The Air Force Research Laboratory Sensors Directorate and the National Museum of the United States Air Force Collection Management Division are teaming up to help address an Air Force need to automatically detect numerous highly mobile ground threats such as anti-aircraft guns, also known as AAA.
In conventional warfare, AAA weapons are used to defend high-asset-value targets on the ground such as surface-to-air missile sites, headquarters, weapons storage sites, bridges, power grids and other vulnerable strategic targets.
“If you can detect an AAA gun, you know there’s a high probability there’s a high-value military target close by,” said David Sobota, with the Sensors Effects and Analysis Branch at AFRL’s Sensors Directorate. Sobota is collaborating with Capt. Yongjun Yoon, who is a radio frequency sensing engineer from the Radio Frequency Technology Branch at AFRL’s Sensors Directorate. “Mitigating the risks of the AAA guns’ lethal attacks will increase flexibility of airborne and air assault operations, which significantly benefits our missions and warfighters,” said Yoon.
Automatically detecting targets is difficult when clutter such as trees, bushes or roads are close to the target, and decoys make the problem even more difficult, according to Sobota. “The problem has been worked on for 30-plus years and we’re currently exploring machine learning and artificial intelligence techniques for target detection.”
Collecting realistic signature data is everything when it comes to radar research.
“What you ideally want to do is collect real-world data and then try to come up with techniques to detect these reflectivity signatures in the real-world,” said Sobota. “Using real anti-aircraft guns from the Air Force museum will help us come up with more reliable detection techniques more quickly.”
The museum’s support, by offering five AAA guns, is a gold mine for this project, Sobota said.
The guns, which are part of the national historical property collection at the NMUSAF, are preserved by the museum’s Collection Management Division for research and possible use in future exhibits.
“We are pleased that these artifacts can be utilized for this research project,” said Roberta Carothers, Collection Management Division chief. “The museum strives to support all operational requests similar to AFRL’s data request to help the warfighter reduce AAA ground threats.”
Sobota just initiated three Small Business Innovation Research contracts, all currently in Phase I, asking companies to do some modeling and simulation. Each is $150,000 for nine months. Some will qualify for Phase IIs, which are $750,000 for two years.
Sobota, Yoon and their team plan to build three mock-ups of common AAA guns so they can be taken to test ranges, so they plan to take radar reflectivity measurements of the museum’s guns using a portable X-band radar. This data will help to determine dominant reflectors needed in their mock-ups, which will be built by their fabrication shop team.
“We know the multiple barrels alone from the AAA gun are very visible to a radar, but the barrels are surrounded by other structures such as shell feeders. All these structures reflect radar energy. The Air Force museum guns will help us build a more realistic mock-up. We will design the mock-up so it looks like a real AAA gun to the radar, but it has to be much lighter and reconfigurable,” Sobota said.
Citing a Government Accountability Office report, he said that during the Vietnam War, AAA weapons were responsible for more than 50 percent of the aircraft shot down. This has been true for most modern conflicts. In the past, AAA were manually loaded and hand cranked by crews of 6 to 10 people.
“They just had mechanical cross hairs to guide their firing,” he said.
“The modern AAA has electro-optical/infrared sensors and radar that let the operator know how much to lead the target. Radar gives them access to range and velocity information and all-weather capability. Modern systems are totally automated and usually have a crew of just two. It has electric servos for fast slewing, auto-loaders and has a much faster firing rate,” Sobota said.
The latest AAA guns are designed specifically to shoot down swarming UAVs, he noted.
“If the Allies could shoot down Nazi buzz bombs (similar to modern UAVs) with an 82 percent success rate in WWII, just imagine how effective these modern guns will be,” Sobota said.
Another aspect that makes AAA research more applicable is the Air Force’s vision of using swarming UAVs, he said, adding, “To recognize targets with a UAV, you have to fly fairly low level just to get the resolution needed to automatically detect these targets. You can’t do this at high altitude – radars just aren’t that good. Radar technology is key to all-weather capability. Other sensors do not have the range, especially in bad weather. You can’t plan your tactics around good weather.”
Another part of the research is determining whether artillery shells in flight can be backtracked and whether the plasma discharge can be detected when fired, Sobota said. “When it fires, the gun shoots out plasma which has a significant radar cross-section and Doppler signature.”
“If we can’t detect the anti-aircraft artillery gun at a safe stand-off distance, you’d like to at least detect the AAA shell/projectiles in flight. In the Air Force’s swarming autonomous UAV vision, you will have numerous expendable or attritable aircraft flying over denied territory. As the adversary is firing at your UAVs, you can detect which AAA are firing, backtrack their projectiles, and either warn the other UAVs to stay away, cue other UAVs to find targets nearby, or destroy the AAA gun itself.”
Sobota said he has already started talking to the Army Research Lab in order to get help collecting data of Doppler gun recoil and direct plasma measurements of firing guns.
“Many countries are working on Mach 6+, 200+ mile railguns, and extended range artillery. More powerful propellants, rocket-assisted, and smart shells are already here,” he said.
Some legacy AAA guns are lethal to 35,000 feet and will become more lethal as tracking improves, said Sobota. The future is extended range artillery with smart shells. Also, technology such as railguns, plasma powered, and electro-thermal chemical guns are making rapid progress.
It’s unknown at this point which technology will win out. Currently, the U.S. Navy and other countries are investing heavily in railguns and they are already testing prototypes, Sobota said.
Today, the Air Force is going up against denied environments with near-peer forces. These adversaries have sophisticated air defenses with AAA and missiles. In the future it will be lasers, railguns, extended-range artillery, AAA and missiles. These systems will be more automated and more lethal, with much quicker reaction times, said Sobota.