Study On High Precision Positioning Of Underwater Control Network

Underwater control network plays an important role in underwater scientific research and engineering application,such as marine plate movement,underwater navigation and positioning,underwater engineering construction and stability monitoring of underwater buildings.Aiming at the problem that the positioning precision of underwater control network is not high enough at present,this paper carries out the corresponding studies,forms a set of positioning methods of underwater control network,and improves positioning precision.The specific work and contributions are as follows:1)In sailing-circle absolute datum transfer,when the prior information(such as depth)is missing or inaccurate,the initial incident angle of the beam cannot be accurately obtained,which leads to poor final positioning accuracy.Therefore,this paper studies the calculation of incident angle and proposes a method for calculating the incident angle of a beam with self-restraint in circular transfer.This method combines a reverse or direct ray tracing method and the least square distance intersection,continuously corrects the incident angle until the coordinates of the underwater control point remain stable,and finally obtains the precise positioning result.2)Although sailing-circle absolute datum transfer has high plane accuracy,its vertical accuracy is low.Therefore,this paper studies the positioning method of circular transfer,deduces the positioning accuracy model of circular transfer,provides a determination principle for designers to determine the appropriate sailing radius and SSP sampling interval,and offers a basis for high-precision determination of underwater control points for circular transfer.This paper also presents an absolute datum transfer method for circular transfer based on depth constraints,which improves the vertical accuracy of circular transfer.3)In order to solve the problem of time-consuming and low precision of underwater control network measurement,this paper introduces the depth difference offered by pressure sensors,and proposes a set of positioning process of underwater control network based on depth constraint,including: unconstrained adjustment with depth constraints,and integrated constraint adjustment,combined constraint adjustment and modified constraint adjustment.The process solves the problems of slow calculation speed and low vertical positioning accuracy of underwater control network.4)In a simulated experiment,data of different depths,geometric incidence angles and SSP sampling intervals proves that in the self-constrained incidence angle calculation method,the positioning accuracy of the method based on reverse ray tracing is higher than that based on direct ray tracing,but its execution speed is much lower than that based on forward ray tracing.In addition,the average R-square value of 0.919 and the RMSE value of 0.197 m are obtained by the circular transfer positioning accuracy model.5)In the field experiment of Songhua Lake,the average positioning accuracy of 2.5 cm and the average vertical accuracy of 2.0 cm are obtained by using the selfconstrained incidence angle calculation method modified by the positioning accuracy model;the depth-constrained circular transfer method improves the vertical accuracy by 4.2 cm compared with the conventional circular transfer method.Field experiments also validate the positioning method of underwater control network.Unconstrained adjustment of depth-constrained underwater control network makes all baseline corrections less than 1.5 cm;the modified constraint adjustment achieves an average positioning accuracy of 7.8 cm,which is 3.4 cm higher than the integrated constraint adjustment or combined constraint adjustment.