MATCHED FILTER DETECTION OF ELECTROMAGNETIC TRANSIENT REFLECTIONS

Abstract

An electromagnetic transient signal is distorted as it travels in the conducting earth. At vertical incidence, the signal is stretched by a time that is proportional to the magnetic permeability, conductivity, and depth squared. The stretch is a function of the travel distance, and a set of filters can be constructed to match the waveforms of signals which have traveled to different depths. Surface waves travel from the source and can overlap the reflected signals. The reflected signals were estimated by subtracting an estimate of the surface wave and then passing the estimated reflections through a set of matched filters. This method was tested by means of numerical models and laboratory models. The latter were coaxial coils on aluminum plates. In both cases, the matched filters determined the depth of the reflected signals.