Pardon this old Marine, but ust how does bottom sounding SONAR remain ELINT free??
Cant everyone and their brother hear it, too?
I'd have to kill you after i told you ;)
It doesn't. The fathometer isn't particularly noisy, but it can be heard.
There are several modes that the fathometer can work, including a "secure" mode. Plus the fact that it's a high frequency narrow beamwidth signal going straight down sort of limits the detection range.