Charter

Sea level changes are of great concern. For decades to centuries the sea level has been measured using tide gauges. However, they only constitute a local datum, affected not only by climate but also by local land height changes. Space geodetic techniques are the only viable tool to establish the necessary global reference frame. Providing this frame facilitates the distinction between the relative and geocentric referenced sea level changes by accounting for the vertical uplift of the station, and is, therefore, an important contribution to climate changes studies.

The goals of the IGS Tide Gauge Benchmark Monitoring – Working Group (TIGA-WG) is to analyze GNSS data from stations directly at or near tide gauges (TG) on a preferably continuous basis and provide information specifically for the vertical rates. TIGA is recognized by the Global Sea Level Observing System (GLOSS) to provide position and vertical rates for GLOSS tide gauges and is an important contribution of the IGS to the goals of the Global Geodetic Observing System (GGOS), the Global Climate Observing System (GCOS) and the World Climate Research Programme (WCRP).

The primary product of TIGA is daily sets of coordinates for analyzing vertical motions of Tide Gauge Benchmarks (TGBM). When sufficient solutions (3 or more) are available, a combination product of all available TIGA solutions will be generated. The products are made public to support and encourage other applications, e.g. sea level studies. The service may further contribute to the calibration of satellite altimeters, other oceanographic applications or the establishment of a World Height System.

Goals and Objectives

1. Maintain a global virtual cGNSS @ TG network
   • Select a set of tide gauges equipped with GNSS, with a long and reliable history, useful for both sea level change studies, and e.g. satellite altimeter calibrations. IGS network operation standards should be applied.
   • Promote the establishment of more continuous operating GNSS stations, in particular in the southern hemisphere.
   • Provide meta information, e.g. on levelling between benchmarks or data access
   • Provide training to tide gauge operators through workshops, encourage station operators to provide necessary metadata. Through GLOSS advice station operators about the operation of cGNSS @ TG stations.
2. Compute precise coordinates and velocities of GNSS stations at or near tide gauges with a delay of a few weeks to months, to allow as many as possible stations to participate. Provide a combined solution as the TIGA official product.
3. Study the impacts of corrections and new models on the GNSS processing of the vertical. Encourage other groups to establish, e.g. nearby absolute gravity sites.
4. Provide advice to new applications.

Organizational Structure

The Pilot Service is utilizing the existing infrastructure of the IGS as much as possible without disrupting standard activities. The processing of GNSS data is performed outside the IGS processing stream, but may be carried out by existing IGS AC’s. A number of TIGA Analysis Centers (TAC) provides daily or weekly solutions using the IGS processing standards. The TIGA network will include stations (TIGA Observing Stations, TOS) that meet IGS network requirements and are collocated with the tide gauges. The time lag for providing GNSS data will be less stringent compared to standard IGS operations, to allow also remote stations to participate. IGS, other IAG Services or Groups, GLOSS and the PSMSL may propose and advice on the inclusion of additional TOS stations.

[Last updated January 2013]