New fast field programs for anisotropic sound propagation through an atmosphere with a wind velocity profile

Two new fast field programs (FFP) have been developed for numerical computation of anisotropic sound propagation through an atmosphere with a wind velocity profile. The first new FFP can be used to compute the near-field and far-field sound pressure. The numerical implementation of the FFP is based on an integration algorithm using a two-dimensional fast Fourier transform with iterative refinement. For studying problems of long-range propagation, a novel far-field expression for sound pressure is derived. The second new FFP is based on this far-field approximation. If the magnitude of wind speed is not very large; this new far-field expression shows that the component of wind perpendicular to the direction of propagation has no effect on long-range propagation. Numerical results from both new fast field programs demonstrate that the effective sound-speed model used in the conventional FFP’s is still valid for propagation within a certain range. However, the agreement between methods becomes worse at longer horizontal distance. These numerical results also show that the effective sound-speed model will produce phase errors for higher angle modes, which is most apparent when a single mode dominates the solution. When many modes are present, the envelopes of the curves match, but the details do not.