Why not X in airborne TEM?

We describe the challenges for the realization of a transient EM (TEM) system capable of measuring both the z-and x-components. This involves significant changes to instrumentation as well as to the processing and inversion algorithms. Geophysical mapping of groundwater resources using TEM involves both delineation of the aquifer structure and the aquifer protection. The demands for the instrumentation and the processing algorithms are quite different for the two tasks. Structural mapping requires large depth penetration and thereby a large transmitter moment while aquifer protection mapping requires early time measurements and extremely accurate determination of the system transfer function. Furthermore, the inversion software must be capable of modelling this system transfer function. For an airborne TEM system systematic analysis of the resolution capabilities of relatively thin low resistive layers in the upper 30 50 m of the subsurface has shown that the resolution is enhanced if not only the transient z-component but also the transient x-component of the induced fields in the Earth is measured and included in the inversion. The abstract will describe and discuss three major challenges related to the inclusion of the x-component in an airborne TEM system.