HIGHER-ORDER PADE APPROXIMATIONS FOR ACCURATE AND STABLE ELASTIC PARABOLIC EQUATIONS WITH APPLICATION TO INTERFACE WAVE-PROPAGATION

Higher-order Pade approximations are applied to derive accurate and stable parabolic equations for sound propagation in oceans bounded below by an elastic bottom or bounded above by ice cover. Accuracy is achieved by placing constraints on the derivatives of the Pade approximations at the point corresponding to the reference wave number. Stability is achieved by requiring that the Pade approximations map part of the lower-left quadrant of the complex plane into the upper half of the complex plane. Elastic parabolic equations based on these Pade series can handle problems involving compressional, shear, and interface waves, very wide propagation angles, and large depth variations and weak range variations in the seismoacoustic parameters. A finite-difference spectral solution is developed for generating reference solutions and starting fields. The rotated elastic parabolic equation is used to investigate the accuracy of the elastic parabolic equation for range-dependent problems.