2019 Vol. 41, No. 5
Display Method:
2019, 41(5): .
Abstract:
2019, 41(5): .
Abstract:
2019, 41(5): 1-11.
doi: 10.3969/j.issn.0253-4193.2019.05.001
Abstract:
Using long-term ocean observation data obtained by HF surface wave radar, the summertime sea surface currents and residual currents characteristics in the Lanshayang sea area of radial sand ridges in the northern Jiangsu Province are analysed in this paper. Results show that, the surface current near the coast is reciprocating, and the direction is generally from northwest to southeast, while the offshore side is rotational. The maximum surface velocity in summer can reach 1.47 m/s so that tidal energy is strong in here. The average flood current velocity is between 0.44 m/s and 0.55 m/s and the average ebb current velocity is between 0.38 m/s and 0.52 m/s. The average velocity in the northwest of the sea area is obviously larger than that of other areas. The surface current is regular semidiurnal tidal current and M2 is the most important constituent, followed by S2. The major axis of M2 tidal current ellipses is between 0.57 m/s and 0.71 m/s, greater than other constituent. The surface residual current velocity is larger in inshore than in offshore, and the direction is generally toward the coast. From offshore to inshore, residual current direction exhibits an anticlockwise deflection.
Using long-term ocean observation data obtained by HF surface wave radar, the summertime sea surface currents and residual currents characteristics in the Lanshayang sea area of radial sand ridges in the northern Jiangsu Province are analysed in this paper. Results show that, the surface current near the coast is reciprocating, and the direction is generally from northwest to southeast, while the offshore side is rotational. The maximum surface velocity in summer can reach 1.47 m/s so that tidal energy is strong in here. The average flood current velocity is between 0.44 m/s and 0.55 m/s and the average ebb current velocity is between 0.38 m/s and 0.52 m/s. The average velocity in the northwest of the sea area is obviously larger than that of other areas. The surface current is regular semidiurnal tidal current and M2 is the most important constituent, followed by S2. The major axis of M2 tidal current ellipses is between 0.57 m/s and 0.71 m/s, greater than other constituent. The surface residual current velocity is larger in inshore than in offshore, and the direction is generally toward the coast. From offshore to inshore, residual current direction exhibits an anticlockwise deflection.
2019, 41(5): 12-22.
doi: 10.3969/j.issn.0253-4193.2019.05.002
Abstract:
This paper simulates the global sea surface wave evolution in 2012, based on a well validated global scale FVCOM wave model, and analyses the global distribution of wind speed, wave parameters and mixing layer depth. Based on the simulation results and observed data, the global distribution patterns of 10 m wind speed, significant wave height and mixing layer depth vary remarkably with season, and they share the most similar trend. By the way of statistic, it is showed the average correlation coefficients between significant wave height, 10 m wind speed, peak period and mixing layer depth are 0.31, 0.25 and 0.12, respectively. For the global distribution of the correlation coefficients, 10 m wind speed and mixing layer depth have high correlation of about 0.5 at low latitudes (0°-20°) in the Indian Ocean, while for the significant wave height it is located at the high latitudes in the Northern Hemisphere and the North Indian Ocean. The correlation coefficients of peak period and mixing layer depth are negative in some areas distributed at low latitudes (0°-30°) in the Indian Ocean. Above all, compared with peak period, significant wave height can better represent the influence of wave energy on surface layer mixing. And significant wave heights and mixing layer depth have stronger correlation than the sea surface wind speed.
This paper simulates the global sea surface wave evolution in 2012, based on a well validated global scale FVCOM wave model, and analyses the global distribution of wind speed, wave parameters and mixing layer depth. Based on the simulation results and observed data, the global distribution patterns of 10 m wind speed, significant wave height and mixing layer depth vary remarkably with season, and they share the most similar trend. By the way of statistic, it is showed the average correlation coefficients between significant wave height, 10 m wind speed, peak period and mixing layer depth are 0.31, 0.25 and 0.12, respectively. For the global distribution of the correlation coefficients, 10 m wind speed and mixing layer depth have high correlation of about 0.5 at low latitudes (0°-20°) in the Indian Ocean, while for the significant wave height it is located at the high latitudes in the Northern Hemisphere and the North Indian Ocean. The correlation coefficients of peak period and mixing layer depth are negative in some areas distributed at low latitudes (0°-30°) in the Indian Ocean. Above all, compared with peak period, significant wave height can better represent the influence of wave energy on surface layer mixing. And significant wave heights and mixing layer depth have stronger correlation than the sea surface wind speed.
