The present study explores the physical and acoustic characteristics of fine sand and clay in novel seabed marine sediments from of Pakistan coastline of the Arabian Sea.The measured physical parameters included mean ...The present study explores the physical and acoustic characteristics of fine sand and clay in novel seabed marine sediments from of Pakistan coastline of the Arabian Sea.The measured physical parameters included mean grain size,mass density,bulk density,salinity,porosity,permeability,pore size and mineralogical composition.Acoustic properties,including sound speed and attenuation,in the high frequency range of 90-170 kHz were analyzed.A controlled laboratory setup with the acoustic transmission method and Fourier transform techniques was utilized to examine the sound propagation and absorption of novel seabed sediments.The standard deviation of mean sound speed in fresh water was 0.75 m/s,and attenuation was observed in the range of 0.43 to 0.61 dB/m.The mean sound velocity in sand and clay varied from 1706 to 1709 m/s and 1602 to 1608 m/s,respectively.Corresponding average attenuation was observed at 80 to 93 dB/m in sandy sediments and from 31.8 to 38.6 dB/m in clayey sediments.Sound velocity variation within sandy sediment is low,consistent with expected results,and smaller than the predicted uncertainty.However,clay sediment exhibited a positive linear correlation and low sound speed variation.Attenuation increased linearly with frequency for both sediments.Finally,the laboratory results were validated by using the Biot−Stoll model.The dispersion of sound speed in sandy and clayey sediments was consistent with the predictions of the Biot−Stoll model.Measured attenuation aligned more with Biot−Stoll model predictions due to improved permeability,tortuosity and pore size parameter fitting.展开更多
Seabed sediment recognition is vital for the exploitation of marine resources.Side-scan sonar(SSS)is an excellent tool for acquiring the imagery of seafloor topography.Combined with ocean surface sampling,it provides ...Seabed sediment recognition is vital for the exploitation of marine resources.Side-scan sonar(SSS)is an excellent tool for acquiring the imagery of seafloor topography.Combined with ocean surface sampling,it provides detailed and accurate images of marine substrate features.Most of the processing of SSS imagery works around limited sampling stations and requires manual interpretation to complete the classification of seabed sediment imagery.In complex sea areas,with manual interpretation,small targets are often lost due to a large amount of information.To date,studies related to the automatic recognition of seabed sediments are still few.This paper proposes a seabed sediment recognition method based on You Only Look Once version 5 and SSS imagery to perform real-time sedi-ment classification and localization for accuracy,particularly on small targets and faster speeds.We used methods such as changing the dataset size,epoch,and optimizer and adding multiscale training to overcome the challenges of having a small sample and a low accuracy.With these methods,we improved the results on mean average precision by 8.98%and F1 score by 11.12%compared with the original method.In addition,the detection speed was approximately 100 frames per second,which is faster than that of previous methods.This speed enabled us to achieve real-time seabed sediment recognition from SSS imagery.展开更多
The stretched structure and heterogeneity of the crust of the Nansha Block,the southern continental margin of the South China Sea(SCS),are not well understood.We used published ocean bottom seismic(OBS)/multichannel r...The stretched structure and heterogeneity of the crust of the Nansha Block,the southern continental margin of the South China Sea(SCS),are not well understood.We used published ocean bottom seismic(OBS)/multichannel reflection seismic(MCS)profiles across the Nansha Block to establish five two-dimensional crustal structure models.Using gravity modelling with magnetic anomaly inversion,we obtained the distribution of density and local magnetic susceptibility of the crust.The models show that the distribution of density and thickness of the upper crust in the Nansha Block is uneven,and the thick upper crust is prevalent in the regions close to the continent-ocean transition(COT)showing different characteristics.The interpreted Mesozoic granite blocks and Precambrian rigid basement reflects the heterogeneity in the material composition of the SCS continental margin.Based on the thinning styles of different crustal layers,we suggest that the Nansha Block has a three-layer thinning pattern.The uppermost pre-rift layer was deformed via brittle fractures,the upper crust was sheared by discrete shear zones,and the lower crust experienced ductile deformation.The inherited pre-rift thermal regime,mechanical state,and material composition of the SCS continental margin affected the extensional structure of the crust.展开更多
通过对南海北部和中部两套时间序列沉积物捕获器中的颗粒物样品进行硅藻分析,揭示了南海北部和中部硅藻通量的季节变化规律及其区域差异和各自对东亚季风气候的响应。研究表明在南海北部和中部海域,硅藻通量可以在一定程度上指示海洋初...通过对南海北部和中部两套时间序列沉积物捕获器中的颗粒物样品进行硅藻分析,揭示了南海北部和中部硅藻通量的季节变化规律及其区域差异和各自对东亚季风气候的响应。研究表明在南海北部和中部海域,硅藻通量可以在一定程度上指示海洋初级生产力水平,其中南海北部硅藻通量明显低于中部,这可能与北部颗粒物样品采集期间发生的El Ni o事件有关;南海北部和中部硅藻通量均存在明显的季节性变化规律,其中东亚冬季风对南海北部海域硅藻的生长有着显著影响,而南海中部则受夏季西南季风的影响更为强烈;南海北部深层硅藻通量高于浅层,这表明南海北部可能存在较强的深层流作用。展开更多
基金financially supported by the National Natural Science Foundation of China(Grant No.12074088).
