2020 Vol. 42, No. 3
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2020, 42(3): .
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2020, 42(3): .
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2020, 42(3): 1-9.
doi: 10.3969/j.issn.0253-4193.2020.03.001
Abstract:
Based on the direct turbulence observations in the Bohai Sea during September 2017, this study investigates the spatial distribution of turbulent mixing in the Bohai Sea and the associated influencing factors. The water column was weakly stratified during the observation period. As influenced by the freshwater input from Yellow River, relatively warm and fresh water was found in the Laizhou Bay. The typical south-north dual-core cold bottom water structure still exited in the central Bohai Sea during the observation period. The observed turbulent kinetic energy (TKE) dissipation rate ε ranged from 10−9 to 10−5 W/kg and statistically satisfied the lognormal distribution. Intensified mixing was found at the nearshore region of the Liaodong Bay and the Bohai Bay. The corresponding vertical eddy diffusivity was about 10−6～10−2 m2/s. In the vertical direct direction, strong mixing occurred near the sea surface and bottom layers. Further analysis shows that the station-averaged TKE dissipation rate are positively related to the wind speed and barotropic tidal velocity. On the other hand, the dissipation rate and buoyancy frequency N satisfied the power function relationship of\begin{document}$\varepsilon = 2.0 \times {10^{ - 8}} + 3.0 \times {10^{ - 7}}{({N^2}/N_0^2)^{ - 5}}$\end{document} ![]()
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Based on the direct turbulence observations in the Bohai Sea during September 2017, this study investigates the spatial distribution of turbulent mixing in the Bohai Sea and the associated influencing factors. The water column was weakly stratified during the observation period. As influenced by the freshwater input from Yellow River, relatively warm and fresh water was found in the Laizhou Bay. The typical south-north dual-core cold bottom water structure still exited in the central Bohai Sea during the observation period. The observed turbulent kinetic energy (TKE) dissipation rate ε ranged from 10−9 to 10−5 W/kg and statistically satisfied the lognormal distribution. Intensified mixing was found at the nearshore region of the Liaodong Bay and the Bohai Bay. The corresponding vertical eddy diffusivity was about 10−6～10−2 m2/s. In the vertical direct direction, strong mixing occurred near the sea surface and bottom layers. Further analysis shows that the station-averaged TKE dissipation rate are positively related to the wind speed and barotropic tidal velocity. On the other hand, the dissipation rate and buoyancy frequency N satisfied the power function relationship of
2020, 42(3): 10-24.
doi: 10.3969/j.issn.0253-4193.2020.03.002
Abstract:
As a new type of coastal ecological protection measure, ecological buffer zone formed by woody plants in coastal areas has attracted more and more attention in coastal engineering projects. It is an urgent problem to be solved that how to carry out the research on the protection effect of woody plants. The numerical simulation method is used in this paper. Firstly, a theoretical model of surface wave attenuation for wave climbing along a slope under the protection of woody vegetation is proposed by including the drag forces of branches and trunks in the N-S equation. Next, the MAC method is used to track the trajectories of water particles on the free surface. Then, taking the wave climbing along a slope of 1/30 as an example, the wave propagation process along an inclined beach with or without vegetation is discussed. The validity of the numerical model is verified by comparing the numerical result and those of the previous experiments. Finally, influences of the vegetation characteristics, such as height, density and tilt angle of plant branches and those of wave factors on wave dissipation are discussed and analyzed, respectively. Additionally, the rules of wave dissipation are summarized. The calculation results of this model can also be applicable to the design of revetment structures and ecological landscape.
As a new type of coastal ecological protection measure, ecological buffer zone formed by woody plants in coastal areas has attracted more and more attention in coastal engineering projects. It is an urgent problem to be solved that how to carry out the research on the protection effect of woody plants. The numerical simulation method is used in this paper. Firstly, a theoretical model of surface wave attenuation for wave climbing along a slope under the protection of woody vegetation is proposed by including the drag forces of branches and trunks in the N-S equation. Next, the MAC method is used to track the trajectories of water particles on the free surface. Then, taking the wave climbing along a slope of 1/30 as an example, the wave propagation process along an inclined beach with or without vegetation is discussed. The validity of the numerical model is verified by comparing the numerical result and those of the previous experiments. Finally, influences of the vegetation characteristics, such as height, density and tilt angle of plant branches and those of wave factors on wave dissipation are discussed and analyzed, respectively. Additionally, the rules of wave dissipation are summarized. The calculation results of this model can also be applicable to the design of revetment structures and ecological landscape.
