Accurately Locating a Vertical Magnetic Dipole Buried in a Conducting Earth

The use of a buried vertical magnetic dipole to determine the position of a point inside the Earth is based on the geometric structure of the measured field. A new systematic technique that improves the location accuracy of the surface point in the axis of the buried dipole is developed and tested. It is based on the use of state-of-the-art topographic equipment for the null-field direction measurements, that are further processed by two estimation algorithms, namely, the extended information filter and the extended Kalman filter. In addition, emphasis is placed on the study of the sources of error in order to establish the accuracy of the method. This analysis is conducted in a half-space model in which electromagnetic propagation is studied by numerical integration of analytical solutions. The results are confirmed by a direct solution of the problem by the finite-element method. From the computations, simple equations are provided for practical use. Then, an experimental study shows that the uncertainty of the null-field direction measurements can be modeled by a Gaussian probability density function. In addition, the data of the field experiment are used to validate the proposed subsurface location technique.