2022 Vol. 44, No. 5
Display Method:
2022, 44(5): 1-11.
doi: 10.12284/hyxb2022097
Abstract:
As China’s first operational ocean color sensor, the coastal zone imager (CZI) carried by Haiyang-1C (HY-1C) satellite is playing an increasingly significant role in offshore ocean environmental monitoring. After the launch of HY-1D satellite, the combination of CZI sensors can provide two observations in three days for coastal zone through dual-satellite system. CZI sensors have demonstrated prominent application advantages for monitoring marine floating algae, oil spill and so on. Since the high spatial resolution optical data contains abundant information about the marine environment, it also brings some distraction to the identification and extraction of specific ocean targets. In this work, a novel CZI algorithm was developed based on cooperation of scaled algae index (SAI) and virtual baseline floating macroalgae height (VB-FAH) to extract floating green tide information in the Yellow Sea from HY-1C satellite CZI measurements. VB-FAH method can be used to enhance the difference between floating algae and sea water, especially for satellite’s sensors with no short-wave infrared bands. After that, the algorithm efficiently rejects the complex interference information in the ocean high spatial resolution optical data by SAI sliding window. The algorithm has high accuracy and time efficiency in the extraction of floating green tide from CZI measurements. Moreover, the study carried out an uncertainty analysis for the area of algae-containing pixels between HY-1C satellite CZI data with 50 m spatial resolution and GF-1 satellite WFV1 data with 16 m spatial resolution. The result indicates that the uncertainty in the inversion results of CZI data mainly comes from the over estimation of small patches of floating algae. The study also pointed out that the uncertainty of optical data for floating algae monitoring is not only from the difference of spatial resolution between two sensors, but also related to the spatial variability of the morphological size of floating algae. Exploring the morphological spatial variability of floating algae will help improve the accuracy of optical data inversion results and clarify the uncertainty.
As China’s first operational ocean color sensor, the coastal zone imager (CZI) carried by Haiyang-1C (HY-1C) satellite is playing an increasingly significant role in offshore ocean environmental monitoring. After the launch of HY-1D satellite, the combination of CZI sensors can provide two observations in three days for coastal zone through dual-satellite system. CZI sensors have demonstrated prominent application advantages for monitoring marine floating algae, oil spill and so on. Since the high spatial resolution optical data contains abundant information about the marine environment, it also brings some distraction to the identification and extraction of specific ocean targets. In this work, a novel CZI algorithm was developed based on cooperation of scaled algae index (SAI) and virtual baseline floating macroalgae height (VB-FAH) to extract floating green tide information in the Yellow Sea from HY-1C satellite CZI measurements. VB-FAH method can be used to enhance the difference between floating algae and sea water, especially for satellite’s sensors with no short-wave infrared bands. After that, the algorithm efficiently rejects the complex interference information in the ocean high spatial resolution optical data by SAI sliding window. The algorithm has high accuracy and time efficiency in the extraction of floating green tide from CZI measurements. Moreover, the study carried out an uncertainty analysis for the area of algae-containing pixels between HY-1C satellite CZI data with 50 m spatial resolution and GF-1 satellite WFV1 data with 16 m spatial resolution. The result indicates that the uncertainty in the inversion results of CZI data mainly comes from the over estimation of small patches of floating algae. The study also pointed out that the uncertainty of optical data for floating algae monitoring is not only from the difference of spatial resolution between two sensors, but also related to the spatial variability of the morphological size of floating algae. Exploring the morphological spatial variability of floating algae will help improve the accuracy of optical data inversion results and clarify the uncertainty.
