Temporal impact of selected GPS errors on point positioning

This paper is aimed at investigating the stability of point positions over time in support of applications that require high position stability when differential GPS is not feasible. One such application is the use of a P3-Orion aircraft offshore for magnetic measurement in support of submarine detection. Temporal changes in several GPS errors lead to variability in the computed positions, so it is not the absolute errors, but rather their temporal variations that are of importance. Furthermore, the temporal variability of the different error sources may dictate a certain algorithm approach and processing strategy. This paper analyzes the temporal variations of the broadcast satellite clock model and orbit parameters, as well as ionospheric errors, because these will typically be the dominant errors for real-time point positioning. These three errors are analyzed independently. A tropospheric correction is applied when computing all of the position results, so the tropospheric error itself is not investigated. Satellite clock and orbit errors are analyzed by comparing broadcast and precise post-mission SV clock corrections and orbits. For the ionosphere, the effect is separated using dual-frequency data. The analysis comprises primarily of assessing error behaviors and magnitudes through time and frequency analyses. In this way, the differences in variability of the errors are easily determined. The effect of each error in the position domain is also investigated in addition to the combined effect. Results show that, on a typical day when single frequency data are processed with broadcast orbit and clock data, the root mean square (RMS) of the changes in the position errors over a 50-s interval is about 5.8 cm in northing, 4.0 in easting, and 11.0 cm in height. When using precise orbits and clocks, in addition to dual frequency data, these values improve by 46–56% to 2.7 cm in northing, 2.2 cm in easting, and 4.9 cm in height. Under severe ionospheric activity, the RMS of the errors decrease from 8.1 to 3.3 cm in northing, 5.7 to 2.6 cm in easting, and 17.0 to 4.9 cm in height, which are improvements of 54–71%. Electronic Publication     

The confidence evaluation for airborne GPS data

l lntroductionIn the winter Of l989 Wuhan Technical Universi-ty of Surveying and Mapping COntracted withTrimble Navigation Ltd. to purchase fOur TrimbIe4000SST receivers. They were required tO suit theaeriaI phWetric work without intreducing avelocity limitation. In February, l993 twO of thereceivers were uPgraded to provide two eventrnarker plugfords and one pulse Per second(lPPS) output axkets. The uPgradd receivers canincormrate external event markers, e. g. the shutter.oPening …     

The application of GPS precise point positioning technology in aerial triangulation

In traditional GPS-supported aerotriangulation, differential GPS (DGPS) positioning technology is used to determine the 3-dimensional coordinates of the perspective centers at exposure time with an accuracy of centimeter to decimeter level. This method can significantly reduce the number of ground control points (GCPs). However, the establishment of GPS reference stations for DGPS positioning is not only labor-intensive and costly, but also increases the implementation difficulty of aerial photography. This paper proposes aerial triangulation supported with GPS precise point positioning (PPP) as a way to avoid the use of the GPS reference stations and simplify the work of aerial photography.Firstly, we present the algorithm for GPS PPP in aerial triangulation applications. Secondly, the error law of the coordinate of perspective centers determined using GPS PPP is analyzed. Thirdly, based on GPS PPP and aerial triangulation software self-developed by the authors, four sets of actual aerial images taken from surveying and mapping projects, different in both terrain and photographic scale, are given as experimental models. The four sets of actual data were taken over a flat region at a scale of 1:2500, a mountainous region at a scale of 1:3000, a high mountainous region at a scale of 1:32000 and an upland region at a scale of 1:60000 respectively. In these experiments, the GPS PPP results were compared with results obtained through DGPS positioning and traditional bundle block adjustment. In this way, the empirical positioning accuracy of GPS PPP in aerial triangulation can be estimated. Finally, the results of bundle block adjustment with airborne GPS controls from GPS PPP are analyzed in detail.The empirical results show that GPS PPP applied in aerial triangulation has a systematic error of half-meter level and a stochastic error within a few decimeters. However, if a suitable adjustment solution is adopted, the systematic error can be eliminated in GPS-supported bundle block adjustment. When four full GCPs are emplaced in the corners of the adjustment block, then the systematic error is compensated using a set of independent unknown parameters for each strip, the final result of the bundle block adjustment with airborne GPS controls from PPP is the same as that of bundle block adjustment with airborne GPS controls from DGPS. Although the accuracy of the former is a little lower than that of traditional bundle block adjustment with dense GCPs, it can still satisfy the accuracy requirement of photogrammetric point determination for topographic mapping at many scales.     

