A new electromagnetic geophysical system has been developed that significantly improves target sensing and imaging capabilities compared to conventional measurements. The Differential Target Antenna Coupling (DTAC) method uses at least two frequencies. One frequency is used as a reference signal to establish the null direction in the magnetic field at that frequency, and then a different frequency is used to measure the change in the null at the new frequency. We can also use an arbitrary number of frequencies with just one reference frequency for wide-bandwidth spectral measurements.

Using numerical simulations, we have demonstrated six key aspects of the vertical array-DTAC method: 1) Errors in the receiver coil orientation have little effect on the measurements; 2) anomalies caused by variations in the background resistivity have little effect on the measurements; 3) surface interference, e.g., fences, buildings, and vehicles, have little effect on the measurements; 4) high resolution mapping of targets has been demonstrated through a series of model simulations; 5) frequency-domain measurements, or off-time transient measurements, can be used to provide the required information. Current airborne electromagnetic (AEM) technology can be adapted to this method; and 6) the method can be adapted to a variety of rapidly moving survey applications, including near-surface targets (civil engineering, water resource, and environmental restoration) as well as deep targets (mining and other natural-resource exploration).

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