2022, 44(5): 12-24.
doi: 10.12284/hyxb2022095
Abstract:
The marine ecological disasters occurred frequently in recent years. A large number of floating algae gather in the sea surface and inshore water, which brings serious harm to the economic activities and ecological health of coastal cities. In this study, HY-1C, GF-1 and HJ-1A/1B satellite remote sensing images were used to extract information and divide the growth stages of Sargassum in the South Yellow Sea from April to June in 2016 to 2020, combined with the MODIS sea surface temperature data, photosynthetically active radiation data and sea surface wind data to explore the effects of environmental factors on the temporal and spatial distribution of Sargassum. The results show that: (1) In terms of time, the Sargassum mainly appeared from April to June every year. Sargassum had the largest range of influence in 2017 and smaller in other years. In terms of space, the Sargassum was first detected in the far sea northeast of the Changjiang River Estuary and disappeared in the sea near 35°−36°N. (2) In terms of growth rate, the growth phase of Sargassum could be divided into three stages: “development-outbreak-extinction”. (3) At different growth stages, sea surface temperature and photosynthetically active radiation had different degrees of influence on Sargassum. The larger area of Sargassum in 2017 was mainly influenced by higher sea surface temperature and photosynthetically active radiation. The southeast monsoon promoted the drift of Sargassum from the southeast to the northwest and north. This shows that the spatiotemporal characteristics of Sargassum are affected by a variety of environmental factors.
The marine ecological disasters occurred frequently in recent years. A large number of floating algae gather in the sea surface and inshore water, which brings serious harm to the economic activities and ecological health of coastal cities. In this study, HY-1C, GF-1 and HJ-1A/1B satellite remote sensing images were used to extract information and divide the growth stages of Sargassum in the South Yellow Sea from April to June in 2016 to 2020, combined with the MODIS sea surface temperature data, photosynthetically active radiation data and sea surface wind data to explore the effects of environmental factors on the temporal and spatial distribution of Sargassum. The results show that: (1) In terms of time, the Sargassum mainly appeared from April to June every year. Sargassum had the largest range of influence in 2017 and smaller in other years. In terms of space, the Sargassum was first detected in the far sea northeast of the Changjiang River Estuary and disappeared in the sea near 35°−36°N. (2) In terms of growth rate, the growth phase of Sargassum could be divided into three stages: “development-outbreak-extinction”. (3) At different growth stages, sea surface temperature and photosynthetically active radiation had different degrees of influence on Sargassum. The larger area of Sargassum in 2017 was mainly influenced by higher sea surface temperature and photosynthetically active radiation. The southeast monsoon promoted the drift of Sargassum from the southeast to the northwest and north. This shows that the spatiotemporal characteristics of Sargassum are affected by a variety of environmental factors.
2022, 44(5): 25-34.
doi: 10.12284/hyxb2022052
Abstract:
As one of the most important water quality parameters, chlorophyll a is an important indicator to evaluate the degree of eutrophication of water bodies and also the main factors of primary productivity state of the oceans. The coastal zone imager (CZI) onboard the Chinese Haiyang-1C (HY-1C) satellite has an advantage observation in high temporal and spatial resolution. In this study, a chlorophyll a concentration retrieval model for CZI onboard the HY-1C satellite is developed from the in-situ measurements in the East China Sea and the South China Sea. The chlorophyll a concentration is retrieved by the model in the measured waters and compared with MODIS chlorophyll a concentration. The chlorophyll a concentration also retrieved in the Zhujiang River Estuary, Changjiang River Estuary and Bohai Bay. The correlation coefficient between the predicted value of the model and the in-situ chlorophyll a concentration is 0.774 3, the average relative error is 24.58%. The accuracy of the model is verified with the in-situ measurements with the correlation coefficient of 0.993 9 and the average relative error of 18.49%. The distribution of chlorophyll a concentration retrieved from CZI is nearly the same as that of MODIS. The chlorophyll a concentration decreases gradually from northwest to southeast and the peak value locates on the west bank of the Zhujiang River Estuary. The inversion of chlorophyll a concentration in Changjiang River Estuary and Bohai Bay accords with the actual situation. The work in this study indicates that HY-1C satellite coastal zone imager data are useful for the monitoring of coastal ocean color in China.
