2016 Vol. 38, No. 1
Display Method:
2016, 38(1): .
Abstract:
Observational study on the upper layer circulation in the southern South China Sea based on CTD data
2016, 38(1): 1-9.
doi: 10.3969/j.issn.0253-4193.2016.01.001
Abstract:
Conductivity-temperature-depth data from four cruises spanning 2009 to 2012 are used to investigate the structure of the upper layer circulation in the middle and southern South China Sea(SCS) during the monsoon transition. In the late spring,2009,the upper structures of the middle and southern SCS have begun to take the summer circulation structure and the Southeast Vietnam Offshore Current(SVOC) has been evident. In November 2010,the dynamic heights in the middle and southern SCS show that the upper structures of the middle and southern SCS have converted to the winter pattern. In this period,the SVOC has been vanished and the Natuna Off-Shelf Current(NOC) has been evident. In October 2011,the structures of the SCS were converting to the winter pattern from the summer characterized by the reductions of the SVOC,but the anticyclonic circulation in the summer pattern still existed. In September 2012,the upper structures of the middle and southern SCS have been similar to the summer pattern mainly be seen in the existed of the SVOC and the structures of the circulation were the same as the summer pattern on either sides of the SVOC. In addition,the analysis results also clearly shows the changing of the circulation of the middle and southern SCS from summer to winter.
Conductivity-temperature-depth data from four cruises spanning 2009 to 2012 are used to investigate the structure of the upper layer circulation in the middle and southern South China Sea(SCS) during the monsoon transition. In the late spring,2009,the upper structures of the middle and southern SCS have begun to take the summer circulation structure and the Southeast Vietnam Offshore Current(SVOC) has been evident. In November 2010,the dynamic heights in the middle and southern SCS show that the upper structures of the middle and southern SCS have converted to the winter pattern. In this period,the SVOC has been vanished and the Natuna Off-Shelf Current(NOC) has been evident. In October 2011,the structures of the SCS were converting to the winter pattern from the summer characterized by the reductions of the SVOC,but the anticyclonic circulation in the summer pattern still existed. In September 2012,the upper structures of the middle and southern SCS have been similar to the summer pattern mainly be seen in the existed of the SVOC and the structures of the circulation were the same as the summer pattern on either sides of the SVOC. In addition,the analysis results also clearly shows the changing of the circulation of the middle and southern SCS from summer to winter.
2016, 38(1): 10-19.
doi: 10.3969/j.issn.0253-4193.2016.01.002
Abstract:
Reanalysis precipitation datasets from Global Precipitation Climatology Project (GPCP) and evaporation datasets from WHOI OAflux project are used to evaluate the historical freshwater flux from 13 CMIP5 climate models. The results show that all models could capture the climatological space distribution while the double ITCZs are widespread and the tropical ocean is the region with most significant uncertainties among the models. Latitudinal distributions of zonal-mean freshwater and their seasonal variations are broadly captured by most of the models. But the models' results are smaller than the reanalysis data,freshwater simulation between 10°S and the equator shows significant bias because of the overestimate of freshwater in the January. On the seasonal timescale,the models show good result in the North Hemisphere,but have some deficiencies in the South Hemisphere. On the interannual timescale,the models could provide a suitable simulation of freshwater space distribution induced by ENSO,but they are deficient in simulating the temporal characteristics. Results of multi-model ensemble are superior to single model in all respects of evaluation.Tropical and sub-tropical ocean will change significant under the circumstance of global warming,where used to be dry will be drier and wet will be wetter. Spatial distribution pattern will not change markedly under different scenarios,but the amplitudes of freshwater flux and the consistency among the models will strengthen under RCP8.5 compared with the RCP4.5.
