Research On Underwater Terrain Navigation Model Solving And Navigation Cell Selecting

Underwater terrain navigation is a way for aiding inertial navigation. This thesis is focus on underwater terrain function approximating, underwater terrain navigation model solving and underwater terrain navigation cell choosing three aspects.Terrain elevation is a nonlinear function of position, terrain function for short. There is no explicit function can describe this function, so interpolation method is used to approximate terrain function. A new interpolation method named "conforming natural neighbor interpolation" (Conforming-NNI) is proposed, in which natural neighbor interpolation is combined with conforming Delaunay triangulation. Compared to constrained natural neighbor interpolation, Conforming-NNI simplifies the procedure of constructing second order constraint Voronoi cells of interpolation target, making interpolation can be implemented more easily, and keeping the advantages of traditional natural neighbor interpolation, such as steady interpolation supports, high smoothness, and shape functions share keronecker delta property etc. An improved algorithm of node refinement scheme called "Endpoint Triangle's Circum-circle Method" (ETCM) is proposed for refining the feature segments in conforming Delaunay triangulation. Time complexity of ETCM goes to nearly linear, meanwhile new nodes quantity and mesh quality of ETCM are almost the same as the best of existing algorithms. Experiment results show that compared with TIN interpolation, interpolation error and the ability of reflecting details of Conforming-NNI is better. Conforming-NNI is competent for approximating terrain function.Underwater terrain navigation system is a nonlinear dynamic system. In this thesis a terrain navigation stochastic differential model (TNSDM) is established, and the feasibility of solving state differential function in variational way is explored, in which the state probability density function (pdf) is approximated in a finite dimensional function space. A modified version of Galerkin Projection Filtering method named "Recursive Galerkin Projection Filter" (RGPF) is proposed, and detail solving procedure of n-dimensional state space is given. Due to programming difficulty of calculate multi-dimension matrix multiplication, RGPF has not been used in the system whose state dimension lager than one. In the simulation of one dimension state space, results show that RGPF can obtain the state pdf in finite dimensional function space, and can track the true state, but its root mean square error (RMSE) and stander deviation is larger than Particle Filter.Common navigation filters are adopted to solve TNSDM in difference way. In order to avoid the divergency phenomenon caused by terrain linearization, interpolation terrain navigation method is proposed, in which Conforming-NNI is used to calculate the water depth from terrain map. Simulation results show that, for same filter, interpolation terrain navigation method can reduce divergency times, estimation error and error range.Due to high cost of high precision water depth measurement, a scheme that the terrain data in vector nautical charts can used as the data source for terrain navigation cell primary selection is proposed. The relation between terrain parameters and navigation error are analyzed through experiments. Methods of constructing the underwater digital elevation model (DEM) based on vector nautical chart are proposed, and experiment results show that the primary navigation cell can be selected from the nautical charts whose scale is larger than 1:50000.