Linking GPS to Tide Gauges and Tide Gauge
- Slides: 20
Linking GPS to Tide Gauges and Tide Gauge Benchmarks Tilo Schöne Geo. Forschungs. Zentrum Potsdam Understanding Sea-level Rise and Variability, WCRP Workshop, UNESCO, 6 - 9 June 2006, PARIS
Why the * Vertical • Long-term stable and consistent frame to relate ALL globally distributed sea level related measurements • Short-term control in earthquake-prone areas • Provide pointwise constraints for e. g. uplift modelers * Workshop related issues
From Tide Gauges to c. GPS@TG • First (known) continuous measurements in Europe by the Royal Society of London (founded in 1660) • Description of a “floating tide gauge device” by Athanasius Kircher in the horologium aestus marini (around 1665) • After 1880 increase in number of tide gauges • … • After 1980 the GPS system was developed • Since 2000 increase in number of GPS equipped tide gauges
Tide Gauges and GPS • Tide gauges have a long technical and measurement • • • history Well maintained and with a stable local network of benchmarks Local water level changes only, even with ties to 1 st order leveling networks Sea level and changes required in long-term stable global reference frames • GPS is the easy-to-use technique to solve for this problem, but …
IGS-GPS network and c. GPS@TGs IGS network: • • © IGSCB Geographically balanced Some clustering in populated areas Optimized point distances Strict requirements on latency (minutes to a few days) c. GPS@TG: • Sites along coastlines • Many clusters in Europe, Japan, USA • Short GPS baselines, sometimes multiple receivers at one site • Many remote and manually operated sites However, the IGS is the best source for GPS time series for many sites
Problems with IGS-solutions and more generally • More tide gauges equipped with GPS than available • • within IGS (completeness) Strict timeliness in GPS data provision (latency) Currently, accuracy and continuity of GPS time series is limited (accuracy of the vertical) Tide gauge / GPS operators are of different agencies Frequent reprocessing of GPS and inclusion of highlatency data is still a challenging task
GFZ-AC (IGS) versus GFZReprocessing Differences due to • Software developments • Better correction models • Improved processing strategies • More complete station coverage
TIGA Tide Gauge Benchmark Monitoring Pilot Project of the IGS
TIGA Pilot Project • Initiated in 2001 • Goals are – Establish, maintain and expand a global c. GPS@TG network – Compute precise station parameters for the c. GPS@TG stations with a high latency – Reprocess all previously collected GPS data at c. GPS@TG stations, if possible back to 1993 – Promote the establishment of links to other geodetic sites which may contribute to vertical motion determination (DORIS, SLR, VLBI, AG)
TIGA Pilot Project • 102 out of 280 c. GPS@TG stations contribute • Processing latency 460 days • Six analysis centers provide solutions • Forward (since GPS week 1121) and backward processing on a best-effort basis • Backward processing to 1993 • Preparations for the combination started at GFZ; will provide a combination solution on a regular basis
TIGA Network Geoscience Australia TOS fully accepted Proposed CTA EUREF DGFI GFZ ULR
GFZ: AC versus TIGA RMS North/East/Height Residuals [mm] ITRF 96 ITRF 97 IGS 00 TIGA Start
m m 3 < < 3 m m < 7 m m TIGA: Combination for 2002 Daniela Thaller, GFZ
TIGA: Combination for 2002 Daniela Thaller, GFZ
Lessons learned (+)* • • Station repeatability (7 mm) same level as IGS Reduced height variability for the reprocessed data More consistent, no discontinuities at ITRF-changes High latency of processing allows more stations to contribute Massive contribution to the new ITRF Loading effects must be evaluated in detail Data useful for e. g. uplift modelers * Workshop related issues
Lessons learned (-)* • Solution becomes outdated (e. g. absolute pcv’s), • • • but cleaned input data are kept No consolidated and agreed data base on station discontinuities is available Few areas are very little represented Meta information (especially ties) are not well documented or updated Loading effects are affecting GPS time series different ashore and inland Distance between GPS and TG benchmarks are to large to be representative and accurate * Workshop related issues
Schedule for TIGA • Starting Summer 2006, GFZ will provide a first set of coordinates/velocities for all TIGA sites based on a combined solution of the recent reprocessing • Reprocessing with absolute pcv’s and based on ITRF 2005 • Studies on optimal combination of TIGA solutions • Independent checks of the results and intercomparison to TG, AG (by the community) • The goal is to turn TIGA into an IGS service It’s a good time to open your c. GPS@TG’s now!
What will you get from us? • Coordinates and velocities (focus on the vertical) for the GPS sites at or near tide gauges (and other GPS sites) • Reference sites and when? • End of 2006, beginning 2007
What do we need from you? • Provision of GPS data at tide gauge sites on a regular basis • Local ties between the GPS and tide gauge benchmark • Maintenance of the “system” • Feedback!
Thanks to • the six analysis centers • • – EUREF (etg) – Geodätisches Forschungsinstitut München (dgf) – Geo. Forschungs. Zentrum Potsdam (gft) – Geoscience Australia (aut) – Universities Canberra, ANU, and Tasmania (cta) – University La Rochelle (ulr) the numerous operators of tide gauges and GPS stations the surveyors carrying out the leveling • the IGS for providing support and the infrastructure
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