Report by the Permanent Service for Mean Sea Level (PSMSL)
for the Period 1995-99 to the XXII General Assembly
of the IUGG, Birmingham, July 1999

Philip L. Woodworth
Director, Permanent Service for Mean Sea Level
Proudman Oceanographic Laboratory, Bidston Observatory
Birkenhead, Merseyside CH43 7RA, United Kingdom

1. Introduction

This report reviews briefly the work of the Permanent Service for Mean Sea Level (PSMSL) during 1995-99. In this period, the PSMSL has data banked a record amount of sea level information, has taken a major role in the development of the Global Sea Level Observing System (GLOSS), and has contributed to important international working groups on climate change and geophysics.

The PSMSL is operated at the Proudman Oceanographic Laboratory (POL), Bidston Observatory under the auspices of the International Council of Scientific Unions, and is a member of the Federation of Astronomical and Geophysical Data Analysis Services (FAGS). The PSMSL reports to the International Association for the Physical Sciences of the Ocean Commission on Mean Sea Level and Tides (IAPSO/CMSLT) and has an Advisory Board consisting of scientists expert in each area of sea level research. Annual reports on the work of the PSMSL are circulated each year to the International Association of Geodesy (IAG), the Intergovernmental Oceanographic Commission (IOC), IAPSO, FAGS, and other relevant bodies and are available publicly via the web at:

This same web page also serves as a source of PSMSL data and ancillary information. Copies of PSMSL data can also be provided via ftp and on CD-ROM and other media.

2. PSMSL Data Receipts for 1995-99

On average, approximately 2000 station-years of data were entered into the PSMSL database during each year of the period. This compares well to rates obtained in previous years. It is particularly gratifying that receipts are now obtained routinely from virtually every corner of the globe, thanks to a large extent to GLOSS and World Ocean Circulation Experiment (WOCE) activities, but also thanks to the generally improving ease of worldwide communications. Figure 1 indicates the locations from which data were received during 1995-99.

3. GLOSS Activities

The Global Sea Level Observing System (GLOSS) is an IOC project, one of the aims of which is to improve the quality and quantity of data supplied to the PSMSL. GLOSS can be considered as one of the first components of the Global Ocean Observing System (GOOS). The PSMSL has taken the lead role in the development of GLOSS with the PSMSL Director (first Dr. David Pugh then Dr. Philip Woodworth) also being GLOSS Chairman. Two major GLOSS Experts meetings (in Pasadena, USA in 1997 and Toulouse, France in 1999) were organised during the period with 'mini-GLOSS meetings' in between.

A particularly important task during the period was the construction of a new Implementation Plan for GLOSS prepared by the PSMSL with contributions from many sea level scientists. The Plan was subsequently presented for endorsement by the 19th Session of the IOC Assembly at UNESCO House in Paris in July 1997, and was printed and circulated by IOC in 1998.

3.1 GLOSS Status

Each year the PSMSL has provided a summary of the status of GLOSS from its viewpoint, the most recent of which can be inspected via:

In brief, GLOSS can be considered approximately two-thirds operational, if one uses data receipts by the PSMSL as a guide to operational status. However, the overall status is somewhat better than that. At some gauge locations (e.g. Tristan da Cunha and some Antarctic sites), the gauges take the form of simple pressure transducers which provide useful information for oceanography (e.g. for WOCE) but which do not supply MSL data, as conventionally defined, which can subsequently be submitted to the PSMSL. This situation is understandable and tolerable if there are good environmental or technical reasons for such a choice of technology. At other locations, while a perfectly good gauge might exist and be providing data of some kind, the expertise or facilities or manpower do not exist in order to process those data routinely and deliver them to the international community. This situation is not an acceptable one, as it clearly requires some kind of investment in hardware, software or training. The job of IOC/GLOSS and of the PSMSL is to remedy such situations as far as possible and to improve GLOSS status as far as possible.

3.2 GLOSS Training Courses, Training Materials and Training Placements

The PSMSL took the lead in the organisation of four GLOSS training courses in this period at Dehra Dun, India (1995), Buenos Aires, Argentina (1996), POL, UK (1997) and Cape Town, South Africa (1998). A further course is planned for Sao Paulo, Brazil in late 1999. Each of these course concerned themselves with background sea level science (climate change, oceanography), the need for related geodetic measurements, and 'hands on training sessions' (HOTS).

The widely-used PSMSL/POL Tidal Analysis Software Kit (TASK) was extended and updated during 1998, particularly with regard to year 2000 compliance. The package is available free to any university or research institute scientist, with a small fee charged to commercial users.

