Dependency of VHF broad band lightning source mapping on Fourier spectra

Abstract

In the VHF broad band interferometer, the Fourier transform is applied to analyze the whole frequency range of lightning radiation sources. The position of a radiation source can be determined by resolving the incident angle for each frequency component against at least three-antenna sensors, and then by averaging the incident angles of all frequency components the angular position can be located. This arithmetic-averaging method as proposed by previous authors has a disadvantage, especially for cloud-to-ground flashes, that is positions of lightning leader channels near ground level can not be mapped well. It is found that Fourier spectral amplitudes of broad band pulses decrease with increasing frequency, and frequency components having low spectral amplitudes give less contribution to the lightning mapping. To improve the mapping, a weighted-averaging method is proposed. The method provides a way to minimize the influence of frequency components, which contribute less to the lightning mapping.