NARCISSUS-2005: a global model of fading channel for application to acoustic communication in marine environment

We present the latest version of an operational numerical model of acoustic impulse response in a random sea-channel, with application primarily to communication in the marine environment. Phenomena taken into account are: random scattering from surface and bottom irregularity; fading from surface waves or swells, and movements of source and receivers relatively to boundaries; Doppler and distortions due to source and receiver movements. Statistics for the sound-fields are evaluated; from these statistics are extracted various scales (Rice number, delay spread, fading rate, etc.) and pseudo-random Monte Carlo simulations of transmitted signals. This model was tried, as a whole, against experimental data collected at sea within various European MAST projects at the end of the 1990s : very shallow coastal waters (North Sea) for project SWAN, continental shelf environment (Mediterranean Sea) for project PROSIM. The validation procedures included investigations of several statistical properties of fading: the "Rice factor" (ratio of the energy of the mean coherent part of the response to the mean energy of the random scattered part of the response), the spectral broadening, the delay spread, the normality of the random part of the response, the shape of the mean and random part of the response (decay as function of delay). Involved signals included frequency modulations and pseudo-random sequences, with frequency ranges from 400 Hz to 6.5 kHz. Source-to-receiver ranges were 500 m, 1.5 km, 5 km and 15 km. The model NARCISSUS, tested as a whole, seems to quite successfully compare with observations.