2020, 42(3): 25-35.
doi: 10.3969/j.issn.0253-4193.2020.03.003
Abstract:
As tidal waves propagate into the estuary, they are featured by significant longitudinal variation in seasonal scale due to the nonlinear interactions between tide and river discharge. In this study, the variations of tide-river dynamics in terms of tidal damping rate, wave celerity and residual water level slope were explored based on long-term time series of tidal water levels from 2002 to 2014 along the tidal reach of the Changjiang River (including the Tianshenggang, Jiangyin, Zhenjiang, Nanjing, Maanshan and Wuhu stations) in together with the monthly averaged river discharge observed at Datong hydrological stations. Subsequently, the underlying controlled factors that influence the tidal wave propagation were discussed. It was shown that the seasonal difference in tide-river dynamics was gradually reduced in the seaward direction. We identified a transitional zone located between the Tianshenggang and Jiangyin stations, where the seasonal differences in tidal range are 0.01 m and −0.04 m, respectively. Generally, upstream from Jiangyin Station the dynamics character was river-dominated, while in the lower reaches it was mainly controlled by the tidal forcing. In addition, we show that there exists a threshold in river discharge in the upper reaches of the tidal reach of the Changjiang River due to the increase of residual water level and hence water depth caused by the residual water level slope. This phenomenon was particularly true in the upstream reach between Maanshan to Wuhu stations, where the threshold of river discharge was approximately 33 000 m3/s. The results obtained from this study can enhance our understanding of tide-river interaction, and will, hopefully, provide guidelines for water resources management in the tidal reach of the Changjiang River.
As tidal waves propagate into the estuary, they are featured by significant longitudinal variation in seasonal scale due to the nonlinear interactions between tide and river discharge. In this study, the variations of tide-river dynamics in terms of tidal damping rate, wave celerity and residual water level slope were explored based on long-term time series of tidal water levels from 2002 to 2014 along the tidal reach of the Changjiang River (including the Tianshenggang, Jiangyin, Zhenjiang, Nanjing, Maanshan and Wuhu stations) in together with the monthly averaged river discharge observed at Datong hydrological stations. Subsequently, the underlying controlled factors that influence the tidal wave propagation were discussed. It was shown that the seasonal difference in tide-river dynamics was gradually reduced in the seaward direction. We identified a transitional zone located between the Tianshenggang and Jiangyin stations, where the seasonal differences in tidal range are 0.01 m and −0.04 m, respectively. Generally, upstream from Jiangyin Station the dynamics character was river-dominated, while in the lower reaches it was mainly controlled by the tidal forcing. In addition, we show that there exists a threshold in river discharge in the upper reaches of the tidal reach of the Changjiang River due to the increase of residual water level and hence water depth caused by the residual water level slope. This phenomenon was particularly true in the upstream reach between Maanshan to Wuhu stations, where the threshold of river discharge was approximately 33 000 m3/s. The results obtained from this study can enhance our understanding of tide-river interaction, and will, hopefully, provide guidelines for water resources management in the tidal reach of the Changjiang River.
2020, 42(3): 36-46.
doi: 10.3969/j.issn.0253-4193.2020.03.004
Abstract:
Using the ECMWF ORAS4 reconstruction data, the different response characteristics of the South China Sea Sea Level Anomaly (SLA) to the Eastern Pacific (EP) El Niño and the Central Pacific (CP) El Niño were analyzed. The South China Sea SLA showed different spatial and temporal evolution during the two types of El Niño. For the EP El Niño, the average SLA in the South China Sea decreased significantly in the autumn and winter of the developing year, with a minimum of −2 cm, and began to rise in the following year, up to 2 cm in the following winter. In terms of spatial distribution, in the autumn and winter of developing year, except for the existence of a positive anomaly to the southeast of Vietnam, in most of the South China Sea, SLAs are characterized by significant negative anomalies; from the spring of the following year, SLA negatively weakens, while the southeastern part of Vietnam was beginning to develop abnormally until the majority of the South China Sea is dominated by positive anomalies. For the CP El Niño, the South China Sea SLA showed significant negative anomalies throughout the El Niño development and decline, the outliers were always maintained at around −2 cm, and spatially represented as a consistent negative anomaly of the whole basin. Compared with the traditional empirical orthogonal decomposition (EOF), the seasonal EOF (S-EOF) can better characterize the temporal and spatial evolution of the South China Sea SLA during the two types of El Niño. The first mode of the S-EOF is CP El Niño mode, while the second mode is more characterized by the evolution of the South China Sea SLA during the EP El Niño. The different variations of the South China Sea SLA during the two types of El Niño are mainly due to the thermal specific volume effect caused by the thermal advection transport anomaly at the channel, but the contribution of the thermosteric sea level is mainly concentrated in the interior South China Sea. While in the coastal regions, such as the western South China Sea, the mechanism of sea level change needs further study.