2019, 41(5): 23-34.
doi: 10.3969/j.issn.0253-4193.2019.05.003
Abstract:
Based on one-year field observation wave data measured in nearshore waters of Xiangshui, the variations of wave heights and periods are investigated, the statistical and spectral characteristics of waves are analyzed and the relationship among the characteristic wave heights, the characteristic wave periods and the wave spectra parameters are identified. Results show that the significant wave height varies from 0.10 m to 2.80 m with the average of 0.56 m, the maximum wave height varies from 0.15 m to 5.58 m with the average of 0.93 m and the mean wave period varies from 1.91 s to 9.02 s with the average of 3.90 s. The probability of huge waves in summer is obviously less than that in winter and spring, showing the seasonal variability. With respect to wave height and wave period distribution, the Weibull distribution works better on the distributions of measured wave height and period. In terms of wave spectrum properties, the percentage of double-peaked spectra is 62.5 during the measurement period. The spectral peak value corresponding to a lower peak frequency is generally higher than the one corresponding to a higher peak frequency, and the lower peak frequency is around 0.04 Hz, the higher peak frequency is between 0.15 Hz to 0.20 Hz, which corresponds to the frequency intervals of the sea swells and wind waves respectively. Besides, the transformations of several characteristic wave heights, characteristic wave periods and the wave spectra parameters are obtained by linear regression analysis, and strong correlations between them are found, however, due to the wave deformation in shallow water, these ratio coefficients are different from those ones in deep water. The research results of this paper could serve as reference and guidance for the design of coastal structures as well as for disaster prevention and mitigation.
Based on one-year field observation wave data measured in nearshore waters of Xiangshui, the variations of wave heights and periods are investigated, the statistical and spectral characteristics of waves are analyzed and the relationship among the characteristic wave heights, the characteristic wave periods and the wave spectra parameters are identified. Results show that the significant wave height varies from 0.10 m to 2.80 m with the average of 0.56 m, the maximum wave height varies from 0.15 m to 5.58 m with the average of 0.93 m and the mean wave period varies from 1.91 s to 9.02 s with the average of 3.90 s. The probability of huge waves in summer is obviously less than that in winter and spring, showing the seasonal variability. With respect to wave height and wave period distribution, the Weibull distribution works better on the distributions of measured wave height and period. In terms of wave spectrum properties, the percentage of double-peaked spectra is 62.5 during the measurement period. The spectral peak value corresponding to a lower peak frequency is generally higher than the one corresponding to a higher peak frequency, and the lower peak frequency is around 0.04 Hz, the higher peak frequency is between 0.15 Hz to 0.20 Hz, which corresponds to the frequency intervals of the sea swells and wind waves respectively. Besides, the transformations of several characteristic wave heights, characteristic wave periods and the wave spectra parameters are obtained by linear regression analysis, and strong correlations between them are found, however, due to the wave deformation in shallow water, these ratio coefficients are different from those ones in deep water. The research results of this paper could serve as reference and guidance for the design of coastal structures as well as for disaster prevention and mitigation.
2019, 41(5): 35-46.
