## 4aPAa1. Approximation of theoretical wind turbulence spectra from wind-speed measurements.

### Session: Thursday Morning, December 5

### Time: 8:00

**Author: Xiao Di**

**Location: Appl. Res. Lab. and the Graduate Program in Acoust., Penn State, P.O. Box 30, State College, PA 16804**

**Author: Kenneth E. Gilbert**

**Location: Appl. Res. Lab. and the Graduate Program in Acoust., Penn State, P.O. Box 30, State College, PA 16804**

**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.]

ASA 132nd meeting - Hawaii, December 1996