Mode scintillation and surface/submerged discrimination in SwellEx-96

Abstract

It has been proposed that the short time-scale scintillation of normal mode amplitudes may be an effective discriminant for passive surface/submerged acoustic source classification in a shallow waveguide [V. Premus, J. Acoust. Soc. Am. (submitted)]. The approach is based on a two part hypothesis which states: (1) platform motion in the vertical due to surface or internal wave action induces observable temporal fluctuations in normal mode amplitudes, and (2) the probability densities of mode amplitude scintillation for surface and submerged sources are well separated under modest depth fluctuation conditions. In this work, results from the application of the mode scintillation classifier to narrow-band vertical array data collected during SwellEx-96 Event S5 are reviewed. Classifier output in the form of a thresholded mode scintillation interest image provides empirical evidence to support the classification hypothesis for the lowest order resolvable modes. Limitations imposed by the non-fully spanning nature of the vertical aperture will be discussed. [Work sponsored in part by SPAWAR, under Air Force Contract No. F19628-95-C-0002. Opinions, interpretations, conclusions, and recommendations are those of the authors and are not necessarily endorsed by the U.S. Air Force.]