Results from applying a Crank-Nicholson parabolic equation method (CN-PE) are presented in situations with a thin screen on a hard ground in a turbulent atmosphere, and with the acoustic source at ground level. The results are evaluated by comparison with G. A. Daigle's model, which uses the sound scattering cross-section by V. I. Tatarskii together with diffraction theory. The results show a fairly good agreement for situations where the receiver is above ground, thus indicating that both methods are applicable to the problem. When the receiver is at ground level the two methods lead to large differences in insertion loss since only the PE method predicts that turbulence causes an increased sound level in the case without a screen. For the situations considered in this paper a turbulent atmosphere is shown to significantly decrease the sound reduction by a screen. An approximation in the representation of a turbulent atmosphere in the CN-PE method is presented, and is shown to lead to an acceptable error in limited cases. [References: 21]
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