Evan K. Westwood
C. T. Tindle
N. R. Chapman
Defence Res. Establishment Pacific, FMO Victoria, BC V0S 1B0, Canada
A normal mode model has been developed for underwater acoustic propagation in an ocean environment with multilayered elastic media below and/or above the water column. The compressional (p-) and shear (s-) wave sound speeds may either be constant or have a gradient (1/c[sup 2] linear with depth) in each layer. Mode eigenvalues are found by analytically computing the downward- and upward-looking plane-wave reflection coefficients R[sub 1] and R[sub 2] at a reference depth in the water and searching the complex k plane for points where R[sub 1]R[sub 2]=1. The complex k-plane search is greatly simplified by following the path along which |R[sub 1]R[sub 2]|=1. The |R[sub 1]R[sub 2]|=1 path connects all the modes, which are found as points on the path where the phase of R[sub 1]R[sub 2] is a multiple of 2(pi). The direction of the path is found from the analytic derivative d(R[sub 1]R[sub 2])/dk. Leaky modes are found, and multiple channels are handled. The eigenvalue finding algorithm appears to be robust and efficient. [Work supported by the ARL Independent Research and Development Program.] [sup a)]On leave from Appl. Res. Lab., The Univ. of Texas at Austin. [sup b)]On leave from Dept. of Phys., Private Bag 92019, Univ. of Auckland, Auckland, New Zealand.