Understanding the topographic patterns of the seafloor is a very important part of understanding our planet.Although the science involved in bathymetric surveying has advanced much over the decades,less than 20%of the...Understanding the topographic patterns of the seafloor is a very important part of understanding our planet.Although the science involved in bathymetric surveying has advanced much over the decades,less than 20%of the seafloor has been precisely modeled to date,and there is an urgent need to improve the accuracy and reduce the uncertainty of underwater survey data.In this study,we introduce a pretrained visual geometry group network(VGGNet)method based on deep learning.To apply this method,we input gravity anomaly data derived from ship measurements and satellite altimetry into the model and correct the latter,which has a larger spatial coverage,based on the former,which is considered the true value and is more accurate.After obtaining the corrected high-precision gravity model,it is inverted to the corresponding bathymetric model by applying the gravity-depth correlation.We choose four data pairs collected from different environments,i.e.,the Southern Ocean,Pacific Ocean,Atlantic Ocean and Caribbean Sea,to evaluate the topographic correction results of the model.The experiments show that the coefficient of determination(R~2)reaches 0.834 among the results of the four experimental groups,signifying a high correlation.The standard deviation and normalized root mean square error are also evaluated,and the accuracy of their performance improved by up to 24.2%compared with similar research done in recent years.The evaluation of the R^(2) values at different water depths shows that our model can achieve performance results above 0.90 at certain water depths and can also significantly improve results from mid-water depths when compared to previous research.Finally,the bathymetry corrected by our model is able to show an accuracy improvement level of more than 21%within 1%of the total water depths,which is sufficient to prove that the VGGNet-based method has the ability to perform a gravity-bathymetry correction and achieve outstanding results.展开更多
The dynamic optimal interpolation(DOI)method is a technique based on quasi-geostrophic dynamics for merging multi-satellite altimeter along-track observations to generate gridded absolute dynamic topography(ADT).Compa...The dynamic optimal interpolation(DOI)method is a technique based on quasi-geostrophic dynamics for merging multi-satellite altimeter along-track observations to generate gridded absolute dynamic topography(ADT).Compared with the linear optimal interpolation(LOI)method,the DOI method can improve the accuracy of gridded ADT locally but with low computational efficiency.Consequently,considering both computational efficiency and accuracy,the DOI method is more suitable to be used only for regional applications.In this study,we propose to evaluate the suitable region for applying the DOI method based on the correlation between the absolute value of the Jacobian operator of the geostrophic stream function and the improvement achieved by the DOI method.After verifying the LOI and DOI methods,the suitable region was investigated in three typical areas:the Gulf Stream(25°N-50°N,55°W-80°W),the Japanese Kuroshio(25°N-45°N,135°E-155°E),and the South China Sea(5°N-25°N,100°E-125°E).We propose to use the DOI method only in regions outside the equatorial region and where the absolute value of the Jacobian operator of the geostrophic stream function is higher than1×10^(-11).展开更多
The Kyushu–Palau Ridge(KPR),an anti-S-shaped submarine highland at the center of the Philippine Sea Plate(PSP),is considered the residual arc of the Izu–Bonin–Mariana Island Arc,which retains key information about ...The Kyushu–Palau Ridge(KPR),an anti-S-shaped submarine highland at the center of the Philippine Sea Plate(PSP),is considered the residual arc of the Izu–Bonin–Mariana Island Arc,which retains key information about the cessation of the Western Philippine Basin(WPB)expansion and the Parece Vela Basin(PVB)breakup.Herein,using the new generation of satellite altimetry gravity data,high-precision seafloor topography data,and newly acquired ship-borne gravity data,the topographic and gravity characteristics of the KPR mid-southern section and adjacent region are depicted.The distribution characteristics of the faults were delineated using the normalized vertical derivative–total horizontal derivative method(NVDR-THDR)and the minimum curvature potential field separation method.The Moho depth and crustal thickness were inverted using the rapid inversion method for a double-interface model with depth constraints.Based on these results,the crust structure features in the KPR mid-southern section,and the“triangular”structure geological significance where the KPR and Central Basin Rift(CBR)of the WPB intersect are interpreted.The KPR crustal thickness is approximately 6–16 km,with a distinct discontinuity that is slightly thicker than the normal oceanic crust.The KPR mid-southern section crust structure was divided into four segments(S1–S4)from north to south,formed by the CBR eastward extension joint action and clockwise rotation of the PVB expansion axis and the Mindanao fault zone blocking effect.展开更多
The Zambezi Delta basin is a passive marginal basin located on the East African coast that has good oil and gas exploration potential.Due to the special geological evolutionary background of the Beira High in the Zamb...The Zambezi Delta basin is a passive marginal basin located on the East African coast that has good oil and gas exploration potential.Due to the special geological evolutionary background of the Beira High in the Zambezi Delta basin,it has a low gravity anomaly,and the existing seismic survey lines do not cover the whole basin;therefore,it is difficult to interpret the structural characteristics of the whole basin based solely on gravity or seismic data.Based on satellite altimetry gravity anomaly data,this study infers the distribution characteristics of faults in the Zambezi Delta basin by using the normalized vertical derivative of the total horizontal derivative(NVDR-THDR)technique.Then,constrained by seismic data,the gravity anomaly at the Moho interface is extracted by using the fast forward method of the double-interface model of the gravity anomaly,and this anomaly is then removed from the Bouguer gravity anomaly to obtain the sedimentary layer gravity anomaly.The thickness of the sedimentary strata is obtained by inversing the sedimentary basement depth of the whole basin.Then,uplifts and depressions are divided based on a sedimentary layer thickness of 3 km.This research demonstrates that the Zambezi Delta basin mainly features nearly SN-trending and NE-trending faults and that these faults exhibit east-west partitioning.The nearly SN-trending strike-slip faults controlled the sedimentary development of the basin,and the NE-trending tensile faults may have acted as migration channels for oil,gas and magma.The“overcompensation”effect of the Moho interface gravity anomaly on the gravity anomaly of the sedimentary layer is caused by the depression of the Moho interface beneath the Beira High,which results in a low gravity anomaly value for the Beira High.The pattern of uplifts and depressions trends NE and has the structural characteristics of east-west blocks.展开更多
