Accurate PE calculations for range-dependent environments based on c updates

Abstract

The standard parabolic approximation to the acoustic wave equation is known to have intrinsic phase errors, which will degrade the accuracy of any PE solution for long-range propagation in the ocean. Pierce recently suggested a remedy to minimize these phase errors by simply choosing an appropriate mean phase speed (c0), eventually updated with range, representing a weighted average of all phase speeds involved in a particular propagation problem. We have now extended Pierce's formalism to include the wide-angle parabolic equation of Thomson and Chapman [J. Acoust. Soc. Am. 74, 1848 (1983)], which inherently has smaller phase errors than the standard parabolic equation. The importance of using c0 updates in PE calculations for range-dependent environments is demonstrated through numerical results for a wedge-shaped ocean. Comparison with alternative solution techniques (coupled modes, intrinsic modes) shows that accurate PE solutions for the wedge problem can be obtained only for single-mode situations, even when using c0 updates with range.