Echo Sounding

Introduction to echo sounding:

Sound waves undergo reflections and obey the laws of reflection. Big walls and auditorium with parabolic smooth surfaces, well polished surfaces and metal surfaces are good reflectors of sound. Cello tape, thermocol, cushions, wall hangings and human beings are good absorbers of sound.

Definition of Echo Sounding:

An echo is a sound repeated by reflection from the surfaces of obstacles.

Reflection of sound in a large empty hall was due to the repeated hearings of sound. This phenomenon is called an echo and is due to the reflection of sound from the surface of obstacles.

The sensation of sound that lasts or persists in our brain for 0.1 second, even after the source of sound has stopped vibrating. Note that if we want to hear distinct echo, the reflected sound or echo must reach the echo 1/10 second or 0.1 second after the direct original sound. If we take the sound speed too be 330m/s, the sound must go to the obstacle and reach the ear of the listener on reflection after 0.1 s. This implies that the total distance covered should be at least  332 x 0.1 = 33.2 m. Thus for hearing distinct echoes, the minimum distance of the obstacle from the source of the sound must be half of the distance i.e., 16.6 m from the source. In a small room, whose walls as the reflecting obstacles, are less than 16.6 m away, no echo is possible. In this case, the original direct sound gets merged into the reflected sound and a sustained sound is heard which is called reverberation.

Echo Sounding:

Echoes may be heard more than once. Multiply echoes may be heard, one after another, when sound is repeatedly reflected from a number of obstacles such as two parallel distinct buildings on cliffs. The phenomenon of echoe’s is used in measuring distance in determining the ocean depths and in locating the presence of under-water objects.