Permanent Service for Mean Sea Level


The Permanent Service for Mean Sea Level (PSMSL)

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). The PSMSL is a member of the Federation of Astronomical and Geophysical Data Analysis Services (FAGS) established by the International Council of Scientific Unions (ICSU). It is supported by FAGS, the Intergovernmental Oceanographic Commission (IOC) and NERC.

As of August 2002, the database of the PSMSL contains over 49000 station-years of monthly and annual mean values of sea level from over 1800 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.



Data for all stations are included in the PSMSL METRIC (or total) data set. The METRIC monthly and annual means for any one station-year are necessarily required to be measured to a common datum, although, at this stage, datum continuity between years is not essential. The year-to-year datum checks become essential, however, if the data are subsequently to be included in the PSMSL 'Revised Local Reference (RLR)' component of the data set.

The 'Revised Local Reference (RLR)' dataset of the PSMSL contains records for which time series analysis of sea level changes can be performed. Long records from this dataset have been the basis of all analyses of secular changes in global sea level during the last century. The geographical distribution of longer RLR records contains significant geographical bias towards the northern hemisphere, a situation which is slowly being rectified by the establishment of the GLOSS global sea level network.


More information on the differences between 'Metric' and 'Revised Local Reference (RLR)' data values is given below.

Obtaining Sea Level Data

Data can be obtained as a complete copy of the PSMSL holdings, or for individual stations. The PSMSL help file is available to:-

  • Explain the format of the Data Catalogue

  • Explain terminology used

  • Differences between the Metric and RLR data sets

The PSMSL Data Catalogue

The catalogue of data held by the PSMSL can be inspected from:

The formats of both versions of the catalogue are explained in the PSMSL help file.

The following two lists will also be of use in understanding the catalogue. These lists include all sites from which the PSMSL has any data irrespective of whether the data are in the RLR data set or not:

Note that a station code followed by 'R' in these two files means that the station is in the RLR data set.

How to Acquire the Complete PSMSL Data Set

GENERAL WARNING: Before using any PSMSL data it is important to acquire an appreciation of some of the terminology used, and especially of the differences between 'Metric' and 'Revised Local Reference (RLR)' data values. PLEASE READ the PSMSL help file.

The complete PSMSL data set of monthly and annual mean values of sea level (psmsl.dat), an associated information file describing the format of the file (psmslrd.hel), and a fortran job which can read the data file (psmslrd.f) can be download from here:

The 'psmsl.dat' file contains all PSMSL data (i.e. all Metric data) with 'RLR factor' information for those station-years which are in the RLR set.

A much smaller file containing only annual mean values from the PSMSL RLR data set (rlrann.dat), an associated information file describing the format of the file (rlrannrd.hel), and a fortran job which can read the data file (rlrannrd.f) can also be download from here:

For people for whom fortran is not convenient, the two files below contain printouts of all monthly values in the PSMSL data set in 'Publication Format':

The PSMSL help file contains a description of the format of these printout files.

PSMSL "Ancillary Time Series" report

The IAPSO Pelagic Tidal Constants Data Set

The PSMSL is responsible to the IAPSO Commission on Mean Sea Level and Tides (CMSLT) for the databanking of pelagic tidal constants. This data set is available here:

Plans have been made with the Commission for the expansion of this activity to include tidal constants from selected conventional gauge sites in order to aid tide model developments.

Other background information relevant to sea level studies available from PSMSL:

PSMSL Contact Information

Permanent Service for Mean Sea Level
Bidston Observatory
Merseyside CH43 7RA
United Kingdom

Telephone: (UK international code 44) 151-653-8633
Fax: (UK international code 44) 151-653-6269

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