Spectral Expansion Gravity Field Model And Its Application In Height Datum Unification And Inertial Navigation Gravity Compensation

The earth’s gravity field,as a reflection of all the earth’s mass,it is very important to study the shape of the earth,the unification of height datum and the gravity compensation of high precision inertial navigation system.With the advancement of the satellite gravity missions,the means for obtaining the earth’s gravity field information are more advanced and the data are more abundant.However,due to the limited coverage of full band and high-precision ground gravity observations,high coverage satellite gravity observations have lower resolution.Different gravity observation methods have different resolution and different spectral characteristics,which is a difficult contradiction between the accuracy and high resolution of the current earth gravity field model.The rapid development of earth related disciplines puts forward new requirements for the establishment of high-precision and highresolution earth gravity field model.Under this background,this paper studies the applicability of spectrum expansion method in gravity field modeling,constructs the refined gravity field model based on spectrum expansion technology,and studies the method of realizing height datum unification and gravity compensation for inertial navigation system based on the refined gravity field model.The main work of this paper is summarized as follows:1.A high-resolution combined gravity field model is modelled based on spectral expansion technology.According to the multi-source data such as satellite gravity,highdegree gravity field model and terrain data,and according to the spectral characteristics of different observation data,this paper introduces two strategies to determine the combined gravity field model by using spectrum expansion technology.The first is to determine the combined gravity field model by combining GOCE/GRACE models,EGM2008 model and RTM model,The GOCE/GRACE models and EGM2008 model are combined by pure combination and least square weighting.The second strategy is to directly combine the high-degree gravity field model and RTM model to determine the combined gravity field model and recover the high-frequency gravity field signal of the high-degree gravity field model.The determined combined gravity field model is applied to realize the unification of height datum and gravity compensation for highprecision inertial navigation system.2.The 1985 height datum gravity potential value in China is determined based on the combined gravity field model.The combined gravity field model was determined by combining the TIM_R5,TIM_R6,DIR R5 and DIR R6 satellite gravity field models with EGM2008 model by pure combination method,and the high frequency gravity field signal of the combined gravity field model was recovered by RTM technique.Finally,the 1985 height datum gravity potential value in China is determined by combining the gravity field model and GNSS/leveling data.The results show that the best combination degree of TIM_R5,TIM_R6,DIR_R5,DIR_R6 and EGM2008 models in Mainland China is 230,240,220 and 240,respectively.Considering the influence of systematic error on the estimation of 1985 height datum gravity potential value in China,the gravity potential value of 1985 height datum determined by combined gravity field model DIR_R6_EGM2008_RTM model is 62636853.29 m2s-2.However,the main systematic errors for determining height datum gravity potential value in China are the gravity field model error rather than the leveling cumulative error,and the systematic errors caused by the gravity field model is more obvious in the west of China.3.The least square weighted method is used to combine DIR_R6 model and EGM2008 model to determine the combined gravity field models,and the RTM technology is used to restore high frequency gravitational field signal of the combined gravity field model.The GBVP approach based on the combined GGM,residual terrain model(RTM),and residual gravity is used to estimate the vertical datum parameters of the North America Vertical Datum of 1988(NAVD88),the Australia Height Datum(AHD),and the Hong Kong Principal Datum(HKPD).The results show that the combined model DIR_R6_EGM2008 model has stronger geoid signal and lower geoid degree error compared with EGM2008 and DIR R6 models.The geopotential values of the North American Vertical Datum of 1988(NAVD88),the Australian Height Datum(AHD),and the Hong Kong Principal Datum(HKPD)are estimated to be equal to 62636861.31±0.96,62653852.60±0.95 and 62636860.55±0.29 m2s-2,respectively.The vertical offsets of NAVD88,AHD,and HKPD with respect to the global geoid are estimated as-0.809±0.090,0.082±0.093,and-0.731±0.030 m,respectively.4.Gravity compensation of inertial navigation system based on combined gravity model is studied.By establishing the error propagation equation of inertial navigation system under the influence of horizontal gravity disturbance,the combined gravity field model EIGEN-6C4_RTM was determined by combining EIGEN-6C4 model and RTM,and the multi-band gravity disturbance determined by the combined gravity field model EIGEN-6C4_RTM is introduced into the inertial navigation calculation.The error and frequency characteristics of inertial navigation system caused by gravity disturbance are analyzed.The results show that the horizontal gravity disturbance can cause the navigation error in the form of Schuler oscillation,and the amplitude of the navigation error is directly proportional to the amplitude of the gravity disturbance.For the carrier running at low speed,the high frequency signal of horizontal gravity disturbance has a more and more significant impact on the position of inertial navigation.The effectiveness of this gravity compensation method is verified by dynamic test,the compensation method can reduce the error oscillation trend of inertial navigation,and the positioning accuracy of inertial navigation system is improved after compensation.