CGPS@TG
Survey on Continuous GPS and Tide Gauge co-localisations
In order to get a better idea about the status and opportunities on continuous GPS positioning of tide gauges, a survey is carried out periodically within various geoscience communities. The survey aims at identifying the existing permanent GPS stations which are close to tide gauges (up to approximately 10-15 km).
The following table displays an on-line updated view of the CGPS@TG information that has been supplied to us so far : click here. The table can be sorted by clicking on the column items, and a version of the view can be downloaded in a format (csv) compatible with applications like excel.
A ’.kmz’ file provides a Google Earth view of the CGPS@TG geographical distribution. The cgpstg.kmz file is consistent with the above mentionned table (updated weekly). Clicking on a station symbol provides ancillary information on the station, and further clicking on the station name, provides an access to the so-called GPS sitelog (if the GPS data are available). The CGPS@TG ’kmz’ view might be useful in conjunction with the ’.kmz’ files of satellite radar altimetry ground tracks provided by CLS, or with the ’.kmz’ file of tide gauge records provided by the PSMSL.
In addition to the periodic surveys, information on CGPS@TG collocations can also be supplied to us any time by filling up this form. Thank you in advance for your collaboration.
GPS position time series and velocities
- ULR3 network (black dots are RF stations)
Several GPS solutions have been produced so far by the ULR analysis centre consortium as new analyses strategies were devised (models, parameterization,…). ULR contributes to the TIGA pilot project, and has recently joined the IGS first reprocessing campaign. Only the latest solution, published in Geophysical Research Letters journal (2009), is provided here, and briefly described below. A preliminary solution over a shorter data span was expressed in the ITRF2000 reference frame, and published in Global and Planetary Change journal (2007), whereas the latest published solution (called ULR3) is expressed in ITRF2005 over a longer period from January 1997 to November 2006.
Main features
Double-differenced ionosphere-free GPS carrier phase observations from a global network of 227 stations were analyzed using GAMIT software version 10.21 (160 were co-located with a tide gauge). Station coordinates, satellite orbits, Earth orientation parameters (EOPs), and zenith tropospheric delay parameters every 2 hours, were estimated. An important feature to outline is the use of absolute antenna phase centre corrections for satellites and receivers. The GAMIT solutions were loosely constrained global solutions. The final step combined weekly solutions over the entire data time span (station coordinates with full co-variances) into a long-term solution using CATREF sofware. This long-term solution (called ULR3) was aligned into the ITRF2005 using minimal constraints over all the transformation parameters with a selected set of IGS RF stations. A detailed description can be found in
Wöppelmann G., C. Letetrel, A. Santamaria, M-N. Bouin, X. Collilieux, Z. Altamimi, S.D.P. Williams, B. Martin Miguez (2009) : Rates of sea-level change over the past century in a geocentric reference frame. Geophys. Res. Lett., 36, L12607, doi:10.1029/2008GL038720.
Please cite this article if you find the results useful. More details on the GPS data processing strategy can be found in the IGS-like ULR analysis centre form associated with this solution too.
Solution data files
The ulr3_detrend.zip file contains individual station data files of weekly position time series residuals in ITRF2005 with respect to the linear long-term combined solution (given in the header in cartesian and geographic coordinates) at the central reference epoch. The format is straightforward. Residuals are expressed in metres in the local frame (North, East, and Up). The velocities are also provided in the header.
The cgpstg_ulr3.kmz file shows a Google Earth presentation of the above weekly data files by cliking on a station symbol. The associated IGS-like sitelog can be accessed too, as well as a view of the position time series in the vertical.
The cgpstg_ulr3table.txt provides the vertical GPS velocities and noise characteristics for the 180 stations fulfilling the criteria of 3.5 years of minimum length with more than 70% of valid data in the time series. Indeed, the errors given in the previous files are formal errors. To assign more realistic uncertainties on the GPS velocities, the noise content in the position time series was examined by the maximum likelihood estimation (MLE) technique using CATS software.