sonar

This term is a portmanteau of sound navigation and ranging. It describes a specialized technology that relies on the reflection of acoustic energy to perceive an environment where light cannot penetrate, such as the deep ocean. It is most commonly associated with military naval operations and marine biology.

As a noun, it can refer to the physical hardware and electronic systems used for detection, or the actual acoustic pulses emitted by those systems. While it functions as a countable noun when referring to different types of systems, it is often used uncountably when referring to the general technology or the sound waves themselves.