doi: 10.3969/j.issn.0253-4193.2019.05.004
Abstract:
On September 8, 2017, at 4:49 (UTC) a magnitude Mw8.2 earthquake took place off the coast of Oaxaca State, Mexico, focal depth of 30 km. Meanwhile, the earthquake triggered moderate intensity tsunami. The tsunami impacted hundreds of kilometers of the coast of Mexico. Tsunami waves were subsequently recorded by Deep-ocean Assessment and Reporting of Tsunami (DART) buoys in the Pacific Ocean and tide gauges off the coast. In this paper, we apply observational data of 2 DART buoys and 6 tide gauges, and isolate the tsunami waves from boservational data by de-tiding and filtering method, and futher analyze the frequency characteristics of the tsunami waves by wavelet analysis. To compute the co-seismic deformation, we employ the half space elastic theory, and then we analyze the near-field characteristics of this tsunami by numerical simulation with MOST (Method Of Splitting Tsunamis) model. The results based on the observational and simulation data show that, apart from the magnitude and geometric distribution of the earthquake, near-field tsunami waves are mainly controlled by topographic distribution off the coast. Especially, the amplitude of tsunami waves may have amplification effect when interacting with specific topography, which will cause much more damage of the tsunami.
On September 8, 2017, at 4:49 (UTC) a magnitude Mw8.2 earthquake took place off the coast of Oaxaca State, Mexico, focal depth of 30 km. Meanwhile, the earthquake triggered moderate intensity tsunami. The tsunami impacted hundreds of kilometers of the coast of Mexico. Tsunami waves were subsequently recorded by Deep-ocean Assessment and Reporting of Tsunami (DART) buoys in the Pacific Ocean and tide gauges off the coast. In this paper, we apply observational data of 2 DART buoys and 6 tide gauges, and isolate the tsunami waves from boservational data by de-tiding and filtering method, and futher analyze the frequency characteristics of the tsunami waves by wavelet analysis. To compute the co-seismic deformation, we employ the half space elastic theory, and then we analyze the near-field characteristics of this tsunami by numerical simulation with MOST (Method Of Splitting Tsunamis) model. The results based on the observational and simulation data show that, apart from the magnitude and geometric distribution of the earthquake, near-field tsunami waves are mainly controlled by topographic distribution off the coast. Especially, the amplitude of tsunami waves may have amplification effect when interacting with specific topography, which will cause much more damage of the tsunami.
2019, 41(5): 47-58.
doi: 10.3969/j.issn.0253-4193.2019.05.005
Abstract:
This study examined the spatial distribution characteristics, motion properties, seasonal, interannual and decadal variations of oceanic rings shed from the Kuroshio Extension (KE) jet using AVISO satellite altimeter observations from January 1993 to December 2015. The results show that 242 cyclones and 276 anticyclones are detected in the past 23 years, and pinch-off rings mostly distribute in the region west of the Shatsky Rise. According to the spatial distribution of the ring formations in the KE region, there are two high value regions of cyclonic rings. One is located at the upstream region between 144°-146°E around the steady meander of the KE jet, the other is located at 156°E west of the Shatsky Ridge. There are two high value regions of anticyclonic rings, one located at downstream region west of the Shatsky Ridge and the other located at 148°E. These pinched-off rings in both the upstream and downstream regions generally propagated westward, but about 88% of the rings are reabsorbed by the jet. The number of ring formations show substantial interannual to decadal-like variability. In the upstream and downstream KE region, decadal-like and interannual variability is dominant, respectively. In the upstream region, these fluctuations of the ring formations are negatively correlated with the strength of the KE jet. In terms of seasonal variation, the most rings formed in summer, and the least in winter.
This study examined the spatial distribution characteristics, motion properties, seasonal, interannual and decadal variations of oceanic rings shed from the Kuroshio Extension (KE) jet using AVISO satellite altimeter observations from January 1993 to December 2015. The results show that 242 cyclones and 276 anticyclones are detected in the past 23 years, and pinch-off rings mostly distribute in the region west of the Shatsky Rise. According to the spatial distribution of the ring formations in the KE region, there are two high value regions of cyclonic rings. One is located at the upstream region between 144°-146°E around the steady meander of the KE jet, the other is located at 156°E west of the Shatsky Ridge. There are two high value regions of anticyclonic rings, one located at downstream region west of the Shatsky Ridge and the other located at 148°E. These pinched-off rings in both the upstream and downstream regions generally propagated westward, but about 88% of the rings are reabsorbed by the jet. The number of ring formations show substantial interannual to decadal-like variability. In the upstream and downstream KE region, decadal-like and interannual variability is dominant, respectively. In the upstream region, these fluctuations of the ring formations are negatively correlated with the strength of the KE jet. In terms of seasonal variation, the most rings formed in summer, and the least in winter.
