Inversion of band‐limited TEM responses

It is shown that the electromagnetic (EM) spectrum is characterized by strong amplitude‐modulated transmitters operating in the target bandwidth of transient electromagnetic (TEM) measurements. As these transmitters cause significant noise in TEM soundings, it is mandatory to band‐limit the input signals to improve the signal‐to‐noise ratio and thereby the depth of exploration. Band‐limitation will distort the TEM responses, which leads to erroneous inversion results if the applied low‐pass filters are not accounted for in the inversion scheme. We incorporate the low‐pass filters in the inversion scheme and test the inversion approach on theoretical and field data. Inversion of band‐limited theoretical responses results in recovery of erroneous resistivity models if the filters are not included in the inversion scheme. By contrast, inversion of band‐limited theoretical and field data, for which the applied low‐pass filters are included in the inversion scheme, leads to recovery of similar resistivity models, independent of the applied cut‐off frequencies.

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