A Brief History of Lightning Detection and Location Systems

Humans have been acutely aware of lightning since time immemorial, resulting in eons of superstition, legend and deification. Yet even with the insights of Benjamin Franklin moving lightning from the realm of mystery into science, the phenomenon remained, though not for lack of trying, one of the last major meteorological processes to be quantitatively monitored, especially in the operational arena. Early methods to climatologically assess electrical storms used audible “thunder day” records collected at government observation stations. In late 1940s Japan, Ted Fujita resorted to paring visual observations of lightning strike azimuths with audible thunder delays to create one of the first plots of the progression of cloud-to-ground (CG) strikes in a small convective storm. Even during the seminal Thunderstorm Project (1946-49), little attention was paid to the electrical processes that gave the thunderstorm its name.

The realization that lightning was a broad-band electromagnetic radiator allowed development of early techniques to electronically count nearby lightning strikes, and then eventually employ “sferics” to monitor electrical activity over larger areas. The mid-20^th century electronics revolution changed the approaches to monitoring many atmospheric processes, and certainly for lightning. Operating at VLF frequencies, magnetic direction finders (MDF) first recorded CG azimuths and, by the 1970s, MDF networks mapped CG flashes via triangulation in real time. This technology gradually evolved into one of the two prototype National Lightning Detection Networks. A second approach, using time of arrival methodology (TOA), provided even better location accuracy with fewer sensor-siting problems. Eventually the best features of MDF and TOA technology were merged into systems typified by the operational U.S. National Lighting Detection Network, unique also in that this data source was developed and is operated by the private sector. Over the prior two decades, techniques have evolved with several networks locating CGs on a global scale. Three-dimensional Lightning Mapping Arrays (LMA) sense myriad VHF sources within the lightning channel, defining the entire lightning discharge over areas of thousands of square kilometers. Parallel efforts, employing optical sensors onboard spacecraft, evolved from polar orbiter sampling, useful for climatology, to the current operational Geostationary Lightning Mapper (GLM) on GOES 16 & 17.