不同星历和钟差产品对GPS动态PPP定位测速结果比较

星历误差和星钟误差是GPS动态精密单点定位的主要误差源,不同的星历和钟差会对结果产生影响。利用IGS网站给出的不同星历和钟差数据进行计算,采用Waypoint软件进行不同的组合计算,对机载GPS数据定位和测速结果进行了分析,得出了一些有益的结论。     

使用参照物的射电望远镜中心坐标测量方法

为满足新建射电望远镜在单站或多站联合进行的深空探测或射电天文观测对中心坐标精确测定的要求,提出一种利用已知精确中心坐标的望远镜作为参照物,测量地平式射电望远镜中心点坐标的方法和测量数据处理方法。这一方法对场地和设备的要求较低,能够得到毫米级或亚毫米级的位置精度。尤其适合对天线阵列的中心位置进行测量。对国家天文台密云观测站的40 m射电望远镜进行了中心坐标测量,位置均方根误差为2.312 mm,满足了后续的观测工作对其位置的需求。     

无人机机载相机曝光时刻摄影中心三维坐标高精度插值算法研究

随着机载定位定向系统（POS）的不断完善,无人机技术已成为高精度摄影测量的重要途径．由于POS系统中全球卫星导航系统（GNSS）接收机的采样频率有限,需要对机载相机曝光点时刻摄影中心三维坐标进行插值计算．本文对常用的四种插值算法进行了研究,并通过实测数据对比不同插值算法的优劣,结果表明,当GNSS原始数据采样频率高于1 Hz时,三次样条插值算法误差均方根误差优于5 cm,更适用于无人机曝光时刻摄影中心三维坐标的高精度插值．      

A consistency test of airborne GPS using multiple monitor stations

In October 1990, several airborne GPS tests were conducted in the Ottawa region by the Canada Centre for Surveying (CCS) and the Canada Centre for Remote Sensing (CCRS). Ashtech XII receivers were located at up to three monitor stations with baseline lengths to the aircraft ranging from 1–200 km. Approximately two hours of airborne data, collected at a 2 Hz rate, were available for each of the three test days. Post-processing of the differential data was done using the University of Calgary's SEMIKIN package which utilizes a Kalman filter algorithm to estimate both the remote receiver's position and velocity. Comparisons were made between the aircraft position and velocity determined from each of the monitor stations to assess the consistency of differential GPS when different reference stations are used. Results show that the degree of consistency is dependent upon the distance to the monitor stations. Agreement at the decimetre-level is achieved in position when the baseline lengths are within 100 km. Agreement in velocity is usually better than 1 cm s^–1 (RMS).     

Assessment of long-range kinematic GPS positioning errors by comparison with airborne laser altimetry and satellite altimetry

Long-range airborne laser altimetry and laser scanning (LIDAR) or airborne gravity surveys in, for example, polar or oceanic areas require airborne kinematic GPS baselines of many hundreds of kilometers in length. In such instances, with the complications of ionospheric biases, it can be a real challenge for traditional differential kinematic GPS software to obtain reasonable solutions. In this paper, we will describe attempts to validate an implementation of the precise point positioning (PPP) technique on an aircraft without the use of a local GPS reference station. We will compare PPP solutions with other conventional GPS solutions, as well as with independent data by comparison of airborne laser data with “ground truth” heights. The comparisons involve two flights: A July 5, 2003, airborne laser flight line across the North Atlantic from Iceland to Scotland, and a May 24, 2004, flight in an area of the Arctic Ocean north of Greenland, near-coincident in time and space with the ICESat satellite laser altimeter. Both of these flights were more than 800 km long. Comparisons between different GPS methods and four different software packages do not suggest a clear preference for any one, with the heights generally showing decimeter-level agreement. For the comparison with the independent ICESat- and LIDAR-derived “ground truth” of ocean or sea-ice heights, the statistics of comparison show a typical fit of around 10 cm RMS in the North Atlantic, and 30 cm in the sea-ice region north of Greenland. Part of the latter 30 cm error is likely due to errors in the airborne LIDAR measurement and calibration, as well as errors in the “ground truth” ocean surfaces due to drifting sea-ice. Nevertheless, the potential of the PPP method for generating 10 cm level kinematic height positioning over long baselines is illustrated.     

