CSAMT Static Shift Recognition and Correction Using Radon Transformation

Abstract

The presence of shallow conductive heterogeneities can cause static shift in controlled source audio-frequency magnetotellurics (CSAMT) apparent resistivity sounding curves. This is observed as a shift along the apparent resistivity axis in double logarithmic coordinates. Such effect can cause difficulties in CSAMT data interpretation. In this letter, we established a new method to identify and correct the CSAMT static shift based on the high-resolution Radon transformation. We took advantage of the property that the static shift of apparent resistivity curves behaves as a point in the Radon domain. We presented 3-D synthetic study to demonstrate that the static shift can be effectively removed from the apparent resistivity curve. However, due to the low resolution and precision, the traditional Radon transform can generate “scissor-tail” and then, the static shift may not be completely removed. We proposed to use a new high-resolution Radon transform by improving the regularization matrix using the least squares inversion. Our numerical simulation shows that by using this high-resolution Radon transform, the static shift converges accurately to a point without showing the “scissor-tail.” In the application to field CSAMT data, the high-resolution Radon transform method was able to correct the static shift effectively; thus, it can improve the precision and accuracy in data interpretation.