Abstract:
Theoretical calculations of ground-to-ground sound propagation in a turbulent atmosphere require the power spectrum for horizontal wind-speed fluctuations, (Phi)[inf xx]. Experimentally, however, the longitudinal spectrum, (Phi)[inf rr], is usually measured. In propagation predictions, a frequently used approximation is (Phi)[inf xx](approximately equal to)(Phi)[inf rr]. Under the assumption of homogeneous, isotropic turbulence, an exact relation between (Phi)[inf xx] and (Phi)[inf rr] is derived and several limiting cases are discussed. For a Kolmogorov spectrum and small-angle scattering, for example, (Phi)[inf xx](approximately equal to)(11/6)(Phi)[inf rr] is found. The practical significance of the relation between (Phi)[inf xx] and (Phi)[inf rr] for analyzing experimental data is discussed. It is shown that, for many situations, the approximation (Phi)[inf xx]=constant x(Phi)[inf rr] is reasonable for comparing predicted and measured sound levels. [Work supported by the Army Research Laboratory and the Applied Research Laboratory, Penn State.]