Using the ECMWF ORAS4 reconstruction data, the different response characteristics of the South China Sea Sea Level Anomaly (SLA) to the Eastern Pacific (EP) El Niño and the Central Pacific (CP) El Niño were analyzed. The South China Sea SLA showed different spatial and temporal evolution during the two types of El Niño. For the EP El Niño, the average SLA in the South China Sea decreased significantly in the autumn and winter of the developing year, with a minimum of −2 cm, and began to rise in the following year, up to 2 cm in the following winter. In terms of spatial distribution, in the autumn and winter of developing year, except for the existence of a positive anomaly to the southeast of Vietnam, in most of the South China Sea, SLAs are characterized by significant negative anomalies; from the spring of the following year, SLA negatively weakens, while the southeastern part of Vietnam was beginning to develop abnormally until the majority of the South China Sea is dominated by positive anomalies. For the CP El Niño, the South China Sea SLA showed significant negative anomalies throughout the El Niño development and decline, the outliers were always maintained at around −2 cm, and spatially represented as a consistent negative anomaly of the whole basin. Compared with the traditional empirical orthogonal decomposition (EOF), the seasonal EOF (S-EOF) can better characterize the temporal and spatial evolution of the South China Sea SLA during the two types of El Niño. The first mode of the S-EOF is CP El Niño mode, while the second mode is more characterized by the evolution of the South China Sea SLA during the EP El Niño. The different variations of the South China Sea SLA during the two types of El Niño are mainly due to the thermal specific volume effect caused by the thermal advection transport anomaly at the channel, but the contribution of the thermosteric sea level is mainly concentrated in the interior South China Sea. While in the coastal regions, such as the western South China Sea, the mechanism of sea level change needs further study.
2020, 42(3): 47-58.
doi: 10.3969/j.issn.0253-4193.2020.03.005
Abstract:
Salinity linear trends and their contributed dynamics processes in the tropical Pacific Ocean were investigated with the Argo salinity and temperature fields, current assimilations and atmospheric reanalysis datasets. The robust salinity anomaly event (SAE) occurred in the tropical Pacific Ocean during 2015−2017, which resulted possibly in the reversing of Argo salinity long-term trends. Such SAE was characterized as distinct regional discrepancies and vertical structures. Significant surface freshening occurred in the northern tropical Pacific (NTP) and Southern Ocean Convergence Zone (SPCZ), whose remarkable freshening maximum could reach 0.71−0.92 and covered the upper mixed layer. Another subsurface salinification in the southern tropical Pacific (STP) with the maximum of 0.46 was found around thermocline layer. Moreover, the salinity anomalies in SAE can expand from west to east along the isopycnal layers. Salinity advection and entrainment were exhibited as the fundamental dynamic processes to the SAE event in the tropical Pacific Ocean, while advection term acted as the major contribution to salinity variability. Both of the dynamic factors played important role on SAE features during the whole event in the NTP and later period in the SPCZ and STP. The surface freshwater flux and subsurface mixing induce by density compensation were also supplements to the SAE events in the NTP freshening and STP salinification respectively.
Salinity linear trends and their contributed dynamics processes in the tropical Pacific Ocean were investigated with the Argo salinity and temperature fields, current assimilations and atmospheric reanalysis datasets. The robust salinity anomaly event (SAE) occurred in the tropical Pacific Ocean during 2015−2017, which resulted possibly in the reversing of Argo salinity long-term trends. Such SAE was characterized as distinct regional discrepancies and vertical structures. Significant surface freshening occurred in the northern tropical Pacific (NTP) and Southern Ocean Convergence Zone (SPCZ), whose remarkable freshening maximum could reach 0.71−0.92 and covered the upper mixed layer. Another subsurface salinification in the southern tropical Pacific (STP) with the maximum of 0.46 was found around thermocline layer. Moreover, the salinity anomalies in SAE can expand from west to east along the isopycnal layers. Salinity advection and entrainment were exhibited as the fundamental dynamic processes to the SAE event in the tropical Pacific Ocean, while advection term acted as the major contribution to salinity variability. Both of the dynamic factors played important role on SAE features during the whole event in the NTP and later period in the SPCZ and STP. The surface freshwater flux and subsurface mixing induce by density compensation were also supplements to the SAE events in the NTP freshening and STP salinification respectively.
