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Wake acoustic analysis and image decomposition via beamforming of microphone signal projections on wavelet subspaces
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2006-05-08
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[PDF-403.64 KB]
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NTL Classification:NTL-AVIATION-AVIATION;NTL-AVIATION-Aviation Safety/Airworthiness;
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Abstract:This paper describes the integration of wavelet analysis and time-domain beamforming
of microphone array output signals for analyzing the acoustic emissions from airplane
generated wake vortices. This integrated process provides visual and quantitative
simultaneous information about the wake signal composition and array resolution for a
particular wavelet subspace during a time interval, T. In the results section, an example is
given on how image processing algorithms might be used to automate the extraction of this
information and select the wavelet subspaces from which to perform image reconstruction.
This process begins with the projection of all the microphone signals on wavelet multiresolution
subspaces. The projections of these signals on the same wavelet subspace or scale
are then beamformed to produce an image of the wake corresponding to that particular
scale. Therefore for each time interval T, the process produces a number of images equal to
that of the wavelet scales. This is equivalent to a more conventional Fourier-based idea of
filtering the microphone signals with band-pass filters having non-uniform bandwidths then
beamform in different sub-bands, but offers greater flexibility and enhanced computational
speed. Results from both approaches will be shown, which ultimately illustrate the
advantages of wavelet analysis over that of the Fourier-based analysis. Amongst the
advantages are the speed of the decomposition and ease of the image reconstruction from
selected subspaces aided by the perfect reconstruction and orthogonality properties of
wavelet analysis.
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