A finite-difference time-domain normal mode method for broadband transmission loss predictions

A broadband deterministic underwater acoustic channel model that integrates a finite-difference time-domain (FDTD) scheme with normal mode theory has been proposed. The former allows the computation of Green's function in the vertical direction across a broad bandwidth in a single time-domain computation without having to repeat at every frequency of interest, while the latter guarantees an accurate calculation of transmission loss in the horizontal direction. To this end, a systematic algorithm with low numerical complexity was developed. Its accuracy was maintained regardless of the bandwidth, frequencies, and size of the channel. The accuracy and the computational efficiency of the proposed algorithm are verified through comparisons with frequencydomain normal mode solutions at low frequencies and ray solutions at high frequencies, for various propagation scenarios.