3D resistivity inversion using 2D measurements of the electric field

Field and 'noisy' synthetic measurements of electric-field components have been inverted into 3D resistivities by smoothness-constrained inversion. Va lues of electrical field can incorporate changes in polarity of the measure d potential differences seen when 2D electrode arrays are used with heterog eneous 'geology', without utilizing negative apparent resistivities or sing ular geometrical factors. Using both the X- and Y-components of the electri c field as measurements resulted in faster convergence of the smoothness-co nstrained inversion compared with using one component alone. Geological str ucture and resistivity were reconstructed as well as, or better than, compa rable published examples based on traditional measurement types. A 2D elect rode grid (20 x 10), incorporating 12 current-source electrodes, was used f or both the practical and numerical experiments; this resulted in 366 measu rements being made for each current-electrode configuration. Consequently, when using this array for practical field surveys, 366 measurements could b e acquired simultaneously, making the upper limit on the speed of acquisiti on an order of magnitude faster than a comparable conventional pole-dipole survey. Other practical advantages accrue from the closely spaced potential dipoles being insensitive to common-mode noise (e.g. telluric) and only 7% of the electrodes (i.e. those used as current sources) being susceptible t o recently reported electrode charge-up effects.