At the end of any project, we need to recover the instrumentation from the seabed. Our instruments do not have mooring ropes and as such do not have anything to simply catch at the surface and haul them up from the seabed. Instead we have to release them from their ballast weights by sending them a uniquely coded signal from the vessel through the water to a receiver attached to them. Each has its own unique identity (name) and so we can only release the one we intend to release and no other. In the water depths of the central Atlantic, an instrument can take more than an hour to ascend to the surface. Once there, it has a radio beacon (VHF) and a flashing light beacon (handy at night) for us to locate them. Then we simply scoop them up, land them on deck and download the data and see what we have recorded.
The instruments we deployed at 13N in the central Atlantic were recovered successfully 6 months later.