2022 Vol. 44, No. 12
Display Method:
2022, 44(12): 1-8.
doi: 10.12284/hyxb2022167
Abstract:
Due to the effect of refraction, a special phenomenon that propagates along the shoreline occurs during the nearshore propagation of waves, which are called edge waves. The edge waves propagate parallel to the shoreline, and their amplitude is the largest at the shoreline, and its amplitude decreases exponentially in the direction away from the shoreline, and their energy is limited to a distance of one wavelength from the coast. So the edge waves have an important impact on the engineering and landforms of the near-shore area. This paper expounds on the research history and research progress of edge waves and mainly introduces the following aspects: (1) the theory of edge waves based on different governing equations and different terrains; (2) the actual observed edge wave characteristics; (3) the wave-making method of edge waves in the physical model test and the observed edge wave characteristics; (4) the application of numerical simulation methods in the study of edge waves. Finally, the future research trend of edge waves is presented.
Due to the effect of refraction, a special phenomenon that propagates along the shoreline occurs during the nearshore propagation of waves, which are called edge waves. The edge waves propagate parallel to the shoreline, and their amplitude is the largest at the shoreline, and its amplitude decreases exponentially in the direction away from the shoreline, and their energy is limited to a distance of one wavelength from the coast. So the edge waves have an important impact on the engineering and landforms of the near-shore area. This paper expounds on the research history and research progress of edge waves and mainly introduces the following aspects: (1) the theory of edge waves based on different governing equations and different terrains; (2) the actual observed edge wave characteristics; (3) the wave-making method of edge waves in the physical model test and the observed edge wave characteristics; (4) the application of numerical simulation methods in the study of edge waves. Finally, the future research trend of edge waves is presented.
2022, 44(12): 9-18.
doi: 10.12284/hyxb2022165
Abstract:
The structure of circulation flow is related to physical processes such as material transport, sediment deposition and landform evolution. According to the continuous stratified tidal current data derived by the prototype observation platform of Modaomen Estuary in flood and dry seasons in 2019, the flow characteristic during the spring and neap tide at wet and dry seasons in the east and west branches were analyzed. Theoretical methods were used to explore plane circulation and gravity circulation structure in the east and west branches. Besides, the longitudinal circulation with the tidal strain circulation was explained by the mixed parameter. Plane circulation flow structure with ebb at west branch and rise at east branch during the dry season was found. Moreover, gravitational circulation at dry season was generally larger than that at wet season, and the gravitational circulation at west branch was stronger than the east branch, with 0.2–0.25 m/s surface velocity and much lower bottom velocity. The tidal strain circulation driven by the tidal asymmetry at wet season spring tide was relatively higher, which tends to favor the magnitude of vertical circulation. Additionally, the muti-layer residual current also displays seasonal and tidal variations. The residual current at wet season was relatively larger than the dry season, with the surface residual flow velocity more than 0.6 m/s during the neap tide at west branch. However, the downstream residual current at surface and upstream residual current at bottom was found at east branch. Much lower residual current velocity was found at dry season, indicating that the impact on the substance transport and morphological evolution was lower.
The structure of circulation flow is related to physical processes such as material transport, sediment deposition and landform evolution. According to the continuous stratified tidal current data derived by the prototype observation platform of Modaomen Estuary in flood and dry seasons in 2019, the flow characteristic during the spring and neap tide at wet and dry seasons in the east and west branches were analyzed. Theoretical methods were used to explore plane circulation and gravity circulation structure in the east and west branches. Besides, the longitudinal circulation with the tidal strain circulation was explained by the mixed parameter. Plane circulation flow structure with ebb at west branch and rise at east branch during the dry season was found. Moreover, gravitational circulation at dry season was generally larger than that at wet season, and the gravitational circulation at west branch was stronger than the east branch, with 0.2–0.25 m/s surface velocity and much lower bottom velocity. The tidal strain circulation driven by the tidal asymmetry at wet season spring tide was relatively higher, which tends to favor the magnitude of vertical circulation. Additionally, the muti-layer residual current also displays seasonal and tidal variations. The residual current at wet season was relatively larger than the dry season, with the surface residual flow velocity more than 0.6 m/s during the neap tide at west branch. However, the downstream residual current at surface and upstream residual current at bottom was found at east branch. Much lower residual current velocity was found at dry season, indicating that the impact on the substance transport and morphological evolution was lower.
