Geomagnetic Field Measurement And Study On Underwater Magnetic Localization Technology

To assure underwater survival capability of submarine, it must be provided with means and competences of both high precise localization and hidden navigation, and then it can make a surprise attack on enemy. INS (Inertial Navigation System) has been the key navigation equipment of submarine due to its excellences such as independence and whole navigation information. But the localization error of INS increases with time due to the inherent drifts and error of its inertial components, so INS must be regulated again and again or correction. Geomagnetic field can provide external resource of correction information with good concealment for submarine. Through the research and application of INS/geomagnetic integrated navigation system, the period of regulation would be prolonged, and long distance navigation precision and automatic navigation ability would be improved. The dissertation will focus on the study of underwater localization method based on geomagnetic anomaly inversion, magnetic gradient measurement technology and INS integrated navigation system with ground speed detected by geomagnetic anomaly inversion.Aimed at these facts that effective geomagnetic map is difficult to build up and geomagnetic anomaly is not forecasted in geomagnetic data, there are some difficulties for explanting terrain matching method to underwater geomagnetic navigation. A new underwater localization method based on geomagnetic anomaly inversion is put forward in this dissertation, where geomagnetic anomaly can be viewed as a magnetic dipole target and the position of vehicle relative to target can be calculated by magnetic magnitude and gradients of target field. The calculated formula of geomagnetic feature inversion is deduced in detail. Focused on both positive/negative symbol in inversion formula and many roots of a six order equation with one variable, three restricted terms of the true root are given according to the factual meaning of inversion, which can be used to select both symbol and many roots. A combined iterative correction with position and magnetic moment is put forward and described in detail. On the other hand, the index function of iterative calculation error and iterative equation of position and magnetic moment are set up, and then the numerical simulation experiment is carried out.The relationship between inherent errors of magnetic field measurement and baseline length is analyzed. Two kinds of magnetometer configuration schemes for ten single-axes and eight single-axes are put forward and compared, and the results show that ten single-axis configuration scheme is better than eight single-axis one. According to two kinds of placement structure of magnetometers, the inherent reason of this difference is analyzed. The essential conditions and optimal matrix of magnetic gradients measurement are analyzed, and thus we can conclude that the simplest configuration is seven single-axis magnetometers. A kind of configuration for seven single-axis magnetometers is put forward, which are installed vertexes of cubic supporter. The feasibility of measurement scheme about scalar magnetometer is discussed.The relationships between the measurement errors of magnetic dipole magnitude and gradients and three-axis nonorthonity, gain and zero-drift error, displacement central inaccuracy and sensitive axis direction deviation of magnetometers are deduced. The calculated errors of magnetic magnitude and gradients caused by no-co-point of magnetometer are analyzed, and two kinds of configuration modes about ten magnetometers are given and compared. These errors are less for the configuration mode where the displacement between the corresponding sensitive axes is equal.The error model applicable to strong noise for nonorthobonality and different sensitivities among three axes of magnetometer is established, and the error parameters identification and related correction algorithm are also given. The relation between correction precision and sampling number is studied on condition of different SNRs. Considering secondly that the zero-drift error of tri-axis magnetometer and registration error among two magnetic measurement coordinate systems, we establish the error model of magnetic component gradiometer and magnetic magnitude gradiometer, and then bring forward their error parameters identification and correction algorithm based on functional link artificial neural network (FLANN) and least-squares method. The experiments prove good convergence and validity of the algorithm in a certain noise range.To verify the feasibility of geomagnetic character inversion based on magnetic anomaly gradients, the ground experiment of geomagnetic gradient measurement and localization is designed. Magnetic gradient measurement device is put up by two three-axis fluxgate magnetometer whose resolution is 1nT, and up-plane software based on Labview is designed and organized. Magnetic gradient measurement and target localization experiments are carried out outdoor, and experimental data disposed show that the feasibility of geomagnetic gradient. Aimed at the problem that target magnetic magnitude is difficult to measure in the geomagnetic background field, new vehicle localization method based on draft depth and magnetic gradients is brought forward. The vertical relative position is directly calculated by twice measurements of draft depth. The effect of draft depth measurement error on localization precision is analyzed. A continuous localization method using magnetic moment of target is put forward to avoid vehicle moving in vertical direction endlessly, and simulation is performed.Finally, effect of underwater vehicle attitude variation on magnetic magnitude, gradients and localization is studied, and results show that magnetic gradients vary with a certain period and however the localization distance isn't related to attitude. According to the relationship between target moment and attitude angles of vehicle, a novel method to calculate attitude variation by target magnetic moments is put forward combined with inversed magnetic moment and one-dimensional tiltmeter. According to the feature that the position of magnetic target is fixed and the localization distance isn't related to attitude, the calculation method of ground speed by twice localization distances is brought forward. The calculated equation of ground speed and its components is deduced, and the calculated error of ground speed is analyzed theoretically. And then, applicable condition of the calculation equation is discussed. Viewed the ground speed as measurement quantity, the geomagnetic/INS integrated navigation system is constructed, and the filter effects of Kalman filter and H∞filter are compared by simulation.