A tide gauge is a piece of equipment used for measuring the changes in sea level with respect to a height reference surface. Although tide gauges have not been used as a primary source of sea-level data for several years, they play a key role in the instrumentation at modern-day tide gauge locations to verify water level.
Types of Tide Gauge Instruments
There are four main types of tide gauges:
- Acoustic systems – These systems make use of the transit time of a sonic pulse to measure sea-surface distance.
- Pressure systems - They monitor sub-surface pressure and convert it into height with reference to water density and gravity of acceleration.
- Radar systems – These systems, similar to acoustic transmission employ radio frequencies to measure sea-surface distance.
A sensor network is used to record measurements of changes in sea levels. A general working principle involves water traveling through a bottom pipe hooked to electronic sensors that are designed to measure the height of this water passing through.
A GPS system is also used for measuring tidal water levels. Water enters the tide gauge through a bottom pipe, and the water level is measured using electronic sensors, usually GPS. The device consists of two antennas and receivers, one pointing to the zenith and the other pointed down towards the sea surface. The former antenna tracks the direct signal, and the latter traps the reflected signal from the water surface. The interference between the direct and reflected signals can be determined by the signal-to-noise ratio data.
This GPS system is still in its early stages of application as this can only be used when the water level is calm. Further research will need to focus on how GPS technology can be applied during different stages of the tidal water movement.
In addition to providing precise tidal information, tide gauges are critical for port and harbor operations, surveying, dredging, instrumentation deployments, and a number of other applications.
Some of the other major applications of tide gauges are listed below:
- Calibration of satellite radar altimeters
- Study of vertical references and their relations
- Improvement of the tide models, usually in complex coastal zones
- Evaluation of the spatial altimetry results
- Validation of the climate models
Products on the Market
The TideMaster Portable Tide Gauge by Valeport, a manufacturer of hydrometric and oceanographic instrumentation, is a great example of advanced instrumentation to measure seawater levels.
This tide gauge can be used in fresh and saltwater with the deployment of up to one year. The system also offers real-time data extraction for the reliability and validity of data.
There are also standalone tide gauge instruments. One in particular currently on the market includes the PTG500e Tide Gauge by Environmental Systems & Services (ES&S) that can be used in remote locations and also as part of a larger network. This particular product is key to modern tide gauge instruments with a unique capability of being able to measure marine data including the direction of wind speed, temperature, and pressure in the atmosphere.
UK National Network
Serious flooding in 1953 as a consequence of storms that hit the North Sea was soon followed by a UK National Tide Gauge Network. The network involved gathering tidal information through the application of tide gauge instrumentation.
The aim is to analyze the data and assess the level of threat of possible flooding that could affect the coastal areas that occupy the British Isles.
The types of tide gauges used in the network include full- and mid-tide bubblers (measure the excess air that is produced as a result of air pressure and water pressure), direct pressure transducers, pneumatic gauges. The data gathered from such instrumentation provides detail on the tidal response, storm surge behavior, and the rise in sea levels.
Sources and Further Reading