2022, 44(12): 19-30.
doi: 10.12284/hyxb2022159
Abstract:
In this study, the harmonic constants of the 5 global vertical displacement loading tide models FES2014, EOT11a, GOT4.10c, GOT4.8 and NAO.99b are validated evaluated to the observed data of 21 GPS stations in Bohai Sea, Yellow Sea, East China Sea and surrounding areas. The results show that the accuracy of the M2 constituents of FES2014 and EOT11a models are relatively high, S2 constituents of NAO.99b and EOT11a models are relatively high, K1 constituents of EOT11a and FES2014 models are relatively high, O1 constituents of EOT11a and GOT4.8 models are relatively high, N2 constituents of EOT11a and FES2014 models are relatively high, K2 constituents of NAO.99b and FES2014 models are relatively high, P1 constituents of EOT11a and GOT4.8 models are relatively high, Q1 constituents of FES2014 and EOT11a models are relatively high. The distribution features of the eight vertical displacement loading tides in Bohai Sea, Yellow Sea, East China Sea and surrounding areas.
In this study, the harmonic constants of the 5 global vertical displacement loading tide models FES2014, EOT11a, GOT4.10c, GOT4.8 and NAO.99b are validated evaluated to the observed data of 21 GPS stations in Bohai Sea, Yellow Sea, East China Sea and surrounding areas. The results show that the accuracy of the M2 constituents of FES2014 and EOT11a models are relatively high, S2 constituents of NAO.99b and EOT11a models are relatively high, K1 constituents of EOT11a and FES2014 models are relatively high, O1 constituents of EOT11a and GOT4.8 models are relatively high, N2 constituents of EOT11a and FES2014 models are relatively high, K2 constituents of NAO.99b and FES2014 models are relatively high, P1 constituents of EOT11a and GOT4.8 models are relatively high, Q1 constituents of FES2014 and EOT11a models are relatively high. The distribution features of the eight vertical displacement loading tides in Bohai Sea, Yellow Sea, East China Sea and surrounding areas.
2022, 44(12): 31-41.
doi: 10.12284/hyxb2022157
Abstract:
The spatio-temporal evolution of backwater influence length in estuaries is essential with regard to the sustainable water resources management in general, such as flood control, water supply, and shipping. In this study, based on the classical riverine backwater theory, we focus on the backwater effect caused by tidal dynamics, making use of a one-dimensional hydrodynamic analytical model to redefine the upstream boundary of the backwater zone (namely backwater limit) in estuaries. The model was subsequently applied to the Changjiang River Estuary to explore the evolution of estuarine backwater dynamics and its underlying mechanism. Results show that the distance from Tianshenggang to backwater limit (i.e., the backwater influence length) has a negatively linear correlation with the upstream river discharge and positively linear correlation with the tidal amplitude of seaward boundary, respectively. The response of the backwater limit to tidal river dynamics is more sensitive than that of the tidal limit, which can effectively characterize the evolution of the tidal river dynamics in tidal reach. The location of the backwater limit in the Changjiang River Estuary has apparent seasonal difference, being 419 km away from Tianshenggang during the spring and 367 km during autumn. The location is situated above the tidal reach during the winter, while the backwater effect caused by tidal dynamics during the summer is negligible. It was shown that the seasonal variations of residual water level slope induced by tide and tide-river interaction are the dominant factors for controlling the location of the backwater limit in the Changjiang River Estuary.
The spatio-temporal evolution of backwater influence length in estuaries is essential with regard to the sustainable water resources management in general, such as flood control, water supply, and shipping. In this study, based on the classical riverine backwater theory, we focus on the backwater effect caused by tidal dynamics, making use of a one-dimensional hydrodynamic analytical model to redefine the upstream boundary of the backwater zone (namely backwater limit) in estuaries. The model was subsequently applied to the Changjiang River Estuary to explore the evolution of estuarine backwater dynamics and its underlying mechanism. Results show that the distance from Tianshenggang to backwater limit (i.e., the backwater influence length) has a negatively linear correlation with the upstream river discharge and positively linear correlation with the tidal amplitude of seaward boundary, respectively. The response of the backwater limit to tidal river dynamics is more sensitive than that of the tidal limit, which can effectively characterize the evolution of the tidal river dynamics in tidal reach. The location of the backwater limit in the Changjiang River Estuary has apparent seasonal difference, being 419 km away from Tianshenggang during the spring and 367 km during autumn. The location is situated above the tidal reach during the winter, while the backwater effect caused by tidal dynamics during the summer is negligible. It was shown that the seasonal variations of residual water level slope induced by tide and tide-river interaction are the dominant factors for controlling the location of the backwater limit in the Changjiang River Estuary.
