Analytical presentation of statistically estimated magnetotelluric transfer functions by a set of polynomials

Abstract

In magnetotelluric studies time variations of the horizontal telluric and magnetic field components at the earth's surface are compared to get detailed information of the electrical conductivity structure of the earth's interior. The development of conductivity models from the data demands the thorough estimation of the transfer functions in the frequency domain between the Fourier transforms of the recorded time series. The analytical presentation of the estimated transfer functions allows an individual selection of a number of frequencies for further investigation. Larsen's presentation (Larsen, 1975, 1980) of the transfer functions by single polynomials demands a complicated calculation of confidence limits. Therefore, the transfer functions are presented here by the sum of polynomials which fulfil an orthogonality criterion. The orthogonality criterion allows a rather simple estimation of the frequency-dependentconfidence limits of the transfer functions. The polynomial method is applied to a 100-day record of the magnetic and telluric field variations near Gottingen. As the telluric field is usually partially disturbed during such a long time interval, the polynomial method is extended to treat telluric time series with missing data. The comparison of the smooth polynomial transfer functions with band-averaged estimates yields a good correlation between the estimates as well as between their confidence intervals.

     ARK: https://n2t.net/ark:/88439/y026544

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