Work package leader :Philip Axe
Proudman Oceanographic Laboratory
Bidston Observatory
Birkenhead
CH64 9XB
United Kingdom
e-mail:
Philip Axe, philip.axe@umf.umu.se
Note: Phil has now moved to Umea University, Sweden, but is still willing to answer queries.
At present, monthly and annual mean sea-level data from many tide gauges
around the world are stored at the Permanent Service for Mean Sea-Level (PSMSL),
at the Proudman Oceanographic Laboratory (POL),
U.K. Between several countries, bilateral agreements have been made on
the exchange of real-time high frequency data. Agreement on the standardization of
procedures and rules for data storage and exchange are required, and the visibility
of sea level databanks needs improving.
This section describes the first
steps taken to identify the availability of hourly sea level data within the
European region (including non-EU states) and the willingness of national
sea-level collection agencies to exchange data.
The document is divided into the following sections:
To provide a solution to these problems within Europe, there is a need for
improved cooperation between the European sea level recording agencies, and also
between the agencies and the user community as a whole. It is an aim of this
work package to promote this cooperation.
The first step in this process was to review what sea level data was already
made available - and how that data could be accessed by interested parties. To
do this, a questionnaires were sent to sea level agencies around Europe. A
description of this questionnaire, and the survey results are available
here.
Click here
for the results of the survey into the availability of high
frequency sea level data around Europe
Given the aims of work packages 1 and 3, it was also desirable to know the extent to which sea level data had been levelled into a geocentric reference frame, by means of GPS, absolute gravimetry, or through co-location with instruments such as DORIS, PRARE, VLBI or SLR. A further questionnaire was sent to European geodetic agencies in December 1997 to obtain this information. The results of this questionnaire are available here:
A joint meeting of those interested in work packages 2 and 5 was held in Ostend, in November 1998. This demonstrated that there was uncertainty as to how many tide gauges were operated in Europe - particularly as many countries have several agencies interested in sea level recording, and had occasionally duplicated effort. To allow the members of Work Package 2 to make an assessment of which gauges were required to meet the project objectives, a further questionnaire was sent out in December 1998. A text version of this questionnaire can be browsed by clicking here.
The results of the questionnaire have been collated to form an online
'EOSS Station Handbook'.
This is analogous to the GLOSS Station Handbook (which may be browsed by
clicking here)
but covers gauges operated by European countries.
There are gaps in some of the records, where information has
not yet been made available. It is hoped to keep this record up to date with the
assistance of the data collection agencies.
Click here to go to the EOSS station
handbook
What sea level parameters need to be banked?
Raw sea level data are of little use unless accompanied by relevant meta-data.
In addition to information such as timings (and time zones), this means that
information on the type of gauge is required (for example, are
the data from a float gauge in a stilling well, from an acoustic gauge, from a
sub-surface pressure transducer etc). Each method has it's own limitations. Are
there density data available to convert the pressure information to surface
elevation? Is the stilling well level representative of the surrounding area, or
is it affected by strong tidal flows, density stratification, siltation?
Datum information is necessary - but then raises the question of the stability
of the datum point. Benchmark descriptions are needed in the meta-data, to allow
long term sea level records to be recovered. Where GPS or similar monitoring of
benchmark stability has taken place, there needs to be a reference or link to
this information. Finally, it is important that there is a contact point for
queries regarding the data, and links to any additional documentation that may
exist. The 'EOSS Station Handbook' is
intended to make this information accessible.
At present, sea level data are quality controlled and archived by the data
collection agency, and in most cases, by the national marine data centre.
Monthly mean sea level data from all gauges should be sent to the Permanent
Service for Mean Sea Level for entry into the global data base as part of its
obligation to ICSU. Hourly
(or higher frequency) data from GLOSS gauges should be sent to the Permanent
Service, and/or made available on a WWW/ftp server at the originating
laboratory (see Chapter 12 of the GLOSS Implementation Plan (op cit)
'Obligations of member states which are committed to GLOSS'
).
If EOSS improves the current situation in Europe with regard to data banking and
data exchange, in terms of making data more accessible to users, then the
current distributed data banking system should remain as it is. If the current
situation does not improve however, there is a case for creating a
regional data bank for all European sea level data.
The ideal solution to the distributed data collection system in Europe is to
have a single database, accessible from the WWW, with documented, quality
controlled data freely available in a single, agreed format.
High frequency (hourly and higher) sea level data is perceived as being a
commercially valuable product, and some sea level recording agencies are
unwilling to simply put data onto a server for academic use, for fear that
commercial organisations might steal the data, rather than approaching the
agency and paying the commercial fee. Many agencies have had their central budgets
reduced, and rely on the income generated from commercial contracts to support
the 'scientific' aspects of their work.
The concept of supplying data at minimum/no cost for academic study is generally
accepted however. Given that the data is of commercial value, the Ostend meeting
agreed that a license system should be adopted, whereby an academic user is
supplied with data after agreeing to certain conditions. The license pattern
adopted is that used by the British Oceanographic Data Centre, and a copy can be
read by clicking here.
It should be noted that the World Meterological Organisation Resolution 40 Annex
1 (
http://www.nws.noaa.gov/im/wmor40a1.htm) identifies 'all available in situ
observations from the marine environment' as being part of the minimum set that
national organisations should exchange (with other national organisations)
without charge or conditions of use. The Resolution does however require that
data supplied by one agency should not be used commercially without the data
originator's permission.
The reader is directed to the
WMO 40 web site for a more detailed discussion of these
problems.
The EOSS handbook contains a list of all the tide gauges in Europe (that are
known to EOSS). With each entry, there is the name, address, fax, telephone and
email of a contact person for that gauge. At present you must contact that
person individually. In future we would like to automate the system. Some data
may be available directly from the web. Where this is so, we have included a
link.
If you have any problems or questions, please contact
PSMSL (psmsl@pol.ac.uk)
UNESCO, 1997, Global Sea Level Observing System (GLOSS) Implementation Plan -
1997, IOC technical series No. 50
Open University, 1988, Waves, tides and shallow-water processes, Open University with
Pergamon Press, Milton Keynes, U.K.
Pugh, D.T. 1987, Tides, surges and mean sea level: a handbook for engineers and
scientists, Wiley, Chichester, U.K.
|
Colin Bray |
Peter Heinen |
Tor Tørressen |
|---|---|---|
|
Ordnance Survey Ireland |
Rijkswaterstaat |
Norwegian Hydrographic Service |
|
Serge Allain |
Igor Strojan |
Philip Axe |
|
EPSHOM |
Hidrometeoroloski Zavod Republike Slovenije |
Proudman Oceanographic Laboratory |
|
Rose Player |
Maria-Jesus Garcia |
Lesley Rickards |
|
Permanent Service for Mean Sea Level |
Instituto Espanol de Oceanografia (IEO) |
British Oceanographic Data Centre |
Click here to return to the EOSS home page.