b'Environmental geophysics Table 1.Tabulated results for two of the tests shown in Figures 2 through 7.The situation isnt quite so bad when the CMD is towed behind a vehicleat Con1 (1.48 mInph1Con2 (2.82 mInph2Con3 (4.49 mInph3least when the CMD is towed so that the spacing)(ppt) spacing)(ppt) spacing)(ppt) nearest point is about 3 m behind the (mS/m) (mS/m) (mS/m) ute. The conductivities are shifted by Broadside test 1% from background for the short and Background 15.53 0.70 19.19 1.79 19.55 5.23 medium length dipoles, and 10% (not With TCM broadside to ute 25.04 3.16 33.91 16.67 35.70 42.45 that great really) for the longest.Ratio 1.61 4.48 1.77 9.31 1.83 8.12 As an aside, isnt the response interesting In-line test when you put the transmitter end Background 28.41 2.80 26.43 1.95 20.74 4.20 directly under the tow bar of either vehicle? And for the ute, the responses With TCM behind ute 28.57 0.74 26.74 1.66 22.86 2.92 are still noticeably noisier up to 2 m Ratio 1.01 0.26 1.01 0.85 1.10 0.69 separation. In Figure 4 it can be seen that the response when the receiver Examination of Figure 1 shows that thispossible to mount the CMD broadside toend is put under the tow bar of the ute site may not have been an optimal placea ute without substantially affecting theis quite different from than when the to run this sort of test as there are largedata. It appears the response is improvedtransmitter end is put under the tow bar. powerlines 100 m from the test area.by mounting the CMD as far back asI am not sure what to make of that. By the Then again, many field areas have nopossible so that the receiving antennaway, I am just about to test this type of cultural noise, so maybe this situation isis far from the engine. The shortesttowed rig in the fieldand we are going closer to field reality. I dont think thatdipole spacing response with the CMDwith the towed configuration with the the powerlines affected my conclusionsmounted toward the rear of the vehicletransmitter end 3 m behind the ute.much at all. and 2 m from the vehicle, is 61% greaterThere are some obvious shortcomings The results, summarised in Figures2than the response with no vehiclein this set of experiments (no prizes through 5, and Table 1 are prettynear the CMD (i.e. background). Theyet Mike). For example, it might (will?) interesting. In nearly all cases, theresponse is about 77% greater for thebe interesting to test these results in in-phase response is compromised bymedium dipole and about 83% greaterother settingsboth more resistive and mounting the CMD anywhere near afor the longest dipole, when comparedconductiveto see if the changes are at vehicle with the engine runningexceptto the background response at the sameleast somewhat consistent (even linearly/towed 2 to 3 m behind the quad bike.location. predictably inconsistent). Also, in these For most data collection exercises thistests the engine was running but the may not be important, as the in-phaseFigure 3 shows that the responsevehicle wasnt movingthere are more supposedly is only used to help identifycomparisons for the experiment wheremoving/rotating bits of metal when you responses from metallic targets. the CMD is mounted broadside to amove and that adds noise. I am hoping to quad bike are only slightly better. In fact,get some results soon comparing walking For the quadrature response/ it may even be acceptable to use thisthe CMD over a line of data and towing conductivity, Figure 2 (and Table 1)configuration if the CMD is mounted 2 mit. Watch this space for those results later shows pretty categorically that it is notfrom the quad bike. this yearI bet you can hardly wait.APRIL 2020 PREVIEW 34'