cb, that's a sweet idea -- extending hydrophone range
outside of the active sonar sensor "sphere".
my only question is... well, better to describe something similar.
if you are approached by an escort that's equipped w/ radar, while he's far away and out of sight, you get a rwr message (radar signals detected) and a bearing line. as soon as he's in range, the line goes away, and "plotting" is done by vision. how do you determine which sensor has priority -- asdic or hydrophone? i'm not explaining myself clearly.
anyway, it's a great thought. will try it out tomorrow. good luck w/ your work.
