2020 Vol. 42, No. 9
Display Method:
2020, 42(9): 1-8.
doi: 10.3969/j.issn.0253-4193.2020.09.001
Abstract:
In order to investigate long-term variations of deep sea currents and temperature in the east of the Luzon Strait, a submarine mooring system was made at 19.75°N, 126.75°E from May 2015 to May 2016 in the Philippine Sea. The vertical distribution of ocean currents and its temporal variation characteristics are analyzed in the paper. Several features show that: (1) In the upper layer (100～160 m) , the average current velocity is about 12.5 cm/s with average flow direction oriented northwest; in the middle layer (810 m), the average current velocity is about 2.6 cm/s with flow direction oriented westward; in the deep layer of 1 550 m and 2 560 m, the average current velocity is small and less than 1 cm/s whereas that in 4 040 m is about 2.3 cm/s and oriented southwest. (2) The kinetic energy of the upper layer is one to two orders of magnitude compared with the middle and the deep layers. In the deep layer, the total kinetic energy and average kinetic energy in the 4 040 m layer is the largest, with smallest total kinetic energy and eddy kinetic energy in the 2 560 m layer, and with smallest averaged kinetic energy and largest eddy kinetic energy in the 1 550 m layer. Meanwhile, eddy kinetic energy is larger than averaged kinetic energy in all the layers. (3) The wavelet analysis shows that ocean current exhibits a low-frequency oscillation period of 81～85 d in layers shallower than 2 560 m, while the current at 4 040 m shows 51 d oscillation period.
In order to investigate long-term variations of deep sea currents and temperature in the east of the Luzon Strait, a submarine mooring system was made at 19.75°N, 126.75°E from May 2015 to May 2016 in the Philippine Sea. The vertical distribution of ocean currents and its temporal variation characteristics are analyzed in the paper. Several features show that: (1) In the upper layer (100～160 m) , the average current velocity is about 12.5 cm/s with average flow direction oriented northwest; in the middle layer (810 m), the average current velocity is about 2.6 cm/s with flow direction oriented westward; in the deep layer of 1 550 m and 2 560 m, the average current velocity is small and less than 1 cm/s whereas that in 4 040 m is about 2.3 cm/s and oriented southwest. (2) The kinetic energy of the upper layer is one to two orders of magnitude compared with the middle and the deep layers. In the deep layer, the total kinetic energy and average kinetic energy in the 4 040 m layer is the largest, with smallest total kinetic energy and eddy kinetic energy in the 2 560 m layer, and with smallest averaged kinetic energy and largest eddy kinetic energy in the 1 550 m layer. Meanwhile, eddy kinetic energy is larger than averaged kinetic energy in all the layers. (3) The wavelet analysis shows that ocean current exhibits a low-frequency oscillation period of 81～85 d in layers shallower than 2 560 m, while the current at 4 040 m shows 51 d oscillation period.
2020, 42(9): 9-21.
doi: 10.3969/j.issn.0253-4193.2020.09.002
Abstract:
In responding to deadly drowning accidents, China's first operational attempt on the rip current hazard prevention for coastal tourism was carried out by the National Marine Hazard Mitigation Service (NMHMS). A great number of recreational beaches in South China are found developing littoral sand bars and rip currents. Present paper, which is part of the nation-wide work, investigate the mechanism, characteristics, and evolution sandbar-induced rip current at three most visited beaches employing multi-techniques as complementary tools. The alongshore sandbar morphology, shorelines, and rip currents are highly dynamic with seasonal variations evidenced by the morphodynamic calculation and the satellite image interpretation. Unconventional contrary seasonal evolution of the rip current is identified at Qing’ao Bay with higher risk in cooler seasons. The rip current shows high sensitivity to the sandbar group pattern, the wave height, and the incident direction according to the phase-resolving hydrodynamic modelling. The wider rip channel between sandbars generated larger rip size compared to narrower gaps, but is not necessarily accompanied by stronger flow velocity. The rip current might be totally absent in small channels when majority of water flows out through neighboring broader pathways. The flow velocity is demonstrated proportional to the wave height and inversely proportional to the incident angle. Alongshore currents dominated over rip currents as the wave incident angle reached 10°−30° in the numerical simulation. It is verified in the field observation that the rip current is most hazardous at low tide when shallower water depth intensifies the topographic effect on waves and currents. The study result provides useful reference for the engineering mitigation and public warning of beach rip hazard. In near future, long time observation for specific sections of shoreline would be conducted to accumulate enough statistics for the rip current prediction and risk governance.