2019, 41(5): 59-69.
doi: 10.3969/j.issn.0253-4193.2019.05.006
Abstract:
Using the SWAN model, the wave fields on the Taiwan Strait with two common wind field data including Cross-Calibrated Multi-Platform (CCMP) and ASCAT-Based Daily (DASCAT) are simulated and analyzed in this paper. A three-month period result during the northeast monsoon is compared with the buoy measured sequential wave height result. The mean of the deviations between them is less than 0.33 m and the root mean square (RMS) value of the deviations is no larger than 0.59 m. The deviations become larger when the buoy measured wave height is greater than 3.5 m or less than 1 m. And the simulation result of 6 h resolution wind field data agrees better with the buoy measured wave height than the 24 h resolution. Among the simulations with the input of the CCMP wind data with 6 h and 24 h resolution and the DASCAT wind data with 24 h resolution, the spatial cross correlation coefficient between either two results are no less than 0.90, the spatial mean of the deviations between either two results is less than 0.32 m and the RMS value of the deviations is less than 0.40 m.
Using the SWAN model, the wave fields on the Taiwan Strait with two common wind field data including Cross-Calibrated Multi-Platform (CCMP) and ASCAT-Based Daily (DASCAT) are simulated and analyzed in this paper. A three-month period result during the northeast monsoon is compared with the buoy measured sequential wave height result. The mean of the deviations between them is less than 0.33 m and the root mean square (RMS) value of the deviations is no larger than 0.59 m. The deviations become larger when the buoy measured wave height is greater than 3.5 m or less than 1 m. And the simulation result of 6 h resolution wind field data agrees better with the buoy measured wave height than the 24 h resolution. Among the simulations with the input of the CCMP wind data with 6 h and 24 h resolution and the DASCAT wind data with 24 h resolution, the spatial cross correlation coefficient between either two results are no less than 0.90, the spatial mean of the deviations between either two results is less than 0.32 m and the RMS value of the deviations is less than 0.40 m.
2019, 41(5): 70-78.
doi: 10.3969/j.issn.0253-4193.2019.05.007
Abstract:
Based on the statistical analysis of the acoustic physical parameters and sedimentary grain size characteristics of the South China Sea sediment samples, it is found that there are significant differences in the acoustic and physical properties for high and low sand content. Empirical formulae are established for sand content and compression wave velocity, porosity, water content and density of seafloor sediments. Based on the theory of sound velocity, the reason for the change of compressive wave velocity caused by the change of sand content is that the volumetric compressive modulus and density change with sand content. The reason for the increase of the compressive wave velocity caused by the increase of sand content is that the increase of sand content causes the compressive bulk modulus to change more than the density change. Combination of data statistics and theoretical analysis demonstrates that sand content is one of the important factors affecting the compression wave velocity of seafloor sediments. This study has important theoretical significance and application value for the acoustic inversion of seafloor sediment particle size parameters and sediment types, the establishment of geoacoustic parameter conversion models, and the exploration of seabed resources.
Based on the statistical analysis of the acoustic physical parameters and sedimentary grain size characteristics of the South China Sea sediment samples, it is found that there are significant differences in the acoustic and physical properties for high and low sand content. Empirical formulae are established for sand content and compression wave velocity, porosity, water content and density of seafloor sediments. Based on the theory of sound velocity, the reason for the change of compressive wave velocity caused by the change of sand content is that the volumetric compressive modulus and density change with sand content. The reason for the increase of the compressive wave velocity caused by the increase of sand content is that the increase of sand content causes the compressive bulk modulus to change more than the density change. Combination of data statistics and theoretical analysis demonstrates that sand content is one of the important factors affecting the compression wave velocity of seafloor sediments. This study has important theoretical significance and application value for the acoustic inversion of seafloor sediment particle size parameters and sediment types, the establishment of geoacoustic parameter conversion models, and the exploration of seabed resources.
