Amooring inoceanography is a collection of devices connected to a wire and anchored on the sea floor. It is theEulerian way of measuringocean currents, since a mooring is stationary at a fixed location. In contrast to that, theLagrangian way measures the motion of an oceanographicdrifter, theLagrangian drifter.
The mooring is held up in the water column with various forms of buoyancy such asglass balls andsyntactic foam floats. The attached instrumentation is wide-ranging but often includesCTDs (conductivity, temperature depth sensors),current meters (e.g.acoustic Doppler current profilers or deprecatedrotor current meters), and biological sensors to measure various parameters. Long-term moorings can be deployed for durations of two years or more, powered withalkaline orlithium battery packs.
Moorings often include surface buoys that transmit real time data back to shore. The traditional approach is to use theArgos System. Alternatively, one may use the commercialIridium satellites which allow higher data rates.
In deeper waters, areas covered bysea ice, 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 anacoustic 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 aconcrete block or small portable anchor.
The buoyancy of thefloats, 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.
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 viawave energy, then returning downward via gravity.[2]
Similar to akite in the wind, the mooring line will follow a so-called (half-)catenary.The influence ofcurrents (andwind if the top buoy is above the sea surface) can be modeled and the shape of the mooring line can be determined by software.[3][4] If the currents are strong (above 0.1m/s) and the mooring lines are long (more than 1km), the instrument position may vary up to 50m.
