When we perform logistic support of underwater search on divers by making use of the
Forward Looking Sonar (FLS), it is known that strong interference lines occasionally appear on
the sonar image in response to the breathing of divers. This seems to be because that the high
frequency respiratory sound is emitted when the diver breathes in the water and is overlapped with
the echo signal from the sonar projector and then has been received all together consequently. To
confirm this, it is necessary to proceed a high frequency analysis of the underwater respiratory
sound of divers in the first stage. But it is important to know ahead of time that we confirm the
frequency band limits of the echo-sounder (R2Sonic2024) we have actually used.
In this study, we carried out an examination of the frequency band limits of sonar by using
the ocean engineering basin, that is, whether the sonar has band filter or not in receiving and how
much band limitation is set in the case of the limits existing.