Total electron content processing from GPS observations to facilitate ionospheric modeling

With the increasing global distribution of high rate dual-frequency global positioning system (GPS) receivers, the production of a real-time atmospheric constituent definition, total electron content (TEC), has become a beneficial contributor to the modeling applications used in the assessment of GPS position accuracy and the composition of the ionosphere, plasmasphere, and troposphere. Historically, TEC measurements have been obtained through post processing techniques to produce the quality of data necessary for modeling applications with rigorous error estimate requirements. These procedures necessitated the collection of large volumes of data to address the various abnormalities in the computation of TEC associated with the use of greater data quality controls and source selection while real-time modeling environments must rely on autonomous controls and filtration techniques to prevent the production of erroneous model results. In this paper we present methods for processing TEC in real time, which utilize several procedures including the application of an ionospheric model to automatically perform quality control on the TEC output and the computational techniques used to address receiver multipath, faulty receiver observations, cycle-slips, segmented processing, and receiver calibrations. The resulting TEC measurements are provided with rigorous error estimates validated using the vertical TEC from the Jason satellite mission.

Calibration errors on experimental slant total electron content (TEC) determined with GPS

The Global Positioning System (GPS) has become a powerful tool for ionospheric studies. In addition, ionospheric corrections are necessary for the augmentation systems required for Global Navigation Satellite Systems (GNSS) use. Dual-frequency carrier-phase and code-delay GPS observations are combined to obtain ionospheric observables related to the slant total electron content (sTEC) along the satellite-receiver line-of-sight (LoS). This observable is affected by inter-frequency biases [IFB; often called differential code biases (DCB)] due to the transmitting and the receiving hardware. These biases must be estimated and eliminated from the data in order to calibrate the experimental sTEC obtained from GPS observations. Based on the analysis of single differences of the ionospheric observations obtained from pairs of co-located dual-frequency GPS receivers, this research addresses two major issues: (1) assessing the errors translated from the code-delay to the carrier-phase ionospheric observable by the so-called levelling process, applied to reduce carrier-phase ambiguities from the data; and (2) assessing the short-term stability of receiver IFB. The conclusions achieved are: (1) the levelled carrier-phase ionospheric observable is affected by a systematic error, produced by code-delay multi-path through the levelling procedure; and (2) receiver IFB may experience significant changes during 1 day. The magnitude of both effects depends on the receiver/antenna configuration. Levelling errors found in this research vary from 1.4 total electron content units (TECU) to 5.3 TECU. In addition, intra-day vaiations of code-delay receiver IFB ranging from 1.4 to 8.8 TECU were detected.     

GPS动态定位数据处理模型的比较研究

The characteristics of three GPS kinematic data processing models, Least Squares （LS）, Kalman filtering and filtering are discussed and their advantages and disadvantages are compared. With observational data and pertinent data processing software, the applicable condition, context and effect of the three models are experimented. Results show that when the mobile platform is in uniform motion, the accuracy of the three models are almost equal; when the mobile platform is in stochastic acceleration, the accuracy of H∞ filtering model is superior to that of LS, while that of Kalman filtering is the worst.     

Temporal and spatial variations of global ionospheric total electron content under various solar conditions

By utilizing the numerical technique of principal component analysis (PCA), this work analyses temporal and spatial variations of the ionosphere under various solar conditions during the period 1999–2013. Applying the PCA technique to the time series of the global ionospheric total electron content (TEC) maps provides an efficient method for analyzing the main ionospheric variability on a global scale that is able to decompose periodic variations (e.g., annual and semiannual oscillations) while retaining the asymmetry in the temporal and spatial domains (e.g., seasonal and equator anomalies). The TEC series of different local times are processed separately at two time scales: (1) the whole 15 years of the period of study and (2) the individual years. In contrast with previous studies, the analysis of the dataset of the 15 years shows that dawn (e.g., LT4–6) and late morning (LT10–12) are the more remarkable characteristic times for ionospheric variability. This study also reveals a cyclic trend of the variability with respect to local times. The first two modes, which contain 80–90% of the total variance, represent spatial distributions and temporal variations with respect to the different stages of the solar cycle and local times. Annual and semiannual variations are demodulated from the first two modes, and the results show that these variations evidently have distinct trends for daytime and nighttime. An exception is that, under active solar conditions, extremely strong solar irradiance during the daytime has a residual effect on the variability of the nighttime.     

