Forward And Inversion Method Of Gravity Data Based On Bodyfitted Grid Generation

Forward and inversion are always one of the most important research contents in the processing and exploration of gravity data.Usually,forward is the basis of inversion,and inversion is the important basis of geological interpretation.At present,the mainstream method of inversion is to divide the inversion space based on the horizontal surface and then to calculate the inversion result.However,the Bouguer gravity anomalies obtained by various corrections are based on the surface of actual terrain in gravity prospecting.Therefore,with the improvement of prospecting accuracy,the inversion gravity technology based on true terrain surface is urgently needed.When the conventional octree structure is used to fit the complex terrain,the stepped boundary will be come out,and the fitting degree is usually inadequate.At present,it is a hot spot to consider the method of inversion calculation by dividing the inversion space into irregular mesh to fit the complex terrain surface.This thesis explores the method based on irregular body-fitted grid to divide the inversion space and establishes the forward and inversion algorithm method of gravity data based on irregular body-fitted grid.Irregular body-fitted grid is a method commonly used in fluid mechanics.Based on the properties of the field intensity distribution near the field source,which is related to the form and intensity of the field source,Poisson equation is used to generate the grid system.The algorithm can transform the irregular computing area in physical space into a regular rectangular region in the computing space.By adjusting the right term of the equation,the shape and density of the curve mesh grid on the actual physical space can be adjusted.The research contents of this thesis are summarized as follows:1.Aimed at the rugged terrain,we study the body-fitted grid generation method in twodimensional space and three-dimensional space.Hilgenstock method,which is stable and adaptable,is improved by using gravity forward and inversion characteristics.The inversion space can be divided into grid with good orthogonality and uniform distribution to the rugged terrain.The model tests show that the body-fitted grid can control the orthogonality of the rugged terrain and make the mesh uniformly distributed without changing the mesh scale size.2.For the two-dimensional space,based on the research of the body-fitted grid generation method,the adaptive grid technology is introduced so that the finally generated two-dimensional adaptive body-fitted grid can not only control the orthogonality with the rugged terrain but also realize the distribution the density of the grid automatically according to the change of the physical property gradient.On this basis,the gravity forward equation based on the polygonal is studied,and the gravity inversion method based on the two-dimensional adaptive body-fitted grid is carried out for the rugged terrain.Through model tests and actual data,it is shown that the inversion method based on the two-dimensional adaptive body-fitted grid can accurately depict the underground geological bodies while keeping the data scale unchanged.3.For three-dimensional space,based on the study of body-fitted grid generation method,the gravity forward equation based on the rectangular division is studied,and for the rugged terrain,the inversion algorithm of physical property constraints of gravity data based on body-fitted grid is deeply studied.Model tests and actual data show that in a three-dimensional space containing rugged terrain information,the gravity inversion method based on the three-dimensional bodyfitted grid can ensure good orthogonality to the rugged terrain and make sure keep the data size scale remain unchanged.It also can be more accurately to describe the occurrence of the underground geological bodies.