Higher order spectra in the processing of magnetotelluric data

Abstract

Magnetotelluric (MT) impedances are estimated from electric and magnetic field data using a higher order spectral (HOS) method. This technique rejects Gaussian noise contaminating the MT signal because of the insensitivity of the third order cumulant to Gaussian signals. The non-Gaussian characteristics of a representative set of MT signals are demonstrated. Artificial non-Gaussian datasets contaminated with varying levels of coherent and incoherent Gaussian noise are analysed using this method and three existing methods: the robust remote reference (RRRMT) method , the time-frequency (TF) method and a variant of the conventional (CONV) method. The resistivity and phase estimates obtained by the HOS method and CONV method are more consistent than those of the TF and the RRRMT methods, and in general the resistivity and phase estimates from the HOS method are subject to the least bias.