In responding to deadly drowning accidents, China's first operational attempt on the rip current hazard prevention for coastal tourism was carried out by the National Marine Hazard Mitigation Service (NMHMS). A great number of recreational beaches in South China are found developing littoral sand bars and rip currents. Present paper, which is part of the nation-wide work, investigate the mechanism, characteristics, and evolution sandbar-induced rip current at three most visited beaches employing multi-techniques as complementary tools. The alongshore sandbar morphology, shorelines, and rip currents are highly dynamic with seasonal variations evidenced by the morphodynamic calculation and the satellite image interpretation. Unconventional contrary seasonal evolution of the rip current is identified at Qing’ao Bay with higher risk in cooler seasons. The rip current shows high sensitivity to the sandbar group pattern, the wave height, and the incident direction according to the phase-resolving hydrodynamic modelling. The wider rip channel between sandbars generated larger rip size compared to narrower gaps, but is not necessarily accompanied by stronger flow velocity. The rip current might be totally absent in small channels when majority of water flows out through neighboring broader pathways. The flow velocity is demonstrated proportional to the wave height and inversely proportional to the incident angle. Alongshore currents dominated over rip currents as the wave incident angle reached 10°−30° in the numerical simulation. It is verified in the field observation that the rip current is most hazardous at low tide when shallower water depth intensifies the topographic effect on waves and currents. The study result provides useful reference for the engineering mitigation and public warning of beach rip hazard. In near future, long time observation for specific sections of shoreline would be conducted to accumulate enough statistics for the rip current prediction and risk governance.
2020, 42(9): 22-29.
doi: 10.3969/j.issn.0253-4193.2020.09.003
Abstract:
To evaluate the wave simulation capacity of the sea ice dissipation source terms in the third-generation wave model WAVEWATCH III V5.16, a nested wave model covering the area from Beaufort Sea to Mackenzie River Estuary is established to simulate the storm waves under the effect of Arctic storms from August 1st to September 31st, 2014. Simulated significant wave heights are calibrated using the measurements from SWIFT buoy. Results show that in the absence of ice data (i.e., with default model settings), in the areas near the ice edge, where wave energy is strongly controlled by sea ice, the performance of IC1 ice source item is the best, of which the results are more in line with the specific ice conditions in the Beaufort Sea.
To evaluate the wave simulation capacity of the sea ice dissipation source terms in the third-generation wave model WAVEWATCH III V5.16, a nested wave model covering the area from Beaufort Sea to Mackenzie River Estuary is established to simulate the storm waves under the effect of Arctic storms from August 1st to September 31st, 2014. Simulated significant wave heights are calibrated using the measurements from SWIFT buoy. Results show that in the absence of ice data (i.e., with default model settings), in the areas near the ice edge, where wave energy is strongly controlled by sea ice, the performance of IC1 ice source item is the best, of which the results are more in line with the specific ice conditions in the Beaufort Sea.
2020, 42(9): 30-37.
doi: 10.3969/j.issn.0253-4193.2020.09.004
Abstract:
On a coastal beach of very mild slope (close to or less than 1∶100), the multiple wave breaking may occur when waves propagate to the coast, companied by the wave recovery process between two breaking. In the current models for calculation of wave height, the wave breaking is usually simulated by the wave energy dissipation. But the establishment of energy dissipation describing wave breaking effect in these models did not automatically take the multiple wave breakings into account, and especially did not accurately simulate the wave recovery in this process. The present study presents a new model of the wave energy dissipation which can overcome this problem. The model is established by re-determining the stable wave energy, the saturated wave height-depth ratio and the dissipation coefficient and by introducing the judgment condition for the occurrence of wave recovery. The model has a very small value of the energy dissipation over wave recovery region and can properly describe the wave motion in wave recovery process. Comparison with measured wave heights shows that the model can give the wave heights on the plane and barred beaches of various bottom slopes (1∶10 to 1∶100), which agree well with the measurement, especially the multiple wave breaking and wave recovery process can be recognized automatically in the numerical simulations.
