Fig. 20From: Simultaneous inversion for source field and mantle electrical conductivity using the variable projection approachRelative errors of the external field coefficients \(\varepsilon _3^1\) with different conductivity models. Errors are shown for the VP inversion result (blue), estimation using a uniform mantle conductivity of 0.1S/m (red), and a simplistic perfect insulator–conductor bi-layer model (orange)Back to article page