Bentley: Over the weekend, the Australian government revealed that its naval divers had suffered “minor injuries” last Tuesday, which were likely the result of sonar pulses from a Chinese navy ship. Divers were clearing fishing nets from the propeller of HMAS Toowoomba in international waters off the coast of Japan.
According to a statement from Deputy Prime Minister Richard Marles, despite HMAS Toowoomba communicating with internationally recognized signals, the Chinese vessel approached the Australian ship and activated its sonar, prompting Australian divers to exit the water. Was forced to. The incident prompted a response from the Australian government, which described the incident as “unsafe and unprofessional”. But what exactly is sonar pulsation, and what kind of injuries can sonar cause to divers?
What is sonar?
Light does not travel smoothly underwater – even in clear water, you can probably see up to a few tens of metres. However, sound travels very well and far under water. This is because water is much denser than air, and can therefore react faster and better to acoustic pressure waves – sound waves. Because of these properties, ships use sonar to navigate through the ocean and “see” underwater. The term “sonar” means sound navigation and ranging. The sonar device sends short acoustic (sound) pulses or pings, and then analyzes the echoes.
Based on the timing, amplitude, phase, and direction of the echoes received by the instrument, you can tell what’s under the water – the sea floor, canyon walls, coral, fish, and of course ships and submarines. Most vessels – from small, private yachts to large commercial tankers – use sonar. However, compared to your off-the-shelf sonar used to find fish, naval sonars are more robust.
What effect does sonar have on divers?
This is a difficult topic to study, because you don’t want to intentionally expose humans to harmful levels of sound. However, there are tales of various navies coming into contact with it. There have also been studies on what humans can hear underwater, with or without a neoprene suit, hood, or helmet. We don’t hear well underwater – this is no surprise, since we evolved to live on land. When this happens, you will hear a sonar sound (medium to high pitch noise) under the water and you will know that you have come into contact with him.
When it comes to naval sonars, human divers rated the sound as “unpleasant to severe” at levels of approximately 150 dB per 1 Pa (decibels relative to a reference pressure of one micropascal, the standard reference for underwater sound). Evaluated in. This would probably be, very roughly, 10 km away from a military sonar. Note that we cannot compare hearing sound underwater with sound received through air, as there are too many physical differences between the two.
The human tolerance limit is about 1 µPa per 180dB, which would be about 500 meters from military sonar. At such levels, humans may experience dizziness, temporary memory loss and effects on concentration, or temporary deafness. We do not know the level of trauma the Australian divers suffered, but their injuries are described as minor. At higher levels received, at closer ranges, or with prolonged exposure, you may see more serious physical or health effects. In extreme cases, especially for impulsive, sudden sound (which is not sonar), the sound can damage tissues and organs.
What does sonar do to marine animals? Some information about what effect noise can have on humans underwater comes from studies and observations of animals. While they generally do not have external ears (except for sea lions), marine mammals do have internal ears that function much like ours. Noise can damage their hearing, just like it does to us. This may be temporary, such as ringing in the ears or decreased sensitivity you might experience after a loud concert, or it may be permanent.
Deep-sea marine mammals rely on sound and hearing to a greater extent than the average human. They use sound to navigate, hunt, communicate with each other, and find mates. Toothed whales and dolphins have developed a biological echo sounder, or biosonar, which sends a series of clicks and listens for echoes. Therefore, interfering with their voice or affecting their ability to hear can disrupt important behavior. Finally, sound can also affect non-mammal organisms, such as fish, which rely on sound rather than vision for many of their life functions. (agency)