LOW-FREQUENCY SOUND-PROPAGATION MODELING OVER A LOCALLY REACTING BOUNDARY WITH THE PARABOLIC APPROXIMATION

There is substantial interest in the analytical and numerical modeling of row-frequency, long-range atmospheric acoustic propagation. Ray-ba sed models, because of their frequency limitations, do not always give an adequate prediction of quantities such as sound-pressure or intens ity levels. However, the parabolic approximation method, widely used i n ocean acoustics and often more accurate than ray models for frequenc ies of interest, can be applied to this type of acoustic propagation i n the atmosphere. Modifications of an existing implicit finite-differe nce implementation for computing solutions to the parabolic approximat ion are discussed. A locally reacting ground surface is used with one- and two-parameter impedance models, while a nonreflecting boundary co ndition is used to handle the upper boundary. Relative sound-pressure level calculations are performed for a number of flow resistivity valu es in both homogeneous and nonhomogeneous atmospheres. Comparisons to experimental data are made which suggest this modeling approach can be useful in the study of these types of propagation problems. (C) 1995 Acoustical Society of America.