Penetration of a Sonic Boom into Water

An aircraft in level flight at a supersonic speed over water produces a sonic-boom pressure on the water surface. Usually the N wave of the incident sound pressure moves across the surface at a subsonic speed, relative to the speed of sound in water. Therefore, the boom energy is totally reflected, and the sound pressure in the water falls off with depth below the surface. The penetration depth, comprising well over half of the underwater energy, is about the same as the N-waveform length on the surface. The analysis shows further that the wave reflected into the atmosphere has (a) two infinitely large pressure spikes at the leading and trailing edges of the N wave, and (b) a weak precursor and a weak tail. The same is true of the underwater wave just at the surface. The spikes, precursor, and tail have positive sound pressures and are even functions of distance from the center of the N wave.