ASA 124th Meeting New Orleans 1992 October

4aPA6. Methods of allowing for linear gradients within fast field layers.

Shahram Taherzadeh

Keith Attenborough

Eng. Mech. Discipline, Open Univ., Milton Keynes MK7 6AA, England

At large ranges or at higher frequencies, it is necessary to incorporate a large number of isovelocity layers to achieve tolerable accuracy in fast field calculations. This has a predictable effect on computation time. There is a standard solution in terms of Airy functions that allows for a linear gradient within each layer. This paper presents a preliminary investigation of an alternative form of solution that involves Hankel functions of complex order. These arise from a transformation of the depth-separated wave equation into a form of Bessel's differential equation. Results have been obtained for a low-frequency case and are compared with results from the standard form in terms of Airy functions.