Transcript Linking GPS to Tide Gauges and Tide Gauge Benchmarks

Linking GPS to
Tide Gauges and Tide Gauge
Benchmarks
Tilo Schöne
GeoForschungsZentrum 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
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Workshop related issues
From Tide Gauges to cGPS@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
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history
Well maintained and with a stable local network of
benchmarks
Local water level changes only, even with ties to 1st
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 cGPS@TGs
IGS network:
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© IGSCB
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
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
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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
high-latency data is still a challenging task
GFZ-AC (IGS) versus GFZReprocessing
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MAC1 (GFZ-TIGA)
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Modified Julian Day
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EISL (GFZ-AC)
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Differences due to
Height change [m]
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• Software developments
• Better correction models
• Improved processing strategies
• More complete station coverage
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TIGA
Tide Gauge Benchmark
Monitoring Pilot Project
of the IGS
TIGA Pilot Project
• Initiated in 2001
• Goals are
– Establish, maintain and expand a global
cGPS@TG network
– Compute precise station parameters for the
cGPS@TG stations with a high latency
– Reprocess all previously collected GPS data at
cGPS@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 cGPS@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]
ITRF96
ITRF97
IGS00
TIGA Start
TIGA: Combination for 2002
Daniela Thaller, GFZ
TIGA: Combination for 2002
Daniela Thaller, GFZ
Lessons learned
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Station repeatability (7mm) 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
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Workshop related issues
Lessons learned
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(-)
• Solution becomes outdated (e.g. absolute pcv’s),
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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
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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
ITRF2005
• 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
cGPS@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
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– EUREF (etg)
– Geodätisches Forschungsinstitut München (dgf)
– GeoForschungsZentrum 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