Short Report of the Meeting of GLOSS Experts in Bordeaux February 1995

Dr.Albert Tolkatchev
Intergovernmental Oceanographic Commission

The GLOSS Group of Experts (GE) is a small group of scientists and tide gauge experts which meets approximately every two years under the auspices of the IOC-coordinated GLOSS project. The Chairman of the GE is David Pugh. The following is a short report of the meeting. A more detailed version can be obtained from Albert Tolkatchev at IOC

IOC Group of Experts on GLOSS Reviews the Status and Future Development of GLOSS

The Group of experts on GLOSS met in Bordeaux from 1 to 3 February 1995. The session was chaired by Dr.David Pugh, Chairman of the Group of Experts. The meeting was preceeded (31 January 1995) by the IOC/GLOSS-IAPSO Workshop on Sea Level Variability and Southern Ocean Dynamics, chaired by Dr. Christian Le Provost.

The Group reviewed the progress in GLOSS development since its third session held in 1992 in Paris. The GLOSS status has continued to improve. Table 1 below shows the number of stations in each of four categories according to definitions of PSMSL:

Category 1: "operational" stations for which the latest data is 1989 or later;

Category 2: "Probably operational" stations for which the latest data is within the period 1980-1989;

Category 3: "Historical" stations for which the latest data is earlier than 1980;

Category 4: for which no PSMSL data exist.

                            Table 1

Category    June 89   Oct 90   Aug 91   Oct 92  Oct 93  Oct 94

1            105      133       136      158     177     183
2             51       50        57       46      33      35
3             47       42        36       29      26      26 
4            103       81        77       73      72      64

Total        306      306       306      306     308     308
It can be seen that there has been a general modest improvement during 1994 in nominal GLOSS status, following the significant improvement obtained in 1993.

The distribution of stations of each category as of October 1994 can be seen by Clicking Here.

The Group proposed some adjustments to the GLOSS network particularly in relation to those stations which are presently not operational and for which no national plans exist to install them, and identified those which could reasonably be encouraged and those which are impractical.

The Group discussed the experience of integration of satellite altimetry and tide-gauges, noting, in particular, the success of the TOPEX/POSEIDON satellite mission in providing global synoptic pictures of sea-surface topography with a high level of precision (around 2cm). This satellite mission, as well as the ERS satellite mission, has proved that those measurements in combination with the in-situ tide gauge measurements could provide the complementary data for producing the products which will allow the monitoring of global and regional sea-level variability and changes.

The Proudman Oceanographic Laboratory of the UK produces altimetric topographic maps of the ocean which are validated by in situ level data from tide gauges. The National Ocean Service/NOAA of the USA also produces global maps of sea-level deviations based on TOPEX/POSEIDON data, and blended (ERS-1 and TOGA tide gauge data) sea-level anomaly maps for the tropical Pacific. Similar products are available from several other centres. The Group wished to encourage other centres to produce similar products for regional sea-level monitoring. The Group emphasised the importance of gravity satellite missions for the development of a precise geoid for oceanographic and geophysiscal research.

Particular attention was given to the connection of some selected GLOSS tide gauge bench marks to a global geodetic reference system. The representatives of the International Global Positioning System Service and experts in global and regional GPS took part in the discussion of this matter. The advances in the Global Positioning System now make it the best method for measuring vertical crustal motions at tide gauge stations to be used to monitor changes in absolute global sea level. The central role now foreseen for GPS, however, should not be interpreted as reason to discontinue or reduce ongoing efforts in complementary techniques, most particularly VLBI. Presently a network of about 50 permanent precision P-code receivers produce GPS data on a daily basis. Some experience on the connection of selected tide gauges to a global reference frame was demonstrated by Norway and a group of countries involved in the Mediterranean project on Sea Level Fluctuations: Geophysical Interpretation and Environmental Impact (SELF). The Group agreed to work with IGS to plan and evaluate the process for accurate connection of TGBM of selected GLOSS stations to the GPS geodetic stations.

The GLOSS Implementation Plan defines that data analysis and product preparation for scientific and/or practical application is an important element of GLOSS. This activity is becoming ever more important in view of the development of the Global Ocean Observing System (GOOS) in which GLOSS has been recognized as an existing operational element. This was emphasized by Dr. Michel Glass, Chairman of I-GOOS, who took part in the meeting.

A number of sea-level products and services has been already produced and provided by international sea-level centers: PSMSL, TOGA Sea Level Center, SOC for ISLP-Pac, WOCE Sea Level Data assembly Centers. These include monthly Pacific Ocean sea-level anomaly maps produced by SOC for ISLP-Pac, altimetric topography maps produced by Proudman Oceanographic Laboratory of UK and National Ocean Service /NOAA of USA.

The data/information services to countries and scientists are critical for the succes of international systems. The PSMSL data set as well as data sets of TOGA and WOCE Sea Level Centers are now available to scientists via internet. The CD-ROM containing datasets of PSMSL and TOGA Sea Level Center has been produced by NODC of USA. The "GLOSS Handbook" produced and up-dated by PSMSL provides details regarding all GLOSS stations. Publication of the booklet "Sea Level Monitoring in the Small Island Developing States", produced with the help of PSMSL and published by IOC, can be also considered as an example of specific products providing sea level data summaries for specific regions or selected locations.

