The international GPS service: A global resource for GPS applications and research

Since June, 1992, the International GPS Service has been coordinating a global civilian GPS infrastructure in order to support numerous GPS applications and research activities. A key aspect of the IGS is the reliability and quality of the analysis products that have been made available over the past five years through the IGS Analysis Centers and the Analysis Center Coordinator. On A daily basis these IGS centers produce precise satellite orbits, Earth orientation parameters, satellite and receiver clocks, atmospheric and ionospheric data. Recent improvements in the IGS include production of predicted (50 cm rms) and rapid orbit products (10 cm rms), generation of an official IGS Earth orientation parameters (eop) series, combined site-specific tropospheric estimates for determining precipitable water vapor, and ionospheric delay estimates from the IGS network. A key project of the IGS is the Densification Project of the International Terrestrial Reference Frame (ITRF) through GPS. On a regular basis station coordinates and velocities of global and regional stations are produced in this precise, truly global reference frame. Additionally, the IGS is now considering its role in supporting upcoming Low Earth Orbiting missions; its potential contribution to long term monitoring of sea level heights and altimeter calibration through the GPS; and extending the IGS infrastructure to support observations and analysis of GLONASS system.