Further work on the relationship between the coherent‐to‐incoherent ratio (CTIR) and the sea surface wave height for one‐way propagation in a shallow ocean channel

Abstract

A 29‐element source array and 32‐element receiver array have been deployed 8.6 km apart in a 120‐m‐deep ocean channel. Both arrays spanned most of the water column. Linear frequency‐modulated (LFM) pulses 150 ms long and 4 kHz wide centered at 3.5 kHz were transmitted from one source at a time and recorded at all receivers during a several day period. During the recordings, the sound speed profile was approximately iso‐velocity and the significant wave height varied from 0.3 to 1.1 m. We average the received signal coherently and incoherently for each source‐receiver pair, average over all pairs, and take the coherent‐to‐incoherent ratio (CTIR). Log<th>(CTIR) is found to depend linearly on time after the initial arrival, with slope proportional to the significant wave height. An earlier talk showed that the average reflection coefficient times the number of surface bounces N was a good predictor of the slope, but subsequently we find that it alone is not sufficient. Here we report a more complete theory that combines N, the average reflection coefficient, and the density of the arrivals. A predictive model for slope versus surface wave height is presented and compared with the measurements. The method can incorporate ray tracing and be extended to non‐iso‐velocity environments.