Polarization analysis of natural and artificially induced geomagnetic micropulsations

Abstract

The polarization characteristics of geomagnetic micropulsations are investigated using quasi-monochromatic wave train theory of physical optics. The polarization of a wave train is analyzed by considering the coherency matrix of the wave field. The elements of the matrix are calculated over the desired frequency band and the polarization parameters evaluated. Since the determinant of the coherency matrix is zero for a totally polarized wave field, this property can be used to separate a partially polarized wave field into its polarized and unpolarized parts. The ellipticity, orientation, and sense of polarization for the polarized portion are then calculated in terms of the matrix elements using power and cross-power spectral analysis techniques. Based on this approach, the polarization of a number of different signals has been digitally determined. Test cases include a random number time series, a constructed signal with a predetermined polarization, and an example typical of geomagnetic micropulsations resulting from high-altitude nuclear weapons tests superimposed on high natural background. The results of these analyses are then compared with those from the standard hodogram technique and the effectiveness of both methods discussed in terms of the signal characteristics.