What is A Hydrophone and How It Work?

What is A Hydrophone?

Hydrophones are underwater microphones designed to monitor underwater noise. A typical hydrophone works by detecting pressure changes in the surrounding environment and converting sound waves into voltage. The speed and distance of the sound wave propagating in the water is proportional to the pressure change, which will determine the nature of the electrical output transmitted.

Just as microphones are used to listen to the sound in the air, hydrophones are used to listen to sound underwater. Microphones convert sound in air into electrical signals. The electrical signals can then be amplified, recorded, played back over loudspeakers, and transmitted over telephone lines. The electrical signals can also be used to measure the characteristics of the sound, such as amplitude and frequency. Similarly, hydrophones convert sound in water into electrical signals that can be amplified, recorded, played back over loudspeakers, and used to measure the characteristics of the sound. Hydrophones listen to sound but do not transmit any sound.

How Does A Hydrophone work?

By amplifying and recording these electrical signals, hydrophones measure ocean sounds with great precision. While a single hydrophone can record sounds from any direction, several hydrophones simultaneously positioned in an array, often thousands of miles apart, result in signals that can be manipulated to “listen” with greater sensitivity than a single device. Omni-directional and hemi-directional hydrophones pick up sound from a particular direction and can be used to track fish movements.

In addition to NOAA's National Marine Sanctuaries, NOAA’s Pacific Marine Environmental Laboratory (PMEL) also frequently uses hydrophones. PMEL acquires long-term data sets of the global ocean acoustics environment to identify and assess acoustic impacts from both human activities and natural processes, such as underwater volcanoes, earthquakes, and icequakes on the marine environment.