Abstract:
Ocean acoustic tomography is a powerful method that uses sound to study
ocean properties such as temperature, which is directly related to sound speed in
water. This thesis focuses on using ambient noise to infer the normal modes of the
ocean waveguide. The modes are a set of orthogonal functions that are solutions to
the depth dependent wave equation, which depends on sound speed and thus on the
temperature. Assuming that noise signals received by a vertical array consist of a
sum of uncorrelated modes, the modeshapes can be determined from an eigenvector
decomposition of the measured cross-spectral density matrix. Several authors have
applied this technique to estimate the modes of shallow water waveguides, but there
have been few opportunities to apply this technique in deep water waveguides. In this
thesis the modeshapes of a deep water environment in the North Pacific are estimated
using ambient noise data measured during the SPICE04 experiment. Although noise
measurements were not the primary focus of SPICE04, the experiment provided a
large data set for this analysis. In addition to acoustic measurements, the experiment
also included extensive sampling of the environmental parameters. This thesis
summarizes some of the noise statistics measured during 2004-2005. The measured
modeshapes derived from the data are compared with the true modes derived from
the measured environmental data.
