Development of the wideband magnetic field wave monitor for the Phase II of Chinese Meridian Project

There are various magnetic field waves with frequencies ranging from mHz to thousands of Hz in the Earth's magnetosphere. These waves can be categorized into three classes depending on their period: ULF (mHz to ~ Hz), ELF (~ Hz to hundreds of Hz), and VLF (hundreds of Hz to thousands of Hz). The regular and continuous ultra-low-frequency (ULF) waves in the magneto-sphere, ranging from 1 mHz to a few Hz, are important to geomagnetic micropulsations. Recently, whistler mode waves generated by lightning and extremely low-frequency (ELF) bursts, which can be attributed to earthquakes, were detected near the surface; their frequencies range from several Hz to a few hundred Hz. The research on the characteristics of ionospheric plasma disturbance caused by the known ground-based very low frequency (VLF) transmitters, whose frequencies range from a few hundred to a few thousand Hz, is of great significance for analyzing changes in the ionospheric environment. These magnetic field waves are crucial for studying various space physical phenomena. As the wave monitoring equipment of global geomagnetic stations measures relative changes and a lack of unified calibration, they cannot conduct joint observations from high to low latitudes and unified comparative studies of the observational data from multiple sensors. The magnetoresistance sensor (ULF: 0.1 mHz–2 Hz), giant magneto-inductance sensor (ELF: 0.2 Hz–2 kHz), and coil sensor (VLF: 0.2–10 kHz) is used to develop a new generation of broadband geomagnetic wave monitors, which are placed on the geomagnetic stations in typical areas such as Mohe (high latitude), Beijing's Ming Tombs (middle latitude), and Sanya Ledong (low latitude), near the 120° meridian chain. Combined with the data of near-Earth space satellites such as FY-3E and SMILE, the observation ability of various wave phenomena in the Earth's magnetosphere will be comprehensively improved. The performance test experiment shows that the developed wave monitor can detect the fluctuating magnetic field at a particular frequency (1 mHz–10 kHz); magnetic field detection ranges of: ± 65000 nT (ULF frequency band), ± 1000 nT (ELF frequency band), and ± 100 pT (VLF band); with low nonlinear errors: ULF frequency band ≤ 0.0446 %, ELF frequency band ≤0.51 %, and VLF frequency band ≤ 1.18 %; and low noise levels: RMS ≤0.5554 nT (ULF frequency band), NPS ≤0.028 nT /√Hz (ELF frequency band), and NPS ≤0.24 pT/√Hz (VLF band). These characteristics enable the proposed broadband geomagnetic wave monitor to meet the Phase II of Chinese Meridian Project magnetic field detection requirements.