On a coastal beach of very mild slope (close to or less than 1∶100), the multiple wave breaking may occur when waves propagate to the coast, companied by the wave recovery process between two breaking. In the current models for calculation of wave height, the wave breaking is usually simulated by the wave energy dissipation. But the establishment of energy dissipation describing wave breaking effect in these models did not automatically take the multiple wave breakings into account, and especially did not accurately simulate the wave recovery in this process. The present study presents a new model of the wave energy dissipation which can overcome this problem. The model is established by re-determining the stable wave energy, the saturated wave height-depth ratio and the dissipation coefficient and by introducing the judgment condition for the occurrence of wave recovery. The model has a very small value of the energy dissipation over wave recovery region and can properly describe the wave motion in wave recovery process. Comparison with measured wave heights shows that the model can give the wave heights on the plane and barred beaches of various bottom slopes (1∶10 to 1∶100), which agree well with the measurement, especially the multiple wave breaking and wave recovery process can be recognized automatically in the numerical simulations.
2020, 42(9): 38-49.
doi: 10.3969/j.issn.0253-4193.2020.09.005
Abstract:
Based on the temperature and salinity grid data of SODA from1980 to 2015 and combined with Argo data, the formation mechanism and seasonal variability of the barrier layer thickness in the Bay of Bengal in Indian Ocean Dipole (IOD) events are revealed. The results show that the barrier layer changed significantly in the IOD event year. In the peak of pure IOD events (pIOD) and the pIOD+El Niño events (September−November), except for the 5 m thickening of the barrier layer in the southwest of the Bay of Bengal, the barrier layer become thinner range from 5 m to 15 m in the equatorial region and the region from Andaman Sea to the northern Bay of Bengal. This form disappears as the pIOD weakens. However, the form is maintained until March to May of the following year in the pIOD+El Niño events. The variation of barrier layer in the nIOD year is roughly opposite to that of the pIOD year. Further analysis shows that the change of isothermal layer caused by the remote forcing of the equatorial wind anomaly in the IOD event is the main cause of the variability of barrier layer. In the IOD+ENSO events, the equatorial wind anomaly is maintained for more than three months after the IOD disappear, making the anomaly of barrier layer last longer in the Bay of Bengal. In addition to the equatorial forcing, the Ekman pumping in the Bay of Bengal and the variability of the salt of mixed layer also have an effect on the interannual variation of the barrier layer thickness.
Based on the temperature and salinity grid data of SODA from1980 to 2015 and combined with Argo data, the formation mechanism and seasonal variability of the barrier layer thickness in the Bay of Bengal in Indian Ocean Dipole (IOD) events are revealed. The results show that the barrier layer changed significantly in the IOD event year. In the peak of pure IOD events (pIOD) and the pIOD+El Niño events (September−November), except for the 5 m thickening of the barrier layer in the southwest of the Bay of Bengal, the barrier layer become thinner range from 5 m to 15 m in the equatorial region and the region from Andaman Sea to the northern Bay of Bengal. This form disappears as the pIOD weakens. However, the form is maintained until March to May of the following year in the pIOD+El Niño events. The variation of barrier layer in the nIOD year is roughly opposite to that of the pIOD year. Further analysis shows that the change of isothermal layer caused by the remote forcing of the equatorial wind anomaly in the IOD event is the main cause of the variability of barrier layer. In the IOD+ENSO events, the equatorial wind anomaly is maintained for more than three months after the IOD disappear, making the anomaly of barrier layer last longer in the Bay of Bengal. In addition to the equatorial forcing, the Ekman pumping in the Bay of Bengal and the variability of the salt of mixed layer also have an effect on the interannual variation of the barrier layer thickness.