2020, 42(3): 59-71.
doi: 10.3969/j.issn.0253-4193.2020.03.006
Abstract:
To recognize the environmental effects on underwater acoustic localization in deep sea and improve the measurement system performance against environmental variations, an simulation method for localization performance evaluation under different oceanographic conditions was presented, in which the sound filed calculation, error propagation and crossing solution were integrated by modelling, and the effects of seasonal environmental variation on localization performance were discussed in the case of Western Pacific. According to simulation results, when the receiving depth was near the surface, the sound channel showed different models in summer and winter, such that the accuracy was worse in summer influnced by seasonal thermocline and better in winter influnced by surface duct, the difference of root mean square error (RMSE) beyond 50 m; when the receiving depth was in the upper ocean, the localization performance had an obviously seasonal change caused by the active range of direct wave, and the accuracy was better in winter than that in summer, the difference of RMSE was 15−20 m; when the receiving depth was near the bottom, the better accuracy was obtained using reliable acoustic path, and the localization performance had little change with season. This work indicates that the seasonal environmental variation induces differences in the sound channel as well as the arrival acoustic information, the error propagation and crossing solution for the localization in the half convergence zone area of deep sea, then exert significant effects on localization performance as the receiving depth in the upper ocean.
To recognize the environmental effects on underwater acoustic localization in deep sea and improve the measurement system performance against environmental variations, an simulation method for localization performance evaluation under different oceanographic conditions was presented, in which the sound filed calculation, error propagation and crossing solution were integrated by modelling, and the effects of seasonal environmental variation on localization performance were discussed in the case of Western Pacific. According to simulation results, when the receiving depth was near the surface, the sound channel showed different models in summer and winter, such that the accuracy was worse in summer influnced by seasonal thermocline and better in winter influnced by surface duct, the difference of root mean square error (RMSE) beyond 50 m; when the receiving depth was in the upper ocean, the localization performance had an obviously seasonal change caused by the active range of direct wave, and the accuracy was better in winter than that in summer, the difference of RMSE was 15−20 m; when the receiving depth was near the bottom, the better accuracy was obtained using reliable acoustic path, and the localization performance had little change with season. This work indicates that the seasonal environmental variation induces differences in the sound channel as well as the arrival acoustic information, the error propagation and crossing solution for the localization in the half convergence zone area of deep sea, then exert significant effects on localization performance as the receiving depth in the upper ocean.
2020, 42(3): 72-82.
doi: 10.3969/j.issn.0253-4193.2020.03.007
Abstract:
Sub-bottom profile is based on the acoustic signal (frequency in hundreds to thousands Hz) in the sediment propagation to reflect the sedimentary formation structure. The seabed reflection coefficient is closely related to the sediments physical properties. The Biot-Stoll theoretical model can predict the physical properties of seabed sediments and establish the relationship between acoustic parameters such as reflection coefficient and physical parameters, but the results obtained by using different parameters in different sea areas are different. For this, this article is based on the measured sediments physical parameters in the northern slope of the South China Sea to establish the relationship between the reflection coefficient and the sediments physical parameters based on Biot-Stoll model. The results show that the calculated value of the model is in good agreement with the measured value of the sample, and the equation for the relationship between the bottom reflection coefficient and the porosity, density, mean grain size of sediments at a frequency of 3.5 kHz is established. The equation has a high fitting degree, and the determination coefficient R2 is all greater than 0.99. On the basis of calculating the seabed reflection coefficient by the typical Chirp profile data, the porosity, density and mean grain size of the sub-bottom sediments are inversed. The relative errors of the inversion porosity, density, mean grain size and the measured porosity, density, mean grain size are all less than 5%, and the results are basically consistent with the measured values, indicating that the inversion method is feasible in the northern continental slope area of the South China Sea.
