Here are some examples, with brief descriptions, of the instruments that have been deployed as part of MOCHA (photographs courtesy of Lisa Beal). You can find Current Meters, CTDs, buoys, acoustic releases, and profilers.
All these instruments are Acoustic Current Meters from different manufacturers. They measure the motion of the water by sending out acoustic pulses and listening for a return echo. The echo bounces off particles which are drifting in the water, such as plankton or sediment. The velocity of these particles towards or away from the instrument can be detected by a frequency shift between the acoustic pulse and its echo - this is called Doppler Shift and is the same phenomenon we have heard when a police car passes by with the siren on. Each instrument has three or four transducer heads, which produce acoustic beams in different directions so that all components of velocity in three-dimensional space are resolved. The instrument on the right collects not just one measurement of velocity from the water, but an entire profile of velocities up to 300 m distant from the instrument. This is particularly useful for looking upwards to the ocean surface from the top of a mooring, which will typically be situated several hundred metres below to avoid the harsh environment of wind and wave action.
These pictures show the types of flotation used to keep moorings vertical in the water. Clusters of glass spheres protected by plastic "hard hats" are the simplest form of buoyancy and are versatile, however one implosion can cause the whole cluster to fail. Syntactic buoys, as shown in the bottom two pictures, consist of tiny glass balls imbedded in plastic. They are far more resistant to failure under pressure and can therefore be made large enough to accommodate and protect instrumentation, such as the acoustic current meter we saw above. They can also carry devices such as strobes, radio transmitters, and ARGO beacons (satellite transmitters) to aid the recovery of the mooring, which can be difficult and hazardous in rough seas. The bottom right picture shows bio-fouling of a buoy that has been deployed for a year at about 300 m depth. Finally, the top right are new "football" floats, designed in separate halves to clamp onto mooring line without requiring a gap in the wire. In this way an entire mooring several thousand metres long can have a continuous connection from all its instruments to a surface data-logger for daily data transmittal to the laboratory. Such a mooring is called Inductive and is still under development.
