Penetration of shaped sonic boom noise into a flat ocean

Abstract

For a flat ocean, the penetrating underwater sound field due to an incident N wave shaped sonic boom has been known since the late 1960s. In the present research the penetrating sound field due to an arbitrarily shaped sonic boom is constructed by 1.) finding the horizontal wavenumber spectrum of the sonic boom, and 2.) superimposing the resulting penetrating waves for each frequency component. A simple algorithm is given to construct such penetrating sonic boom waveforms using fast Fourier transforms. The method is implemented in a symbolic manipulation program but should be straightforward for coding in a conventional Fortran or C computer program. Using the procedure with N wave input data gives results in agreement with the known analytical solution for incident W wave sonic booms. As examples of the predicted underwater sound field from incident arbitrarily shaped sonic booms, the resulting waveforms are provided for booms produced by hypothetical High Speed Civil Transport configurations, as well as by experimentally measured booms produced by operating U.S. Air Force aircraft. One notes from these predictions that the underwater sound field below a depth of 16 m should be relatively insensitive to perturbations induced on the incident sonic booms due to mechanisms such as atmospheric turbulence.