The Earth Gravity Field Model And Its Application In Tunnel Survey

As one of the most active areas of research of the physical geodesy, the accuracy and resolution of the earth gravity field model has achieved a major breakthrough, especially on the improvement of the ground and the air of gravity measurement techniques, and new methods of satellite gravity measurements realized. As the most advanced models, EGM96 has reached decimeter-class. Using local and global gravity field models can resolve earth gravity field, which can conveniently and quickly calculate geoids undulation, gravity anomaly, deflection of the vertical, disturbances gravity and other gravitational field parameter. Such theoretical and practical application of advantage, make local and global gravity field models in a broad area of disciplines and applications in geodesy, geophysics, geodynamics, oceanography, space science and military applications.This paper describes the definition and intension of the earth gravity field model, and introduces the process of deducting expressions of the earth gravity field model with spherical harmonic function in detail. The calculation of the height anomaly, gravity anomaly and deflection of the vertical of an arbitrary point with EGM96 is introduced and several kinds of methods for calculating geopotential coefficients of the earth have been summed up. This paper introduces the present situations and technical models for refining provincial (municipal) geoids in china, and discusses the reduction of surface observations. The paper realizes the visualization of the earth gravity field model. Based on the above theory, using seven points' data of the horizontal control network of the Erlang mountain tunnel, we can compute the deflections of the vertical of the control points, and according to conversion of the surface direction observations, have calculated and analyzed influence of the deflections of the vertical to horizontal control survey.