Joint analysis of the shaft-rate magnetic fields for vector sensors

The corrosion and corrosion resistance current of the submarine modulated by the propeller rotation will produce extremely low frequency (ELF) electromagnetic field in the seawater, which can be used as the attack feature for underwater weapons. However, ELF noise is highly process-sensitive, rendering it as a non-stationary signal, and, hence, traditional Fourier analysis method is not adequate. In this paper, one of the statistical methods, KPSS test, is used to check the stationarity of the measured 3-axis data. The data are then decomposed jointly by multivariate empirical mode decomposition (MEMD) and the corresponding slow fluctuations are subtracted to eliminate the non-stationarity of the data. By using the least squares method, the hum of the shaft-rate magnetic fields is estimated. Moreover, quantile-quantile plot is adopted to check if the remaining noise data is consistent with normal distribution. Our analysis shows that the measured shaft-rate magnetic fields are short-time stationary. In addition, the background noise follows normal distribution regardless of shaft-rate magnetic fields and the slow fluctuation noise caused by the rotation of fluxgate sensors in the earth´s magnetic field.