Upcoming TALKS

Date: Tuesday December 7, 2021 at 4:00 PM EST

Title  More EM myths and Old-fashioned Methods.

Speaker: Greg Hodges, Senior Geophysicist at Sander Geophysics.

 Location:  Please register here

Abstract

There are a few myths about EM held by many people that deserve study. Some of them are a result of limited experience with either time or frequency domain EM, or limited experience with multiple geological environments. Other misconceptions come from thinking that the two different mathematical models, time domain and frequency-domain, make things happen differently in the earth. Don’t ever think that the model defines the earth – it only attempts to imitate it.

Are time domain EM and frequency domain EM the same thing, or different? The answer is: “Yes”. The earth is not frequency domain. The arrow of time is not oscillatory. But it is important to recognize that what you will see from the earth depends on how you look at it. The nature of the response depends on how you energize the earth and how you measure the response.

Debunking other myths: Current rings propagate downward with time, but that doesn’t always mean that depth correlates to time of the response. Calculating new parameters from the same data is not adding new information. B-field from a coil is not really B-field. In-phase is real, but on-time is not in-phase. Bandwidth is about more than electronics. FDEM has IP effects. Levelling EM data damages the EM data quality.

Sometimes a pencil and paper (and your brain) can do a better job of modeling than the best computer.


 



     

 



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