On the relationship between sea state and the coherent‐to‐incoherent intensity ratio for high frequency, shallow water propagation

A 29‐element source array and 32‐element receiver array have been deployed in shallow water to investigate various aspects of the acoustic channel. Both arrays spanned much of the water column. Source‐receiver range was 800 m, and 3.5 kHz pulses were transmitted using one source at a time and recorded on all elements. In this analysis, we compare the ratio of coherently to incoherently averaged intensities for each source‐receiver pair, and averaged over all such pairs, to measure surface roughness. We find that the coherent‐to‐incoherent intensity ratio decreases with time after the direct path arrival, and that the slope becomes more negative as wind speed and thus surface roughness increases. A simple model for signal phase variation induced by surface scatter shows a direct relationship between the degree of phase variation and wind speed. The relationship between the slope of the coherent‐to‐incoherent intensity ratio and a physics‐based model of incoherent sea surface forward scatter is also conside...