浅海声传播和混响的选频衰减

Frequency-selective attenuation of sound propagation and reverberation in Shallow Water

在强负跃层浅海的爆炸声实验中，发现当声源和接收器都位于跃层之上时，平均混响强度和某一航向的声传播损失在频率１０００－２０００Ｈｚ之间出现强烈的异常衰减现象，而且很有意思的是发射和接收均无指向性的平均混响强度的异常衰减与该航向声传播损失的异常衰减具有中心频率相同、带宽一致、附加衰减值相近的窄带共振或选频衰减特权。显然，这一异常衰减现象无法用各向异性的机理（内波、海面或海底的有规律起伏等）来解释。根据本文实验所得的传播损失和混响强度的深度结构以及一些间接的证据，我们认为这一选频附加衰减是由分散活动干跃居上部的有鳔鱼（极可能是鱼）所引起的。

ln the summer of 1991 studies of sound propagation and reverberation were carried out in the Huanghai (Yellow) Sea with a strong thermocline by using explosive sound sources. Experimental results of both the sound transmission loss along a certain course and the average reverberation intensity showed an ab- normally large attenuation over a frequency range from 1 000 to 2 000 Hz when both the source and the re- ceiver were located above the thermocline. An interesting point is that the anomalous attenuation of the aver- age reverberation intensity obtained by using omnidirectional source and receiver and that of the transmission loss along the certain course exhibit a resonance-like or frequency-selective characteristic with the same centre frequency , similar bandwidth and comparable extra attenuation values. Obviously , this anomalous attenuation cannot be explained by any anisotropic mechanism (e. g. , internal waves , regular fluctuations of sea surface or bottom, etc. ). On the basis of the dependences of the transmission loss and reveberation intensity obtained by the authors and some indirect evidences, it is believed the observed reqency-selective atten- uation is due to fish with swimbladders. (probably, anchovies ) living dispersedly above the thermocline.