2022, 44(12): 42-54.
doi: 10.12284/hyxb2022163
Abstract:
This paper analyzes and discusses the long-term variation characteristics of Arctic sea ice using the latest sea ice and sea surface temperature (SST) data from 1951 to 2021 provided by Hadley Center and NCEP/NCAR reanalysis data from the Climate Prediction Center of National Oceanic and Atmospheric Administration (NOAA). The relationship between the rapid decrease of Arctic sea ice and surface sea temperature anomaly (SSTA) in tropical oceans is also investigated, revealing that there is a close relationship between the changes in tropical sea surface temperature field and the Arctic sea ice variation. The results show that the most significant sea ice changes occur in the Greenland Sea, the Kara Sea and the Barents Sea. Notably, the influence of the different tropical ocean areas on the Arctic sea ice shows noticeable temporal and spatial differences. The tropical Atlantic has the earliest impact on Arctic sea ice cover, followed by the Indian and Pacific oceans. Meanwhile, we found that 26-month, 30-month and 34-month lag is the optimal time-lagged correlation time period between Arctic sea ice and SSTA in the tropical Atlantic, the tropical Indian Ocean and Middle-Eastern Pacific, respectively and the mean value among them is a 33-month lag. The most substantial impact of SST on arctic sea ice occurs in the Indian Ocean, followed by the Pacific Ocean and the weakest in the Atlantic Ocean. When the tropical oceans appear positive (negative) SSTA, the arctic sea ice tends to be less (more). Moreover, Arctic Oscillation (AO), the Pacific-North American teleconnection (PNA), North Atlantic Oscillation (NAO) contribute significantly to the Arctic sea ice change, which are the key processes leading to the abnormal Arctic sea ice change. The AO, PNA and NAO are not only influenced by the SST of the tropical ocean, but also by the Pacific Ocean Decadal Oscillation (PDO) of the Atlantic Multi-decadal Oscillation (AMO). Our study aims to provide theoretical support for future research on the mechanism of the rapid decline of Arctic sea ice and global warming.
This paper analyzes and discusses the long-term variation characteristics of Arctic sea ice using the latest sea ice and sea surface temperature (SST) data from 1951 to 2021 provided by Hadley Center and NCEP/NCAR reanalysis data from the Climate Prediction Center of National Oceanic and Atmospheric Administration (NOAA). The relationship between the rapid decrease of Arctic sea ice and surface sea temperature anomaly (SSTA) in tropical oceans is also investigated, revealing that there is a close relationship between the changes in tropical sea surface temperature field and the Arctic sea ice variation. The results show that the most significant sea ice changes occur in the Greenland Sea, the Kara Sea and the Barents Sea. Notably, the influence of the different tropical ocean areas on the Arctic sea ice shows noticeable temporal and spatial differences. The tropical Atlantic has the earliest impact on Arctic sea ice cover, followed by the Indian and Pacific oceans. Meanwhile, we found that 26-month, 30-month and 34-month lag is the optimal time-lagged correlation time period between Arctic sea ice and SSTA in the tropical Atlantic, the tropical Indian Ocean and Middle-Eastern Pacific, respectively and the mean value among them is a 33-month lag. The most substantial impact of SST on arctic sea ice occurs in the Indian Ocean, followed by the Pacific Ocean and the weakest in the Atlantic Ocean. When the tropical oceans appear positive (negative) SSTA, the arctic sea ice tends to be less (more). Moreover, Arctic Oscillation (AO), the Pacific-North American teleconnection (PNA), North Atlantic Oscillation (NAO) contribute significantly to the Arctic sea ice change, which are the key processes leading to the abnormal Arctic sea ice change. The AO, PNA and NAO are not only influenced by the SST of the tropical ocean, but also by the Pacific Ocean Decadal Oscillation (PDO) of the Atlantic Multi-decadal Oscillation (AMO). Our study aims to provide theoretical support for future research on the mechanism of the rapid decline of Arctic sea ice and global warming.
2022, 44(12): 55-69.
doi: 10.12284/hyxb2022153
Abstract:
Using 0.1°×0.1° high-resolution temperature, salinity, velocity and sea surface height (SSH) data from the ocean general circulation model for the earth simulator (OFES) model, this study analyzes the capability and applicability of the eSQG (effective Surface Quasi-Geostrophy) method in vertical velocity diagnosis in the South China Sea (SCS), as well as the spatiotemporal variation of vertical velocities. The diagnosed vertical velocities ωeSQG from SSH with the eSQG method are of the same order of 10−5 m/s as the “true” vertical velocities ωOFES from the OFES model. ωeSQG shows spatial variations with higher values in northern basin. The correlation coefficients of the horizontal distribution of ωeSQG and ωOFES (rs) are greater in deep basin than that in the whole SCS, suggesting that the eSQG method is more efficient in vertical velocity diagnosis in deep water far from boundaries. Vertically, the correlation coefficient has maximum values occurring in the subsurface layer at about 150 m. ωeSQG is stronger in summer and rs show seasonal variation with higher values in winter, indicating more efficient in eSQG diagnosis in winter. ωeSQG is reliable in the regions southwest of Taiwan and east of Vietnam, where the temporal correlation coefficients of ωeSQG and ωOFES (rt) exceed 0.6, while ωeSQG is poorly correlated to ωOFES in the shelf regions in the southern and northwestern SCS with rt mostly under 0.2. rs in the same region is varying at periods of about 18−55 d. ωeSQG performs better as the distributions of the SSH and the sea surface density are in same phase. ωeSQG varies little as the temporal resolution of SSH varies, while rs increases as spatial resolution reduced to 0.25° in mesoscales.