Eddy properties in the Bay of Bengal are studied from 22 a archiving, validation and interpretation of satellite oceanographic(AVISO) data using a sea level anomaly(SLA)-based eddy identification. A geographical d...Eddy properties in the Bay of Bengal are studied from 22 a archiving, validation and interpretation of satellite oceanographic(AVISO) data using a sea level anomaly(SLA)-based eddy identification. A geographical distribution and an eddy polarity, an eddy lifetime and propagation distances, eddy origins and terminations,eddy propagation directions and trajectories, eddy kinetic properties, the evolution of eddy properties,seasonal and interannual variabilities of eddy activities are analyzed in this area. Eddies exist principally in the western Bay of Bengal and most of them propagate westward. The polarity distribution of eddies shows cyclones prefer to occur in the northwest and south of the Bay of Bengal, while anticyclones mainly occur in the east of the bay. Five hundred and sixty-five cyclones and 389 anticyclones with the lifetime that exceeds 30 d are detected during the 22 a period, and there is a preference for the cyclones for all lifetime and propagation distances. The kinetic properties of all observed eddies show the average amplitude of the cyclones is larger than that of the anticyclones, whereas that is opposite for average radius, and their average velocities are basically the same. Moreover, the evolution of eddies properties reveals that the eddies with a long lifetime that exceeds 90 d have a significant double-stage feature of the former 50 d growth period and the dying period after 50 d. For the seasonal variability of the eddies, the cyclones occur more often in spring while the anticyclones occur more often in summer. The analysis of long-lived eddy seasonal distributions shows that there is the obvious seasonal variation of the eddy activities in the Bay of Bengal. The interannual variability of an eddy number shows an obvious negative correlation with the EKE variation.展开更多
The deep ocean below 2000 m is a large water body with the sparsest data coverage,challenging the closure of the sea-level budget and the estimation of the Earth’s energy imbalance.Whether the deep ocean below 2000 m...The deep ocean below 2000 m is a large water body with the sparsest data coverage,challenging the closure of the sea-level budget and the estimation of the Earth’s energy imbalance.Whether the deep ocean below 2000 m is warming globally has been debated in the recent decade.However,as the regional signals are generally larger than the global average,it is intriguing to investigate the regional temperature changes.Here,we adopt an indirect method that combines altimetry,GRACE,and Argo data to examine the global and regional deep ocean temperature changes below 2000 m.The consistency between high-quality conductivity-temperature-depth(CTD)data from repeated hydrographic sections and our results confirms the validity of the indirect method.We find that the deep oceans are warming in the Middle East Indian Ocean,the subtropical North and Southwest Pacific,and the Northeast Atlantic,but cooling in the Northwest Atlantic and Southern oceans from 2005 to 2015.展开更多
Total sea level variations(SLVs) are caused by two major components:steric variations due to thermal expansion of seawater,and mass-induced variations due to mass exchange between ocean and land.In this study,the g...Total sea level variations(SLVs) are caused by two major components:steric variations due to thermal expansion of seawater,and mass-induced variations due to mass exchange between ocean and land.In this study,the global SLV and its steric and mass components were estimated by satellite altimetry,Argo float data and the Gravity Recovery and Climate Experiment(GRACE) data over 2005-2014.Space gravimetry observations from GRACE suggested that two-thirds of the global mean sea level rise rate observed by altimetry(i.e.,3.1 ± 0.3 mm/a from 2005 to 2014) could be explained by an increase in ocean mass.Furthermore,the global mean sea level was observed to drop significantly during the2010/2011 La Nina event,which may be attributed to the decline of ocean mass and steric SLV.Since early 2011,the global mean sea level began to rise rapidly,which was attributed to an increase in ocean mass.The findings in this study suggested that the global mean sea-level budget was closed from 2005 to 2014 based on altimetry,GRACE,and Argo data.展开更多
The Kuroshio Extension (KE) plays an important role in climate and environmental change in the North Pacific. In this paper, more than 20 years of merged absolute dynamic topography and merged sea level anomaly prod...The Kuroshio Extension (KE) plays an important role in climate and environmental change in the North Pacific. In this paper, more than 20 years of merged absolute dynamic topography and merged sea level anomaly products from satellite altimetry are used to analyze the stability of the KE system. By analyzing the annually averaged sea surface topography, the variations of inter-annual path and annually averaged eddy kinetic energy at the KE region, the KE's two dynamic states are given as: the relatively stable state during 1993 1995, 2002-2005, and 2010-2012, and the unstable dynamic state among 1996-2001 and 2006-2009. During the stable state, the KE spindle had a shorter path length and smaller time-varying amplitude, as well as a trend to move northward. While during the unstable state, the KE spindle had a longer path length and an integral southward transport trend, and was observed to oscillate significantly over time. The analysis on the KE's upstream and downstream region gives the same variations, indi- cating that they are significantly affected by the El Nino events. The power spectrum of the mean latitudinal position variation of the KE's upstream and downstream shows significant quasi-decadal oscillation characteristics and strong annual signals. Furthermore, the correlation of the strength vari- ation between the southern RG and the KE's upstream is calculated to be 0.50 after low-pass filtering, and that of the mean latitudinal position variation between the southern RG and the KE's upstream/ downstream are 0.75/0.69 after low-pass filtering, respectively. The strong correlations demonstrated that the southern RG and the KE are closely linked.展开更多
