 IGS Organization InformationA diagram showing the organization of the IGS is illustrated here. The GPS stations shown below the GPS satellites are permanent and operate continuously, receiving and recording the L-band and dual-frequency signals transmitted by the GPS satellites. The station data of the IGS network is accessed by Operational Data Centers (ODCs) through various communication schemes, such as the Internet, telephone, INMARSAT, radio modem, and V-SAT. The Operational Data Centers are responsible for the direct interface to the GPS receiver, connecting to the remote site daily and downloading and archiving the raw receiver data. The quality of these data are validated by checking the number of observations, number of observed satellites, date and time of the first and last record in the file. The data are then translated from raw receiver format to a common format called Receiver Independent Exchange (RINEX) and compressed. Both the observation and navigation files (and ideally meteorological data) are then transmitted to the Regional or Global Data Centers .
Regional Data Centers More detail concerning the IGS data flow can be found in the IGS Annual Reports, in the section on Data Centers. The IGS Analysis Centers retrieve the data sets from the Global Data Centers and produce GPS ephemerides, station coordinates, earth rotation parameters, etc. These products are then sent to the Analysis Center Coordinator who uses an orbit combination technique to produce the official IGS orbits (the rapid orbit available on a daily basis and the final orbit, available with a delay of approximately 8 to 10 days and based on weekly fits). The products generated are sent back to the Global Data Centers and the Central Bureau Information System (CBIS) for archiving and user access. The Central Bureau is responsible for the overall coordination and management of the service. The International Governing Board (GB) is the body that oversees the activities and direction of the IGS. The success of the IGS is due to the voluntary and active participation of Associate Members and Contributing Organizations. The 1994 IGS Annual Report, available from the Central Bureau, describes the fundamental organization of the IGS in greater detail, as well as the evolution of the GPS tracking network that comprises in the current IGS network. Associate Analysis Centers -- Pilot Project for the Densification of the ITRFThe Associate Analysis Centers produce unique products within the IGS. In September of 1995, the highly successful Pilot Project for the Densification of the ITRF reference frame, using the IGS network, officially began. The project was designed as conceptual proof of the distributed processing of GPS data from many stations, and relies on the Global Network Associate Analysis Centers (GNAACs) for a combination of results submitted by IGS Analysis Centers and the Regional Network Associate Analysis Centers (RNAACs). This combination of solutions produces precise station locations and velocities in a consistent reference frame. The Call for Participation at the Regional Level was announced in January 1996. It is interesting to note that EUREF, the Subcommission for Europe within the IAG Commission X on Global and Regional Geodetic Networks, is an RNAAC which combines a number of solutions from various RNAACs within Europe and passes this regionally-combined solution on to the GNAACs. Additional detailed information can also be found in the IGS Reports series on the CBIS.Other types of Associate Analysis Centers that support the use of GPS data and products in other research areas (such Ionospheric and atmospheric applications) are being considered.
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This page last updated: 21 June 2000 |