Methods to Reduce Banding Effects in 3-D Resistivity Inversion

Three-dimensional surveys are required to accurately resolve structures in very complex areas. In many cases the 3-D data set is collated from a series of parallel 2-D survey lines, and frequently the distance between the lines is more than the electrode spacing along the lines. The inversion of such data sets frequently produce models with banded near-surface anomalies that are aligned parallel (or perpendicular) to the lines. It is shown that such banded structures can be caused by the data acquisition geometry. Several modifications to the smoothness-constrained least-squares inversion method are examined to reduce such artifacts in the inversion model. One method is to use a higher damping factor for the model cells in the near-surface layers. The banding effects can also be reduced using a model discretization such that the width and length of the model cells are similar although the spacing between the lines is larger than the in-line electrode spacing. The remaining banding artifacts can be further reduced by modifying the horizontal roughness filter used such that it has components in the diagonal directions as well as in the directions along and perpendicular to the 2-D survey lines.