Sub-bottom profile is based on the acoustic signal (frequency in hundreds to thousands Hz) in the sediment propagation to reflect the sedimentary formation structure. The seabed reflection coefficient is closely related to the sediments physical properties. The Biot-Stoll theoretical model can predict the physical properties of seabed sediments and establish the relationship between acoustic parameters such as reflection coefficient and physical parameters, but the results obtained by using different parameters in different sea areas are different. For this, this article is based on the measured sediments physical parameters in the northern slope of the South China Sea to establish the relationship between the reflection coefficient and the sediments physical parameters based on Biot-Stoll model. The results show that the calculated value of the model is in good agreement with the measured value of the sample, and the equation for the relationship between the bottom reflection coefficient and the porosity, density, mean grain size of sediments at a frequency of 3.5 kHz is established. The equation has a high fitting degree, and the determination coefficient R2 is all greater than 0.99. On the basis of calculating the seabed reflection coefficient by the typical Chirp profile data, the porosity, density and mean grain size of the sub-bottom sediments are inversed. The relative errors of the inversion porosity, density, mean grain size and the measured porosity, density, mean grain size are all less than 5%, and the results are basically consistent with the measured values, indicating that the inversion method is feasible in the northern continental slope area of the South China Sea.
2020, 42(3): 83-96.
doi: 10.3969/j.issn.0253-4193.2020.03.008
Abstract:
The horizontal suspended and bed-load sediment transport in the bottom boundary layer were computed by applying a one-dimensional parameterized scheme to the in-situ data obtained from two stations in the Bohai Strait during a winter field investigation in 2018. In the parameterized scheme, a simplified one-dimensional advection-diffusion equation was used to calculate the vertical suspended sediment concentration in the bottom boundary layer. Aiming at verifying the reliability of the parameterization scheme, two models of bed shear stress calculation, four critical bed-shear stress methods and two advection-diffusion solutions were compared based on the observations. It showed that: (1) bed shear stress calculated by different models are fairly consistent; (2) the critical bed-shear stress is affected by sediment cohesive effects; (3) stratification effect of sediment concentration and the difference of critical bed-shear stress with different particle size fractions need to be considered solving the one-dimensional advection-diffusion equation. Based on the optimal parameterization obtained from the comparisons, sediment transport of the two stations was further calculated: (1) during resuspension events, the ratio of the horizontal suspended sediment flux within 5 meters above bottom accounting for the suspended sediment flux throughout the entire water column which is about 21% in T01 and 17% in T02 is significantly higher than the ratio of the water flux within the same layers; (2) the mean suspended sediment flux estimated by the parameterization scheme in winter is about 16% higher than the result estimated from the conventional method which ignores the vertical variation of suspended sediment concentration in the bottom boundary layer; (3) bed-load transport is generally 2 orders of magnitude smaller than the suspended load transport.
The horizontal suspended and bed-load sediment transport in the bottom boundary layer were computed by applying a one-dimensional parameterized scheme to the in-situ data obtained from two stations in the Bohai Strait during a winter field investigation in 2018. In the parameterized scheme, a simplified one-dimensional advection-diffusion equation was used to calculate the vertical suspended sediment concentration in the bottom boundary layer. Aiming at verifying the reliability of the parameterization scheme, two models of bed shear stress calculation, four critical bed-shear stress methods and two advection-diffusion solutions were compared based on the observations. It showed that: (1) bed shear stress calculated by different models are fairly consistent; (2) the critical bed-shear stress is affected by sediment cohesive effects; (3) stratification effect of sediment concentration and the difference of critical bed-shear stress with different particle size fractions need to be considered solving the one-dimensional advection-diffusion equation. Based on the optimal parameterization obtained from the comparisons, sediment transport of the two stations was further calculated: (1) during resuspension events, the ratio of the horizontal suspended sediment flux within 5 meters above bottom accounting for the suspended sediment flux throughout the entire water column which is about 21% in T01 and 17% in T02 is significantly higher than the ratio of the water flux within the same layers; (2) the mean suspended sediment flux estimated by the parameterization scheme in winter is about 16% higher than the result estimated from the conventional method which ignores the vertical variation of suspended sediment concentration in the bottom boundary layer; (3) bed-load transport is generally 2 orders of magnitude smaller than the suspended load transport.