2020, 42(9): 50-60.
doi: 10.3969/j.issn.0253-4193.2020.09.006
Abstract:
In this study, we investigated clay mineral assemblages together with other provenance indicators of Core ARC7-LIC retrieved from the southern Alpha Ridge, in order to reveal the changes in sediment deposition, ocean circulation in the western Arctic Ocean, and the development of surrounding ice sheet through the mid-late Pleistocene (～MIS 29). Changes in clay mineral composition in Core ARC7-LIC suggest a transition of Siberian sourced material during MIS 29−13 towards a North American sourced material during MIS 12−1. This transition reflects the change of the circulation in the western Arctic Ocean before and after the Mid-Brunhes Event, which features an amplification of glacial-interglacial cycles in the post Mid-Brunhes Event. An exceptionally high smectite peak characterizes MIS 12, which is inferred to be from North American source. Laurentide ice sheet discharges icebergs and fine material in the western Arctic Ocean since MIS 16. The amplitude of ice sheet growth and decay increases since MIS 12. During MIS 6, 4 and 3, the asynchronous variations of Ca/Al and kaolinite suggest heterogeneous development of Laurentide ice sheet on the Canadian Arctic Archipelago and Alaska-Mackenzie sides.
In this study, we investigated clay mineral assemblages together with other provenance indicators of Core ARC7-LIC retrieved from the southern Alpha Ridge, in order to reveal the changes in sediment deposition, ocean circulation in the western Arctic Ocean, and the development of surrounding ice sheet through the mid-late Pleistocene (～MIS 29). Changes in clay mineral composition in Core ARC7-LIC suggest a transition of Siberian sourced material during MIS 29−13 towards a North American sourced material during MIS 12−1. This transition reflects the change of the circulation in the western Arctic Ocean before and after the Mid-Brunhes Event, which features an amplification of glacial-interglacial cycles in the post Mid-Brunhes Event. An exceptionally high smectite peak characterizes MIS 12, which is inferred to be from North American source. Laurentide ice sheet discharges icebergs and fine material in the western Arctic Ocean since MIS 16. The amplitude of ice sheet growth and decay increases since MIS 12. During MIS 6, 4 and 3, the asynchronous variations of Ca/Al and kaolinite suggest heterogeneous development of Laurentide ice sheet on the Canadian Arctic Archipelago and Alaska-Mackenzie sides.
2020, 42(9): 61-68.
doi: 10.3969/j.issn.0253-4193.2020.09.007
Abstract:
Hydrothermal venting systems mostly develop on the localized bathymetric highs of mid-ocean ridges with different spreading rates, and porous-elastic thermodynamic numerical models, which is filled with Darcian fluid can intuitively model the geometry, temperature structure and venting location of the hydrothermal systems in oceanic crust. Simulation results and the experimental-analytical model reveal that bathymetric highs with different sizes show a varied influence on the geometry of hydrothermal convection, the greater and wider bathymetric highs, the greater deflection of underlying plume to the bathymetric highs. Adopting the cross-axis bathymetry of the EPR 9°17′N and Lucky Strike hydrothermal fields into the model, our simulations produce vents fitting the realistic location of these two fields well. Finally, our schematic model for bathymetric relief deflecting underlying plumes indicates that the lower bathymetry and its underlying porous oceanic crust act as the main recharge zone, while the bathymetric high focuses the most of the discharge hot fluid due to the reduce of the overlying pressure of seawater.
Hydrothermal venting systems mostly develop on the localized bathymetric highs of mid-ocean ridges with different spreading rates, and porous-elastic thermodynamic numerical models, which is filled with Darcian fluid can intuitively model the geometry, temperature structure and venting location of the hydrothermal systems in oceanic crust. Simulation results and the experimental-analytical model reveal that bathymetric highs with different sizes show a varied influence on the geometry of hydrothermal convection, the greater and wider bathymetric highs, the greater deflection of underlying plume to the bathymetric highs. Adopting the cross-axis bathymetry of the EPR 9°17′N and Lucky Strike hydrothermal fields into the model, our simulations produce vents fitting the realistic location of these two fields well. Finally, our schematic model for bathymetric relief deflecting underlying plumes indicates that the lower bathymetry and its underlying porous oceanic crust act as the main recharge zone, while the bathymetric high focuses the most of the discharge hot fluid due to the reduce of the overlying pressure of seawater.
