Tide gauge

A tide gauge records water level at a coastal location relative to a fixed point on land. Its measurements reveal tides, storm surges, and long-term sea-level change.

Still well: A chamber connected to open water through a restricted opening, which dampens waves while tracking the underlying water level. Many float-operated gauges use one to suppress waves without losing the tide.
Storm surge: An abnormal rise in coastal water level caused mainly by a storm's winds and low atmospheric pressure. Rapid gauge observations reveal dangerous storm-driven rises at the coast.
Tide: The periodic rise and fall of sea level, driven chiefly by the Moon's and Sun's gravitational forces. The tide is the repeating signal a coastal gauge records alongside longer-term changes.
Tide staff: A graduated scale installed in water or at a shoreline for direct visual readings of water level. Unlike a recording gauge, a staff usually requires an observer to take individual readings.
Float-operated tide gauge: A gauge in which a float follows water level and drives a mechanical or electronic recording system. Its float converts movement inside a still well into a water-level record.
Sea-level rise: A long-term increase in the average height of the ocean surface relative to land. Long gauge records track relative sea-level change at specific coastlines.
Mean sea level: The average sea-surface height over a stated period, used as a reference for measuring sea-level change. Gauge records are commonly summarized as long-term changes in local mean sea level.
Satellite altimeter: An instrument aboard a satellite that measures distance to Earth's surface using reflected radar or laser pulses. It measures sea-surface height from orbit rather than at one fixed coastal point.
Pressure sensor: A device that measures pressure and can infer water depth from the pressure exerted by the water column. Submerged pressure sensors provide an alternative to measuring level with a float.
Tsunami warning system: A system that detects tsunamis and distributes alerts to reduce harm in exposed areas. Coastal gauges can confirm tsunami waves and measure their local effects.

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