posted on Nov, 4 2017 @ 10:59 PM
The USN is big on modal analysis. Everything that moves in air or water puts out subtle frequencies due to inherent modal properties of the vehicle.
The shape of the vehicle itself even has a unique modal signature. Broadband analysis using Fourier and Gaussian filters can discover enough
information to actually classify a submarine unique from any other. This tech was in it's infancy when I was in the service, but one can just imagine
how the computing power of today has taken it to a whole new level.