Evidence for single-mode propagation and its implications for range-dependent geoacoustic inversion in the SWAT experiment

Abstract

During the Shallow Water Acoustic Technology (SWAT) experiments, which were conducted in October 2000 on the New Jersey Shelf, a 20 Hz pure tone was transmitted from a source in 73 m of water to two drifting receivers. The behavior of the pressure magnitude and phase out to ranges of about 8 km suggest that the field is dominated by a single normal mode. In particular, an adiabatic modal interpretation of the phase variation with range is consistent with an independent autoregressive spectral estimate of the wave number content of the field. It is then shown, within the context of an isovelocity bottom model with varying water depth, that the measured range-varying bathymetry does not account for the range dependence in the single modal eigenvalue. On the other hand, an alternative interpretation of the data in terms of a wave guide with constant depth and range-varying sound speed in the bottom yields reasonable estimates of the lateral seabed variability. [Work supported by ONR.]