Correction Of Anisotropic Effect In Electromagnetic Methods

In resistivity surveying, we encountered a phenomenon called apparent anisotropic effect which is corrected by using two directions of measurements at right angles to each other and the use of the concept of a directionnal invariant. The same effect is observed in magnetotellurics, in the Slingram method and in VLF-EM. Based on the same concept, the aim of this work is to evaluate how the invariant can be applied to the VCP Slingram configuration in order to enhance a resistivity variation map. For this purpose, synthetic models have been used to illustrate the advantages of this technique. We also develop in this paper the concept of the invariant in the VLF-EM method by considering the real component measurements that are obtained with two perpendicular or nearly perpendicular directions of the primary polarising field. The method has been tested on synthetic data.