Wave impedance technique to derive distance from nearby lightning discharges

Summary form only given. We discuss the results of application of the ELF-VLF wide-band measurement technique for locating nearby lightning discharges. The measurements were performed at Singapore from the field site on board the research vessel. Three field components, namely, vertical electric and two orthogonal horizontal magnetic fields, were digitally recorded and used for the analysis. The distance from the lightning discharge was established using the characteristic frequency dependence of the complex wave impedance spectra pertinent to the nearby lightning discharges of vertical orientation (Korol et al., 1993). The method implies the frequency dependence of the transition range between the static, induction and radiation field components of the wide-band radio signal, similarly to the well-known E-H field technique (Ruhnke, 1971; Kononov et al., 1986). The technique suggested is distinguished by the wide-band measurements that include completely the ELF/VLF range. The horizontal Poynting vector components (Rafalsky et al., 1994) were used to find the source bearing. This technique eliminates an ambiguity in the arrival angle automatically. Simultaneously, a product of the electric and magnetic field components integrated over the pulse duration depends only on coherent portions of a signal. This allows for extraction of the linearly polarised signal, improving the output accuracy of the direction finding. After the source coordinates were established, we used the spectra of the electric and magnetic field components to reconstruct the spectra of the particular current moments of the lightning observed