Test of the Principle of Operation of a Wideband Magnetic Direction Finder for Lightning Return Strokes

Abstract

The principle of operation of a wideband crossed-loop magnetic-field direction finder is studied by comparing the bearing determined from the NS and EW magnetic fields at various times up to 155 ?s after return stroke initiation with the TV-determined lightning channel base direction. For 40 lightning strokes in the 3 to 12 km range, the difference between the bearings found from magnetic fields sampled at times between 1 and 10 ?s and the TV channel-base data has a standard deviation of 3°?4°. Included in this standard deviation is a 2°?3° measurement error. For fields sampled at progressively later times, both the mean and the standard deviation of the difference between the direction-finder bearing and the TV bearing increase. Near 150 ?s, means are about 35° and standard deviations about 60°. The physical reasons for the late-time inaccuracies in the wideband direction finder and the occurrence of these effects in narrow-band VLF direction finders are considered.