Reanalysis precipitation datasets from Global Precipitation Climatology Project (GPCP) and evaporation datasets from WHOI OAflux project are used to evaluate the historical freshwater flux from 13 CMIP5 climate models. The results show that all models could capture the climatological space distribution while the double ITCZs are widespread and the tropical ocean is the region with most significant uncertainties among the models. Latitudinal distributions of zonal-mean freshwater and their seasonal variations are broadly captured by most of the models. But the models' results are smaller than the reanalysis data,freshwater simulation between 10°S and the equator shows significant bias because of the overestimate of freshwater in the January. On the seasonal timescale,the models show good result in the North Hemisphere,but have some deficiencies in the South Hemisphere. On the interannual timescale,the models could provide a suitable simulation of freshwater space distribution induced by ENSO,but they are deficient in simulating the temporal characteristics. Results of multi-model ensemble are superior to single model in all respects of evaluation.Tropical and sub-tropical ocean will change significant under the circumstance of global warming,where used to be dry will be drier and wet will be wetter. Spatial distribution pattern will not change markedly under different scenarios,but the amplitudes of freshwater flux and the consistency among the models will strengthen under RCP8.5 compared with the RCP4.5.
2016, 38(1): 20-30.
doi: 10.3969/j.issn.0253-4193.2016.01.003
Abstract:
The sea area in the eastern part of Liaodong Bay Mouth is a key passage through which the mass and energy are exchanged between the Liaodong Bay and the central Bohai Sea. In this paper,based on the eight-month continuous observed data obtained from the seabed based platform,we firstly analyzed the characteristics of tide and tidal current,and then discussed the seasonal variation regularities of residual current and sea bottom temperature in the sea area by means of spectral and harmonic analysis. The results were shown as follows: the tide in the sea area was an irregular semi-diurnal one with the mean tidal range 0.95 m and the maximum possible tidal range 2.27 m,respectively. The tidal current was an irregular semi-diurnal one,and the M2 tidal current constituent was dominant. The motion type of the principle tidal current constituents was rectilinear,with the maximum tidal velocity in the direction of southwest-northeast. The residual current showed remarkable seasonal features. In autumn,the residual current flowed southwestward and showed a parabolic-shaped profile,with the maximum velocity observed in the mid-layer. In winter,the residual current flowed in the direction of west-southwest with little variability of velocity in vertical. In spring,the residual current,showing a cyclonic spiral,was weakened from the surface to the bottom layers. Affected by tidal current,horizontal temperature gradient in the sea bottom and diurnal variation of SST,the high-frequency variation of bottom temperature was observed in the bottom layer. In autumn,the signal of semi-diurnal period was dominant,whereas in winter the signal of diurnal period was notable. These pulses of short-term variability were considerably suppressed in spring.
The sea area in the eastern part of Liaodong Bay Mouth is a key passage through which the mass and energy are exchanged between the Liaodong Bay and the central Bohai Sea. In this paper,based on the eight-month continuous observed data obtained from the seabed based platform,we firstly analyzed the characteristics of tide and tidal current,and then discussed the seasonal variation regularities of residual current and sea bottom temperature in the sea area by means of spectral and harmonic analysis. The results were shown as follows: the tide in the sea area was an irregular semi-diurnal one with the mean tidal range 0.95 m and the maximum possible tidal range 2.27 m,respectively. The tidal current was an irregular semi-diurnal one,and the M2 tidal current constituent was dominant. The motion type of the principle tidal current constituents was rectilinear,with the maximum tidal velocity in the direction of southwest-northeast. The residual current showed remarkable seasonal features. In autumn,the residual current flowed southwestward and showed a parabolic-shaped profile,with the maximum velocity observed in the mid-layer. In winter,the residual current flowed in the direction of west-southwest with little variability of velocity in vertical. In spring,the residual current,showing a cyclonic spiral,was weakened from the surface to the bottom layers. Affected by tidal current,horizontal temperature gradient in the sea bottom and diurnal variation of SST,the high-frequency variation of bottom temperature was observed in the bottom layer. In autumn,the signal of semi-diurnal period was dominant,whereas in winter the signal of diurnal period was notable. These pulses of short-term variability were considerably suppressed in spring.
