Infrasound produced by a small pile fire

• Small pile fires produce infrasound in the near infrasound band (1–20 Hz). • Spectral content of fire infrasound correlates with flame flickering frequency. • Infrasonic remote sensing has potential for monitoring large fires. We document the characteristics of infrasound from a compact (<3-m burn diameter) wood pile fire using arrays located at 50 and 600 m. Infrasound from our controlled burn is present throughout the entire near-infrasound range (1–20 Hz), but its peak infrasound energy trends from 1.3 to 1 Hz over an hour correlating with a transition from relatively tall and narrow flame to a broader pile of coals with shorter flame. Observed infrasound frequencies correlate with flame flickering – quantified through spectral analysis of video – suggesting that flame and gas pulsing is the mechanism for the <2 Hz infrasound. Although the amplitude of the pile fire infrasound is low (<0.1 Pa at 50 m) it is a stationary source and detectable using array processing at 600 m. Given this demonstrated capability for remote surveillance of a small fire we contend that remote infrasound monitoring has potential application for larger wildfires.