Combined GPS/GLONASS data processing

To obtain the GLONASS satellite position at an epoch other than reference time, the satellite's equation of motion has to be integrated with broadcasting ephemerides. The iterative detecting and repairing method of cycle slips based on triple difference residuals for combined GPS/GLONASS positioning and the iterative ambiguity resolution approach suitable for combined post processing positioning are discussed systematically. Experiments show that millimeter accuracy can be achieved in short baselines with a few hours' dual frequency or even single frequency GPS/GLONASS carrier phase observations, and the precision of dual frequency observations is distinctly higher than that of single frequency observations.     

Combined GPS/GLONASS data processing

To obtain the GLONASS satellite position at an epoch other than reference time,the satellite‘s equation of motion has to be integrated with broadcasting ephemerides.The iterative detecting and repairing method of cycle slips based on triple difference residuals for combined GPS/GLONASS positioning and the iterative ambiguity resolution approach suitable for combined post processing positioning are discussed systematically.Experiments show that millimter accuracy can be achieved in short baselines with a few hours‘ dual frequency or even single frequency GPS/GLONASS carrier phase observation,and the precision of dual frequency observations is distinctly higher than that of single frequency observations.     

GPS监测网数据处理方案研究

处理大尺度ＧＰＳ监测网多期复测成果的时期,数据处理方案是一个重要问题。作者在处理首都圈ＧＰＳ地形变监测网数据的过程中,经过长期探索和大量试算,提出了制定数据处理方案的基本原则：要采用一个自洽的地球参考框架和常数系统;要采用精度最高的同一种粗密星历和相应的地球自转参数;要采用最先进的同一种数据处理软件以及采用同一的参考基准和约束条件。由于地壳处于运动之中,大尺度ＧＰＳ监测网的参考基准应是动态基准。研     

Revisit the calibration errors on experimental slant total electron content (TEC) determined with GPS

The calibration errors on experimental slant total electron content (TEC) determined with global positioning system (GPS) observations is revisited. Instead of the analysis of the calibration errors on the carrier phase leveled to code ionospheric observable, we focus on the accuracy analysis of the undifferenced ambiguity-fixed carrier phase ionospheric observable determined from a global distribution of permanent receivers. The results achieved are: (1) using data from an entire month within the last solar cycle maximum, the undifferenced ambiguity-fixed carrier phase ionospheric observable is found to be over one order of magnitude more accurate than the carrier phase leveled to code ionospheric observable and the raw code ionospheric observable. The observation error of the undifferenced ambiguity-fixed carrier phase ionospheric observable ranges from 0.05 to 0.11 total electron content unit (TECU) while that of the carrier phase leveled to code and the raw code ionospheric observable is from 0.65 to 1.65 and 3.14 to 7.48 TECU, respectively. (2) The time-varying receiver differential code bias (DCB), which presents clear day boundary discontinuity and intra-day variability pattern, contributes the most part of the observation error. This contribution is assessed by the short-term stability of the between-receiver DCB, which ranges from 0.06 to 0.17 TECU in a single day. (3) The remaining part of the observation errors presents a sidereal time cycle pattern, indicating the effects of the multipath. Further, the magnitude of the remaining part implies that the code multipath effects are much reduced. (4) The intra-day variation of the between-receiver DCB of the collocated stations suggests that estimating DCBs as a daily constant can have a mis-modeling error of at least several tenths of 1 TECU.     