The elastic thickness of the lithosphere(Te)is a key parameter used to describe the strength of the lithosphere.It is usually estimated by a spectral analysis between gravity and topography.In previous research on the...The elastic thickness of the lithosphere(Te)is a key parameter used to describe the strength of the lithosphere.It is usually estimated by a spectral analysis between gravity and topography.In previous research on the estimation of Te,altimetry data were used on both the gravity data and topography data,which could lead to deviations.The study described in this paper analyzed the effects of using gravity anomalies derived from different data sources on the estimation of Te,Taking the western Pacific region as an example,this study analyzed the impact of the repeated presence of altimetry satellite data on the calculation of the effective elastic thickness and found that if gravity anomalies and topography model both contain altimetry satellite data,they systematically overestimate effective elasticity.For a uniform area,the difference in Te can reach up to 30%.For a Te distribution,the difference can reach up to about16%.After eliminating this effect,the effective elastic thickness of the western Pacific region was found to be 10 km,and the statistical results of the effective elastic thickness distribution showed that the effective elastic thickness of the lithosphere in most areas of the western Pacific is about 12 km.The paper shows the importance of choosing the appropriate gravity model in evaluating the elastic thickness of lithosphere in the oceans.A figure of Te at seamounts with loading ages demonstrates that Te in the western Pacific is generally distributed within the 100-300℃isotherm depth and does not increase with loading age.展开更多
The impact of climate change on sea level has received a great deal of attention by scientists worldwide. In this context, the problem of sea levels on global and regional scales have been analyzed in a number of stud...The impact of climate change on sea level has received a great deal of attention by scientists worldwide. In this context, the problem of sea levels on global and regional scales have been analyzed in a number of studies based on tide gauges observations and satellite altimetry measurements. This study focuses on trend estimates from 18 high-quality tide gauge stations along the Mediterranean Sea coast. The seasonal Mann-Kendall test was run at a 5% significance level for each of the 18 stations for the period of 1993-2015 (satellite altimetry era). The results of this test indicate that the trends for 17 stations were statistically significant and showed an increase (no significant trend was observed only at one station). The rates of sea level change for the 17 stations that exhibit significant trends, estimated using seasonal Sen's approach, range after correction for Vertical Land Motion (VLM) from 1.48 to 8.72 mm/a for the period 1993-2015. Furthermore, the magnitude of change at the location of each tide gauge station was estimated using the satellite altimetry measurements. Thus, the results obtained agree with those from the tide-gauge data analysis.展开更多
The northern Egyptian continental margin is characterized by interesting tectonic settings as well as trade and industry district in Egypt. In the current study, the contribution role of satellite altimetry gravity da...The northern Egyptian continental margin is characterized by interesting tectonic settings as well as trade and industry district in Egypt. In the current study, the contribution role of satellite altimetry gravity data in the Environmental geophysical investigation is presented to give a complete view of the marine gravity field of the study area. The satellite data showed only minor deviations in some partial regions of the area investigated such as Nile Deep Sea Fan, Levant Basin, Eratosthenes Seamount and Herodotus basin. The interpretations of the entire data illustrated that the differences between the satellite and the shipboard data were small in some regions particularly near to land. Furthermore, a number of strong deviations in some regions were spatially correlated with bathymetric depth together with the appearance of geological structures.展开更多
Sinking of the Nile Delta region of Egypt is one of urgent issues to be investigated due to its vital importance to numerous perspectives such as economic, environmental and social impact on the whole Egyptian territo...Sinking of the Nile Delta region of Egypt is one of urgent issues to be investigated due to its vital importance to numerous perspectives such as economic, environmental and social impact on the whole Egyptian territory. This contribution represents one of the project outcomes entitled “Evaluation of Nile Delta Sinking Hypothesis Using the Global Positioning System (GPS), Tide Gauge and Satellite Altimetry and Gravity Techniques” that has been funded by the Science & Technology Development FUND (STDF), Egypt in the period from 2013 till 2017. To detect the rates of the horizontal and vertical movements, three main geodetic techniques;Global Positioning System (GPS) measurements of Delta region, time-varying gravity models of the Gravity Recovery and Climate Experiment (GRACE) mission to monitor the temporal changes over the delta regions and satellite altimetry time series have been used. Our findings regarding the GPS technique show that the northern part of the Nile Delta region suffers from clear subsidence especially at the eastern and western side as represented by Port Said, Mansoura, Gamalyia, Alexandria and Edfena stations. The central part as well as the surrounding areas of Nile Delta suffers from clear uplift as represented by Tanta, Damnhour and Hamoul stations. Satellite gravity results show erosion rates of the conjunction part of Nile Delta and Mediterranean contact, especially at its eastern (Port Said surrounding areas) and western (Alexandria surrounding areas) parts. As we go inland to the southern part of the Nile Delta, the temporal gravity variations pattern decreases showing that the Delta subsidence follows the regular subsidence pattern, except that for the northern contact part of the Delta to the Mediterranean Sea. This is also supported by satellite altimetry missions which shows a continuously rising rate of the Mediterranean Sea level as detected from the Saral/AltiKa mission.展开更多
