On-line Resources Supporting the Data, Products, and Information Infrastructure for the International DORIS Service

The International DORIS Service (IDS) was formed under the direction of the International Association of Geodesy (IAG) in 2003 to support geodetic research utilizing DORIS data and products. The IDS is organized into a hierarchy of components: network of Tracking Stations, Satellite Segment, Data Centers, Analysis Centers, Central Bureau, and Governing Board. The DORIS infrastructure consists of a globally distributed network of over 50 ground beacons and a constellation of five satellites equipped with receivers that relay range rate measurements through a central collection facility to the IDS archives. The Data Centers and Central Bureau supporting the IDS are the primary means of distributing DORIS data, products, and general information to the user community. These facilities utilize Web and ftp servers, as well as an email service, to support the users of DORIS data and products. The current status and recent developments of these components are discussed, as well as a review of available information, data, and geodetic product types.     

Robust combination of IGS analysis center GLONASS clocks

GPS Solutions - The International GNSS Service (IGS) Analysis Centers (ACs) generate precise GNSS products by integrating tracking data from globally distributed IGS stations. The ACs’...     

The International GNSS Service in a changing landscape of Global Navigation Satellite Systems

The International GNSS Service (IGS) is an international activity involving more than 200 participating organisations in over 80 countries with a track record of one and a half decades of successful operations. The IGS is a service of the International Association of Geodesy (IAG). It primarily supports scientific research based on highly precise and accurate Earth observations using the technologies of Global Navigation Satellite Systems (GNSS), primarily the US Global Positioning System (GPS). The mission of the IGS is “to provide the highest-quality GNSS data and products in support of the terrestrial reference frame, Earth rotation, Earth observation and research, positioning, navigation and timing and other applications that benefit society”. The IGS will continue to support the IAG’s initiative to coordinate cross-technique global geodesy for the next decade, via the development of the Global Geodetic Observing System (GGOS), which focuses on the needs of global geodesy at the mm-level. IGS activities are fundamental to scientific disciplines related to climate, weather, sea level change, and space weather. The IGS also supports many other applications, including precise navigation, machine automation, and surveying and mapping. This article discusses the IGS Strategic Plan and future directions of the globally-coordinated ~400 station IGS network, tracking data and information products, and outlines the scope of a few of its numerous working groups and pilot projects as the world anticipates a truly multi-system GNSS in the coming decade.     

M_DCB: Matlab code for estimating GNSS satellite and receiver differential code biases

Global navigation satellite systems (GNSS) have been widely used to monitor variations in the earth’s ionosphere by estimating total electron content (TEC) using dual-frequency observations. Differential code biases (DCBs) are one of the important error sources in estimating precise TEC from GNSS data. The International GNSS Service (IGS) Analysis Centers have routinely provided DCB estimates for GNSS satellites and IGS ground receivers, but the DCBs for regional and local network receivers are not provided. Furthermore, the DCB values of GNSS satellites or receivers are assumed to be constant over 1?day or 1?month, which is not always the case. We describe Matlab code to estimate GNSS satellite and receiver DCBs for time intervals from hours to days; the software is called M_DCB. The DCBs of GNSS satellites and ground receivers are tested and evaluated using data from the IGS GNSS network. The estimates from M_DCB show good agreement with the IGS Analysis Centers with a mean difference of less than 0.7?ns and an RMS of less than 0.4?ns, even for a single station DCB estimate.     

The international global navigation satellite systems service (IGS): development and achievements

Since 21 June 1992 the International GPS Service (IGS), renamed International GNSS Service in 2005, produces and makes available uninterrupted time series of its products, in particular GPS observations from the IGS Global Network, GPS orbits, Earth orientation parameters (components x and y of polar motion, length of day) with daily time resolution, satellite and receiver clock information for each day with different latencies and accuracies, and station coordinates and velocities in weekly batches for further analysis by the IERS (International Earth Rotation and Reference Systems Service). At a later stage the IGS started exploiting its network for atmosphere monitoring, in particular for ionosphere mapping, for troposphere monitoring, and time and frequency transfer. This is why new IGS products encompass ionosphere maps and tropospheric zenith delays. This development became even more important when more and more space-missions carrying space-borne GPS for various purposes were launched. This article offers an overview for the broader scientific community of the development of the IGS and of the spectrum of topics addressed today with IGS data and products.     

Research on a method of real-time combination of precise GPS clock corrections

GPS Solutions - The acquisition of real-time satellite orbit and clock corrections is necessary for real-time PPP. There are nine International GNSS Service (IGS) analysis centers (ACs) that...     

