Detection and assessment of secondary sonic booms in New England

Measurements in summer 1979 and subsequent analysis demonstrate that secondary sonic booms frequently reported by New England residents are caused by inbound Concord flights to New York. Ray trace computations, based on meteorological data and FAA radar tracking of Concord flights, predict signal arrival times within 20 s and predict wave front azimuthal angles with 4°. Present paper focuses on analysis and is based on comprehensive report (FAA-AEE-80-22) with same title. Sound paths leaving aircraft trajectory normal to Mach cone that reach New England classify as (1) ground wave (plane to ground, then diffracted creeping wave), (2) type I secondary sonic boom (plane to mesophere to ground), and (3) type II secondary sonic boom (plane to ground to mesophere to ground). Refraction in the mesosphere back to the ground is possible only when mesospheric winds cause effective sound speed at some altitude above aircraft to exceed that at ground. The ground wave, which has very low amplitude but is discernible in infrasonic pressure records, arrives first and is explained by Ingard-Pridmore-Brown theory of penetration into a shadow zone. Geometrical acoustics predicts type I and II secondary sonic boom arrivals only at and beyond focus lines (where ray-tube areas vanish), but a diffraction model based on theory of wave phenomena near caustics yields arrivals on near side of focus lines. [Work supported by Federal Aviation Administration.]