Linking GPS to Linking GPS to Tide Gauges and Tide Tide Gauges and Tide Gauge BenchmarksGauge Benchmarks

Tilo SchöneTilo Schöne

GeoForschungsZentrum GeoForschungsZentrum PotsdamPotsdam

Understanding Sea-level Rise and Variability, WCRP Workshop,UNESCO, 6 - 9 June 2006, PARIS

Why the VerticalWhy the Vertical**

• Long-term stable and consistent frame Long-term stable and consistent frame to relate ALL globally distributed sea to relate ALL globally distributed sea level related measurementslevel related measurements

• Short-term control in earthquake-Short-term control in earthquake-prone areasprone areas

• Provide pointwise constraints for e.g. Provide pointwise constraints for e.g. uplift modelersuplift modelers

* Workshop related issues

From Tide Gauges to From Tide Gauges to cGPS@TGcGPS@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 GPSTide Gauges and GPS

• Tide gauges have a long technical and Tide gauges have a long technical and measurement historymeasurement history

• Well maintained and with a stable local Well maintained and with a stable local network of benchmarksnetwork of benchmarks

• Local water level changes only, even with ties Local water level changes only, even with ties to 1st order leveling networksto 1st order leveling networks

• Sea level and changes required in long-term Sea level and changes required in long-term stable global reference framesstable global reference frames

• GPS is the easy-to-use technique to GPS is the easy-to-use technique to solve for this problem, solve for this problem, butbut … …

IGS-GPS network and IGS-GPS network and cGPS@TGscGPS@TGs

IGS network:• Geographically balanced• Some clustering in populated

areas• Optimized point distances• Strict requirements on latency

(minutes to a few days)

cGPS@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

© IGSCB

However, the IGS is the best source for However, the IGS is the best source for GPS time series for many sitesGPS time series for many sites

Problems with IGS-Problems with IGS-solutionssolutionsand more generallyand more generally

• More tide gauges equipped with GPS than More tide gauges equipped with GPS than available within IGS (available within IGS (completenesscompleteness))

• Strict timeliness in GPS data provision (Strict timeliness in GPS data provision (latencylatency))

• Currently, accuracy and continuity of GPS time Currently, accuracy and continuity of GPS time series is limited (series is limited (accuracy of the verticalaccuracy of the vertical))

• Tide gauge / GPS operators are of different Tide gauge / GPS operators are of different agenciesagencies

• Frequent reprocessing of GPS and inclusion of Frequent reprocessing of GPS and inclusion of high-latency data is still a challenging taskhigh-latency data is still a challenging task

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KERG (GFZ-AC)

KERG (GFZ-TIGA)

GFZ-AC (IGS) versus GFZ-GFZ-AC (IGS) versus GFZ-ReprocessingReprocessing

Differences due to

•Software developments•Better correction models• Improved processing

strategies•More complete station

coverage

TIGATIGATide Gauge Benchmark Tide Gauge Benchmark

Monitoring Pilot Project Monitoring Pilot Project of the IGSof the IGS

TIGA Pilot ProjectTIGA Pilot Project

• Initiated in 2001Initiated in 2001

• Goals areGoals are– Establish, maintain and expand a global Establish, maintain and expand a global

cGPS@TG network cGPS@TG network – Compute precise station parameters for the Compute precise station parameters for the

cGPS@TG stations with a high latencycGPS@TG stations with a high latency– Reprocess all previously collected GPS data Reprocess all previously collected GPS data

at cGPS@TG stations, if possible back to 1993at cGPS@TG stations, if possible back to 1993– Promote the establishment of links to other Promote the establishment of links to other

geodetic sites which may contribute to geodetic sites which may contribute to vertical motion determination (DORIS, SLR, vertical motion determination (DORIS, SLR, VLBI, AG)VLBI, AG)

TIGA Pilot ProjectTIGA Pilot Project

• 102 out of 280 cGPS@TG stations 102 out of 280 cGPS@TG stations contributecontribute

• Processing latency 460 daysProcessing latency 460 days

• Six analysis centers provide solutionsSix analysis centers provide solutions

• Forward (since GPS week 1121) and Forward (since GPS week 1121) and backward processing on a best-effort basisbackward processing on a best-effort basis

• Backward processing to 1993Backward processing to 1993

• Preparations for the combination started at Preparations for the combination started at GFZ; will provide a combination solution on GFZ; will provide a combination solution on a regular basisa regular basis