Using 0.1°×0.1° high-resolution temperature, salinity, velocity and sea surface height (SSH) data from the ocean general circulation model for the earth simulator (OFES) model, this study analyzes the capability and applicability of the eSQG (effective Surface Quasi-Geostrophy) method in vertical velocity diagnosis in the South China Sea (SCS), as well as the spatiotemporal variation of vertical velocities. The diagnosed vertical velocities ωeSQG from SSH with the eSQG method are of the same order of 10−5 m/s as the “true” vertical velocities ωOFES from the OFES model. ωeSQG shows spatial variations with higher values in northern basin. The correlation coefficients of the horizontal distribution of ωeSQG and ωOFES (rs) are greater in deep basin than that in the whole SCS, suggesting that the eSQG method is more efficient in vertical velocity diagnosis in deep water far from boundaries. Vertically, the correlation coefficient has maximum values occurring in the subsurface layer at about 150 m. ωeSQG is stronger in summer and rs show seasonal variation with higher values in winter, indicating more efficient in eSQG diagnosis in winter. ωeSQG is reliable in the regions southwest of Taiwan and east of Vietnam, where the temporal correlation coefficients of ωeSQG and ωOFES (rt) exceed 0.6, while ωeSQG is poorly correlated to ωOFES in the shelf regions in the southern and northwestern SCS with rt mostly under 0.2. rs in the same region is varying at periods of about 18−55 d. ωeSQG performs better as the distributions of the SSH and the sea surface density are in same phase. ωeSQG varies little as the temporal resolution of SSH varies, while rs increases as spatial resolution reduced to 0.25° in mesoscales.
2022, 44(12): 70-83.
doi: 10.12284/hyxb2022141
Abstract:
Sea ice thickness is a crucial parameter for monitoring and studying sea ice in the Bohai Sea. Aiming to get more reliable data conveniently, we improved the ice thickness retrieval algorithm based of MODIS data, including the ice separation process and ice thickness calculation method. In terms of ice-water separation process, some steps like binary processing, threshold discrimination were added based on sea ice extracting with Canny edge detector, which successfully realized the automatic high-precision extraction of sea ice range in the Bohai Sea. Meanwhile, through experiments, we optimize the parameters of the exponential model between sea ice thickness and albedo, including sea ice attenuation coefficient and sea water albedo parameters, to make it more consistent with the physical characteristics of the Bohai Sea area. The sea ice thickness retrieval results of the improved algorithm are compared with the measured data of the Bohai offshore oil platform, and the error reasons are analyzed. The results show that the average absolute error decreases from 7.05 cm to 2.74 cm, and the correlation coefficient increases from 0.434 to 0.485.
Sea ice thickness is a crucial parameter for monitoring and studying sea ice in the Bohai Sea. Aiming to get more reliable data conveniently, we improved the ice thickness retrieval algorithm based of MODIS data, including the ice separation process and ice thickness calculation method. In terms of ice-water separation process, some steps like binary processing, threshold discrimination were added based on sea ice extracting with Canny edge detector, which successfully realized the automatic high-precision extraction of sea ice range in the Bohai Sea. Meanwhile, through experiments, we optimize the parameters of the exponential model between sea ice thickness and albedo, including sea ice attenuation coefficient and sea water albedo parameters, to make it more consistent with the physical characteristics of the Bohai Sea area. The sea ice thickness retrieval results of the improved algorithm are compared with the measured data of the Bohai offshore oil platform, and the error reasons are analyzed. The results show that the average absolute error decreases from 7.05 cm to 2.74 cm, and the correlation coefficient increases from 0.434 to 0.485.
