| 摘要 |
PROBLEM TO BE SOLVED: To efficiently detect an underwater vessel from broadband radiated sound, such as friction sound between the underwater vessel and water (sea water, fresh water or mixture water of the two), even when operation sound of a propelling machine of the underwater vessel is low.SOLUTION: An acoustic sensor 110 converts acoustic waves generated from an underwater vessel 300 existing under water to electric signals. A directivity forming section 150 forms cardioid type directivity for each prescribed frequency component on the basis of the electric signals. A directivity ratio calculating section 160 calculates a directivity ratio, which is a ratio of a signal level in a maximal sensitivity direction to a signal level in a minimal sensitivity direction for each of the prescribed frequency components, on the basis of the cardioid type directivity formed by the directivity forming section 150. A directivity ratio distribution generating section 170 composes the directivity ratio calculated for each of the prescribed frequency components by the directivity ratio calculating section 160, and generates a directivity ratio distribution showing a distribution of the directivity ratio for each of the frequency components. |
