The electromagnetic wave experiment for CSES mission: Search coil magnetometer

The seismic activities on the Earth can produce a disturbance of the electromagnetic field and particles in the ionosphere. The search coil magnetometer (SCM) mounted on China Seismo-Electromagnetic satellite (CSES) is designed to measure the magnetic field fluctuation of low frequency electromagnetic waves in the frequency range of 10 Hz–20 kHz. The SCM comprises a three-axis search coil sensor mounted on a 4.5 m boom and an electronic box inside satellite module. The sampling rate of the SCM is 51.2 kHz and the time resolution of the power spectrum density (PSD) is 2 s. The frequency resolution is 12.5 Hz. There are three operation modes: survey, detailed survey and calibration. In the survey mode, the SCM can provide a PSD in the whole frequency range of 10 Hz–20 kHz and wave forms in the low frequency range below 2 kHz while in the detailed survey mode the SCM can provide both PSD and wave forms in the whole frequency range of 10 Hz–20 kHz. The sensitivity of the SCM instrument is 5.0×10−4 nT Hz−1/2 at 10 Hz, 5.0×10−5 nT Hz−1/2 at 200 Hz, 3.4×10−5 nT Hz−1/2 at 2 kHz and 1.1×10−4 nT Hz−1/2 at 20 kHz. The telemetry rate is ∼0.85 Mbps in the survey mode and ∼3.0 Mbps in the detailed survey mode. The phase difference between three axes can be made generally with a precision of less than 1.0°. The dynamic range of the SCM instrument is over 100 dB. The orthogonality of three mechanical axes of search coil senor is better than 0.13°. The performance of SCM can satisfy the requirement of scientific objectives of CSES mission.