A Technique for Accurately Locating Lightning at Close Ranges

Abstract

A VHF lightning direction-finding technique, that can be applied to locate close lightning accurately, has been built and successfully tested. The technique, originally proposed by Oetzel and Pierce (Radio Sci., 4, 199?202, 1969), measures the direction of arrival of the received VHF impulses emitted by a lightning discharge. The direction of arrival is calculated from time-of-arrival measurements between spaced receivers having a separation of the order of 100 m. The shortness of this baseline avoids pulse-identification ambiguities and simplifies the equipment and display requirements. The time-of-arrival measurements are made with high-resolution (10 nsec) digital time-interval counters along with an on-line digital computer to process, store and display the data. The direction-finder has a very fast data acquisition rate and can establish the direction of at least 5000 impulses per second. It is thus feasible to locate, with a high degree of spatial and temporal resolution, the origins of the successive VHF impulses radiated during a lightning flash. Hence the development of lightning discharges within a thundercloud can be traced. A description of the instrumentation techniques and of the results from a successful test conducted in Albuquerque, N.M., is presented.