How We Observe the Ocean
Tide Gauges
Hundreds of tide gauges of varying designs are deployed at coastal sites worldwide to directly measure variability and long-term trends of sea level, and to calibrate and validate measurement of sea level over the open ocean by satellite altimeters. Older tide stations are being upgraded with modern technology, particularly in less developed countries. Permanent Global Positioning System (GPS) receivers are being installed at select stations to accurately distinguish climate-related changes in sea level from geologic changes in land surface height. These Climate Reference Stations are also being upgraded for real-time reporting, not only for climate monitoring purposes, but also to support marine hazard warning (e.g., tsunami warning).
The term "tide gauge" is really a bit of a misnomer in current usage, since the instruments actually measure changes in sea level rather than just tides, which are only one contributor to sea level fluctuation. Because tides are now well understood their contribution can be accounted for, thereby permitting accurate observation of sea level variability and change attributable to other causes.
- Global Sea Level Observing System
- Tide Gauge Links
The Global Sea Level Observing System (GLOSS) is an international programme conducted under the auspices of the Joint Technical Commission for Oceanography and Marine Meteorology (JCOMM) of the World Meteorological Organization (WMO) and the Intergovernmental Oceanographic Commission (IOC), with the goal of creating high quality global and regional sea level networks for application to climate, oceanographic and coastal sea level research. The main component of GLOSS is the 'Global Core Network' (GCN), which currently consists of 289 sea level stations around the world designed to provide an approximately evenly-distributed sampling of global coastal sea level variations. Another component of GLOSS is the Long Term Trends (LTT) set of gauge sites (some, but not all, of which are in the GCN) designed to monitor long term trends in global sea level. These sites, which include Global Positioning System (GPS) receivers to monitor vertical land movements,contribute to long term climate change studies such as those of the WMO-UNEP Intergovernmental Panel on Climate Change (IPCC). GLOSS stations, in particular those located on islands, are also used for altimeter calibration.
Near real-time data are distributed by the University of Hawaii data assembly center. Historical data are archived and distributed by the NOAA National Oceanographic Data Center and by the British Oceanographic Data Centre. Tide gauge data sets are also available from the Permanent Service for Mean Seal Level (PSMSL), at the UK National Oceanography Center.
International Coordination
Tide Gauge Data Archives
- University of Hawaii Data Assembly Center
- NOAA National Oceanographic Data Center
- British Oceanographic Data Centre
Sea Level Trends, Anomalies and Data