PRECURSOR WAVES FROM A CONTINUOUS TRANSITION LAYER IN THE SOUND SPEED PROFILE.
CAMBRIDGE ACOUSTICAL ASSOCIATES INC MASS
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If a sound speed profile exhibits a relatively abrupt transition between two more or less uniform regions of differing sound speeds, it is often observed that among the signals produced by a distant sound source is one which arrives earlier than all others. This type of signal, which has been variously referred to as the precursor wave, the lateral wave or the head wave, is not explainable on the basis of ray acoustics. In the past, theoretical investigations have been made of the formation of precursors on both sharply abrupt and continuous transition layers. Following the methods of Lang, the author considers the precursors arising from a point sound source located in a homogeneous half-space connected to another isovelocity domain of higher sound speed through a transition zone in which the square of the index of refraction is a linear function of height. High frequency asymptotic expressions for the precursor pressures are developed for both the transition zone and the half-space in which the sound source is located. By means of Fourier transformation, the treatment is extended to include transient sound sources. Author