An improved scale model measurement facility for studying geophysical cross-borehole sensing

A scale model developed for experimentally studying cross-borehole geophysical imaging is described. The model is about 1/40 scale and operates in the 2-3 GHz region. Earth in the form of sandy loam was used and reflections from the sides and bottom were substantially reduced over those that characterized an earlier version. The electrical permittivities of the sandy loam at VHF (i.e. 50-60 MKz) and 2-3 GHz match very closely. Time domain results are included to show that reflections from the sides and the bottom of the model are minimal. Measured results using the model are discussed. Comparison with scaled numerical simulations is included. The pattern of the vertical component of the electric field, measured along a vertical path that extends above and below the target, corresponds quite well with numerical simulation results. It is anticipated that this model will prove useful as an adjunct to both theoretical and field work in subsurface exploration.<>