Inversion of the full-depth sound speed profile based on remote sensing data and surface sound speed
2022, 44(12): 84-94.
doi: 10.12284/hyxb2022149
Abstract:
The ocean sound speed profile (SSP) determines the underwater acoustic propagation, and it is very important to obtain SSP in near real-time for underwater acoustic communication, positioning, and fish detecting. The single Empirical Orthogonal Function regression (sEOF-r) method inverts the SSP by establishing a linear regression relationship between the empirical orthogonal coefficient of the SSP and the sea surface remote sensing data. However, the ocean is a complex dynamical system, and the SSP and the remote sensing data are not simple linear. Therefore, based on the Argo historical gridded dataset, self-organizing map (SOM) was used to establish the nonlinear mapping between sea surface data, such as sea level anomaly (SLA), sea surface temperature (SST) and surface sound speed measured by surface velocimeter, and SSP anomaly. The three-dimensional sound speed field is then inverted by the near real-time remote sensing data and the surface sound speed. The results of the SSP inversion showed that, under the advantage of multi-source information fusion, the algorithm generated a smaller inversion error than linear inversion and had better robustness. It improved the average accuracy of inversion by about 2 m/s than sEOF-r method, and improved by about 1 m/s than classical SOM method that without considering the surface sound speed.
The ocean sound speed profile (SSP) determines the underwater acoustic propagation, and it is very important to obtain SSP in near real-time for underwater acoustic communication, positioning, and fish detecting. The single Empirical Orthogonal Function regression (sEOF-r) method inverts the SSP by establishing a linear regression relationship between the empirical orthogonal coefficient of the SSP and the sea surface remote sensing data. However, the ocean is a complex dynamical system, and the SSP and the remote sensing data are not simple linear. Therefore, based on the Argo historical gridded dataset, self-organizing map (SOM) was used to establish the nonlinear mapping between sea surface data, such as sea level anomaly (SLA), sea surface temperature (SST) and surface sound speed measured by surface velocimeter, and SSP anomaly. The three-dimensional sound speed field is then inverted by the near real-time remote sensing data and the surface sound speed. The results of the SSP inversion showed that, under the advantage of multi-source information fusion, the algorithm generated a smaller inversion error than linear inversion and had better robustness. It improved the average accuracy of inversion by about 2 m/s than sEOF-r method, and improved by about 1 m/s than classical SOM method that without considering the surface sound speed.
2022, 44(12): 95-108.
doi: 10.12284/hyxb2022143
Abstract:
The South Kunsong area is a negative tectonic unit in the western part of the Wan’an Basin, in which the N−S trending faults run through the north and the south. The unique tectonic characteristics make it a window for studying the tectonic evolution and regional fault strike-slip activities in the western part of the Wan’an Basin. The sedimentary strata in the study area are divided into three sets of structural layers, the structure-sedimentary filling section in the South Kunsong area is drawn by the back stripping method, and the tectonic subsidence and tectonic subsidence rate in the South Kunsong area are calculated. Settlement process and controlling factors. The research results show that the fault combination styles in the lower and middle structural layers are mainly core-type faults, "Y"-type faults, stepped faults and high-angle flower-shaped structures. W−E trending and NE−SW trending; the upper tectonic layer is not developed with faults and is stable deposition; under the control of regional strike-slip faults and the South China Sea spreading movement, the tectonic evolution of the South Kunsong area has experienced four stages since the Eocene: the initial stage. During the rifting period, extensional fault-deflection period, strike-slip reformation period and thermal subsidence period, the stratigraphic structure properties of the Cenozoic also showed a three-stage transformation of extension and strike-slip, control of strike-slip faults, and thermal subsidence.
The South Kunsong area is a negative tectonic unit in the western part of the Wan’an Basin, in which the N−S trending faults run through the north and the south. The unique tectonic characteristics make it a window for studying the tectonic evolution and regional fault strike-slip activities in the western part of the Wan’an Basin. The sedimentary strata in the study area are divided into three sets of structural layers, the structure-sedimentary filling section in the South Kunsong area is drawn by the back stripping method, and the tectonic subsidence and tectonic subsidence rate in the South Kunsong area are calculated. Settlement process and controlling factors. The research results show that the fault combination styles in the lower and middle structural layers are mainly core-type faults, "Y"-type faults, stepped faults and high-angle flower-shaped structures. W−E trending and NE−SW trending; the upper tectonic layer is not developed with faults and is stable deposition; under the control of regional strike-slip faults and the South China Sea spreading movement, the tectonic evolution of the South Kunsong area has experienced four stages since the Eocene: the initial stage. During the rifting period, extensional fault-deflection period, strike-slip reformation period and thermal subsidence period, the stratigraphic structure properties of the Cenozoic also showed a three-stage transformation of extension and strike-slip, control of strike-slip faults, and thermal subsidence.
