Catfish Charlie, the CIA’s Robotic Spy
spectrum.ieee.org
spectrum.ieee.org
Salinity and temperature are of critical importance in computing the location of natural waveguides that occur when a reversal of the sound speed gradient occurs at depth in the thermocline, corresponding to the minimum sound speed at that vertical position for a very large horizontal distance. In temperate waters, this can be quite close to the surface -- i.e. within the comfortable range of military submarines -- leading to the so-called Deep Sound Channels (https://en.wikipedia.org/wiki/SOFAR_channel) where any sound can be readily detected.