VLF signal recognition by cross-spectral analysis

The analyses of very low frequency (VLF) magnetospheric plasma waves conducted on the GEOS 1 satellite are evaluated. A digital correlator was included in the wave experiment on the satellite which allowed the onboard computation of autocorrelation and cross-correlation functions, thereby reducing the demands on the telemetry link. The correlation functions were Fourier transformed on ground to produce spectrograms of good quality for investigations of magnetospheric plasma waves. Results show that the cross-spectral phase signature of VLF waves can be effectively employed for extracting the signals from incoherent background noise. In addition, these findings indicate that the cross-spectral phase can yield information on the propagation characteristics of the various components which comprise a VLF event. The potential of this method for distinguishing signal from noise and for displaying wave propagation characteristics is evaluating using VLF hiss and chorus observed on GEOS 1.