2019 Vol. 38, No. 7
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2019, 38(7): .
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2019, 38(7): .
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2019, 38(7): 1-13.
doi: 10.1007/s13131-019-1453-5
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In this paper, we discuss the interfacial internal waves with a rigid boundary in a three-layer fluid system, where the density of the upper layer fluid is smaller than that of the lower layer. With the Lagrangian matching conditions at the interfaces, the first-order solutions, the second-order solutions and the third-order asymptotic solutions for the interfacial internal waves are obtained in the Lagrangian description using the perturbation method, and the mass transport velocity, the wave frequency, the mean level and the particle trajectory are also given. The results show that the discontinuities across the interfaces appear for the mass transport velocity, wave frequency and mean level, but we find that these discontinuities may disappear if the water depth ratio and the density ratio of the three layer fluids satisfy certain conditions.
In this paper, we discuss the interfacial internal waves with a rigid boundary in a three-layer fluid system, where the density of the upper layer fluid is smaller than that of the lower layer. With the Lagrangian matching conditions at the interfaces, the first-order solutions, the second-order solutions and the third-order asymptotic solutions for the interfacial internal waves are obtained in the Lagrangian description using the perturbation method, and the mass transport velocity, the wave frequency, the mean level and the particle trajectory are also given. The results show that the discontinuities across the interfaces appear for the mass transport velocity, wave frequency and mean level, but we find that these discontinuities may disappear if the water depth ratio and the density ratio of the three layer fluids satisfy certain conditions.
2019, 38(7): 14-21.
doi: 10.1007/s13131-019-1454-4
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The electromagnetic separation method is a new approach to treat ship-based marine oily wastewater, in which oil droplets are dispersed in seawater (oil-seawater mixed flow). In order to clarify the separation process and determine the separation characteristics, the flow field and volume fraction of the oil droplets of the oil-seawater mixed flow under an applied electromagnetic field with different operating conditions were investigated by 2D numerical simulations with the Eulerian model. The results show that:(1) the downward Lorentz force causes seawater to flow downwards and the oil droplets to move upwards due to the electromagnetic separation force in the effective section of the separation channel; (2) the volume fraction of the oil droplets at the top of the outlet section increases with the current density, magnetic field, and the diameter of the oil droplet and decreases with the inlet velocity of the oily seawater. The results provide useful guidance for the design of electromagnetic separation devices of the oil-seawater mixed flow.
The electromagnetic separation method is a new approach to treat ship-based marine oily wastewater, in which oil droplets are dispersed in seawater (oil-seawater mixed flow). In order to clarify the separation process and determine the separation characteristics, the flow field and volume fraction of the oil droplets of the oil-seawater mixed flow under an applied electromagnetic field with different operating conditions were investigated by 2D numerical simulations with the Eulerian model. The results show that:(1) the downward Lorentz force causes seawater to flow downwards and the oil droplets to move upwards due to the electromagnetic separation force in the effective section of the separation channel; (2) the volume fraction of the oil droplets at the top of the outlet section increases with the current density, magnetic field, and the diameter of the oil droplet and decreases with the inlet velocity of the oily seawater. The results provide useful guidance for the design of electromagnetic separation devices of the oil-seawater mixed flow.
2019, 38(7): 22-35.
doi: 10.1007/s13131-019-1455-3
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A three-dimensional wave-current-sediment coupled numerical model is developed to understand the sediment transport dynamics in the Zhujiang (Pearl) River Estuary (ZRE), China. The model results are in good agreement with observed data, and statistics show good model skill scores. Numerical studies are conducted to assess the scenarios of suspended sediment in the ZRE under the effects of different forcing (river discharges, waves, and winds). The model results indicate that the estuarine gravitational circulation plays an important role in the development of estuarine turbidity maximum in the ZRE, particularly during neap tides. The increased river discharge can result in a seaward sediment transport. The suspended sediment concentration (SSC) in the bottom increases with both wave bottom orbital velocity and wave height. Because of the shallow water depth, the effect of waves on sediment in the west shoal is greater than that in the east channel. The southwesterly wind-induced wave affects the SSC more than those resulting from the northeasterly wind, while the northeasterly wind-driven circulation has a slightly greater influence on the SSC than that of the southwesterly wind. However, a steady southwesterly wind condition favors the increase of the SSC in the Lingding Bay more so than a steady northeasterly wind condition. If the other forcings are same, the averaged SSC under a steady southwesterly wind condition is about 1.1 times that resulting from a steady northeasterly wind.
