International Association of Geodesy
 Permanent Service for Mean Sea Level (PSMSL)
Chair: P.L. Woodworth




Terms of Reference:

The PSMSL is a service aiming at providing all sorts of data concerning the mean sea level, and at stimulating all related developments. Their use has many applications within oceanography, climate change studies, geology, surveying and geodesy. This last field of application explains why this service is related to the IAG Section V (Geodynamics).

Since 1933, the Permanent Service for Mean Sea Level (PSMSL) has been responsible for the collection, publication, analysis and interpretation of sea level data from the global network of tide gauges. It is based at the Proudman Oceanographic Laboratory (POL), Bidston Observatory which is a component of the UK Natural Environment Research Council (NERC).

Data

The database of the PSMSL contains about 50.000 station-years of monthly and annual mean values of sea level from about 2000 tide gauge stations around the world received from almost 200 national authorities. On average, approximately 2000 station-years of data are entered into the database each year.

The data provide information on:

  •  Long Term Sea Level Trends: The PSMSL data set is the main source of information on long-term changes in global sea level during the last two centuries. The data have been employed intensively in studies such as those of the Intergovernmental Panel on Climate Change. 

  • The Seasonal Cycle of Coastal Sea Level: Considerably more data can be used for seasonal cycle studies than for a long-term trend. These data can be used in studies of the global distribution of the seasonal sea level cycle. The data show the relatively large amplitudes of the seasonal effects on the oceans and their variability. For instance, the annual mean sea level can vary considerably (typically by 10’s cm) from year to year in response to varying meteorological and oceanographic forcings. The interannual El Nino related changes in the Pacific are some of the largest and most well known.

  • Vertical Land Movements Tide Gauges: Vertical land movements are an important signal in sea level records. Over the past few years, considerable developments have taken place with the Global Positioning System (GPS) and other advanced geodetic techniques for monitoring rates of vertical land movements, with the aim of eventually removing the land movement signals from the sea level records. Presently, a coordination of efforts has been done with organization of centers to analyze such data, in particular with the development of the International GPS Service for Geodynamics (IGS). In addition, differential measurements to ‘fundamental points’ can be performed by using GPS data within the global GPS network itself.

Activity Report for 1999-2003 of the Permanent Service for Mean Sea Level (PSMSL)