Deep Caller for Ocean Acoustic Releases

We relate about the custom-made modification of a Benthos deep-ocean acoustic release into a "deep caller,'' an acoustic transducer for calling and releasing ocean acoustic transponding releases that cannot be reached from a standard deck unit. The self-contained deep caller can be lowered down to 12 km on any nonconducting winch cable. It may prove useful to retrieve subsurface instrumentation like a seafloor lander hidden behind large rocks or in a narrow canyon, or moorings in very deep topographic depressions. We used it to retrieve a 7-km-long mooring from 10 910-m depth in the Challenger Deep, Mariana Trench, that a standard deck unit could not reach.