Robert A. Koch D. P. Knobles
Appl. Res. Lab., Univ. of Texas, P. O. Box 8029, Austin, TX 78713-8029
A new algorithm for calculating the normal modes that are used to describe underwater acoustic propagation is presented. The algorithm is especially relevant for broadband normal mode calculations in which normal mode eigenvalues, depth functions, and attenuations are needed. The new algorithm uses an expansion technique to construct normal mode eigenvalues and depth functions for some frequency from eigenvalues and depth functions previously calculated at another, higher frequency. Comparisons of the estimated eigenvalues, depth functions, and attenuations with exact results are presented for several shallow water environments. A broadband propagation model that uses normal mode sets calculated with the new algorithm has been developed. Transmission loss and impulse responses based on estimated and exact normal mode sets are compared. [This work was supported by the Office of Naval Research through Block RL3B and Block CS3A.]