南海北部声散射季节变化

Seasonal Variation of Sound Scattering in the Northern South China Sea

声散射是重要的声学现象,海洋水体产生的高频声散射信号既可用于开展多种目的的声学海洋学研究,也可能对水下声学设备产生干扰,而海洋水体背景声散射具有显著的时空变异特征,因此针对特定海区开展声散射时变观测具有重要意义。本文利用在南海北部布放的锚系系统所搭载的声学多普勒流速剖面仪,获取了覆盖4个季节的累计约80 d的声散射数据,数据包括75 kHz和300 kHz两个频段,观测水深几乎覆盖了从海面到约600 m水深的整个水体。结果表明,水体在垂向上分布着上散射层和深散射层2个主要散射层。上散射层分布深度在冬夏较浅,位于约100 m以浅,在春秋较深,位于约200 m以浅;深散射层分布深度同样为冬季最浅,位于约300 m以深,但夏季则最深,位于约400 m以深。因此,两散射层的距离在夏季最远,在春秋最近。2个散射层的声散射强度(Sv)同样具有明显的季节变化,上散射层散射强度夏秋较强而春冬较弱,深散射层则正好相反。

Sound scattering is an important acoustic phenomenon.High-frequency acoustic scattering signals generated by seawater bodies can be used to conduct acoustic oceanographic research for various purposes and may interfere with the underwater acoustic equipment.However,the background sound scattering of seawater bodies is characterized by significant spatial and temporal variations.As a result,it is of great significance to carry out the observations of timevarying sound scattering in a specific sea area.In this study,sound scattering data of 80 days covering four seasons are collected by using two ADCPs equipped in a mooring system in the Northern South China Sea.The data include two frequency bands of 75 kHz and 300 kHz and involve almost the whole water column from the surface to about 600 m deep.There exist two acoustic scattering layers in the vertical direction of the water column:one is the upper scattering layer,which is distributed at a water depth shallower than about 100 m in winter and summer and about 200 m in spring and autumn,and the other is the lower scattering layer,which lies at a water depth deeper than about 300 m in winter and about 400 m in summer.Therefore,the distance between the two scattering layers is the farthest in summer and the closest in spring and autumn.The acoustic scattering intensity in the two scattering layers also shows significant seasonal variations.In the upper layer the acoustic scattering intensity is stronger in summer and autumn and weaker in spring and winter,whereas in the deep layer the acoustic scattering intensity is exactly the opposite.