2022, 44(12): 109-115.
doi: 10.12284/hyxb2022151
Abstract:
Quaternary distribution, Quaternary confined aquifer productivity, distribution of freshwater and seawater resources, confined groundwater age and renewability are further studied based on recently completed hydrogeological borehole, engineering pores and AMS 14C dating combined with previous data. The first confined aquifer productivity in Shepan tideland reclamation area of Sanmen Bay coastal zone is better, most of groundwater is fresh water. As a whole, freshwater resources of confined aquifer at Changjie Town of Ninghai County are distributed by herringbone patterns. Freshwater resources are mainly distributed in first confined aquifer at Dahu-Cheaogang of north Changjie Town, and freshwater resources are mainly distributed in second confined aquifer at Dahu-Xiayangtu of Changjie Town. The Quaternary confined aquifer ages are generally older. The groundwater ages of the first confined aquifer in Shepan tideland reclamation area are 21 642−22 012 cal a BP, the groundwater is not affected by late transgression. The groundwater ages of the second confined aquifer in Xiayangtu tideland reclamation area are of Changjie Town are 35 052−45 439 cal a BP, the groundwater in partial site is affected by late transgression. Under present unexploited conditions the condition of confined groundwater recharge is bad, the renewability of groundwater resources is not good. Therefore, the management of groundwater resources should be strengthened in emergency water source.
Quaternary distribution, Quaternary confined aquifer productivity, distribution of freshwater and seawater resources, confined groundwater age and renewability are further studied based on recently completed hydrogeological borehole, engineering pores and AMS 14C dating combined with previous data. The first confined aquifer productivity in Shepan tideland reclamation area of Sanmen Bay coastal zone is better, most of groundwater is fresh water. As a whole, freshwater resources of confined aquifer at Changjie Town of Ninghai County are distributed by herringbone patterns. Freshwater resources are mainly distributed in first confined aquifer at Dahu-Cheaogang of north Changjie Town, and freshwater resources are mainly distributed in second confined aquifer at Dahu-Xiayangtu of Changjie Town. The Quaternary confined aquifer ages are generally older. The groundwater ages of the first confined aquifer in Shepan tideland reclamation area are 21 642−22 012 cal a BP, the groundwater is not affected by late transgression. The groundwater ages of the second confined aquifer in Xiayangtu tideland reclamation area are of Changjie Town are 35 052−45 439 cal a BP, the groundwater in partial site is affected by late transgression. Under present unexploited conditions the condition of confined groundwater recharge is bad, the renewability of groundwater resources is not good. Therefore, the management of groundwater resources should be strengthened in emergency water source.
2022, 44(12): 148-160.
doi: 10.12284/hyxb2022147
Abstract:
Coastal salt marsh margin, as the transition zone between salt marsh and tidal flat, presents three types of three-dimensional form: smooth, transition and cliff. And it shows different curvilinear features in the planar shape. As a high dynamic bio-geomorphic system, marsh margin changes rapidly due to the influence of natural processes and human activities. But the lack of high-resolution observational data makes further understanding of this change difficult. Here, we address this challenge using UAV-based Structure-from-Motion (UAV-SfM) photogrammetry which has the advantages of high resolution, non-invasive, repeatability, and low cost. We conducted two aerial surveys of salt marsh on Jiangsu coast, to obtain orthophotographs and Digital Surface Model (DSM) with cm-level pixel resolutions. And it supports us to determine the location of marsh margin, classify the type of the margin, and quantitatively describe the topography changes. We found the smooth and cliff margin are stable and dominant. The smooth margin has complex planar shape and retreats slowly. And the transition and cliff margin have regular shape and retreat fast. The transition margin changes drastically and turns to the cliff margin. This work proves that UAV-SfM photogrammetry is suitable for efficient and accurate quantification of the topography of marsh margin, and provides a new perspective for understanding the evolution process of marsh margin.
Coastal salt marsh margin, as the transition zone between salt marsh and tidal flat, presents three types of three-dimensional form: smooth, transition and cliff. And it shows different curvilinear features in the planar shape. As a high dynamic bio-geomorphic system, marsh margin changes rapidly due to the influence of natural processes and human activities. But the lack of high-resolution observational data makes further understanding of this change difficult. Here, we address this challenge using UAV-based Structure-from-Motion (UAV-SfM) photogrammetry which has the advantages of high resolution, non-invasive, repeatability, and low cost. We conducted two aerial surveys of salt marsh on Jiangsu coast, to obtain orthophotographs and Digital Surface Model (DSM) with cm-level pixel resolutions. And it supports us to determine the location of marsh margin, classify the type of the margin, and quantitatively describe the topography changes. We found the smooth and cliff margin are stable and dominant. The smooth margin has complex planar shape and retreats slowly. And the transition and cliff margin have regular shape and retreat fast. The transition margin changes drastically and turns to the cliff margin. This work proves that UAV-SfM photogrammetry is suitable for efficient and accurate quantification of the topography of marsh margin, and provides a new perspective for understanding the evolution process of marsh margin.
