AEM Bathymetry near Busselton, Western Australia - Comparison of 25 Hz and 12.5 Hz GEOTEM in Areas of High Conductance

Julian Vrbancich; Peter Wolfgram; Daniel Sattel

doi:10.1071/ASEG2003ab177

ISSN: 2202-0586
E-ISSN:

oa AEM Bathymetry near Busselton, Western Australia - Comparison of 25 Hz and 12.5 Hz GEOTEM in Areas of High Conductance
Authors Julian Vrbancich^a, Peter Wolfgram^b and Daniel Sattel^c
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^a Defence Science and Technology Organisation (DSTO), , Australia, PO Box 44, Pyrmont, , NSW, 2009, [email protected] ^b Fugro Airborne Surveys, 65 Brockway Rd, Floreat, WA, 6014, Australia, [email protected] ^c Fugro Airborne Surveys, 65 Brockway Rd, Floreat, WA, 6014, Australia, [email protected]
Publisher: Australian Society of Exploration Geophysicists
Source: ASEG Extended Abstracts, Volume 2003, Issue ASEG2003 - 16th Geophysical Conference, Aug 2003, p. 1 - 4
DOI: https://doi.org/10.1071/ASEG2003ab177
- Published online: 01 Aug 2003

Abstract

Airborne electromagnetic (AEM) data were collected offshore Busselton, Western Australia, using GEOTEM^TM operating at both 12.5 Hz and 25 Hz over the same survey area. The survey covered a region in shallow water up to 35 m depth, and two overlapping tie lines skirting Cape Naturaliste extending into deeper water. The objectives were to compare 12.5 Hz (8 ms pulse) and 25 Hz (4 ms pulse) AEM data in an area of high conductance using conductivity depth sections to map water depth and seafloor resistivity, and to compare B-field and dB/dt responses.

CDI processing of the data with EMFlow software showed that for this dataset, CDIs based on the B-field are better suited for high-conductance targets than CDIs based on the dB/dt data. Water depth was best resolved using 25 Hz B-field data. Sub-sea material and deeper water depths below 45 m was best resolved with 12.5 Hz Bz field data. The 25 Hz dBz/dt data gave the poorest results, due to changes in the bird position not being accounted for in the CDI algorithm.

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References

Smith, R. and Annan, P., 1998, The use of B-field measurements in an airborne time-domain system: Part I: Benefits of B-field versus dB/dt data: Exploration Geophysics, 29, 24-29.
Smith, R.S., and Annan, A.P., 2000, Using an induction coil sensor to indirectly measure the B_field response in the bandwidth of the transient electromagnetic method: Geophysics, 65, 1489-1494.
Smith, R., 2001a, On removing the primary field from fixed-wing time-domain airborne electromagnetic data: some consequences for quantitative modelling, estimating bird position and detecting perfect conductors: Geophysical Prospecting, 49, 405-416.
Smith, R.S., 2001b, Tracking the transmitting-receiving offset in fixed-wing transient EM systems: methodology and applications: Exploration Geophysics, 32, 14-19
Vrbancich, J., Annetts, D.W., Macnae, J., Sattel, D., and Lane, R., 2001, Time domain airborne electromagnetic reconnaissance for seadepth measurement and shipwreck localisation: Extended Abstracts, ASEG 15th Geophysical Conference, Brisbane, Australia.
Wolfgram, P. and Thomson, S., 1998, The use of B-field measurements in an airborne time-domain system Part II: Examples in conductive regimes: Exploration Geophysics, 29, 225-229.

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Article Type: Research Article

Keyword(s): AEM; bathymetry; CDI; seafloor resistivity

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