Australian naval personnel injured by sonar pulses from Chinese warship

Australian naval personnel have sustained minor injuries after being subjected to sonar pulses from a Chinese warship.

HMAS Toowoomba had been operating in international waters off Japan in support of a United Nations mission to enforce sanctions when the incident occurred on Tuesday.

Naval divers were working to clear fishing nets from the Australian frigate's propellers, when the Chinese warship began operating its hull-mounted sonar.

According to Defence Minister Richard Marles, the Australian frigate provided multiple warnings to vessels in the area that diving operations were underway.

"Despite acknowledging Toowoomba's communications, the Chinese vessel approached at a closer range," he said.

"Soon after, it was detected operating its hull-mounted sonar in a manner that posed a risk to the safety of the Australian divers who were forced to exit the water."

It's understood the divers suffered injuries to their ears, likely due to the sonar pulses.

The federal government has expressed its serious concerns to the Chinese government, with Marles labelling the incident "unsafe and unprofessional interaction".

And he says ADF vessels have run maritime surveillance activities in the area "for decades", doing so in accordance with international law.

While the frigate was in international waters, it still fell within Japan's Exclusive Economic Zone. It was sailing towards Japan, where it had a scheduled port visit.

The incident comes less than a fortnight after Anthony Albanese made the first official visit to Beijing by an Australian prime minister in seven years, meeting President Xi Jinping.

The discussion was described by the prime minister as one of "goodwill", and Xi credited Albanese for working to stabilise the relationship between the two countries after years of rising tensions.

And only days ago, Xi met with US President Joe Biden in San Francisco, where the two leaders pledged to resume military-to-military communications.

In May last year, tensions between Australia and China were heightened by the presence of a Chinese surveillance ship operating off the West Australian coast, close to a secretive naval communications base at Exmouth.

What is a sonar pulse?

Sonar is an acronym for Sound Navigation And Ranging. There are two types of sonar:

• Passive sonar involves listening, via specialised transducers called hydrophones (underwater microphones), for signs of nearby ships. It does not reveal the user's location.
• Active sonars are used to determine relevant positions of submerged objects by emitting a sound signal that travels through water, reflects off an object, and bounces back to a receiver. Sound signals are not emitted continuously, rather as short bursts or pings during operation. They can detect an underwater threat and target its position.

Submarines, warships and other naval platforms use sonar for two main reasons:

• To safely navigate deep waters and avoid obstacles
• Anti-submarine warfare (ASW)

*Information gathered from the Australian Government Department of Climate Change, Energy, Environment and Water, and Naval Technology.

* This story was first published by the ABC.