b'Environmental geophysics Environmental geophysicsreceiver and transmitting antennae;included as black dashes on the two for this survey that distance was 7.5 m.resistivity-depth sections shown later.Positions are recorded using a DGPS system attached to the transmitter.Onto the survey at hand. The field area The receiver/transmitter pair areis in Perth, along the Swan River, and carried over a given survey area atis a site that was heavily polluted back walking speed. Data are sampled atinto the 60s and 70s by local industry. ~500 kHz and stacked for two secondsAccording to Greg, there was a large for each reading. At a walking speedfertiliser plant and a landfill both of 5 km/hr, data are collected at ~3 mabout a kilometre or so northwest of intervals. Data are windowed into 22this study site (up-gradient for the approximately logarithmically-spacedgroundwater in the area) and the window intervals. The first windowgroundwater was heavily affected Mike Hatchis centred ~6 sec after transmitterby both. The area seemed to have Associate Editor forshutoff and is nominally 4 sec wide.been affected by multiple pollution EnvironmentalgeophysicsThe last window is centred ~2.3sources: back in the 80s Greg sent some michael.hatch@adelaide.edu.au msec after transmitter shutoff and isstudents to the area (wow youre that nominally 1 msec wide. These data areold Greg?) with a Geonics EM-31 and processed by stacking and averagingended up digging up raw sulphur that Inverting Loupe data the raw data and then correcting forhad been dumped and buried in the system response in the same wayarea. The fertiliser plant and landfill Welcome readers to this issuesthat airborne EM data are treated. Thewere both cleaned up in the 90s, but column on geophysics applied to theresults are output into the Amira TEMGreg (and others) are interested in environment. This months column isfile format (which is pretty convenient,knowing whether things are as clean about some interesting data collected inexcept it includes no information aboutas hoped. Figure 1 shows the field WA by Andrew Duncan and Greg Street /data repeatability, which is useful inarea, with the Loupe data traverse Loupe Geophysics. As background, a fewthe inversion processminor gripehighlighted in purple. All of those data months ago I wrote in this column thatfrom Mike). The data were invertedwere inverted, and two resistivity-depth I would be interested in inverting otherusing Aarhusinv (the engine that drivessections were prepared from that as data sets using Aarhusinv/Workbench,Aarhus GeoSoftwares Workbenchwell; the location of Line 4 is shown in and Greg kindly took me up on my offer.program) in a 12 layer smooth- red, Line 5 is shown in yellow. Figure 2 Coincidentally I was already interestedmodel configuration. Aarhusinv andshows the Line 4 inverted resistivity-in playing with data from that system, asWorkbench both incorporate depthdepth section, while Figure 3 shows the the Loupe is very new and I think it hasof investigation (DOI) informationLine 5 resistivity-depth section. Figure 4 potential to become an important tool inestimates as described in Christiansenis a resistivity-depth section cut at 10 m the near-surface geophysical world. and Auken (2012). This information isdepth.First, a brief description of the Loupe system (Street et al 2018). The Loupe is a backpack-portable, two-person, time-domain electromagnetics (TEM) system that effectively uses the same configuration (basically a Slingram) as a number of airborne EM systems to allow data to be collected continuously. The transmitter system (carried by one person on a backpack) is a 13-turn induction loop that is ~600 mm in diameter; the coil is mounted horizontally, so the signal is effectively a vertical dipole. It transmits a 20 amp, 50% duty-cycle current waveform at 75 Hz typically, from a height of about 1 m. The receiver system is carried by a second person. It comprises three orthogonal receiver coils with an effective area of 200 m2 (after amplification); Hx, Hy and Hz are measured. The signals from the receiver coils are carried to the transmitter via an umbilical cable that also serves to Figure 1.Overview of survey area in Perth, WA. All survey lines are shown in purple; the location of Line 4 maintain a set distance between theis highlighted in red, the location of Line 5 is in yellow. Distances along Lines 4 and 5 are shown in white.41 PREVIEW DECEMBER 2020'