As one of the most important water quality parameters, chlorophyll a is an important indicator to evaluate the degree of eutrophication of water bodies and also the main factors of primary productivity state of the oceans. The coastal zone imager (CZI) onboard the Chinese Haiyang-1C (HY-1C) satellite has an advantage observation in high temporal and spatial resolution. In this study, a chlorophyll a concentration retrieval model for CZI onboard the HY-1C satellite is developed from the in-situ measurements in the East China Sea and the South China Sea. The chlorophyll a concentration is retrieved by the model in the measured waters and compared with MODIS chlorophyll a concentration. The chlorophyll a concentration also retrieved in the Zhujiang River Estuary, Changjiang River Estuary and Bohai Bay. The correlation coefficient between the predicted value of the model and the in-situ chlorophyll a concentration is 0.774 3, the average relative error is 24.58%. The accuracy of the model is verified with the in-situ measurements with the correlation coefficient of 0.993 9 and the average relative error of 18.49%. The distribution of chlorophyll a concentration retrieved from CZI is nearly the same as that of MODIS. The chlorophyll a concentration decreases gradually from northwest to southeast and the peak value locates on the west bank of the Zhujiang River Estuary. The inversion of chlorophyll a concentration in Changjiang River Estuary and Bohai Bay accords with the actual situation. The work in this study indicates that HY-1C satellite coastal zone imager data are useful for the monitoring of coastal ocean color in China.
2022, 44(5): 35-46.
doi: 10.12284/hyxb2022021
Abstract:
A support vector machine (SVM) sea ice classification method of Haiyang-1C (HY-1C) satellite coastal zone imager (CZI) images based on the optimal feature set is proposed in this paper. The spectral features and the texture features of CZI images are extracted, and then distance separability criterion is used for feature selection to obtain the optimal feature set. The sea ice classification experiment and analysis of the three CZI images of Liaodong Bay are carried out based on SVM classification method with the optimal feature set as the input of the classifier. The results show that the sea ice classification accuracy obtained by the proposed method is better than that of only using the spectral features or the texture features. The sea ice classification accuracy of December 19, 2020, January 10, 2021 and January 16, 2021 are 93.67%, 91.75% and 84.89%, respectively, all above 80%. The sea ice area of Liaodong Bay is estimated according to the sea ice classification map. It is found that the sea ice area of Liaodong Bay in the three images increased successively, and the maximum area is about 11 998.98 km2.
A support vector machine (SVM) sea ice classification method of Haiyang-1C (HY-1C) satellite coastal zone imager (CZI) images based on the optimal feature set is proposed in this paper. The spectral features and the texture features of CZI images are extracted, and then distance separability criterion is used for feature selection to obtain the optimal feature set. The sea ice classification experiment and analysis of the three CZI images of Liaodong Bay are carried out based on SVM classification method with the optimal feature set as the input of the classifier. The results show that the sea ice classification accuracy obtained by the proposed method is better than that of only using the spectral features or the texture features. The sea ice classification accuracy of December 19, 2020, January 10, 2021 and January 16, 2021 are 93.67%, 91.75% and 84.89%, respectively, all above 80%. The sea ice area of Liaodong Bay is estimated according to the sea ice classification map. It is found that the sea ice area of Liaodong Bay in the three images increased successively, and the maximum area is about 11 998.98 km2.
2022, 44(5): 47-61.
doi: 10.12284/hyxb2022029
Abstract:
Chinese Ocean Color Temperature Scanner (COCTS) of Haiyang 1C/D (HY-1C/D) satellite is mainly used to detect ocean water color, water temperature and other elements. These elements can only be achieved by processing satellite data, and geometric positioning is the core of preprocessing, which directly affects quality of these elements. COCTS has the characteristics of 114° field of view and quaternary whisk broom point by point. A set of complete geometric positioning method has been developed based on COCTS characteristics. The satellite position and velocity corresponding to the sampling time are obtained by using the interpolation method in the satellite ephemeris extracted from 0 level data, and then the transformation matrix from orbital coordinate system (ORB) to earth-centered rotating coordinate system (ECR) will be achieved. Based on the quaternary whisk broom point by point, the ORB viewing vector of every sampling point in a sweep can be calculated by rotating center viewing vector around X and Y axis in corresponding angles. The relationship model of viewing vector and the earth intersection point can be established to carry out geolocation of remote sensing images obtained from band data. This article uses interpolation to replace the traditional complex method that requires 6 orbital elements to calculate the satellite position, and directly calculates ORB to ECR transformation matrix rather than the traditional two-step transformation method. After multiple sets of data calculation and qualitative and quantitative verification, the HY-1C/D COCTS geometric positioning results are consistent. As a result of the sampling pixel scale effect, the error increases gradually from Nadir to the edge of two sides and from the equator to two poles, all within the error of 2 pixels. This method meets certain positioning accuracy requirements and can be employed for geometric positioning of COCTS.
