深海低声速沉积层简正波用于海底参数反演

Application of deep-sea low-speed sediment borne mode for geoacoustic inversion

现有深海地声参数反演研究通常基于全波场理论,存在计算量大、多值性以及需要准确的水文环境信息等问题。针对这一问题,提出一种基于简正波频散特征的深海低声速沉积层海底参数反演方法。在南中国海北部大陆坡海域的一次实验中,坐底式水听器(深度约1740 m)接收的沉底弹信号中观察到一种低频成分先到而高频成分后至的到达结构,由被限制在低声速沉积层的简正波组成。通过匹配沉积层简正波60220 Hz频段内的到达时间差对实验海域的低声速海底参数进行反演,得到沉积层厚度为16.4 m,沉积层声速为1450.5 m/s,与底质采样数据比较吻合,且具有较高的可信度,验证了所提方法的有效性。由于沉积层密度对简正波频散特征的敏感性较差,其反演结果可信度不是很高,需要进一步研究。

The existing studies of deep-sea geoacoustic inversion are usually based on the full wave theory,which has problems of high calculation,multi-values and the need for accurate environment information.To solve this issue,an inversion method for deep-sea low-speed sediment based on modal dispersion characteristics is proposed.In an experiment conducted over the northern continental slope of the South China Sea,an arrival with low frequencies arriving earlier and high frequencies arriving later,corresponding to trapped modes in the low-speed sediment,was observed in the signals recorded by a bottom-mounted sensor(1740 m)from bottom-exploded charges.By matching the modal time difference in 60–220 Hz frequency band,the thickness and sound speed of sediment in the experimental area are inverted,and the results are 16.4 m and 1450 m/s respectively,which are consistent with the sediment sampling data and have high confidence,verifying the effectiveness of the proposed method.Due to the poor sensitivity of sediment density to the modal dispersion characteristics,the inverted sediment density is not very reliable,so further research is required.