Underwater acoustics is a very important branch of acoustics. At Ideatec, we’ll tell you all about the key aspects of the study of sound waves in water.
Acoustics for other purposes: underwater acoustics
Acoustics is the branch of physics concerned with the study of the production and propagation of sound waves. Within this field, there are a wide variety of sub-fields, such as electroacoustics, architectural acoustics and underwater acoustics.
The latter refers to the propagation of sound within water and the study of the noise sources located there. Sounds in water travel at 1,500 metres per second, a speed much greater than that of sound travelling through air, which is 350 metres per second. Consequently, there are so-called transmission channels, which allow low frequencies or bass tones to be heard over great distances.
Underwater acoustics emerged as a discipline in the early 20th century, and its development was closely linked to the development of electronics and military applications, as its period of significant growth began after the Second World War. Its study combines three disciplines: marine biology, geology and geophysics.
Hydrophones: the allies of underwater acoustics
Advances in technology have now made it possible to record sounds at the bottom of the oceans and seas with complete fidelity, with the recordings able to be stored on flash drives for subsequent processing and analysis. The ability to capture and analyse sound in water has opened up various fields of research into seabed fauna and has helped us to understand the causes of various natural phenomena.
Hydrophones, or underwater microphones, are used to ensure the success of underwater acoustic research. These are devices designed to capture sound sources in a liquid, particularly in water. There are models that emit sound waves themselves, but these are less common.
Sound waves are present in water in the form of pressure. Hydrophones are responsible for converting this pressure into electrical energy, that is, into a sound spectrum audible to humans, enabling its comprehension and study. For this reason, they must be adapted to different pressures.
When different hydrophones pick up sound signals, the source can be located using triangulation. The source is then displayed on a monitor, and its position and direction are determined using algorithms. However, before analysing the sound recorded by the hydrophone or sonar, it must be filtered to remove background noise, such as water movement, man-made noise or thermal noise.
Hydrophones are very useful for detecting a hydroacoustic event. This term refers to underwater noise, which can range from sounds made by animals to the noise of a boat’s engine. It is very important to analyse the frequency, amplitude and duration of the noise to determine whether it is a hydroacoustic anomaly.