TABLE OF CONTENTS Lightning detection and location systems can be divided into two categories. In the detection systems belonging to the first category the number of lightning flashes striking a given area is obtained without any specific knowledge concerning actual location of the flashes. Lightning flash counters fall into this category. Detection systems that can pin point the point of a strike or the detailed geometry of the lightning channel fall into the second category. Examples are the magnetic direction finding systems, time of arrival systems and radio interferometric systems.
In lightning flash counters the lightning-generated electric field is received by a standardised electric field sensor (a vertical or a horizontal antenna) and the resulting current is passed through an electronic circuit. When the output voltage of the electronic circuit exceeds a threshold a counter is triggered. In order to avoid multiple counts due to subsequent strokes the trigger circuit has a dead time of about one second.
The first standard lightning flash counter was the one approved by the International Radio Consulative Committee (CCIR) [227]. This counter is fitted with a 7 m long vertical antenna that acts as the field sensor. The bandwidth of the electronic circuitry of this counter has 3 dB points at 3 kHz and 50 kHz with the peak at 10 kHz. CCIR counters respond mainly to the radiation field of the lightning return strokes and Pierce [228] suggested the advantages of having a counter that responds to...