This paper focuses on the study of ocean bathymetric inversion from satellite altimeter data by using FFT technique.In this study,the freeair gravity anomalies over the South China Sea are determined by the satellite ...This paper focuses on the study of ocean bathymetric inversion from satellite altimeter data by using FFT technique.In this study,the freeair gravity anomalies over the South China Sea are determined by the satellite altimeter data of GEOSAT,ERS1,ERS2 and T/P.And the 2.5′×2.5′ bathymetry model in South China Sea is calculated from the gravity anomalies with the inversion model given.After the analysis of the inversion and the comparison between the results,some conclusions can be drawn.展开更多
A new computational procedure for derivation of marine geoid on a 2.5′×2.5′grid in a non-tidal system over the South China Sea and the Philippine Sea from multi-satellite altimeter sea surface heights is discus...A new computational procedure for derivation of marine geoid on a 2.5′×2.5′grid in a non-tidal system over the South China Sea and the Philippine Sea from multi-satellite altimeter sea surface heights is discussed. Single-and dual-satellite crossovers were performed, and components of deflections of the vertical were determined at the crossover positions using Sand-well's computational theory, and gridded onto a 2.5′×2.5′resolution grid by employing the Shepard's interpolation procedure. 2.5′×2.5′grid of EGM96-derived components of deflections of the vertical and geoid heights were then used as reference global geopotential model quantities in a remove-restore procedure to implement the Molodensky-like formula via 1D-FFT technique to predict the geoid heights over the South China Sea and the Philippine Sea from the gridded altimeter-derived components of deflec-tions of the vertical. Statistical comparisons between the altimeter-and the EGM96- derived geoid heights showed that there was a root-mean-square agreement of ±0.35 m between them in a region of less tectonically active geological structures. However, over areas of tectonically active structures such as the Philippine trench, differences of about -19.9 m were obtained.展开更多
A tide model (named DN1.0), which contains 12 principal constituents over China seas and the Northwest Pacific is estimated by along-track harmonic analysis with TOPEX/Poseidon altimetry data taken from 1993 to 2002. ...A tide model (named DN1.0), which contains 12 principal constituents over China seas and the Northwest Pacific is estimated by along-track harmonic analysis with TOPEX/Poseidon altimetry data taken from 1993 to 2002. CSR3.0, FES95.2 and DN1.0 are used respectively to detide the data for the time series of sea level anomaly (SLA) in the Yellow Sea, East China Sea, South China Sea and Northwest Pacific. The SLA curves and the power spectral density show that the major components that exist in SLA in China seas arise from the error of the tide models.展开更多
The calibration of the sea surface height(SSH)measured by satellite altimeters is essential to understand altimeter biases.Many factors affects the construction and maintenance of a permanent calibration site.In order...The calibration of the sea surface height(SSH)measured by satellite altimeters is essential to understand altimeter biases.Many factors affects the construction and maintenance of a permanent calibration site.In order to calibrate Chinese satellite altimetry missions,the feasibility of maintaining a calibration site based on the Qianliyan islet in Yellow Sea of China is taken into account.The related calibration facilities,such as the permanent tide gauge,GNSS reference station and meteorological station,were already operated by the Ministry of Natural Resources of China.The data could be fully used for satellite altimeter calibration with small fiscal expenditure.In addition,the location and marine environments of Qianliyan were discussed.Finally,we used the Jason-3 mission to check the possibility of calibration works.The result indicates that the brightness temperatures of three channels measured by microwave radiometer(MWR)and the derived wet tropospheric correction varies smoothly,which means the land contamination to MWR could be ignored.The high frequency waveforms at the Qianliyan site present no obvious difference from the normal waveforms received by satellite radar altimeter over the open ocean.In conclusion,the Qianliyan islet will not influence satellite altimetry observation.Following these analyses,a possible layout and mechanism of the Qianliyan calibration site are proposed.展开更多
With the improvements in the density and quality of satellite altimetry data,a high-precision and high-resolution mean sea surface model containing abundant information regarding a marine gravity field can be calculat...With the improvements in the density and quality of satellite altimetry data,a high-precision and high-resolution mean sea surface model containing abundant information regarding a marine gravity field can be calculated from long-time series multi-satellite altimeter data.Therefore,in this study,a method was proposed for determining marine gravity anomalies from a mean sea surface model.Taking the Gulf of Mexico(15°–32°N,80°–100°W)as the study area and using a removal-recovery method,the residual gridded deflections of the vertical(DOVs)are calculated by combining the mean sea surface,mean dynamic topography,and XGM2019e_2159 geoid,and then using the inverse Vening-Meinesz method to determine the residual marine gravity anomalies from the residual gridded DOVs.Finally,residual gravity anomalies are added to the XGM2019e_2159 gravity anomalies to derive marine gravity anomaly models.In this study,the marine gravity anomalies were estimated with mean sea surface models CNES_CLS15MSS,DTU21MSS,and SDUST2020MSS and the mean dynamic topography models CNES_CLS18MDT and DTU22MDT.The accuracy of the marine gravity anomalies derived by the mean sea surface model was assessed based on ship-borne gravity data.The results show that the difference between the gravity anomalies derived by DTU21MSS and CNES_CLS18MDT and those of the ship-borne gravity data is optimal.With an increase in the distance from the coast,the difference between the gravity anomalies derived by mean sea surface models and ship-borne gravity data gradually decreases.The accuracy of the difference between the gravity anomalies derived by mean sea surface models and those from ship-borne gravity data are optimal at a depth of 3–4 km.The accuracy of the gravity anomalies derived by the mean sea surface model is high.展开更多
