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????????????????棬??????????????????η??????????????????Σ????????????????????????????θ?????????????????κ???????????????????????б?????????????????????θ??????????θ???????????????????????С??????θ????1 000 m?????????????0??5 mGal?????????????????????????????????Χ?????????θ??????????????????????????????????????????????????????????????????????????????

Study on Topography Correction based on Spherical Approximation

Assuming the geoid as spherical approximation，the topography correction was calculated by dividing the actual topography into the Bouguer shell and the rough terrain based on the radius of the calculated point.The comparison of the local terrain correction with the Bouguer planar shows that there is difference between the rough terrain correction and the local terrain correction；the difference is small in the even area.It is more than 0.5 mGal in the areas where the elevation is higher than 1 000 m.The integral range of the spherical rough terrain correction is easy to extend，so it can present the more signals than the local terrain correction，and it is more consistant with the actual earth shape.The regular topography correction calculated with the Bouguer shell and the Bouguer planar is the same in shape，but the difference of range is very large.