A three-dimensional wave-current-sediment coupled numerical model is developed to understand the sediment transport dynamics in the Zhujiang (Pearl) River Estuary (ZRE), China. The model results are in good agreement with observed data, and statistics show good model skill scores. Numerical studies are conducted to assess the scenarios of suspended sediment in the ZRE under the effects of different forcing (river discharges, waves, and winds). The model results indicate that the estuarine gravitational circulation plays an important role in the development of estuarine turbidity maximum in the ZRE, particularly during neap tides. The increased river discharge can result in a seaward sediment transport. The suspended sediment concentration (SSC) in the bottom increases with both wave bottom orbital velocity and wave height. Because of the shallow water depth, the effect of waves on sediment in the west shoal is greater than that in the east channel. The southwesterly wind-induced wave affects the SSC more than those resulting from the northeasterly wind, while the northeasterly wind-driven circulation has a slightly greater influence on the SSC than that of the southwesterly wind. However, a steady southwesterly wind condition favors the increase of the SSC in the Lingding Bay more so than a steady northeasterly wind condition. If the other forcings are same, the averaged SSC under a steady southwesterly wind condition is about 1.1 times that resulting from a steady northeasterly wind.
2019, 38(7): 36-47.
doi: 10.1007/s13131-019-1456-2
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A wave forecasting system using FUNWAVE-TVD which is based on the fully nonlinear Boussinesq equations by Chen (2006) was developed to provide an accurate wave prediction in the Port of Busan, South Korea. This system is linked to the Korea Operational Oceanographic System (KOOS) developed by Park et al. (2015). The computational domain covers a region of 9.6 km×7.0 km with a grid size of 2 m in both directions, which is sufficient to resolve short waves and dominant sea states. The total number of grid points exceeds 16 millions, making the model computational expensive. To provide real-time forecasting, an interpolation method, which is based on pre-calculated results of FUNWAVE-TVD and SWAN forecasting results at the FUNWAVE-TVD offshore boundary, was used. A total of 45 cases were pre-calculated, which took 71 days on 924 computational cores of a Linux cluster system. Wind wave generation and propagation from the deep water were computed using the SWAN in KOOS. SWAN results provided a boundary condition for the FUNWAVE-TVD forecasting system. To verify the model, wave observations were conducted at three locations inside the port in a time period of more than 7 months. A model/model comparison between FUNWAVE-TVD and SWAN was also carried out. It is found that, FUNWAVE-TVD improves the forecasting results significantly compared to SWAN which underestimates wave heights in sheltered areas due to incorrect physical mechanism of wave diffraction, as well as large wave heights caused by wave reflections inside the port.
A wave forecasting system using FUNWAVE-TVD which is based on the fully nonlinear Boussinesq equations by Chen (2006) was developed to provide an accurate wave prediction in the Port of Busan, South Korea. This system is linked to the Korea Operational Oceanographic System (KOOS) developed by Park et al. (2015). The computational domain covers a region of 9.6 km×7.0 km with a grid size of 2 m in both directions, which is sufficient to resolve short waves and dominant sea states. The total number of grid points exceeds 16 millions, making the model computational expensive. To provide real-time forecasting, an interpolation method, which is based on pre-calculated results of FUNWAVE-TVD and SWAN forecasting results at the FUNWAVE-TVD offshore boundary, was used. A total of 45 cases were pre-calculated, which took 71 days on 924 computational cores of a Linux cluster system. Wind wave generation and propagation from the deep water were computed using the SWAN in KOOS. SWAN results provided a boundary condition for the FUNWAVE-TVD forecasting system. To verify the model, wave observations were conducted at three locations inside the port in a time period of more than 7 months. A model/model comparison between FUNWAVE-TVD and SWAN was also carried out. It is found that, FUNWAVE-TVD improves the forecasting results significantly compared to SWAN which underestimates wave heights in sheltered areas due to incorrect physical mechanism of wave diffraction, as well as large wave heights caused by wave reflections inside the port.