2020, 42(3): 97-106.
doi: 10.3969/j.issn.0253-4193.2020.03.009
Abstract:
Resuspension and its distribution of sediment depend upon three interacting components namely the characteristics of the mobile sediment, the bed forms and the forcing hydrodynamics. A good understanding of the process of sediment resuspension is important in sediment transport. In this paper, in-situ measurements of wave, current, and suspended sediment concentration profiles in the marine ranching of Xiangyun Bay were carried out. The vertical distribution characteristics of suspended sediment in the bottom boundary layer under the wave-current action were analyzed. The results show that the resuspension of seabed sediments in the study area is controlled by storm-waves. The bottom shear stress under storm wave is 10−15 times of the critical shear stress of sediment, resuspension of sediment lags behind storm-wave for 2−3 hours. The type of vertical distribution of suspended sediment is "I" under small wave load, the vertical distribution of suspended sediment in the bottom boundary layer presents a power exponential function, which is "L" type under storm-wave. Bedforms evolved with wave and current action, and which affected the resuspension process of sediments.\begin{document}${u_{*w}}{\rm{/}}{u_{*c}} = 1.00$\end{document} ![]()
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\begin{document}${u_{*w}}{\rm{/}}{u_{*c}}$\end{document} ![]()
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Resuspension and its distribution of sediment depend upon three interacting components namely the characteristics of the mobile sediment, the bed forms and the forcing hydrodynamics. A good understanding of the process of sediment resuspension is important in sediment transport. In this paper, in-situ measurements of wave, current, and suspended sediment concentration profiles in the marine ranching of Xiangyun Bay were carried out. The vertical distribution characteristics of suspended sediment in the bottom boundary layer under the wave-current action were analyzed. The results show that the resuspension of seabed sediments in the study area is controlled by storm-waves. The bottom shear stress under storm wave is 10−15 times of the critical shear stress of sediment, resuspension of sediment lags behind storm-wave for 2−3 hours. The type of vertical distribution of suspended sediment is "I" under small wave load, the vertical distribution of suspended sediment in the bottom boundary layer presents a power exponential function, which is "L" type under storm-wave. Bedforms evolved with wave and current action, and which affected the resuspension process of sediments.
2020, 42(3): 107-117.
doi: 10.3969/j.issn.0253-4193.2020.03.010
Abstract:
Due to the influence of runoff and estuarine morphology, asymmetrical phenomena of hydrodynamics, suspended sediment concentration (SSC) and salinity occurs between the flooding and ebbing stage in the estuary. Such a phenomena also shows significant regional and seasonal differences. Based on hydrological survey in July 2013 and January 2014 in the Changjiang River Estuary, it is found that suspended sediment concentration in the branched channels of the Changjiang River Estuary has asymmetric characteristics, which varies with flood and dry season as well as spring and neap tide. In terms of spatial variability, there exists along channel difference, inter-channel difference as well as water colume difference. The evolution of the estuary controlls the overall SSC difference between the North Branch and South Branch. The flood and dry seasons affect the redistribution process of SSC in the estuary. Spring tides has a stronger impact on SSC asymmetry than that of neap tides. Theseasonal wave condition affect the SSC asymmetric distribution in the turbidity maximum zone of the estuary along the north-south direction. The high sediment concentration near the bottom contributes significantly to the SSC asymmetry between flooding and ebbing stages at the river mouth.
Due to the influence of runoff and estuarine morphology, asymmetrical phenomena of hydrodynamics, suspended sediment concentration (SSC) and salinity occurs between the flooding and ebbing stage in the estuary. Such a phenomena also shows significant regional and seasonal differences. Based on hydrological survey in July 2013 and January 2014 in the Changjiang River Estuary, it is found that suspended sediment concentration in the branched channels of the Changjiang River Estuary has asymmetric characteristics, which varies with flood and dry season as well as spring and neap tide. In terms of spatial variability, there exists along channel difference, inter-channel difference as well as water colume difference. The evolution of the estuary controlls the overall SSC difference between the North Branch and South Branch. The flood and dry seasons affect the redistribution process of SSC in the estuary. Spring tides has a stronger impact on SSC asymmetry than that of neap tides. Theseasonal wave condition affect the SSC asymmetric distribution in the turbidity maximum zone of the estuary along the north-south direction. The high sediment concentration near the bottom contributes significantly to the SSC asymmetry between flooding and ebbing stages at the river mouth.
