Inversion of the physical properties of seafloor surface sediments based on AUV sub-bottom profile data in the northern slope of the South China Sea

Hang Zhou,Qingjie Zhou,Chengyi Zhang,Shan Gao,Baohua Liu,Bigui Huang,Xishuang Li,Jie Liu,Lejun Liu

doi:10.1038/s41598-021-86161-x

Abstract

Based on the seafloor reflection coefficient obtained from autonomous underwater vehicle (AUV) sub-bottom profile survey data of the northern slope of the South China Sea, combined with the sample test data of seafloor surface sediments, we use the Biot–Stoll model to establish the equations relating the seafloor reflection coefficient to the porosity, density, and mean grain size of the sediments at the dominant frequency of 5 kHz (the dominant frequency of the AUV sub-bottom profiler). The physical property parameters such as the porosity, density, and mean grain size of seafloor surface sediments are further inverted. Comparison of inversion results with measured results shows that the overall deviation ratios of the inverted mean grain size, porosity, and density of the surface sediments are in the ranges of − 13.56 to 14.44%, − 6.15 to 8.06%, and − 10.85 to 0.46%, respectively. Among them, the mean grain size directly reflects the size of seafloor sediment particles, and the particles are finer in deeper water. Overall, the inversion results are basically consistent with the measured values and thus can well reflect the variation characteristics of the physical properties of seafloor surface sediments.

Highlights

Biot–Stoll model is highly accurate and widely used to predict the acoustic parameters of sandy s ediments[20]
Chen et al (2017) inverted the physical properties of seafloor sediments in the Qiongzhou Strait based on the Biot–Stoll model and the Chirp sub-bottom profile data and introduced the Gardner empirical formula to supplement the physical property inversion of the sediments in the high-reflection zone; the inversion results were slightly different from the measured values but agreed o verall[24]
The physical properties of the seafloor surface sediments are inverted from the seafloor reflection coefficients that are calculated using the sub-bottom profile data, compared with the measured physical properties at the sampling points to evaluate the applicability of this method

Summary

Introduction

Biot–Stoll model is highly accurate and widely used to predict the acoustic parameters of sandy s ediments[20]. The use of the Biot–Stoll model and sub-bottom profile data to invert the physical properties of seafloor surface sediments is becoming an emerging direction for the application of sub-bottom profile data. Schock (2004) used Chirp sonar data and the Biot–Stoll model to invert the physical properties (e.g., velocity, density, porosity) of the sediments of Fort Walton Beach in the United States and the seafloor of the South China Sea, and the inversion results strongly agreed with the laboratory m easurements[21,22]. In this study, based on the AUV sub-bottom profile survey data of the northern slope area of the South China Sea as well as the seafloor surface sediment sampling and testing data of this area, the correlation between the seafloor reflection coefficient and the physical properties of the sediments is established using the Biot–Stoll model. The samples were retrieved, and water content analysis, grain size analysis, and soil specific gravity testing were performed in the laboratory to obtain parameters such as water content, grain size, wet density, void ratio, and grain density

Discussion

Conclusion