Research On Aided Navigation Method Based On Gravity And Gravity Gradient Information Fusion

As the main equipment for ocean exploration,underwater vehicles have been widely used in civil and military applications.Inertial navigation system(INS)is widely applied to the underwater vehicle because of its passive and autonomous navigation characteristics.However,the positioning error of inertial navigation system will gradually accumulate with the increase of time,which will lead to large positioning error in long time navigation.Based on gravity field navigation does not need to transmit or receive radio wave information,and it can ensure the concealment and safety of underwater vehicle.Therefore,gravity field can be used to assist navigation of inertial navigation system,so as to reduce inertial navigation error and improve navigation accuracy.Gravity field based aided navigation is mainly gravity aided navigation and gravity gradient aided navigation.The reference map is one of the key elements of the gravity field aided navigation.It is an important means to obtain the gravity reference map and the gravity gradient reference map by measuring instrument.At present,there have been public gravity data in some parts of the world,but there is no public gravity gradient data.Therefore,there are mainly two methods for the preparation of reference map: one is gravity and gravity gradient data obtained through spherical harmonic model of the earth's gravity field,the other is gravity and gravity gradient data acquired by terrain elevation method.In this paper,gravity and gravity gradient data are calculated from terrain anomalies using topographic elevation forward modeling,and high-frequency information contained in gravity gradient maps and low-frequency information contained in gravity maps are analyzed using gravity reference maps and gravity gradient reference map data.In order to make full use of the high and low frequency characteristics of gravity and gravity gradients,gravity and gravity gradient data are fused to aid navigation.In the frequency domain,Gaussian low-pass filters and Gaussian high-pass filters are used to filter gravity data and gravity gradient data,respectively,the filtered data is added again to fusion.The data is high-pass filtered,and the filtered data is added and fused.Then,the fused spectrum map is inverse-Fourier transformed to obtain a fused time-domain map.Finally,the matching simulation is performed.Simulation shows that the aided navigation method based on gravity and gravity gradient data fusion is improved the precision of navigation.