Preliminary Observations of 1–16 Hz Natural Background Infrasound and Signals from Apollo 14 and Aircraft

Abstract

Summary Infrasound with frequencies of 1–16 Hz, detected by an array of four thermistor flow‐meter microphones in Sterling Forest, New York, was observed to have a continuous background with peak energy distributed near 16 Hz in frequency, with amplitudes of about 1 dyn cm‐2, and arriving from the south‐west and south‐east at slightly above the speed of sound in air at ground level. The same array of microphones detected 5 dyn cm‐2 signals from the Apollo 14. The earlier part of the 10‐min signal arrived from the first stage re‐entry, the later from the launch site vicinity. It is shown that aircraft beyond the visible and audible range can be detected and tracked by monitoring the infrasound emitted throughout most of the 1–16 Hz frequency band. Copyright © 1971, Wiley Blackwell. All rights reserved