Experimental determination of the effective structure-function parameter for atmospheric turbulence

The effective structure-function parameter for scattering by atmospheric tu rbulent velocity fluctuations has normally been assumed to be C-eff(2) = 4C (v)(2)/c(0)(2), where C-v(2) is the velocity structure-function parameter a nd c(0) the sound speed. However, a new derivation by Ostashev [Waves Rando m Media 4, 403-428 (1994)], which takes into account the vectorial nature o f the wind velocity field suggests that C-eff(2) = 22C(v)(2)/3c(0)(2) . An experiment was designed to determine the correct value of the coefficient. Sound-pressure amplitude variances were monitored fur several discrete freq uencies between 380 and 3800 Hz, at distances up to 250 m. Cup and hot-wire anemometers were used to determine C-v(2). A theory for scattering by iner tial-subrange turbulence was then used to calculate the C-eff(2) coefficien t from the amplitude variance and C-v(2). Datasets recorded under different atmospheric conditions yielded different relationships between the coeffic ients and failed to verify either the 4 or 22/3 value. Some possible explan ations for this behavior are discussed, including the need for more realist ic meteorological modeling. (C) 1999 Acoustical Society of America. [S0001- 4966(99)04302-7].