Research On Problems Of Underwater Gravity Aided Inertial Navigation

Under the condition of existing technology,submarines mainly rely on the inertial navigation system during navigation,but errors of the inertial navigation system will accumulate with time.As a result,a single inertial navigation system cannot provide accurate navigation information for a long time.It has already become a hotspot of underwater navigation technical researches to modify inertial navigation system errors by utilizing gravity aided underwater navigation.By starting from the key technology of gravity aided underwater navigation,based on the latest research achievements at home and abroad,systematic analysis,research and simulation assessment validation were conducted for key technology involved by gravity aided navigation through simulation calculation according to ship load gravity measurement data of some sea areas and DTU10 global gravity anomaly numerical model in this paper.Major research work and innovation points of this paper are as follows:1.The research background of this paper is mainly introduced.The development and application statuses of gravity aided underwater navigation are summarized;the research progress and existing problems of key technology involved by gravity aided underwater navigation are concluded;the research direction of this paper is clarified.2.Based on the basic principle of satellite altimetry,and a mathematical model of marine gravity anomaly based on satellite altimetry data inversion is given.Besides,the processing flow for ship load gravity measurement data in sea areas is described simply,and a deep analysis is made on major influence factors like E?tv?s effect correction and CC effect correction.DTU10 global gravity anomaly numerical model is simply introduced,and accuracy evaluation is conducted via ship load gravity measurement data.The overall accuracy of this model is better than ±5 mGal,reaching the accuracy of ±3.5 mGal in some sea areas.3.Ambient field grid transformation technology of gravity aided navigation is studied,and four mathematical models of grid transformation,including weighted inverse distance method,Kriging method,radial basis function and Shepard method,are analyzed.According to the complexity of gravity anomaly,two test blocks covering flat sea area and complex sea area are selected by setting DTU10 gravity anomaly numerical model as basic data.By considering the application scene of establishing ambient field of aided navigation,two test schemes including grid encryption and measuring line grid transformation are designed.According to the results,weighted inverse distance method has the poorest grid transformation accuracy,and Kriging method is slightly inferior to radial basis function and Shepard method in the grid transformation effect.The grid transformation accuracy of radial basis function and Shepard method is about ±0.1 mGal,and these two will not be restricted to the complexity degree of ambient field gravity anomaly change and the application scene.4.The mathematical model of marine gravity characteristic parameters are analyzed and discussed,and extraction methods of sea gravity anomaly characteristic parameters are analyzed.The defect of wrong selection might appear easily when suitable matching areas are selected by aiming at a single gravity characteristic parameter.Hence,a suitable matching area selection method based on multi-parameter gravity information entropy is proposed.According to the experimental results,this method can integrate several different gravity anomaly characteristic parameters,and qualitatively determine the suitability of this sea area.In order to quantitatively determine the adaptation level of the sea area selected,a suitable matching area selection method based on fuzzy integration decision-making is proposed.This method solves the overall evaluation index of the target sea area via fuzzy decision-making theory,to provide technical support for suitable matching area selection of gravity aided underwater navigation.5.The principles and characteristics of three most frequently-used matching methods,including SITAN algorithm(Sandia inertial terrain aided navigation algorithm),TERCOM algorithm(terrain contour matching algorithm)and ICCP algorithm(iterative closest contour point algorithm),are analyzed and compared.The differences between SITAN algorithm and TERCOM algorithm are compared from the aspects of aided navigation instantaneity,filtering algorithm adaptation and gravity ambient field dependency.A simulation experiment is conducted to verify that the ICCP algorithm matching effect is different in the area where ambient field change different and that its matching precision can reach 1n mile in sea areas with obvious changes of gravity anomaly ambient field.The algorithm is proved to completely satisfy the precision index requirement of matching area selection.