2022, 44(12): 116-125.
doi: 10.12284/hyxb2022155
Abstract:
How to study the response process of wetland system under the influence of extreme weather events such as typhoon, and then put forward effective ecological integrity maintenance and management schemes is of great significance to wetland management and ecological security maintenance in key areas. In this paper, during the process of “Chanthu” Typhoon in September 2021, hydrodynamic observation points were set up on the South Bank of Nanhui east tidal flat, surface sediments were collected, tidal flat surface elevation was measured, and vegetation images were obtained by unmanned aerial vehicle. Using ArcGIS spatial analysis, the hydrodynamic and sedimentary changes of Nanhui east tidal flat and the response of tidal flat surface elevation, surface sediments and vegetation distribution area were discussed. The results show that the average effective wave height and wave energy at the edge of the vegetation are 1.54 times and 2.14 times in the typhoon, the average current velocity near the bottom layer is 0.23 m/s, and a “high suspended sediment concentration layer” (>10 g/L) with a thickness of more than 1 m appears on the tidal flat for 8.13 h. After the typhoon, the tidal flat surface of Scirpus mariqueter and Spartina alterniflora distributed sparsely below 4 m eroded 0−4.8 cm, and the tidal flat surface with lush growth of Spartina alterniflora and Phragmites australis above 4 m deposited 0−14.7 cm. The distribution area of vegetation in the study area decreased by 1827.67 m2, accounting for 1.63% of the total vegetation before the typhoon, including 31.9% of the eroded tidal flat vegetation and 68.1% of the deposited tidal flat vegetation. The wetland management after the typhoon process can be summarized as follows: (1) The wetland basically shows the characteristics of coexistence of erosion and accretion areas after the typhoon process; (2) For the tidal flat surface with an elevation lower than 4 m, it is suggested to determine the elevation suitable for vegetation growth, combine the erosion and deposition changes during the typhoon process, and use the “microbial film” and vegetation patch transplantation to dissipate waves, consolidate the tidal flat and promote accretion, so as to accelerate the rapid restoration of the wetland after the impact of the typhoon process.
How to study the response process of wetland system under the influence of extreme weather events such as typhoon, and then put forward effective ecological integrity maintenance and management schemes is of great significance to wetland management and ecological security maintenance in key areas. In this paper, during the process of “Chanthu” Typhoon in September 2021, hydrodynamic observation points were set up on the South Bank of Nanhui east tidal flat, surface sediments were collected, tidal flat surface elevation was measured, and vegetation images were obtained by unmanned aerial vehicle. Using ArcGIS spatial analysis, the hydrodynamic and sedimentary changes of Nanhui east tidal flat and the response of tidal flat surface elevation, surface sediments and vegetation distribution area were discussed. The results show that the average effective wave height and wave energy at the edge of the vegetation are 1.54 times and 2.14 times in the typhoon, the average current velocity near the bottom layer is 0.23 m/s, and a “high suspended sediment concentration layer” (>10 g/L) with a thickness of more than 1 m appears on the tidal flat for 8.13 h. After the typhoon, the tidal flat surface of Scirpus mariqueter and Spartina alterniflora distributed sparsely below 4 m eroded 0−4.8 cm, and the tidal flat surface with lush growth of Spartina alterniflora and Phragmites australis above 4 m deposited 0−14.7 cm. The distribution area of vegetation in the study area decreased by 1827.67 m2, accounting for 1.63% of the total vegetation before the typhoon, including 31.9% of the eroded tidal flat vegetation and 68.1% of the deposited tidal flat vegetation. The wetland management after the typhoon process can be summarized as follows: (1) The wetland basically shows the characteristics of coexistence of erosion and accretion areas after the typhoon process; (2) For the tidal flat surface with an elevation lower than 4 m, it is suggested to determine the elevation suitable for vegetation growth, combine the erosion and deposition changes during the typhoon process, and use the “microbial film” and vegetation patch transplantation to dissipate waves, consolidate the tidal flat and promote accretion, so as to accelerate the rapid restoration of the wetland after the impact of the typhoon process.
