Diffraction of sonic boom past the nominal edge of the corridor

Abstract

According to ray acoustics sonic boom is limited to a ’’corridor’’ on the ground by atmospheric refraction. Beyond the edge of the corridor on either side lies a region void of incident or reflected rays—the ’’shadow zone’’—the treatment of which is beyond the scope of ray acoustics. In this paper, a technique is developed for extending the prediction of the sonic boom signature into the shadow zone using diffraction theory. The calculations indicate that the portion of this region lying along the horizontal plane boundary behaves like a low‐pass acoustic filter. This has the effect of progressively rounding and attenuating the sonic boom signature as the shadow zone is penetrated—an observable characteristic of experimental records. In a separate calculation, an empirical variable reflection factor based on the angle of incidence of the shock wave in the sound field is obtained to correct the bell‐shaped 3/4‐power curve of amplitude variation across the corridor.