Effects of notch-filtering on the ELF sferics and the physical parameters

For ELF stations using hardware notch-filters to suppress power-grid emissions, the amplitude and the phase of the recorded sferics will inevitably be distorted. The phase shift causes the event time to move and hinders cross-comparing of events between different platforms. Notch-filtering also create fictitious dips in the current moment spectrum of the ELF sferics that lead to error in deducing ...