New radar technology lets aircraft sensors penetrate clouds, dust

Electro-optical infrared sensors guide aircraft at high speeds and high altitudes, however they can still be thwarted by clouds and dust. However, with the new video synthetic aperture radar (ViSAR) technology that DARPA successfully tested last week, aircraft sensors may soon be able to penetrate even the most obscure conditions.

“The electro-optical infrared (EO/IR) sensors on board the test aircraft went blank whenever clouds obscured the view, but the synthetic aperture radar tracked ground objects continuously throughout the flight.” said Bruce Wallace, Program Manager within DARPA’s Strategic Technologies Office.

Synthetic aperture radar tracks target ranges by measuring the return time of electromagnetic pulses, in the same way that traditional radar systems do. However, according to a report by the Sandia National Laboratories, synthetic aperture radars achieve a much more accurate azimuth measurement, or the tracking-distance along the earth’s surface, by using an extremely high frequency pulse emission.

Typically, extremely high frequencies can only be achieved using massive antennas, too large to be installed on aircraft. Yet, the synthetic aperture radar system compiles the pulse emission data as the aircraft flies in order to simulate the effect of a large antenna, hence the characterization as “synthetic.” According to the DARPA press release, synthetic aperture radar used to have frame rates that were too slow to provide streaming data in real-time. Now, DARPA has taken a major step to overcome this problem.

“The recent flight tests of the ViSAR sensor…proved that we can take uninterrupted live video of targets on the ground even when flying through or above clouds,” said Wallace.  

Another new feature of the sensor is that it can fit onto a standard EO/IR sensor gimbal. According to DARPA, the ultimate goal is to have synthetic aperture radar system payloads that integrate with the standard gimbals and produce high resolution video data-streams in cloudy or dusty conditions.

The synthetic aperture is being developed through DARPA’s ViSAR program, begun in 2013. The program was created to address the capability gap of aircraft sensors operating in clouded conditions. The EO/IR sensors depend on the target-background contrast, and the light wave or temperature source.

Following this first publically-announced successful test, DARPA will continue to work on the user-interface aspect of the sensor software.

“We don’t want operators in the back of an aircraft to need special radar training to interpret the sensor’s data,” explained Wallace. “Refining the ViSAR sensor’s visualization software to provide operators a representation they’re used to seeing is the next step in the program…we are working to make the visual interface as easy to interpret as existing EO/IR sensor displays,” he said.

DARPA’s latest successful test was conducted using a modified DC-3 aircraft, however DARPA said that the technology will be compatible across different aircraft. According to the Department of Defense, Northrop Grumman with L3 Technologies are contracted to contribute to the development process.