2016, 38(1): 31-45.
doi: 10.3969/j.issn.0253-4193.2016.01.004
Abstract:
Systematic observations of lateral flows and sediment transport were conducted in the 2012 flood season in a wide and shallow estuary of Huangmaohai,Pearl River. The lateral distributions of flows,salinity and sediment were identified,and the lateral dynamics and the mechanism of sediment transport were examined. Lateral flows were found to indeed occur in the estuary. A two-layer lateral residual flow developed on the west shoal and in the North Channel,a three-layer lateral residual flow developed on the top of the mouth shoal,and a lateral residual flow was directed westwards downstream of the mouth shoal. Net longitudinal sediment dispersal appeared that seaward transports occur in the deep channel,landward transports on the west shoal,and seaward transports on and downstream of the mouth shoal. Net lateral sediment transport existed that the westward transport appears on and downstream of the mouth shoal,while the westward transport occurs in the North Channel and the eastward transport on the west shoal. The reverse lateral sediment transport between the channel and the shoal resulted in the sediment convergence near the deep channel. The landward sediment fluxes on the west shoal plays an important role in the deposition of the west shoal. The mean lateral momentum balance showed that a clockwise lateral residual circulation (looking landwards) is controlled by the interaction between Coriolis effect and lateral baroclinic forcing. Lateral advection influences greatly the lateral dynamics,which has been regarded to be unimportant. The mechanism decomposition of lateral sediment fluxes over a tidal cycle showed that the lateral sediment transport is driven mainly by the Eulerian advection and tidal pumping.
Systematic observations of lateral flows and sediment transport were conducted in the 2012 flood season in a wide and shallow estuary of Huangmaohai,Pearl River. The lateral distributions of flows,salinity and sediment were identified,and the lateral dynamics and the mechanism of sediment transport were examined. Lateral flows were found to indeed occur in the estuary. A two-layer lateral residual flow developed on the west shoal and in the North Channel,a three-layer lateral residual flow developed on the top of the mouth shoal,and a lateral residual flow was directed westwards downstream of the mouth shoal. Net longitudinal sediment dispersal appeared that seaward transports occur in the deep channel,landward transports on the west shoal,and seaward transports on and downstream of the mouth shoal. Net lateral sediment transport existed that the westward transport appears on and downstream of the mouth shoal,while the westward transport occurs in the North Channel and the eastward transport on the west shoal. The reverse lateral sediment transport between the channel and the shoal resulted in the sediment convergence near the deep channel. The landward sediment fluxes on the west shoal plays an important role in the deposition of the west shoal. The mean lateral momentum balance showed that a clockwise lateral residual circulation (looking landwards) is controlled by the interaction between Coriolis effect and lateral baroclinic forcing. Lateral advection influences greatly the lateral dynamics,which has been regarded to be unimportant. The mechanism decomposition of lateral sediment fluxes over a tidal cycle showed that the lateral sediment transport is driven mainly by the Eulerian advection and tidal pumping.
2016, 38(1): 56-68.