2020, 42(9): 69-78.
doi: 10.3969/j.issn.0253-4193.2020.09.008
Abstract:
In order to solve the problem of spatial distribution of fracture system at the end of methane leakage system, based on the high-resolution three-dimensional seismic data in the north of South China Sea, the spatial structure and distribution characteristics of fractures in bottom simulating reflector (BSR) distribution area are described by using visualization and coherent body technology. The geological genetic types of fractures are described. The relationship between fractures and other types of transport systems on methane gas accumulation is discussed. The fractures in the upper part of BSR interface are far less than those in the lower part of BSR interface, which makes the methane gas supply larger than that in the process of hydrate accumulation. It has a general indicating role in studying hydrate accumulation and detecting methane gas leakage. According to the development scale of fractures, the study area can roughly identify four types of fractures, they are each short fractures, long fractures, fracture bundles, and fracture groups, which enhance the leakage capacity of fluids in turn. These fractures often coexist in multiple types in the stratum, or form a leakage system together with other geological structures. These results and understandings are of great significance to improve the gas hydrate accumulation model and mechanism of methane leakage system in deep-water basin.
In order to solve the problem of spatial distribution of fracture system at the end of methane leakage system, based on the high-resolution three-dimensional seismic data in the north of South China Sea, the spatial structure and distribution characteristics of fractures in bottom simulating reflector (BSR) distribution area are described by using visualization and coherent body technology. The geological genetic types of fractures are described. The relationship between fractures and other types of transport systems on methane gas accumulation is discussed. The fractures in the upper part of BSR interface are far less than those in the lower part of BSR interface, which makes the methane gas supply larger than that in the process of hydrate accumulation. It has a general indicating role in studying hydrate accumulation and detecting methane gas leakage. According to the development scale of fractures, the study area can roughly identify four types of fractures, they are each short fractures, long fractures, fracture bundles, and fracture groups, which enhance the leakage capacity of fluids in turn. These fractures often coexist in multiple types in the stratum, or form a leakage system together with other geological structures. These results and understandings are of great significance to improve the gas hydrate accumulation model and mechanism of methane leakage system in deep-water basin.
2020, 42(9): 79-86.
doi: 10.3969/j.issn.0253-4193.2020.09.009
Abstract:
The simulation of wave time series or wave elevation histories is of great significance for the accurate study of real wave-action on marine structures. In this paper, a method of simulating multi-directional irregular wave elevations is proposed based on a linear single-summation model. To evaluate the effectiveness of the proposed method, theoretical simulated regular waves, unidirectional and multidirectional irregular waves are deterministically simulated. The consistence between the simulated wave time series and the original ones is verified. The simulated accuracy range is further evaluated based on the quantitative error analysis along the spatial dimension represented by the ratio of rr/Ls (in which, rr denotes the separations of the two wave gauges, and Ls dotes the significant wave length). It is suggested that the optimum relative separations of the wave gauges should be less than 0.12Ls when the proposed method is used to reconstruct multidirectional irregular waves.
The simulation of wave time series or wave elevation histories is of great significance for the accurate study of real wave-action on marine structures. In this paper, a method of simulating multi-directional irregular wave elevations is proposed based on a linear single-summation model. To evaluate the effectiveness of the proposed method, theoretical simulated regular waves, unidirectional and multidirectional irregular waves are deterministically simulated. The consistence between the simulated wave time series and the original ones is verified. The simulated accuracy range is further evaluated based on the quantitative error analysis along the spatial dimension represented by the ratio of rr/Ls (in which, rr denotes the separations of the two wave gauges, and Ls dotes the significant wave length). It is suggested that the optimum relative separations of the wave gauges should be less than 0.12Ls when the proposed method is used to reconstruct multidirectional irregular waves.
