KEGS Ottawa November Meeting

   

Tuesday, November 15th 
4:30 p.m.

Harrison Hall 
Room 177 
601 Booth Street  

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Greg Hodges
Sander Geophysics

EM: It's not one size fits all

 

Abstract: Despite decades of development, and dozens of salesman’s claims, there is no “ideal” airborne (or ground) EM system or method of processing. The choice of system depends on the target, host, and environment, and natural conductivity varies by eight orders of magnitude, depth of interest by three orders of magnitude, survey size by two, and cost by one. No single system can be “all things to all rocks”. Geophysicists using EM need to be familiar with all the types of EM and how they interact with the target(s) of choice, to choose the most cost-effective method.

This talk aims to dispel some myths and misconceptions about EM; shedding some light on the darkness between time-domain and frequency domain EM, in-phase and on-time, the merits of fixed-wing or helicopter, and on how EM fields interact with our inhomogeneous, conductive, polarizable, magnetic earth. (Hint: the earth is time-domain, not frequency domain – but time and depth are not always related, and only frequency domain has in-phase.) Greg will also compare the difference uses and merits of smooth and discrete, 1D and 3D inversion – and old fashioned anomaly interpretation.

Failure to understand the options in EM leaves system choice in the hands of the salespeople – something most geophysicists would not consider ideal!

 

Biography: Greg Hodges is a Senior Geophysicist at Sander Geophysics. Since 1980 his career has included most types of mineral exploration geophysics, with a strong concentration on electromagnetic methods. His career experience has been relatively equally divided between time-domain and frequency-domain EM, and between airborne and ground (including borehole). He's worked as a ground geophysical contractor, in junior and major mining companies, and (for the last 22 years) for airborne geophysical contractors in R&D and applications development. Along the way he's had the good fortune to do development work with some of the leading practical experts in both time- and frequency-domain EM.