Geometric Error Analysis of Frequency-Domain Magnetic Dipole-Dipole System

During the underground exploratio with frequency domain electromagnetic instruments based on magnetic dipole model, systematic errors are caused by the position and attitude changes of transmitting and receiving coils due to installation errors, the sway of instruments, as well as the geometric distortion of materials and other factors. The quantitative analysis of geometric errors for frequency-domain electromagnetic instruments has a great guiding significance in instrument production, field operation and system correction. According to the sources of the errors, the geometric errors were divided into two categories, one is the primary field error, the other is the secondary field error. By introducing the tensor matrixes of the primary field and the secondary field, we forwarded the primary field and the secondary fields from nine configurations based on homogeneous earth model, and quantitatively analyzed the features and changes of the geometric errors of the nine configurations in a differential way. Numerical results show that, in the primary field errors introduced by the geometric distortion, only PERyz and PERzy coil configurations do not contain linear term of the position change; only VCA, VCP and HCP configurations do not contain linear term of attitude change. In the secondary field errors introduced by the geometric distortion, PERzx and PERxz coil configurations have the maximum relative error; VCA, VCP and HCP coil configurations are greatly influenced by the change of height and coil separation, which needs real-time measurement for correction; and the VCP coil configuration is least influenced by the change of coil separation and attitude.