2020, 42(9): 87-99.
doi: 10.3969/j.issn.0253-4193.2020.09.010
Abstract:
Based on extensive experiments on the mooring tension of a rectangular cylinder, the present investigation compares the mooring tension of a floating rectangular cylinder under freak and random waves and quantifies the difference through experimental measurements. The effects of the relative wave height, relative period and freak wave parameter α1 on the mooring tension are investigated. The results show that, the freak wave parameter α1 has significant effect on the mooring tension of the floater. With α1=2.0～2.83, the maximum mooring tension under freak wave were 1.9 times larger than that under random wave. With Hs/d=0.032～0.097, the maximum mooring tension under freak wave are significantly larger than those under irregular waves, but the 1/3 large value and average value under freak and irregular waves are almost the same. For the effect of the relative period, the critical variation of mooring tension occur at period within Tp<T0p. The time-frequency spectra of the mooring tension under freak and random waves are calculated by wavelet analysis to investigate the time-frequency structure characteristics and variation. The time-frequency characteristics of mooring tension are significantly different from those of random wave.
Based on extensive experiments on the mooring tension of a rectangular cylinder, the present investigation compares the mooring tension of a floating rectangular cylinder under freak and random waves and quantifies the difference through experimental measurements. The effects of the relative wave height, relative period and freak wave parameter α1 on the mooring tension are investigated. The results show that, the freak wave parameter α1 has significant effect on the mooring tension of the floater. With α1=2.0～2.83, the maximum mooring tension under freak wave were 1.9 times larger than that under random wave. With Hs/d=0.032～0.097, the maximum mooring tension under freak wave are significantly larger than those under irregular waves, but the 1/3 large value and average value under freak and irregular waves are almost the same. For the effect of the relative period, the critical variation of mooring tension occur at period within Tp<T0p. The time-frequency spectra of the mooring tension under freak and random waves are calculated by wavelet analysis to investigate the time-frequency structure characteristics and variation. The time-frequency characteristics of mooring tension are significantly different from those of random wave.
2020, 42(9): 100-109.
doi: 10.3969/j.issn.0253-4193.2020.09.011
Abstract:
This paper constructs a convolutional neural network based on TensorFlow. According to the idea of migration learning, the classical handwritten digit recognition is introduced as an introduction. The influence of different cost functions and activation function combinations on the classification results of convolutional neural network models is evaluated. Taking HJ-1A/B sea ice images as experimental data source, we analysis the influence of different function combinations on remote sensing sea ice image classification. It turns out that the cross-entropy cost function and the ReLU activation function are optimally combined. The feasibility of CNN in remote sensing sea ice classification is proved, and the classification results of the sea ice images in the Bohai Sea are verified. The calibration accuracy of the labeled samples is 98.4%. The model is then used to identify the unlabeled test samples. The influence of the window size on the sea ice classification results is discussed, and the optimal window size is 2×2 in the 400×400 small-scale classification experiment. Finally, the identification and verification of the entire Bohai Sea area is carried out, and the effect is good.
This paper constructs a convolutional neural network based on TensorFlow. According to the idea of migration learning, the classical handwritten digit recognition is introduced as an introduction. The influence of different cost functions and activation function combinations on the classification results of convolutional neural network models is evaluated. Taking HJ-1A/B sea ice images as experimental data source, we analysis the influence of different function combinations on remote sensing sea ice image classification. It turns out that the cross-entropy cost function and the ReLU activation function are optimally combined. The feasibility of CNN in remote sensing sea ice classification is proved, and the classification results of the sea ice images in the Bohai Sea are verified. The calibration accuracy of the labeled samples is 98.4%. The model is then used to identify the unlabeled test samples. The influence of the window size on the sea ice classification results is discussed, and the optimal window size is 2×2 in the 400×400 small-scale classification experiment. Finally, the identification and verification of the entire Bohai Sea area is carried out, and the effect is good.
