The use of phased rays in very shallow water

Numerical predictions are studied of propagation in isovelocity water over a lossy bottom with the depth and frequency such that only one, two, or three normal modes exist. Comparison of the result from a new “Phased Ray” model with the normal mode result shows that it is the phase change upon reflection that is the major cause of the disagreement between the Phased Ray and Mode models. The possibility of controlling the phase of the plane wave reflection coefficient by tuning an overlying layer of silt, or whatever, is also demonstrated. The case is then put forward, when dealing with problems where the bottom has irregular contours or where the surface is rough, i.e., where there are no normal mode solutions, for modelling the propagation with rays corrected to agree in general properties with the normal mode solutions of nearly the same problems.