Acoustic release

Early use of acoustic releases for oceanography are reported in the 1960s,[2] when it was recognized that deep ocean currents could more accurately be measured with sea floor mounted rather than ship board instruments.

An obvious means of recovery was the use of a surface marker buoy linked to the sea floor instrument, but in areas of high ship traffic or the presence of ice bergs, this proved problematic.

There are many tense moments while waiting for the mooring to come to the surface; it may be difficult to spot as it floats low in the water so it usually carries a radio transmitter and a light to assist in locating it.

There are also variations of this use, where a light-load release sets free a flotation sphere, which travels to the surface trailing a strong tether that remains attached to the instrument.

Release mechanisms can fail due to bio-fouling or corrosion that can impair the motion of its components, failure modes that designers try to counter by minimizing the count of moving parts subject to seizing or applying high torque to overcome resistance.

But failures also occur due to factors of use and environment such as rigging and ocean currents or surge that can result in an entanglement of the device.

The command transmission system for shallow water releases must also be resistant to multi-path propagation (reverberations or echoes) which can corrupt a signal.

If a release should fail to surface, the underwater vehicle can be deployed and the ranging function can be used to home in on the stuck instrument, recovering it using the manipulator of the ROV or other methods.

This information can be used to position the surface vessel above the instrument for ease of recovery following release, or to evaluate the health and status of a device.

Sketch of an acoustic release working with a high-torque electrical motor.
Figure 1: Method of the operation of an Acoustic Release device
Figure 2: Example of a release mechanism, shown here in the closed or pre-release position. To release, a jolt of electricity melts fusible wire (B), allowing lever (A) to open and release the anchor line attachment loop (C).
Figure 3: An acoustic transducer, part of a surface control station, is lowered over the side of a boat to establish communication with an acoustic release.
Figure 4: An acoustic release interrogator (A) is mounted on a ROV, allowing the ROV to home in on the acoustic release to observe or recover in case of a release failure.