Shallow Inductive Electric Field Response Measured with Capacitive Sensors

Abstract

Modelling software developed and results from a prototype instrument shows that a new Capacitive Array Resistivity with Inductive Source (CARIS) method being developed has potential for detecting both conductive and resistive objects and near surface conductivity contrasts. Detecting buried resistive objects has possible application in near surface exploration. Applications could include identification and mapping of chromite and mineral containing quartz veins as well as alteration, silicification. It also shows potential for other near surface applications such as UXO, archaeology, void detection, pipe delineation, or fracture detection. A prototype 100kHz CARIS instrument has been designed and built. The prototype CARIS instrument has been tested with highly repetitive results under laboratory conditions, showing good comparison with expected results from modelling. Results have shown the ability of the system to reliably detect resistive objects within a conductive uniform half-space (salt water) environment. The CARIS system has also undergone preliminary testing in the field. Initial results from field testing show high repeatability but also high lateral variability. This appears to be due to sensitivity to near surface moisture and soil consolidation contrasts. Currently a larger second prototype operating at 5kHz is in production aimed at reducing the sensitivity to soil effects moisture and consolidation effects and increasing the depth of investigation.