[0016] Helms, U.S. Pat. No. 4,507,611, discloses a method of detecting surface and subsurface anomalies of the earth using vertical current measurements. The vertical current manifests itself as alternating current signals which can be measured and represents surface and subsurface anomalies. Local variation in the detected current signals are measured and correlated with the spatial relation to the points of measurement to determine significant measurements indicative of surface and subterranean anomalies.
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