doi: 10.3969/j.issn.0253-4193.2016.01.006
Abstract:
Influence of annual cycle on the local air-sea processes during El Niño events is investigated based on the Hadley Centre (HadISST1) sea surface temperature (SST) analysis data,10 m wind data from the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-40 reanalysis and the CMAP precipitation data. In the observation,SST anomalies associated with El Niño over the equatorial eastern Pacific are meridionally quasi-symmetric about the equator. However,corresponding atmospheric responses display a strong southward movement during the El Niño decaying phase. During the El Niño developing phase (largely before November),almost meridionally symmetric zonal wind and precipitation anomalies are observed over the equatorial central Pacific. After the El Niño peak month (about December),the equatorial westerly and precipitation anomalies shift rapidly southward with a center at about 5°S. Then the zonal wind anomalies stay there till the El Niño's termination. Meanwhile,negative precipitation and anticyclonic anomalies over the western Pacific shift northward. The inconsistence of the meridional movements of the El Niño SST anomalies and the associated atmospheric responses is mainly due to seasonally southward displacement of background warm SSTs along with the seasonal march of solar insolation. There is nonlinear relationship between convection and overall SST. That is,convective precipitation will be rapidly enhanced when total SST exceeds a certain threshold. Thus the corresponding convection anomalies are also displaced southward along with the southward shift of the SST and the zonal wind anomaly also appears south of the equator. In addition,the precipitation over northern hemisphere will be further suppressed due to the enhanced convection in southern hemisphere trough the meridional circulation,which can enhance the negative rainfall and anticyclone anomalies in the western Pacific and move northward. These observed analyses are supported by two experiments with and without considering the annual cycle. Southward shifts of the westerly anomalies and anticyclonic anomalies over the western North Pacific during the El Niño decaying phase are well simulated by the experiment with the annual cycle. However,these observed phenomena are not reproduced by the experiment without consideration of the annual cycle. Therefore,the annual cycle of climatological warm SSTs over the central Pacific plays a crucial role on the local atmospheric responses during the El Niño events.
Influence of annual cycle on the local air-sea processes during El Niño events is investigated based on the Hadley Centre (HadISST1) sea surface temperature (SST) analysis data,10 m wind data from the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-40 reanalysis and the CMAP precipitation data. In the observation,SST anomalies associated with El Niño over the equatorial eastern Pacific are meridionally quasi-symmetric about the equator. However,corresponding atmospheric responses display a strong southward movement during the El Niño decaying phase. During the El Niño developing phase (largely before November),almost meridionally symmetric zonal wind and precipitation anomalies are observed over the equatorial central Pacific. After the El Niño peak month (about December),the equatorial westerly and precipitation anomalies shift rapidly southward with a center at about 5°S. Then the zonal wind anomalies stay there till the El Niño's termination. Meanwhile,negative precipitation and anticyclonic anomalies over the western Pacific shift northward. The inconsistence of the meridional movements of the El Niño SST anomalies and the associated atmospheric responses is mainly due to seasonally southward displacement of background warm SSTs along with the seasonal march of solar insolation. There is nonlinear relationship between convection and overall SST. That is,convective precipitation will be rapidly enhanced when total SST exceeds a certain threshold. Thus the corresponding convection anomalies are also displaced southward along with the southward shift of the SST and the zonal wind anomaly also appears south of the equator. In addition,the precipitation over northern hemisphere will be further suppressed due to the enhanced convection in southern hemisphere trough the meridional circulation,which can enhance the negative rainfall and anticyclone anomalies in the western Pacific and move northward. These observed analyses are supported by two experiments with and without considering the annual cycle. Southward shifts of the westerly anomalies and anticyclonic anomalies over the western North Pacific during the El Niño decaying phase are well simulated by the experiment with the annual cycle. However,these observed phenomena are not reproduced by the experiment without consideration of the annual cycle. Therefore,the annual cycle of climatological warm SSTs over the central Pacific plays a crucial role on the local atmospheric responses during the El Niño events.
2016, 38(1): 69-81.
doi: 10.3969/j.issn.0253-4193.2016.01.007
Abstract:
Synthetic aperture radar (SAR),a sensor with all weather and day and night working capacity,has been widely considered as a powerful tool for sea surface oil spill detection. However,lookalikes frequently appear in SAR images,limiting the performance of SAR to detect oil spilled at sea. Thus it is important to study how to effectively differentiate oil spill from lookalike. By using Object-based Image Analysis (OBIA),a number of oil spill and lookalike samples are extracted from 20 scenes of ENVISAT ASAR images. The object-based geometric,physical and textural features of the samples are analyzed with the objective of determining the best feature variables for oil spill and lookalike separation. The conclusions derived from feature analysis are utilized for the construction of an FL-based oil spill classifier. The proposed method can effectively single out oil spill from lookalike,giving the crisp probability of a dark segment being oil spill at the same time. Oil spill detection experiment indicates that our method can produce satisfactory result.