2019, 41(5): 79-96.
doi: 10.3969/j.issn.0253-4193.2019.05.008
Abstract:
Based on regional tectonic evolution history, basin types in the southern Pacific region are classified and the petroleum geology of the major basin types is studied. The petroleum occurrences and resource potential are finally analysed in an objective to provide support for international cooperation between countries. Our studies show that:(1) The southern Pacific region underwent four stages including Hunter-Bowen orogeny, Antarctic Plate separates form the Australia Plate, the Tasman and Coral seas expending and oceanic crust subduction and arc-land collision occurred in Papua New Guinea, and formed six types of basin that is cratonic basin, rift basin, late permian-triassic foreland basin, paleogene-neogene foreland basin, paleogene-present forearc basin and the back-arc basin. The eastern inland of Australia is mainly the cratonic basin, and the southern margin and sea area of eastern Australia and the New Zealand are mainly the rift basin; (2) The rift margin basin is widely distributed in the south of Australia and the sea area of eastern Australia and the New Zealand. The most concentrated oil and gas accumulation in the rift basin in the study area, but the southern and eastern regions are different, the ratio of oil to gas is about 2:1 in the south margin rift basin. However, there is no hydrocarbon accumulation in the rift basin in the eastern sea because of poor hydrocarbon accumulation conditions; (3) According to the remaining recoverable reserves and prospective resource in basin, analyze the resource potential of sedimentary basins in the eastern of Australia. It is believed that the oil and gas resources in the cretaceous-paleogene rift basin and the paleogene-neogene foreland basin have the greatest potential, and the Gippsland Basin, Taranaki Basin and Papua Basin are optimized as favorable ones for hydrocarbon exploration in the southern Pacific region.
Based on regional tectonic evolution history, basin types in the southern Pacific region are classified and the petroleum geology of the major basin types is studied. The petroleum occurrences and resource potential are finally analysed in an objective to provide support for international cooperation between countries. Our studies show that:(1) The southern Pacific region underwent four stages including Hunter-Bowen orogeny, Antarctic Plate separates form the Australia Plate, the Tasman and Coral seas expending and oceanic crust subduction and arc-land collision occurred in Papua New Guinea, and formed six types of basin that is cratonic basin, rift basin, late permian-triassic foreland basin, paleogene-neogene foreland basin, paleogene-present forearc basin and the back-arc basin. The eastern inland of Australia is mainly the cratonic basin, and the southern margin and sea area of eastern Australia and the New Zealand are mainly the rift basin; (2) The rift margin basin is widely distributed in the south of Australia and the sea area of eastern Australia and the New Zealand. The most concentrated oil and gas accumulation in the rift basin in the study area, but the southern and eastern regions are different, the ratio of oil to gas is about 2:1 in the south margin rift basin. However, there is no hydrocarbon accumulation in the rift basin in the eastern sea because of poor hydrocarbon accumulation conditions; (3) According to the remaining recoverable reserves and prospective resource in basin, analyze the resource potential of sedimentary basins in the eastern of Australia. It is believed that the oil and gas resources in the cretaceous-paleogene rift basin and the paleogene-neogene foreland basin have the greatest potential, and the Gippsland Basin, Taranaki Basin and Papua Basin are optimized as favorable ones for hydrocarbon exploration in the southern Pacific region.
2019, 41(5): 97-106.
doi: 10.3969/j.issn.0253-4193.2019.05.009
Abstract:
Three dimensional seismic data were used to describe the inversion structures and their formation stage in the Songnan-Baodao Sag. Combined with tectonic settings and geodynamics of the South China Sea, the mechanism of reverse structures was discussed. The results show that the inversion structure belts of Songnan-Baodao mainly formed by a series of large fold anticline. The anticline is characterized by a raised top and a concave bottom. A series of the weak strike-slip faults which are NWW trending and the tensional shear of NNW trending structures were detected along the inversion structures belt. The inversion structures and their associated structures conform to the characteristic of NEE right shear stress field. The inversion time is consistent with the Dongsha movement. That indicates the inversion structures can be controlled by the right-lateral sliding stress field generated by the Dongsha movement in the northeast South China Sea during the Late Miocene. The inversion structures are beneficial to the reconstruction and modification of traps in the study area. In addition, it has important geological significance to understand hydrocarbon migration and redistribution in the eastern new area of Qiongdongnan Basin.
