The IGS GLONASS Pilot Project … Transitioning an Experiment into an Operational GNSS Service

During the last few years, Russia has been slowly rebuilding its GLONASS constellation and appears to be committed to further launches and other improvements in the future. As of August 2004, there were 10 operational satellites. These represent a significant complement to the GPS constellation, providing opportunities for enhanced navigation and positioning accuracy, atmospheric modeling, time transfer, and Earth orientation estimation. The 6-month IGEX-98 campaign in 1998-99 established the first global network of GLONASS tracking stations to exploit GLONASS. There has been a continuously operating global network of GLONASS tracking stations ever since. Subsequently, the International GPS Service (IGS) created a pilot project (IGLOS) with the objective of integrating GLONASS stations and GLONASS orbit computation into the IGS’s standard operations. The initial experiment and the follow-on pilot project were made possible by the availability of combined GPS-GLONASS geodetic-quality receivers and the existing IGS infrastructure for data communications, data storage and retrieval, and orbit computation. Over 50 stations comprise the GLONASS tracking network within the IGS. Four organizations now routinely compute precise GLONASS orbits, and a combined orbit product is generated as well. The precise orbit accuracy has reached the decimeter level. Time standardization, reference frames, file formats, and station logs are some of the areas that have been addressed to handle GLONASS and GPS in the same operations. This has been a very successful endeavor, and has allowed IGS to work through many of the issues involving combined GNSS operations and products. Although some problems still exist including the uneven global distribution of stations, the desire to have GLONASS adopt a realization of the International Terrestrial Reference Frame instead of the current PZ-90 reference frame, and a limited user community due to past uncertainty regarding the long-term viability of GLONASS, the IGLOS pilot project is providing timely data and products that can provide concrete benefits for a number of applications.