Mode processing of transient signals using a deficient vertical receiving array, with application to LOAPEX measurements

Abstract

Mode processing of transient signals in a deep ocean environment using a deficient vertical receiving array is considered. Here, ‘‘deficient’’ implies that the vertical array is too sparse to resolve modes and/or has gaps. It is well known that mode processing of cw signals using a deficient array leads to significant modal cross‐talk, i.e., nonzero projections of mode n energy onto mode m, m≠n. It is shown, using simulated wave fields, that when phase‐coherent processing is employed, transient signals are less sensitive to modal cross‐talk than their cw counterparts. An explanation of this behavior is provided. Mode processing of a subset of the measurements made during the LOAPEX experiment at approximately 1 Mm range with f0=75 Hz, Δf=35 Hz is shown to give robust estimates of modal group time spreads for mode numbers 0≤m≤70. [Work supported by ONR.]