Acoustic (sound) waves have been called the “daylight” of the ocean. Unlike the air, light in the ocean is absorbed within tens of meters and the vast reaches of the ocean depths are almost completely dark. However, the ocean is largely transparent to acoustic waves. Many organisms living in the ocean have adapted to the use of acoustic waves to get information about their environment, and many ocean observing technologies have been developed along similar lines.
Physics Across Oceanography: Fluid Mechanics and Waves by Susan Hautala is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.