2019, 38(7): 48-56.
doi: 10.1007/s13131-018-1081-z
Abstract:
The effects of hurricane forward speed (V) and approach angle (θ) on storm surge are important and a systematic investigation covering possible and continuous ranges of these parameters has not been done before. Here we present such a study with a numerical experiment using the Finite Volume Community Ocean Model (FVCOM). The hurricane track is simplified as a straight line, such that V and θ fully define the motion of the hurricane. The maximum surge is contributed by both free waves and a forced storm surge wave moving with the hurricane. Among the free waves, Kelvin-type waves can only propagate in the down-coast direction. Simulations show that those waves can only have a significant positive storm surge when the hurricane velocity has a down-coast component. The optimal values of V and θ that maximize the storm surge in an idealized semi-circular ocean basin are functions of the bathymetry. For a constant bathymetry, the maximum surge occurs when the hurricane approaches the coast from the normal direction when the free wave generation is minimal; for a stepped bathymetry, the maximum surge occurs at a certain acute approach angle which maximizes the duration of persistent wind forcing; a step-like bathymetry with a sloped shelf is similar to the stepped bathymetry, with the added possibility of landfall resonance when the free and forced waves are moving at about the same velocity. For other cases, the storm surge is smaller, given other parameters (hurricane size, maximum wind speed, etc.) unchanged.
The effects of hurricane forward speed (V) and approach angle (θ) on storm surge are important and a systematic investigation covering possible and continuous ranges of these parameters has not been done before. Here we present such a study with a numerical experiment using the Finite Volume Community Ocean Model (FVCOM). The hurricane track is simplified as a straight line, such that V and θ fully define the motion of the hurricane. The maximum surge is contributed by both free waves and a forced storm surge wave moving with the hurricane. Among the free waves, Kelvin-type waves can only propagate in the down-coast direction. Simulations show that those waves can only have a significant positive storm surge when the hurricane velocity has a down-coast component. The optimal values of V and θ that maximize the storm surge in an idealized semi-circular ocean basin are functions of the bathymetry. For a constant bathymetry, the maximum surge occurs when the hurricane approaches the coast from the normal direction when the free wave generation is minimal; for a stepped bathymetry, the maximum surge occurs at a certain acute approach angle which maximizes the duration of persistent wind forcing; a step-like bathymetry with a sloped shelf is similar to the stepped bathymetry, with the added possibility of landfall resonance when the free and forced waves are moving at about the same velocity. For other cases, the storm surge is smaller, given other parameters (hurricane size, maximum wind speed, etc.) unchanged.
2019, 38(7): 57-66.
doi: 10.1007/s13131-019-1457-1
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The Impact of the Indian Ocean Dipole (IOD) and the El Niño Southern Oscillation (ENSO) event for Indonesian rainfall has been investigated for the period from 1950 to 2011. Inter-annual change of IOD and ENSO indices are used to investigate their relationship with Indonesian rainfall. By using the wavelet transform method, we found a positive significant correlation between IOD and Indonesian rainfall on the time scale of nearly 2.5-4 years. Furthermore, the positive significant correlation between ENSO (sea surface temperature anomaly at Niño3.4 area indices) and Indonesian rainfall exists for shorter than 2 years and between 5.5 to 6.5-year time scales.
The Impact of the Indian Ocean Dipole (IOD) and the El Niño Southern Oscillation (ENSO) event for Indonesian rainfall has been investigated for the period from 1950 to 2011. Inter-annual change of IOD and ENSO indices are used to investigate their relationship with Indonesian rainfall. By using the wavelet transform method, we found a positive significant correlation between IOD and Indonesian rainfall on the time scale of nearly 2.5-4 years. Furthermore, the positive significant correlation between ENSO (sea surface temperature anomaly at Niño3.4 area indices) and Indonesian rainfall exists for shorter than 2 years and between 5.5 to 6.5-year time scales.
