Wave normal directions and wave distribution functions for ground based transmitter signals observed on Geos 1

Methods for determining the wave normal direction of electromagnetic wave fields observed in space from the simultaneous measurement of part or all of six wave components are assessed. Crossproduct method, Means's method, and maximum entropy method predictions are compared for 7 nearly successive 1 sec whistler mode pulses at 10.2 and 11.33 kHz observed onboard Geos 1. Signal to noise ratio, stationarity, degree of polarization, and polarization value are considered. For plane wave signals, signal to noise ratio is the key parameter for the crossproduct method. For highly polarized waves, polarization value deduced from a spectral matrix, is the key parameter for Means's method and the maximum entropy method. Wave type does not greatly influence results. Methods based on the spectral matrix are subject to estimation errors, but must be used if the electromagnetic field is of the plane wave type and the signal to noise ratio is high.