Performance of various predicted GNSS global ionospheric maps relative to GPS and JASON TEC data

When using predicted total electron content (TEC) products to generate preliminary real-time global ionospheric maps (GIMs), validation of these ionospheric predicted products is essential. In this study, we evaluate the accuracy of five predicted GIMs, provided by the international GNSS service (IGS), over continental and oceanic regions during the period from September 2009 to September 2015. Over continental regions, the GPS TEC data collected from 41 IGS continuous tracking stations are used as a reference data set. Over oceanic regions, the TEC data from the JASON altimeter are used for comparison. An initial performance comparison between the IGS combined final GIM product and the predicted GIMs is also included in this study. The evaluation results show that the predicted GIMs produced by CODE outperform the other predicted GIMs for all three validation results. The accuracy of the 1-day predicted GIMs, produced by the IGS associate analysis centers (IAACs), is higher than that of the 2-day predicted GIMs. Compared to the 2-day UPC predicted GIMs, the 2-day ESA predicted GIMs are observed to have slightly worse performances over ocean regions and better positioning performances over continental regions.     

Anomaly analysis of 18 years of newly merged GPS ephemeris from four IGS data centers

The merged GPS navigation files from the International GNSS Service (IGS) data centers, i.e., the Crustal Dynamics Data Information System (CDDIS), the Bundesamt für Kartographie und Geodäsie (BKG), the Scripps Institution of Oceanography (SIO), and the Institut Geographique National (IGN) are occasionally contaminated by anomalies and inconsistent user range accuracy (URA). This contamination impairs the performance assessment of GPS service, especially the system integrity. We remerged these files starting Day of Year (DOY) 1, 2000 using all available navigation data files from IGS stations. To effectively get the upper bound URA, a frequency-dependent pattern recognition method was developed. In addition, a comprehensive comparison between the navigation data remerged by us and those provided by the four IGS data centers was performed. The compared results revealed that T_GD and Issue of Data Clock (IODC) were the dominating anomalies in the merged navigation data from CDDIS and SIO for the first several years after 2000, and M₀, Ω₀, ω, and a_f0 were the dominant anomalies in the merged data from IGN. In addition to a number of missing records, many records with incorrect PRN (pseudo-random noise number), identifying a GPS satellite, were found in files from the IGS data centers. Although the number of anomalies in the merged files from CDDIS has continued to decrease in recent years, they have not disappeared and would affect system-level assessment and scientific applications to a certain extent. The results also revealed that our remerged files were more complete, clean, compact and consistent, making them more suitable for GPS system performance assessment and related research studies. Moreover, those data are now openly available.     

Use of IGS products in TAI applications

The Bureau International des Poids et Mesures (BIPM) is in charge of producing International Atomic Time TAI. In this aim, it uses clock data from more than 60 laboratories spread worldwide. For two decades, GPS has been an essential tool to link these clocks, and products from the International GNSS Service (IGS) have been used to improve the quality of these time links since its creation in the early 1990s. This paper reviews the various interactions between the IGS and time activities at the BIPM, and shows that TAI has greatly benefited from IGS products so that their availability is now an essential need for the quality of TAI links. On the other hand, IGS has also benefited from introducing time laboratories equipped with highly stable clocks in its network of stations. In the future, similar products will be needed for an ensemble of satellite systems, starting with GLONASS and GALILEO. It will be a major challenge to the IGS to obtain a consistent set of products, particularly for what concerns satellite clocks and inter-system bias values.     

A new type of troposphere zenith path delay product of the international GNSS service

The International GNSS Service (IGS) has been producing the total troposphere zenith path delay (ZPD) product that is based on combined ZPD contributions from several IGS Analysis Centers (AC) since GPS week 890 in 1997. A new approach to the production of the IGS ZPD has been proposed that replaces the direct combination of diverse ZPD products with point positioning estimates using the IGS Combined Final orbit and clock products. The new product was formally adopted in 2007 after several years of concurrent production with the legacy product. We describe here the advantages of the new approach for the IGS ZPD product, which enhance the value of the new ZPD product for climate studies. We also address the impact the IGS adoption in November 2006 of new GPS antenna phase center standards has had on the new ZPD product. Finally we describe plans to further enhance the ZPD products.     

