Non-linear conjugate gradient inversion for global EM induction: Resolution studies

摘要: SUMMARY We develop a non-linear conjugate gradient inversion for global long period electromagnetic induction studies. The scheme requires computation of derivatives the regularized penalty functional. We derive analytical and numerical expressions these derivatives, associated Jacobian, show how can be efficiently implemented by generalizing extending an existing finite difference forward solver. Using layered spherical harmonics to parametrize model space, we invert range synthetic data sets test inversion, study vertical horizontal resolution currently available sets. conclude that long-period geomagnetic observatory in 5–107 d resolve large scale (300–500 km vertically, thousands horizontally) heterogeneities mantle electrical conductivity reliably at depths ∼ 670–1600 km. By response 0.2–5 (including daily variation periods), upper-mantle structure could also resolved.