Three dimensional seismic data were used to describe the inversion structures and their formation stage in the Songnan-Baodao Sag. Combined with tectonic settings and geodynamics of the South China Sea, the mechanism of reverse structures was discussed. The results show that the inversion structure belts of Songnan-Baodao mainly formed by a series of large fold anticline. The anticline is characterized by a raised top and a concave bottom. A series of the weak strike-slip faults which are NWW trending and the tensional shear of NNW trending structures were detected along the inversion structures belt. The inversion structures and their associated structures conform to the characteristic of NEE right shear stress field. The inversion time is consistent with the Dongsha movement. That indicates the inversion structures can be controlled by the right-lateral sliding stress field generated by the Dongsha movement in the northeast South China Sea during the Late Miocene. The inversion structures are beneficial to the reconstruction and modification of traps in the study area. In addition, it has important geological significance to understand hydrocarbon migration and redistribution in the eastern new area of Qiongdongnan Basin.
2019, 41(5): 107-117.
doi: 10.3969/j.issn.0253-4193.2019.05.010
Abstract:
Sansha Yongle Blue Hole (SYBH), known as the deepest blue hole worldwide, is located in the Xisha Yongle Atoll. Due to its comparatively quiescent internal environment, SYBH has been set as a natural laboratory for understanding how different factors impact the sedimentation rate changes. The grain sizes analyses of a 24 cm long pushcore collected at the bottom of SYBH reveals that the sediments there are primarily consisted of sand with mean grain sizes varying from 22.9 to 123.9 μm. Meanwhile significant grain size coarsening is observed 0 cm, 4 cm, 9.5 cm and 21 cm, in the pushcore. We adopte CRS model of 210Pb and related analysis to calculate the age of the sediments, and find the oldest sediment was preserved in 1896, and the mean sedimentation rate is 0.19 cm/a. Sharp increases of the sedimentation rate is observed at 4 cm and 9.5 cm. We hypothesize that such increased sedimentation rate near the top pushcore, is a result of anthropogenic influences that happened in the Xisha district within the past few years. Analysis of historical typhoon records near our study area indicates six of typhoon events presumably contribute to the grain size variation in the SYBH during 1999-2001 and 2010-2011, i.e., 199902, 199915, 200110, 201002 and 201118. Thus, we can conclude that the sedimentation rate of sediment at the bottom of SYBH is mainly affected by typhoon events and there is also anthropogenic influence recently.
Sansha Yongle Blue Hole (SYBH), known as the deepest blue hole worldwide, is located in the Xisha Yongle Atoll. Due to its comparatively quiescent internal environment, SYBH has been set as a natural laboratory for understanding how different factors impact the sedimentation rate changes. The grain sizes analyses of a 24 cm long pushcore collected at the bottom of SYBH reveals that the sediments there are primarily consisted of sand with mean grain sizes varying from 22.9 to 123.9 μm. Meanwhile significant grain size coarsening is observed 0 cm, 4 cm, 9.5 cm and 21 cm, in the pushcore. We adopte CRS model of 210Pb and related analysis to calculate the age of the sediments, and find the oldest sediment was preserved in 1896, and the mean sedimentation rate is 0.19 cm/a. Sharp increases of the sedimentation rate is observed at 4 cm and 9.5 cm. We hypothesize that such increased sedimentation rate near the top pushcore, is a result of anthropogenic influences that happened in the Xisha district within the past few years. Analysis of historical typhoon records near our study area indicates six of typhoon events presumably contribute to the grain size variation in the SYBH during 1999-2001 and 2010-2011, i.e., 199902, 199915, 200110, 201002 and 201118. Thus, we can conclude that the sedimentation rate of sediment at the bottom of SYBH is mainly affected by typhoon events and there is also anthropogenic influence recently.