文摘The present study explores the physical and acoustic characteristics of fine sand and clay in novel seabed marine sediments from of Pakistan coastline of the Arabian Sea.The measured physical parameters included mean grain size,mass density,bulk density,salinity,porosity,permeability,pore size and mineralogical composition.Acoustic properties,including sound speed and attenuation,in the high frequency range of 90-170 kHz were analyzed.A controlled laboratory setup with the acoustic transmission method and Fourier transform techniques was utilized to examine the sound propagation and absorption of novel seabed sediments.The standard deviation of mean sound speed in fresh water was 0.75 m/s,and attenuation was observed in the range of 0.43 to 0.61 dB/m.The mean sound velocity in sand and clay varied from 1706 to 1709 m/s and 1602 to 1608 m/s,respectively.Corresponding average attenuation was observed at 80 to 93 dB/m in sandy sediments and from 31.8 to 38.6 dB/m in clayey sediments.Sound velocity variation within sandy sediment is low,consistent with expected results,and smaller than the predicted uncertainty.However,clay sediment exhibited a positive linear correlation and low sound speed variation.Attenuation increased linearly with frequency for both sediments.Finally,the laboratory results were validated by using the Biot−Stoll model.The dispersion of sound speed in sandy and clayey sediments was consistent with the predictions of the Biot−Stoll model.Measured attenuation aligned more with Biot−Stoll model predictions due to improved permeability,tortuosity and pore size parameter fitting.
基金funded by the Natural Science Foundation of Fujian Province(No.2018J01063)the Project of Deep Learning Based Underwater Cultural Relics Recognization(No.38360041)the Project of the State Administration of Cultural Relics(No.2018300).
文摘Seabed sediment recognition is vital for the exploitation of marine resources.Side-scan sonar(SSS)is an excellent tool for acquiring the imagery of seafloor topography.Combined with ocean surface sampling,it provides detailed and accurate images of marine substrate features.Most of the processing of SSS imagery works around limited sampling stations and requires manual interpretation to complete the classification of seabed sediment imagery.In complex sea areas,with manual interpretation,small targets are often lost due to a large amount of information.To date,studies related to the automatic recognition of seabed sediments are still few.This paper proposes a seabed sediment recognition method based on You Only Look Once version 5 and SSS imagery to perform real-time sedi-ment classification and localization for accuracy,particularly on small targets and faster speeds.We used methods such as changing the dataset size,epoch,and optimizer and adding multiscale training to overcome the challenges of having a small sample and a low accuracy.With these methods,we improved the results on mean average precision by 8.98%and F1 score by 11.12%compared with the original method.In addition,the detection speed was approximately 100 frames per second,which is faster than that of previous methods.This speed enabled us to achieve real-time seabed sediment recognition from SSS imagery.
基金Supported by the National Natural Science Foundation of China(Nos.42076078,41776057,42176055)the Open Foundation of Key Laboratory of Submarine Geosciences,Ministry of Natural Resources(No.KLSG2004)。
文摘The stretched structure and heterogeneity of the crust of the Nansha Block,the southern continental margin of the South China Sea(SCS),are not well understood.We used published ocean bottom seismic(OBS)/multichannel reflection seismic(MCS)profiles across the Nansha Block to establish five two-dimensional crustal structure models.Using gravity modelling with magnetic anomaly inversion,we obtained the distribution of density and local magnetic susceptibility of the crust.The models show that the distribution of density and thickness of the upper crust in the Nansha Block is uneven,and the thick upper crust is prevalent in the regions close to the continent-ocean transition(COT)showing different characteristics.The interpreted Mesozoic granite blocks and Precambrian rigid basement reflects the heterogeneity in the material composition of the SCS continental margin.Based on the thinning styles of different crustal layers,we suggest that the Nansha Block has a three-layer thinning pattern.The uppermost pre-rift layer was deformed via brittle fractures,the upper crust was sheared by discrete shear zones,and the lower crust experienced ductile deformation.The inherited pre-rift thermal regime,mechanical state,and material composition of the SCS continental margin affected the extensional structure of the crust.
文摘通过对南海北部和中部两套时间序列沉积物捕获器中的颗粒物样品进行硅藻分析,揭示了南海北部和中部硅藻通量的季节变化规律及其区域差异和各自对东亚季风气候的响应。研究表明在南海北部和中部海域,硅藻通量可以在一定程度上指示海洋初级生产力水平,其中南海北部硅藻通量明显低于中部,这可能与北部颗粒物样品采集期间发生的El Ni o事件有关;南海北部和中部硅藻通量均存在明显的季节性变化规律,其中东亚冬季风对南海北部海域硅藻的生长有着显著影响,而南海中部则受夏季西南季风的影响更为强烈;南海北部深层硅藻通量高于浅层,这表明南海北部可能存在较强的深层流作用。
