The Utility Of Horizontal Component Measurements In Random-Walk TEM Surveys

Laboratory tests and field examples of the horizontal field component measurements in shallow transient electromagnetic (TEM) surveys show the utility of these data in target characterization in reconnaissance, random-walk surveys for unexploded ordnance (UXO) and underground utilities. For example, prior work has shown that the Hx component (which we define as the horizontal field component in the direction of travel of the measurement system) is often useful in distinguishing small 3-D targets from linear features (such as buried pipelines or power lines). The current work expands on this capability, which is particularly important in UXO projects in which random transects are evaluated to determine a statistical estimate of density and distribution of potential ordnance and explosives. Anomalies from pipelines or power lines can skew the statistical evaluation toward over-estimating the number of potential UXO in a given area. The current research provides examples of the additional information that is available in the horizontal components of TEM surveys, particularly in the early time after transmitter turnoff. For example, the Hy component data are useful in estimating the orientation of linear features such as pipes and power lines with respect to the survey lines.