Synthetic aperture radar (SAR),a sensor with all weather and day and night working capacity,has been widely considered as a powerful tool for sea surface oil spill detection. However,lookalikes frequently appear in SAR images,limiting the performance of SAR to detect oil spilled at sea. Thus it is important to study how to effectively differentiate oil spill from lookalike. By using Object-based Image Analysis (OBIA),a number of oil spill and lookalike samples are extracted from 20 scenes of ENVISAT ASAR images. The object-based geometric,physical and textural features of the samples are analyzed with the objective of determining the best feature variables for oil spill and lookalike separation. The conclusions derived from feature analysis are utilized for the construction of an FL-based oil spill classifier. The proposed method can effectively single out oil spill from lookalike,giving the crisp probability of a dark segment being oil spill at the same time. Oil spill detection experiment indicates that our method can produce satisfactory result.
2016, 38(1): 82-93.
doi: 10.3969/j.issn.0253-4193.2016.01.008
Abstract:
The concentration and composition of suspended particulate matter (SPM) of the water samples,which were obtained in the northern of Bering Sea during the 4th Chinese Arctic Research Expedition,were measured to understand the distribution and origin of the SPM. The results showed that the concentration of the SPM was higher in the bottom water and lower in the surface. The surface highest SPM regions were in the west of the Bering Strait and the east of Bering Continental Shelf off the Alaska coast,while the bottom highest SPM regions were in the west of Bering Strait and the southwest of Bering Continental Shelf. The resuspension of bottom material by the shelf currents was the main reason of the higher concentration of the SPM in the bottom water. Bering Slope Current and Anadyr Current transported SPM northward,and Bering Slope Current also controlled the concentration of SPM along the shelf break zone. The concentration of SPM in bottom water decreased from south to north gradually. In the northwest of the St. Lawrence Island and off the Chukchi Peninsula,the SPM is mainly composed of diatoms,while in the east part of the Bering Sea where is also controlled by Alaskan Coastal Current the SPM is mainly composed of terrigenous clastic mineral.
The concentration and composition of suspended particulate matter (SPM) of the water samples,which were obtained in the northern of Bering Sea during the 4th Chinese Arctic Research Expedition,were measured to understand the distribution and origin of the SPM. The results showed that the concentration of the SPM was higher in the bottom water and lower in the surface. The surface highest SPM regions were in the west of the Bering Strait and the east of Bering Continental Shelf off the Alaska coast,while the bottom highest SPM regions were in the west of Bering Strait and the southwest of Bering Continental Shelf. The resuspension of bottom material by the shelf currents was the main reason of the higher concentration of the SPM in the bottom water. Bering Slope Current and Anadyr Current transported SPM northward,and Bering Slope Current also controlled the concentration of SPM along the shelf break zone. The concentration of SPM in bottom water decreased from south to north gradually. In the northwest of the St. Lawrence Island and off the Chukchi Peninsula,the SPM is mainly composed of diatoms,while in the east part of the Bering Sea where is also controlled by Alaskan Coastal Current the SPM is mainly composed of terrigenous clastic mineral.
2016, 38(1): 94-105.