2022, 44(12): 126-135.
doi: 10.12284/hyxb2022145
Abstract:
The topography of the seafloor is extremely important for marine scientific surveys and research. Echo-sounding technology, represented by multi-beam sounding, is costly and inefficient, and has only achieved about 20% of the world’s seabed mapping for decades. For the remaining void area, especially the deep ocean, it can be obtained by regression analysis using gravity anomalies and vertical gravity gradient anomalies, but the robustness of scale factor is poor. To address this issue, and considering the different advantages of the two kinds of gravity data in the characterization of the long and short wavelengths of the seafloor topography, a method which combining sliding window weighting and robust regression analysis was introduced in this paper. The experimental results in the Emperor Seamount in the Pacific Ocean (35°−45°N, 165°−175°E) indicate that: taking the ship test data as the checking condition, the standard deviation of the constructed model is 61.02 m, compared with the single gravity data inversion model, the accuracy was improved 14.92% (gravity anomalies) and 2.08% (vertical gravity gradient anomalies), which can better reflect the topographic trend of the Emperor Seamount Chain.
The topography of the seafloor is extremely important for marine scientific surveys and research. Echo-sounding technology, represented by multi-beam sounding, is costly and inefficient, and has only achieved about 20% of the world’s seabed mapping for decades. For the remaining void area, especially the deep ocean, it can be obtained by regression analysis using gravity anomalies and vertical gravity gradient anomalies, but the robustness of scale factor is poor. To address this issue, and considering the different advantages of the two kinds of gravity data in the characterization of the long and short wavelengths of the seafloor topography, a method which combining sliding window weighting and robust regression analysis was introduced in this paper. The experimental results in the Emperor Seamount in the Pacific Ocean (35°−45°N, 165°−175°E) indicate that: taking the ship test data as the checking condition, the standard deviation of the constructed model is 61.02 m, compared with the single gravity data inversion model, the accuracy was improved 14.92% (gravity anomalies) and 2.08% (vertical gravity gradient anomalies), which can better reflect the topographic trend of the Emperor Seamount Chain.
2022, 44(12): 136-147.
doi: 10.12284/hyxb2022161
Abstract:
Medium and high spatial resolution wide-band optical satellites have become the main data source for red tide monitoring, but unlike the ocean color satellite sensors, the medium and high spatial resolution satellite sensors are mainly oriented to terrestrial applications with a small number of bands and a large band width, and the resulting impact on red tide detection has yet to be studied. Therefore, this paper explores the effects of band settings, spectral response functions, signal-to-noise ratio and spatial resolution on red tide detection based on the actual hyperspectral data of different dominant species of red tide, spatio-temporally synchronized GF-1 WFV2 and GF-1 WFV3 sensor images, Sentinel-2A MSI sensor images and GF-6 WFV sensor images, and analyzes the advantages of red-edge band on red tide detection. Our results show that: the band settings have a great influence on the red tide detection, especially the central wavelength and band width of the red band and the red edge band; the red tide detection accuracy is greatly influenced by the spectral response function and less influenced by the signal-to-noise ratio under the same band settings; the spatial resolution has a greater influence on the red tide detection, and the improvement of spatial resolution helps to improve the accuracy of red tide detection. The experiments of red-edge band red tide detection show that red-edge band red tide detection has obvious advantages over red-light band red tide detection, and the F1-Score is improved by 11% on average. The results of this paper provide a theoretical basis for the data selection of red tide detection from medium and high spatial resolution satellites on the one hand, and a reference for the design of medium and high spatial resolution satellite sensors on the other hand.
Medium and high spatial resolution wide-band optical satellites have become the main data source for red tide monitoring, but unlike the ocean color satellite sensors, the medium and high spatial resolution satellite sensors are mainly oriented to terrestrial applications with a small number of bands and a large band width, and the resulting impact on red tide detection has yet to be studied. Therefore, this paper explores the effects of band settings, spectral response functions, signal-to-noise ratio and spatial resolution on red tide detection based on the actual hyperspectral data of different dominant species of red tide, spatio-temporally synchronized GF-1 WFV2 and GF-1 WFV3 sensor images, Sentinel-2A MSI sensor images and GF-6 WFV sensor images, and analyzes the advantages of red-edge band on red tide detection. Our results show that: the band settings have a great influence on the red tide detection, especially the central wavelength and band width of the red band and the red edge band; the red tide detection accuracy is greatly influenced by the spectral response function and less influenced by the signal-to-noise ratio under the same band settings; the spatial resolution has a greater influence on the red tide detection, and the improvement of spatial resolution helps to improve the accuracy of red tide detection. The experiments of red-edge band red tide detection show that red-edge band red tide detection has obvious advantages over red-light band red tide detection, and the F1-Score is improved by 11% on average. The results of this paper provide a theoretical basis for the data selection of red tide detection from medium and high spatial resolution satellites on the one hand, and a reference for the design of medium and high spatial resolution satellite sensors on the other hand.
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