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Pattern recognition for VLF studies
Author(s) -
Jones Dyfrig
Publication year - 1973
Publication title -
radio science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.371
H-Index - 84
eISSN - 1944-799X
pISSN - 0048-6604
DOI - 10.1029/rs008i005p00467
Subject(s) - whistler , spectrogram , noise (video) , acoustics , physics , signal (programming language) , polarization (electrochemistry) , very low frequency , noise floor , magnetosphere , fourier transform , computer science , noise measurement , noise reduction , telecommunications , magnetic field , speech recognition , artificial intelligence , chemistry , quantum mechanics , image (mathematics) , programming language
The pattern‐recognition technique to be described requires the simultaneous recording of a signal on two antennas, for example, orthogonal magnetic or electric sensors; after these signals are cross‐correlated, a fast Fourier transform yields the complex cross‐spectrogram. Provided that the polarization of the waves does not vary rapidly with time, it is possible to reject unwanted noise and to recognize the signal by utilizing the phase information in the cross‐spectrum. This technique has been tested using computer‐simulated signals, and it has been found that variable frequency signals, for example, whistlers, which are more than 12 db below an incoherent‐noise background and more than 18 db below a coherent‐noise background, are still recognized and are recorded to the exclusion of noise. The technique is applicable to plasma waves recorded on spacecraft as well as to electro‐magnetic waves. Although the polarizations of ground‐recorded VLF signals are usually more complicated than those in the magnetosphere, the method is still relevant.