Training materials continued to be made available to the community by means of CD-ROM, and a training web page is planned for 1999, accessible from the same pages as given above.

In 1996, the British Council funded an Indian scientist (Mr. C.Biswas of the Survey of India) to visit and study tide gauge techniques at POL. This successful visit followed that of another Indian scientist (Dr. Antony Joseph) from the National Institute of Oceanography the previous year. Consultations have taken place with colleagues from Viet Nam and Ghana with regard to collaborative gauge installations in those countries.

3.3 GLOSS Newsletters

The PSMSL publishes a newsletter for the GLOSS community called the GLOSS Bulletin which can found on the web at:

An updated two page brochure advertising GLOSS has also been produced by the PSMSL. Two thousand copies were printed for circulation in the UK and we hope that GLOSS National and Regional Contacts will arrange for printing in their own countries. Copies of the files which make up the brochure (Corel Draw files) may be sent to anyone interested who can edit and adapt them according to local interests.

3.4 GLOSS Handbook and the WOCE Sea Level CD-ROM

In preparation for the International WOCE Conference in Halifax, Canada in May 1998, the PSMSL and the British Oceanographic Data Centre (BODC) published a new CD-ROM containing WOCE Sea Level Centre data sets together with an updated version of the GLOSS Handbook product and the PSMSL data set. Copies have been distributed widely. In addition, the updated GLOSS Handbook can be inspected via the above GLOSS web page.

4. Geodetic Fixing of Tide Gauge Benchmarks

A major development with regard to tide gauge benchmark fixing has been the establishment of the International GPS Service for Geodynamics (IGS). In March 1997, a meeting on tide gauge benchmark fixing was held at the Jet Propulsion Laboratory, prior to a meeting of the GLOSS Experts. This meeting was organised jointly by the IGS Central Bureau (Director, Dr. Ruth Neilan), the PSMSL and IOC/GLOSS and resulted in an excellent workshop report on the use of GPS at gauge sites for measuring long term changes in vertical land movements and for altimeter calibration. In May 1999, a follow-up meeting was held at Toulouse, France, also alongside a GLOSS meeting, with plans for a Manual on ‘How to Operate GPS at Gauges’ put in place for probable publication in 1999.

5. Scientific Study Groups

5.1 Intergovernmental Panel on Climate Change ( IPCC) Third Assessment Report

The third scientific assessment of the Intergovernmental Panel on Climate Change (IPCC) commenced with a meeting in Bad Munstereifel, Germany at the end of the June 1998 and with a first drafting session in Paris in December. At the Bad Munstereifel meeting, there was considerable discussion as to whether there should be a dedicated sea level chapter and working group, as for the second assessment. In the end, the conclusion was that there should be, and the following people were eventually delegated to act as Lead Authors:

John Church		CSIRO Marine Research, Australia (Joint Coordinator)
Jonathan Gregory	Hadley Centre, UK (Joint Coordinator)
Philippe Huybrechts	Free University of Brussels, Belgium
Michael Kuhn		University of Innsbruck, Austria
Kurt Lambeck		Australian National University
Dahe Qin		Chinese Academy of Sciences
Philip Woodworth	Proudman Oceanographic Laboratory, UK and PSMSL
The latter's role in this is, of course, to provide some linkage to GLOSS and the PSMSL. The December IPCC meeting was followed by the first International CLIVAR (Climate Variability and Prediction) Conference, also held in Paris.

5.2 Tidal Science '96

A meeting entitled Tidal Science '96 was held at the Royal Society in October of that year to celebrate Dr. David Cartwright's seventieth birthday and also the major advances in global tide modelling during the last decade, largely thanks to the availability of TOPEX/POSEIDON data. Papers stemming from the meeting were published in a special issue of Progress in Oceanography (Volume 40, Numbers 1-4) during 1998 with Dr. Richard Ray (Goddard Space Flight Center) and Dr. Philip Woodworth (PSMSL Director) acting as editors.

5.3 Altimetry and Gravity Field Activities

Participation has continued in European and US altimeter working groups with PSMSL-related scientists becoming Principal Investigators for the JASON (TOPEX/POSEIDON Follow On) mission during the period, and Co-Investigators for the Envisat mission of the European Space Agency (ESA). PSMSL-related scientists have also become members of the Mission Advisory Group (MAG) of the ESA Gravity Field and Steady State Ocean Circulation Experiment (GOCE) mission, which is now at the end of the Phase-A development stage, and of the US/German Gravity Recovery And Climate Experiment (GRACE). The provision of a more precise model of the Earth's gravity field and geoid is of great importance to a range of oceanographic and geophysical studies which impact on sea level research.