2020, 42(9): 110-118.
doi: 10.3969/j.issn.0253-4193.2020.09.012
Abstract:
Based on the 634 MODIS images acquired in 2017, a total of 1 793 internal waves information are extracted. The paper analyzes the spatial distribution of internal waves in three typical regions of the Andaman Sea, quantitatively counts the characteristic parameters such as the length of the leading waves and the area of the wave packets. The potential sources of internal waves are discussed by ray tracing method and estimates the generation period of internal waves. The results show that the internal waves in the northern Andaman Sea have a small spatial scale. The average length of the leading waves is about 107 km, the average wave packet area is about 1 860 km2, and the propagation direction is mainly eastward and southwestward. The average length of the leading waves in the central Andaman Sea is about 133 km, and the average wave packet area is about 3503 km2. More than 70% of the internal waves propagate in the northeast direction. The average length of the leading waves in the northern part of the Sumatra Island is about 131 km, the average wave packet area is about 2 997 km2, and the propagation direction of internal waves is mainly eastward, northeastward and southeastward. There are 7 potential internal wave sources in the Andaman Sea. The internal waves generation period is between 11.5 hours and 13 hours, which has obvious characteristics of half-day period.
Based on the 634 MODIS images acquired in 2017, a total of 1 793 internal waves information are extracted. The paper analyzes the spatial distribution of internal waves in three typical regions of the Andaman Sea, quantitatively counts the characteristic parameters such as the length of the leading waves and the area of the wave packets. The potential sources of internal waves are discussed by ray tracing method and estimates the generation period of internal waves. The results show that the internal waves in the northern Andaman Sea have a small spatial scale. The average length of the leading waves is about 107 km, the average wave packet area is about 1 860 km2, and the propagation direction is mainly eastward and southwestward. The average length of the leading waves in the central Andaman Sea is about 133 km, and the average wave packet area is about 3503 km2. More than 70% of the internal waves propagate in the northeast direction. The average length of the leading waves in the northern part of the Sumatra Island is about 131 km, the average wave packet area is about 2 997 km2, and the propagation direction of internal waves is mainly eastward, northeastward and southeastward. There are 7 potential internal wave sources in the Andaman Sea. The internal waves generation period is between 11.5 hours and 13 hours, which has obvious characteristics of half-day period.
2020, 42(9): 119-133.
doi: 10.3969/j.issn.0253-4193.2020.09.013
Abstract:
In this paper, three methods for continuous visualization of mesoscale eddies are proposed, which are based on the technique of 2D streamline visualization and technique of mesoscale eddies identification: the method of eddy visualization based on OW parameters, the method of eddy visualization based on grid template and the method of eddy visualization method based on vector template. These three methods are respectively based on Okubo-Weiss algorithm, Faghmous algorithm and Liu's algorithm for eddy recognition, and the visualization results of the flow field are filled into the eddy to obtain better visualization effect. In the process of visualization, we introduce the transfer function to conduct real-time interaction between the color and transparency of the streamline in the eddy, which can control the display effect of setting the velocity, vorticity, OW parameters and other information by setting the color and position of the Key point on the control interface. In addition, we also compared the advantages and disadvantages of the three methods in terms of performance and display effect. In terms of performance, the performance is from high to low: the method of eddy visualization based on OW parameters, the method of eddy visualization based on grid template and the method of eddy visualization method based on vector template. In terms of display effect, the method of eddy visualization based on OW parameters is the worst among the three, with more chaotic short lines and smaller eddy boundary, which is limited to the core region of the eddy. The method of eddy visualization based on grid template has better display effect than the first method, with fewer messy short lines and relatively complete eddy. However, due to the lack of high resolution of data, the eddy boundary appears jagged after being put up for more than one time. The method of eddy visualization method based on vector template has the best display effect. The eddy is complete and full. At the same time, since the eddy boundary is reconstructed and vectorized, the eddy boundary is smoother. Compared with the traditional method of continuous visualization of eddies with long time series, these three methods provide a beautiful, dynamic and more informative visualization method. At the same time, they can become a practical tool for researchers to study eddies due to the addition of transfer function.
