Echo sounding

Echo sounding is a way out measure the depth of water. This is done by sending out sound waves, and measuring how long it takes for the echo of the sound to come back. The speed of sound in the water is known, so the depth can be calculated. It is a kind of sonar. Note that the word sounding is used for all kinds of technologies, even though some do not use sound. Before echo sounding was used (in the early 20th century), sounding lines were lowered into the water to measure the depth.

Diagram showing the basic principle of echo sounding

The sound reflects off the seafloor and returns to the transducer. The time the sound takes to travel to the bottom and back is used to calculate the distance to the seafloor. Water depth is estimated by using the speed of sound through the water (approximately 1,500 meters per second). The product is divided by two because the measured time is the round-trip time (from the transducer to the seafloor and back to the transducer). The faster the sound pulses return to the transducer from the ocean floor, the shallower the water depth is and the higher the elevation of the sea floor. The sound pulses are sent out regularly as the ship moves along the surface, which produces a line showing the depth of the ocean beneath the ship. This continuous depth data is used to create bathymetry maps of the survey area.