CTA

DGFIULR

GeoscienceAustralia

EUREF

GFZ

TIGA NetworkTIGA Network

TOS fully accepted Proposed

GFZ: AC versus TIGAGFZ: AC versus TIGA

ITRF96 ITRF97 IGS00

TIGA StartTIGA Start

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TIGA: Combination for 2002TIGA: Combination for 2002

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Daniela Thaller, GFZ

TIGA: Combination for 2002TIGA: Combination for 2002

Daniela Thaller, GFZ

Lessons learned (+)Lessons learned (+)**

• Station repeatability (7mm) same level as IGSStation repeatability (7mm) same level as IGS

• Reduced height variability for the reprocessed Reduced height variability for the reprocessed datadata

• More consistent, no discontinuities at ITRF-More consistent, no discontinuities at ITRF-changeschanges

• High latency of processing allows more stations High latency of processing allows more stations to contribute to contribute

• Massive contribution to the new ITRFMassive contribution to the new ITRF

• Loading effects must be evaluated in detailLoading effects must be evaluated in detail

• Data useful for e.g. uplift modelersData useful for e.g. uplift modelers

* Workshop related issues

Lessons learned (-)Lessons learned (-)**

• Solution becomes outdated (e.g. absolute Solution becomes outdated (e.g. absolute pcv’s), but cleaned input data are keptpcv’s), but cleaned input data are kept

• No consolidated and agreed data base on No consolidated and agreed data base on station discontinuities is availablestation discontinuities is available

• Few areas are very little representedFew areas are very little represented

• Meta information (especially ties) are not Meta information (especially ties) are not well documented or updatedwell documented or updated

• Loading effects are affecting GPS time series Loading effects are affecting GPS time series different ashore and inlanddifferent ashore and inland

• Distance between GPS and TG benchmarks Distance between GPS and TG benchmarks are to large to be representative and are to large to be representative and accurateaccurate

* Workshop related issues

Schedule for TIGASchedule for TIGA• Starting Summer 2006, GFZ will provide a first Starting Summer 2006, GFZ will provide a first

set of coordinates/velocities for all TIGA sites set of coordinates/velocities for all TIGA sites based on a combined solution of the recent based on a combined solution of the recent reprocessingreprocessing

• Reprocessing with absolute pcv’s and based on Reprocessing with absolute pcv’s and based on ITRF2005ITRF2005

• Studies on optimal combination of TIGA solutionsStudies on optimal combination of TIGA solutions

• Independent checks of the results and Independent checks of the results and intercomparison to TG, AG (by the community)intercomparison to TG, AG (by the community)

• The goal is to turn TIGA into an IGS serviceThe goal is to turn TIGA into an IGS service

It’s a good time to open your It’s a good time to open your cGPS@TG’s now!cGPS@TG’s now!

What will you get from What will you get from us?us?• Coordinates and velocities (focus on Coordinates and velocities (focus on

the vertical) for the GPS sites at or the vertical) for the GPS sites at or near tide gauges (and other GPS near tide gauges (and other GPS sites)sites)

• Reference sitesReference sites

and when?and when?• End of 2006, beginning 2007End of 2006, beginning 2007

What do we need from What do we need from you?you?• Provision of GPS data at tide gauge Provision of GPS data at tide gauge

sites on a regular basissites on a regular basis

• Local ties between the GPS and tide Local ties between the GPS and tide gauge benchmarkgauge benchmark

• Maintenance of the “system”Maintenance of the “system”

•Feedback!Feedback!

Thanks toThanks to• the six analysis centersthe six analysis centers

– EUREF (etg)EUREF (etg)– Geodätisches Forschungsinstitut München (dgf)Geodätisches Forschungsinstitut München (dgf)– GeoForschungsZentrum Potsdam (gft)GeoForschungsZentrum Potsdam (gft)– Geoscience Australia (aut)Geoscience Australia (aut)– Universities Canberra, ANU, and Tasmania (cta)Universities Canberra, ANU, and Tasmania (cta)– University La Rochelle (ulr)University La Rochelle (ulr)

• the numerous operators of tide gauges and GPS the numerous operators of tide gauges and GPS stationsstations

• the surveyors carrying out the levelingthe surveyors carrying out the leveling

• the IGS for providing support and the the IGS for providing support and the infrastructureinfrastructure