Study On Fast Calculation Method Of Airborne Gravity Terrain Correction

Compared with surface gravity exploration,aerial gravity exploration has the advantages of simplicity,economy and rapidity.In gravity exploration,the measured gravity data not only reflect the density distribution of underground material,but also relate to the shape of the earth,the elevation of the survey point and the topographic fluctuation.Therefore,before inversion and interpretation of airborne gravity data,a series of corrections should be made to the relative gravity values of each observation point to obtain gravity anomalies reflecting underground density distribution.Bouguer gravity anomaly is one of the most widely used gravity anomalies.It is obtained by terrain correction,middle layer correction,height correction and latitude correction after subtracting normal gravity from observed gravity values.Among them,terrain modification is one of the key links.Conventional terrain correction methods of airborne gravity need to divide the topography around the observation points into several square cylinders.The sum of the gravity influence values of these cylinders on the observation points is the terrain correction values of the observation points.Generally,the data of the observation points of airborne gravity is large,and the forward calculation of the cylinders involved is also much,and the calculation speed is slow.Technology of geometric trellis separation and storage is a fast forward computation method based on the translation equivalence and reciprocal symmetry between the uniformly partitioned mesh model and the measured points.However,this technique is applied in the condition of horizontal observation plane and horizontal model.The terrain of airborne gravity terrain correction is undulating,and the observation surface is undulating.Therefore,this paper uses the interpolation method to apply this technology to airborne gravity terrain correction.In this paper,the difference and relationship between airborne gravity terrain correction and ground gravity terrain correction are introduced firstly.Then,based on the rectangular terrain correction method of ground gravity,the conventional terrain correction method of airborne gravity is generalized.Using linear interpolation,the geometric trellis separation and storage technique in fast forward modeling is applied to airborne gravity terrain correction,and it is regarded as a fast calculation method for airborne gravity terrain correction.Then the error caused by the interpolation method is discussed and analyzed in detail.Finally,through model test and calculation of actual data,the conclusion is drawn,when the number of observation points is large,the fast algorithm can greatly improve the calculation speed of airborne gravity terrain correction on the premise of ensuring certain accuracy.