A coherent line source in a turbulent atmosphere

Abstract

The sound field of a coherent line source in a nonrefracting, turbulent atmosphere is studied. An expression for the sound pressure level in the frequency domain is developed, based on a discretization of the line source into a set of point sources. Atmospheric turbulence is taken into account by the mutual coherence function. Numerical computations for various turbulent atmospheres show that the geometrical attenuation is 3 dB per distance doubling (3 dB/dd) at a small distance (cylindrical spreading), 6 dB/dd at a large distance (spherical spreading), and 7.5 dB/dd in a transition region. The anomalous value of 7.5 dB/dd is confirmed by an analytic approximation. Next, a computational method in the time domain is developed, for arbitrary wave forms emitted by the source. Atmospheric turbulence is taken into account in this method by including random fluctuations of the acoustic travel times, based on the spectral density of the travel time correlation function. For a harmonic coherent line source, the method yields results that agree with results computed in the frequency domain.