Abstract

Because of water’s conductivity properties, electromagnetic geophysical surveys are often used in the detection and monitoring of subsurface water. The common coil receiver is a simple and inexpensive instrument that measures the derivative of the magnetic field strength. It has a frequency bandwidth dependent on its physical geometry and a frequency-dependent amplitude response. Generally, these instruments have a limited useful frequency response, requiring different sets of coils if information over more than a few discrete frequencies within a narrow bandwidth is desired.

The use of wide bandwidth receivers in electromagnetic geophysical surveys can provide information that limited bandwidth instruments can not. A magnetic field receiver with a small physical size allows array measurements of electromagnetic fields in a manner similar to arrays used for seismic measurements. This makes feasible 2-D and 3-D electromagnetic imaging. The wide bandwidth of the receiver also allows time and frequency domain measurements to be made simultaneously. Although not a topic for this discussion, it has been shown that reactions of different liquid organic compounds with clays have varying transient responses to a given stimulus; a measurement tool with a sufficiently wide bandwidth to measure these variations allows the possibility of subsurface contaminant identification.

A wide bandwidth, vector-field sensitive receiver has been developed and field-tested for functionality in geophysical applications. The frequency domain results of the detection of subsurface water flow are discussed herein. The availability of such a receiver allows the possibility of not only detecting a conductivity anomaly such as subsurface water flow but the possible identification of contaminants within the water as well.