The Network Strategy Of Underwater Gliders For The Observation Of Three-Dimensional Structure Of Mesoscale Eddies

As a widespread oceanic mesoscale phenomenon,mesoscale eddies have an important impact on the transport of heat and matter in the global ocean and play an important role in regulating global climate variation.Investigating the three-dimensional(3D)structure of mesoscale eddies will help us to understand the dynamic variation of mesoscale phenomena.However,our understanding of their fine 3D thermohaline and biogeochemical structure remains incomplete due to the scarcity of high-resolution measurements.The observation network constructed by underwater gliders can carry a variety of sensors to simultaneously obtain ocean information at different locations,so as to perform long-term,large-scale,high-precision,multi-parameter and continuous 3D ocean feature observation.In this paper,based on the"Petrel ?" underwater gliders developed by Tianjin University,the network strategy of underwater gliders was investigated and the 3D structure observation of an anticyclonic eddy in the northern South China Sea was conducted to verify the research.The main research results and innovations of this paper are as follows.1.Based on the parameterized mesoscale eddy model,the ability of the glider observation network with different configurations to capture and reconstruct the 3D structure of mesoscale eddies was verified by numerical simulation and sea trials.A comprehensive metric is proposed to evaluate the reconstruction performance of the glider network.According to the relationship between the comprehensive metric and the configuration of the glider network,the optimal topological structure and number of gliders of the network is determined.2.The data from HYCOM(Hybrid Coordinate Ocean Model Navy Coupled Ocean Data Assimilation)and the satellite altimeter observations are analyzed using the vertical empirical orthogonal function analysis,to obtain the corresponding empirical orthogonal functions and determine the locations of the irregular sampling points of the underwater glider observation network.The validity of the vertical empirical orthogonal function analysis is verified by analyzing the normalized root-mean-square error and correlation coefficient of the reconstructed mesoscale temperature field.Considering the distribution of the irregular sampling points,k-means clustering method is adopted to perform the clustering analysis of the sampling points,and then the tasks of each glider in the glider network are divided.3.Based on the "Petrel II" underwater gliders,a glider network was established to observe the three-dimensional structure of a mesoscale eddy in northern South China Sea.By using observations of satellite altimeters,the center location,radius,amplitude,translation velocity and trajectory of the anticyclonic eddy are estimated and the source of the eddy is discussed in combination with the observations of underwater gliders.By analyzing the glider observations,the author reveals the vertical structure of the potential temperature,salinity and potential density anomaly inside the anticyclonic eddy,and discusses the vertical structure of the dissolved oxygen,chlorophyll and colored dissolved organic matter concentration.From multiple aspects,the vertical structure of the the anticyclonic eddy is fully obtained.By combining the high-resolution observations of 12 "Petrel ?" gliders and the measurements of the satellite altimeters,the fine 3D structure of the anticyclonic eddy in the northern South China Sea is reconstructed using the composite analysis method,which verifies the effectiveness of the glider observation network to resolve the 3D structure of mesoscale eddies.4.To estimate the parameters of the mesoscale eddy,a nonlinear kinematic system of the eddy is established.By using the Discrete Extended Kalman Filtering(EKF)method,the nonlinear system of the mesoscale eddy is analyzed and the time-varying parameters of the eddy model are estimated.Taking the observations of "Petrel?" glider network as the measurements of the eddy system,the eddy center position,translation velocity,radius and intensity of the eddy are estimated and predicted.The research builds up a good basis for the glider-based autonomous tracking control of mesoscale eddies.