![BrnBld MooringSketch](https://upload.wikimedia.org/wikipedia/commons/7/77/BrnBld_MooringSketch.svg)
A mooring in oceanography is a collection of devices connected to a wire and anchored on the sea floor. It is the ''Lagrangian and Eulerian specification of the flow field, Eulerian way'' of measuring ocean currents, since a mooring is stationary at a fixed location. In contrast to that, the ''Lagrangian way'' measures the motion of an oceanographic
drifter
A drifter is a vagrant who moves from place to place without a fixed home or employment.
Drifter(s) or The Drifter(s) may also refer to:
Films and television Films
* ''The Drifter'' (1917 film), an American film directed by Fred Kelsey
* ''Th ...
, the
Lagrangian drifter.
Construction principle
The mooring is held up in the water column with various forms of buoyancy such as
glass balls and
syntactic foam
Syntactic foams are composite materials synthesized by filling a metal, polymer, or ceramic matrix with hollow spheres called microballoons or cenospheres or non-hollow spheres (e.g. perlite). In this context, "syntactic" means "put together." ...
floats. The attached instrumentation is wide-ranging but often includes
CTDs (conductivity, temperature depth sensors),
current meter
A current meter is an oceanographic device for flow measurement by mechanical, tilt, acoustical or electrical means.
Different reference frames
In physics, one distinguishes different reference frames depending on where the observer is located, ...
s (e.g.
acoustic Doppler current profilers or deprecated
rotor current meters), and biological sensors to measure various parameters. Long-term moorings can be deployed for durations of two years or more, powered with
alkaline
In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a base (chemistry), basic, ionic compound, ionic salt (chemistry), salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as ...
or
lithium battery packs.
Components
Top buoy
![Surface buoy with meteorological sensors](https://upload.wikimedia.org/wikipedia/commons/0/06/Surface_buoy_with_meteorological_sensors.jpg)
Surface buoys
Moorings often include surface buoys that transmit real time data back to shore. The traditional approach is to use the
Argos System
Argos is a global satellite-based system that collects, processes, and disseminates environmental data from fixed and mobile platforms around the world. The worldwide tracking and environmental monitoring system results from Franco-America ...
. Alternatively, one may use the commercial
Iridium satellite
Iridium is a chemical element with the symbol Ir and atomic number 77. A very hard, brittle, silvery-white transition metal of the platinum group, it is considered the second-densest naturally occurring metal (after osmium) with a density of ...
s which allow higher data rates.
![Syntactic foam sphere](https://upload.wikimedia.org/wikipedia/commons/b/b7/Syntactic_foam_sphere.jpg)
Submerged buoys
In deeper waters, areas covered by
sea ice
Sea ice arises as seawater freezes. Because ice is less dense than water, it floats on the ocean's surface (as does fresh water ice, which has an even lower density). Sea ice covers about 7% of the Earth's surface and about 12% of the world's oce ...
, areas within or near shipping lines or areas that are prone to theft or vandalism, moorings are often submerged with no surface markers. Submerged moorings typically use an
acoustic release or a Timed Release that connects the mooring to an anchor weight on the sea floor. The weight is released by sending a coded acoustic command signal and stays on the ground. Deep water anchors are typically made from steel and may be as large as 100 kg. A common deep water anchor consists of a stack of 2–4 railroad wheels. In shallow waters anchors may consist of a
concrete block
A concrete masonry unit (CMU) is a standard-size rectangular block used in building construction. CMUs are some of the most versatile building products available because of the wide variety of appearances that can be achieved using them.
Tho ...
or small portable anchor.
The buoyancy of the ''floats'', i.e. of the top buoy plus additional packs of glass bulbs of foam, is sufficient to carry the instruments back to the surface. In order to avoid entangled ropes, it has been practical to place additional floats directly above each instrument.
Instrument housing
Prawlers
Prawlers (profiling crawlers) are sensor bodies which climb and descend the cable, to observe multiple depths. The energy to move is "free," harnessed by ratcheting upward via
wave energy
Wave power is the capture of energy of wind waves to do useful work – for example, electricity generation, water desalination, or pumping water. A machine that exploits wave power is a wave energy converter (WEC).
Waves are generated by wind p ...
, then returning downward via gravity.
Depth correction
Similar to a
kite
A kite is a tethered heavier than air flight, heavier-than-air or lighter-than-air craft with wing surfaces that react against the air to create Lift (force), lift and Drag (physics), drag forces. A kite consists of wings, tethers and anchors. ...
in the wind, the mooring line will follow a so-called (half-)
catenary
In physics and geometry, a catenary (, ) is the curve that an idealized hanging chain or cable assumes under its own weight when supported only at its ends in a uniform gravitational field.
The catenary curve has a U-like shape, superficia ...
.
The influence of
current
Currents, Current or The Current may refer to:
Science and technology
* Current (fluid), the flow of a liquid or a gas
** Air current, a flow of air
** Ocean current, a current in the ocean
*** Rip current, a kind of water current
** Current (stre ...
s (and
wind
Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few hou ...
if the top buoy is above the sea surface) can be modeled and the shape of the mooring line can be determined by software.
If the currents are strong (above 0.1
m/s) and the mooring lines are long (more than 1
km), the instrument position may vary up to 50
m.
See also
*
Benthic lander
Benthic landers are observational platforms that sit on the seabed or benthic zone to record physical, chemical or biological activity. The landers are autonomous and have deployment durations from a few days (for biological studies) to several y ...
, a mooring which does not have any mooring line
References
{{physical oceanography, expanded=other
Oceanography
Physical oceanography
Oceanographic instrumentation
Ocean currents
Biological oceanography
de:Boje (Schifffahrt)