The process of finding objects by emitting sound waves and interpreting the reflected sound is known as "sonar" (SOund Navigation And Ranging) when used underwater, and "radar" (RAdio Detection And Ranging) when used in air or space. Both sonar and radar are techniques used for detecting and locating objects at a distance by sending out waves and analyzing the waves that bounce back.
Sonar: Sonar is primarily used underwater for navigation, communication, and detecting underwater objects. It works by emitting sound waves (usually in the form of a "ping") from a transducer, and then measuring the time it takes for the sound waves to bounce back after hitting an object. By knowing the speed of sound in water and the time delay, the distance to the object can be calculated. Sonar can be passive (only listening to sounds in the environment) or active (emitting sound waves and listening to the echoes).
Radar: Radar, on the other hand, is used in air and space to detect and track objects like airplanes, ships, weather patterns, and even celestial bodies. Instead of sound waves, radar systems emit radio waves, and then analyze the reflected radio waves, or "radar echoes." The time it takes for the radio waves to return allows the system to determine the distance to the object. By analyzing the frequency shift (Doppler effect) in the returning waves, radar can also determine the object's relative speed and direction of movement.
Both sonar and radar are critical technologies with numerous applications, including navigation, military surveillance, weather monitoring, collision avoidance systems, and more. Each has its specific advantages and limitations, depending on the medium in which they operate (water, air, or space) and the desired range and accuracy of detection.