b'Environmental geophysics Environmental geophysics2 km from the survey area is far enough.height setting was set to zero. Remember Except when that is impractical or unsafethat the CMD uses a single 10 000 Hz or??? Sometimes 500 m is all you cantransmitter, and has three receiver coils get, and that distance probably mattersfixed in the 4.5 m long tube. The closest less now that we can include transmitterspacing (shallowest data - labelled in infinite locations in at least somethe figures and table here as con1 or inversions. inph1) is 1.48 m. The middle spacing (con2 and inph2) is 2.82 m between the In the problem at hand, I am runningtransmitter and receiver coils. The longest surveys with a terrain conductivity meterspacing (deepest datacon3 and inph3) (TCM). In this case a GF Instruments CMDis 4.49 m. I tried to collect at least 100 Explorer (similar but different to thatdata points per experiment. Data were old stalwart the Geonics EM31 or one ofcollected in two configurations. First, with the DualEM devices). So, how far is farthe CMD mounted broadside and parallel Mike Hatchenough? I will need to mount and run ato the ute and quad bike, to simulate Associate Editor for TCM from a ute (Australian abbreviationmounting the CMD to the side of a ute or Environmental geophysicsfor a utility vehicle), as the survey area isquad bike ( Figure 1a and b shows the test firstname.lastname@example.org just too large for me to walk. Or, maybesetup; Figure 1c shows a typical broadside the system should be dragged behindsetup in the field). I also collected data that ute on a sled? I know that many havewith the CMD on the ground behind the Mundane applieddone this testing before, but alas I havevehicles, to simulate mounting a TCM on never seen the results, so we have toa sled or other device and towing it.geophysics keep reinventing the wheel.For the broadside experiments, the CMD In the name of mundane science, Iwas set at 730 mm height, with the Welcome readers to this issuesrecently borrowed a CMD Explorerend labelled T (the transmitter end) column on geophysics applied tofrom the School of the Environment atforward. Intuitively it seems better to the environment. In this column I amFlinders University and took a quad bikehave the receiver as far away as possible going to expound on some fascinatingand a Toyota Hilux ute (both courtesyfrom the running motor, and yes motors research on which I have been workingof Zonge Engineering) and set up somewere running during all tests. For the ute (is there a Nobel Prize for Mundanecardboard boxes and a tape measure andexperiments I ran two sets of tests, first Applied Geophysics?if so, this workdid the tests. Figure 1ac shows two ofwith the CMD centred lengthwise along would be in the running). It is actuallythe setups; Figures 2 through 5 show thethe ute, and then the second, with the part of a larger topic that has alwaysresults graphically, and Table 1 reviewsCMD offset 1.35 m back from the centre. interested me in applied geophysics: howsome of the results. For the quad bike experiments, I only ran far is infinitely far? Or more realistically,with the system centred. Figure 1 shows how far is far enough? For example, in aFirst lets review the setups. All datathe setups for the broadside tests.pole-dipole/resistivity survey the remotewere collected with the GF Instruments transmitter electrode needs far enoughCMD Explorer instrument (http://www. For the towed simulation, the CMD away that the roving electrode may begfinstruments.cz/) running in continuouswas laid on the ground. Most of considered to act like a transmittingmode, collecting high-moment datathe experiments were run with the pole. Conventional wisdom is thatat one second intervals. The internaltransmitter end near the vehicle.Figure 1.a) TCM device broadside to ute; b) mounted broadside to quad bike; c) CMD mounted broadside to ute. Note proximity to carpark in a) and to overhead powerlines in b).31 PREVIEW APRIL 2020'