Spectral Analysis of VLF Transients Using Fourier Transform Methods

Abstract - Very Low Frequency (VLF) electromagnetic signals in the range of 1–30 kHz are widely used for investigating ionospheric and magnetospheric processes. These signals are typically non‑stationary and contain transient components arising from lightning discharges, power‑line interference, and seismic disturbances. Traditional Fourier Transform techniques provide global frequency information but lack temporal localization. This paper presents a detailed investigation of Fourier Transform (FT), Fast Fourier Transform (FFT), and Short Time Fourier Transform (STFT) for spectral analysis of VLF transients. The limitations associated with fixed resolution analysis are discussed, and the results demonstrate the importance of time–frequency representation for non‑stationary geophysical signals. Key Words: Fourier Transform, spectral characteristics and non‑stationary geophysical signals