The Group encouraged global and regional sea-level centers to produce such products and services which are useful for scientific and practical applications, both on global and regional scales. Specifically, it was proposed to consider: preparation of regional and local sea-level products required for the coastal zone protection and management, particularly related to storm surges, tsunami, coastal erosion; analysis of seasonal and interannual sea level variability and sea level monitoring for certain oceanic regions (Indian Ocean, Norh and Tropical Atlantic, South Pacific, Southern Ocean, Arctic Ocean); and sea level anomaly maps based on satellite altimetry and in situ measurements.

With regard to data/informations services the Group encouraged the PSMSL to work with NODC of USA in producing a GLOSS CD-ROM containing all information on GLOSS stations, GLOSS sea level data set, GLOSS related reports, documentation, GLOSS national and international contacts etc. The Group also supported strongly the initiative of PSMSL to produce the GLOSS Bulletin newsletter for wide distribution through electronic mailing systems. In fact the electronic mailing systems, particularly the Internet, have become an important tool for rapid exchange of sea level data and information and communication among GLOSS national and international contacts.

Many countries which have expressed their willingness and readiness to participate in GLOSS require long-term regular assistance in the provision of instruments, spare parts, their installation and up-grading and training of specialists in sea level measurements, interpretation and analysis. The Group noted that many countries, particularly from such IOC regions as IOCEA, IOCINCWIO, IOCINDIO, IOCARIBE and WESTPAC had approached IOC for such assistance. The existing problems in establishing GLOSS in some regions, particularly in the West Africa, were clearly demonstrated by Dr.L.Awosika, IOCEA Regional Coordinator for GLOSS who called upon other countries and IOC to assist the countries of the region in establishing regional GLOSS network.

GLOSS has demonstrated real partnership among the countries as in most cases such assistance has been provided on a bilateral basis and the Group wished to encourage such partnership. The Group felt however that training activities related to GLOSS should receive more substantial support either through IOC or other international funds, for example GEF, or national funds such as JICA and SAREC. The Group also invited the IOC to consider inclusion of GLOSS related training in the training courses on physical oceanography. IHB welcomed such cooperation in organizing training courses in hydrography and nautical cartography. The Group requested the IOC to provide support for the Training Workshop on Sea Level Interpretation and Analysis for the specialists of the Countries participating in the Pilot Activity on Sea Level Changes and Associated Coastal Impacts in the Indian Ocean (November 1995, India), a second Sea Level Training Seminar for the African and South American Portuguese and Spanish-Speaking Countries (1995-96, Argentina). The Group also requested the IOC to resume sea level training courses at POL, UK and to organize training for other IOC regions: IOCEA and IOCARIBE in particular.

The Group reviewed the activities of the international sea- level centers. Those include:

Permanent Service for Mean Sea Level (PSMSL). Established in 1933 and operated by POL (UK) the PSMSL deals with collection, publication and interpretation of sea level data from the global network of tide-gauges and acts as a Global GLOSS Center.

Specialised Oceanographic Centre for the IGOSS Sea Level Programme in the Pacific (SOC for ISLP-Pac) established in 1984 and operated by Hawaii University. This activity was an early, and very successful example of operational oceanography.

Specialized Sea Level Centers established in support two major oceanographic programmes of the World Climate Reserarch Programme:
TOGA Sea Level Center (Hawaii, USA)
WOCE Data Assembly Centres : Fast Delivery Data Assembly Center operated by the University of Hawaii (USA) and the Delayed Mode Sea Level Data Assembly Center operated by BODC(UK).

All these centers actively interact among themselves and in the final analysis data from specialised centers are submitted to PSMSL.

Since its launching in 1985 the GLOSS has encouraged the regional cooperation in establishing regional sea level observing systems required for provision of data and preparation of sea level products of scientific and practical value for the countries of the region. In addition to the Operational Sea Level Programme in the Pacific the following regional GLOSS activities have been initiated:
Sea-Level Programme in the IOCARIBE region as a component of the regional programme on ocean processes and climate (coordinator - Dr.G.Maul);
IOC-UNEP-WMO Pilot Monitoring Activity on Sea Level Changes and Associated Coastal Impacts in the Indian Ocean (coordinator - Dr.S.Shetye);
IGOSS Sea-Level Pilot Project in the North and Tropical Atlantic (coordinator - Dr.A.Bolduc);
Sea-Level Pilot Project for the Southern Ocean (coordinator-Dr.T.Murty);
European network for sea level and coastal land level monitoring -"EuroGLOSS" ( Dr.P.Woodworth - EuroGLOSS liaison with GLOSS);
GLOSS development in the South American group of countries. (Dr.A.Mesqita and E.Rodrigues liaison).

Those projects are at different stages of development. The Group of Experts wished to encourage those regional activities and invited them to focus on the sea-level products which will be of scientific and practical value for the countries of the region and which will contribute to the implementation of GLOSS as well as on training activities.

Some regional activities such as ASEAN Sea Level Programme and the South Pacific Sea Level and Climate Monitoring Project (Dr.T.Murty as a liaison) have been developed as multilateral cooperation programmes not directly related to GLOSS. The Group however recognized those activities as an important contribution to GLOSS through the establishment regional sea-level networks and related training activities.

Finally the Group of Experts formulated plan of action for GLOSS development for the 1995-1997 period and proposed to hold its Fifth session early in 1997.