GBM快速轨道产品及非差模糊度固定对其精度的改进

GNSS是实时定位导航最重要的方法,精密卫星轨道钟差产品是GNSS高精度服务的前提。国际GNSS服务中心(IGS)及其分析中心长期致力于GNSS数据处理的研究及高精度轨道和钟差产品的提供。GFZ作为分析中心之一,提供GBM多系统快速产品。本文基于2015—2021年GBM提供的精密轨道产品,阐述了数据处理策略,分析了轨道的精度,介绍了非差模糊度固定的原理和对精密定轨的影响。结果表明:GBM快速产品中的GPS轨道精度与IGS后处理精密轨道相比的精度约为11~13 mm,轨道6 h预报精度约为6 cm;GLONASS预报精度约为12 cm,Galileo在该时期的精度均值为10 cm,但是在2016年底以后精度提升到5 cm左右;北斗系统的中轨卫星(medium earth orbit,MEO)在2020年以后预报精度约为10 cm;北斗的静止轨道卫星(geostationary earth orbit,GEO)卫星和QZSS卫星的预报精度在米级;卫星激光测距检核表明,Galileo、GLONASS、BDS-3 MEO卫星轨道精度分别为23、41、47 mm;此外,采用150 d观测值的试验结果表明,采用非差模糊度固定能显著改善MEO卫星轨道精度,对GPS、GLONASS、Galileo、BDS-2和BDS-3的MEO卫星的6 h时预报精度改善率分别为9%~15%、15%~18%、11%~13%、6%~17%和14%~25%。     

GNSS科学发展与前景

GNSS早已成为多学科研究的强大工具。着重介绍了近几年来GNSS系统及其观测技术,特别是数据处理方法和技术的重大发展,阐述了数据格式标准化的进展、全球与区域参考框架现状、参考框架对地壳运动研究的影响和IGS的产品等。同时对利用GNSS观测研究成果,主要是地壳运动的研究成果也作了较为详细的介绍。     

The IGS-combined station coordinates, earth rotation parameters and apparent geocenter

The International GNSS Service (IGS) routinely generates a number of weekly, daily and sub-daily products. Station coordinates and velocities, earth rotation parameters (ERPs) and apparent geocenter are among these products generated weekly by the IGS Reference Frame Coordinator. They have been determined since 1999 by combining independent estimates from at least seven IGS Analysis Centers (ACs). Two Global Network Associate Analysis Centers (GNAACs) also provide independent combinations using the same AC weekly solutions and they are currently used to quality control the IGS combination. The combined solutions are aligned to an IGS realization (IGS05) of the ITRF2005 using a carefully selected set of the IGS Reference Frame (RF) stations (nominally 132). During the combination process, the contributing solutions are compared and outliers are removed to ensure a high level of consistency of the estimated parameters. The ACs and the weekly combined solution are consistent at the 1–2 and 3–4 mm levels for the horizontal and vertical components. Similarly, the excess Length of Day (LOD), the pole positions and pole rates are consistent at the 10μs, 0.03–0.05 mas and 0.10–0.20 mas/day levels, respectively. The consistency of the apparent geocenter estimate is about 5 mm in the X and Y components and 10 mm in the Z component. Comparison of the IGS-combined ERP estimates with the IERS Bulletin A suggests a small bias of the order of ?0.04 mas and + 0.05 mas (both ±0.05 mas) in the x and y components.     

The activities of the Ionosphere Working Group of the International GPS Service (IGS)

This article is based on a position paper presented at the IGS Network, Data and Analysis Center Workshop 2002 in Ottawa, Canada, 8–11 April 2002, and introduces the IGS Ionosphere Working Group (Iono_WG). Detailed information about the IGS in general can be found on the IGS Central Bureau Web page: http://igscb.jpl.nasa.gov. The Iono_WG commenced working in June 1998. The working group's main activity currently is the routine production of ionosphere Total Electron Content (TEC) maps with a 2-h time resolution and daily sets of GPS satellite and receiver hardware differential code bias (DCB) values. The TEC maps and DCB sets are derived from GPS dual-frequency tracking data recorded with the global IGS tracking network. In the medium- and long-term, the working group intends to refine algorithms for the mapping of ionospheric parameters from GPS measurements and to realize near–real–time availability of IGS ionosphere products. The paper will give an overview of the Iono_WG activities that include a summary of activities since its establishment, achievements and future plans. Electronic Publication     

Consistency of seven different GNSS global ionospheric mapping techniques during one solar cycle

In the context of the International GNSS Service (IGS), several IGS Ionosphere Associated Analysis Centers have developed different techniques to provide global ionospheric maps (GIMs) of vertical total electron content (VTEC) since 1998. In this paper we present a comparison of the performances of all the GIMs created in the frame of IGS. Indeed we compare the classical ones (for the ionospheric analysis centers CODE, ESA/ESOC, JPL and UPC) with the new ones (NRCAN, CAS, WHU). To assess the quality of them in fair and completely independent ways, two assessment methods are used: a direct comparison to altimeter data (VTEC-altimeter) and to the difference of slant total electron content (STEC) observed in independent ground reference stations (dSTEC-GPS). The main conclusion of this study, performed during one solar cycle, is the consistency of the results between so many different GIM techniques and implementations.     

