Airborne resistivity mapping

A brief overview is presented of the theory and techniques for mapping the electrical resistivity of surficial formations by interpreting airborne electromagnetic induction data. Although the method has not yet reached its full potential, useful information can be obtained on the thickness, the conductivity, and the depth below the surface of any conductive unconsolidated material. Practical applications of this geophysical method include the mapping of aquifers, the delineation of salt-water intrusions, and the estimation of the depth of valley fill material. The instrumentation is described and both time- and frequency-domain systems are discussed. Methods and examples of automated data interpretation are given. On the basis of the results available it is concluded that with the available equipment and using the limited methods of interpretation described, one can map the thickness of the uppermost layer (be it conductive or resistive) to a depth somewhat greater than 50 m with an accuracy of about 10-20 m