How did sonar contribute to discoveries about the ocean bottom?

SONAR stands for Sound Navigation And Ranging. It is a technique which is used to detect objects, navigate or communicate under water surface. It uses the principle of Echo.

The sound waves bounce off back from nearby objects which obstruct the path of these waves. Using the time of sending and receiving of sound wave and speed of sound in water, the angle of echo and the change in frequency, the distance to the object is calculated. Also, the motion of the object can be detected.