ratio of the standard deviation of phase with that of code. The area gives an indication of the number of grid points inside the search space. Received: 11 November 1996 / Accepted: 21 March 1997     

GPS工程测量网数据处理与质量评估方法研究

探讨直接利用平差结果分析GPS网起算点的兼容性问题,达到剔除含有粗差已知点的目的.针对短基线(10～15 km以下)工程测量网,总结GPS工程测量网数据处理与质量评估方法.对某铁路工程测量控制网的观测资料进行数据处理与质量评估试验,结果表明:平面点位精度在x方向上优于0.75 cm,y方向上优于0.70 cm,点位精度...     

Establishment and data processing of high-precision city subsidence monitoring network by GPS surveying instead of leveling

The feasibility of monitoring the change of city settlement using GPS surveying instead of leveling is studied. A fiducial network and a monitoring network are established in Ningbo city. Two periods of GPS observation are completed. Some measures are taken during the observation in order to ensure to obtain the high-precise height component. The Saastamoinen model is adopted in the data processing of the dry component part of the tropospheric delay. The wet component change of the tropospheric delay is estimated by stochastic processes model. When Bernese software is used to process the data, the millimeter level precision of height measuring is achieved.     

Accuracy of GPS-derived relative positions as a function of interstation distance and observing-session duration

 Ten days of GPS data from 1998 were processed to determine how the accuracy of a derived three-dimensional relative position vector between GPS antennas depends on the chord distance (denoted L) between these antennas and on the duration of the GPS observing session (denoted T). It was found that the dependence of accuracy on L is negligibly small when (a) using the `final' GPS satellite orbits disseminated by the International GPS Service, (b) fixing integer ambiguities, (c) estimating appropriate neutral-atmosphere-delay parameters, (d) 26 km ≤ L ≤ 300 km, and (e) 4 h ≤T ≤ 24 h. Under these same conditions, the standard error for the relative position in the north–south dimension (denoted S _n and expressed in mm) is adequately approximated by the equation S _n =k _n /T ^0.5 with k _n =9.5 ± 2.1 mm · h^0.5 and T expressed in hours. Similarly, the standard errors for the relative position in the east–west and in the up-down dimensions are adequately approximated by the equations S _e =k _e /T ^0.5 and S _u =k _u /T ^0.5, respectively, with k _e =9.9 ± 3.1 mm · h^0.5 and k _u =36.5 ± 9.1 mm · h^0.5. Received: 5 February 2001 / Accepted: 14 May 2001     

结合深度学习的高光谱与多源遥感数据融合分类

高光谱数据具有丰富的光谱特征,但是其空间分辨率相对较低.一些遥感数据具有与高光谱数据互补的优势,例如提供更精细的空间信息的高空间分辨率数据和具有高度信息的激光雷达LiDAR(Light Detection and Ranging)数据.通过将高光谱数据与多源遥感数据进行融合,可以弥补高光谱数据空间分辨率相对较低,空间特...     

一类小波基函数的构造及其在测量数据处理中的应用探讨

Shannon函数有很好的滤波性能,但向两端衰减速度缓慢;Gauss“窗”函数有很好的控制小波衰减的特性,但其低通滤波效果较差。根据这两个函数各自的优点构造了一类新的小波基函数,分别为满足低通的父小波和带通的一阶、二阶母小波,讨论了它们的正交性、完备性和紧支集性等性质,以GPS资料为例,分析其信号平滑和压缩效应、边缘效应和奇异点检测,得出一些有益的结论,为大地测量数据处理提供一种小波分析方法。     

Design, analysis, and inference for studies comparing thematic accuracy of classified remotely sensed data: a special case of map comparison

Assessing thematic map accuracy is a special type of map comparison that is frequently applied to remote sensing classification problems. For map comparisons in the accuracy assessment setting, one map represents the classified output and the other map represents the true or “reference” condition. Several articles in this special issue describe state-of-the-art map comparison analysis tools that could serve to quantify accuracy of a single map. However, accuracy assessment objectives generally extend beyond describing accuracy of a single map to comparing accuracy of several maps. Consequently, interest focuses on comparing map comparison measures when these measures are used to represent accuracy. The virtual workshop emphasizes the analysis component of map comparisons, but it is also important to examine the underlying study designs generating the data input into these analyses. The study designs for accuracy comparisons implemented in remote sensing practice often investigate only a single test site, thus limiting our ability to generalize the results of these accuracy comparisons. Map accuracy comparison studies can be designed to provide stronger generalizations by incorporating experimental design principles such as replication and blocking, and identifying an experimental unit appropriate for the application. It is also important to recognize the role of statistical hypothesis testing and inference for different objectives that motivate map accuracy comparisons. Deciding which of two maps to use for a particular site can be addressed by enumerative inference and does not require hypothesis testing. For the objective of a more general comparison of classification procedures, analytic inference is appropriate and hypothesis testing plays a more prominent role.     

Comparative analysis on utilisation of linear spectral unmixing and band ratio methods for processing ASTER data to delineate bauxite over a part of Chotonagpur plateau,Jharkhand, India

We have attempted comparative analysis of the utility of linear spectral unmixing (LSU) method and band ratios for delineating bauxite from laterite within the lateritic bauxite provinces of Chotonagpur Plateau, Jharkhand of India. This was attempted based on processing of visible–near infrared (VNIR) and shortwave infrared (SWIR) spectral bands of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) sensor. In LSU method, spectral features of main constituent minerals of lateritic bauxite are used to decompose the pixel spectra to estimate the relative abundance of bauxite and laterite in each pixel to spatially delineate bauxite within laterite. We have also compared the bauxite map derived using LSU method with bauxite maps of two band ratios in terms of spatial disposition of bauxite. We also have attempted to relate the abundance values of pixels of LSU-based bauxite map with band ratio values of bauxite pixels of two selected bauxite indices.