Chinese scientists detect ‘spy balloon’ as small as F-35 stealth fighter on radar

Despite the US military struggling to detect a balloon in its airspace, Chinese scientists have a simple method using common weather radar.

Science

Stephen Chenin Beijing

Published: 10:00pm, 26 Jun 2024

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While the US military struggles to detect spy balloons, Chinese scientists can offer a simple, efficient and low-cost solution.

According to recently declassified official information, the Chinese military conducted a field test of this unprecedented air-floating balloon detection technology in Wayao village, Neijiang, in the southwest province of Sichuan in January 2022.

The radar cross-section (RCS) of the balloon used in the test was only 16 square centimetres (2.48 square inches) . In comparison, the RCS of the F-35 stealth fighter is generally considered to be 15 square centimetres.

These balloons have a very low speed and are therefore more difficult to detect than aeroplanes. Under complex terrain and electromagnetic interference in the open environment, traditional radar detection methods cannot distinguish them from background noise.

The People’s Liberation Army (PLA) has launched 14 such balloons at various times and locations. With the help of the new radar technology, their probability of detecting and locking onto such targets soared from close to zero to 100 per cent.

“In military terms, air-floating balloons have functions such as creating false air situations, dropping lethal weapons, creating public opinion or psychological warfare, and intelligence reconnaissance,” wrote the project team led by Yin Jiapeng, an associate researcher on radar technology with the PLA National University of Defence Technology, in a peer-reviewed paper published in journal Acta Aeronautica et Astronautica Sinica on May 29.

“It is of great significance and increasingly urgent to detect and warn air-floating balloons in a timely and efficient manner,” Yin and his colleagues said.

In January 2023, a balloon from China entered US airspace.

Many Americans saw this giant balloon. Some even thought it was a UFO and shared videos on social media.

But the powerful air defence system of the US military did not detect it. Under intense public pressure, the military used fighter jets to track the balloon, which flew over a large part of the country.

PLA scientists have revealed they can detect a balloon with a radar signature as small as that of an F-35 stealth fighter using a civilian weather radar. Photo: National University of Defence Technology of the Chinese People’s Liberation Army

The Pentagon admitted similar balloons had often entered the United States before, and that their radar had limited detection abilities for such objects.

“I will tell you that we did not detect those threats, and that’s a domain awareness gap,” Air Force General Glen VanHerck, head of the US Northern Command and the North American Aerospace Defence Command (NORAD), said after the balloon was shot down by an F-22 on February 4, 2023.

The White House said they would take measures to monitor these balloons in the future, but defence suppliers said this would require a large-scale hardware upgrade to the existing radar system.

“We don’t, as a country, have persistent sensors that can detect low profiles and low heat signatures on our borders,” Riki M. Ellison, chairman and founder of the Missile Defence Advocacy Alliance, told Time magazine in February last year.

Ellison’s group has urged the US government to spend more money on radars and interceptors designed to defend American airspace.

“It’s about spending money the right way … the American public has to be protected,” he said.

However, Yin’s team have said this is not necessary. They only used a common weather radar in their test and did not make any hardware modifications.

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The Chinese scientists say that existing civilian radar is already very powerful and it can even map the outline of a floating cloud. It only requires upgrading the signal processing software to detect various types of balloons.

In the paper, the PLA team disclosed a unique algorithm they developed that could accurately detect the spatial disturbance of the electric field caused by the balloon and identify and locate it based on other physical parameters.

The difficulty of this technology lies in how to extract the balloon’s signal from background noise such as ground clutter and radio frequency interference. Researchers provided detailed methods for eliminating noise and reducing false alarm rates in the paper.

This technology even eliminates the need to change the radar’s operating mode. It is “easy to implement, does not require prior knowledge about clutter, does not require the accumulation of multi-frame data and does not require staring at the target,” Yin and his colleagues wrote.

High-performance weather radars are widespread around the world, and using them to track balloons is more economical and effective than military radars.

“Software upgrades can achieve the detection of air-floating balloons, giving weather radars new functions without changing the radar hardware configuration and without increasing hardware costs,” Yin’s team added.