Numerical estimation of geoelectrical data errors. Comparison with the method of reciprocal measurements

MARTINELLI, PATRICIA; GRUNHUT DUENYAS VIVIAN; BORDON, PABLO; ROBLEDO, FABIANA

Conference Proceedings, 25th European Meeting of Environmental and Engineering Geophysics

EAGE

Año: 2019; p. 1 - 5

The geoelectrical method, or Electrical Resistivity Tomography (ERT), is a geophysical technique widely used for studying the electrical properties of the subsurface. Usually, the data are acquired along survey lines using some standard electrode array, and then are interpreted by applying 2D or 3D inversion methods. These inversions are generally made without including any information on data errors, due to the difficulty for obtaining adequate error estimations. Low random errors do not guarantee good data quality, since data with atypical values ?caused by systematic sources of error such as poor soil-electrode contact, electrode polarization, or equipment malfunction? often have low standard deviations (Zhou and Dahlin 2003, Loke et al. 2013). One way to improve the subsoil models is to not include this type of data in the inversions. The problem is that they are not always easy to identify, especially when a relatively high lateral variability of the data is expected, due to the characteristics of the studied area. Then, instead of this, a common approach is to perform successive inversions, such that in each inversion, the data with fitting errors exceeding a certain value in the previous one are not considered. Even when this procedure is applied carefully, there is a risk of eliminating from the models anomalies that are not artifacts, but correspond to real changes in the resistivity of the subsoil. A more objective procedure, which leads to more reliable results, is to invert the complete datasets considering appropriate estimations of data errors, including the non-random part. This can be achieved by carrying out direct and reciprocal measurements (Parasnis 1988, Park and Van 1991). This well-known methodology generally gives good results. However, it doubles acquisition time and is only applicable with some electrode arrays.