CLEAN Based on Spatial Source Coherence
01 Dec 2007-Vol. 6, Iss: 4, pp 357-374
TL;DR: A new version of the classical deconvolution method CLEAN is proposed here: CLEAN-SC, which is based on spatial source coherence, and side lobes can be removed of actually measured beam patterns of measured noise sources.
Abstract: To obtain higher resolution acoustic source plots from microphone array measurements, deconvolution techniques are becoming increasingly popular. Deconvolution algorithms aim at identifying Point Spread Functions (PSF) in source plots, and may therefore fall short when actual beam patterns of measured noise sources are not similar to synthetically obtained PSF's. To overcome this, a new version of the classical deconvolution method CLEAN is proposed here: CLEAN-SC. By this new method, which is based on spatial source coherence, side lobes can be removed of actually measured beam patterns. Essentially, CLEAN-SC iteratively removes the part of the source plot which is spatially coherent with the peak source. A feature of CLEAN-SC is its ability to extract absolute sound power levels from the source plots. The merits of CLEAN-SC were demonstrated using array measurements of airframe noise on a scale model of the Airbus A340 in the 8×6 m2 closed test section of DNW-LLF.
Citations
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TL;DR: In this paper, an experimental survey on a set of airfoils made of different porous materials was carried out to gain a better understanding of the aeroacoustic effects of the third property that is equivalent to an increased permeability of the plumage to air.
Abstract: Owls are commonly known for their quiet flight, enabled by three adaptions of their wings and plumage: leading edge serrations, trailing edge fringes and a soft and elastic downy upper surface of the feathers. In order to gain a better understanding of the aeroacoustic effects of the third property that is equivalent to an increased permeability of the plumage to air, an experimental survey on a set of airfoils made of different porous materials was carried out. Several airfoils with the same shape and size but made of different porous materials characterized by their flow resistivities and one non-porous reference airfoil were subject to the flow in an aeroacoustic open jet wind tunnel. The flow speed has been varied between approximately 25 and 50 m/s. The geometric angle of attack ranged from −16° to 20° in 4°-steps. The results of the aeroacoustic measurements, made with a 56-microphone array positioned out of flow, and of the measurements of lift and drag are given and discussed.
242 citations
Delft University of Technology1, German Aerospace Center2, Institut national des sciences Appliquées de Lyon3, Langley Research Center4, Rolls-Royce Deutschland5, Brandenburg University of Technology6, Technical University of Berlin7, Peking University8, École de technologie supérieure9, École centrale de Lyon10
TL;DR: This paper provides a review of the most well-known and state-of-the-art acoustic imaging methods and recommendations on when to use them, as well as a broad overview for general aeroacoustic experts.
Abstract: Phased microphone arrays have become a well-established tool for performing aeroacoustic measurements in wind tunnels (both open-jet and closed-section), flying aircraft, and engine test beds. This paper provides a review of the most well-known and state-of-the-art acoustic imaging methods and recommendations on when to use them. Several exemplary results showing the performance of most methods in aeroacoustic applications are included. This manuscript provides a general introduction to aeroacoustic measurements for non-experienced microphone-array users as well as a broad overview for general aeroacoustic experts.
199 citations
TL;DR: The main concepts of beamforming, starting from the very basics and progressing on to more advanced concepts and techniques are presented, in order to give the reader the possibility to identify concepts and references which might be useful for her/his work.
191 citations
TL;DR: In this paper, four different steering vector formulations from the literature are examined, and their theoretical background is discussed, and it is shown that none of the formulations provide both the correct location and source strength.
Abstract: Acoustic source mapping techniques using acoustic sensor arrays and delay-and-sum beamforming techniques suffer from bad spatial resolution at low-aperture-based Helmholtz numbers. This is especially a problem for three-dimensional map grids, when the sensor array is not arranged around the region spanned by the grid but on only one side of it. Then, the spatial resolution of the result map in the direction pointing away from the array is much worse than in the other lateral directions. Consequently, deconvolution techniques need to be applied. Some of the most efficient deconvolution techniques rely on the properties of the spatial beamformer filters used. As these properties
are governed by the steering vectors, four different steering vector formulations from the literature are examined, and their theoretical background is discussed. It is found that none of the formulations provide both the correct location and source strength. As a practical example the CLEAN-SC deconvolution methodology is applied to simulated data for a three-source scenario. It is shown that the different steering vector formulations are not equally well suited for three-dimensional application. The two preferred formulations enable the correct estimation of the source location at the cost of a negligible error in the estimated source strength.
