Abstract:

The effective structure-function parameter for scattering by atmospheric, turbulent velocity fluctuations has normally been assumed to be C[inf eff][sup 2]=4C[inf V][sup 2]/c[inf 0][sup 2] However, a new derivation by V. E. Ostashev [Waves Random Media 4, 403--428 (1994)], which takes into account the vectorial nature of the wind velocity field, suggests that C[inf eff][sup 2]=22C[inf V][sup 2]/3c[inf 0][sup 2]. An experiment was designed to determine the correct value of the coefficient. Amplitude variances were monitored for several discrete frequencies between 380 and 3500 Hz, at distances up to 675 m. Cup and hot-wire anemometers were used to determine C[inf V][sup 2]. A theory for scattering by inertial-subrange turbulence was then used to calculate the C[inf eff][sup 2] coefficient from the amplitude variance and C[inf V][sup 2]. Although there is some tendency in favor of the 22/3 coefficient, the results cannot be considered conclusive. The main difficulty appears to be obtaining a sufficiently accurate measurement of C[inf V][sup 2].