Investigation of long-range sound propagation in surface ducts

• Published in: Chinese physics B 2013-12, Vol.22 (12), p.297-307
• Main Author: 段睿 杨坤德 马远良
• Format: Article
• Language: English
• Subjects: Angles (geometry); Beams (radiation); Ducts; Lobes; Mathematical analysis; Pollution sources; Sonar; Sound propagation; Transmission loss; 几何形状; 声音传播; 截止频率; 无源声纳; 管道; 表面; 远距离; 震源深度
• ISSN: 1674-1056; 2058-3834; 1741-4199
• DOI: 10.1088/1674-1056/22/12/124301

Understanding the effect of source-receiver geometry on sound propagation in surface ducts can improve the performance of near-surface sonar in deep water. The Lloyd-mirror and normal mode theories are used to analyze the features of surface-duct propagation in this paper. Firstly, according to the Lloyd-mirror theory, a shallow point source generates directional lobes, whose grazing angles are determined by the source depth and frequency. By assuming a part of the first lobe to be just trapped in the surface duct, a method to calculate the minimum cutoff frequency （MCF） is obtained. The presented method is source depth dependent and thus is helpful for determining the working depth for sonar. Secondly, it is found that under certain environments there exists a layer of low transmission loss （TL） in the surface duct, whose thickness is related to the source geometry and can be calculated by the Lloyd-mirror method. The receiver should be placed in this layer to minimize the TL. Finally, the arrival angle on a vertical linear array （VLA） in the surface duct is analyzed based on normal mode theory, which provides a priori knowledge of the beam direction of passive sonar.