Frequency Extraction of Global Constant Frequency Electromagnetic Disturbances from Electric Field VLF Data on CSES

The electromagnetic data observed with the CSES (China Seismo-Electromagnetic Satellite, also known as Zhangheng-1 satellite) contain numerous spatial disturbances. These disturbances exhibit various shapes on spectrogram, and constant frequency (CFEDs), such artificially transmitted very-low-frequency (VLF) radio waves, power line harmonics, interference from satellite platform itself, appear horizontal lines. To exploit this feature, we proposed an algorithm based computer vision technology that automatically recognizes these lines spectrogram extracts frequencies CFEDs. First, VLF waveform collected electric field detector (EFD) are converted into a time–frequency using short-time Fourier Transform (STFT). Next, CFED automatic recognition is used to identify spectrogram. third step determine range proportional relationship between domain of satellite’s height Finally, confirm presence CFEDs in extract their true frequencies. We statistically analyzed 1034 orbit spectrograms 8 periods (5 days per period) identified approximately 200 Among them, two strong signals persisted throughout entire orbit. This study establishes foundation for detecting anomalies due artificial sources, particularly short-term earthquake prediction. Additionally, it contributes research other aspects suppression cleaning waves.