2020, 42(3): 118-128.
doi: 10.3969/j.issn.0253-4193.2020.03.011
Abstract:
Based on the buoys data over the China offshore area during July 1, 2018 to August 6, 2018 collected by the Ministry of Natural Resources, three SST reanalysis products (OISST, OSTIA SST, RTG SST) were validated and compared through analyzing the mean bias, root mean square error (RMSE), correlation coefficient and standard deviation bias. The comparison results show that in the whole time, three SST reanalysis products we used are comparable to the buoys data. The mean bias and correlation coefficient between OSTIA SST dataset and buoy SST data is 0.12℃ and 0.94, better than OISST dataset (−0.85℃, 0.90) and RTG SST dataset (−0.17℃, 0.86). Compared with 80% buoys, the reliability of OSTIA SST dataset is higher than OISST dataset and RTG SST dataset significantly. During typhoon transit periods, absolute values of mean bias and RMSE (correlation coefficient) between OSTIA SST dataset and buoy SST data are smaller (larger) than RTG SST dataset and OISST dataset, which means that OSTIA SST dataset can capture the basic characteristics of SST over the China offshore area more accurately in severe sea conditions.
Based on the buoys data over the China offshore area during July 1, 2018 to August 6, 2018 collected by the Ministry of Natural Resources, three SST reanalysis products (OISST, OSTIA SST, RTG SST) were validated and compared through analyzing the mean bias, root mean square error (RMSE), correlation coefficient and standard deviation bias. The comparison results show that in the whole time, three SST reanalysis products we used are comparable to the buoys data. The mean bias and correlation coefficient between OSTIA SST dataset and buoy SST data is 0.12℃ and 0.94, better than OISST dataset (−0.85℃, 0.90) and RTG SST dataset (−0.17℃, 0.86). Compared with 80% buoys, the reliability of OSTIA SST dataset is higher than OISST dataset and RTG SST dataset significantly. During typhoon transit periods, absolute values of mean bias and RMSE (correlation coefficient) between OSTIA SST dataset and buoy SST data are smaller (larger) than RTG SST dataset and OISST dataset, which means that OSTIA SST dataset can capture the basic characteristics of SST over the China offshore area more accurately in severe sea conditions.
2020, 42(3): 129-139.
doi: 10.3969/j.issn.0253-4193.2020.03.012
Abstract:
Jason-3 satellite was successfully launched on January 17, 2016, and was put on its nominal orbit on February 12, 2016. Jason-3 was flying in formation with Jason-2 only 1 minute 20 seconds, and was about 560 km from Jason-2. Jason-2 was moved to its new interleaved orbit on September 1, 2016. Two orbits were parallel to increase the spatial coverage of satellite observations. The objectives of this paper are to assess Jason-3 data quality and to estimate the altimetry system performance includes validation of Jason-3 data availability and data quality monitoring of Jason-3 and radiometer parameters. The objectives focused on comprehensive comparison of the parameters of the Jason-2 and Jason-3, accurately evaluated the consistency of the two altimeter parameters using the opportunity that the missions were on the same ground track during the formation flight phase, analyzed the ability and stability of the Jason-3 from the perspective of global data, verified Jason-3 data accuracy by self-crossover analysis and dual crossover analysis with Jason-2. From the results presented here, it is demonstrated that the Jason-3 mission fulfils the requirements of high precision altimetry. It allows continuing the observation of the sea surface height variations at the same or higher accuracy as Jason-1, Jason-2 and T/P. In addition, significant wave height quality of Jason-3 data is significantly better than the Jason-2.
Jason-3 satellite was successfully launched on January 17, 2016, and was put on its nominal orbit on February 12, 2016. Jason-3 was flying in formation with Jason-2 only 1 minute 20 seconds, and was about 560 km from Jason-2. Jason-2 was moved to its new interleaved orbit on September 1, 2016. Two orbits were parallel to increase the spatial coverage of satellite observations. The objectives of this paper are to assess Jason-3 data quality and to estimate the altimetry system performance includes validation of Jason-3 data availability and data quality monitoring of Jason-3 and radiometer parameters. The objectives focused on comprehensive comparison of the parameters of the Jason-2 and Jason-3, accurately evaluated the consistency of the two altimeter parameters using the opportunity that the missions were on the same ground track during the formation flight phase, analyzed the ability and stability of the Jason-3 from the perspective of global data, verified Jason-3 data accuracy by self-crossover analysis and dual crossover analysis with Jason-2. From the results presented here, it is demonstrated that the Jason-3 mission fulfils the requirements of high precision altimetry. It allows continuing the observation of the sea surface height variations at the same or higher accuracy as Jason-1, Jason-2 and T/P. In addition, significant wave height quality of Jason-3 data is significantly better than the Jason-2.
