Using Airborne Gravity Gradient Data Recover Regional Gravity Field

The Earth’s gravity field which restricts the movements and changes of the matter in thewhole Earth system is one of the basic physical fields of the Earth. At the same time, all thephysical events within the system are reflected in the Earth’s gravity field. Therefore,achieving high precision of the Earth’s gravity field plays an important role in solidgeophysics, oceanography and other related scientific researches. With the development ofspace science and technology, the observation technology of exploring the Earth’s gravitywhich use the plane as observation vehicle has been constantly developing. Meanwhile, thedevelopment of the airborne gravity measurement system has brought the improvement ofobservation precision of the Earth’s gravity field. This makes it possible to achieve theEarth’s gravity field model with higher precision and higher resolution.In theory, airborne gravity gradient (AGG) measurement can receive a higher gravityobservation precision and resolution than airborne scalar or vector gravity measurement andwhich has important application value in geophysical prospecting and other fields. Therefore,researches on the theory and methodology of AGG data processing have more realisticsignificance at present. For the regional gravity field approximation, the rectangular harmonicanalysis (RHA) is an ideal and practical method. The downward continuation of ill-posedproblems can be overcomed by appropriating regularization method, using AGG data to makerectangular harmonic analysis, taking some effective measures to control of edge effect.Under the background of the scientific research, the theory and methods for thedetermination of the earth’s gravity field based on AGG technique are studied in thisdissertation, the corresponding AGG data processing program and numerical simulationsoftware package with autonomous copyright are developed. The ultimate purpose is toestablish the foundation of the AGG practical data processing and related application researchand to accumulate experience for the development of our country’s AGG system and thefoundation of high-precision gravity field models using AGG data in the future.The main contents and contributions in this dissertation are listed below:1. Summarizing the influence of the Earth’s gravity field to the related science fieldsystematically, reviewing the development of gravity field approximation theorycomprehensively, and introducing the development process of airborne gravity gradient measurement system briefly, summarizing and commenting on the research progress inrecovering the Earth’s gravity field and theAGG data processing internal and external.2. Research on the fundamental theories of the AGG, including the coordinate referencesystem, the principle of AGG, the gravitational gradient tensor transformation betweendifferent coordinate systems, AGG measurement errors， weaken measures and so on.Moreover, the data preprocessing process of AGG theory is expatiated.3. The key techniques in recovering the Earth’s gravity field using AGG data arestudied and analyzed in details. Rectangular harmonic analysis (RHA) is proposed for AGGand the formula for the rectangular harmonic coefficient based on the disturbing gravitypotential is derived independent. The numerical solution methods for the gravity fielddetermination are investigated in details, including the methods for solving ill-posedproblems. This paper mainly studying the principle and mathematical model of Tikhonovregularization, Ridge estimate and Truncated singular value decomposition, in order toprovide the model and arithmetic foundation for the software programming. By extending thesize of computation area, the edge effect of RHA is successfully decreased. Numericalcalculation shows that: when the extended parameter values between50-60km, the resultaccuracy is improved remarkably. In the regularization parameter selection method, GCVmethod was obtained optimal parameters are relatively stable4. Because the lack of actual airborne gravity gradient data we using simulated data todo the experiment, in order to verify the reasonableness of the proposed recovery regionalgravity field model. This paper build a mathematical model to simulate airborne gravitygradient measurement data, in order to simulate the AGG observation data. Using simulationvalues and combined it with AGG mathematical model to calculate the potential coefficientsand the next step is computational model of gravity disturbance. Finally, by EGM2008Earthgravity field models combined with ultra-high degree Earth’s gravity field parametercalculation software, a gravity disturbance "true value" is calculated. Numerical calculationsshow that: based on the continuation of TSVD value and the real value of difference within±20mGal, most computing point of difference between the true value does not exceed±5mGal. TSVD regularization method can realize the stable downward continuation of gravityfield signal. Therefore, in this paper, the airborne gravity gradient data recovery regionalgravity field computation model is feasible.5. This paper develops a multifunctional software system for using AGG data torecovery the regional gravity field which contains a number of modules, such as the basic theory of airborne gravity gradient measurement (reference system, coordinatetransformation), data simulation, AGG rectangular harmonic analysis model, regularizationmethod and the gravity field parameter assignment, and so on.