Line-of-bearing tracking of an airborne target with a distributed acoustic sensing system

Recent years have seen a significant proliferation of fiber-optic distributed acoustic sensing (DAS) systems and their uses. As the technology became more sophisticated, new applications and areas of research emerged. Older versions of DAS are “intensity only” systems, meaning there is no signal coherence between neighboring spatial channels. Newer DAS systems are coherent, which allows for more sophisticated signal processing techniques, such as beamforming. Despite this, few works explore the coherent signal processing of DAS arrays with the goal of tracking or localizing acoustic sources. This work investigates the ability of a coherent DAS system to track the acoustic signatures of low-altitude airborne targets. An experiment was performed with a shallow-buried DAS array and a circling aircraft. Multiple beamforming algorithms were tested and compared on the recorded DAS data. The acoustic line-of-bearing (LOB) tracks were evaluated with a ground-truth vehicle track obtained from radar data. Accurate LOB tracks were obtained, providing evidence that acoustic signals undergoing complex air-ground-cable propagation and transmission can maintain sufficient spatial coherence to make coherent signal processing and acoustic tracking feasible.