Sound intensity distribution as an underwater acoustic investigation process

The subject matter of this research is underwater noise generated by sailing vessels in shallow seas. The classical method for measurement of underwater noise involves measuring effective acoustic pressure and fits for purposes in the free far field of the source. Despite its popularity, the method does have some significant limitations. Investigations of underwater noise generated by moving vessels in shallow seas are almost solely confined to the near field. In addition, this has a high level of interference and numerous wave reflections. This is why, as well as using the acoustic pressure measurement method, a complementary method for measuring acoustic wave intensity is used increasingly often. The measurements were taken using an underwater measurement module equipped with a set of detectors. Submerged at 20m, the object moved along a designated trajectory at a preset speed (as determined by the parameters of the ship’s machinery). Because all of the on-board equipment generates ship-specific noise, additional measurements were taken of the vibrations generated by selected ship’s machines to identify those sources. If known, the distribution of the acoustic field from vessels helps to identify the characteristic frequencies generated by the ship’s equipment and machinery. The paper includes a comparison of acoustic wave intensity and acoustic pressure measurements taken under the same ambient conditions and over the same period.