This site gives information about a subset of products of the International GNSS Service (IGS): final , Earth Rotation Parameters (ERPs) and coordinates of the apparent geocenter. This introductory page provides general background information.
The IGS collects data from a global network of more than 400 permanent GNSS stations. Ten Analysis Centers (ACs) routinely generate various products from these data. The Analysis Center Coordinator (ACC) has overall responsibility for generating the main official IGS combined products from the AC products.
The combination of the IGS final products, performed on a weekly basis, involves two main steps :
- Products related to the terrestrial frame, including ERPs, are obtained by a combination of SINEX files submitted by the ACs. This work is the main task of the IGS Reference Frame Working Group (RFWG). It has been performed at Natural Resources Canada until January 2010 and was then taken on by the Institut Géographique National.
This site is dedicated to that particular set of products.
- Satellite orbits and clocks are then combined by the ACC (NOAA’s National Geodetic Survey since 2008).
Each week, nine IGS ACs submit SINEX solutions including station positions, daily ERPs and the full covariance matrix. These solutions are combined in a standard least-squares adjustment to form the IGS weekly combined solutions.
Those include :
- weekly combined station positions,
- daily combined ERP,
- weekly coordinates of the apparent geocenter.
Independent combinations of the AC SINEX solutions are also performed by two Global Network Associate Analysis Centers (GNAACs). They are used for comparison and validation of the IGS SINEX combination.
The combined solution for week N is made available on Thursday of week N+2 (delay of 12 days for the last day of the week to 18 days for the first day of the week). The latest combination covered GPS week 2261.
Besides the weekly combined solutions, a long-term cumulative solution is updated and released each week. In that solution, a piecewise linear (position+velocity) model is used to describe station motions. It is obtained by stacking the weekly combined solutions in a standard least-squares adjustment. The residuals of this stacking are of particular interest since they depict non-linear station motions.
IGS Reference Frames
Another task of the RFWG is the definition and maintenance of the Terrestrial Reference Frames used by the IGS. Those are of particular importance since they form the base to which all IGS products are referred. Their long-term stability is especially vital for the consistency and stability of the IGS products.
The latest IGS Reference Frame, IGS08, came in use on GPS week 1632 (17th April 2011). It was derived from the latest release of the International Terrestrial Reference Frame, ITRF2008. For a complete chronology of the IGS Reference Frames, see ACC-IGS-FRAMES.
ACs & GNAACs contrib. to the SINEX combinations
- COD: Centre for Orbit Determination in Europe, Switzerland
- EMR: Natural Resources Canada, Canada
- ESA: European Space Operation Centre, Germany
- GFZ: GeoForschungsZentrum, Germany
- GRG: Groupe de Recherche en Géodésie Spatiale, France
- JPL : Jet Propulsion Laboratory, USA
- MIT: Massachusetts Institute of Technology, USA
- NGS: National Geodetic Survey, USA
- SIO: Scripps Institution of Oceanography, USA
- MIG: Massachusetts Institute of Technology, USA
- NCL: University of Newcastle-upon-Tyne, UK
Other ACs contributing to reprocessing activities
- GT1: GeoForschungsZentrum, Germany
- PD1: Potsdam-Dresden Reprocessing, Germany
- UL1: Université de la Rochelle, France
In the following, “yy” stands for the 2-digit year number, “wwww” for the GPS week and “ww” for the week number in the year :
- igsyyPwwww.snx: Weekly combined solution
- igsyyPwwww.ssc: Weekly combined solution without covariance matrix
- igsyyPwwww.erp: Weekly combined ERPs
- igsyyPwwww.res: Residuals between AC solutions and weekly combined solution
- igsyyPwwww.itr: Residuals between AC solutions and IGS Reference Frame
- igsyyPwwww.sum: Combination summary
- IGSyyPww.snx: Cumulative solution
- IGSyyPww.ssc: Cumulative solution without covariance matrix
- IGSyyPww.res: Residuals between AC solutions and cumulative solution
These official products are available at the IGS Global Data Centres :
- CDDIS (Maryland, USA): ftp://cddis.gsfc.nasa.gov/gps/products
- ENSG (France): ftp://igs.ensg.eu/pub/products
- IGN (France): ftp://igs.ign.fr/pub/products
- KASI (Korea): ftp://nfs.kasi.re.kr/gps/products
- SOPAC (California, USA): ftp://garner.ucsd.edu/pub/products
Other by-products of the SINEX combinations, such as time series of coordinates, residuals and statistics are available from this website, or directly at :
- ENSG (France): ftp://igs-rf.ensg.eu/pub
- IGN (France): ftp://igs-rf.ign.fr/pub