Directional response of a towed array in shallow sea

In a recent paper, M.J. Buckingham carried out a theoretical treatment of the directional response of a towed line array in shallow sea. The analysis was based on the description of the sound field in terms of normal mode solution of the wave equation. An important limitation of this analysis is that it assumes the normal modes to propagate unattenuated in the channel. In the present paper realistic modal attenuation in the shallow water channel is considered, and this leads to significant quantitativie differences from the analysis given by Buckingham. Specifically, the effect of `beam splitting¿ discussed by Buckingham becomes insignificant for reasonable distances of the array from the source. The beam broadening observed by Buckingham is a phenomenon which occurs when the source bearing is within a small region around the endfire direction. Finally, the problem of signal rejection by the array is also seen to be significantly reduced in magnitude.