Electrical conductivity in the lower mantle: Constraints from CHAMP satellite data by time-domain EM induction modelling

Time-domain EM induction is used to obtain 1-D conductivity structure in the Earth using seven years of vector magnetometer measurements by the CHAMP satellite. An optimal model is obtained by means of quasi-Newton minimization with regularization. Sensitivity of data to deep Earth conductivity is checked by limited grid search of the model space in the vicinity of the optimal model. While regularization plays a considerable role in constraining the conductivity model, data misfit poses upper limits on the lower mantle and D″D″ conductivity at 2 S/m, and 10 S/m, respectively.