Underwater (UW) acoustics are used for communication in a broad range of applications, with increasing numbers near shore in shallow water, including environmental monitoring, disaster prevention, assisted navigation, distributed tactical surveillance, and mine reconnaissance. While considerable efforts have been made to characterize radio frequency (RF) wireless channels, less attention has been given to shallow water acoustic channels. This paper analyzes data gathered in a very shallow estuary and quantifies how the channel's characteristics constrain the design of an acoustic digital communication system. The channel's scattering function, multipath intensity profile, coherence bandwidth, Doppler power spectrum, and coherence time are presented. Amplitude fluctuations over time are displayed, and maximum likelihood estimation is utilized to fit the data to the Rayleigh, Rice, and Nakagami-m distributions often used to model fading channels.
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