The Research And Application Of Terrain Correction Method In Gravity Prospecting

Gravity is a traditional method of geophysical exploration. Gravity anomalies reflect density variations of subsurface geological bodies. The complete Bouguer reduction includes, in addition to the height correction, both the latitude and terrain correction. In mountainous areas, the topographical effect of the area around the computation points is differential. If neglecting the topographical effect of the terrain reduction, the interpreters may obtain the data including much false anomaly, and the image of anomaly can be obviously distortion. So, the decision of interpreting may be affected. With the error of gravity meters becoming smaller and smaller, the availability of improved terrain and geoid databases, enhanced computational power, and increasing use of global positioning system(GPS) technology to establish the location and heights of gravity stations, in rugged topography terrain corrections are the most important source of error in the reduced Bouguer anomalies. Therefore, the available reduction procedures don’t satisfy the demand. So we must improve the precision of complete Bouguer correction of Bouguer gravity anomaly.Different methods of terrain correction have different precisions. This article first studies and analyzes the disadvantages of traditional square-domain integral(volume integral) as follow: on the one hand, the square-domain can not fit the actual terrain well because of its square columns fitting; on the other hand, the terrain correction precision of the numerical integral employed in traditional methods is too low to meet the demand of high-precision gravity survey. This article studies and simulates the surface integral based on the ground surface, and then replace the original trapezoidal integral with Gauss numerical integral of relatively high precision. The result shows that the Gauss numerical integral not only realizes the best fitting to arbitrary terrain but also obviously enhances the precision of terrain correction, which is verified by the practical application. In total, this article proves that the terrain correction methods based on surface integral are better than traditional ones based on square domain.In order to verify the application effect of the surface integral, this paper uses the actual terrain data of two work area, computes separetely the terrain correction to the survey zone in square-domain and surface integral methods,and studies the computational results of the two methods under different terrain conditions. This paper compares the errors between total terrain correction and local gravity anomaly obtained after the terrain correction, and analyzes the individual characteristics of the two methods. It is proved that the terrain correction method based on surface integral is superior to the one based on traditional square-domain terrain correction method on the aspects of both computational result and computational efficiency.The terrain correction method based on surface integral is successfully applied to the processing of practical date, and good results are achieved.In order to improve the accuracy and efficiency of acquiring the node elevation in the terrain correction of gravity in both intermediate and far zones. we have a preliminary discussion on the use of software Google Earth to acquire node elevation in a certain area of Tibet, and verify the feasibility of using acquired elevation to carry out the gravity terrain correction in both intermediate and far zones.