2019, 41(5): 118-127.
doi: 10.3969/j.issn.0253-4193.2019.05.011
Abstract:
The estuarine tidal flats are always under the influences of both river inputs and tidal currents. The morphological statuses of estuarine tidal flats are always being dynamic due to both human impacts and natural variations. The human modifications particularly show a strong influence on the short-term morphological changes and sediment characteristics in estuarine tidal flats. A huge embankment was construct in the eastern Chongming tidal flats in the Changjiang River Estuary from 2013 to 2014. Based on Terrestrial Laser Scanner system, non-ground points fitering method, sediment samples and laboratory analyses, this study aim to explore the response of morphplogy and sediment characteristics to human modification in an estuarine tidal flat. The results show that:(1) significant erosion occurs in the southern part while even though light deposition appears in the northern part, the entire tidal flat still experiences significant erosion after the completion of the embankment, with a average decrease of 4 cm in elevation; (2) the median particle size of the sediments increases from 29 μm to 38 μm after the construction; (3) after the completion of the embankment, sediment particle size in the southern part and the flat front increases while decreases in the northern part. The results indicate that human modifications would lead to severe erosion and surficial sediment coarsening, but the response of morphological changes and sediment characteristics still varies in different zones of tidal flats. This study also finds that even though it is riverine sediment input that plays a dominantly role in long-term evolution of estuarine tidal flats, human modifications could change short-term tidal flat morphodynamic processes remarkably.
The estuarine tidal flats are always under the influences of both river inputs and tidal currents. The morphological statuses of estuarine tidal flats are always being dynamic due to both human impacts and natural variations. The human modifications particularly show a strong influence on the short-term morphological changes and sediment characteristics in estuarine tidal flats. A huge embankment was construct in the eastern Chongming tidal flats in the Changjiang River Estuary from 2013 to 2014. Based on Terrestrial Laser Scanner system, non-ground points fitering method, sediment samples and laboratory analyses, this study aim to explore the response of morphplogy and sediment characteristics to human modification in an estuarine tidal flat. The results show that:(1) significant erosion occurs in the southern part while even though light deposition appears in the northern part, the entire tidal flat still experiences significant erosion after the completion of the embankment, with a average decrease of 4 cm in elevation; (2) the median particle size of the sediments increases from 29 μm to 38 μm after the construction; (3) after the completion of the embankment, sediment particle size in the southern part and the flat front increases while decreases in the northern part. The results indicate that human modifications would lead to severe erosion and surficial sediment coarsening, but the response of morphological changes and sediment characteristics still varies in different zones of tidal flats. This study also finds that even though it is riverine sediment input that plays a dominantly role in long-term evolution of estuarine tidal flats, human modifications could change short-term tidal flat morphodynamic processes remarkably.
2019, 41(5): 128-137.
doi: 10.3969/j.issn.0253-4193.2019.05.012
Abstract:
Confined groundwater discharge is a major form of submarine groundwater discharge. Because this process occurs in the bottom of seawater, detection is more difficult. To explore the detection capabilities of the marine multi-electrode resistivity method for this process, according to the typical geological model of the confined aquifer in the seabed, the geoelectric models with different drainage stages were constructed. Simulate sea surface and sea floor detection conditions, and compare the resulting resistivity profiles. The results of the study indicate that the water surface multi-electrode resistivity detection profile can clearly depict the migration and mixing process of freshwater excreted into the sea in seawater. However, the anomalous profile and resolution of the profile are affected by the detection device, electrode pole pitch, and seawater depth. Seabed surface detection results are more capable of reflecting the exchange process of brackish water in sediments, and the seawater intrusions in sediments can be well reflected.
Confined groundwater discharge is a major form of submarine groundwater discharge. Because this process occurs in the bottom of seawater, detection is more difficult. To explore the detection capabilities of the marine multi-electrode resistivity method for this process, according to the typical geological model of the confined aquifer in the seabed, the geoelectric models with different drainage stages were constructed. Simulate sea surface and sea floor detection conditions, and compare the resulting resistivity profiles. The results of the study indicate that the water surface multi-electrode resistivity detection profile can clearly depict the migration and mixing process of freshwater excreted into the sea in seawater. However, the anomalous profile and resolution of the profile are affected by the detection device, electrode pole pitch, and seawater depth. Seabed surface detection results are more capable of reflecting the exchange process of brackish water in sediments, and the seawater intrusions in sediments can be well reflected.
