Effect Analysis Of Underwater Glider Motion Characteristics On CTD Measurement Quality

The conductivity,temperature,depth(CTD),and the derived density and sound velocity of seawater are basic marine physical parameters.The existing CTD observation platforms can't meet all the requirements of precision,economy and maneuverability.The underwater glider is a new and promising marine observation platform which can conduct long-endurance,long-duration,three-dimensional and subtle CTD data collection tasks with glider payload CTD.However,the CTD measurement method based on the glider has not formed a specification and the effect of the glider motion on CTD measurement quality needs further investigation.Based on the Petrel II underwater glider developed by Tianjin University,this paper studies the relation between the glider motion characteristics and CTD measurement quality,which can provide theoretical guidance for the quick and effective collection of highprecision and high-temporal-spatial-resolution CTD data.Main contributions of the work can be concluded as follows:(1)According to other widely-used CTD observation platforms and the working characteristics of the glider,the motion specifications of velocity,stability and turbulence are put forward to make data measurement subtle,quick and effective.To balance the spatial resolution and quickness,the dynamic model of the glider in vertical plane is established to calculate the maximum vertical velocity,which is verified by the filed trial data.The vertical velocity distribution statistics and attitude angles of whole profile are analyzed to demonstrate the stability of the glider.(2)The operation principles of the spiral motion of the glider using rotational battery pack and vertical rudder are explained.Momentum theory and moment of momentum theory are used to establish the kinematic and dynamic models.The simulations of two types of turning motions are conducted using the hydrodynamic coefficients of the Petrel II.The velocity and turbulence flow fields in glide and spiral motion is simulated using computational fluid dynamics software.The results show that attitude angles have a side effect on the measurement quality and the CTD receives less disturbance when located at the front.(3)The data from the glider and the shipped CTD is analyzed and compared.The result shows that the glider has more stable vertical velocity than the shipped CTD and that the temperature,salinity and density curves of the glider are in good agreement with those of the shipped CTD.The data from the glider with different rotation angles shows that the attitude has a side effect on the CTD measurement quality based on spiking and continuity tests of temperature and salinity.