That's not true. I was working on a system to do (not on subs, but the techniques are applicable) that a few years ago. With a big enough array, anything is pos

That's not true. I was working on a system to do (not on subs, but the techniques are applicable) that a few years ago. With a big enough array, anything is possible, see the entire field of radio-astronomy. This includes sparse arrays, as long as you have good enough time sync to do coherent integration.