2019, 41(5): 138-145.
doi: 10.3969/j.issn.0253-4193.2019.05.013
Abstract:
High frequency (HF) ground wave radar is an important means of sea monitoring, HF radar routine observations of sea current have been operated for decades of years. Gaps in current data often occur due to external interferences. In order to ensure the integrity and accuracy of regional data, a back propagation (BP) neutral network interpolation model for ocean current is established by combining BP network technology and spatial interpolation. Two other interpolation methods, inverse distance weighted method and linear interpolation method, are adopted for comparison to validate the performance of the BP neutral network interpolation model. Simulations are conducted to analysis the performance of this new model in the cases of large areas of ocean current loss, large current velocity and relatively small current velocity. The results show that the prediction effect of the BP neutral network method is obviously better than the other two methods, and the new model also achieves good results in the absence of a wide range of current.
High frequency (HF) ground wave radar is an important means of sea monitoring, HF radar routine observations of sea current have been operated for decades of years. Gaps in current data often occur due to external interferences. In order to ensure the integrity and accuracy of regional data, a back propagation (BP) neutral network interpolation model for ocean current is established by combining BP network technology and spatial interpolation. Two other interpolation methods, inverse distance weighted method and linear interpolation method, are adopted for comparison to validate the performance of the BP neutral network interpolation model. Simulations are conducted to analysis the performance of this new model in the cases of large areas of ocean current loss, large current velocity and relatively small current velocity. The results show that the prediction effect of the BP neutral network method is obviously better than the other two methods, and the new model also achieves good results in the absence of a wide range of current.
2019, 41(5): 146-158.
doi: 10.3969/j.issn.0253-4193.2019.05.014
Abstract:
Oil spill is a common problem faced by marine countries, but there is still no reliable and practical method for oil slick accurate identification and quantity measurement via remote sensing technology. Based on the UAV hyperspectral imaging experiment, methods of oil spill detection and thickness estimation are studied. In the experiment, the UAV hyperspectral remote sensing and field spectral data of oil spill with different quantities are obtained in an oil spill experiment tank of large outdoor flume under the condition of simulating real marine environment. Then the feature spectral bands based oil spill detection and oil slick thickness estimation models are found. At last we get the following conclusions:(1) 675 nm and 699 nm are the effective characteristic bands of oil spill detection, however, they have no detection capability for the very thin oil slick (thickness ≤ 5 μm), (2) 3 kinds of oil slick thickness estimation models witch are Normalized Difference Oil Spill Index (NDOSI) model, inverse proportion model and absorption line height model are proposed, in which the inverse ratio model is the only choice for thin and thick(thickness>50 μm) oil slick. For the medium thickness oil slick, the NDOSI model is the best choice, and the inverse scale model and the oil spill absorption baseline height model have better inversion ability, and in cloudy weather, the inverse scale model is the best.
Oil spill is a common problem faced by marine countries, but there is still no reliable and practical method for oil slick accurate identification and quantity measurement via remote sensing technology. Based on the UAV hyperspectral imaging experiment, methods of oil spill detection and thickness estimation are studied. In the experiment, the UAV hyperspectral remote sensing and field spectral data of oil spill with different quantities are obtained in an oil spill experiment tank of large outdoor flume under the condition of simulating real marine environment. Then the feature spectral bands based oil spill detection and oil slick thickness estimation models are found. At last we get the following conclusions:(1) 675 nm and 699 nm are the effective characteristic bands of oil spill detection, however, they have no detection capability for the very thin oil slick (thickness ≤ 5 μm), (2) 3 kinds of oil slick thickness estimation models witch are Normalized Difference Oil Spill Index (NDOSI) model, inverse proportion model and absorption line height model are proposed, in which the inverse ratio model is the only choice for thin and thick(thickness>50 μm) oil slick. For the medium thickness oil slick, the NDOSI model is the best choice, and the inverse scale model and the oil spill absorption baseline height model have better inversion ability, and in cloudy weather, the inverse scale model is the best.
Email alert
RSS