A. Tolkachev
Technical Secretary - Paris, France

The Global Sea Level Observing System is an international system initiated in 1985 and coordinated by IOC, to provide high-quality standardised sea level data from a global network of sea level stations.

The GLOSS network has been designed to observe large-scale sea level variations of global implications, and stations were identified at intervals of approximately 1000 km along the continental coasts and on islands, but generally not closer than 500 km. Priority is given to gauges that have been functioning for a long period, with an accuracy of 10 mm in level, 1 minute in time, and linked to bench marks against which their datum is checked regularly.

This network monitors sea level changes that could be indicative of global warming ocean circulation patterns, climate variability, etc., and contributes data to international programmes such as TOGA and WOCE.

The elements of GLOSS are:

A global network of permanent sea level stations to obtain standardised sea level observations.

Data collection for international exchange with unified formats and standard procedures.

Data analysis and product preparation for scientific and/or practical applications.

Assistance and training for improving national sea level network.

A selected set of GLOSS tide-gauge bench-marks accurately connected to a global geodetic reference system.

The Permanent Service for Mean Sea Level (PSMSL) collects and archives data from GLOSS stations in the form of monthly mean values, but hourly and daily values are also expected to be made available from all stations by the originators. The development of GLOSS is seen as a dynamic activity, supervised by a group of experts, who are guiding the GOOS development in a manner most useful to ocean science and for the analysis of global changes. At October 1993, 210 stations provide sea level data to PSMSL. GLOSS is recognised as an existing activity of the Global Ocean Observing System (GOOS). The proposed GLOSS network consists of 308 sea level stations that will be operated and maintained by 87 countries. The GLOSS Handbook, a PC-based data set describing the current status of each tide gauge in the GLOSS network, is being maintained by PSMSL The Manual on Sea Level Measurement and Interpretation (IOC M&G No. 14) provides recommended procedural guides for sea-level measurements, their analysis and for assisting those Member States who wish to install or reactivate their sea-level stations.

Many countries participating in GLOSS have already received support and assistance in the form of training of their specialists and the provision of equipment either through IOC and/or through bilateral and multilateral cooperation.