Chinese Ocean Color Temperature Scanner (COCTS) of Haiyang 1C/D (HY-1C/D) satellite is mainly used to detect ocean water color, water temperature and other elements. These elements can only be achieved by processing satellite data, and geometric positioning is the core of preprocessing, which directly affects quality of these elements. COCTS has the characteristics of 114° field of view and quaternary whisk broom point by point. A set of complete geometric positioning method has been developed based on COCTS characteristics. The satellite position and velocity corresponding to the sampling time are obtained by using the interpolation method in the satellite ephemeris extracted from 0 level data, and then the transformation matrix from orbital coordinate system (ORB) to earth-centered rotating coordinate system (ECR) will be achieved. Based on the quaternary whisk broom point by point, the ORB viewing vector of every sampling point in a sweep can be calculated by rotating center viewing vector around X and Y axis in corresponding angles. The relationship model of viewing vector and the earth intersection point can be established to carry out geolocation of remote sensing images obtained from band data. This article uses interpolation to replace the traditional complex method that requires 6 orbital elements to calculate the satellite position, and directly calculates ORB to ECR transformation matrix rather than the traditional two-step transformation method. After multiple sets of data calculation and qualitative and quantitative verification, the HY-1C/D COCTS geometric positioning results are consistent. As a result of the sampling pixel scale effect, the error increases gradually from Nadir to the edge of two sides and from the equator to two poles, all within the error of 2 pixels. This method meets certain positioning accuracy requirements and can be employed for geometric positioning of COCTS.
2022, 44(5): 62-70.
doi: 10.12284/hyxb2022083
Abstract:
The research of tidal changes is vital to ocean engineering, the protection of flooding as well as the utilization of ocean resources in coastal areas. Previous studies are mainly based on long-term hourly tide gauges whose number and location are highly limited. Previous study indicated that the long-term trends of tidal amplitudes are abnormally large in the central deep basin of the South China Sea (SCS) based on 25-year satellite altimeter data, which is not realistic and the resultant of the interference of ocean mesoscale variability on tidal harmonic analysis. In this paper, we use 27-year T/P-Jason satellite altimeter data processed by X-TRACK software to study the long-term tidal trends in the SCS. The satellite altimeter data processed by X-TRACK obviously improves the accuracy and completeness of satellite data in the SCS. Meanwhile, the weighted least square method is used to eliminate the effect of tidal aliasing caused by long period sampling. We find that in most areas of the SCS, the amplitudes of four major tidal constituents have significant long-term trends. The significant positive and negative long-term trends of amplitudes and phases are mainly distributed in the coastal areas such as the western Luzon Strait, the Strait of Malacca and Taiwan Strait, where the water depth and shoreline change dramatically. The largest positive long-term trend of amplitudes can reach 2.75 mm/a and the largest negative long-term trend of amplitudes can reach −2.16 mm/a. The long-term trends of tidal amplitudes in the SCS should be related to river flow and human interference.
The research of tidal changes is vital to ocean engineering, the protection of flooding as well as the utilization of ocean resources in coastal areas. Previous studies are mainly based on long-term hourly tide gauges whose number and location are highly limited. Previous study indicated that the long-term trends of tidal amplitudes are abnormally large in the central deep basin of the South China Sea (SCS) based on 25-year satellite altimeter data, which is not realistic and the resultant of the interference of ocean mesoscale variability on tidal harmonic analysis. In this paper, we use 27-year T/P-Jason satellite altimeter data processed by X-TRACK software to study the long-term tidal trends in the SCS. The satellite altimeter data processed by X-TRACK obviously improves the accuracy and completeness of satellite data in the SCS. Meanwhile, the weighted least square method is used to eliminate the effect of tidal aliasing caused by long period sampling. We find that in most areas of the SCS, the amplitudes of four major tidal constituents have significant long-term trends. The significant positive and negative long-term trends of amplitudes and phases are mainly distributed in the coastal areas such as the western Luzon Strait, the Strait of Malacca and Taiwan Strait, where the water depth and shoreline change dramatically. The largest positive long-term trend of amplitudes can reach 2.75 mm/a and the largest negative long-term trend of amplitudes can reach −2.16 mm/a. The long-term trends of tidal amplitudes in the SCS should be related to river flow and human interference.