147 citations
TL;DR: In this article, a fast beamforming method is proposed that can be used in conjunction with a phased microphone array in applications with focus on the correct quantitative estimation of acoustic source spectra.
141 citations
References
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Journal Article•
TL;DR: In this article, the authors present CLEAN, a method for high-resolution radio interferometry that avoids the effects of the prominent and extended sidelobe patterns of the corresponding synthesized beam.
Abstract: In high-resolution radio interferometry it is often impossible for practical reasons to arrange for the measured baselines to be regularly distributed. The standard Fourier inversion methods may then produce maps which are seriously confused by the effects of the prominent and extended sidelobe patterns of the corresponding synthesized beam. Some methods which have been proposed for avoiding these difficulties are discussed. In particular, the procedure CLEAN is described in some detail. This has been successfully applied to measurements taken with several different radio telescopes and appears to be the best method available at the time of writing.
960 citations
"CLEAN Based on Spatial Source Coher..." refers background or methods in this paper
...so that we have, analogously to Eqn (9),...
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...Using CB, source powers Pj (0) are calculated for points ξ → j on the scan grid: (9)...
[...]
...Only for iteration i = 0, which is equivalent to CB, a double summation, Eqn (9), is required....
[...]
Journal Article•
921 citations
TL;DR: DecDeconvolution Approach for the Mapping of Acoustic Sources (DAMAS) as mentioned in this paper removes beamforming characteristics from output presentations, and a unique linear system of equations accounts for reciprocal influence at different locations over the array survey region.
594 citations
04 May 2004
TL;DR: The Deconvolution Approach for the Mapping of Acoustic Sources (DAMAS) method removes beamforming characteristics from output presentations and appears to dramatically increase the value of arrays to the field of experimental acoustics.
Abstract: Current processing of acoustic array data is burdened with considerable uncertainty. This study reports an original methodology that serves to demystify array results, reduce misinterpretation, and accurately quantify position and strength of acoustic sources. Traditional array results represent noise sources that are convolved with array beamform response functions, which depend on array geometry, size (with respect to source position and distributions), and frequency. The Deconvolution Approach for the Mapping of Acoustic Sources (DAMAS) method removes beamforming characteristics from output presentations. A unique linear system of equations accounts for reciprocal influence at different locations over the array survey region. It makes no assumption beyond the traditional processing assumption of statistically independent noise sources. The full rank equations are solved with a new robust iterative method. DAMAS is quantitatively validated using archival data from a variety of prior high-lift airframe component noise studies, including flap edge/cove, trailing edge, leading edge, slat, and calibration sources. Presentations are explicit and straightforward, as the noise radiated from a region of interest is determined by simply summing the mean-squared values over that region. DAMAS can fully replace existing array processing and presentations methodology in most applications. It appears to dramatically increase the value of arrays to the field of experimental acoustics.
349 citations
23 May 2005
TL;DR: The DAMAS deconvolution algorithm represents a breakthrough in phased array imaging for aeroacoustics, potentially eliminating sidelobles and array resolution effects from beamform maps and two extensions are proposed.
Abstract: The DAMAS deconvolution algorithm represents a breakthrough in phased array imaging for aeroacoustics, potentially eliminating sidelobles and array resolution effects from beamform maps . DAMAS is an iterative non-negative least squares solver. The original algorithm is too slow and lacks an explicit regularization method to prevent noise amplification. Two extensions are proposed, DAMAS2 and DAMAS3. DAMAS2 provides a dramatic speedup of each iteration and adds regularization by a low pass filter. DAMAS3 also provides fast iterations, and additionally, reduces the required number of iterations. It uses a different regularization technique from DAMAS2, and is partially based on the Wiener filter. Both DAMAS2 and DAMAS3 restrict the point spread function to a translationally-invariant, convolutional, form. This is a common assumption in optics and radio astronomy, but may be a serious limitation in aeroacoustic beamforming. This limitation is addressed with a change of variables from (x,y,z) to a new set, (u,v,w). The concepts taken together, along with appropriate array design, may permit practical 3D beamforming in aeroacoustics.
306 citations