Theoretical study of concentric loop coils attitude correction in helicopter-borne TEM

During the helicopter time electromagnetic (TEM) survey, transmitting and receiving coils fixed in the bird can be rotated by flight speed, bumpy, wind direction, etc. Meanwhile, the coupling change between coils and earth causes the attitude error to TEM survey data, so it's crucial to study a correction algorithm of the coils attitude. Based on building up the bird and earth bi-coordinate system, we determine the rotation matrix of variable transform in the bi-coordinate system, deduce the calculation expression of airborne TEM response while the vertical circle-coils attitude of layered earth is changing, and obtain the coefficients of TEM response for the rolled and pitched coils. Through simulating the changing coils attitude corresponding to the TEM survey effect, we propose a geometric algorithm for the attitude error correction, which is the foundation for accurate processing and interpretation airborne TEM data.