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Proceedings Paper

Demodulation schemes for vibrometers and associated effects on target classification
Author(s): Brendan Ruck; Harvey Lewis; Andrew M. Rogoyski; Mark Bernhardt; Maxwell Hadley; Meryl Welch; Andrew J. Seedhouse
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Paper Abstract

Non co-operative target identification using laser vibrometry is typically based upon characterization of the frequency spectra obtained after demodulating the vibrometer's output signal. The characterization uses information gleaned from certain identifiable features, such as tonals, which can be extracted from the vibration spectra. The success of this classification is dependent upon the performance of the demodulation scheme adopted. This paper investigates a number of different digital demodulation strategies that can be used on down-shifted and digitized vibrometer output in which the gross Doppler term has been removed. This paper presents an assessment of the likely impact of demodulation schemes upon several critical classification cues, for example signal-to-noise ratio, frequency and bandwidth. These cues help to parameterize the vibration spectrum and may in themselves be used to classify targets. Only digital schemes are considered here, in contrast to conventional vibrometer technology which uses analogue demodulation schemes. The investigations take the form of a general review, followed by a detailed description of each demodulation method. Each method is applied to a representative modulated signal, and its performance assessed qualitatively. Of key importance in this analysis are the different time-frequency representations (TFRs) of the digitized vibrometer signal, in addition to phase- differencing methods, which are used to derive the instantaneous frequency. TFRs which have been examined are the short-time Fourier Transform, Wigner and Choi-Williams distributions.

Paper Details

Date Published: 8 September 1998
PDF: 12 pages
Proc. SPIE 3380, Laser Radar Technology and Applications III, (8 September 1998); doi: 10.1117/12.327190
Show Author Affiliations
Brendan Ruck, Logica UK Ltd. (United Kingdom)
Harvey Lewis, Logica UK Ltd. (United Kingdom)
Andrew M. Rogoyski, Logica UK Ltd. (United Kingdom)
Mark Bernhardt, Defence Evaluation and Research Agency Farnborough (United Kingdom)
Maxwell Hadley, Defence Evaluation and Research Agency Farnborough (United Kingdom)
Meryl Welch, Defence Evaluation and Research Agency Farnborough (United Kingdom)
Andrew J. Seedhouse, Defence Evaluation and Research Agency Farnborough (United Kingdom)

Published in SPIE Proceedings Vol. 3380:
Laser Radar Technology and Applications III
Gary W. Kamerman, Editor(s)

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