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Facilitating Access to Global Observing Systems Data and Information

Global Sea-Level Observing System (GLOSS)
Program Overview

The Global Sea-Level Observing System (GLOSS) is an operational system established by the IOC in 1985 to provide monitoring of global sea levels, to help develop national capabilities to assess and anticipate severe sea level events, and to provide ground truth for satellite altimeter missions.

Data Access

The Program

GLOSS aims at the establishment of high quality global and regional sea level networks for application to climate, oceanographic and coastal sea level research. The program became known as GLOSS as it provides data for deriving the 'Global Level of the Sea Surface'.

The GLOSS program is managed by an international GLOSS Group of Experts supported by a Technical Secretary at IOC, and a group of National and Regional GLOSS Contacts.

The main component of GLOSS is the 'Global Core Network' (GCN) of 290 sea level stations around the world for long term climate change and oceanographic sea level monitoring. The present definition of the GCN (the definition is modified every few years) is called GLOSS02 (List of GLOSS Core Network (GCN) - GLOSS02 Stations)

There are three sub-networks, the GLOSS LTT (Long Term Trends), the GLOSS OC (ocean circulation) and the GLOSS ALT (altimetery).

The program strives to provide high quality data, as far as possible with common operating and reporting standards, and with guarantees of longevity.

Operations include;

  • monitoring the status of gauges within the GLOSS Core Network and scientific and regional sub-networks
  • provision of advice and technical support to gauge operators where required
  • supply of training to sea level scientists and technicians
  • continuous linkage with related technical areas such as altimetry, GPS and absolute gravity
  • definition and implementation of data flow mechanisms


The data produced by GLOSS has application to climate, oceanographic, and coastal sea level research. The core network provides an approximately evenly-distributed sampling for climate research. The LTT set of gauge sites provide information on long term trends and accelerations in global sea level change, for monitoring vertical land movements, and for long term climate change studies. An important client is the WMO-UNEP Intergovernmental Panel on Climate Change (IPCC)

Other important GLOSS users include the satellite services for ground truth for altimeter data and mission intercalibrations. The ocean circulation set, including in particular gauge pairs at straits and in polar area, complements altimetric coverage of the open deep ocean and is used within programs such as WOCE and CLIVAR.

GLOSS is a component of the Global Ocean Observing System (GOOS), and as a major contributor to its Climate and Coastal Modules.

Scientific and Regional Sub-Networks

The scientific and regional sub-networks include:

  • The GLOSS-Long Term Trends network formonitoring long term trends and accelerations in global sea level; ~190 sites at PSMSL of which 88 are in the GLOSS core network were identified in the 1997 GLOSS Implementation Plan.
  • The GLOSS-OC network for ocean circulation monitoring across ocean basins and straits.~50 sites were identified in the 1997 GLOSS Implementation Plan.
  • TheGLOSS-ALT (altimeter) network for satellite altimeter calibration. As more GLOSS stations become associated with GPS and DORIS measurements identification of this subset becomes of less significance.

Data Overview

The GLOSS Station Handbook summarizes in tabular form the basic information on tide gauge stations (not all active) in the GLOSS Core network, providing a one-stop shop with links to the databases described below. The latest status of the Core Network is reported here.

Daily mean and Hourly height data from the GLOSS network: the Joint Archive for Sea Level (JASL) at UHSLC, and the Delayed Mode Centre at the British Oceanographic Data Centre (BODC) both hold data covering in some cases many decades. The available data lags by two or more years on the present during which time quality control and adjustment to local benchmarks is done. The data are now referred to the RLR reference used by PSMSL. Plots, maps, and quality control information are available.

A subset of the stations provide data within a month to six weeks to the Fast Delivery Center at UHSLC.

Monthly and Annual Mean Data are available from PSMSL. The data have been quality controlled and where possible placed in datasets with a common reference (RLR) otherwise they are in Metric datasets referred to local benchmarks (as are the UHSLC and BODC databases). There are maps, plots, and documentation for many stations. This database is not limited to the GLOSS stations. However the site does contain an identifier for the GLOSS stations from which users can cross-reference to the GLOSS Station Handbook.

Note that the JASL and BODC also act in similar capacities for the Clivar research program and may be referred to variously as GLOSS, PSML, WOCE, or Clivar Centers.