Source effect impact on the magnetotelluric transfer functions

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Tomasz Ernst
Krzysztof Nowożyński
Waldemar Jóźwiak


It is known that the deviation from the plane wave assumption (the so-called source effect) has an

impact on the results of vertical transfer function (VTF) estimation, especially for long periods. We

observe the so-called seasonal effect, i.e. the VTF calculated from the data measured in the summer

months is different from the VTF estimated from the winter months data. This is related to the

length of the day, as in the diurnal data the effect of deviation from the plane wave is greater. In the

present work, its potential effect on the estimation of the impedance tensor for magnetotelluric

soundings is investigated. A unique, very long series of magnetotelluric recordings at the Belsk

Magnetic Observatory was used for the analysis. The results showed that we do not observe the

summer-winter seasonal changes as it is in the case of VTF. Small differences can be noticed as a

result of TF estimation separately for diurnal and nocturnal data. The analysis of prediction errors

confirms this finding and proves that the daily data are more distorted (distant with the plane

wave). More detailed analyzes were performed by making a precise selection of data, dividing them

into those that fulfill and those that do not fulfill the assumptions of the plane wave. The results

show that the impedances estimated from data separated in this way may differ by several percent.

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How to Cite
Ernst, T., Nowożyński, K. and Jóźwiak, W. (2022) “Source effect impact on the magnetotelluric transfer functions”, Annals of Geophysics, 65(1), p. GM104. doi: 10.4401/ag-8751.
Geomagnetism and Paleomagnetism