China is building world’s most powerful laser radar to study Earth’s solar shield

China has started building the world’s most powerful laser radar designed to study the physics of the Earth’s high atmosphere, according to state media reports and scientists informed of the project.

It is described as having a detection range of 1,000km (600 miles) – 10 times that of existing lasers – and will be used to study atmospheric particles that form the planet’s first line of defence against hostile elements from outer space such as cosmic rays and solar winds.

The facility, to be built on a site that remains classified, is expected to be up and running within four years and will form part of an ambitious project to reduce the risk from abnormal solar activities.

The radar will use a high-energy laser beam that can pierce through clouds, bypass the International Space Station and reach the outskirts of the atmosphere, beyond the orbiting height of most Earth observation satellites.

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There, the air becomes so thin that scientists will be able to count the number of gas atoms found within a radius of several metres.

These high-altitude observations could greatly expand our knowledge of a part of the atmosphere that has been little studied because the distances involved mean no one has been able to make direct observations from the ground.

“The large-calibre laser radar array will achieve the first detection of atmospheric density of up to 1,000km in human history,” said a statement posted on the website of the Chinese Academy of Sciences on Tuesday, a day after the launch of the project.

But the claim has been greeted with some scepticism in the scientific world.

“I think the 1,000km is a misprint!” professor Geraint Vaughan, director of observations at the National Centre for Atmospheric Science in the UK, replied when asked about the project.

Vaughan, who is also a Fellow of the Royal Meteorological Society, said that while he thought the Chinese announcement was “very interesting”, it did not seem possible with existing technology.

At present, the effective range of atmospheric lasers is about 100 kilometres.

Some other senior scientists in China and overseas also expressed doubt about the project, although they requested anonymity due to the sensitivity of the issue.

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“There are other approaches, such as launching a satellite. Building such a huge, expensive machine on the ground does not make sense,” said a Beijing-based laser scientist.

But several researchers told the South China Morning Post that the project did exist, and insisted that 1,000km range was not a mistake.

Hua Dengxin, a professor at Xian University of Technology and a lead scientist in China's laser radar development programmes, said: “I have heard of the project, yes. But I cannot speak about it.”

According to publicly available information, the facility will use several large optical telescopes to pick up the faint signals reflected by the high-altitude atoms when the laser is fired at them.

The project is part of the Meridian Space Weather Monitoring Project, an ambitious programme that started in 2008 to build one of the largest, most advanced observation networks on Earth to monitor and forecast solar activities.

By 2025 Meridian stations containing some of the world’s most powerful radar systems will be established across the world – with facilities in Arctic and Antarctic, South China Sea, the Gobi desert, the Middle East, Central Asia and South America.

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The purpose of the Meridian project, according to the Chinese government, is to reduce the risk abnormal solar activities pose to a wide range of Chinese assets including super-high voltage power grids, wireless communication, satellite constellations, space stations or even a future base on the Moon.

Chinese laser scientists have developed some of the world’s most sophisticated systems in recent years, including ranging stations that can track the movement of satellites and space debris, which the Pentagon has claimed have temporarily blinded some American scientists.

Last year researchers based in Xian, the capital of Shaanxi province, announced that they had developed a “laser AK-47” that could set fire to target from a distance of 800 metres.

The Chinese government is also funding the development of a laser satellite that can penetrate seawater to a depth of 500 metres from space to detect the waves generated by submarines.

The use of such a powerful laser raises concerns that passing objects such as planes, satellites or spacecraft – to say nothing of birds – may be at risk from its beams.

But Professor Qiao Yanli, engineer in chief at the Anhui Institute of Optics and Fine Mechanics, part of the Chinese Academy of Sciences, said there was an “extremely low” risk of this happening.

“The sky is enormous. Getting hit by a tiny beam is almost impossible,” he said.

Some much smaller laser radars, such as those installed in auto-driving test vehicles, have reportedly damaged digital cameras by burning a few pixels on sensor.

But spacecraft such as earth observation satellites, according to Qiao, usually have some protection mechanisms, such as a warning system, to avoid permanent damage caused by an accidental laser hit.

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Professor Li Yuqiang, a researcher at the Yunnan Observatories in Kunming, whose team has measured the distance between the Earth and the Moon by shooting lasers at a reflector placed on the lunar surface during the US Apollo 15 mission, said detecting atom-sized targets on the fringes of the atmosphere posed many technical challenges.

“The number of photons [particles of light] reflected by the sparse gas particles will be very small. Even if they can be picked up by large telescopes on the ground, the analysis will require some very good algorithms to separate the useful signals from the noise,” Li said.

“How that can be achieved is beyond the scope of my knowledge.”