GNSS/GPS Velocity Documentation

Here you will find extended documentation (beyond our web services' API documentation) for our production web services.

GNSS/GPS Velocity Solutions

Expanded documentation describing parameter options for the GNSS/GPS velocity solutions web service is provided below. The parameter options are described in the following sections, for example ("analysisCenter") describes the Analysis Center options. The station velocity solution is based on analysis of the stations total long-term position time series. Station offsets due to earthquakes and equipment changes are estimated, and low-quality outliers (e.g., due to snow) are removed in order to generate long term secular velocity estimate solutions. Details regarding station velocities, including information on how they are generated by the GAGE Analysis Center Coordinator, are available from the GAGE GNSS Derived Products page [link] and from Herring et al. (2016).

• Station (“station”)

  The four character station identifier. Example: P201. “Station” is synonymous with “site”. The velocity solution is based on analysis of the station’s position time series.

• Analysis Centers (“analysisCenter”)

  GNSS/GPS site velocity solutions are generated by the GAGE Analysis Center Coordinator and are made available as PBO combined solutions (default), NMT Analysis Center solutions, or CWU Analysis Center solutions.

  The GAGE GNSS/GPS AC’s at New Mexico Tech (NMT) and Central Washington University (CWU) analyze data and generate products from more than 2,000 GNSS/GPS stations in the PBO, COCONet, TLALOCnet and SCIGN networks as well as NGS CORS and other regional stations in middle and eastern North America. The NMT AC uses GAMIT/GLOBK analysis software. The CWU AC uses GIPSY/OASIS analysis software. The GAGE GNSS/GPS Analysis Center Coordinator (ACC) at MIT generates a combination solution based on the individual NMT and CWU solutions. These three time series are referred to as PBO, NMT and CWU solutions, respectively, and correspond to the PBO, NMT and CWU AC parameter options in the web service. The combined “PBO” solutions are considered to the be standard GAGE data product.

• Reference Frame Information (“referenceFrame”)

  GNSS/GPS station velocities are available in different reference frames. The default frame is IGS08, the global reference frame based on ITRF2008. Solutions are also available in a North America fixed reference frame called NAM08, which is realized by rotating ITRF2008 to North America using the Euler vector published by Altimimi et al. (2012).

• Results Content ("report")

  Select the results content. "Long" will output all content from the source velocity file including cartesian and geodetic velocity components, reference coordinates and associated error estimates and covariances. The "short" (default) option will output a simplified version of the source file which only includes geodetic velocity components, reference coordinates, and the date range (“epochs”) over which the velocity is based.

• Solution Type ("solutionType")

  Select the type of velocity solution. Snapshot “snaps” (default) velocity solutions are generated on a monthly basis, while Final “final” velocity solutions are generated annually. Final solutions are based on a more computationally robust analysis method, but snapshot solutions are very close in quality. Because snapshot solutions are generated more frequently than final solutions, snapshot solutions may be available for more stations (e.g., new stations built since the last Final solution was generated) and may be affected by transient effects from recent geophysical phenomena (e.g., earthquakes, snow, etc.).

References

Herring, T. A., T. I. Melbourne, M. H. Murray, M. A. Floyd, W. M. Szeliga, R. W. King, D. A. Phillips, C. M. Puskas, M. Santillan, and L. Wang (2016), Plate Boundary Observatory and related networks: GPS data analysis methods and geodetic products, Rev. Geophys., 54, doi:10.1002/2016RG000529.

Altamimi, Z., L. Métivier, and X. Collilieux (2012), ITRF2008 plate motion model, J. Geophys. Res., 117, B07402, doi:10.1029/2011JB008930.

Acknowledgements and Attribution

The GAGE GNSS/GPS Analysis Centers process data from more than 2,000 GNSS/GPS stations. Most of these stations are operated by GAGE as part of the PBO, COCONet, TLALOCnet and smaller regional networks. Also processed are stations from the Southern California Integrated GPS Network (SCIGN), the NASA Global Geodetic Network (GGN), the International GNSS Service (IGS) network, the Rio Grande Rift network, the GPS Array for Mid America (GAMA), the Basin and Range Geodetic Network (BARGEN), the Idaho National Laboratory (INL) network, the Pacific Northwest Geodetic Array (PANGA), the Western Canada Deformation Array, SuomiNet, GulfNet, and stations near the epicenter of the 23 August 2011 M5.8 Mineral, VA earthquake. Data from GNSS/GPS stations not archived by GAGE are obtained from the NOAA National Geodetic Survey (NGS) Continuously Operating Reference Station (CORS) data center, the NASA Crustal Dynamics Data Information System (CDDIS), the U.S. Geological Survey, the Scripps Orbit and Permanent Array Center (SOPAC), and the International GNSS Service (IGS).