SOME THEORETICAL PROBLEMS ON MODE FILTERING IN SHALLOW WATER

Since the mode filtering is a certain sort of "space filtering", the matter of the utmost concerns the "side lobe" produced by some simplified processing in practice instead of the ideal orthogonal operation.In this paper, the following problems are discussed theoretically:(1) "side lobe" produced by using an integration in the water column instead of halfspace; (2) "side lobe" produced by using a finite discrete sampling; (3) "side lobe" produced by a hard-clipped eigenfunction; and (4) "side lobe" produced by the inclination of the vertical array.Some analytic results and numerical examples are shown for a special case in which the sound speed profile is isovelocity in the water column.It is found that the effect of array inclination is serious and an approach of phase compensation in proposed.