Technologies Of Geomagnetic Gradient Aided Navigation And Magnetic Target Detection

In the early 21st century,geomagnetic vector component and full tensor magnetic gradient airborne survey techniques have emerged.Gradient measurements ensure common-mode rejection of the field from Earth's core,regional fields from the deep crust and geomagnetic variations from the ionosphere and magnetosphere.Gradient measurements also provide valuable additional information,compared to conventional total-field measurements.As a major development orientation,research into magnetic gradient aided inertial navigation system(MGAINS),using full tensor magnetic gradient survey data that meets the airborne geomagnetic field survey trend.It has overriding advantages of passivity,covertness,multi-source and efficiency simultaneously.However,MGAINS is still in the theoretical exploration stage,many problems remain to solve and improve putting into practical application.This dissertation takes the actual demand of cruise missile in cruising and terminal guidance stage as research background.Based on a detailed analysis of the related technology research with magnetic added navigation and magnetic anomaly detection,the issue centers around a frequency gradient forward method based on discrete cosine transform,the reference gradient map composition,geomagnetic data compression,non-liner filtering algorithms for MGAINS and inversion of magnetic anomaly target.Reference gradient map plays a basic role in the research of MGAINS.Owing to the limitation of geomagnetic vector measurement technology,as large-scale and fine measured data still needs much material and time.The lack of geomagnetic gradient data already becomes a bottleneck for the research of magnetic gradient aided navigation algorithm.Therefore composing the reference gradient map through forward method is widely adopted.In order to obtain accurate full tensor magnetic gradient data,the fast frequency method based on discrete cosine transform has investigated in detail.The dissertation provides three definitions of ?/2 Phase-shifted cosine transform in Cartesian coordinate system,and derive a theorem of ?/2 Phase-shifted cosine transform time-differentiation.By using the potential field theory,a unified formula has deduced in order to calculate the full tensor magnetic gradient from the pre-existing magnetic anomaly data.Take the theoretical models and measured data as the reference,analyse the precision of DCT and FFT frequency forward methods.Numerical analysis demonstrated that the edge effect error of gradient data could be decreased in comparison to the FFT forward method.Hitherto,the main study of MGAINS has been on the need of geomagnetic navigation algorithm simulation.The research of the composition of small-scale and high precision navigation reference map is only in its infancy.The model of International Geomagnetic Reference Field(IGRF)and World Magnetic Model(WMM)merely reflect the basic geomagnetic field,it does not to embody the features of the crustal anomaly field.Due to its low accuracy,can not directly generate digital reference map,and results in undesirable precision for the requirements of navigation.Consequently,integration of extensive data sources is vital to the research of the composition of geomagnetic gradient reference map in navigation area.The dissertation takes advantage of Digital elevation model(DEM)and pseudo-magnetic field to present the forward theoretical formula of full tensor geomagnetic gradient data.The composition method of reference map combined with geomagnetic field model has provided the necessary basic condition for the practicality of MGAINS.With the development of construction method of reference map database in navigation,the data volume of database is on the dramatic increase.In order to circumvent the anti-missile system,the cruise missile needs long-distance transmission of reference map data to change routes temporarily for maneuvering flight.Therefore,we need to study compression method of navigation data and rapid real-time reconstruction algorithm to enhance the maneuverability of missiles.The main drawbacks to the traditional data compression methods are the problems of contour texture and detail information of high frequency loss.In order to reserve the key feature information of high frequency,the dissertation presents novel methods for geomagnetic data compression and reconstruction.Algorithms base upon discrete cosine transform for frequency divisive data compression,and takes advantage of compressed sensing theory.The accurate reconstruction utilizes partial cosine transform measurements,and consists of solving l1-norm and total-variation minimization programs.The dissertation concentrates on the requirements for different tactics of cruise missile in cruising and terminal guidance stage.We studies on the geomagnetic gradient aided positioning algorithm and magnetic anomaly detection technology,by using the high precision geomagnetic gradient navigation reference map that we constructed.Firstly,in the non-liner filtering algorithm for geomagnetic gradient aided positioning,we present MGAINS Particle Filter(PF)equation state equation and measurement equation under tight coupling.The simulation results verify the effectiveness and robustness of the proposed method.Secondly,we apply full tensor magnetic gradient to improve magnetic anomaly detection method and enhance the effect of magnetic target identification.Meanwhile,it is an essential principle that we combine magnetic anomaly detection technology with geomagnetic gradient aided positioning algorithm,and establish a unified model of particle filter.Cruise missiles finally actualize the magnetic target identification in terminal guidance stage.