2019, 38(7): 67-73.
doi: 10.1007/s13131-019-1458-0
Abstract:
The 2015/2016 El Niño event reached the threshold of super El Niño event, and was comparable to the super events in 1982/1983 and 1997/1998. Interestingly, the tropical cyclones (TCs) were found to have very late onsets in the decaying years of the super El Niño events. This study discusses the causes of late TC onsets related with atmospheric circulation, disturbance sources and trigger mechanisms. The analysis shows that the western North Pacific subtropical high (WNPSH) from January-June during the decaying years of the super El Niño events were stronger than the climatic mean, which resulted in a relatively stable atmospheric state by inhibiting deep convection. As a disturbance source, the April-June intertropical convergence zone (ITCZ) during the decaying years of the super El Niño events were significantly weaker than its climatic mean. The cross-equatorial flow and monsoon trough, as important TC generation triggers, were weaker from April-June during the decaying years of the super El Niño events, which further reduced the probability of TC generation. As for the late TC onsets, the role of atmospheric circulation anomalies (i.e., subtropical-high, the ITCZ, cross-equatorial flow, and monsoon trough) were more important. The cross-equatorial flow may take as predictor of TC onsets in the decaying years of the super El Niño events.
The 2015/2016 El Niño event reached the threshold of super El Niño event, and was comparable to the super events in 1982/1983 and 1997/1998. Interestingly, the tropical cyclones (TCs) were found to have very late onsets in the decaying years of the super El Niño events. This study discusses the causes of late TC onsets related with atmospheric circulation, disturbance sources and trigger mechanisms. The analysis shows that the western North Pacific subtropical high (WNPSH) from January-June during the decaying years of the super El Niño events were stronger than the climatic mean, which resulted in a relatively stable atmospheric state by inhibiting deep convection. As a disturbance source, the April-June intertropical convergence zone (ITCZ) during the decaying years of the super El Niño events were significantly weaker than its climatic mean. The cross-equatorial flow and monsoon trough, as important TC generation triggers, were weaker from April-June during the decaying years of the super El Niño events, which further reduced the probability of TC generation. As for the late TC onsets, the role of atmospheric circulation anomalies (i.e., subtropical-high, the ITCZ, cross-equatorial flow, and monsoon trough) were more important. The cross-equatorial flow may take as predictor of TC onsets in the decaying years of the super El Niño events.
2019, 38(7): 74-83.
doi: 10.1007/s13131-019-1459-z
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To determine the grid resolutions of the WRF model in the typhoon simulation, some sensitivity analysis of horizontal and vertical resolutions in different conditions has been carried out. Different horizontal resolutions (5, 10, 20, 30 km), nesting grids (15 and 5 km), different vertical resolutions (35-layers, 28-layers, 20-layers) and different top maximum pressures (1 000, 2 000, 3 500, 5 000 Pa) had been used in the mesoscale numerical model WRF to simulate the Typhoon Kai-tak. The simulation results of typhoon track, wind speed and sea level pressure at different horizontal and vertical resolutions have been compared and analyzed. The horizontal and vertical resolutions of the model have limited effect on the simulation effect of the typhoon track. Different horizontal and vertical resolutions have obvious effects on typhoon strength (defined by wind speed) and intensity (defined by sea level pressure, SLP), especially for sea level pressure. The typhoon intensity simulated by the high-resolution model is closer to the real situation and the nesting grids can improve computational accuracy and efficiency. The simulation results affected by vertical resolution using 35-layers is better than the simulation results using 20-layers and 28-layers simulations. Through comparison and analysis, the horizontal and vertical resolutions of WRF model are finally determined as follows:the two-way nesting grid of 15 and 5 km is comprehensively determined, and the vertical layers is 35-layers, the top maximum pressure is 2 000 Pa.
