Ocean currents are a key element in ocean processes and in meteorology,affecting material transport and modulating climate change patterns.The Doppler frequency shift information of the synthetic aperture radar(SAR)ec...Ocean currents are a key element in ocean processes and in meteorology,affecting material transport and modulating climate change patterns.The Doppler frequency shift information of the synthetic aperture radar(SAR)echo signal can reflect the dynamic characteristics of the sea surface,and has become an essential sea surface dynamic remote sensing parameter.Studies have verified that the instantaneous Doppler frequency shift can realize the SAR detection of the sea surface current.However,the validation of SAR-derived ocean current data and a thorough analysis of the errors associated with them remain lacking.In this study,we derive high spatial resolution flow measurements for the Kuroshio in the East China Sea from SAR data using a theoretical model of shifts in Doppler frequency driven by ocean surface current.Global ocean multi observation(MOB)products and global surface Lagrangian drifter(GLD)data are used to validate the Kuroshio flow retrieved from the SAR data.Results show that the central flow velocity for the Kuroshio derived from the SAR is 0.4–1.5 m/s.The error distribution between SAR ocean currents and MOB products is an approximate standard normal distribution,with the 90%confidence interval concentrated between–0.1 m/s and 0.1 m/s.Comparative analysis of SAR ocean current and GLD products,the correlation coefficient is 0.803,which shows to be significant at a confidence level of 99%.The cross-validation of different ocean current dataset illustrate that the SAR radial current captures the positions and dynamics of the Kuroshio central flow and the Kuroshio Counter Current,and has the capability to monitor current velocity over a wide range of values.展开更多
The development of space-air-ground integrated networks (SAGIN) requires sophisticated satellite Internet emulation tools that can handle complex, dynamic topologies and offer in-depth analysis. Existing emulation pla...The development of space-air-ground integrated networks (SAGIN) requires sophisticated satellite Internet emulation tools that can handle complex, dynamic topologies and offer in-depth analysis. Existing emulation platforms struggle with challenges like the need for detailed implementation across all network layers, real-time response, and scalability. This paper proposes a digital twin system based on microservices for satellite Internet emulation,namely Plotinus,which aims to solve these problems. Plotinus features a modular design, allowing for easy replacement of the physical layer to emulate different aerial vehicles and analyze channel interference. It also enables replacing of path computation methods to simplify testing and deploying algorithms. In particular, Plotinus allows for real-time emulation with live network traffic,enhancing practical network models. The evaluation result shows Plotinus’s effective emulation of dynamic satellite networks with real-world devices. Its adaptability for various communication models and algorithm testing highlights Plotinus’s role as a vital tool for developing and analyzing SAGIN systems, offering a cross-layer,real-time,and scalable digital twin system.展开更多
Arabidopsis thaliana(A.thaliana)has long been a model species for dicotyledon study,and was the first flowering plant to get its genome completed sequenced[1].Although most wild A.thaliana are collected in Europe,seve...Arabidopsis thaliana(A.thaliana)has long been a model species for dicotyledon study,and was the first flowering plant to get its genome completed sequenced[1].Although most wild A.thaliana are collected in Europe,several studies have found a rapid A.thaliana west-east expansion from Central Asia[2].The Qinghai-Tibet Plateau(QTP)is close to Central Asia and known for its high alti-展开更多
Control system is very important for each autonomous surface vehicle(ASV),which involves the problem of maintaining the vehicle's position and heading using feedback controller and achieving the desired forces thr...Control system is very important for each autonomous surface vehicle(ASV),which involves the problem of maintaining the vehicle's position and heading using feedback controller and achieving the desired forces through thrust allocation.In this paper,we present a practical thrust allocator for under-actuated and fully-actuated vehicles,which can be represented as a quadratic programming(QP)problem with linear constraints.Such an optimization method allows us to consider common propulsion system,including tunnel thruster,azimuth thruster,and-xed propeller with rudder.These linear constraints enable us to explicitly account for the rate,amplitude and azimuth constraints of each propeller on the vessel.The proposed methods have been illustrated by simulated and experimental maneuvers for di®erent thruster layout of a vehicle.展开更多