基金The National Key R&D Program of China under contract Nos 2022YFC3003800,2020YFC1521700 and 2020YFC1521705the National Natural Science Foundation of China under contract No.41830540+3 种基金the Open Fund of the East China Coastal Field Scientific Observation and Research Station of the Ministry of Natural Resources under contract No.OR-SECCZ2022104the Deep Blue Project of Shanghai Jiao Tong University under contract No.SL2020ZD204the Special Funding Project for the Basic Scientific Research Operation Expenses of the Central Government-Level Research Institutes of Public Interest of China under contract No.SZ2102the Zhejiang Provincial Project under contract No.330000210130313013006。
文摘Understanding the topographic patterns of the seafloor is a very important part of understanding our planet.Although the science involved in bathymetric surveying has advanced much over the decades,less than 20%of the seafloor has been precisely modeled to date,and there is an urgent need to improve the accuracy and reduce the uncertainty of underwater survey data.In this study,we introduce a pretrained visual geometry group network(VGGNet)method based on deep learning.To apply this method,we input gravity anomaly data derived from ship measurements and satellite altimetry into the model and correct the latter,which has a larger spatial coverage,based on the former,which is considered the true value and is more accurate.After obtaining the corrected high-precision gravity model,it is inverted to the corresponding bathymetric model by applying the gravity-depth correlation.We choose four data pairs collected from different environments,i.e.,the Southern Ocean,Pacific Ocean,Atlantic Ocean and Caribbean Sea,to evaluate the topographic correction results of the model.The experiments show that the coefficient of determination(R~2)reaches 0.834 among the results of the four experimental groups,signifying a high correlation.The standard deviation and normalized root mean square error are also evaluated,and the accuracy of their performance improved by up to 24.2%compared with similar research done in recent years.The evaluation of the R^(2) values at different water depths shows that our model can achieve performance results above 0.90 at certain water depths and can also significantly improve results from mid-water depths when compared to previous research.Finally,the bathymetry corrected by our model is able to show an accuracy improvement level of more than 21%within 1%of the total water depths,which is sufficient to prove that the VGGNet-based method has the ability to perform a gravity-bathymetry correction and achieve outstanding results.
基金supported by National Natural Science Foundation of China under Grants 42192531 and 42192534the Special Fund of Hubei Luojia Laboratory(China)under Grant 220100001the Natural Science Foundation of Hubei Province for Distinguished Young Scholars(China)under Grant 2022CFA090。
文摘The dynamic optimal interpolation(DOI)method is a technique based on quasi-geostrophic dynamics for merging multi-satellite altimeter along-track observations to generate gridded absolute dynamic topography(ADT).Compared with the linear optimal interpolation(LOI)method,the DOI method can improve the accuracy of gridded ADT locally but with low computational efficiency.Consequently,considering both computational efficiency and accuracy,the DOI method is more suitable to be used only for regional applications.In this study,we propose to evaluate the suitable region for applying the DOI method based on the correlation between the absolute value of the Jacobian operator of the geostrophic stream function and the improvement achieved by the DOI method.After verifying the LOI and DOI methods,the suitable region was investigated in three typical areas:the Gulf Stream(25°N-50°N,55°W-80°W),the Japanese Kuroshio(25°N-45°N,135°E-155°E),and the South China Sea(5°N-25°N,100°E-125°E).We propose to use the DOI method only in regions outside the equatorial region and where the absolute value of the Jacobian operator of the geostrophic stream function is higher than1×10^(-11).
基金‘Research on Deep Structural Differences between Potential Oil-rich Depressions in Offshore basins of China Sea’from the scientific and technological project of CNOOC Research Institute Co.,Ltd.,under contract No.CCL2021RCPS0167KQN‘Resource Potential,Accumulation Mechanism and Breakthrough Direction of Potential Oil-rich Depressions in Offshore China Sea’,under contract No.220226220101+1 种基金the Project of China Geological Survey under contract No.DD20191003the National Natural Science Foundation of Shandong Province of China under contract No.ZR2022MD047。
文摘The Kyushu–Palau Ridge(KPR),an anti-S-shaped submarine highland at the center of the Philippine Sea Plate(PSP),is considered the residual arc of the Izu–Bonin–Mariana Island Arc,which retains key information about the cessation of the Western Philippine Basin(WPB)expansion and the Parece Vela Basin(PVB)breakup.Herein,using the new generation of satellite altimetry gravity data,high-precision seafloor topography data,and newly acquired ship-borne gravity data,the topographic and gravity characteristics of the KPR mid-southern section and adjacent region are depicted.The distribution characteristics of the faults were delineated using the normalized vertical derivative–total horizontal derivative method(NVDR-THDR)and the minimum curvature potential field separation method.The Moho depth and crustal thickness were inverted using the rapid inversion method for a double-interface model with depth constraints.Based on these results,the crust structure features in the KPR mid-southern section,and the“triangular”structure geological significance where the KPR and Central Basin Rift(CBR)of the WPB intersect are interpreted.The KPR crustal thickness is approximately 6–16 km,with a distinct discontinuity that is slightly thicker than the normal oceanic crust.The KPR mid-southern section crust structure was divided into four segments(S1–S4)from north to south,formed by the CBR eastward extension joint action and clockwise rotation of the PVB expansion axis and the Mindanao fault zone blocking effect.
