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
· 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.
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.
Current Membership:
Workplan 2011-2012
-
Provide a product based on the most recent
reprocessing, with
o mean rate per TOS with reliable error estimates
o time series of the vertical with scaled formal errors
o full SINEX combined product
-
Prepare the next reprocessing campaign
-
Work with GLOSS on the improvement of the network
situation
-
Maintain and expand the current inventory of GNSS @ TG
stations at www.sonel.org
-
Encourage station operators through GLOSS to provide
regular leveling between benchmarks
-
Setup a data base for station discontinuities (IGS
SINEX discontinuity file for non-IGS TIGA stations)
-
Study the effect of applying atmospheric loading
correction to GNSS on the measurement level in the tide gauge / sea level
context
-
Work with COST Action ES0701 on the “Detection
of Offsets in GNSS timeseries Experiment (DOGEx)”
Last
edited: 26 November 2010, established April 2001