Theory And Methodology Of Earth's Gravitational Field Model Recovery By Leo Data

With the launching of Low Earth Orbit (LEO) gravity satellites such as CHAllenging Minisatellite Payload (CHAMP),Gravity Recovery And Climate Experiment (GRACE), Gravity field and steady-state Ocean Circulation Explorer (GOCE), satellite gravity observation has become another revolutionary breakthrough in Geodesy following the Global Positioning System (GPS). The Earth's gravitational field with high precision and resolution can be recovered by GRACE satellite data. However, the gravity information contained in the GRACE range and range-rate observations has not still been fully utilized up to now. This project mainly studies the theory and methodology to recover the Earth's gravitational field using GRACE satellite observations. The existing numerical methods are compared, and several improved methods are proposed. The main contents and innovation of the thesis are summarized as follows:1. The significance of satellite gravity observations is analyzed and the latest research progress of Earth's gravitational field has been reviewed. Three approaches to determine the Earth's gravitational field with satellite gravity data, i.e., direct approach, time-wise approach and space-wise approach, have been studied.2. The coordinate transform formulae between the quasi-inertial coordinate system and the Earth fixed coordinate system have been specified in detail following IERS conventions2003. A variety of force models of GRACE satellites have been calculated. Several numerical integration methods have been analyzed. The interpolation method of shifted polynomial has been studied. The method of QR decomposition to eliminate the local unknown parameters has been introduced. The detailed calculation steps of the preconditioned conjugate gradient algorithm to resolve the normal equations have been presented. The accuracy assessment methods of the Earth's gravitational field model have been described.3. Six methods (Kaula linear perturbation approach, point acceleration approach, short-arc integral approach, average acceleration approach, energy conservation approach and traditional dynamical integral approach) have been studied. The advantages and disadvantages of each approach have been analyzed. The observation equations of satellite range and range-rate have been presented. I has used one month simulated GRACE satellite data to recover the Earth's gravitational field up to degree and order80to verify the validity and reliability of the traditional dynamical integral approach.4. A method based on strict satellite's orbital perturbation theory has been introduced. The strict numerical calculation formulae of the approach have been derived based on the interpolation formulae of shifted polynomial. One month simulated satellite data have been used to recover the Earth's gravitational field with degree and order100, which verifies the validity and reliability of the approach.5. A short-arc integral approach with gradient correction has been presented. The impact of gradient correction of force models on satellite orbit has been analyzed. One month simulated data have been used to recover the Earth's gravitational field with degree and order120, which validates the precision of the approach.6. An improved short-arc integral approach has been first proposed based on another gradient correction. The mathematical formulae of the approach have been closely derived. The results of one month simulated data show that the improved approach is better than the short-arc integral approach. One month of simulated GRACE Follow-on satellite data have been used to analyze the precision of the resolved Earth's gravitational field model with the improved approach. The degree choice about the interpolation formulae of shifted polynomial has also been analyzed.7. A set of satellite gravity recovery software SWJTU-GRS has been developed. The software can be used to simulate GRACE satellite observations, prepocess GRACE satellite data, recover the Earth's gravitational field with various approaches, calculate and check the internal and external precision of the gravitational field model. The optimal arc and the weight between orbit and satellite-to-satellite observations in the improved short-arc integral approach have been analyzed.8. Four approaches have been compared through both theoretical analysis and the numerical calculation of one month of GRACE satellite data between2008.1.1-2008.1.31. The results show that the four approaches have almost the same accuracy when using only orbital observations. However, the improved short-arc integral approach is better than the short-arc integral approach, traditional dynamical integral approach and the gradient corrected short-arc integral approach when using satellite range observations.9. The gradient corrected short-arc integral approach and improved short-arc integral approach have been used respectively to derive two Earth's gravitational field models SWJTU2010S1and SWJTU2010S2up to degree and order120based on nearly200days of GRACE satellite orbits, ranges and range-rates from2008.1.1to2008.8.1. The resolution of the two models is167km (half wavelength) and the overall geoid accuracies are14.00cm and11.63cm, respectively. The overall accuracy of the two models is better than the model EIGEN-GRACE02S, EIGEN-GRACE0lS but less than the model EIGEN-CG01C.10. The preprocessing approach of GOCE precise orbits has been presented. The approach to establish normal equations has been derived to eliminate two classes of local parameters. I has used the short-arc integral approach to recover an Earth's gravitational field with degree and order110based on GOCE orbits of61days from2009.11.2to2010.1.2. The geoid height error of the model at degree106is±9.6cm and the model has low precision in zonal spherical harmonic coefficients. Another Earth's gravitational field model with degree and order110has been derived by combined satellite orbits of GOCE and GRACE. The geoid height error of the model at degree106is±6.9cm and the accuracy of zonal spherical harmonic coefficients has been significantly improved.