2022, 44(5): 71-79.
doi: 10.12284/hyxb2022085
Abstract:
Based on the long-term observation obtained from two sets of submarine mooring system deployed at Niulang Seamount in the western Pacific, the vertical distribution of the deep currents and the temporal variation characteristics were analyzed in the paper. The results show that: (1) The annual mean ocean currents and the variations were the largest in the upper layer, the second in the middle and deep layers, and the smallest in the middle-deep layers. (2) The subtropical countercurrent was at the depth shallower than 150 m, and the northward current was at depth deeper than 150 m and at the middle layers; the near bottom current was weak southward at the summit of the seamount, but southwestward at the bottom of the seamount. (3) Both at the summit and bottom of the seamount, the currents showed a seasonal oscillation with the most energetic oscillation at a period of about 100 d throughout the water column; at depth above 2 000 m, currents showed a synchronous oscillation in the throughout the water column, with the oscillation amplitude decreasing with depth; current oscillation at deep layers (below 2 000 m) were in opposite phase with that at the upper layers, and the oscillation amplitude was the strongest at 4 000 m.
Based on the long-term observation obtained from two sets of submarine mooring system deployed at Niulang Seamount in the western Pacific, the vertical distribution of the deep currents and the temporal variation characteristics were analyzed in the paper. The results show that: (1) The annual mean ocean currents and the variations were the largest in the upper layer, the second in the middle and deep layers, and the smallest in the middle-deep layers. (2) The subtropical countercurrent was at the depth shallower than 150 m, and the northward current was at depth deeper than 150 m and at the middle layers; the near bottom current was weak southward at the summit of the seamount, but southwestward at the bottom of the seamount. (3) Both at the summit and bottom of the seamount, the currents showed a seasonal oscillation with the most energetic oscillation at a period of about 100 d throughout the water column; at depth above 2 000 m, currents showed a synchronous oscillation in the throughout the water column, with the oscillation amplitude decreasing with depth; current oscillation at deep layers (below 2 000 m) were in opposite phase with that at the upper layers, and the oscillation amplitude was the strongest at 4 000 m.
2022, 44(5): 80-91.
doi: 10.12284/hyxb2022031
Abstract:
In this study, Argo surface salinity, OSCAR current and other data are used to explore the influence of oceanic advection transport on the surface salinity in the Tropical Indian Ocean based on the advection term of the salinity budget equation. The adjustment mechanism of the spatial structure of surface salinity by oceanic advection is revealed by freshwater transport calculation along 6 key sections. The results show that the oceanic advection which transports the high-salinity water in the Equatorial Western Indian Ocean (EWIO) and the Arabian Sea (AS) to the Equatorial Eastern Indian Ocean (EEIO), the Bay of Bengal (BOB) and the Andaman Sea, and also transports the low-salinity water in the EEIO, the BOB and the Andaman Sea to the EWIO, the AS and the Equatorial Southern Indian Ocean, plays a role in adjusting the basic balance of salinity in the Indian Ocean. The analysis of freshwater transport along sections shows that the inconsistency between the center of high precipitation and low salinity in the western sea area of Sumatra, and the inconsistency between the center of high evaporation and high salinity in the western sea area of Australia, are both caused by oceanic advection. In summer, the high-salinity water in the EWIO and the AS transported by the southwest monsoon forced circulation into the BOB, is the main reason for the high surface salinity in the BOB.
