Research On Transversal Strapdown INS And Error Depression Technology In Polar Region

Inertial navigation system is a kind of self-contained navigation method,and it can be used in ship and underwater vehicle.However,when the system uses common mechanizations in polar region it would face problems of accuracy decrease and tracing the north difficultly and so on.And the worst of it is,at the polar point the existing coordinate systems have no north direction at all,so it is impossible for us to give the north benchmark.To solve the mentioned problems,we propose a kind of mechanization based on transversal coordinate for strapdown inertial navigation system(SINS),and then make the research on the working principle of SINS based on transversal coordinate.In this thesis the main contents are as following.We construct the transversal coordinate framework,and then design the mechanization of SINS based on transversal coordinate.Utilizing the technologies of space analytic geometry,we deduce the transforming expressions of position,velocity and attitude from a normal coordinate to a transversal coordinate.So SINS could make the transformation between these two coordinates automatically.By the analysis of errors of transversal SINS,we find that there are three kinds of oscillations existing in the system,and they are Shuler,Foucault and earth periodical oscillations.In addition,we find the transversal longitude and latitude errors are drift terms related with time.In term of the oscillatory errors in the transversal coordinate system,we make use of Doppler Velocity Log(DVL)and transversal SINS to construct the external damped transversal SINS.Through the analysis of the characteristic equation of the system damped by the external damping network,we find that the performance of the azimuth damping of the transversal SINS is due to the parameter setting along with the position of the ship.All about the issue in this thesis gives the design criteria for the transversal SINS.Next aiming at removing the effect of measurement errors from DVL on a transversal SINS,we carry out the work about the transformation function from measurement errors to outputs of a transversal SINS,together with analysis on the effects of the different forms of external velocities on the damped system.Besides we give an error restraint scheme with a dual-cascade-system configuration.The switch time of the damping states is decided by the dual-cascade-system configuration,and the smooth switch substitutes for the step switch here since this switch can reduce the effect of measurement errors form DVL on the external damped transversal SINS.Referring the analysis above,we know that the azimuth angle,longitude and latitude error divergences which can not be restrained by the damping technology as it bounds the oscillation errors existing in the transversal SINS.In order to limit the divergent errors in the transversal SINS,we propose an integrated navigation system including gravity anomaly and SINS.In terms of the problems the gravity model is nonlinear and there is a specific analytic formula,we use a particle filter and gravity anomaly data to accomplish the data fusion.With the consideration of the particle degeneracy for the standard particle filter,we make the improvement of the common particle filter and take the Cubature Kalman Filter(CKF)in the particle filter configuration.The details include that CKF makes use of the latest measurement information to derive the importance density function and Gauss-Newton iteration yields the posterior density of the system states in the phase of measurement updating,which will improve the particle filter performance effectively and(?)the accuracy of gravity anomaly matching.At last the error divergences could be limited effectively.In some parts of polar region where gravity anomaly can not be matched with transversal SINS,we design the transversal SINS/gravity anomaly/DVL integrated navigation system working in different ways and the corresponding measurement equations so as to restrain the navigation system errors.Moreover we give estimates on ocean current by a scheme of ship-heading-change model constraint.This could avoid the effects of ocean current on the outputs of DVL,and improve the performance of integrated navigation system effectively.