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A tide gauge is a device for measuring sea level and detecting tsunamis.
Sensors continuously record the height of the water level with respect to a height reference surface close to the geoid. The water enters the device by the bottom pipe (far end of the tube, see picture), and electronic sensors measure its height and record it to a tiny computer.
Data are available for over 1750 stations worldwide. At some places records cover centuries, for examle in Amsterdam where data dating back to 1700 is available.They provide us with very good information.Other places that contain tide gauges are the stations that are situated in Antarctica and maybe the Arctic.
Tide gauges are used to measure tides and quantify the size of tsunamis.
The measurements make it possible to derive the mean sea level. Using this method, sea level slopes up to several 0.1 m/1000 km and more have been detected.
A tsunami can be detected when the sea level begins to rise.