Estimation of magnetotelluric transfer functions from radio transmitters

Abstract

A new method to estimate magnetotelluric (MT) transfer functions using radio transmitters as the source has been developed using an extended version of Weidelt’s C function expansion. The expansion coefficients are found from solving a mixed determined linear inverse problem by a truncated singular‐value decomposition technique with a truncation level determined automatically from the data. Synthetic tests with both noise‐free and noisy data show the new method is accurate and robust with respect to lack of transmitters in certain bands. A test profile with 42 stations from a dump‐site investigation in the Netherlands shows that the estimated transfer functions are remarkably stable and smooth as a function of frequency and distance along the profile. Compared with the standard band‐averaging technique, even the formal error bars are generally smaller and more realistic with the new method because the bias introduced by assuming that transfer functions are constant in a small subband is removed.