The Detailed Time-frequency Analysis of The HF/VHF Emissions Accompanied with CG Lightning Flashes

In order to obtain the time-frequency domain characteristics of the electromagnetic signal from the whole stages of the Cloud-to-Ground (CG) lightning flashes, including the preliminary breakdown processes, the stepped leaders, the return strokes and the subsequent strokes, we use the lightning signal acquisition platform to collect the electromagnetic signal waveforms concentrated at low frequency(LF), High frequency and Very High frequency (HF/VHF), and carry out the segmentation filtering and the Fourier transform. With the help of Lightning location system (LLS), the time and location of the CG lightning flashes are determined. In this paper, the radiated signal characteristics of CG lightning at different locations and different amplitudes are compared and analyzed. It is concluded that the amplitude of preliminary breakdown processes and return stroke processes is much higher than that of the leaders processes in the frequency range of 30- 350kHz, the preliminary breakdown process, leader and first return stroke of CG lightning have a wide radiation spectrum from 0 to 60MHz, and the subsequent return stroke signal spectra range is relatively concentrated below 10MHz.