Evaluation of the impact of atmospheric pressure loading modeling on GNSS data analysis

In recent years, several studies have demonstrated the sensitivity of Global Navigation Satellite System (GNSS) station time series to displacements caused by atmospheric pressure loading (APL). Different methods to take the APL effect into account are used in these studies: applying the corrections from a geophysical model on weekly mean estimates of station coordinates, using observation-level corrections during data analysis, or solving for regression factors between the station displacement and the local pressure. The Center for Orbit Determination in Europe (CODE) is one of the global analysis centers of the International GNSS Service (IGS). The current quality of the IGS products urgently asks to consider this effect in the regular processing scheme. However, the resulting requirements for an APL model are demanding with respect to quality, latency, and—regarding the reprocessing activities—availability over a long time interval (at least from 1994 onward). The APL model of Petrov and Boy (J Geophys Res 109:B03405, 2004) is widely used within the VLBI community and is evaluated in this study with respect to these criteria. The reprocessing effort of CODE provides the basis for validating the APL model. The data set is used to solve for scaling factors for each station to evaluate the geophysical atmospheric non-tidal loading model. A consistent long-term validation of the model over 15 years, from 1994 to 2008, is thus possible. The time series of 15 years allows to study seasonal variations of the scaling factors using the dense GNSS tracking network of the IGS. By interpreting the scaling factors for the stations of the IGS network, the model by (2004) is shown to meet the expectations concerning the order of magnitude of the effect at individual stations within the uncertainty given by the GNSS data processing and within the limitations due to the model itself. The repeatability of station coordinates improves by 20% when applying the effect directly on the data analysis and by 10% when applying a post-processing correction to the resulting weekly coordinates compared with a solution without taking APL into account.     

The International GLONASS Service – Pilot Project

The International GLONASS Service – Pilot Project (IGLOS-PP), a project of the International GPS Service, was launched in order to underscore the importance and benefits of integrating data from multiple systmes and techniques within IGS products. At first this article summarizes the contributing organizations and the available infrastructure. Later on the GLONASS related modeling techniques at the involved IGS Analysis Centers are described and we conclude with some remarks concerning the advantages for the expected user commmunity. ? 2001 John Wiley & Sons, Inc.     

基于INDY控件的实时精密单点定位星历获取程序设计

IGS提供实时的预报产品—超快速精密星历IGU,这种超快速星历为实时精密单点定位的实现提供了实时的高精度数据支撑。由于IGU存储在网络服务器中,设计实现IGS数据文件实时获取的下载程序是实时精密单点定位的基础。通过在C++Builder 2007平台上利用Indy控件设计编译了IGS数据文件的下载程序并进行实验。实验表明:该程序支持多线程并发和断点续传功能,可以实现IGS数据文件的实时下载。     

Global GPS data analysis at the National Geodetic Survey

NOAA’s National Geodetic Survey (NGS) has been one of the Analysis Centers (ACs) of the International GNSS Service (IGS) since its inception in 1994. Solutions for daily GPS orbits and Earth orientation parameters are regularly contributed to the IGS Rapid and Final products, as well as solutions of weekly station positions. These solutions are combined with those of the other ACs and then the resultant IGS products are distributed to users. To perform these tasks, NGS has developed and refined the Program for the Adjustment of GPS EphemerideS (PAGES) software. Although PAGES has continuously evolved over the past 15 years, recent efforts have focused mostly on updating models and procedures to conform more closely to IGS and the International Earth Rotation Service (IERS) conventions. Details of our processing updates and demonstrations of the improvements will be provided.     

多分析中心站坐标产品的综合方法研究

首先介绍了多分析中心产品融合处理的两种综合策略,然后基于解层面的综合策略,提出了站坐标和地球自转参数同时综合的方法。采用国际GNSS服务组织（International GNSS Service,IGS）9个分析中心1 a的数据进行试验,从站坐标、地球自转参数精度以及地心运动3个方面验证了该方法的正确性。结果表明,基于综合方法得到的综合解和IGS综合解处于同一精度水平。站坐标在平面和高程方向的一致性分别为0.5 mm和1.0 mm,极移和极移速率的一致性分别优于7.0×10-6"和40.0×10-6"/d,日长参数优于7.7×10-6 s/d。所提出的综合方法可用于全球连续监测评估系统（international GNSS monitoring and assessment system,iGMAS）的站坐标/地球自转参数产品综合。