ERSC 3V93 Lecture Notes - Lecture 42: Electrode Array, Overvoltage, Rc Circuit
4 May 2016
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Document Summary
Fixed array systems e. g. geoscan rm15 traverse in steps". Can be applied to many of same applications as em conductivity. Map aquifers, fractured bedrock, conductive contaminant plumes. Map soil salinity, saline water intrusion voids, measure formation porosity (downhole mostly) archaeology poor for resolving stratigraphic boundaries (in z) Continuous resistivity profile collected with towed streamer graphite electrodes boat towed ves. Map bottom sediment type imaging the saltwater/freshwater interface in estuary. After current is switched off (or turned on), the voltage between potential electrodes takes 1s to 1 min to decay (or build up) The ground acts somewhat like a capacitor. Overvoltage decay times and rise times are measured and are diagnostic of the nature of the subsurface. Metallic deposits with low em anomalies and high resistivity. The decay and buildup time resembles the discharge and charge time of acapacitor through a finite resistance.
