Study Of Strapdown Inertial Navigation Error Model And Initial Alignment Technology

This dissertation performs research in the theory and methods of initial alignment of Strapdown inertial navigation system. This dissertation mainly studies on initial alignment error model, observability analysis method and state-space parameter design method, fast initial stationary base initial alignment methods and moving base initial alignment methods aided by GNSS. The central ideas and new standpoints are listed as follows:(1) The definition of reference frames and navigation algorithm of Strapdown inertial navigation system are researched. The main error sources of SINS are dissertated. Besides, the error equations and error model with 15 dimension state variables are given.(2) Single channel error model based on constant speed assumption is established, and the solutions of the north channel and the east channel of model are derived by using Laplace transform and inverse Laplace transform. Taking advantage of numerical computation of intact error model, single error simulation of SINS, Monte Carlo simulation of random errors and simulation of multiple motion patterns, the single channel error model is analyzed and assessed in detail. Error propagation characteristic of SINS in short time is also analyzed.(3) The theory and methods of observability analysis of SINS are researched. The new error observation equation is constructed based on single channel error model. And state-space dimension reduction method based on observation matrix projection onto the orthonormal basis is proposed, which simplifies observability analysis and analyzes astringency of state variables and steady estimated precision of misalignment angles. Different state-space parameter designs according to different observation variables.(4) Analytic coarse alignment method, compass alignment algorithm and Kalman filter alignment algorithm are researched. The relation between velocity error observation and large azimuth misalignment angle is derived by using large azimuth misalignment angle error model, and fast coarse azimuth alignment method is proposed. Iterative alignment scheme is designed and fast initial alignment on stationary base is implemented by using measured data.(5) Moving base initial alignment methods aided by GNSS is researched. The azimuth alignment aided by computed azimuth by using GNSS position information is given and error analysis is made. An improving azimuth computing method by using quintic B-spline fitting GNSS track function is proposed. Based on geometric rotation transformation fundamental, another azimuth alignment method by using initial position, GNSS observation positions far from start point and SINS calculating positions is proposed, and error analysis is also made. By integrating fast horizontal alignment method and two azimuth alignment methods, iterative alignment scheme on moving base is given. The initial alignment on moving base is implemented by using measured data.