Tide gauge

A tide gauge is the instrument that records the height of the sea surface over time, the sensor from which tidal levels, chart datum, and mean sea level at a place are derived. Types range from the old float-in-a-stilling-well chart recorder to seabed pressure transducers, acoustic and radar gauges that range to the surface from above, and bubbler systems. The record gives the times and heights of high and low water that, harmonically analyzed, yield the constituents used to predict the tide and compile the tide tables. A network of permanent gauges defines and monitors mean sea level and underpins the vertical datum of the charts, and feeds real-time water-level data to the IHO S-104 service for ECDIS.