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.

[1]  Brian R. Spies,et al.  Depth of investigation in electromagnetic sounding methods , 1989 .

[2]  George V. Keller,et al.  Electrical Methods in Geophysical Prospecting , 1981 .

[3]  I. Müller,et al.  VLF GROUND SURVEYS, A POWERFUL TOOL FOR THE STUDY OF SHALLOW TWO‐DIMENSIONAL STRUCTURES* , 1983 .

[4]  A. Benson,et al.  Mapping groundwater contamination using dc resistivity and VLF geophysical methods; a case study , 1997 .

[5]  D. Beamish,et al.  A STUDY OF MAGNETOTELLURIC STATIC DISTORTION IN THE CONTEXT OF INTRUSIVE VOLCANISM1 , 1993 .

[6]  David Beamish.  Three-dimensional modelling of VLF data , 1998 .

[7]  A. T. Price.  The theory of geomagnetic induction , 1973 .

[8]  P. Turberg,et al.  Hydrogeological investigation of porous environments by radio magnetotelluric-resistivity (RMT-R 12–240 kHz) , 1994 .

[9]  P. Kaikkonen,et al.  2-D nonlinear joint inversion of VLF and VLF-R data using simulated annealing , 1998 .

[10]  J. D. McNeill,et al.  7. Geological Mapping Using VLF Radio Fields , 1991 .

[11]  A. Tabbagh,et al.  Invariants for correcting field polarisation effect in MT-VLF resistivity mapping , 1994 .

[12]  William Rodi,et al.  Nonlinear conjugate gradients algorithm for 2-D magnetotelluric inversion , 2001 .

[13]  S. Constable,et al.  Occam's inversion to generate smooth, two-dimensional models from magnetotelluric data , 1990 .

[14]  Philip E. Wannamaker,et al.  A stable finite element solution for two-dimensional magnetotelluric modelling , 1987 .

[15]  R. Parker,et al.  Occam's inversion; a practical algorithm for generating smooth models from electromagnetic sounding data , 1987 .

[16]  Elizabeth R. McNew,et al.  Surface Geophysical Surveys of the Freshwater‐Saltwater Interface in a Coastal Area of Long Island, New York , 1995 .

[17]  L. Cagniard.  Basic theory of the magneto-telluric method of geophysical prospecting , 1953 .

[18]  A. Tabbagh,et al.  VLF resistivity mapping and verticalization of the electric field , 1991 .

[19]  David Beamish,et al.  Two-dimensional, regularised inversion of VLF data , 1994 .