John M. Svoboda

Combined Electrical and Magnetic Resistivity Tomography: Synthetic Model Study and Inverse Modeling

Electrical Resistivity Tomography (ERT), which has seen increasingly wide use for environmental monitoring, uses the measurement of electrical potentials induced by a low-frequency electric current source. An alternative technique, magnetometric resistivity (MMR), measures the magnetic fields created by the same type of low-frequency electric current source used for ERT. Combining these two methods and thus the two types of data, provides an opportunity for producing improved subsurface images in a wider range of environments. This paper discusses the use of a fully three-dimensional inverse routine that combines magnetic and electric field measurements. The algorithm is based on a 3-D finite difference forward algorithm. The magnetic fields are modeled by applying the reciprocity theorem to model the electric fields induced by a coil of unit moment at a frequency of one radian per second. Using this method, allows for an adjoint formulation for calculating sensitivities of both magnetic and electric fiel...

Measuring Subsurface Conductivity Using Integrated ERT and MMR Measurements: Experimental Results

INEEL scientists developed MMR instrumentation to spatially resolve the surface magnetic field associated with an induced subsurface alternating current low between borehole ERT electrode pairs. The instrumentation consists of a variable frequency alternating current source and a synchronously detected, spatially resolved vector B-field measurement system. In the past year numerical codes were developed for the simulation of MMR data. Comparison of the results of numerical codes against a comprehensive set of field measurements at the Mud Lake, Idaho sediment beds allow for instrumentation and code enhancement as well as initial interpretations of MMR results in terms of subsurface structures.