doi: 10.3969/j.issn.0253-4193.2016.01.009
Abstract:
Surface sediment samples were collected from the lagoon of Xincun,Hainan Island in China during August 2013,investigating grain size distribution pattern and sediment types. Furthermore,modern sedimentary environment can be well classified by grain size parameters,water depth and hydrodynamic conditions using system cluster and principal component analysis (PCA). The result indicates that sediment samples are characterized by silt and silty sand,which distribute in the central lagoon and near-shore shallow water area,respectively. The mean grain size varies from 0 to 8 Ф,with an average value of 4.6 Ф. The silt has the highest content with 52% in average,and the average content of sand and clay is 43% and 5%. A significant relationship was found between the mean grain size and water depth,which suggested that surface sediment becomes finer gradually with increasing water depth. There are two groups based on cluster analysis of grain size data: the mean grain size of group 1 is more than 5.5 Ф,with an average value of 6.8 Ф,whereas the mean grain size of group 2 is composed of less than 3.5 Ф,with an average value of 2.2 Ф. Furthermore,there are also two different relationships between the mean grain size and sorting/skewness/kurtosis. The average value of root mean square velocity (RMSV) is 7.5 cm/s and 6.9 cm/s during spring and neap tide; standard deviation is 15.3 cm/s and 14.9 cm/s,respectively. There is a significant positive relationship between very fine sand fraction (63 to 125 μm) and RMSV when RMSV>4 cm/s. The results suggested that RMSV determines the variability of very fine sand fraction in the lagoon. System cluster and PCA were used to identify the proper grain size parameters associated with mean grain size,kurtosis,and sorting. Therefore,the modern sedimentary environment can be well classified into three types using mean grain size,kurtosis,sorting,high-spatial resolution RMSV and water depth. In particular,the results suggest the importance of proper grain size parameters and high-spatial resolution hydrodynamic data in differentiate the coastal sedimentary environments.
Surface sediment samples were collected from the lagoon of Xincun,Hainan Island in China during August 2013,investigating grain size distribution pattern and sediment types. Furthermore,modern sedimentary environment can be well classified by grain size parameters,water depth and hydrodynamic conditions using system cluster and principal component analysis (PCA). The result indicates that sediment samples are characterized by silt and silty sand,which distribute in the central lagoon and near-shore shallow water area,respectively. The mean grain size varies from 0 to 8 Ф,with an average value of 4.6 Ф. The silt has the highest content with 52% in average,and the average content of sand and clay is 43% and 5%. A significant relationship was found between the mean grain size and water depth,which suggested that surface sediment becomes finer gradually with increasing water depth. There are two groups based on cluster analysis of grain size data: the mean grain size of group 1 is more than 5.5 Ф,with an average value of 6.8 Ф,whereas the mean grain size of group 2 is composed of less than 3.5 Ф,with an average value of 2.2 Ф. Furthermore,there are also two different relationships between the mean grain size and sorting/skewness/kurtosis. The average value of root mean square velocity (RMSV) is 7.5 cm/s and 6.9 cm/s during spring and neap tide; standard deviation is 15.3 cm/s and 14.9 cm/s,respectively. There is a significant positive relationship between very fine sand fraction (63 to 125 μm) and RMSV when RMSV>4 cm/s. The results suggested that RMSV determines the variability of very fine sand fraction in the lagoon. System cluster and PCA were used to identify the proper grain size parameters associated with mean grain size,kurtosis,and sorting. Therefore,the modern sedimentary environment can be well classified into three types using mean grain size,kurtosis,sorting,high-spatial resolution RMSV and water depth. In particular,the results suggest the importance of proper grain size parameters and high-spatial resolution hydrodynamic data in differentiate the coastal sedimentary environments.
2016, 38(1): 106-115.
doi: 10.3969/j.issn.0253-4193.2016.01.010
Abstract:
Tidal creek system,one of the most particular geomorphology units in muddy flat,is widely developed on central Jiangsu coast. This paper focuses on their evolutionary process in response to reclamation activities using TM/ETM+data of 2001-2013 and field investigation. The watershed area of tidal creeks decreased from 293.94 km2 in 2001 to 103.40 km2 in 2013 following sequential reclamation,which caused the decreasing of tidal creeks' length with power function and tidal creeks' width with exponential function. The average change rate of tidal creeks' length and width was 2.60 km and 0.67 m with 1 km2 reclamation. The drainage pattern of tidal flat was changed from tidal creeks to beach,which implied that the tidal creeks systems in study area have a retrograde and demise tendency. The fractal dimension value D of each single tidal creeks and tidal creek systems were calculated from box-counting method. Results of calculation and analysis indicated that the fractal dimension value D in the region is greater than that of each tidal creek systems,followed by each single tidal creek. The fractal dimension value D in the region is positively correlated with the bifurcation ratio of tidal creek systems,and decreased from 1.26 in 2001 to 1.13 in 2013 with influences of reclamation. The fractal dimension value D of single tidal creek is positively correlated with the meandering of tidal creek. According to the retrograde and demise process of tidal creeks studied the results suggested that the tidal creek inheriting the runoff from land was the earliest tidal creeks,followed by the tidal creek scoured by the currents on tidal flat and tidal creek scoured by the converged tidal currents,whose primary form could be eroded indentation.