局域差分GPS的数学模型

局域差分GPS中,用户到基准站的距离对定位精度有着决定性影响。利用基准站生成用户误差改正数,其算法很多。文中针对局域差分GPS的数学模型空间相关性,介绍几种常用的内插方法,如加权平均法、线性内插法、低次曲面模型法及三角形内插法,并分析各种方法的内插系数和内插质量因子。利用局域差分GPS进行定位时,只有当用户站位于基准站构成的多边形网内时,才可能得到较高的精度。     

GPS与INSAR数据融合研究展望

分析了GPS与INSAR数据融合的必要性与可行性 ,讨论了GPS与INSAR数据融合存在的主要问题 ,进一步探讨了利用GPS数据改善INSAR相位解缠算法 ,利用GPS与INSAR数据融合建立水汽模型和大气层延迟误差改正模型 ,以及GPS高时间分辨率和高平面位置精度与INSAR高空间分辨率和高高程变形精度有效统一的问题。     

Accurate absolute GPS positioning through satellite clock error estimation

 An algorithm for very accurate absolute positioning through Global Positioning System (GPS) satellite clock estimation has been developed. Using International GPS Service (IGS) precise orbits and measurements, GPS clock errors were estimated at 30-s intervals. Compared to values determined by the Jet Propulsion Laboratory, the agreement was at the level of about 0.1 ns (3 cm). The clock error estimates were then applied to an absolute positioning algorithm in both static and kinematic modes. For the static case, an IGS station was selected and the coordinates were estimated every 30 s. The estimated absolute position coordinates and the known values had a mean difference of up to 18 cm with standard deviation less than 2 cm. For the kinematic case, data obtained every second from a GPS buoy were tested and the result from the absolute positioning was compared to a differential GPS (DGPS) solution. The mean differences between the coordinates estimated by the two methods are less than 40 cm and the standard deviations are less than 25 cm. It was verified that this poorer standard deviation on 1-s position results is due to the clock error interpolation from 30-s estimates with Selective Availability (SA). After SA was turned off, higher-rate clock error estimates (such as 1 s) could be obtained by a simple interpolation with negligible corruption. Therefore, the proposed absolute positioning technique can be used to within a few centimeters' precision at any rate by estimating 30-s satellite clock errors and interpolating them. Received: 16 May 2000 / Accepted: 23 October 2000     

GPS水准拟合模型的比较与分析

二次曲面模型是GPS高程异常拟合的常用方法,但在地形起伏较大的地区拟合残差较大。文中比较与分析常用的几种拟合模型,介绍一种改进的二次曲面拟合方法,通过实例验证模型的拟合精度,得出几点有益的结论,对实际生产有一定的参考价值。     

无初始化的GPS辅助空中三角测量

简要介绍了以航线为单元 ,通过相位平滑递推算法在航求解双差载波相位观测量整周相位模糊度 ,进而确定各摄站空间位置的无初始化GPS动态定位原理 ,对某测区一组实际航摄资料进行GPS数据处理和GPS辅助光束法区域网平差 ,证实所介绍的算法是正确的、有效的 ,所获取的GPS摄站坐标可满足空中三角测量的精度要求 ,并且用该数据与经初始化GPS动态定位获取的GPS摄站坐标数据进行GPS辅助光束法区域网平差的总体精度是完全一致的。     

Toward a Differential Calculus for Temporal Map Analysis

Investigators in many fields are analyzing temporal change in spatial data. Such analyses are typically conducted by comparing the value of some metric (e. g., area, contagion, or diversity indices) measured at time T₁ with the value of the same metric measured at time T₂ . These comparisons typically include the use of simple interpolation models to estimate the value of the metric of interest at points in time between observations, followed by applications of differential calculus to investigate the rates at which the metric is changing. Unfortunately, these techniques treat the values of the metrics being analyzed as if they were observed values, when in fact the metrics are derived from more fundamental spatial data. The consequence of treating metrics as observed values is a significant reduction in the degrees of freedom in spatial change over time. This results in an oversimplified view of spatio-temporal change. A more accurate view can be produced by (1) applying temporal interpolation models to observed spatial data rather than derived spatial metrics; (2) expanding the metric of interest's computational equation by replacing the terms relating to the observed spatial data with their temporal interpolation equations; and (3) differentiating the expanded computational equation. This alternative, three-step spatio-temporal analysis technique will be described and justified. The alternative technique will be compared to the conventional approach using common metrics and a sample data set.     