To determine the grid resolutions of the WRF model in the typhoon simulation, some sensitivity analysis of horizontal and vertical resolutions in different conditions has been carried out. Different horizontal resolutions (5, 10, 20, 30 km), nesting grids (15 and 5 km), different vertical resolutions (35-layers, 28-layers, 20-layers) and different top maximum pressures (1 000, 2 000, 3 500, 5 000 Pa) had been used in the mesoscale numerical model WRF to simulate the Typhoon Kai-tak. The simulation results of typhoon track, wind speed and sea level pressure at different horizontal and vertical resolutions have been compared and analyzed. The horizontal and vertical resolutions of the model have limited effect on the simulation effect of the typhoon track. Different horizontal and vertical resolutions have obvious effects on typhoon strength (defined by wind speed) and intensity (defined by sea level pressure, SLP), especially for sea level pressure. The typhoon intensity simulated by the high-resolution model is closer to the real situation and the nesting grids can improve computational accuracy and efficiency. The simulation results affected by vertical resolution using 35-layers is better than the simulation results using 20-layers and 28-layers simulations. Through comparison and analysis, the horizontal and vertical resolutions of WRF model are finally determined as follows:the two-way nesting grid of 15 and 5 km is comprehensively determined, and the vertical layers is 35-layers, the top maximum pressure is 2 000 Pa.
2019, 38(7): 84-95.
doi: 10.1007/s13131-019-1460-6
Abstract:
Recent studies have shown that specific geochemical characteristics of sediments can be used to reconstruct past methane seepage events. In this work, the correlation between the Sr/Ca and Mg/Ca ratios of sediment samples is analyzed and the sulfate concentration profile in Site C14 from cold-seep sediments in the Qiongdongnan Basin in northern South China Sea is obtained. The results confirmed that, sulfate at 0-247 cm below sea floor (Unit I) is mainly consumed by organic matter sulfate reduction (OSR), while sulfate at 247-655 cm (Unit Ⅱ) is consumed by both the OSR and the anaerobic oxidation of methane (AOM). In addition, the bottom sediment layer is affected by weak methane seepage. The Mo and U enrichment factors also exhibit similar trends in their respective depth profiles. The responses of trace elements, including Co/Al, Ni/Al, Cr/Al and Zn/Al ratios to methane seepage allowed the study of depositional conditions and methane seepage events. Based on the results, it is speculated that the depositional conditions of Unit Ⅱ changed with depth from moderate conditions of sulfidic and oxic conditions to locally anoxic conditions, and finally to suboxic conditions due to methane fluid leakage. The stable isotope values of chromium-reducible sulfide produced by AOM and those of sulfide formed by OSR in the early diagenetic environment suffered serious depletion of 34S. This was probably due to weak methane leakage, which caused the slower upward diffusion and the effect of early diagenesis on the samples. It is necessary to consider the effects of depositional environments and diagenesis on these geochemical parameters.
Recent studies have shown that specific geochemical characteristics of sediments can be used to reconstruct past methane seepage events. In this work, the correlation between the Sr/Ca and Mg/Ca ratios of sediment samples is analyzed and the sulfate concentration profile in Site C14 from cold-seep sediments in the Qiongdongnan Basin in northern South China Sea is obtained. The results confirmed that, sulfate at 0-247 cm below sea floor (Unit I) is mainly consumed by organic matter sulfate reduction (OSR), while sulfate at 247-655 cm (Unit Ⅱ) is consumed by both the OSR and the anaerobic oxidation of methane (AOM). In addition, the bottom sediment layer is affected by weak methane seepage. The Mo and U enrichment factors also exhibit similar trends in their respective depth profiles. The responses of trace elements, including Co/Al, Ni/Al, Cr/Al and Zn/Al ratios to methane seepage allowed the study of depositional conditions and methane seepage events. Based on the results, it is speculated that the depositional conditions of Unit Ⅱ changed with depth from moderate conditions of sulfidic and oxic conditions to locally anoxic conditions, and finally to suboxic conditions due to methane fluid leakage. The stable isotope values of chromium-reducible sulfide produced by AOM and those of sulfide formed by OSR in the early diagenetic environment suffered serious depletion of 34S. This was probably due to weak methane leakage, which caused the slower upward diffusion and the effect of early diagenesis on the samples. It is necessary to consider the effects of depositional environments and diagenesis on these geochemical parameters.
