Study Of Depth Solution Of The 3D Inversion Problem For Airborne Gravity Gradients

Airborne gravity gradient tensor measurement is the revolutionary technology in geophysical exploration. It has many advantages, especially, anomaly of gravity gradient which has higher resolution than gravity anomaly can reflect the details of subsurface geological body, using the information of various gradient components can improve accuracy of geologic interpretation. It has a broad application prospect in the actual exploration.Recently, airborne gravity gradient tensor measurement has developed very quickly. Abroad, it has made great progress on the research of airborne gravity gradiometric system and inversion method. In China, there is little achievement in the field of airborne gravity gradient measurement. Fortunately, we have been carried out the research of airborne gravity gradiometer recently. And for airborne gravity gradient tensor measurement, researches of inversion method and software have been carried out in advance. Based on this project, we study the forward theory, inversion method of 3D gravity gradients, and regularized inversion at first in this thesis. It also improves ShengJun (2008) calculation program for forward modeling and inversion, and achieves accurate inversion calculation accuracy. Second, we focused on solving low depth resolution in the regularized inversion of anomaly of airborne gravity gradient, and present an effective and practical method to solve this problem.Generally speaking, the low depth resolution of inversion is one of the common fatal weaknesses of potential filed. Similar as other gravity and magnetic data, the airborne gravity gradient data lacks the depth resolution inherently; the density structure obtained from inversion always tends to be concentrated in the near surface, which is the low depth resolution of inversion, commonly known as "the drift"of the model, which severely restrict the inversion effect. So, in order to achieve the real 3D density distribution, we must solve the depth resolution problem. This paper introduces the weighting technique in regularized inversion to improve depth resolution. Firstly, we present a depth weighting function which is appropriate for airborne gravity gradient inversion, and emphatically study on the inversion effect by selecting different weighting parameters. Model tests show that weighting effect in the inversion entirely depends on the weighting parameter selected. Secondly, we also present the selection principle of weighting parameter. Model tests show that weighting function we choose can improve the depth resolution of inversion. The weighting parameter (weighting function) based on the above principle can improve the depth resolution of airborne gravity gradient components at different levels. In addition, studies have shown that joint inversion of airborne gravity gradient multi-component with no weighting technology has a higher depth resolution than single-component.