We investigated the morphology and sedimentary state of an extensive modern canyon system on the northwest continental slope of Palawan Island in the southern South China Sea using multibeam bathymetry data and chirp ...We investigated the morphology and sedimentary state of an extensive modern canyon system on the northwest continental slope of Palawan Island in the southern South China Sea using multibeam bathymetry data and chirp sub-bottom profiles.The canyon system in Northwest Palawan consists of a fairly large dendritic canyon,a braided canyon,and a set of short,straight,and slope-confined gullies.The erosion state covers 71%of the system.Sediment accumulates downstream of the bend's inner side in the proximal main stem of the dendritic canyon and is eroded in its outer side.In the distal main stem,sediment is deposited inside and outside the bend.In most of the system's tributaries,decreasing slope gradients result in more sediment deposition.There is thick aggradation of sediment waves in the interfluve throughout the system,which exhibit increasing levels of stratification as the slope decreases.The lack of slump scars and headward erosion at the canyon heads,as well as the presence of regular gullies and sediment wave fields,suggest that large areas of unconfined downslope turbidity currents formed the system.We propose that frequent storms in northwestern Palawan triggered these currents by resuspending sediments on the shelf.展开更多
Climate change and anthropogenic activities have profoundly affected coastal systems,making geomorphological research a critical focus for coastal protection and sustainable development.In this study,a comprehensive c...Climate change and anthropogenic activities have profoundly affected coastal systems,making geomorphological research a critical focus for coastal protection and sustainable development.In this study,a comprehensive classification of beach states around Hainan Island is conducted for the first time by utilizing theΩ-RTR model and geological control modes.Six distinct classic beach states ranging from dissipative to reflective are identified:barred dissipative beaches or no-barred dissipative beaches(BD or NBD),barred beaches(B),low-tide terrace or low-tide bar with rip(LTTR or LTBR),and reflective state(R).Among these,the BD and B types are predominant on Hainan Island.Notably,the beach states are subject to multiple factors,such as hydrodynamic forcings,geomorphic features and underlying substrates,and exhibit remarkable spatiotemporal variability.During extreme events,hydrodynamic forcings impact beach states more substantially than geological and geomorphic features do,leading to a more homogeneous distribution of beach states.Under normal circumstance,beach states are predominantly controlled by geological and geomorphic features.Coastal geological and geomorphic features have a pronounced influence on beach morphology and stability.For example,hard substrates underpin wide and stable dissipative beaches,whereas softer substrates lead to narrower,erosion-prone beaches.Three geological control modes are identified,namely,gently sloping hard substrates with dissipative beaches,moderately sloping hard substrates with seasonally variable reflective beaches,and steeply sloping soft substrates with dynamic sandbar-dominated beaches.These findings highlight the necessity of integrating geological settings in tandem with hydrodynamic forcings into coastal management practices.A dual-mode strategy is proposed:maintaining geomorphic self-organization on hard-substrate coasts under normal conditions and implementing hybrid engineering–ecological measures(e.g.,artificial sand replenishment and vegetation restoration)on erosion-prone soft substrates.展开更多
基于明暗恢复形状(shape from shading,简称SFS)方法进行海底侧扫声呐图像三维重建时,会因为方法中反射模型与海底表面不相符而降低重建精度。为此文章在分析大陆架海底表面特点及侧扫声呐工作机理的基础上,提出了基于SFS混合反射模型...基于明暗恢复形状(shape from shading,简称SFS)方法进行海底侧扫声呐图像三维重建时,会因为方法中反射模型与海底表面不相符而降低重建精度。为此文章在分析大陆架海底表面特点及侧扫声呐工作机理的基础上,提出了基于SFS混合反射模型的侧扫声呐图像海底地形重建方法。首先在保留Lambert漫反射模型的基础上引入Blinn-Phong镜面反射模型,并基于侧扫声呐图像粗糙度进行漫反射系数、镜面反射系数和镜面反射指数的自适应设计,从而形成适合复杂海底表面的混合反射模型;然后线性化处理辐射照度方程,并采用牛顿-拉夫逊方法来获得海底表面高程;最后根据海底点设计反演高程约束系数来约束表面高程,进而完成侧扫声呐图像的三维重建。试验测试结果表明,相较于其他三维重建方法,文中方法的平均绝对误差值VMAE平均降低了32.18%、相关系数值VCC平均提高了29.62%、信噪比值VSNR平均提升了27.23%,有效实现了侧扫声呐图像三维重建。展开更多
珠江口洪季悬浮泥沙的浓度分布与输运通量受多种动力因素的影响,其中斜压效应不可忽视。本文采用Coupled Ocean-Atmosphere-Wave-Sediment Transport Modeling System(COAWST)海洋模型系统,以2022年6月份(洪季)的珠江口为例,研究斜压效...珠江口洪季悬浮泥沙的浓度分布与输运通量受多种动力因素的影响,其中斜压效应不可忽视。本文采用Coupled Ocean-Atmosphere-Wave-Sediment Transport Modeling System(COAWST)海洋模型系统,以2022年6月份(洪季)的珠江口为例,研究斜压效应对悬沙浓度分布与输运通量的影响。采用控制实验,研究有无斜压作用时悬沙浓度分布的变化;分析有无斜压作用时的泥沙输运通量与海底冲淤的变化情况,结果表明有斜压作用时悬浮泥沙的输运路径、通量均与无斜压时不同,伶仃洋的悬沙除向西口外输运外,还随着河口羽流的扩展向西南方向输运。有斜压作用时在伶仃洋的西南端及下游的西南沿岸均有明显的海底淤积,而无斜压作用时泥沙淤积主要发生于伶仃洋的西口附近及磨刀门口外落潮射流末端。利用悬沙输运方程进行诊断分析,揭示了斜压作用导致悬沙浓度分布与输运通量变化的动力机制,表明斜压作用虽然减小了底切应力与垂向混合系数,但由于增大的海底泥沙可侵蚀量及垂向悬沙梯度,悬沙输运方程中的再悬浮量与垂向混合通量要比无斜压时要大。本研究对河口区的悬沙输运过程与机理分析具有一定的指导意义。展开更多
基金jointly supported by Natural Science Foundation of China(Nos.42076083 and 41706043)。
文摘We investigated the morphology and sedimentary state of an extensive modern canyon system on the northwest continental slope of Palawan Island in the southern South China Sea using multibeam bathymetry data and chirp sub-bottom profiles.The canyon system in Northwest Palawan consists of a fairly large dendritic canyon,a braided canyon,and a set of short,straight,and slope-confined gullies.The erosion state covers 71%of the system.Sediment accumulates downstream of the bend's inner side in the proximal main stem of the dendritic canyon and is eroded in its outer side.In the distal main stem,sediment is deposited inside and outside the bend.In most of the system's tributaries,decreasing slope gradients result in more sediment deposition.There is thick aggradation of sediment waves in the interfluve throughout the system,which exhibit increasing levels of stratification as the slope decreases.The lack of slump scars and headward erosion at the canyon heads,as well as the presence of regular gullies and sediment wave fields,suggest that large areas of unconfined downslope turbidity currents formed the system.We propose that frequent storms in northwestern Palawan triggered these currents by resuspending sediments on the shelf.