2020, 42(3): 140-148.
doi: 10.3969/j.issn.0253-4193.2020.03.013
Abstract:
Although the length of short array multi-channel streamers is limited,the absence of equipment for positioning and depth fixing, e.g., birds, magnetic compass, tail mark, etc., will bring some problems, such as inaccurate seismic geometric definition, to the subsequent procedure of data processing. In addition, different sinking depths without correction of depth fixing at different receiving sections along the short towing cable will destroy the relationship of the theoretical hyperbolic curve between time and distance. As to the short-array multi-channel seismic reflection data, therefore, we utilize the surveying navigation data to calculate the real shot track points, and then the interpolation algorithm weighted with inverse ratio of distance is employed to estimate the trajectory coordinates of the receiving points, which aids in obtaining the authentic geometric parameters of the total array. In order to resolve the distortion of time-distance curve caused by inconsistent depth of receiving cable, we calculate the theoretical reflecting positions of common mid-point (CMP) with hyperbolic curve and gauge the static correction of receiving arrays with different sinking depths. Finally, distortions of the reflection event caused by the non-uniform sinking depths of receiving array are eliminated by the fitting algorithm of static correction. The application of above processing processes to the short-array seismic reflection data collected in the Ross Sea, West Antarctica produces high-resolution stacked seismic reflection profiles, which provides great technical assistance for following work of geological interpretation.
Although the length of short array multi-channel streamers is limited,the absence of equipment for positioning and depth fixing, e.g., birds, magnetic compass, tail mark, etc., will bring some problems, such as inaccurate seismic geometric definition, to the subsequent procedure of data processing. In addition, different sinking depths without correction of depth fixing at different receiving sections along the short towing cable will destroy the relationship of the theoretical hyperbolic curve between time and distance. As to the short-array multi-channel seismic reflection data, therefore, we utilize the surveying navigation data to calculate the real shot track points, and then the interpolation algorithm weighted with inverse ratio of distance is employed to estimate the trajectory coordinates of the receiving points, which aids in obtaining the authentic geometric parameters of the total array. In order to resolve the distortion of time-distance curve caused by inconsistent depth of receiving cable, we calculate the theoretical reflecting positions of common mid-point (CMP) with hyperbolic curve and gauge the static correction of receiving arrays with different sinking depths. Finally, distortions of the reflection event caused by the non-uniform sinking depths of receiving array are eliminated by the fitting algorithm of static correction. The application of above processing processes to the short-array seismic reflection data collected in the Ross Sea, West Antarctica produces high-resolution stacked seismic reflection profiles, which provides great technical assistance for following work of geological interpretation.
2020, 42(3): 149-156.
doi: 10.3969/j.issn.0253-4193.2020.03.015
Abstract:
Compared with shore-based GNSS-R technology, the airborne GNSS-R has the advantages of high spatial resolution, wide monitoring range, high-resolution monitoring of specific areas, and flexible height and azimuth adjustments. This paper mainly studies the airborne GNSS-R altimetry model, based on the shore-based GNSS-R code altimetry principle, corrects the atmospheric delay, antenna distance, etc., optimizes the airborne altimetry model, and uses the DTU10 global sea level average height and tide. The model verifies the accuracy of the onboard GNSS-R altimetry model. By analyzing the GNSS-R airborne data of the CSIC-IEEC in the Baltic Sea in Finland on November 11, 2011, the inversion of the experimental data at different elevation angles was successfully carried out, and the inversion of the sub-meter airborne sea surface height was successfully achieved. The conclusion that the elevation angle has a great influence on the accuracy of the altimetry results qualitatively analyzes the error range caused by the elevation angle. The results of this paper demonstrate the feasibility of sea level altimetry for airborne GNSS-R.
Compared with shore-based GNSS-R technology, the airborne GNSS-R has the advantages of high spatial resolution, wide monitoring range, high-resolution monitoring of specific areas, and flexible height and azimuth adjustments. This paper mainly studies the airborne GNSS-R altimetry model, based on the shore-based GNSS-R code altimetry principle, corrects the atmospheric delay, antenna distance, etc., optimizes the airborne altimetry model, and uses the DTU10 global sea level average height and tide. The model verifies the accuracy of the onboard GNSS-R altimetry model. By analyzing the GNSS-R airborne data of the CSIC-IEEC in the Baltic Sea in Finland on November 11, 2011, the inversion of the experimental data at different elevation angles was successfully carried out, and the inversion of the sub-meter airborne sea surface height was successfully achieved. The conclusion that the elevation angle has a great influence on the accuracy of the altimetry results qualitatively analyzes the error range caused by the elevation angle. The results of this paper demonstrate the feasibility of sea level altimetry for airborne GNSS-R.
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