b'Environmental geophysics Environmental geophysicsMike Hatch Associate Editor forEnvironmental geophysics michael.hatch@adelaide.edu.auWelcome readers to this issues column on geophysics applied to the environment. Recently I was contacted by one of my previous contributors, who had a column idea that I thoughtFigure 1.AgTEM cart side view.was worth sharing. In this column I am happy to reintroduce Dave Allen, founder and main thinker behind Groundwater Imaging, who is spruiking developments to his towed TEM system that he calls AgTEM. Here is what Dave has to say:AgTEMa development storyDave Allen Ground Water Imaging Pty LtdFigure 2.AgTEM front loop (Slingram) may be added as an option to create a second independent dataset.David@GroundwaterImaging.comimage conductive features up to 100 mwas frustrated with the slow progress AgTEM (Figures 1 and 2) is a toweddeep below otherwise resistive strata.laying loops. I put together my first transient electromagnetic (TEM) systemThe system is normally towed behindtowed system, looping a whole lot of initially designed to survey cleared,a 4WD ute (Figure 2) but can also bewire around a wooden structure and levelled agricultural landmostly totowed by quadbikes, ATVs and eventhen towing it behind a ute. Being nave map salinity and help site bores. Overfloated behind a boat. There is a newabout the limited capacity of transmitters time it has been recognised as beinglightweight version that can be hand- to turn off current rapidly I hooked up useful for mining and geotechnicalcarried in difficult terrain. 20 turns to a Geonics EM37 transmitter applications as well. AgTEM processingand surveyed away. Unfortunately, the provides maps and vertical sectionsHow did we get here? Well, back in theresults were disappointing due to the of bulk earth resistivity from just a1990s I was doing 100 m x 100 m looplong turnoff time and induction into the few metres below the surface to tensTEM surveys working for one of themetal towing vehicle. In the end it was of metres depth (Figure 3 shows anold contracting companies (Geoterrex)an expensive experiment: the transmitter example data set). It is well suited tonear Cloncurry in NW Queensland andlasted that survey but shortly after some DECEMBER 2021 PREVIEW 46'