In this study, Argo surface salinity, OSCAR current and other data are used to explore the influence of oceanic advection transport on the surface salinity in the Tropical Indian Ocean based on the advection term of the salinity budget equation. The adjustment mechanism of the spatial structure of surface salinity by oceanic advection is revealed by freshwater transport calculation along 6 key sections. The results show that the oceanic advection which transports the high-salinity water in the Equatorial Western Indian Ocean (EWIO) and the Arabian Sea (AS) to the Equatorial Eastern Indian Ocean (EEIO), the Bay of Bengal (BOB) and the Andaman Sea, and also transports the low-salinity water in the EEIO, the BOB and the Andaman Sea to the EWIO, the AS and the Equatorial Southern Indian Ocean, plays a role in adjusting the basic balance of salinity in the Indian Ocean. The analysis of freshwater transport along sections shows that the inconsistency between the center of high precipitation and low salinity in the western sea area of Sumatra, and the inconsistency between the center of high evaporation and high salinity in the western sea area of Australia, are both caused by oceanic advection. In summer, the high-salinity water in the EWIO and the AS transported by the southwest monsoon forced circulation into the BOB, is the main reason for the high surface salinity in the BOB.
2022, 44(5): 92-101.
doi: 10.12284/hyxb2022077
Abstract:
The dramatic change of sea ice in the Beaufort Sea has an important impact on the regional ecosystem and economic activities. Based on the sea ice concentration released by the National Ice and Snow Center of the United States, the mechanism of extremely low summer sea ice in the Beaufort Sea in 2019 is discussed. The sea ice area in the melt season (May–September) of 2019 is 1.38×105 km2, far lower than the average of 2.28×105 km2 from 1998 to 2020. According to the statistics of the sea ice area in the preceding autumn (October–December 2018) and winter (January–April 2019) of 2019, there is no significant difference between the 2019 and the average results of 1998–2019, so it is not the main reason for the extremely low ice event. Combining the data of sea ice drift field, sea ice thickness, 10 m wind field, and net sea surface heat flux, it is found that the sea ice in May of 2019 decreased by 2.33×105 km2, which is the largest of sea ice loss in May since 1998, accounting for 62% of the loss of sea ice area in the melt season. Different from the mechanism of extremely low summer sea ice area in 1998, 2008, 2012, and 2016, decreasing sea ice thickness and abnormally strong wind field in May 2019 contribute to the rapid sea ice export, resulting in the formation of open water in the south of Beaufort Sea on May 16, 2019. The abnormally high sea surface net heat flux makes the sea ice melt more, resulting in the abnormal phenomenon of sea ice in the summer of 2019. With the continuous thinning of sea ice thickness, the response of sea ice to wind field is stronger and stronger, and the time of sea ice retreat is advanced, the phenomenon of extremely low summer ice condition in the Beaufort Sea may appear more frequently.
The dramatic change of sea ice in the Beaufort Sea has an important impact on the regional ecosystem and economic activities. Based on the sea ice concentration released by the National Ice and Snow Center of the United States, the mechanism of extremely low summer sea ice in the Beaufort Sea in 2019 is discussed. The sea ice area in the melt season (May–September) of 2019 is 1.38×105 km2, far lower than the average of 2.28×105 km2 from 1998 to 2020. According to the statistics of the sea ice area in the preceding autumn (October–December 2018) and winter (January–April 2019) of 2019, there is no significant difference between the 2019 and the average results of 1998–2019, so it is not the main reason for the extremely low ice event. Combining the data of sea ice drift field, sea ice thickness, 10 m wind field, and net sea surface heat flux, it is found that the sea ice in May of 2019 decreased by 2.33×105 km2, which is the largest of sea ice loss in May since 1998, accounting for 62% of the loss of sea ice area in the melt season. Different from the mechanism of extremely low summer sea ice area in 1998, 2008, 2012, and 2016, decreasing sea ice thickness and abnormally strong wind field in May 2019 contribute to the rapid sea ice export, resulting in the formation of open water in the south of Beaufort Sea on May 16, 2019. The abnormally high sea surface net heat flux makes the sea ice melt more, resulting in the abnormal phenomenon of sea ice in the summer of 2019. With the continuous thinning of sea ice thickness, the response of sea ice to wind field is stronger and stronger, and the time of sea ice retreat is advanced, the phenomenon of extremely low summer ice condition in the Beaufort Sea may appear more frequently.
