Filling in the gaps ? validation and integration of airborne EM data with surface and subsurface observations for catchment management ? an example from Bendigo, Victoria, Australia

Abstract

An airborne electromagnetic (AEM) survey was flown with the TEMPEST AEM System over the Kamarooka study area north of Bendigo. Conductivity values derived from AEM measurements were compared with borehole conductivity values obtained with an EM39 induction probe, indicating an approximately 1:1 relationship between the two quantities when taking into account the vertical (several metres) and horizontal (100 m) resolution of the AEM values. The thickness of Tertiary and Quaternary cover overlying Paleozoic basement was mapped by resolving the transition from moderately conductive cover to resistive basement. Palaeodrainage lines were mapped in the lower parts of the survey area using the topography of this interface, and in the upper portions of these buried valleys by tracing low amplitude magnetic trends associated with the valley infill material. The lateral extent and depth to a shallow (0 to 15 m), highly conductive layer was mapped. This layer was interpreted to correspond to high salt concentrations at the groundwater table. Areas where this layer intersects the land surface correlate with mapped areas of saline discharge. The conductivity values derived from TEMPEST AEM data provided a regularly sampled 3D framework into which surface observations and sparsely distributed sub-surface observations were incorporated as part of an ongoing integrated hydrogeological investigation.