Feasibilty Research Of Strategy For Mesoscale Eddy Observation Based On Underwater Glider

Mesoscale eddy is a kind of ocean phenomenon which can be found in each sea area in the world.It can be characterized by long-term closed circulation,which has the typical spatial scale of tens or hundreds kilometers and time scale of tens or hundred days.Mesoscale eddy is an important component of marine physical environment.Because it has significant effect on marine physics,chemistry and creature,etc.mesoscale eddy is of important research significance and also hot issue in marine research.There are some limitations to the observation platforms currently in use,such as submersible mooring,satellite altimeter and buoy.The observations to the mesoscale eddy are still not perfect.The underwater glider is a kind of autonomous underwater mobile observation platform,which was applied to the marine observation at the end of the 20 th century.It has the advantages of strong endurance,long distance,low noise,lightweight and convenience of launch and recovery,and plays an important role in the field of oceanographic measurement.The underwater glider developed by our country has also entered the application stage.The underwater glider can conducts observations of the ocean hydrological parameters with the mounted various sensors.Therefore,the idea of observing the mesoscale eddy by the underwater glider was proposed in the current work.Achievements in the thesis provide a new way to perfect mesoscale eddy observation.At the same time,they also provide a theoretical guidance for the application of underwater glider in mesoscale eddy observation.Based on the existing data and research achievements of mesoscale eddy observations,the space-time characteristics,temperature and salinity characteristics,velocity characteristics of mesoscale eddy were qualitatively analyzed.Based on the analysis,two observation strategies including observation along the circumferential direction and along the radius direction were proposed.Through the computational fluid dynamics(CFD)numerical simulation with the moving grid method and the six degrees of freedom(6-DOF)model,the 6-DOF space motion of the glider was simulated and the motion characteristics of the glider were analyzed in the two observation strategies.In the circumferential observation,the moving direction of the glider is in line with the direction of the mesoscale eddy in the vertical plane,and the glider is in the vertical flow field.The horizontal moving distance of the glider is longer than that in the condition of static water.The vertical moving distance and pitch angle of the glider are less than those in static water.The lateral displacement,roll angle,yaw angle have no significant change.In the radial observation,the glider is in the lateral flow field.Compared with the navigation in the static water,the lateral displacement increases almost linearly,the yaw angle increases,while the horizontal displacement,vertical displacement,pitch angle and roll angle have little change.The glider will have a significant lateral displacement during flight from the eddy boundary to eddy center.At the eddy boundary,the current with greater speed makes the larger lateral displacement.with the glider moving toward the eddy center,the lateral deviation also decreases.Based on the results of the 6-DOF simulation for the glider,take example of a mesoscale eddy with radius of 100 km,the route adjustment schemes of the glider were developed for different observation strategies.In the circumferential observation,trajectory of the glider will be out of the preset ideal circular area after 24 profiles and have to be adjusted during the glider flights from outer boundary to inner boundary,and then to outer boundary of the ideal circular area.In the radial observation from the outer boundary to the center of mesoscale eddy,the glider will exceed the preset ideal band area after 5 profiles and have to do an adjustment for its trajectory.To demonstrate the validity of simulation,the trial of mesoscale eddy observation is implemented.By analyzing the dive velocity and pitch attitude of underwater glider,the accuracy of simulation is verified,and it is proved that the analysis of observation Strategy is correct.