New and improved parabolic equation models

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Abstract
The stability of the self starter and the accuracy of the elastic parabolic equation have been improved. The self starter is an initial condition that is generated by applying an operator to the source term [IEEE J. Ocean. Eng. 22, 102–109 (1997)]. Although the self starter is continuous, numerical difficulties can arise for problems involving relatively deep water and/or low bottom attenuation and/or high frequency. This problem has been eliminated by placing the pole of the smoothing operator far from the eigenvalues of the depth separated wave equation. The improved self starter has been incorporated into Version 1.1 of RAM (range‐dependent acoustic model), which is available by anonymous ftp from ram.nrl.navy.mil. The elastic parabolic equation accounts for compressional and shear waves in the sediment. Handling a sloping ocean bottom is complicated by the change in the number of dependent variables across the interface. Gradual slopes can be handled accurately by applying a coordinate translation to flatten the ocean bottom interface. Energy is conserved and the adiabatic mode solution is invariant under this mapping. This approach has been incorporated into Version 1.0 of RAMS, which is also available by ftp. [Work supported by ONR.]

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