A CONSTRAINED INDEPENDENT COMPONENT ANALYSIS BASED APPROACH TO SEPARATE THE WEAK OCEAN INDUCED MAGNETIC SIGNALS FROM THE OBSERVATORY RESIDUALS

A long-standing question in oceanic magnetic studies is the detectability of the weak magnetic signals from motional induction at ground observatories or at the aeromagnetic altitudes. We test this with the monthly mean Kuroshio currents from the global oceanic circulation model for the past decade. The motion induced magnetic anomalies are computed in a spherical Earth model from a 3-D EM induction code. The temporal variation of the vertical component of the induced field is then compared with the residuals of the same component at the Japanese magnetic observatories. The results show that the induced signals are weak relative to the observatory residuals. A Constrained Independent Component Analysis (cICA) algorithm is used to separate the weak signals from the residuals. The prerequisite for this algorithm is the design of an apriori signal. An approach combining stochastic resonance and higher order statistics is proposed for the design of this reference signal in order to perform source separation of ocean induced magnetic signals. The preliminary results from the simulations and its application to the observatory data located off the coast of Japan are presented.