Frequency or Time Domain HEM Systems for Defining Spatial Processes of Salinisation?

Airborne EM methods have considerable potential for providing detailed spatial information on the distribution of salinity in soils and groundwater, across the floodplains of the Lower Murray River in southern Australia. This potential is examined along with the relative merits of high resolution airborne electromagnetic technologies, specifically the RESOLVE frequency domain helicopter EM (FDHEM) and the SkyTEM time domain helicopter EM (TDHEM) systems. For a coincident area, these two data sets were inverted for conductivity and depth using a smooth model Occams inversion, a conductivity depth transform (CDI) obtained using EMFlow and a Laterally Constrained Inversion (LCI) technique for defining variations in near surface conductivity and sediment salt load . Results from the two systems are comparable, both indicating the presence of an extensive flushed zone adjacent to the Murray River, and identifying finer scale variations between losing and gaining groundwater on the floodplains adjacent to the Murray River. Both systems effectively map the near surface conductive Blanchetown Clay in the adjacent highlands and the high saline groundwater system at depth