基金The National Natural Science Foundation of China under contract Nos 42176174 and 41706196the Open Research Fund of the State Key Laboratory of Estuarine and Coastal Research under contract No.SKLECKF202104+3 种基金the Zhejiang Provincial Natural Science Foundation of China under contract No.LY22D010002the National Science Foundation for Post-doctoral Scientists of China under contract No.2020M683258the Chongqing Technology Innovation and Application Development Special Project under contract No.cstc2020jscx-msxm X0193the Sichuan Science and Technology Program under contract No.2018JY0484
文摘Ocean currents are a key element in ocean processes and in meteorology,affecting material transport and modulating climate change patterns.The Doppler frequency shift information of the synthetic aperture radar(SAR)echo signal can reflect the dynamic characteristics of the sea surface,and has become an essential sea surface dynamic remote sensing parameter.Studies have verified that the instantaneous Doppler frequency shift can realize the SAR detection of the sea surface current.However,the validation of SAR-derived ocean current data and a thorough analysis of the errors associated with them remain lacking.In this study,we derive high spatial resolution flow measurements for the Kuroshio in the East China Sea from SAR data using a theoretical model of shifts in Doppler frequency driven by ocean surface current.Global ocean multi observation(MOB)products and global surface Lagrangian drifter(GLD)data are used to validate the Kuroshio flow retrieved from the SAR data.Results show that the central flow velocity for the Kuroshio derived from the SAR is 0.4–1.5 m/s.The error distribution between SAR ocean currents and MOB products is an approximate standard normal distribution,with the 90%confidence interval concentrated between–0.1 m/s and 0.1 m/s.Comparative analysis of SAR ocean current and GLD products,the correlation coefficient is 0.803,which shows to be significant at a confidence level of 99%.The cross-validation of different ocean current dataset illustrate that the SAR radial current captures the positions and dynamics of the Kuroshio central flow and the Kuroshio Counter Current,and has the capability to monitor current velocity over a wide range of values.
基金supported in part by the National Natural Science Foundation of China under Grant 62341105.
文摘The development of space-air-ground integrated networks (SAGIN) requires sophisticated satellite Internet emulation tools that can handle complex, dynamic topologies and offer in-depth analysis. Existing emulation platforms struggle with challenges like the need for detailed implementation across all network layers, real-time response, and scalability. This paper proposes a digital twin system based on microservices for satellite Internet emulation,namely Plotinus,which aims to solve these problems. Plotinus features a modular design, allowing for easy replacement of the physical layer to emulate different aerial vehicles and analyze channel interference. It also enables replacing of path computation methods to simplify testing and deploying algorithms. In particular, Plotinus allows for real-time emulation with live network traffic,enhancing practical network models. The evaluation result shows Plotinus’s effective emulation of dynamic satellite networks with real-world devices. Its adaptability for various communication models and algorithm testing highlights Plotinus’s role as a vital tool for developing and analyzing SAGIN systems, offering a cross-layer,real-time,and scalable digital twin system.
基金supported by the National Natural Science Foundation of China (91131901)the specimen platform of China (teaching specimens sub-platform) and PSCIRT project
文摘Arabidopsis thaliana(A.thaliana)has long been a model species for dicotyledon study,and was the first flowering plant to get its genome completed sequenced[1].Although most wild A.thaliana are collected in Europe,several studies have found a rapid A.thaliana west-east expansion from Central Asia[2].The Qinghai-Tibet Plateau(QTP)is close to Central Asia and known for its high alti-
基金supported by the Key R&D Program of Guangdong(2020B1111010002)the Key R&D Program of Hainan(ZDYF2021GXJS041)and the National Natural Science Foundation of China(U2141234).
文摘Control system is very important for each autonomous surface vehicle(ASV),which involves the problem of maintaining the vehicle's position and heading using feedback controller and achieving the desired forces through thrust allocation.In this paper,we present a practical thrust allocator for under-actuated and fully-actuated vehicles,which can be represented as a quadratic programming(QP)problem with linear constraints.Such an optimization method allows us to consider common propulsion system,including tunnel thruster,azimuth thruster,and-xed propeller with rudder.These linear constraints enable us to explicitly account for the rate,amplitude and azimuth constraints of each propeller on the vessel.The proposed methods have been illustrated by simulated and experimental maneuvers for di®erent thruster layout of a vehicle.