Precise Orbit Determination And The Earth Gravity Field Recovery By One Step Method For GRACE

As a basic physics field, the earth gravity field, which reflects the earth’s mass distribution and moving law, plays an important role. In recent tens of years, as the gravity satellites such as CHAMP, GRACE and GOCE launched, satellite-borne gravity measurement technology has become an important method to get the low and middle degree information and time-variation of the earth gravity field. To get highly precise gravity field and its time-variation, satellite-borne GPS quality control, satellite dynamic model extraction, huge amounts of parameters evaluation and high performance computing are the most complicated technology problems to be overcome. This thesis focuses on the basic theory and algorithm related to LEOs’precise orbit determination and the earth gravity field recovery, programs a suit of software named Satellite Precise Orbit Determination And Gravity Field Recorvey System or SPODAGRS for short autonomously, realizes precise orbit determination for GRACE at several centimeters’level and completes the earth gravity field recovery by one step method. The main works and contributions are as the following:1. The transformation for time systems and coordinate systems is researched and realized. Based on IERS 2010 and SOFA, this thesis realizes the time systems’transformation, coordinate systems’transformation and reference frameworks’transformation for satellite precise orbit determination.2. The theory and algorithm of LEOs’precise orbit determination is expounded systematicly. The basic principle of dynamic orbit determination and collocation integration is researched deeply and the satellite acceleration’s derivative with respect to the position, the velocity, and dynamic parameters is induced and formated based on vector derivative law. Specially, the formula about the earth gravity, gravity gradient and the derivative of the gravity with respect to the potential coefficient with the cartesian coordinate in ECEF, which can avoid the singularity near the field of both poles, is induced based on mathematical induction.3. An efficient algorithm of satellite precise orbit determination is proposed. Aimed at the plenty of piece-wise dynamic parameters and the low performing efficiency, the mapping relationship about the unknown parameters related to design matrix and normal matrix is analysed. By introducing piece-wise initial orbits and performing parameter transformation for dynamic parameters and then eliminating the dead parameters from the normal equation, the dimension of collocation integration and normal equation decreases rapidly and the performing efficiency increases greatly. The experiment indicates that the time consumed is saved 78% at most by using efficient algorithm, compared to the traditional algorithm.4. A circle-skipping detected method based on KBR’s first-order derivative and second-order derivative is proposed by analysing the basic observing model of KBR data derived from GRACE-A and GRACE-B satellites. Reduced dynamic orbit determination for double satellites is realized based on pseudo stochastic pulse model and empirical force model with 9 parameters by using satellite-borne GPS and KBR data. The experiment indicates that the RMS in R, T and N directions is less than 0.03m. Compared to the single satellite orbit determination, the RMS is improved by 0.001m usually and 0.003m at most.5. Aimed at the problem that the non-conservative force is so complicated that its model is difficult to establish, the basic principle that the data from GRACE satellite-borne accelerometers is used as non-conservative force instead is researched and the dynamic orbit determination with double satellites is realized by using satellite-borne GPS data adding to KBR data. The experiment indicates that the RMS in the R and T directions is less than 0.01m and 0.03m separately and less than 0.04m mostly in the N direction.6. Aimed at the problem that more than one days of GRACE data needs to be combined to solve the normal equation in the dynamic method for the earth gravity field recovery, the basic principle of combined estimate for more than one days of satellites data is researched and a general method for the orbit combination based on the efficient algorithm is proposed. The formula of parameter transformation and its detailed procedure is supplied.7. Using the GRACE precise orbit data for the earth gravity field recovery, three gravity field models named GR-EMP-2-1, GR-PLU-2-1 and GR-ACC-2-1 with sixty degrees and orders are derived based on the empirically dynamic model with nine parameters, the pseudo stochastic pulse model and accelerometer data instead of non-conservative force. Compared to the precise orbit from GFZ, the RMS of final orbits is less than 0.002m,0.000m and 0.006m respectively. Compared to the earth gravity field DIR_R5, the GR-PLU-2-1 and GR-EMP-2-1 models are better and the STD of global geoid is 0.28m and 0.44m respectively. Compared to the surveyed data from GPS/leveling, the STD is 0.22m and 0.27m respectively.8. Aimed at the problem that the theory is not rigorous in the earth gravity field recovery by two step method, the more rigorous one step method is researched. Using satellite-borne GPS and KBR data of two GRACE satellites, as well as empirical force model with 9 parameters, pseudo stochastic pulse model and data from satellite-borne accelerometers to replace non-conservative force, then three gravity field models named GR-EMP-1-2-KBR, GR-PLU-1-2-KBR and GR-ACC-1-2-KBR are obtained respectively and the first two models are more precise. Compared to DIR_R5 model, the STD of global geoid height of the two models is 0.54m and 0.55m respectively. Compared to the surveyed data from GPS/leveling, the STD of height anomaly of the two models are 0.58m and 0.56m respectively. However, compared to the DIR_R5, the STD of the global geoid height about GR-EMP-1-2 and GR-PLU-1-2, using only satellite-borne GPS data, is 0.91m and 0.79m. Compared to the surveyed data from GPS/leveling, the STD of height anomaly are 1.26m and 1.40m respectively. The results indicate that the KBR observations have a significant effect on the recovery of the earth gravity field, which can improve its precision dramatically.9. Aimed at the problem that the amount of computation is large and the computation time is long, a new solution of parallel computing is proposed. This solution makes full use of the advantages of the existing computer hardware, the multi thread parallel computing, multi process parallel computing and multi computer distributed computing based on the network environment, and realizes the distributed computing method based on the network environment for the earth gravity field recovery, greatly improving the calculation efficiency.10. A software named SPODAGRS for short is developed autonomously. Based on the standard C++programming language and SOCKET network programming API, SPODAGRS is realized independently and autonomously. The system realizes the main function of GPS orbit fitting with dynamic smoothing method, LEOs’orbit fitting, geometry orbit determination, dynamic orbit determination, reduced dynamic orbit determination and especially the earth gravity field recovery by one or two step.