2022, 44(5): 102-112.
doi: 10.12284/hyxb2022081
Abstract:
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2022, 44(5): 113-123.
doi: 10.12284/hyxb2022075
Abstract:
To understand the internal physical mechanism of wave breaking, it is important to study the distribution characteristics of the particle velocity field under breaking wave. In addition, a comparative study of the evolution characteristics of the gas-liquid mixing zone caused by different types of breaking is beneficial to the improvement of the whitecap coverage model. In the laboratory wave flume, a critical wave, a single spilling wave, and a single plunging wave are generated in deep water based on the linear phase focusing theory. The velocity fields below the wave surface and the velocity fields in the gas-liquid mixing zone are measured using particle image velocimetry (PIV) and bubble image velocimetry (BIV), respectively. The distribution characteristics of the velocity field at the extreme state of different breaking types are compared and discussed. The results show that the horizontal velocity u and vertical velocity v of the spilling wave are extremely asymmetrical in the front part and back part of the wave crest. In addition, the maximum horizontal velocity umax is not at the top of the wave peak, but at the pre-peak position about 0.7\begin{document}$\eta_{\max} $\end{document} ![]()
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To understand the internal physical mechanism of wave breaking, it is important to study the distribution characteristics of the particle velocity field under breaking wave. In addition, a comparative study of the evolution characteristics of the gas-liquid mixing zone caused by different types of breaking is beneficial to the improvement of the whitecap coverage model. In the laboratory wave flume, a critical wave, a single spilling wave, and a single plunging wave are generated in deep water based on the linear phase focusing theory. The velocity fields below the wave surface and the velocity fields in the gas-liquid mixing zone are measured using particle image velocimetry (PIV) and bubble image velocimetry (BIV), respectively. The distribution characteristics of the velocity field at the extreme state of different breaking types are compared and discussed. The results show that the horizontal velocity u and vertical velocity v of the spilling wave are extremely asymmetrical in the front part and back part of the wave crest. In addition, the maximum horizontal velocity umax is not at the top of the wave peak, but at the pre-peak position about 0.7
2022, 44(5): 124-133.
doi: 10.12284/hyxb2022101
Abstract:
Hollow blocks have good water blocking and siltation promotion functions, and have been widely used in ecological restoration projects in recent years. In this paper, combined with flume experiment and Flow-3D numerical simulation, the water blocking effect and sedimentation characteristics of open and semi-closed hollow blocks are analyzed. The results show that the permeability of the hollow block plays a leading role in the internal flow velocity and turbulence intensity, and the semi-open hollow block with small permeability has a better effect in slowing down and turbulence control. The suspended sediment concentration near the bottom of open and semi-closed hollow blocks increases by 56% and 75%, respectively. Both of them can promote the deposition of sediment in the block. The environment of low flow velocity, sediment micro-deposition and water and sediment connected inside and outside by hollow blocks is the habitat requirement of macrobenthos, the structure of low turbulent flow inside the semi-enclosed hollow block is more favorable for the habitat and reproduction of macrobenthos.
Hollow blocks have good water blocking and siltation promotion functions, and have been widely used in ecological restoration projects in recent years. In this paper, combined with flume experiment and Flow-3D numerical simulation, the water blocking effect and sedimentation characteristics of open and semi-closed hollow blocks are analyzed. The results show that the permeability of the hollow block plays a leading role in the internal flow velocity and turbulence intensity, and the semi-open hollow block with small permeability has a better effect in slowing down and turbulence control. The suspended sediment concentration near the bottom of open and semi-closed hollow blocks increases by 56% and 75%, respectively. Both of them can promote the deposition of sediment in the block. The environment of low flow velocity, sediment micro-deposition and water and sediment connected inside and outside by hollow blocks is the habitat requirement of macrobenthos, the structure of low turbulent flow inside the semi-enclosed hollow block is more favorable for the habitat and reproduction of macrobenthos.