In this paper, three methods for continuous visualization of mesoscale eddies are proposed, which are based on the technique of 2D streamline visualization and technique of mesoscale eddies identification: the method of eddy visualization based on OW parameters, the method of eddy visualization based on grid template and the method of eddy visualization method based on vector template. These three methods are respectively based on Okubo-Weiss algorithm, Faghmous algorithm and Liu's algorithm for eddy recognition, and the visualization results of the flow field are filled into the eddy to obtain better visualization effect. In the process of visualization, we introduce the transfer function to conduct real-time interaction between the color and transparency of the streamline in the eddy, which can control the display effect of setting the velocity, vorticity, OW parameters and other information by setting the color and position of the Key point on the control interface. In addition, we also compared the advantages and disadvantages of the three methods in terms of performance and display effect. In terms of performance, the performance is from high to low: the method of eddy visualization based on OW parameters, the method of eddy visualization based on grid template and the method of eddy visualization method based on vector template. In terms of display effect, the method of eddy visualization based on OW parameters is the worst among the three, with more chaotic short lines and smaller eddy boundary, which is limited to the core region of the eddy. The method of eddy visualization based on grid template has better display effect than the first method, with fewer messy short lines and relatively complete eddy. However, due to the lack of high resolution of data, the eddy boundary appears jagged after being put up for more than one time. The method of eddy visualization method based on vector template has the best display effect. The eddy is complete and full. At the same time, since the eddy boundary is reconstructed and vectorized, the eddy boundary is smoother. Compared with the traditional method of continuous visualization of eddies with long time series, these three methods provide a beautiful, dynamic and more informative visualization method. At the same time, they can become a practical tool for researchers to study eddies due to the addition of transfer function.
2020, 42(9): 134-142.
doi: 10.3969/j.issn.0253-4193.2020.09.014
Abstract:
As an important water quality parameter, the distribution and dynamic change of suspended sediment have a profound impact on the ecology, environment and material circulation of the estuary and the near shore. GF-4 satellite has the ability to observe at any time, can quickly provide a large number of observation data, and has the application potential in water color remote sensing. In order to explore the monitoring effect of GF-4 satellite on suspended sediment in water, takes the Hangzhou Bay as the research area in this paper, constructs suspended sediment concentration inversion model, and uses GOCI satellite to cross verify. The results show that the index model established by using the ratio of remote sensing reflectance of the 5th and 4th band of GF-4 as the remote sensing factor has a high inversion accuracy, with a determination coefficient of 0.92, a root mean square error of 273.6 mg/L and an mean relative error of 17.2%. The cross-validation results show that GF-4 satellite data, as a new remote sensing data source, is similar to the distribution of GOCI satellite inversion suspended sediment concentration in the low concentration region, but the difference increases with the increase of concentration in the high concentration region. The research shows that GF-4 satellite is suitable for high precision inversion in the waters with low suspended sediment concentration and can be applied in most marine areas of China.
As an important water quality parameter, the distribution and dynamic change of suspended sediment have a profound impact on the ecology, environment and material circulation of the estuary and the near shore. GF-4 satellite has the ability to observe at any time, can quickly provide a large number of observation data, and has the application potential in water color remote sensing. In order to explore the monitoring effect of GF-4 satellite on suspended sediment in water, takes the Hangzhou Bay as the research area in this paper, constructs suspended sediment concentration inversion model, and uses GOCI satellite to cross verify. The results show that the index model established by using the ratio of remote sensing reflectance of the 5th and 4th band of GF-4 as the remote sensing factor has a high inversion accuracy, with a determination coefficient of 0.92, a root mean square error of 273.6 mg/L and an mean relative error of 17.2%. The cross-validation results show that GF-4 satellite data, as a new remote sensing data source, is similar to the distribution of GOCI satellite inversion suspended sediment concentration in the low concentration region, but the difference increases with the increase of concentration in the high concentration region. The research shows that GF-4 satellite is suitable for high precision inversion in the waters with low suspended sediment concentration and can be applied in most marine areas of China.
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