Experimental Studies and Verification of a Differential Target Antenna Coupling Method for Sensing and Imaging Subsurface Targets

Abstract

We have developed a new electromagnetic geophysical system, the Differential Target Antenna Coupling (DTAC) method, which can significantly improve target sensing and imaging capabilities compared to conventional measurements. In a companion paper, we developed the theory behind this method. In the current paper, we show an experimental validation of the method by comparing the measured and calculated responses for a variety of precisely known, small-scale targets. Excellent agreement has been obtained in all cases where the target was in contact with the earth. The DTAC method uses at least two frequencies. One frequency is used as a reference signal to establish the null direction at that frequency, and then a different frequency is used to measure the change in the null at that new frequency. We can also use an arbitrary number of frequencies with just one reference frequency for wide-bandwidth measurements. The DTAC method is not sensitive to the orientation of the receiver coil and it is relatively insensitive to variations in the background resistivity. Small-scale prototype measurements show that the DTAC method can detect targets deeper and with greater resolution of target dip, strike, and thickness than conventional methods. It is also possible to orient the DTAC array so that it is not sensitive to surface interference.