Dark Matter
It is worth pointing out that the "grid" you can see is approx 1km in the North South direction and just 450 metres East West. Each sweep is just over 200 metres from the last.
It strikes me that this is too "fine" a grid for a pinger search - and rather more a sonar search. Each pass would have to sweep a 200 metre or so wide path, but I rather hope somone with undersea submerisble/sonar expertise might step forward.