IGS Analysis Center Coordinator (ACC) at NOAA/NGS

General Information About the IGS Products

This site gives information about the products of the International GNSS Service (IGS), especially their quality. This introductory page provides general background information. Most of the other pages here contain figures and tables summarizing the results from the IGS product combinations. Those pages are mainly of interest to the IGS Analysis Centers and other GNSS specialists.

The tables and figures for the Final products are updated weekly. Other pages are updated shortly after the corresponding combinations. The figures show the results of the past 60 weeks except for the "Final (ALL)" plots which show the results of the IGS orbit combinations since their beginning in late 1993.

The IGS Analysis Center Coordinator (ACC) has overall responsibility for generating the main official IGS combined products. Currently, there are three IGS product lines for GNSS satellite orbits and clocks, namely the IGS Final, the IGS Rapid, and the IGS Ultra-rapid products. During the periods 2008-2011 and 2012-2015, the IGS ACC functions are performed by NOAA's National Geodetic Survey (NGS) in Silver Spring, Maryland, USA. During previous periods, the ACC functions were performed by the GeoForschnungsZentrum (GFZ Department 1) in Potsdam, Germany (2003-2008), Center for Orbit Determination in Europe (CODE) in Bern, Switzerland and Vienna, Austria (1999-2003), and Natural Resources Canada (NRC) in Ottawa, Canada (1994-1998).

Certain IGS product combination tasks are shared. For the Final products, those components involving the terrestrial reference frame, including the Earth rotation parameters, are produced by a combination of SINEX file submissions, work done at Natural Resources Canada in Ottawa, Ontario, Canada, through January 2010 and done since that time at Institut Géographique National in Paris, France. The internally realized timescales of the IGS, formed by a weighted ensemble of the frequency standards available in the IGS clock products, are maintained by the Naval Research Laboratory, Space Applications Branch, in Washington, DC, USA. Such high-stability timescales are supported for the IGS Rapid and Final products.

The available IGS products are:

IGS Final products (IGS)
The IGS Final products have the highest quality and internal consistency of all IGS products. They are made available on a weekly basis, by each Friday, with a delay up to 13 (for the last day of the week) to 20 (for the first day of the week) days. The IGS Final products are the basis for the IGS reference frame and are intended for those applications demanding high consistency and quality.
IGS Rapid products (IGR)
The IGS Rapid products have a quality nearly comparable to that of the Final products. They are made available on a daily basis with a delay of about 17 hours after the end of the previous observation day; i.e., the IGS Rapid products are released daily at about 17:00 UTC. For most applications the user of IGS products will not notice any significant differences between results obtained using the IGS Final and the IGS Rapid products.
IGS Ultra-rapid products (IGU)
To reduce the age of the prior, discontinued Predicted orbits, the IGS started the Ultra-rapid products officially week 1087, in November 2000. Like the former IGS Predicted products, the Ultra-rapid products are available for real time and near real time use. The Ultra-rapid products are released four times per day, at 03:00, 09:00, 15:00, and 21:00 UTC. (Until week 1267 they were released twice daily.) In this way the average age of the predictions is reduced to 6 hours (compared to 36 hours for the old IGS Predicted products and 9 hours for the twice-daily Ultra-rapids). The shorter latency should lead to significantly improved orbit predictions and reduced errors for user applications. Contrary to all other IGS orbit products the IGS Ultra-rapid orbit files contain 48 hours of tabulated orbital ephemerides, and the start/stop epochs continuously shift by 6 hours with each update. All other orbit products contain strictly the 24 hours from 00:00 to 23:45. The first 24 hours of each IGS Ultra-rapid orbit are based on the most recent GPS observational data from the IGS hourly tracking network. At the time of release, the observed orbits have an initial latency of 3 hours. The next 24 hours of each file are predicted orbits, extrapolated from the observed orbits. The orbits within each Ultra-rapid product file are, however, continuous at the boundary between the observed and predicted parts. Normally, the predicted orbits between 3 and 9 hours into the second half of each Ultra-rapid orbit file are most relevant for true real time applications.

Where to get more information about the IGS?

For more information about the International GNSS Service please visit the IGS Central Bureau, which is located at the Jet Propulsion Laboratory in Pasadena, California, USA.

IGS Central Bureau (IGSCB)

Some especially helpful IGSCB pages:

Where and when to get IGS products?

For product archive locations at the IGS Global Data Centers please refer to the information in the link below.

How to use IGS products?

The links below address some frequently asked questions regarding the generation and use of IGS products.

General IGS Product Information

Miscellaneous advice and information for ACs

21 February 2013, originator IGS ACC