Analysis of optimal conditions for recording signals when studying the atmospheric boundary layer with the acoustic method of partial reflection

Abstract

Equations for the coefficient of partial reflection K from stratified inhomogeneities in the atmospheric boundary layer have been derived on the basis of the Epstein transition and symmetrical layer models as functions of three dimensionless parameters, i.e., the relative layer altitude, its relative thickness, and the relative variations in the effective sound speed in a layer. The equations have been obtained for the relative layer altitude at which the total internal reflection appears; the behavior of the function K is studied at close altitudes. Significant weakening of the dependence of coefficient K on the relative layer thickness in these conditions is shown, which makes it possible to record partially reflected signals in a wide range of wave-lengths or frequencies of the sounding signal. In other cases, the coefficient of partial reflection K strongly depends on the layer thickness. According to experimental data on variations in the amplitude of received acoustic signals with an increase in the source-detector distance, a technique for the parameterization of the additional impedance attenuation of sound that propagates over the earth’s surface has been developed, and these parameters have been experimentally estimated for different stratification conditions and sounding signal frequencies. Many records of background acoustic noises typical for one or another measurement sites have been distinguished and classified, a technique for estimating the minimum signal amplitude distinguishable against noises has been developed, and the corresponding estimates have been made. Based on these data and the specifications of three different industrial acoustic sources, the parameter limits provided by these sources have been estimated for the method of partial reflection.