Study On The External Correction Method Of High-precision Gravity Measurements And Its Application

Existing external gravity correction methods including four processes which are latitudecorrection, elevation correction, intermediate layer correction and topographic correction. Theexternal gravity correction methods exist in a large number of simplifying assumptions inorder to reduce the amount of calculation and improve the efficiency of operation. However,there are some question casused by the simplifying assumptions, for example, calculationerrors in normal gravity field, errors caused by the difference between the geoid and thereference ellipsoid and the errors in intermediate layer correction and topographic correctioncasused by the improper selection of the density. On the other hand, in plateau mountainousarea, the formations offen outcrop to the surface. So, cut off all the part which distributionabove the geoid will cause the contradiction between the gravity anomaly and the structuralshape. With the emphases of exploration in China gradually shifted to the western mountainsand the improvement of the accuracy of gravity measurement, this gravity correction methodwhich exist in a large number of simplifying assumptions will become the primary factorrestricting the exploration of gravity.Aiming at these problems in the current gravity external correction, the paper proposes anew gravity correction which cancels the topography correction and the intermediate layercorrection. At first, the paper derived the earth surface normal gravity formula in WGS84geodetic cocordinate system based on the Stokes’ theorem and makes the WGS84referenceellipsoid as boundary conditions. We can use the formula to calculate the normal gravity fieldof every survey point in the earth surface directly and then make it as the correction valuesubtract from the absolute gravity value. Through this method, we can calculate the gravityanomaly into the position of survey points in the earth surface. Questions in existing gravitycorrection can be avoided in the method proposed in the paper. The method can improve theaccuracy of gravity correction and retain the integral tectonic framework.The paper research and develop an absolute gravity two-dimensional modeling systembased on the WGS84reference esspsoid. And then design some models using the modelingsystem to verify the validity and efficiency of the method from three perspectives. Using actual data of two exploration blocks of Zhenba Mountain in Sichuan andQinggelidi moutainous verified the gravity correction method proposed in the paper canimprove the accuracy and exploration effect of gravity exploration.