2019, 38(7): 96-106.
doi: 10.1007/s13131-019-1461-5
Abstract:
The seabed scouring and silting are very important to the construction of port and waterway engineering. Seabed deposition and erosion change is complicated due to the influence of sediment supply, human activities and other factors. The Yangshan Deepwater Port is the new deep water harbor, which is an important part of the Shanghai International Shipping Service Center. Its construction has received much attention. At present, the water depth from the 1st to the 3rd harbor district is currently suitable under regular dredging and tidal current action. The fourth harbor district will be built in the world's largest fully-automated deep water wharf. In the study, bathymetry change of the entire sea area of the Yangshan Deepwater Port and the 4th harbor district (i.e., Phase IV project) waters were analyzed quantitatively using multiyear bathymetric, hydrological and sediment data. The results show that from 1998 to 2010, seabed changes are characterized by large volumes of erosion and sedimentation, which the southern part was deposited and the northern part was eroded in the inner harbor waters, but the seabed of the Kezhushan inlet was eroded. Seabed changes of Phase IV project waters generally show a scour tendency in recent few years with the annual scour rate about 0.7 m. Among the many factors, the existence of Kezhushan inlet and its influence of the western water flow play an important positive role in water depth changes under the ebb tide action.
The seabed scouring and silting are very important to the construction of port and waterway engineering. Seabed deposition and erosion change is complicated due to the influence of sediment supply, human activities and other factors. The Yangshan Deepwater Port is the new deep water harbor, which is an important part of the Shanghai International Shipping Service Center. Its construction has received much attention. At present, the water depth from the 1st to the 3rd harbor district is currently suitable under regular dredging and tidal current action. The fourth harbor district will be built in the world's largest fully-automated deep water wharf. In the study, bathymetry change of the entire sea area of the Yangshan Deepwater Port and the 4th harbor district (i.e., Phase IV project) waters were analyzed quantitatively using multiyear bathymetric, hydrological and sediment data. The results show that from 1998 to 2010, seabed changes are characterized by large volumes of erosion and sedimentation, which the southern part was deposited and the northern part was eroded in the inner harbor waters, but the seabed of the Kezhushan inlet was eroded. Seabed changes of Phase IV project waters generally show a scour tendency in recent few years with the annual scour rate about 0.7 m. Among the many factors, the existence of Kezhushan inlet and its influence of the western water flow play an important positive role in water depth changes under the ebb tide action.
2019, 38(7): 107-113.
doi: 10.1007/s13131-019-1462-4
Abstract:
Excess pore water pressure is an important parameter that can be used to analyze certain physical characteristics of sediment. In this paper, the excess pore water pressure of subseafloor sediment and its variation with tidal movement was measured following the installation of a wharf in Qingdao, China by using a fiber Bragg grating (FBG) piezometer. The results indicated that this FBG piezometer is effective in the field. The measured variation of excess pore water pressure after installation is largely explained by the dissipation of excess pore water pressure. The dissipation rate can be used to estimate the horizontal consolidation coefficient, which ranged from 1.3×10–6 m2/s to 8.1×10–6 m2/s. The measured values during tidal phases are associated with the variability of tidal pressure on the seafloor and can be used to estimate the compressibility and the permeability of the sediment during tidal movement. The volume compression coefficient estimated from tidal oscillation was approximately 2.0×10–11 Pa–1, which was consistent with the data from the laboratory test. The findings of this paper can provide useful information for in situ investigations of subseafloor sediment.
Excess pore water pressure is an important parameter that can be used to analyze certain physical characteristics of sediment. In this paper, the excess pore water pressure of subseafloor sediment and its variation with tidal movement was measured following the installation of a wharf in Qingdao, China by using a fiber Bragg grating (FBG) piezometer. The results indicated that this FBG piezometer is effective in the field. The measured variation of excess pore water pressure after installation is largely explained by the dissipation of excess pore water pressure. The dissipation rate can be used to estimate the horizontal consolidation coefficient, which ranged from 1.3×10–6 m2/s to 8.1×10–6 m2/s. The measured values during tidal phases are associated with the variability of tidal pressure on the seafloor and can be used to estimate the compressibility and the permeability of the sediment during tidal movement. The volume compression coefficient estimated from tidal oscillation was approximately 2.0×10–11 Pa–1, which was consistent with the data from the laboratory test. The findings of this paper can provide useful information for in situ investigations of subseafloor sediment.