长距离GPS/BDS双系统网络RTK方法

基于区域参考站网的网络实时动态定位(real-time kinematic,RTK)方法是实现全球定位系统(global positioning system,GPS)、北斗卫星导航系统(BeiDou satellite navigation system,BDS)高精度定位的主要手段.研究了一种长距离GPS/BDS双...     

机载LiDAR系统定位方程、误差分析与精度评定

本文从机载LiDAR系统几何定位方程出发、基于误差传播规律推导了机载LiDAR系统的综合误差计算公式,分别研究了IMU测角、GPS、激光测距、扫描角等多种误差源对激光脚点定位精度的影响规律,从理论上分析了机载LiDAR系统定位精度.本文的结果对实际应用具有重要的参考价值.     

Trajectory models and reference frames for crustal motion geodesy

We sketch the evolution of station trajectory models used in crustal motion geodesy over the last several decades, and describe some recent generalizations of these models that allow geodesists and geophysicists to parameterize accelerating patterns of displacement in general, and postseismic transient deformation in particular. Modern trajectory models are composed of three sub-models that represent secular trends, annual oscillations, and instantaneous jumps in coordinate time series. Traditionally the trend model invoked constant station velocity. This can be generalized by assuming that position is a polynomial function of time. The trajectory model can also be augmented as needed, by including one or more logarithmic transients in order to account for typical multi-year patterns of postseismic transient motion. Many geodetic and geophysical research groups are using general classes of trajectory model to characterize their crustal displacement time series, but few if any of them are using these trajectory models to define and realize the terrestrial reference frames (RFs) in which their time series are expressed. We describe a global GPS reanalysis program in which we use two general classes of trajectory model, tuned on a station by station basis. We define the network trajectory model as the set of station trajectory models encompassing every station in the network. We use the network trajectory model from the each global analysis to assign prior position estimates for the next round of GPS data processing. We allow our daily orbital solutions to relax so as to maintain their consistency with the network polyhedron. After several iterations we produce GPS time series expressed in a RF similar to, but not identical with   ITRF2008. We find that each iteration produces an improvement in the daily repeatability of our global time series and in the predictive power of our trajectory models.     

机载激光雷达系统定位精度分析

从机载激光雷达系统误差的产生机制出发,分别对姿态角误差、DGPS误差、瞬时扫描角误差、激光测距误差对激光脚点定位精度的影响进行定量的分析,从理论上分析了机载激光雷达系统的定位精度。本文的结果对实际应用具有重要的参考价值。     

高精度GPS差分载波相位多普勒/INS新型全组合解算机载TLS外方位元素

在提出单历元解算GPS模糊度技术的基础上 ,使用INS间接法误差模型 ,提出了一种GPS双差载波相位多普勒 /INS全组合Kalman滤波的新方法 ,高精度直接解算机载TLS中的外方位元素。仿真数据试验表明 ,其姿态精度高于 1 0″,位置精度高于 1 0cm。     

一种基于改进UKF滤波的GPS+PDR组合定位方法

针对接收信号质量恶化的环境,提出了一种适用于信号遮蔽环境的改进GPS+PDR组合定位算法。该方法用短时间内的陀螺仪积分数据校正数字罗盘的航向偏差,在一定程度上消除了数字罗盘受到的偶发干扰。采用约束残差的无迹卡尔曼滤波（UKF）算法对GPS和行人航迹推算（PDR）定位信息进行融合处理,有效克服了PDR定位中累积航向误差产生的位置漂移问题,提高了算法的定位精度和稳定性。试验结果表明,改进算法能有效抑制数字罗盘的漂移误差,航向相对误差平均降低56%;行人步行时,GPS定位标准误差为2.67 m,单纯PDR定位标准误差为6.83 m;随机给予若干点GPS数据辅助定位,标准误差降至3.12 m;全程融合GPS与PDR定位,标准误差可降至1.94 m。