Helicopter Location Using Infrasound Arrays

Abstract Three multinode infrasound station arrays were deployed along the perimeter of a prescribed burn at Eglin Air Force Base, Florida. One six-node station and two two-node stations monitored the fire progression while a helicopter encircled the burning area, generating significant acoustic signals. Fundamental-mode power analysis and beamforming search were used to extract estimated infrasound wave propagation direction and wavespeed. The three stations triangulated azimuth angles to estimate helicopter location. Elevation was estimated using variations of spectrum power, and apparent source speed was extracted via Doppler shift. Publicly available Global Positioning System locations provided true helicopter location, speed, and flight orientation compared here with acoustically derived estimates, thus providing uncertainty limits. For the six-node, hexagonal station array, the median angle error was 9° with an interquartile distance of 9.8°. Overall, helicopter location errors, using three station arrays, ranged from 10s to 100s of meters. Spatially distributed multinode stations can be effective at tracking moving sources such as helicopters, especially if each station array has three or more distributed sensor nodes.