Linear filtering of VLF dip-angle measurements

TL;DR: In this paper, the authors proposed an interpretation technique based on discrete linear filtering of VLF data, where the output of the described filtering results is expressed in terms of an equivalent current density at a specified depth that would cause the measured magnetic field.

Abstract: The suggested interpretation technique is based on discrete linear filtering of VLF data. The output of the described filtering results is expressed in terms of an equivalent current density at a specified depth that would cause the measured magnetic field. The most practical six-point filter gives an accuracy of 8%. The filter is an extension of the commonly used Fraser filter to process VLF dip-angle data. Filtering the same data set for various depths gives an idea about the change of current density with depth. Areas with high current-density correspond to good conductors. The conductor dip can also be determined. The use of the technique is illustrated on theoretical and field examples. In all cases a good correlation with original models and other types of geophysical measurements was obtained. As shown in the last example, the filtering technique is also applicable in interpretation of other electromagnetic methods.