A VHF technique for space‐time mapping of lightning discharge processes

Abstract

Instrumentation using fast logic circuits and a wide band receiving system (20–80 MHz) to determine direction of arrival of individual VHF electromagnetic impulses from lightning discharge processes was tested successfully at the Kennedy Space Center (KSC) during the 1976 Thunderstorm Research International Program (Trip 76). Time difference of arrival of impulses was used to measure the azimuth from a pair of horizontally spaced antennas and the elevation from a pair of vertically spaced antennas. Although the base line of each pair was only 13.74 m, the time difference measurements were made with 0.4‐ns resolution so that the direction to the source could be determined to an accuracy of ±0.5°. Directions of the individual impulses were represented in real time on a 60° azimuth and 30° elevation format and photographed with a 16‐mm movie camera. Two stations separated by about 17.8 km simultaneously recorded direction data for discharges from over three dozen thunderstorms in the KSC area. A description of this technique and the results of the Florida tests are presented. Analysis of these data revealed that (1) fine structure of lightning discharges could be accurately located and tracked with this technique by using triangulation methods, (2) branching and structure in the discharge processes could be observed, (3) most lightning activity occurred about 5–6 km high, near the −10°C temperature level, and (4) considerable movement of discharge centers occurred as the lightning processes permeated the thunderstorm volume at progression speeds of about 50–150 km/s.