2019, 38(7): 114-120.
doi: 10.1007/s13131-019-1463-3
Abstract:
Knowledge of the surface ocean dynamics and the underlying controlling mechanisms is critical to understand the natural variability of the ocean and to predict its future response to climate change. In this paper, we highlight the potential use of Volunteer Observing Ship (VOS), as carrier for automatic underway measuring system and as platform for sample collection, to enhance the observing capacity for the surface ocean. We review the concept, history, present status and future development of the VOS-based in situ surface ocean observation. The successes of various VOS projects demonstrate that, along with the rapid advancing sensor techniques, VOS is able to improve the temporal resolution and spatial coverage of the surface ocean observation in a highly cost-effective manner. A sustained and efficient marine monitoring system in the future should integrate the advantages of various observing platforms including VOS.
Knowledge of the surface ocean dynamics and the underlying controlling mechanisms is critical to understand the natural variability of the ocean and to predict its future response to climate change. In this paper, we highlight the potential use of Volunteer Observing Ship (VOS), as carrier for automatic underway measuring system and as platform for sample collection, to enhance the observing capacity for the surface ocean. We review the concept, history, present status and future development of the VOS-based in situ surface ocean observation. The successes of various VOS projects demonstrate that, along with the rapid advancing sensor techniques, VOS is able to improve the temporal resolution and spatial coverage of the surface ocean observation in a highly cost-effective manner. A sustained and efficient marine monitoring system in the future should integrate the advantages of various observing platforms including VOS.
2019, 38(7): 121-128.
doi: 10.1007/s13131-019-1449-8
Abstract:
This paper describes investigations of the internal waves in the Andaman Sea using Moderate Resolution Imaging Spectroradiometer (MODIS) imagery over the period of June 2010 to May 2016. Results of the spatial and temporal distribution, generation sources and propagation characteristics of internal waves are presented. The statistical analysis shows that internal waves can be observed in almost the entire area of the Andaman Sea. Most internal waves are observed in the northern, central and southern regions of the Andaman Sea. A significant number of internal waves between 7°N and 9°N in the East Indian Ocean are also observed. Internal waves can be observed year-round in the Andaman Sea, while most of internal waves are observed between February and April, with a maximum frequency of 15.03% in March. The seasonal distribution of the internal waves shows that the internal waves have mostly been observed in the dry season (February to April), and fewer internal waves are observed in the rainy season (May to October). The double peak distribution for the occurrence frequency of internal waves is found. With respect to the lunar influence, more internal waves are observed after the spring tide, which implies the spring tide may play an important role in internal wave generation in the Andaman Sea. Generation sources of internal waves are explored based on the propagation characteristics of internal waves. The results indicate that six sources are located between the Andaman Islands and the Nicobar Islands, and one is located in the northern Andaman Sea. Four regions with active internal wave phenomenon in the Andaman Sea were presented during the MODIS survey, and the propagation speed of internal waves calculated based on the semidiurnal generation period is smaller than the results acquired from pairs of the images with short time intervals.
This paper describes investigations of the internal waves in the Andaman Sea using Moderate Resolution Imaging Spectroradiometer (MODIS) imagery over the period of June 2010 to May 2016. Results of the spatial and temporal distribution, generation sources and propagation characteristics of internal waves are presented. The statistical analysis shows that internal waves can be observed in almost the entire area of the Andaman Sea. Most internal waves are observed in the northern, central and southern regions of the Andaman Sea. A significant number of internal waves between 7°N and 9°N in the East Indian Ocean are also observed. Internal waves can be observed year-round in the Andaman Sea, while most of internal waves are observed between February and April, with a maximum frequency of 15.03% in March. The seasonal distribution of the internal waves shows that the internal waves have mostly been observed in the dry season (February to April), and fewer internal waves are observed in the rainy season (May to October). The double peak distribution for the occurrence frequency of internal waves is found. With respect to the lunar influence, more internal waves are observed after the spring tide, which implies the spring tide may play an important role in internal wave generation in the Andaman Sea. Generation sources of internal waves are explored based on the propagation characteristics of internal waves. The results indicate that six sources are located between the Andaman Islands and the Nicobar Islands, and one is located in the northern Andaman Sea. Four regions with active internal wave phenomenon in the Andaman Sea were presented during the MODIS survey, and the propagation speed of internal waves calculated based on the semidiurnal generation period is smaller than the results acquired from pairs of the images with short time intervals.