基金The Science and Technology Basic Investigation Program of China,No.2022FY202404。
文摘Climate change and anthropogenic activities have profoundly affected coastal systems,making geomorphological research a critical focus for coastal protection and sustainable development.In this study,a comprehensive classification of beach states around Hainan Island is conducted for the first time by utilizing theΩ-RTR model and geological control modes.Six distinct classic beach states ranging from dissipative to reflective are identified:barred dissipative beaches or no-barred dissipative beaches(BD or NBD),barred beaches(B),low-tide terrace or low-tide bar with rip(LTTR or LTBR),and reflective state(R).Among these,the BD and B types are predominant on Hainan Island.Notably,the beach states are subject to multiple factors,such as hydrodynamic forcings,geomorphic features and underlying substrates,and exhibit remarkable spatiotemporal variability.During extreme events,hydrodynamic forcings impact beach states more substantially than geological and geomorphic features do,leading to a more homogeneous distribution of beach states.Under normal circumstance,beach states are predominantly controlled by geological and geomorphic features.Coastal geological and geomorphic features have a pronounced influence on beach morphology and stability.For example,hard substrates underpin wide and stable dissipative beaches,whereas softer substrates lead to narrower,erosion-prone beaches.Three geological control modes are identified,namely,gently sloping hard substrates with dissipative beaches,moderately sloping hard substrates with seasonally variable reflective beaches,and steeply sloping soft substrates with dynamic sandbar-dominated beaches.These findings highlight the necessity of integrating geological settings in tandem with hydrodynamic forcings into coastal management practices.A dual-mode strategy is proposed:maintaining geomorphic self-organization on hard-substrate coasts under normal conditions and implementing hybrid engineering–ecological measures(e.g.,artificial sand replenishment and vegetation restoration)on erosion-prone soft substrates.
文摘基于明暗恢复形状(shape from shading,简称SFS)方法进行海底侧扫声呐图像三维重建时,会因为方法中反射模型与海底表面不相符而降低重建精度。为此文章在分析大陆架海底表面特点及侧扫声呐工作机理的基础上,提出了基于SFS混合反射模型的侧扫声呐图像海底地形重建方法。首先在保留Lambert漫反射模型的基础上引入Blinn-Phong镜面反射模型,并基于侧扫声呐图像粗糙度进行漫反射系数、镜面反射系数和镜面反射指数的自适应设计,从而形成适合复杂海底表面的混合反射模型;然后线性化处理辐射照度方程,并采用牛顿-拉夫逊方法来获得海底表面高程;最后根据海底点设计反演高程约束系数来约束表面高程,进而完成侧扫声呐图像的三维重建。试验测试结果表明,相较于其他三维重建方法,文中方法的平均绝对误差值VMAE平均降低了32.18%、相关系数值VCC平均提高了29.62%、信噪比值VSNR平均提升了27.23%,有效实现了侧扫声呐图像三维重建。
文摘珠江口洪季悬浮泥沙的浓度分布与输运通量受多种动力因素的影响,其中斜压效应不可忽视。本文采用Coupled Ocean-Atmosphere-Wave-Sediment Transport Modeling System(COAWST)海洋模型系统,以2022年6月份(洪季)的珠江口为例,研究斜压效应对悬沙浓度分布与输运通量的影响。采用控制实验,研究有无斜压作用时悬沙浓度分布的变化;分析有无斜压作用时的泥沙输运通量与海底冲淤的变化情况,结果表明有斜压作用时悬浮泥沙的输运路径、通量均与无斜压时不同,伶仃洋的悬沙除向西口外输运外,还随着河口羽流的扩展向西南方向输运。有斜压作用时在伶仃洋的西南端及下游的西南沿岸均有明显的海底淤积,而无斜压作用时泥沙淤积主要发生于伶仃洋的西口附近及磨刀门口外落潮射流末端。利用悬沙输运方程进行诊断分析,揭示了斜压作用导致悬沙浓度分布与输运通量变化的动力机制,表明斜压作用虽然减小了底切应力与垂向混合系数,但由于增大的海底泥沙可侵蚀量及垂向悬沙梯度,悬沙输运方程中的再悬浮量与垂向混合通量要比无斜压时要大。本研究对河口区的悬沙输运过程与机理分析具有一定的指导意义。