GPS长基线数据处理的软件实现

GPS长基线数据处理在大地测量和大型精密工程中有广泛的应用,GAMIT等国际高精度GPS数据处理软件虽能满足GPS长基线数据处理的解算精度要求,但操作复杂,且对用户的GPS理论有较高的要求。本文在分析长基线GPS数据处理中各类因素影响及误差消除方法基础上,结合图形用户界面程序设计思想,设计并实现了GPS长基线数据处理软件。经不同长度的基线数据解算结果表明,该软件可实现上千公里基线的解算,基线解算精度高,与GAMIT的解算精度相当,且解算过程自动化程度高,用户操作简单,为大范围高精度GPS数据处理提供了一种简便可行的平台。     

GPS data processing with equivalent observation equations

A unified GPS data processing method based on equivalent observation equations is proposed. The theoretic background of this method is given in detail. By selecting the unknowns to be eliminated as vector of zeros, i.e. the satellite clock errors, all clock errors, the clock and ambiguity parameters or user-defined unknowns, the equivalent observation equations can be formed. These equations are equivalent to the zero-, single-, double-, triple- or user-defined differenced equations. The advantages of the method are that the various GPS data processing methods are unified to a unique one, whereas the observation vector remains the original one and the weight matrix keeps the un-correlated diagonal form. Using this equivalent method one may selectively reduce the number of unknowns without having to deal with the correlations. Several special cases of single, double and triple difference are discussed in detail to illustrate the theory. Electronic Publication     

GPS精密单点定位的数据处理方法综述

在GPS精密单点定位数据处理中,通常采用基于非差观测值的处理方法。然而精密单点定位也可通过观测值不同差分组合以减少某些未知参数,且在理论上与非差模型等价。文中介绍基于非差和差分模型的精密单点定位的几种数据处理方法,并对各种模型进行比较。     

基于EMD的桥梁GPS动态监测数据处理

采用GPS监测运营期大跨度桥梁时,受到交通载荷和观测噪声的影响,GPS监测序列中的振动信号(mm级)完全被湮没,如何从监测序列中提取桥梁变形信息及其振动特性是桥梁健康检测的重要内容。文中利用EMD方法对GPS监测序列进行处理,得到一定数量的本征模态函数(IMF),选取特定的IMF做信号重构和功率谱分析,得到桥梁变形信息和振动特性,相较于传统FFT方法,能准确识别结构振动频率,同时提取变形特征。     

基于LabView的GPS数据采集及处理

首先介绍全球定位系统(GPS)的基本工作原理及其通常所采用的通信协议,然后阐述了基于LabView的GPS串口数据采集及处理程序的设计思路和主要功能,最后程序实现了对GPS定位信息的采集、存储及对定位信息的实时显示。     

GPS天线相位模型变化对高精度GPS测量解算的影响研究

GPS天线存在相位中心偏差,在高精度测量中必须对其进行补偿改正。本文针对GPS天线的两种改正模型:相对改正模型和绝对改正模型,在讨论了它们所具有的相同改正办法的基础上,分析了它们在测定方法上存在区别,最后通过一个算例分别研究了这两种模型对GPS测量解算精度的影响,得出了一些有意义的结论。     

GPS slant total electron content accuracy using the single layer model under different geomagnetic regions and ionospheric conditions

The use of observations from the Global Positioning System (GPS) has significantly impacted the study of the ionosphere. As it is widely known, dual-frequency GPS observations can provide very precise estimation of the slant Total Electron Content (sTEC—the linear integral of the electron density along a ray-path) and that the precision level is bounded by the carrier-phase noise and multi-path effects on both frequencies. Despite its precision, GPS sTEC estimations can be systematically affected by errors in the estimation of the satellites and receivers by Inter-Frequency Biases (IFB) that are simultaneously determined with the sTEC. Thus, the ultimate accuracy of the GPS sTEC estimation is determined by the errors with which the IFBs are estimated. This contribution attempts to assess the accuracy of IFBs estimation techniques based on the single layer model for different ionospheric regions (low, mid and high magnetic latitude); different seasons (summer and winter solstices and spring and autumn equinoxes); different solar activity levels (high and low); and different geomagnetic conditions (quiet and very disturbed). The followed strategy relies upon the generation of a synthetic data set free of IFB, multi-path, measurement noise and of any other error source. Therefore, when a data set with such properties is used as the input of the IFB estimation algorithms, any deviation from zero on the estimated IFBs should be taken as indications of the errors introduced by the estimation technique. The truthfulness of this assessment work is warranted by the fact that the synthetic data sets resemble, as realistically as possible, the different conditions that may happen in the real ionosphere. The results of this work show that during the high solar activity period the accuracy for the estimated sTEC is approximately of ±10 TECu for the low geomagnetic region and of ±2.2 TECu for the mid-latitude. During low solar activity the accuracy can be assumed to be in the order of ±2 TECu. For the geomagnetic high-disturbed period, the results show that the accuracy is degraded for those stations located over the region where the storm has the strongest impact, but for those stations over regions where the storm has a moderate effect, the accuracy is comparable to that obtained in the quiet period.     

