The IGS Tide Gauge Benchmark Monitoring Project
Sea level is a very sensitive parameter to natural and human-driven climate related changes. For more than a century tide gauges (TGs) have been the most important measuring devices for the sea level. Today radar altimetry (RA) gives highly precise global measurements of the actual sea level and sea level changes. However, TG measurements remain a valuable tool, e.g. as a time series by itself or as a reference data set for RA monitoring.
One limiting factor for using TGs is the globally uneven distribution of TG measurements and the stability of the TG benchmark (TGBM). Both are accuracy-degrading for sea level studies. For RA calibration this fact will map in a global uncertainty and geographically correlated errors, especially in the long-term and for older missions.
The International GPS Service (IGS) plays a significant role in promoting, establishing and the densification of a global reference system by GPS. Moreover, coordinates published and distributed by the IGS are used in numerous scientific applications, ranging from plate tectonic studies to atmospheric sounding. In contrast, since the beginning of the GPS era several studies have revealed the uncertainty in the GPS height component. Especially when studying sea level changes, where the GPS height of the benchmark is used for defining an absolute sea level datum, problems occur when correcting the time series for height changes of the TGBM.
To overcome this problem and to demonstrate IGS's capability to provide products also for the sea level research, in 2001 the IGS Tide Gauge Benchmark Monitoring Pilot Project (TIGA-PP) was initiated. The primary product of the service will be time series of coordinates for analyzing vertical motions of TGBMs. Different Analysis Centers are providing weekly solutions for selected GPS stations near TGs on a continuous basis. Currently efforts are being made to establish a combination center at GFZ in order to provide a consistent data set of height time series for further analysis and combination with tide gauge records.
For up-to-date information about TIGA see the WEB page at http://op.gfz-potsdam.de/tiga.