[last updared 2004]
About the IGS
The IGS global system of satellite tracking stations, Data Centers, and Analysis Centers puts high-quality GPS data and data products on line in near real time to meet the objectives of a wide range of scientific and engineering applications and studies.
The IGS collects, archives, and distributes GPS observation data sets of sufficient accuracy to satisfy the objectives of a wide range of applications and experimentation. These data sets are used by the IGS to generate the data products mentioned above which are made available to interested users through the Internet. In particular, the accuracies of IGS products are sufficient for the improvement and extension of the International Terrestrial Reference Frame (ITRF), the monitoring of solid Earth deformations, the monitoring of Earth rotation and variations in the liquid Earth (sea level, ice-sheets, etc.), for scientific satellite orbit determinations, ionosphere monitoring, and recovery of precipitable water vapor measurements.
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.
For more information concerning IGS organization, click here.
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).
The IGS has developed a worldwide system comprising satellite tracking stations, Data Centers, and Analysis Centers to put high-quality GPS data and data products on line within a day of observations. For example, following the Northridge, California, earthquake in January 1994, analysis teams using IGS-supplied data and products were able to quickly evaluate the disaster's immediate effects by determining station displacements accurately to within a few millimeters.
The IGS global network of permanent tracking stations, each equipped with a GPS receiver, generates raw orbit and tracking data. The Operational Data Centers, which are in direct contact with the tracking sites, collect the raw receiver data and format them according to a common standard, using a data format called Receiver Independent Exchange (RINEX). The formatted data are then forwarded to the Regional or Global Data Centers. To reduce electronic network traffic, the Regional Data Centers are used to collect data from several Operational Data Centers before transmitting them to the Global Data Centers. Data not used for global analyses are archived and available for online access at the Regional Data Centers. The Global Data Centers archive and provide on-line access to tracking data and data products.
Products and Applications
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. For example, geodynamics investigators who use GPS in local regions can include data from one or more nearby IGS stations, fix the site coordinates from such stations to their ITRF values, and more importantly, use the precise IGS orbits without further refinement. Data from an investigator's local network can then be analyzed with maximum accuracy and minimum computational burden. Furthermore, the results will be in a well-defined global reference frame.
An additional aspect of IGS products is for the densification of the ITRF at a more regional level. This is accomplished through the rigorous combination of regional or local network solutions utilizing the Solution Independent Exchange Format (SINEX) and a process defined in the densification section.
In the future, the IGS infrastructure could become a valuable asset for support of new ground-based applications and could also contribute to space-based missions in which highly accurate flight and ground differential techniques are required.