基金The Petrochina Basic Prospective Science and Technology Research Project–Overseas deepwater ultra-deepwater oil and gas exploration technology research topic,under contract No.2021DJ2403。
文摘The Zambezi Delta basin is a passive marginal basin located on the East African coast that has good oil and gas exploration potential.Due to the special geological evolutionary background of the Beira High in the Zambezi Delta basin,it has a low gravity anomaly,and the existing seismic survey lines do not cover the whole basin;therefore,it is difficult to interpret the structural characteristics of the whole basin based solely on gravity or seismic data.Based on satellite altimetry gravity anomaly data,this study infers the distribution characteristics of faults in the Zambezi Delta basin by using the normalized vertical derivative of the total horizontal derivative(NVDR-THDR)technique.Then,constrained by seismic data,the gravity anomaly at the Moho interface is extracted by using the fast forward method of the double-interface model of the gravity anomaly,and this anomaly is then removed from the Bouguer gravity anomaly to obtain the sedimentary layer gravity anomaly.The thickness of the sedimentary strata is obtained by inversing the sedimentary basement depth of the whole basin.Then,uplifts and depressions are divided based on a sedimentary layer thickness of 3 km.This research demonstrates that the Zambezi Delta basin mainly features nearly SN-trending and NE-trending faults and that these faults exhibit east-west partitioning.The nearly SN-trending strike-slip faults controlled the sedimentary development of the basin,and the NE-trending tensile faults may have acted as migration channels for oil,gas and magma.The“overcompensation”effect of the Moho interface gravity anomaly on the gravity anomaly of the sedimentary layer is caused by the depression of the Moho interface beneath the Beira High,which results in a low gravity anomaly value for the Beira High.The pattern of uplifts and depressions trends NE and has the structural characteristics of east-west blocks.
基金The National Natural Science Foundation of China under contract No.41576176the National High Technology Research and Development Program(863 program)of China under contract No.2013AA122803the Project of ESA-MOST Dragon-3 Cooperation Programme
文摘Eddy properties in the Bay of Bengal are studied from 22 a archiving, validation and interpretation of satellite oceanographic(AVISO) data using a sea level anomaly(SLA)-based eddy identification. A geographical distribution and an eddy polarity, an eddy lifetime and propagation distances, eddy origins and terminations,eddy propagation directions and trajectories, eddy kinetic properties, the evolution of eddy properties,seasonal and interannual variabilities of eddy activities are analyzed in this area. Eddies exist principally in the western Bay of Bengal and most of them propagate westward. The polarity distribution of eddies shows cyclones prefer to occur in the northwest and south of the Bay of Bengal, while anticyclones mainly occur in the east of the bay. Five hundred and sixty-five cyclones and 389 anticyclones with the lifetime that exceeds 30 d are detected during the 22 a period, and there is a preference for the cyclones for all lifetime and propagation distances. The kinetic properties of all observed eddies show the average amplitude of the cyclones is larger than that of the anticyclones, whereas that is opposite for average radius, and their average velocities are basically the same. Moreover, the evolution of eddies properties reveals that the eddies with a long lifetime that exceeds 90 d have a significant double-stage feature of the former 50 d growth period and the dying period after 50 d. For the seasonal variability of the eddies, the cyclones occur more often in spring while the anticyclones occur more often in summer. The analysis of long-lived eddy seasonal distributions shows that there is the obvious seasonal variation of the eddy activities in the Bay of Bengal. The interannual variability of an eddy number shows an obvious negative correlation with the EKE variation.
基金This work is supported by the National Natural Science Foundation of China(Grant No.41904081).
文摘The deep ocean below 2000 m is a large water body with the sparsest data coverage,challenging the closure of the sea-level budget and the estimation of the Earth’s energy imbalance.Whether the deep ocean below 2000 m is warming globally has been debated in the recent decade.However,as the regional signals are generally larger than the global average,it is intriguing to investigate the regional temperature changes.Here,we adopt an indirect method that combines altimetry,GRACE,and Argo data to examine the global and regional deep ocean temperature changes below 2000 m.The consistency between high-quality conductivity-temperature-depth(CTD)data from repeated hydrographic sections and our results confirms the validity of the indirect method.We find that the deep oceans are warming in the Middle East Indian Ocean,the subtropical North and Southwest Pacific,and the Northeast Atlantic,but cooling in the Northwest Atlantic and Southern oceans from 2005 to 2015.
基金supported by the National Key Basic Research Program of China(973 program,2012CB957703 and2013CB733305)the National Natural Science Foundation of China(41431070,41174066 and 41321063)
文摘Total sea level variations(SLVs) are caused by two major components:steric variations due to thermal expansion of seawater,and mass-induced variations due to mass exchange between ocean and land.In this study,the global SLV and its steric and mass components were estimated by satellite altimetry,Argo float data and the Gravity Recovery and Climate Experiment(GRACE) data over 2005-2014.Space gravimetry observations from GRACE suggested that two-thirds of the global mean sea level rise rate observed by altimetry(i.e.,3.1 ± 0.3 mm/a from 2005 to 2014) could be explained by an increase in ocean mass.Furthermore,the global mean sea level was observed to drop significantly during the2010/2011 La Nina event,which may be attributed to the decline of ocean mass and steric SLV.Since early 2011,the global mean sea level began to rise rapidly,which was attributed to an increase in ocean mass.The findings in this study suggested that the global mean sea-level budget was closed from 2005 to 2014 based on altimetry,GRACE,and Argo data.
