Sferic signals for lightning sourced electromagnetic surveys

Abstract

Lightning strikes generate electromagnetic (EM) waves, known as sferics, which are used in passive Audio-Frequency Magnetotelluric (AMT) and Geomagnetic depth soundings (GDS). Global lightning networks detect sferics and catalogue the time and location of up to four million lightning strikes per day. In this research, we use lightning network data and model earth-ionosphere waveguide propagation to predict time of arrival, azimuth, and amplitude for each known sferic in our time series EM data. Since conductors effectively rotate electromagnetic fields, we can in principle infer the location and geometry of local and regional structures by calculating the rotation of measured data from their predicted arrival azimuths.