The waveform of the recording.
From SOSUS to wind farms
Back in the 1960s, 70s, and 80s, this kind of sonic technology was deeply important to the military, which used the Sound Surveillance System (SOSUS) to track things like Soviet submarine movements. (Think of Hunt for Red October spy games here.) Using underwater beamforming and triangulation, the system could identify submarines many hundreds or even thousands of miles away. The SOSUS mission was declassified in 1991.
Today, high-tech sonic buoys, gliders, tags, and towed arrays are also used widely in non-military research. The National Oceanic and Atmospheric Administration (NOAA), in particular, runs a major system
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