Detection of errors with the Tripotential array and their reduction by a filtering technique

In order to investigate the effect of lateral errors on the sounding curves and subsequently their reduction, a site where considerable amount of inhomogeneities were thought to exist because of the excavations made during the building work previously carried out was chosen as a study area. Using the tripotential system of sounding promoted by Carpenter and Habberjam (Geophysics 21: 455-469, 1956), several soundings were performed. For some small electrode spacings, the three apparent resistivity curves were locally divergent indicating the existence of small-scale lateral errors; in other cases, these curves cross each other indicating the existence of additional observational errors. Some soundings showed continuous divergence of the three apparent resistivity curves as an indication of the existence of a major lateral discontinuity. Because of the interference of these disturbing effects, the interpretation of the soundings based on a horizontally layered earth is erroneous. One of these soundings containing these kinds of errors is taken as example. In order to reduce the effect of local inhomogeneities, an approach based on the linear filtering technique is suggested. As a check of the effectiveness of this method, the recalculated values of the two lateral error tests suggested by the authors were reduced when the three smoothed apparent resistivity curves were used. However, this method seemed more suitable for a flat trend data than for a data with a trend.