Channel characterization for communications in very shallow water

Abstract

Broadband acoustic transmissions (7 kHz to 17 kHz) taken from July 4, 2000 to July 8, 2000, in the shallow water near Scripps Pier at La Jolla, California, are used to extract the time-varying channel parameters of coherence time and multipath time delay spread, as functions of frequency and the environmental variables of wave height and tidal fluctuations. Tidal fluctuations, which have a significant effect on water depth at the receiver and transmitter, are shown to strongly correlate to variations in the multipath delay spread. Variations in the coherence time for the channel, as measured by the drop off in correlation between initial and successive impulse responses, are shown to be inversely related to variations in the measured wave height. The coherence time of the channel was found to decrease with increasing center frequency. A scatter plot of the receiver signal-to-noise ratio as a function of wave height and water depth indicates when the shallow water environment allows a viable communications channel to exist.