GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 3.2 GNGTS 2024 2.3. Ground TEM acquisitons Several ground transient electromagnetc (TEM) soundings have been measured with the ABEM WalkTEM 2 instrument in central-loop confguraton, with two diferent transmiter units (TX-20 and TX-60, with 20 ampere and 60 ampere peak-to-peak maximum current, respectvely) and three transmiter sizes (Fig. 2, top right map): ● Thirty 40x40 m 2 Tx-20 soundings, with 30 minutes of stacking tme and 10 ms of acquisiton tme; ● Five 100x100 m 2 Tx-60 soundings, with 60 minutes of stacking tme and 30 ms of acquisiton tme; ● One 200x200 m 2 Tx-60 sounding, with 100 minutes of stacking tme and 30 ms of acquisiton tme. All soundings were measured with two diferent receivers, RC5 and RC200, with 5 m 2 and 200 m 2 efectve area, respectvely. The 40x40 m 2 soundings reached approximately 300 m of depth of investgaton (Christansen and Auken, 2012), while the 100x100 m 2 went down to ≈400 m and the 200x200 m 2 down to ≈700 m. 2.4. tTEM and Loupe acquisitons The tTEM system (Auken et al., 2019) has been employed to acquire more than 55 km of data (Fig. 2, botom right) through a 3x3 m 2 transmiter with receiver in ofset confguraton. This system allows to carry out contnuous TEM measurements when pulled by an ATV vehicle at the max speed of 20 km/h, to retrieve subsoil models up to ≈100 meters of depth. Almost the same area was surveyed with the Loupe portable system (Street & Duncan 2018) with 20 km of lines. 2.5. DCIP acquisitons The DCIP data have been measured with the ABEM Terrameter LS2 system in 100% duty cycle (Olsson et al., 2015) with full waveform acquisiton, and gated afer harmonic denoising and drif removal following Olsson et al. (2016). As shown in Fig. 2, top right panel, approximately 4 km of data have been measured with 10 m electrode spacing, and another 4 km with 5 m electrode spacing. The gradient protocol has been used for acquisiton, with 12 seconds of acquisiton tme and two stacks per quadrupole, with mean injected current of approximately 0.5 Amperes. The number of quadrupoles acquired among the diferent profles ranges between 1400 and 2700 ca., depending on the profle length and the electrode spacing. 2.6.Drillings Three boreholes few hundred meters deep (100 m, 190 m, 350 m) are being drilled, with lithological descripton and resistvity log; the 200 m deep borehole was completed in December 2023, while the other two will be completed within Spring 2024.