Origines

Since the late 1980s, the U.S. Global Positioning System (GPS) constellation of satellites has come to play a major role in regional and global studies of Earth. In the face of continued growth and diversification of GPS applications, the worldwide scientific community has made an effort to promote international standards for GPS data acquisition and analysis, and to deploy and operate a common, comprehensive global tracking system.

As part of this effort, the IGS was formally recognized in 1993 by the International Association of Geodesy (IAG), and began routine operations on January 1, 1994, providing GPS orbits, tracking data, and other data products in support of geodetic and geophysical research. In particular, since January 1994, the IGS has made available to its user community the IGS official orbit based on contributions from the seven current IGS Analysis Centers. The IGS also supports a variety of governmental and commercial activities and develops international GPS data standards and specifications. A description of the development and evolution of the IGS can be found in a number of publications, with detailed documentation contained in the IGS Annual Report Series published by the IGS Central Bureau via the World Wide Web. This series contains the yearly contributions from all components of service and demonstrates that the key to success of the IGS has been the broad support of the international geodynamics and geodetic communities and their sponsoring organizations. This Information System is sponsored by the National Aeronautic and Space Administration (NASA) and managed for NASA by the Jet Propulsion Laboratory (JPL) of the California Institute of Technology (Caltech).

Missions

The primary mission of the International GPS Service, as stated in the organization’s 2002-2007 Strategic Plan, is :

The International GPS Service is committed to providing the highest quality data and products as the standard for global navigation satellite systems (GNSS) in support of Earth science research, multidisciplinary applications, and education. These activities aim to advance scientific understanding of the Earth system components and their interactions, as well as to facilitate other applications benefiting society.

The IGS Terms of Reference (comparable to the by-laws of the organization) describes in broad terms the goals and organization of the IGS.
To accomplish its mission, the IGS has a number of components: an international network of over 350 continuously operating dual-frequency GPS stations, more than a dozen regional and operational data centers, three global data centers, seven analysis centers and a number of associate or regional analysis centers. The Central Bureau for the service is located at the Jet Propulsion Laboratory, which maintains the Central Bureau Information System (CBIS) and ensures access to IGS products and information. An international Governing Board oversees all aspects of the IGS. The IGS is an approved service of the International Association of Geodesy since 1994 and is recognized as a member of the Federation of Astronomical and Geophysical Data Analysis Services (FAGS) since 1996.

The International GNSS Service is committed to providing the highest quality data and products as the standard for Global Navigation Satellite Systems (GNSS) in support of Earth science research, multidisciplinary applications, and education. These activities endeavor to advance scientific understanding of the Earth system components and their interactions, as well as to facilitate other applications benefiting society. The Service also develops the necessary standards and specifications and encourages international adherence to its conventions.

Produits

The IGS collects, archives, and distributes GPS observation data sets of sufficient accuracy to meet the objectives of a wide range of scientific and engineering applications and studies. These data sets are used to generate the following products :

• GPS satellite ephemerides
• GLONASS satellite ephemerides
• Earth rotation parameters
• IGS tracking station coordinates and velocities
• GPS satellite and IGS tracking station clock information
• Zenith tropospheric path delay estimates
• Global ionospheric maps

IGS products support scientific activities such as improving and extending the International Earth Rotation Service (IERS) Terrestrial Reference Frame (ITRF), monitoring deformations of the solid Earth and variations in the liquid Earth (sea level, ice sheets, etc.), and in Earth rotation, determining orbits of scientific satellites and monitoring the ionosphere.

Centres d’Analyse

The analysis centers fall into two categories: Analysis Centers (ACs) and Associate Analysis Centers (AACs). The Analysis Centers receive and process tracking data from one or more data centers for the purpose of producing IGS products. The Analysis Centers are committed to submit products for combination into IGS products, without interruption, using designated standards and conventions, and within a specified time delay to meet IGS requirements. The Analysis Centers generally provide the core products of ephemerides, Earth rotation parameters, station coordinates, and clock information, as well as other recommended products, such as rapid, predicted or real-time orbit and Earth rotation solutions. Associate Analysis Centers produce specialized products recognized by the Governing Board, e.g., ionospheric information, tropospheric parameters, or station coordinates and velocities for a global or regional sub-network. The "Charter for Analysis Centers and Associate Analysis Centers" is a policy statement of the Governing Board and is available from the Central Bureau.

Coordinateur des Centres d’Analyse

The Analysis Center Coordinator (ACC, also referred to as the Analysis Coordinator) assists the Analysis Centers. The ACC monitors the activities of the Analysis Centers to ensure that the IGS objectives are carried out. Specific expectations include quality control, performance evaluation, and continued development of appropriate analysis standards. The Analysis Coordinator is also responsible for the appropriate combination of the Analysis Centers" products into a single set of orbit and clock products, which are official IGS products delivered to the Global Data Centers. The Analysis Center Coordinator is a voting member of the IGS Governing Board and interacts regularly with the Central Bureau and the IERS. The Analysis Coordinator (or designee as approved by the Governing Board) is one of the two IGS representatives to the IERS Directing Board. Generally the responsibilities for the Analysis Coordinator shall rotate among the Analysis Centers with appointments and terms specified by the Governing Board.

Données

Tracking stations network

IGS Stations provide continuous tracking using high-accuracy receivers and have data transmission facilities allowing for rapid (minimally daily) data transmission to the data centers (see below). The stations must meet physical and operational requirements as defined in the "IGS Site Guidelines" document available from the Central Bureau. The ensemble of the IGS stations is the IGS network.

Data centers

IGS data centers fall into three categories: Operational, Regional, and Global Data Centers. Each has varied duties which must be carried out continually and with a minimum of delay or downtime, although the multiplicity of DCs provides a measure of redundancy. The description and responsibilities of each type of DC are detailed in the separate policy document "IGS Data Centers Charter" and include duties such as collecting data from GPS tracking stations and ancillary equipment, data validation, permanent archival, providing online availability, and transmittal to and equalization with other DCs. The set of DCs provides for open access to IGS data and products by IGS participants and all external users. DCs are approved by the IGS GB following demonstration of qualifications and commitment.