Tide gauge measurements and satellite radar altimetry are the primary observation methods to study sea level change and sea level variations. Analysis of tide gauge measurements with the purpose of sea level change research requires a well defined vertical reference frame to separate apparent sea level changes from climate induced changes. Such a reference frame can be realized through precise positions of Global Navigation Satellite System (GNSS) stations located at or near tide gauges. Establishing such reference frame is one of the aims of the International GNSS Service Tide Gauge Benchmark Monitoring Pilot Project TIGA. The required accuracies are about 5-10 mm for station positions and less than 1 mm/year for vertical velocities.
GNSS data from more than 600 stations globally distributed are being processed at GFZ TIGA analysis centre using EPOS-Potsdam software (version 8) covering the time span from 1995 till end of 2012 using consistent models. Weekly coordinates of GNSS stations, vertical velocities, and daily values of the Earth Rotation Parameters (x and y pole coordinates and their rates, Length of Day) will be estimated. In addition, precise orbits and clocks are derived from a basic set of globally distributed stations. These data sets will be made public and contributes to the TIGA combination.