CORRELATION BETWEEN THE OPTICAL SIGNATURES AND CURRENT WAVE-FORMS OF LONG SPARKS - APPLICATIONS IN LIGHTNING RESEARCH

Broad-band optical output (500-850 nm) and channel current of 500 mm l ong sparks were measured. Experiment was conducted for several current rise times. The optical rise time and current rise time show a linear relationship. During the rising portion the optical signal closely fo llows the current wave shape. There is no detectable variation in the time separation between the starting point of the optical signal and t hat of the current signal, with varying current rise time or current a mplitude. One can apply this result to use the optical signal, which i s measurable, to estimate the information regarding the variation of c urrent with altitude of long spark channels. One such case, that will be benefited from the results of this research, is the measurement of peak current along the channel of both artificial and natural lightnin g. For a 250 mm gap we performed the experiment by increasing the curr ent amplitude between about 0.5 kA and about 3.5 kA, for the same curr ent rise time. The current rise time and optical rise time remain appr oximately at a steady level with current amplitude, while the former i s always slightly less than the latter. Hence, we suggest that the res ults obtained in this work may be extended to the measurements of the current along lightning channels where the peak currents are in the ra nge of few tens of kiloamperes. For a given current pulse half-width, that of the optical pulse shows a linear variation with current amplit ude. We also observed a linear relationship between the current amplit ude and the optical amplitude in the range of current amplitudes relev ant to this experiment. (C) 1998 Elsevier Science B.V. All rights rese rved.