Passive Ranging of Tonal Sources in Shallow Water Using the Waveguide Invariant

Abstract

Shallow water, coastal regions with high volumes of shipping traffic provide an excellent opportunity to passively characterize the ocean acoustic propagation environment. In this paper, a hybrid maximum-likelihood method is presented for estimating the value of the waveguide invariant parameter, $\beta$, which succinctly characterizes the interference structure inherent to ducted acoustic propagation. A similar method is also presented by which the range can be estimated to a tonal source that later transits a shallow water region that has previously been characterized by $\beta$. This paper focuses solely on tonal acoustic sources, exploiting one of the defining characteristics of cargo ship emissions. The methods presented require minimal a priori environmental knowledge and relatively few assumptions regarding the acoustic sources. $\beta$ is estimated through spectral analysis of the fading pattern of a received acoustic signal from a transiting cargo ship that broadcasts its GPS location through Automatic Identification System (AIS) data. Range is estimated using a similar method, but also requiring a rough source velocity estimate. Close agreement is seen between simulated results obtained using Kraken and experimental results using data from the Swellex ’96 experiment, in which a shallow source was used to estimate the range to a deep source.