Study On The Earth Gravity Field Model Determined By Combined GRACE And GPS Satellites

Satellite gravity measurement is an important means to determine the Earth's gravity field model.The successful implementation of the GRACE satellite gravity measurement mission has made the Earth's gravity field model with unprecedented precision and spatiotemporal resolution,the determined time-varying Earth's gravitaty field model also gives people a new source of understanding of the Earth's system mass migration.In the processing of GRACE data,domestic scholars often adopt a "two-step method" for determining the gravity satellites' orbit and gravity field model in steps.With the development of relevant models and computational conditions,the “one-step” solution for the realization of theoretically more rigorous observations of various types of joint navigation satellites and gravity satellites is an inevitable trend.At present,some scholars have realized a one-step method in narrow sense for direct calculation using on-board GPS observations.This thesis will further study how to complete the one-step solution of dynamics combined with GPS and GRACE observations.In order to facilitate the error control,this thesis considers the method of generalized one-step method for the precise orbit data of GPS and GARCE satellites as pseudo-observation values.According to the principle of the dynamic integral method determined by the Earth's gravity field model,the thesis studies the establishment of the solar radiation model,the most important part of the non-conservative force of GPS satellites.At the same time,the methods for determining the attitude yaw angle of different types of GPS satellites in different periods(nominal attitude,earth shadow period and maneuver period)are discussed.Finally,a set of low-degree gravity field models were computed by using GPS satellites alone.A set of time-varying gravity field models was computed by combining GPS and GRACE satellites,and the results of the thesis were compared with the results of other institutions.The main works in this thesis are as follows:1.Based on the in-depth study of the dynamics method of determining the gravity field model,form the observation equation of the dynamic one-step method,write the program,and construct the solving platform using the orbit data as the observation value.2.In-depth study and analysis of GPS satellite attitude determination methods,clarify the satellite coordinate system axis orientation in different periods,realize the conversion process of satellite orbit data to yaw angle,and prepare for the establishment of solar radiation pressure(SRP)model.The empirical SRP model of CODE series is given.Long-radius orbit integration is performed using parameters fitted by different SRP models.The prediction accuracy of different models is compared.The original version of the nine-parameter model is selected in the final solution.3.Using GPS orbit to obtain a set of time-varying models of low-order gravity field,the obtained SRP parameters(D direction constant term parameter)are consistent with the magnitude and change period of GAMIT solution,and compare the trend of the C20 time series with the results of other organizations using SLR and GARCE solutions.4.A set of time-varying gravity field models is obtained by combining GPS and GRACE orbit data.The RMS value of the difference between the integrated orbit of the initial parameters of the solution and original orbit is in the order of centimeters.The trend of calculated C20 time series is more consistent with the results of GFZ.The formal error of every degree is similar to other organizations,and the accuracy in the higher-degree parameters is better than that of JPL.The equivalent water height change analysis of the time-varying model shows obvious seasonal signals in the Amazon region and southern Africa.