Study on influence and correction of coil attitude and bird swing for the fixed-wing time-domain electromagnetic system

During surveys of the fixed-wing time-domain electromagnetic system,the changing transmitter and receiver coil attitude and bird swing can introduce the system parameter errors into the survey data including the direction of transmitter magnetic moment,the component and position of receiver coils,as well as the horizontal distances between transmitter loop and the receiver coils,consequently affecting the inversion results.Based on the forward modeling of the fixed-wing time-domain electromagnetic,this paper suggests the rotation matrix of the transmitter and receiver coil according to the attitude variation algorithm,and obtains the swing Green′s tensor by using the relative position between transmitter loop and receiver coils.Then the expression of three-component electromagnetic response with arbitrary attitude and swingangle is derived.The electromagnetic response in respect to the bird rotation and swing is studied.The simulation results indicate that the pitch of the transmitter and receiver coil and the in-line swing have the greatest influence on the electromagnetic response.Therefore,the variation of the electromagnetic response when the in-line swing angle and the pitch of the transmitter and receiver coil coexist is analyzed.On this basis,the relationship between the response coefficient and earth conductivity is discussed.Meanwhile,the correction of attitude and bird swing of the fixed-wing airborne electromagnetic system is conducted.The inversion results of a quasi-two-dimensional layered earth model show that the accuracy after correction is enhanced by 33.1%.