2022, 44(5): 134-147.
doi: 10.12284/hyxb2022079
Abstract:
In this paper, MIKE3 is used to establish a three-dimensional hydrodynamic model of Zhoushan and Ningbo. Based on the tidal current verification with the measured data, the difference between the three-dimensional model and the two-dimensional model is compared. Also, the influence of the change of the tidal current field around the Zhoushan Green Petrochemical Phase III reclamation project before and after the implementation is mainly predicted and analyzed. The results show that: (1) Under the same initial conditions, the tidal level and tidal current validation results of two-dimensional model and three-dimensional model are good, and the two-dimensional results are closer to the measured values in some cases. (2) The three-dimensional vertical velocity distribution shows a decreasing trend with the increase of water depth. In general, the tidal current fitting is good, and the relative error of velocity below 0.6H water depth is between 10% and 15%. Considering that the model may not consider the influence of wind field and wave, the calculated surface velocity of local stations is slightly larger than the measured value; the vertical distribution of flow direction is nearly consistent. (3) Before and after the reclamation project, there was no obvious influence on the tidal current field around the project. Only in the northeast, southeast and northwest corner of Dayushan Island, affected by the “bend improvement” and the channel closure between small islands, there is a change in the local tidal current form. On the whole, the layout of reclamation projects conforming to the shoreline will have an effect on the local coastal tidal current, and almost no effect on the large scale tidal current field in the far sea.
In this paper, MIKE3 is used to establish a three-dimensional hydrodynamic model of Zhoushan and Ningbo. Based on the tidal current verification with the measured data, the difference between the three-dimensional model and the two-dimensional model is compared. Also, the influence of the change of the tidal current field around the Zhoushan Green Petrochemical Phase III reclamation project before and after the implementation is mainly predicted and analyzed. The results show that: (1) Under the same initial conditions, the tidal level and tidal current validation results of two-dimensional model and three-dimensional model are good, and the two-dimensional results are closer to the measured values in some cases. (2) The three-dimensional vertical velocity distribution shows a decreasing trend with the increase of water depth. In general, the tidal current fitting is good, and the relative error of velocity below 0.6H water depth is between 10% and 15%. Considering that the model may not consider the influence of wind field and wave, the calculated surface velocity of local stations is slightly larger than the measured value; the vertical distribution of flow direction is nearly consistent. (3) Before and after the reclamation project, there was no obvious influence on the tidal current field around the project. Only in the northeast, southeast and northwest corner of Dayushan Island, affected by the “bend improvement” and the channel closure between small islands, there is a change in the local tidal current form. On the whole, the layout of reclamation projects conforming to the shoreline will have an effect on the local coastal tidal current, and almost no effect on the large scale tidal current field in the far sea.
2022, 44(5): 148-160.
doi: 10.12284/hyxb2022063
Abstract:
When oil spill occurs and the large scale covering on the sea surface has not been formed, it is hard to find oil film by existing oil spill detection technology. To solve this problem, a novel method for discriminating of oil spill by monitoring the area of oil film is presented based on thermal infrared video image, which combined with the diffusion characteristic of oil spill. Firstly, foreground regions (real oil film region and look-alikes interference region) on the sea surface are extracted and the actual physical area of each region is calculated based on single-frame thermal infrared image processing (i.e., the pixel area calculation method from the previous research). According to the video image processing, the change of the actual physical area of each region is tracked in real-time. The area change rate threshold is set to discriminate whether oil film on the foreground regions, then whether oil spill happened can be determined. The experimental results show that the proposed method can effectively discriminate oil film formed by different viscosity of oil and maintain good identification accuracy under sea surface with waves and floating objects. This strategy is suitable for specific scenes such as wharves and ships, and also can provide technical support for pollution control of oil spill.
When oil spill occurs and the large scale covering on the sea surface has not been formed, it is hard to find oil film by existing oil spill detection technology. To solve this problem, a novel method for discriminating of oil spill by monitoring the area of oil film is presented based on thermal infrared video image, which combined with the diffusion characteristic of oil spill. Firstly, foreground regions (real oil film region and look-alikes interference region) on the sea surface are extracted and the actual physical area of each region is calculated based on single-frame thermal infrared image processing (i.e., the pixel area calculation method from the previous research). According to the video image processing, the change of the actual physical area of each region is tracked in real-time. The area change rate threshold is set to discriminate whether oil film on the foreground regions, then whether oil spill happened can be determined. The experimental results show that the proposed method can effectively discriminate oil film formed by different viscosity of oil and maintain good identification accuracy under sea surface with waves and floating objects. This strategy is suitable for specific scenes such as wharves and ships, and also can provide technical support for pollution control of oil spill.
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