Stability validation on the VLF waveform data of the China-Seismo-Electromagnetic Satellite

The China-Seismo-Electromagnetic Satellite(CSES),which was launched in February 2018,carries the search coil magnetometer(SCM)and the electric field detector(EFD)to realize the high-resolution electromagnetic field and wave detection in the upper ionosphere.Due to the complexity and variability of the ionospheric environment,the stability of such a high sampling rate and high-precision electromagnetic field detection systems is always an essential link in data processing and the scientific application of CSES.This work evaluates the stability of the very-low-frequency(VLF)band detection by validating the systemic sampling-time differences between SCM and EFD in the VLF burst-mode observations.The optimal waveform data preprocessing method is put forward according to the noise levels of the VLF burst-mode observation and the inherent design characteristics of EFD.The VLF waveform data of EFD is rebuilt by filling the data gaps among the sampling sub-periods,making it with a similar sample length to SCM.Then by precisely intercepting the maximum and minimum values of the burst-mode waveforms,the variation of the sampling-time difference between EFD and SCM is statistically evaluated.Results show that during the three years'operation,the sampling-time difference between EFD and SCM predominately keeps below 0.5 s,indicating good stability of EFD and SCM on orbit.Then we developed an automatic synchronization tool based on the similarity function and STA/LTA(short time average over long time average)characteristic function.This tool can effectively realize the precise synchronization between SCM and EFD in the VLF burst-mode observation.This work is helpful to upgrade the data quality of CSES and provides technical support for electromagnetic wave propagation studies.