Could ghost imaging spy satellite be a game changer for Chinese military?
Scientists are developing a probe to track stealth bombers at night
China is developing a new type of spy satellite using ghost imaging technology that could change the game of military cat and mouse within a decade, according to scientists involved in the project.
Existing camouflage techniques – from simple smoke bombs used to hide tanks or soldiers on battlefields to the hi-tech radar absorption materials on a stealth aircraft or warship – would be of no use against ghost imaging, physics experts said.
Quantum ghost imaging can achieve unprecedented sensitivity by detecting not just the extremely small amount of light straying off a dim target, but also its interactions with other light in the surrounding environment to obtain more information than traditional methods.
A satellite equipped with the new quantum sensor would be able to identify and track targets that are currently invisible from space, such as stealth bombers taking off at night, according to researchers.
The Northrop Grumman B-2 Spirit operated by the United States is the world’s only stealth bomber in service able to deliver a strategic strike on an enemy.
B-2s take flight mostly under the cover of night, in part to avoid high-definition optical cameras on spy satellites. They have a special coating to deflect or absorb microwaves of certain bandwidths produced by space-based synthetic aperture radars, as well as heat-suppression technology to dodge infrared sensors. Its successor, the B-21, is under development with improved but similar technologies. It is expected to enter service by 2025.
Gong Wenlin, research director at the Key Laboratory for Quantum Optics, Chinese Academy of Sciences in Shanghai – whose team is building the prototype ghost imaging device for satellite missions – said their technology was designed to catch “invisibles” like the B-2s.
He said his lab, led by prominent quantum optics physicist Han Shensheng, would complete a prototype by 2020 with an aim to test the technology in space before 2025. By 2030 he said there would be some large-scale applications.
While ghost imaging has already been tested on ground-based systems, Gong’s lab is in a race with overseas competitors, including the US Army Research Laboratory, to launch the world’s first ghost imaging satellite.
The team showed the engineering feasibility of the technology with a ground experiment in 2011. Three years later the US army lab announced similar results.
“We have beat them on the ground. We have confidence to beat them again in space,” Gong said.
The ghost imaging satellite would have two cameras, one aiming at the targeted area of interest with a bucket-like, single pixel sensor while the other camera measured variations in a wider field of light across the environment.
The target could be illuminated by almost any light source such as the sun, moon or even a fluorescent light bulb. Alternatively, a pair of physically “entangled” or “correlated” laser beams could be generated from the satellite to light up the object and its surroundings.
By analysing and merging the signals received by the two cameras with a set of sophisticated algorithms in quantum physics, scientists could conjure up the imaging of an object with extremely high definition previously thought impossible using conventional methods.
Gong said darkness, cloud, haze and other negative elements impairing visibility would no longer matter.
“A ghost imaging satellite will reveal more details than the most advanced radar satellite,” the research director said.
Because quantum imaging can collect data from a wide spectrum of light, the images they produce would look “more natural” to human eyes than the black-and-white radar images based on the echo of high-frequency electromagnetic waves of narrow bandwidths, he said.
The ghost camera could also identify the physical nature or even chemical composition of a target, according to Gong. This meant the military would be able to distinguish decoys such as fake fighter jets on display in an airfield or missile launchers hidden under a camouflage canopy.
Tang Lingli, a researcher with the Academy of Opto-Electronics, Chinese Academy of Sciences in Beijing, said numerous new devices had been built, tested in the field and were ready for deployment on ground-based radar stations, planes and airships.
“Satellite is the next step,” she said.
Tang said ghost imaging could be achieved using different methods in either quantum or classical physics, and it would work best with other intelligence gathering methods including optical cameras and synthesised aperture radars.
“Each detection method has its unique advantages. It depends on the circumstances and nature of the mission as to which one should be used, if not all [of them],” said Tang, who is also the general secretary of the National Committee on Remote Sensing Technology Standardisation and a supervisor of the national ghost imaging project.
Xiong Jun, a professor of physics who studied quantum optics at Beijing Normal University, said ghost imaging could become a game changer for military operations.
Some 200 quantum optics scientists gather in China every year to share their new discoveries and the latest advances in engineering applications.
Xiong said he had seen ghost imaging used in ground-based radar systems and spy planes, but the satellite project had not been publicly discussed because of its sensitivity.
Many engineering challenges would have to be overcome to build such a satellite, he said.
If the satellite used a natural light source such as the sun and moon, it would need to have extremely fast sensors to detect the tiny changes in light down to a few nanoseconds – or one thousand-millionths of a second – and catch the quantum physics in action.
If it used an artificial light source such as a laser, it would need to be very powerful to reach a distant target near the ground.
But Xiong noted that China had built and run the world’s first and only quantum satellite, which provided a large amount of experimental data – and engineering experience – for its scientists.
He said that satellite could generate a pair of entangled laser pulses and send them to different locations on the ground, and the ghost imaging satellite would use similar techniques.
“The theory of ghost imaging has been well established and understood,” Xiong said. “The speed of application very much depends on the government and the amount of money it’s willing to spend.”