Geobandwidth: comparing time domain electromagnetic waveforms with a wire loop model
Greg Hodges 1 2 Tianyou Chen 11 CGG Airborne Surveys, 2505 Meadowvale Boulevard, Mississauga, Ontario L5N 5S2, Canada.
2 Corresponding author. Email: greg.hodges@cgg.com
Exploration Geophysics 46(1) 58-63 https://doi.org/10.1071/EG14032
Submitted: 19 March 2014 Accepted: 10 June 2014 Published: 21 July 2014
Abstract
We compare time domain systems of different waveform shape, power and receiver sampling times using a wire loop conductor model to define a comprehensive ‘geobandwidth’ that shows the strength of the response over a range of time constants, analogous to a range of conductance. Frequency domain EM responses can also be calculated as a function of time constant for a wire loop model, giving a consistent comparison method for all time domain waveforms and frequency domain. Arbitrary waveforms can be modelled as a sum of simple short ramps, and the geobandwidth determined numerically. Peak time constant (time constant of peak response) or equivalent frequency can be determined analytically or numerically. The frequency content of a time-domain EM system can be characterised by the peak time constant or the equivalent frequency. The results of these calculations are used to compare response amplitude across a wide range of geological target conductance. Systems can be compared on the basis of signal or signal/noise ratio.
Key words: electromagnetic time domain, frequency, waveform.
References
Becker, A., 1969, Simulation of time-domain, airborne electromagnetic system response: Geophysics, 34, 739–752| Simulation of time-domain, airborne electromagnetic system response:Crossref | GoogleScholarGoogle Scholar |
Chen, S. D., Lin, J., and Zhang, S., 2012, Effect of transmitter current waveform on TEM response: Chinese Journal of Geophysics, 55, 709–716
Chen, T., Hodges, G., and Miles, P., 2013, The MULTIPULSE™ – high resolution and high power in one TDEM system: 13th SAGA biennial and 6th AEM conference proceedings.
Davis, A. C., and Macnae, J., 2008, Quantifying AEM system characteristics using a ground loop: Geophysics, 73, F179–F188
| Quantifying AEM system characteristics using a ground loop:Crossref | GoogleScholarGoogle Scholar |
Grant, F. S., and West, G. F., 1965, Interpretation theory in applied geophysics: MacGraw Hill.
Hodges, G., and Yin, C., 2004, Geologically constrained conversion of frequency domain EM data to time domain: 74th International Meeting, SEG, Expanded Abstracts, 656–659.
Liu, G., 1998, Effect of transmitter current waveform on airborne TEM response: Exploration Geophysics, 29, 35–41
| Effect of transmitter current waveform on airborne TEM response:Crossref | GoogleScholarGoogle Scholar |
Mallick, K., 1972, INPUT response to a single-turn conductive circuit: Geoexploration, 10, 255–259
| INPUT response to a single-turn conductive circuit:Crossref | GoogleScholarGoogle Scholar |
McCracken, K. G., Oristaglio, M. L., and Hohmann, G. W., 1986, A comparison of electromagnetic exploration systems: Geophysics, 51, 810–818
| A comparison of electromagnetic exploration systems:Crossref | GoogleScholarGoogle Scholar |
Stolz, E. M., and Macnae, J., 1998, Evaluating EM waveforms by singular-value decomposition of exponential basis functions: Geophysics, 63, 64–74
| Evaluating EM waveforms by singular-value decomposition of exponential basis functions:Crossref | GoogleScholarGoogle Scholar |
Wolfgram, P., and Karlik, G., 1995, Conductivity-depth transform of GEOTEM data: Exploration Geophysics, 26, 179–185
| Conductivity-depth transform of GEOTEM data:Crossref | GoogleScholarGoogle Scholar |
Yin, C., and Hodges, G., 2009, Wire-loop surface conductor for airborne EM system testing: Geophysics, 74, F1–F8
| Wire-loop surface conductor for airborne EM system testing:Crossref | GoogleScholarGoogle Scholar |