During a multi-service exercise, the U.S. Army Engineer Research and Development Center (ERDC) Cold Regions Research and Engineering Laboratory (CRREL) successfully demonstrated a groundbreaking technology to detect airborne targets. The project, called TripLine, was developed by ERDC and uses emitted sounds to passively detect the targets. The technology was showcased during Arctic Edge 22, a bi-annual event hosted by the Alaskan Command at Joint Base Elemendorf-Richardson, Alaska, committed to the defense of North America with roots going back more than five decades.
The TripLine project started in 2017 and utilizes technology to detect airborne targets through soundwaves that interact with the ground and transfer a portion of the acoustic energy into the ground. The transferred soundwave energy subsequently interacts with buried sensing fiberoptic cable and induces a small, but highly perceptible, change in the cable that can be measured, analyzed and recorded by the TripLine system. This atmosphere-to-terrain energy transfer enables the presence of aircraft near the TripLine system to be automatically detected. Further, beamforming techniques are employed within the TripLine system, which aids in providing a range and line-of-bearing (LOB) estimates. The system continues to provide updates regarding aircraft range and LOB, as long as the emitted sound energy produces a signal in excess of the background noise.
Dr. Sergey Vecherin, a research physicist at CRREL who is developing a suite of algorithms for Tripline and leading the algorithm-developing team (AlgoTeam), said TripLine aims to be a low-maintenance system suitable and operational in Arctic conditions.
“Tripline is a system for automatic detection of acoustic sources with some unique operation capabilities,” said Vecherin. “Other systems cannot do what Tripline can, either due to scientific or operational limitations.”
When the first TripLine experiments were conducted in 2017, the goal was to prove sensor success for the desired sources in principle. In 2019, Tripline was used in another field experiment for different sources and different locations, and in August 2020 it underwent a very successful demonstration in New Mexico.
The TripLine system has been tested and proven to have a high detection probability and a low false alarm rate in several different environments that had a nearly ideal soil structure for the sensing system. These soils are relatively loose, sandy soils with low contrast in air-ground acoustic impedance, and under these conditions, the acoustic detection system has performed nearly flawlessly.
One remaining demonstration of the system needed to be performed, a test of the technology under highly challenging soil conditions. It was determined that the cold, austere environments of the Arctic would present one of the greatest challenges to the sensor system due to the high acoustic impedance from frozen soils, as well as the noise damping from snow and ice coverage. In the Arctic Edge 2022 exercise, TripLine was tested under extremely challenging environmental conditions. Vecherin said, “So far, TripLine has successfully passed all the tests, indicating the high value of the technology.”
The highly complex terrain conditions around JBER were found to be ideal for the Tripline demonstration project as the ground was completely frozen, most likely well below the buried sensing cable. The goal of the demonstration effort was to show that the TripLine sensing system is capable of detecting airborne objects within proximity of JBER, despite the frozen soil and thick coverage of snow and ice. Between February 25 and March 16, 2022, numerous commercial and military aircraft had flight paths near Joint Base Elmendorf-Richardson, and the TripLine event utilized those flights to demonstrate that it could detect and monitor movement across the region in real time with a high detection probability and very low false alarm rate.
This successful live demonstration proves that the acoustic sensing system reliably functions in austere environments, despite being buried in frozen soil and under several feet of snow and ice. In addition, this successful demonstration opens the opportunity for the Department of Defense to deploy this new technology in locations around the globe where airborne threats have traditionally been a challenge to detect and monitor in real-time.