Lightning return stroke current identification via field measurements

 An inverse procedure is presented for identifying and reconstructing the waveform of the lightning return stroke current. It is based only on the acquisition of the electromagnetic field radiated by the discharge channel in various locations on the ground and at various frequencies, and requires no information about the channel base current. The fundamental idea is shown to come from an electrostatic problem in which the linear charge density of a vertical thin wire is determined starting from the measured field. Three versions of this procedure have been developed: in the first, the identification is carried out by means of the measurement of the electric field at various distances from the lightning channel at a given frequency; in the second, only two sensors for the electric field are necessary, but various sampling frequencies; in the third, only one observation point is needed, for the measurement of both the electric and the magnetic field. A simulated validation of all the approaches is provided as well as a detailed analysis of their numerical accuracy.