When one is faced with the possibility of a lightning hazard, there are two methods of protection: (i) identify and avoid the hazard and (ii) harden tile system of interest to withstand the effects of nearby and direct strikes.
In the last 10 years, exceptional progress has been made in the technology for identifying and locating natural CG lightning, and commercial nationwide networks of lightning sensors with a wideband magnetic direction-finding technology that produce lightning locations in real time are now operational in the United States and in about IS other countries [ 59]-[63]. Many networks are being used both for research and for providing warnings of natural lightning in a variety of applications. Two addition techniques for lightning location have recently become available commercially, time-of-arrival and interferometry, with these technologies now being used in the U.S. and in several other countries [64]-[69].
In order to design better lightning protection systems to improve the capability of ground-based facilities and of aircraft and space vehicles to withstand the effects of nearby or direct strikes, it is essential to understand the nature of the lightning environment near and at the point ofa direct strike. Among the most important parameters responsible for coupling lightning signals to electronic systems is the maximum current and the maximum rate of change of current with respect to time. Return stroke current measurements made on towers with wideband transient recorders I 701-1 72 1, currents measured during lightning strikes to a F-l06B research aircraft (731. and retum stroke current measurements in rocket-initiated discharges [ 341, 13.51 show that the peak current rate-of-rise is considerably larger than was believed to be the case a decade or two ago. A maximum value of 3.8 x 10’1 A/s has been measured on the F-106 B aircraft in flight, and values above 2 x 10” A/s occurred frequently 1731. Only a few measurements of current rate of rise have been made with sufficient bandwidth on natural retum strokes. but from this small sample a peak value of 1.8 x lO1] A/s has been observed 1701-[72]. Finally, the rocket-triggered discharges to saltwater at the NASA Kennedy Space Center have produced a peak current rate-of-rise for return strokes of 4.1 x lo1’ A/s [ 341, [ 3 S ] .T hus, from the limited data that are available, we expect that a peak current rate-of-rise near 5 x 10I1 A/s is possible, even at flight altitudes.
Although considerable progress has been made recently in understanding lightning vis-a-vis lightning protection, we still need to understand more thoroughly the following important aspects of lightning: the total wave shapes of the currents that are associated with all of the salient lightning processes in both natural and triggered events, the physical processes by which natural lightning attaches to ground-based structures and to aircraft, and the role of the structures and aircraft in initiating lightning.