The ULR6a GPS solution is a preliminary version of the reanalysis of 19 years of GPS data from 1995 to 2014 that has been undertaken within the framework of the 2nd data reprocessing campaign of the International GNSS Service (IGS). Its associated vertical velocity field is expressed in ITRF2008.
Double-differenced ionosphere-free GPS carrier phase observations from a global network of 754 stations were reanalyzed using GAMIT/GLOBK software version 10.5. The data set covered the period January 1995 to December 2013. Station coordinates, satellite orbits, Earth orientation parameters (EOPs), and zenith tropospheric delay parameters every hour, were estimated. The data analysis strategy (models, corrections...) was compliant with the specifications adopted by the IGS for this reanalysis (more information here). Details can also be found in the IGS-like ULR analysis centre form associated with this solution.
The GPS velocities were obtained in the final step of the analysis which combined the daily GAMIT/GLOBK global network solutions (station coordinates with full co-variances) from the entire data time span into a long-term solution using CATREF software. This long-term solution (ULR6a) was aligned to ITRF2008 using minimal constraints over a selected set of IGS Reference Frame stations. A detailed description can be found in the reference below.
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 (Williams, 2008). Time series were detrended at the CATREF stage. Details on the GPS velocity uncertainty assessment are given in the reference below.
Vertical velocities table
The ULR6a_Vertical-Velocities_Table provides the vertical GPS velocities and uncertainties for the 493 stations fulfilling the criteria of 3 years of minimum length without discontinuities and with data gaps not exceeding 30%.
Daily time series
The ULR6_neu.zip file contains individual station data files of daily position time series in ITRF2008 with respect to the position at the reference epoch. These positions are expressed in meters in the local frame (North, East, and Up). The reference position and the 3D velocity in the local coordinate system (East, North, Up) are provided in the header of each file.
The ULR6a_discontinuities_Table.txt file provides the position offsets that were estimated.
The long-term solution ULR6a in SINEX format (567 Mo) can be downloaded too. However, we recommend its use only to those familiar with SINEX files, and having a good geodetic background and experience.
General information Access the data by clicking on the Download tab
Title: GPS Solution ULR6a
DOI identifier: 10.26166/sonel_ulr6a
Publisher: SONEL Data Center
Publication year: 2016
Temporal coverage: 1995-01-01 / 2014-12-31
Alvaro Santamaria-Gomez , Médéric Gravelle , Guy Wöppelmann 
Affiliation:  GET, Observatoire Midi-Pyrénées/CNRS/IRD/UPS, Toulouse, France.
 LIENSs, CNRS/ULR, La Rochelle, France.
GPS, tide gauge, vertical land movements
LIENSs, La Rochelle, France
IGN, Saint Mandé, France
La Rochelle Université, La Rochelle, France
Data use information
Citation: A. Santamaria-Gomez, M. Gravelle, G. Wöppelmann (2016): GPS Solution ULR6. SONEL Data Center. doi: 10.26166/sonel_ulr6a.
Use rights: The ULR6a solution is freely available to anyone. It is asked to all users to acknowledge the SONEL Data Centre in their research papers.
The ULR6a solution has taken part to the second reprocessing campaign of the International GNSS Service (IGS). It corresponds to 749 stations for which the entire dataset between 1995.0 and 2013.9 was reprocessed using the most up-to-date models and corrections available at that time.
First, daily solutions are computed through the adjustment of positions of the global network of stations, Earth Orientation parameters, satellite orbits and zenith tropospheric delays. This process results in global daily solutions that are expressed in their own (daily) terrestrial frame.
Then, the daily times series are obtained after the combination of these daily solutions. The velocities are estimated simultaneously of the mean station position, station position offsets and transformation parameters (translation, rotation and scale) for the alignment to a unique terrestrial reference frame (ITRF08). A minimum of three continuous years without an offset (e.g., due to an equipment change or an earthquake) in the time series were required to estimate a “robust” vertical velocity, leading to a fields of 498 vertical velocities, among which 322 are nearby a tide gauge (<15 km).
The formal uncertainty of the estimated velocities has been computed taking into account the time-correlated noise in the residual time series to make them as realistic as possible. The median uncertainty on the estimated vertical velocities is about 0.36 mm/year.
SONEL URL: http://www.sonel.org/
This solution has been proceeded thanks to the data provided by the Data Providers who collaborate with SONEL.
|Analysis center:||ULR||Number of stations:||674|
|Date of publication:||2016||Reference Frame||194|
|Time span:||1995.0 - 2013.9||Others||77|
|Reference Frame:||ITRF 2008|
|Estimated (robust) velocities:||493|
|Average of formal errors:||0.54 mm/yr|
|Median of formal errors:||0.36 mm/yr|
Santamaría-Gómez A., M. Gravelle, S. Dangendorf, M. Marcos, G. Spada, G. Wöppelmann (2017). Uncertainty of the 20th century sea-level rise due to vertical land motion errors. Earth and Planetary Science Letters, 473, 24-32.