Infrasonic Attenuation and Ambient Noise

A number of experiments carried out over the past two decades tend to confirm the existence of two major anomalies at infrasonic frequencies, (i) Long-range propagation measurements in the sound channel show extra attenuation that cannot be the result of medium absorption (ii) Vertical directionality measurements of ambient noise show a broad maximum in the axial direction where a minimum is expected. A possible mechanism for both phenomena is scattering by internal waves or eddies.