基金supported by the National Basic Research Program of China(2013CB733302,2012CB957703)the National Natural Science Foundation of China(41210006,41304003)
文摘The Kuroshio Extension (KE) plays an important role in climate and environmental change in the North Pacific. In this paper, more than 20 years of merged absolute dynamic topography and merged sea level anomaly products from satellite altimetry are used to analyze the stability of the KE system. By analyzing the annually averaged sea surface topography, the variations of inter-annual path and annually averaged eddy kinetic energy at the KE region, the KE's two dynamic states are given as: the relatively stable state during 1993 1995, 2002-2005, and 2010-2012, and the unstable dynamic state among 1996-2001 and 2006-2009. During the stable state, the KE spindle had a shorter path length and smaller time-varying amplitude, as well as a trend to move northward. While during the unstable state, the KE spindle had a longer path length and an integral southward transport trend, and was observed to oscillate significantly over time. The analysis on the KE's upstream and downstream region gives the same variations, indi- cating that they are significantly affected by the El Nino events. The power spectrum of the mean latitudinal position variation of the KE's upstream and downstream shows significant quasi-decadal oscillation characteristics and strong annual signals. Furthermore, the correlation of the strength vari- ation between the southern RG and the KE's upstream is calculated to be 0.50 after low-pass filtering, and that of the mean latitudinal position variation between the southern RG and the KE's upstream/ downstream are 0.75/0.69 after low-pass filtering, respectively. The strong correlations demonstrated that the southern RG and the KE are closely linked.
基金funded by Guangdong Province Introduced Innovative R&D Team of Geological Processes and Natural Disasters around the South China Sea,China(No.2016ZT06N331)the National key Research and Development Program of China,China(No.2017YFC1500101)Guangdong Province Natural Science Foundation,China(No.2018A030310314)。
文摘The elastic thickness of the lithosphere(Te)is a key parameter used to describe the strength of the lithosphere.It is usually estimated by a spectral analysis between gravity and topography.In previous research on the estimation of Te,altimetry data were used on both the gravity data and topography data,which could lead to deviations.The study described in this paper analyzed the effects of using gravity anomalies derived from different data sources on the estimation of Te,Taking the western Pacific region as an example,this study analyzed the impact of the repeated presence of altimetry satellite data on the calculation of the effective elastic thickness and found that if gravity anomalies and topography model both contain altimetry satellite data,they systematically overestimate effective elasticity.For a uniform area,the difference in Te can reach up to 30%.For a Te distribution,the difference can reach up to about16%.After eliminating this effect,the effective elastic thickness of the western Pacific region was found to be 10 km,and the statistical results of the effective elastic thickness distribution showed that the effective elastic thickness of the lithosphere in most areas of the western Pacific is about 12 km.The paper shows the importance of choosing the appropriate gravity model in evaluating the elastic thickness of lithosphere in the oceans.A figure of Te at seamounts with loading ages demonstrates that Te in the western Pacific is generally distributed within the 100-300℃isotherm depth and does not increase with loading age.
文摘The impact of climate change on sea level has received a great deal of attention by scientists worldwide. In this context, the problem of sea levels on global and regional scales have been analyzed in a number of studies based on tide gauges observations and satellite altimetry measurements. This study focuses on trend estimates from 18 high-quality tide gauge stations along the Mediterranean Sea coast. The seasonal Mann-Kendall test was run at a 5% significance level for each of the 18 stations for the period of 1993-2015 (satellite altimetry era). The results of this test indicate that the trends for 17 stations were statistically significant and showed an increase (no significant trend was observed only at one station). The rates of sea level change for the 17 stations that exhibit significant trends, estimated using seasonal Sen's approach, range after correction for Vertical Land Motion (VLM) from 1.48 to 8.72 mm/a for the period 1993-2015. Furthermore, the magnitude of change at the location of each tide gauge station was estimated using the satellite altimetry measurements. Thus, the results obtained agree with those from the tide-gauge data analysis.
文摘The northern Egyptian continental margin is characterized by interesting tectonic settings as well as trade and industry district in Egypt. In the current study, the contribution role of satellite altimetry gravity data in the Environmental geophysical investigation is presented to give a complete view of the marine gravity field of the study area. The satellite data showed only minor deviations in some partial regions of the area investigated such as Nile Deep Sea Fan, Levant Basin, Eratosthenes Seamount and Herodotus basin. The interpretations of the entire data illustrated that the differences between the satellite and the shipboard data were small in some regions particularly near to land. Furthermore, a number of strong deviations in some regions were spatially correlated with bathymetric depth together with the appearance of geological structures.
文摘Sinking of the Nile Delta region of Egypt is one of urgent issues to be investigated due to its vital importance to numerous perspectives such as economic, environmental and social impact on the whole Egyptian territory. This contribution represents one of the project outcomes entitled “Evaluation of Nile Delta Sinking Hypothesis Using the Global Positioning System (GPS), Tide Gauge and Satellite Altimetry and Gravity Techniques” that has been funded by the Science & Technology Development FUND (STDF), Egypt in the period from 2013 till 2017. To detect the rates of the horizontal and vertical movements, three main geodetic techniques;Global Positioning System (GPS) measurements of Delta region, time-varying gravity models of the Gravity Recovery and Climate Experiment (GRACE) mission to monitor the temporal changes over the delta regions and satellite altimetry time series have been used. Our findings regarding the GPS technique show that the northern part of the Nile Delta region suffers from clear subsidence especially at the eastern and western side as represented by Port Said, Mansoura, Gamalyia, Alexandria and Edfena stations. The central part as well as the surrounding areas of Nile Delta suffers from clear uplift as represented by Tanta, Damnhour and Hamoul stations. Satellite gravity results show erosion rates of the conjunction part of Nile Delta and Mediterranean contact, especially at its eastern (Port Said surrounding areas) and western (Alexandria surrounding areas) parts. As we go inland to the southern part of the Nile Delta, the temporal gravity variations pattern decreases showing that the Delta subsidence follows the regular subsidence pattern, except that for the northern contact part of the Delta to the Mediterranean Sea. This is also supported by satellite altimetry missions which shows a continuously rising rate of the Mediterranean Sea level as detected from the Saral/AltiKa mission.