2019, 38(7): 129-136.
doi: 10.1007/s13131-019-1464-2
Abstract:
We present a novel sea-ice classification framework based on locality preserving fusion of multi-source images information. The locality preserving fusion arises from two-fold, i.e., the local characterization in both spatial and feature domains. We commence by simultaneously learning a projection matrix, which preserves spatial localities, and a similarity matrix, which encodes feature similarities. We map the pixels of multi-source images by the projection matrix to a set fusion vectors that preserve spatial localities of the image. On the other hand, by applying the Laplacian eigen-decomposition to the similarity matrix, we obtain another set of fusion vectors that preserve the feature local similarities. We concatenate the fusion vectors for both spatial and feature locality preservation and obtain the fusion image. Finally, we classify the fusion image pixels by a novel sliding ensemble strategy, which enhances the locality preservation in classification. Our locality preserving fusion framework is effective in classifying multi-source sea-ice images (e.g., multi-spectral and synthetic aperture radar (SAR) images) because it not only comprehensively captures the spatial neighboring relationships but also intrinsically characterizes the feature associations between different types of sea-ices. Experimental evaluations validate the effectiveness of our framework.
We present a novel sea-ice classification framework based on locality preserving fusion of multi-source images information. The locality preserving fusion arises from two-fold, i.e., the local characterization in both spatial and feature domains. We commence by simultaneously learning a projection matrix, which preserves spatial localities, and a similarity matrix, which encodes feature similarities. We map the pixels of multi-source images by the projection matrix to a set fusion vectors that preserve spatial localities of the image. On the other hand, by applying the Laplacian eigen-decomposition to the similarity matrix, we obtain another set of fusion vectors that preserve the feature local similarities. We concatenate the fusion vectors for both spatial and feature locality preservation and obtain the fusion image. Finally, we classify the fusion image pixels by a novel sliding ensemble strategy, which enhances the locality preservation in classification. Our locality preserving fusion framework is effective in classifying multi-source sea-ice images (e.g., multi-spectral and synthetic aperture radar (SAR) images) because it not only comprehensively captures the spatial neighboring relationships but also intrinsically characterizes the feature associations between different types of sea-ices. Experimental evaluations validate the effectiveness of our framework.
2019, 38(7): 137-143.
doi: 10.1007/s13131-019-1465-1
Abstract:
Global navigation satellite system (GNSS)/acoustic positioning precision is determined by the positioning geometry and the ranging precision; thus optimizing GNSS buoys array is meaningful to improve the positioning accuracy and reliability. An analytical method is proposed for optimizing the GNSS buoys array with regard to the cutoff angle constraints for underwater acoustic observations. For the practical limitation of coplanarity of GNSS buoys and the cutoff angle, an algorithm is proposed to analytically minimize the position dilution of precision (PDOP). The proposed method is validated to give complete solutions of PDOP minimization with five GNSS buoys. At last, in order to search a best configuration among the PDOP solution set, we propose a search algorithm to get the solution with the smallest geometric dilution of precision (GDOP). It indicates that within a given region, the GDOP minimization at the center of a region is equivalent to the PDOP mean minimization over the region. The relation between the positioning accuracy and the positioning geometry with five known points is illustrated in an experiment performed in South China Sea.
Global navigation satellite system (GNSS)/acoustic positioning precision is determined by the positioning geometry and the ranging precision; thus optimizing GNSS buoys array is meaningful to improve the positioning accuracy and reliability. An analytical method is proposed for optimizing the GNSS buoys array with regard to the cutoff angle constraints for underwater acoustic observations. For the practical limitation of coplanarity of GNSS buoys and the cutoff angle, an algorithm is proposed to analytically minimize the position dilution of precision (PDOP). The proposed method is validated to give complete solutions of PDOP minimization with five GNSS buoys. At last, in order to search a best configuration among the PDOP solution set, we propose a search algorithm to get the solution with the smallest geometric dilution of precision (GDOP). It indicates that within a given region, the GDOP minimization at the center of a region is equivalent to the PDOP mean minimization over the region. The relation between the positioning accuracy and the positioning geometry with five known points is illustrated in an experiment performed in South China Sea.
