||<p>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.</p>