Extremal bias coupling in magnetotellurics

Bias effects due to uncorrelated noise on electrical and magnetic channels are cast into a quantitative framework which allows for an immediate conservative judgment of impedance tensor quality from a single station set up. The horizontal magnetic field is regarded as input to a linear system with the horizontal electrical field and the vertical magnetic field as outputs. The coherence between inputs, the predicted coherence between outputs and inputs, and the polarization characteristics of the inputs determine the extremal bias effects. Exact expressions for impedance tensor elements and tipper elements are given. Moreover, rotation angles of principal impedance direction, skew, and ellipticity are calculated. Finally, we study some practical examples that show some of the characteristics predicted by our model.