In-flight measurements of lightning and thunderstorm radiation

Thunderstorms emit bursts of energetic radiation. Moreover, a lightning stepped leader produces x-ray pulses. These phenomena, their interrelation and impact on terrestrial atmosphere and near space are not fully understood yet. The In-flight Lightning Strike Damage Assessment System ILDAS was developed in an EU FP6 project (http://ildas.nlr.nl/) to provide information on threat that lightning poses to aircraft. It is intended to localize the lightning attachment points in order to reduce maintenance time and to build statistics on lightning current. The system consists of one E-field sensor, eight H-field sensors and was recently extended with two LaBr₃ scintillation detectors to measure hard radiation inside the aircraft. One of the unique features of the system is the ability to reconstruct a lightning current direction for any instance in time. The x-rays generated by the lightning flash are measured in synchronization better than 10 ns with the lightning current information during a period of 1 second around the strike. Numerous fast x-ray bursts of 1-4 μs duration have been measured. The x-rays occur during initiation phase of lightning leader and during attachment phases of subsequent discharges and return strokes.