Airborne Lightning Warning Systems: A Survey.

Abstract : Lightning warning systems for airborne use may be classified in accord with their application as near-zone warning systems, and distant warning systems. The near-zone systems considered here are essentially electrostatic field detectors (field mill, radioactive probe, and corona point) that can warn of the presence not only of thunderstorms but of high electric fields associated with nonthundery clouds that may nevertheless cause triggered strikes to aircraft (far outnumbering strikes due to natural lightning, according to pilot reports). Lightning-strike and high-field statistics, and associated corona effects, are discussed in connection with triggering of strikes. The distant warning systems considered, aside from airborne weather radar, include RF electric and magnetic sferics detectors, as well as optical systems and the above-mentioned near-zone detectors modified to also detect sferics. The sferics detectors sense electromagnetic fields radiated by lightning and pre-lightning discharges, and may be classified according to their applications as single-station bearing detectors (crossed loops-wideband or narrowband, multiple loops, time-of-arrival and interferometer systems), and as single-station range detectors (crossed loops, 500-KHz-pulse-height, spectral-amplitude-ratio/group-delay-difference, electric amplitude, e.g. 1/r-cubed, and ratio-of-magnetic-to-electric-amplitude systems). Many of the systems surveyed have virtues warranting their consideration, as individuals or in combinations, for airborne warning and avoidance application. However, they all have advantages and disadvantages that require further investigation, careful testing and evaluation.