Many people interested in tide gauges and altimetry will also be interested in bottom pressure measurements. Dr. Chris Hughes from POL has recently taken a lead in trying to get global bottom pressure measurements and data sets on a better footing, providing potentially a component of GOOS parallel to GLOSS. He calls this activity GLOUP. For more information, see:

It is intended that this activity will be discussed at a business meeting of the IAPSO/CMSLT during the IUGG General Assembly . If approved, this activity will formally be managed by the PSMSL and will encompass the data collection of pelagic tidal constants which the PSMSL has been responsible to the Commission for during the last decade.

7. UK and European Projects

During the period, POL and PSMSL contributed strongly to a UK proposal for a large 'thematic' programme of research into sea level changes. This proposal was highly graded by the UK Natural Environment Research Council with decisions on ultimate funding expected later in 1999.

A European Union (EU) funded sea level study called SELF-2 for the Mediterranean took place during the period with POL participation, with concentration at POL on mean sea level changes, storm surge modelling, absolute gravity and tidal loading. Consultations and site visits also took place with colleagues in Greece with regard to collaborative upgrading of the Greek tide gauge sites. The EU EOSS project (formerly called NOSS) aims to enhance sea level (tide gauges) and land level (GPS) monitoring, and associated data exchange, in Europe primarily by sets of bilateral (i.e. no new cost) agreements. First activities in this five year project have centred around the North Sea, where most of the countries which have so far signed up to the project commitments are located. Mr. Philip Axe from POL has taken the lead in informing the EOSS group of the activities in PSMSL and GLOSS and in leading Work Package 5 which is associated with data exchange issues. Philip has also attended all twice-yearly Management Meetings. In addition, several other PSMSL-related POL staff have contributed to EOSS activities during the period. It is to be hoped that EOSS will result in the more reliable provision of sea and land level information from the European region. More information on EOSS can be obtained at:

8. Publicity

The PSMSL has endeavoured to publicise sea level data and their use as often as possible through brochures, web pages, newspaper and TV articles, seminars etc. Open Days took place at POL (including PSMSL) on several occasions during the period, attended by approximately 2000 members of the public on each occasion, as well as local dignitaries and Members of Parliament.

9. PSMSL/WOCE Centre Staffing

The PSMSL was joined at the start of 1997 by Mr. Philip Axe from the University of Plymouth. Philip has recently finished his Ph.D studies on coastal processes in the south of England. His main duties at the PSMSL and WOCE Centre include the bringing up to date of several WOCE-related sea level data sets, overlaps with the various European and global GPS/tide gauge activities, and of course scientific analysis of the data.

10. Meetings and Visitors

Many scientific meetings have been attended over the period and a large number of scientists and others interested in sea level research have visited the PSMSL. Summaries of meetings and visitors each year can be found in the PSMSL Annual Reports.


It can be seen that 1995-99 has been a further active period with regard to important workshops and conferences, and a busy one with regard to data acquisition and analysis.

Particular thanks as usual go to Elaine Spencer who has been PSMSL Technical Secretary since 1974. The PSMSL is very much her data set. Unfortunately, both Elaine and her husband Bob, who will be well known to a number of PSMSL/GLOSS people though his deployments of tide gauges and bottom pressure recorders, decided to take early retirement in May 1999. I am sure that the sincere thanks and best wishes of the sea level community will be extended to them both.

P.L.Woodworth (July 1999)


Prof. Paul Paquet, President Federation of Astronomical and Geophysical Data Analysis Services (FAGS)
Dr. Niels Andersen, Secretary FAGS
Dr. Patricio Bernal, Secretary Intergovernmental Oceanographic Commission (IOC)
Dr. Colin Summerhayes, Director GOOS Office IOC
Dr. Thorkild Aarup, GLOSS Technical Secretary IOC
Prof. Jacquie McGlade, Director Centre for Coastal and Marine Sciences (CCMS)
Dr. Ed Hill, Director CCMS Proudman Oceanographic Laboratory (POL)
Dr. Christian Le Provost, President IAPSO Commission MSL and Tides
Dr. Martine Feisel, Institut Geographique National, France (for IAG)

PSMSL Advisory Group:
Dr. Ruth Neilan, Jet Propulsion Laboratory, USA
Dr. Gary Mitchum, University of South Florida, USA
Prof. Bruce Douglas, University of Maryland, USA
Dr. Richard Warrick, University of Waikato, New Zealand
Dr. David Pugh, Southampton Oceanography Centre, UK
Dr .Georges Balmino, Bureau Gravimetrique International, Toulouse, France