Broadband radio interferometer utilizing a sequential triggering technique for locating fast-moving electromagnetic sources emitted from lightning

A broadband radio interferometer to investigate the location of fast-moving electromagnetic (EM) sources emitted from lightning discharges has been designed. A sequential triggering technique was applied to the system for recording the data of broadband electromagnetic pulses from 25 to 250 MHz. Once the electromagnetic pulse is detected and its amplitude exceeds a threshold level, the triggering circuit is turned on to record the waveform and get ready to acquire another pulse afterwards. This technique can overcome the limitation of the digitizer's memory due to such high digitization rate and very large bandwidth. We have implemented our system to locate and retrace fast-moving electromagnetic sources emitted from lightning discharges during a field experiment in Australia in summer 1997. As one of the results, a cloud-to-ground lightning discharge has been reconstructed in the two-spatial dimension and in time sequence.