A scale-model study of down-hole VHF dipole arrays with application to subsurface exploration

The cross-borehole measurement technique at VHF frequencies typically employs winched single transmitting and receiving dipoles in various offset configurations to detect a buried target and estimate its vertical position from the pattern of forward scatter. Signal-to-noise ratio (SNR) and clutter from random scatterers in the host medium are practical limitations to target detection that can be modified by means of synthetic collinear arrays whose electric fields are determined as a function of vertical position from the measured amplitude and phase of a single element as it moves in the borehole. The present paper compares theoretical calculations based on a thin bare dipole in a moderately lossy host medium with a combination of laboratory scale model measurements and simple synthetic array techniques to indicate the potential advantages of the latter to geophysical exploration