| 摘要 |
PROBLEM TO BE SOLVED: To obtain a conversion method in which an acoustic parameter can be estimated by using BL data in a range at a critical angle or lower by retrieving the critical angle first regarding the BL data and finding the sound-velocity initial value and the density initial value of a seabed deposition layer on the basis of the critical angle. SOLUTION: First, by using a critical-angle retrieval means, regarding BL data for which an incident complementary angle is set on the horizontal axis of two-dimensional coordinates and for which a reflection loss is set on the vertical axis, it is judged whether the difference value between an approximate straight line to be found regarding first three data points in the order of the small magnitude of the incident complementary angle and the respective data points exceeds a threshold value or not. When the difference value does not exceed the threshold value, a discrimination processing operation is repeated regarding an approximate straight line which is found by increasing the data points one by one, and a critical angle is found on the basis of the incident complementary angle when the difference value exceeds the threshold value. Then, a sound-velocity initial value is decided by a sound-velocity initial- value decision means 3 on the basis of the critical angle, and a density initial value is decided by a density-initial-value decision means 4 on the basis of the sound-velocity initial value. Then, an acoustic-parameter estimation means 5 estimates an acoustic parameter expressed by the sound velocity, the density and the attenuation factor of a seabed deposition layer by using the sound-velocity initial value, the density initial value and an attenuation-factor initial value. |
