Publication Date:
2014-02-24
Description:
[1] The VHF Broadband Digital Interferometer (DITF) developed by Osaka University has been improved to allow continuous sampling over the entire duration of a lightning flash and to utilize a generalized cross-correlation technique for determining the lightning source directions. Time series waveforms of 20-80 MHz signals received at three orthogonally located antennas are continuously digitized over multi-second intervals, as opposed to sequences of short-duration triggers. Because of the coherent nature of the measurements, radiation sources are located down into the ambient receiver and environmental noise levels, providing a quantum leap in the ability to study lightning discharge processes. When post-processed using cross-correlation, the measurements provide angular uncertainties less than 1 degree and time resolution better than 1 μ s. Special techniques have been developed to distinguish between actual lightning sources and noise events, with the result being that on the order of 50,000-80,000 radiation sources are located for a typical lightning flash. In this study, 2-dimensional interferometer observations of a classic bi-level intracloud flash are presented and combined with 3-dimensional Lightning Mapping Array observations to produce a quasi-3D map of lightning activity with the time resolution of the interferometer. As an example of the scientific utility of the observations, results are presented for the 3D progression speed of negative leaders associated with intracloud K-leaders.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
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