ИСТИНА

The thin-sheet approach is a very useful interpretation tool in electromagnetic (EM) methods. However, this study is the first one to address the issue of uniqueness of corresponding inverse problem. Two approaches to thin-sheet modelling are considered. The first one, classical thin-sheet modelling, is based on zero-thickness sheets with integral conductivities. The second one, average-sheet modelling, is based on the following concept. Suppose the anomaly has a non-zero thickness small enough to assume the total electrical field to be a constant in a vertical direction inside this anomaly. The anomaly conductivity distribution is a 2D function. The equations for inside the anomalies are obtained using vertical integral averaging of 3D EM integral equation. The EM fields outside of the anomalies are evaluated by continuation formulas from the EM integral equations approach. Note that in our study the number of sheets can be arbitrary large. Moreover, in case of the average-sheet modelling the anomalies can be in contact with each other in vertical direction. We obtain the following uniqueness result. Suppose that the anomalies are horizontally finite, and the normal section and the normal field are known. Then in order to find number of anomalies and determine their depth and (integral) conductivities it is sufficient to know the horizontal components of electrical field at single frequency in single horizontal plane. This result can be generalized to the interpretation of horizontal components of magnetic field or impedance tensor.