基于浅地层剖面数据和改进地声模型的底质反演方法

Seabed classification based on sub-bottom profile data in modified geo-acoustic model

浅地层剖面仪发射的声脉冲能够穿透海底面进入沉积层内部,其回波中携带了丰富的底质信息。地声模型是底质声学与物理性质关系的数学描述,广泛用于海底声学与地声反演研究。本文通过对浅地层剖面数据的处理、解译得到海底反射系数,与考虑底质松密影响的改进Biot-Stoll模型相结合,提出底质反演新方法并开展实例验证。研究结果表明:通过对浅地层剖面原始记录的读取、解译,提取反射波振幅,并结合设备声源级,可有效求取海底反射系数。通过引入相对密度改进孔隙度计算公式,进而在基于Biot-Stoll模型构建海底反射系数和底质平均粒径关系过程中进一步考虑了底质松密的影响。基于山东威海某海域及文献的算例均显示,本文提出的改进地声模型可缩小底质反演与实测结果之间的相对误差、提升基于浅地层剖面数据的海底底质地声反演精度。

The echoes signal of sub-bottom profilers(SBP)carry abundant information of sediment because the acoustic pulses emitted by SBP can penetrate the seafloor surface into the interior of sediment layers and get reflected from different impedance interface.A geoacoustic model describing the relationship between the acoustics and physical properties of sediments mathematically,is widely used in sediment classification and acoustics inversion.We applied the method to obtain the bottom reflection coefficients by decoding the SBP data,and then combined it with a modified Biot-Stoll model considering the influence of sediment’s degree of compaction,based on which a new method of sediment inversion was proposed to evaluate its capacity by examples.Results show that the bottom reflection coefficient of seafloor can be effectively obtained by decoding the original records of SBP,extracting the amplitude of the reflected waves,and combining with the sound source level of the equipment.To build the relationship between bottom reflective coefficient and mean grain size,the degree of sediment compaction was considered based on Biot-Stoll model and the parameter of relative density was introduced into the porosity calculation formula.Examples of both measured data of Weihai sea area and those obtained from available literatures indicate that the presented method could reduce the relative error between the inversion and the measured mean grain sizes,contributing to improve the accuracy of submarine sediment geoacoustic inversion based on SBP data.