TITLE

Improved time-frequency analysis of ASDEX Upgrade reflectometry data using the reassigned spectrogram technique

AUTHOR(S)
Varela, P.; Silva, A.; da Silva, F.; da Graça, S.; Manso, M. E.; Conway, G. D.; the ASDEX Upgrade Team
PUB. DATE
October 2010
SOURCE
Review of Scientific Instruments;Oct2010, Vol. 81 Issue 10, p10D925
SOURCE TYPE
Academic Journal
DOC. TYPE
Article
ABSTRACT
The spectrogram is one of the best-known time-frequency distributions suitable to analyze signals whose energy varies both in time and frequency. In reflectometry, it has been used to obtain the frequency content of FM-CW signals for density profile inversion and also to study plasma density fluctuations from swept and fixed frequency data. Being implemented via the short-time Fourier transform, the spectrogram is limited in resolution, and for that reason several methods have been developed to overcome this problem. Among those, we focus on the reassigned spectrogram technique that is both easily automated and computationally efficient requiring only the calculation of two additional spectrograms. In each time-frequency window, the technique reallocates the spectrogram coordinates to the region that most contributes to the signal energy. The application to ASDEX Upgrade reflectometry data results in better energy concentration and improved localization of the spectral content of the reflected signals. When combined with the automatic (data driven) window length spectrogram, this technique provides improved profile accuracy, in particular, in regions where frequency content varies most rapidly such as the edge pedestal shoulder.
ACCESSION #
54857971

 

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