Tidal creek system,one of the most particular geomorphology units in muddy flat,is widely developed on central Jiangsu coast. This paper focuses on their evolutionary process in response to reclamation activities using TM/ETM+data of 2001-2013 and field investigation. The watershed area of tidal creeks decreased from 293.94 km2 in 2001 to 103.40 km2 in 2013 following sequential reclamation,which caused the decreasing of tidal creeks' length with power function and tidal creeks' width with exponential function. The average change rate of tidal creeks' length and width was 2.60 km and 0.67 m with 1 km2 reclamation. The drainage pattern of tidal flat was changed from tidal creeks to beach,which implied that the tidal creeks systems in study area have a retrograde and demise tendency. The fractal dimension value D of each single tidal creeks and tidal creek systems were calculated from box-counting method. Results of calculation and analysis indicated that the fractal dimension value D in the region is greater than that of each tidal creek systems,followed by each single tidal creek. The fractal dimension value D in the region is positively correlated with the bifurcation ratio of tidal creek systems,and decreased from 1.26 in 2001 to 1.13 in 2013 with influences of reclamation. The fractal dimension value D of single tidal creek is positively correlated with the meandering of tidal creek. According to the retrograde and demise process of tidal creeks studied the results suggested that the tidal creek inheriting the runoff from land was the earliest tidal creeks,followed by the tidal creek scoured by the currents on tidal flat and tidal creek scoured by the converged tidal currents,whose primary form could be eroded indentation.
2016, 38(1): 116-123.
doi: 10.3969/j.issn.0253-4193.2016.01.011
Abstract:
In the sea-floor sediments velocity prediction,there exist many problems according to the empirical equations,such as poor accuracy,the narrow scope of application,lack of exact physical meaning. Based on the existing BP neural network,genetic algorithm (GA) is used to optimize the initial weights and threshold. A sea-floor sediment sound velocity forecasting model is established with the relationship of water content,porosity and velocity. Measurement data of study samples from the southern South China Sea are applied. These data are divided into two parts,120 groups including continental shelf,slope,trough samples selected as the training data,the other 6 groups as test data. Experiments show that BP neural network based on GA is superior to the traditional single-parameter,double-parameter sound velocity forecasting empirical equation,which is recommended for the forecasting sound velocity of sea-floor sediments. This GA-BP method has certain scientific basis and broad application prospects in the future,can provide reference for the establishment of the accurate,uniform model.
In the sea-floor sediments velocity prediction,there exist many problems according to the empirical equations,such as poor accuracy,the narrow scope of application,lack of exact physical meaning. Based on the existing BP neural network,genetic algorithm (GA) is used to optimize the initial weights and threshold. A sea-floor sediment sound velocity forecasting model is established with the relationship of water content,porosity and velocity. Measurement data of study samples from the southern South China Sea are applied. These data are divided into two parts,120 groups including continental shelf,slope,trough samples selected as the training data,the other 6 groups as test data. Experiments show that BP neural network based on GA is superior to the traditional single-parameter,double-parameter sound velocity forecasting empirical equation,which is recommended for the forecasting sound velocity of sea-floor sediments. This GA-BP method has certain scientific basis and broad application prospects in the future,can provide reference for the establishment of the accurate,uniform model.
