Abstract:

The problem of sound propagation in narrow waters can readily be related to room acoustic problems. Different methods from room acoustics were investigated for a possible application to the underwater acoustics of fjords and straits. The frequency range of interest is 1 Hz--100 kHz, and the sound field at ranges to ~1000 m from the source is computed. For the very low-frequency range both near-field and far-field propagation must be considered. In the very-low-frequency range, 1 to ~50 Hz (possibly 500 Hz), finite-element methodology is applied. In the medium-frequency range ~50 Hz to ~10 kHz, room acoustic methods are applied. In the high-frequency range ~10 to 100 kHz, conventional underwater acoustic methods are used. The room acoustic method chosen is a hybrid model combining image source modeling and ray tracing, and with the most important quality; a diffusivity parameter of the boundaries, which makes it unnecessary to know the exact geometry of the area modeled. However, the diffusivity parameter cannot be computed, it must be assessed from experimental data. Numerous experiments have been carried out in several fjords in western Norway to validate and optimize the methods.