Atide gauge is a device for measuring the change insea level relative to avertical datum.[2][3] It is also known as amareograph,[4]marigraph,[5] andsea-level recorder.[6]When applied tofreshwater continentalwater bodies, the instrument may also be called alimnimeter.[7][8]
Sensors continuously record the height of thewater level with respect to a height reference surface close to thegeoid. Water enters the device by the bottom pipe (far end of the tube, see picture), and electronic sensors measure its height and send the data to a tiny computer.[citation needed]
Historical data are available for about 1,450 stations worldwide, of which about 950 have provided updates to the global data center since January 2010.[9] At some places records cover centuries, for example inAmsterdam where data dating back to 1700 is available.[10]
When it comes to estimating the greater ocean picture, new modern tide gauges can often be improved upon by using satellite data.[citation needed]
Tide gauges are used to measuretides and quantify the size oftsunamis. The measurements make it possible to derive the meansea level. Using this method, sea level slopes up to several 0.1 m/1000 km and more have been detected.[citation needed]
A tsunami can be detected when the sea level begins to rise, although warnings fromseismic activity can be more useful.[citation needed]
Sea-level measurements were made using simple measuring poles or "tide staffs" until around 1830, when self-recording gauges with mechanicalfloats and stilling wells were introduced.[11]
Tidal poles and float gauges were the primary means of sea-level measurement for over 150 years and continue to operate at some locations today. While still part of modern-day tide gauge instrumentation, these technologies have since been superseded by pressure gauges (similar todepth gauges), acoustic/ultrasonic gauges, and radar gauges.[citation needed]
The following types of tide gauges have been used historically:[12]
Tide gauges have a practical application in the shipping and fishing industries where low or high tide levels can hinder or prohibit access to shallow bays or locations with bridges. An example is theCascais tide gauge in Portugal, which was originally installed because of the sand bar in the RiverTagus that causes difficulties for shipping enteringLisbon port. Because of similar problems many industries have installed private tide gauges in ports around the world, and also rely on government agencies (such asNOAA).
Data collected from tide gauges is also of interest to scientists measuring global weather patterns, the mean sea water level, and trends - notably those potentially associated with global warming.
In recent years new technologies have developed allowing for real-time, remote tide information to be published online via a solar powered wireless connection to a tide sensor. Acoustic/ultrasonic sensors[13] have already been deployed to great effect and the data is regularly broadcast viaTwitter and also displayed online.[14]
