RES2DINV is a computer program which will automatically determine a two- dimensional (2- D) resistivity model for the subsurface for the data obtained from electrical imaging surveys (Griffiths and Barker 1993). Since it is a Windows based program, all Windows compatible graphics cards and printers are automatically supported. It has been tested with video screen modes of up to 1600 by 1200 pixels and 256 colours.

RES3DINV is a computer program which will automatically determine a three- dimensional (3- D) resi0stivity model for the subsurface using the data obtained from a 3- D electrical imaging E- SCAN type of survey (Li and Oldenburg 1992). The electrodes for such a survey are arranged in a rectangular grid (Figure 1). It should first be emphasised that full 3D surveys are not merely a series of 2D surveys, but a different approach has to be used. More details on the practical use of the pole- pole, pole- dipole and dipole- dipole arrays for 3D surveys are given in Appendices A, B and C. The most common arrays used for 3- D surveys are the pole- pole, pole- dipole and dipole- dipole arrays. Other arrays do not provide sufficient data coverage for a full 3- D inversion. On a computer with sufficient memory, this program can handle survey grids with up to 43 by 43 (or 1849) electrodes!

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