Frequency spectra features of electric field waveforms produced by close and middle-range compact intracloud discharges and their discrimination from cloud-to-ground lightning

Abstract

This paper is aimed at extending the studies already presented in the literature for distant type of compact intracloud lightning discharges and their identification. Several electric field recordings of close and middle–range compact intracloud lightning discharges in the bandwidth from 0.5 Hz – 3 MHz were processed to identify specific features of their frequency spectra. Spectrograms of narrow bipolar pulses were compared with fast Fourier transform results obtained for typical electric field signatures of cloud-to-ground lightning to find their unique features. Electric field data from the Kennedy Space Center, Florida, and Lightning Observatory in Rzeszow, Poland, were used for analysis. Comparison of spectrograms for close compact intracloud discharges and cloud-to-ground lightning revealed high level of similarity, mainly because their measured lightning electric fields were dominated by the electrostatic component. Hence, it was impossible to discriminate between those two types of lightning using Fourier transform-based methods found in the literature. An alternative analysis applying short-time Fourier transform was proposed. It showed a better identification performance than the ordinary Fourier transform. The newly developed method can be implemented in lightning location systems to improve their accuracy in identification of such lightning events that can adversely affect the performance of power systems.