Quantitative 2D VLF data interpretation

The ability of the VLF-R (Resistivity) method to provide quantitative subsurface resistivity information is examined. The frequencies used in conventional VLF (15 to 30 kHz) provide the deepest penetrations of the multi-frequency, extended method of RadioMT. Both methods are considered. VLF data, being effectively single frequency, are insufficient to resolve one-dimensional (1D) (vertical) structure in any detail. At the site investigation scale, however, it is the departures from the background (vertically uniform) structure that are of interest. Improved methodologies for the quantitative assessment of VLF data derive from advances in regularised inversion techniques. Hydrogeological and waste-site examples of VLF-R survey data, aided by wide-band (VLF/RadioMT) synthetic modelling and inversion studies, are used to illustrate their shallow (0 to 20 m) resolution capabilities in conductive environments.