Computational comparison of broadband acoustic models.

Abstract

Broadband acoustic propagation models vary greatly in their computation times. To define the speed-versus-accuracy tradeoffs, two questions are addressed: (1) For ducted environments, how does the parabolic equation (PE) model compare with the faster Labianca virtual-mode model (VM) and the FAME eigenray part of the generic sonar model (GSM)? (2) In nonducted environments, must a GSM complex transmission loss (TL) be computed for all the signal frequencies, or is a single frequency of computation sufficient (i.e., is it fair to assume that the only frequency dependence in the complex-TL phase is in the ray time delay)? To answer these questions, the effects of the computed complex-TL on sine-wave-burst and HFM-burst signals are presented. The multipath arrival structures of the environments enforced a 4-s received-signal duration, and the transmit signals enforced a bandwidth of 200 Hz. The results are as follows: (1) A weak duct shows favorable comparison between GSM, VM, and PE models; however, a strong duct does not, and in fact reveals numerical instability in the PE computations. (2) Single-frequency GSM captures the basic arrival structure of multiple-frequency GSM, but the multipath interference is different and sensitive to the dominant signal frequency. It is concluded that GSM (but not single-frequency GSM) may in most practical cases yield adequate predictions for the acoustic filtering of broadband signals.