Make software that can analyze input from a webcam or similar that records the surface of the water and extrapolates any local sources of ripples, this could be used to locate a person if they fell overboard. Then every cruiseliner, naval ship, etc. could be equipt with it. The only question is how much such a camera would cost that records in enough detail to pick up the ripples.

Alternatively a transversely flexible matrix of accelerometers with floats that is laid on the surface of the water could be used.

Probably use machine learning for the software part.

The idea is a setup that cruise liners and other large ships can use to retrieve someone should they fall overboard. Just recently someone fell overboard a military ship and they never could find him. The setup would be one of two things:

a) A video camera combined with software that runs on the ship's computers to analyze ripples in the water to determine any local sources of ripples, even small ripples. That way you can just point the video camera down at the water - anywhere, or at least the side they fell off from - and determine their location. The question with this option is how much a suitable camera would cost.

b) A transversely flexible matrix of accelerometer points attached to tiny floats that you lay on top of the water, which relays the information to software to map the waves and determine the person's location in much the same manner as above but just using a more direct means of recording ripples. *Might* be cheaper and/or more effective than the first option.

Perhaps people don't fall off and get lost that often, but hey, if cruise liners start implementing this system then people are going to start asking, "does this cruise liner have the Man Overboard system installed?"