What is a tide gauge?
Tide gauges are instruments that measure sea level in relation to a reference point.
They come in many forms, with the simplest and oldest form resembling a ruler: a vertical staff is simply attached to the coast, and readings of the height of the sea surface is recorded.
In the modern day, tide gauges have evolved into more complex instruments, such as pressure gauges. Pressure gauges are small instruments installed below the sea surface that measure liquid pressure at a designated depth.
When sea levels rise, the pressure gauge experiences increased pressure due to an increased volume of water above the gauge.
But the increased pressure could also be due to changes in the atmospheric pressure due to various weather phenomena. Typically, each underwater pressure gauge is therefore paired with a similar gauge on land to measure atmospheric pressure. By accounting for atmospheric pressure, the gauge can isolate the pressure exerted by the water alone, allowing for a more precise measurement of sea-level changes.
Pressure gauges are usually used in pairs – one underwater, and one above ground (Source: Jay Wong/Earth Observatory of Singapore)
Tide gauges have been a cornerstone in the measurement of sea-level changes as they provide continuous measurements to a high degree of accuracy, up to millimetre-level accuracy