文摘This paper focuses on the study of ocean bathymetric inversion from satellite altimeter data by using FFT technique.In this study,the freeair gravity anomalies over the South China Sea are determined by the satellite altimeter data of GEOSAT,ERS1,ERS2 and T/P.And the 2.5′×2.5′ bathymetry model in South China Sea is calculated from the gravity anomalies with the inversion model given.After the analysis of the inversion and the comparison between the results,some conclusions can be drawn.
基金Funded by the National Natural Science Foundation of China (No.40474004).
文摘A new computational procedure for derivation of marine geoid on a 2.5′×2.5′grid in a non-tidal system over the South China Sea and the Philippine Sea from multi-satellite altimeter sea surface heights is discussed. Single-and dual-satellite crossovers were performed, and components of deflections of the vertical were determined at the crossover positions using Sand-well's computational theory, and gridded onto a 2.5′×2.5′resolution grid by employing the Shepard's interpolation procedure. 2.5′×2.5′grid of EGM96-derived components of deflections of the vertical and geoid heights were then used as reference global geopotential model quantities in a remove-restore procedure to implement the Molodensky-like formula via 1D-FFT technique to predict the geoid heights over the South China Sea and the Philippine Sea from the gridded altimeter-derived components of deflec-tions of the vertical. Statistical comparisons between the altimeter-and the EGM96- derived geoid heights showed that there was a root-mean-square agreement of ±0.35 m between them in a region of less tectonically active geological structures. However, over areas of tectonically active structures such as the Philippine trench, differences of about -19.9 m were obtained.
基金Supported by Open Research Fund Program of the Key Laboratory of Geospace Environment and Geodesy, Ministry of Education, China (No.1469990324233-03-04).
文摘A tide model (named DN1.0), which contains 12 principal constituents over China seas and the Northwest Pacific is estimated by along-track harmonic analysis with TOPEX/Poseidon altimetry data taken from 1993 to 2002. CSR3.0, FES95.2 and DN1.0 are used respectively to detide the data for the time series of sea level anomaly (SLA) in the Yellow Sea, East China Sea, South China Sea and Northwest Pacific. The SLA curves and the power spectral density show that the major components that exist in SLA in China seas arise from the error of the tide models.
基金supported by the National Natural Science Foundation of China under Grants No. 42174001
文摘The calibration of the sea surface height(SSH)measured by satellite altimeters is essential to understand altimeter biases.Many factors affects the construction and maintenance of a permanent calibration site.In order to calibrate Chinese satellite altimetry missions,the feasibility of maintaining a calibration site based on the Qianliyan islet in Yellow Sea of China is taken into account.The related calibration facilities,such as the permanent tide gauge,GNSS reference station and meteorological station,were already operated by the Ministry of Natural Resources of China.The data could be fully used for satellite altimeter calibration with small fiscal expenditure.In addition,the location and marine environments of Qianliyan were discussed.Finally,we used the Jason-3 mission to check the possibility of calibration works.The result indicates that the brightness temperatures of three channels measured by microwave radiometer(MWR)and the derived wet tropospheric correction varies smoothly,which means the land contamination to MWR could be ignored.The high frequency waveforms at the Qianliyan site present no obvious difference from the normal waveforms received by satellite radar altimeter over the open ocean.In conclusion,the Qianliyan islet will not influence satellite altimetry observation.Following these analyses,a possible layout and mechanism of the Qianliyan calibration site are proposed.
基金The National Natural Science Foundation of China under contract Nos 42274006,42174041,41774001the Research Fund of University of Science and Technology under contract No.2014TDJH101.
文摘With the improvements in the density and quality of satellite altimetry data,a high-precision and high-resolution mean sea surface model containing abundant information regarding a marine gravity field can be calculated from long-time series multi-satellite altimeter data.Therefore,in this study,a method was proposed for determining marine gravity anomalies from a mean sea surface model.Taking the Gulf of Mexico(15°–32°N,80°–100°W)as the study area and using a removal-recovery method,the residual gridded deflections of the vertical(DOVs)are calculated by combining the mean sea surface,mean dynamic topography,and XGM2019e_2159 geoid,and then using the inverse Vening-Meinesz method to determine the residual marine gravity anomalies from the residual gridded DOVs.Finally,residual gravity anomalies are added to the XGM2019e_2159 gravity anomalies to derive marine gravity anomaly models.In this study,the marine gravity anomalies were estimated with mean sea surface models CNES_CLS15MSS,DTU21MSS,and SDUST2020MSS and the mean dynamic topography models CNES_CLS18MDT and DTU22MDT.The accuracy of the marine gravity anomalies derived by the mean sea surface model was assessed based on ship-borne gravity data.The results show that the difference between the gravity anomalies derived by DTU21MSS and CNES_CLS18MDT and those of the ship-borne gravity data is optimal.With an increase in the distance from the coast,the difference between the gravity anomalies derived by mean sea surface models and ship-borne gravity data gradually decreases.The accuracy of the difference between the gravity anomalies derived by mean sea surface models and those from ship-borne gravity data are optimal at a depth of 3–4 km.The accuracy of the gravity anomalies derived by the mean sea surface model is high.