Using resistivity or logarithm of resistivity to calculate Depth of Investigation index to assess reliability of Electrical Resistivity Tomography
Résumé
We conducted a comparative study to determine the most efficient and reliable way to calculate the Depth of Investigation (DOI) index to assess the quality of Electrical Resistivity Tomography (ERT) models. We compared the results of using resistivity and logarithm of resistivity after testing them on four synthetic models by direct modeling and a field case where the resistivity model was validated by auger drillings. We tested the two most commonly used acquisition arrays, Dipole-Dipole and Wenner-Schlumberger. The index calculated with the logarithm of resistivity clearly appears to be more satisfactory than the resistivity-based index. The method based on resistivity systematically overestimates risk (high DOI) in areas of high resistivity and it underestimates in conductive zones. As a result, we strongly recommend the use of the logarithm of inverted resistivity to calculate the DOI index.