Joint Inversion Of Gravity And Gravity Gradient Based On Irregular Grid

Gravity exploration has become an important part of geophysical exploration because of its fast,easy-to-operate,and low-cost characteristics.With the advancement of measurement technology,the application of gravity gradient data has received more and more attention.From theoretical analysis,gravity gradient data is the second derivative of gravity data along the three directions of x,y,z,so it has more high-frequency information.Joint inversion of gravity and gravity gradient data can achieve the complementarity of the two,To reduce the ambiguity of inversion.Regarding the model space for inversion calculation,regular or irregular division can be used.The division method of regular hexahedron is simple and tidy,and is convenient for rapid calculation.However,in actual production,there may be uneven undulating terrain on the ground,and the division method of irregular grid can more accurately fit the terrain undulations.Research Gravity and gravity gradient inversion based on irregular grids can help improve the accuracy of inversion calculations.Therefore,this paper carried out a joint inversion of gravity and gravity gradients based on irregular grids.First of all,this paper chooses tetrahedron of arbitrary shape as the basic unit of irregular grid division,gives the basic principle of arbitrary tetrahedron forward calculation,realizes the gravity forward calculation,and discusses in detail the possible encounters in the forward calculation process.The problems and corresponding solutions have also realized the six-component forward calculation of the gravity gradient of any tetrahedron.Through a trial calculation of a regular hexahedron model,the relative error between the tetrahedral division method and the hexahedral analytical calculation method is compared,and the accuracy and rationality of the forward calculation method described in this article are verified.Secondly,this article introduces the basic principles of regularization inversion,and applies regularization inversion to gravity and gravity gradient inversion.It also discusses how to apply the roughness matrix of the smooth constraint of the regular grid to the irregular grid similarly when the irregular grid is divided.Aiming at the situation that the boundary of smooth constrained inversion results is blurred and the scope is divergent,this paper also conducts focused inversion,and discusses the joint inversion of gravity,gravity gradient and their different combinations in the case of smooth inversion and focused inversion.The results show that whether it is focused inversion or smooth inversion,gravity gradient data has a stronger lateral resolution capability than gravity data.Gravity contains more deep information.Joint inversion can improve the resolution and have different components.Combination,the effect of joint inversion is also different.Finally,this article applies the theory described in the article to the theoretical model calculations with terrain,introduces the selection method of the model inversion initial value under the undulating terrain model,and discusses the inversion results,which have achieved good results.