2016, 38(1): 124-132.
doi: 10.3969/j.issn.0253-4193.2016.01.012
Abstract:
In order to monitor the landslide which may occur in island effectively and find the induction factor of landslide to achieve the purpose of monitoring and preventing landslide hazard,we describe the compositions and monitoring projects of landslide monitoring system used in Shanhou Village of the northern Changshan Island. The monitoring system contains 4 different methods. By analyzing the 4 different methods we find that 3D laser scanning data is intensive in the lower part of landslide and UAV remote sensing data is intensive in the upper part of landslide. We should choose the dense data to compute the excavation volume and slippage of landslide in different period accurately. Displacement sensor can get real-time landslide slip data. Research also finds that the quarrying and rainfall are the two most important factors causing Shanhou Village landslide slip,quarrying decreases the whole volume of landslid and rainfall leads to landslide tensile and gravel slump. In the end,because of the limitation of monitoring area,the monitoring system can only monitor the surface deformation of the landslide. Research results can provide references for landslide monitoring and early warning in other islands.
In order to monitor the landslide which may occur in island effectively and find the induction factor of landslide to achieve the purpose of monitoring and preventing landslide hazard,we describe the compositions and monitoring projects of landslide monitoring system used in Shanhou Village of the northern Changshan Island. The monitoring system contains 4 different methods. By analyzing the 4 different methods we find that 3D laser scanning data is intensive in the lower part of landslide and UAV remote sensing data is intensive in the upper part of landslide. We should choose the dense data to compute the excavation volume and slippage of landslide in different period accurately. Displacement sensor can get real-time landslide slip data. Research also finds that the quarrying and rainfall are the two most important factors causing Shanhou Village landslide slip,quarrying decreases the whole volume of landslid and rainfall leads to landslide tensile and gravel slump. In the end,because of the limitation of monitoring area,the monitoring system can only monitor the surface deformation of the landslide. Research results can provide references for landslide monitoring and early warning in other islands.
2016, 38(1): 133-142.
doi: 10.3969/j.issn.0253-4193.2016.01.013
Abstract:
Regular wave propagation on 3-D local permeable seabed is studied by higher-order boundary element method based on the linear potential flow theory. The control equation of permeable seabed is derived from the Darcy law. The boundary condition on the permeable seabed's surface is developed by the continuous conditions of normal velocity and pressure on the interface between permeable seabed and water. The boundary integral equations,which can be solved to obtain the diffraction potentials of permeable seabed,are established by the adoption of wave Green function based on the theory of wave diffraction. Then,when wave pass through the permeable seabed,the diffraction potentials of free surface and the variation of wave amplitude can be calculated after solving the boundary integral equations by higher-order boundary element method. The validity and effectiveness of the present frequency domain method is verified by the results comparison with time domain method,in that case the wave diffractions on cylindrical hump seabed are considered. The characteristic of wave propagation on 3-D local rectangular permeable seabed is investigated by the present numerical method,and the effects of parameters such as wave length and the porosity parameter are discussed further.
Regular wave propagation on 3-D local permeable seabed is studied by higher-order boundary element method based on the linear potential flow theory. The control equation of permeable seabed is derived from the Darcy law. The boundary condition on the permeable seabed's surface is developed by the continuous conditions of normal velocity and pressure on the interface between permeable seabed and water. The boundary integral equations,which can be solved to obtain the diffraction potentials of permeable seabed,are established by the adoption of wave Green function based on the theory of wave diffraction. Then,when wave pass through the permeable seabed,the diffraction potentials of free surface and the variation of wave amplitude can be calculated after solving the boundary integral equations by higher-order boundary element method. The validity and effectiveness of the present frequency domain method is verified by the results comparison with time domain method,in that case the wave diffractions on cylindrical hump seabed are considered. The characteristic of wave propagation on 3-D local rectangular permeable seabed is investigated by the present numerical method,and the effects of parameters such as wave length and the porosity parameter are discussed further.
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