GPS与全站仪数据椭球面联合平差

传统的基于平面的平差计算常遇到投影和换带的问题,不利于整网平差。文中探究以地球椭球面为统一计算基准面进行联合平差的理论和方法,并推导适用的函数模型和随机模型。根据上述模型编制能够完成椭球面联合平差计算的软件,通过和COSA软件计算结果进行对比,验证它的可行性和有效性,可以有效地避免投影和换带所带来的一系列问题。     

An integrated GPS–accelerometer data processing technique for structural deformation monitoring

Global Positioning System (GPS) is being actively applied to measure static and dynamic displacement responses of large civil engineering structures under winds. However, multipath effects and low sampling frequencies affect the accuracy of GPS for displacement measurement. On the other hand, accelerometers cannot reliably measure static and low-frequency structural responses, but can accurately measure high-frequency structural responses. Therefore, this paper explores the possibility of integrating GPS-measured signals with accelerometer-measured signals to enhance the measurement accuracy of total (static plus dynamic) displacement response of a structure. Integrated data processing techniques using both empirical mode decomposition (EMD) and an adaptive filter are presented. A series of motion simulation table tests are then performed at a site using three GPS receivers, one accelerometer, and one motion simulation table that can simulate various types of motion defined by input wave time histories around a pre-defined static position. The proposed data processing techniques are applied to the recorded GPS and accelerometer data to find both static and dynamic displacements. These results are compared with the actual displacement motions generated by the motion simulation table. The comparative results demonstrate that the proposed technique can significantly enhance the measurement accuracy of the total displacement of a structure.     

全球范围IGS监测站GPS观测数据质量分析

全球卫星导航系统(GNSS)的持续完善及其在多领域内的大量应用,拓展了国际GNSS服务组织(IGS)连续监测站的服务领域,从而提升了对其观测数据的质量要求,因此有必要对大范围内IGS站点卫星观测数据质量进行分析.结合目前各GNSS的全球覆盖程度以及发展成熟度,本文以GPS为对象,对全球范围IGS站点该系统的原始观测数据质量进行评价,包括数据所受多径影响、数据观测完整程度以及数据中跳变比例三方面,得出了关于IGS站点GPS数据质量的分析结果,该结果可为地学研究及工程应用过程中站点的选取作参考.     

Accuracy assessment of the GPS-based slant total electron content

The main scope of this research is to assess the ultimate accuracy that can be achieved for the slant total electron content (sTEC) estimated from dual-frequency global positioning system (GPS) observations which depends, primarily, on the calibration of the inter-frequency biases (IFB). Two different calibration approaches are analyzed: the so-called satellite-by-satellite one, which involves levelling the carrier-phase to the code-delay GPS observations and then the IFB estimation; and the so-called arc-by-arc one, which avoids the use of code-delay observations but requires the estimation of arc-dependent biases. Two strategies are used for the analysis: the first one compares calibrated sTEC from two co-located GPS receivers that serve to assess the levelling errors; and the second one, assesses the model error using synthetic data free of calibration error, produced with a specially developed technique. The results show that the arc-by-arc calibration technique performs better than the satellite-by-satellite one for mid-latitudes, while the opposite happens for low-latitudes.     

Integrated data processing method for GPS and INS field test over Rocky Mountain

IntroductionGPS/INS integrated system exploited the INSand differential GPS pseudo-range and carrierphase technique to promote the accuracy of thedynamic platform navigation and positioning,and increase the reliability and stabilization.Incalculation, Kal…