Applying normal mode method for calculation of acoustic wave propagation in the muddy bottom coastal regions

Normal mode method is a proper way to calculate propagation of acoustic waves produced by low frequency sources in the underwater environment and it has its best efficiency when media can be considered horizontally stratified. The authors became interested in the problem when their tests illustrated that the noise produced by distant vessels is of low frequency type. Thus to investigate how waves produced by this type of source propagates in the underwater environment, they regarded the problem of computing pressure and acoustic energy magnitude at each point of the media by using the wave equation. In this paper, first the results of their tests for obtaining the shipping noise spectrum is presented. In this paper, first the results of their tests for obtaining the shipment noise spectrum is presented. After that they use the normal mode method for computing acoustic wave propagation in the coastal environments for a few real speed and density profiles that are obtained by their CTD metering tests. For each computation up to 15 modes are used and to evaluate the precision of the results, the calculation done by other workers for the Munk profile is compared with the outputs of their program is that the bottom is considered as a layer with different speed and density, so that the method is applicable in most real cases and gives acceptable results, specially in the muddy bottom condition.