Name the waves used for echo depth sounding

1. Name the waves used for echo depth sounding.
2. Give one reason for their use for the above purpose.
3. Why are the waves mentioned by you not audible to us?

Answer

1. Ultrasonic waves.
2. They can travel un-deviated through long distances.
3. Frequency of ultrasonic waves is above 20000 Hz and audible range of frequency is 20 Hz to 20000 Hz.