| 31. |
- Ferreol, A., et al.
(författare)
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On the resolution probability of MUSIC in presence of modelling errors
- 2008
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Ingår i: IEEE Transactions on Signal Processing. - 1941-0476 .- 1053-587X. ; 56:5, s. 1945-1953
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Tidskriftsartikel (refereegranskat)abstract
- The problem of resolving closely spaced signal sources using an antenna array remains a difficult one, although several estimation methods are available in the literature. When the array correlation matrix is known, the resolution capability of subspace algorithms is infinitely high. However, in the presence of modeling errors the resolution deteriorates, even for a known correlation matrix. In this paper, we analyze the MUSIC method, by way of three different definitions of the resolution. Assuming Gaussian circular random modeling errors, we determine the corresponding expressions of the probability of source resolution versus the model mismatch. A first series of simulations validates the mathematical expression of the three resolution probabilities. A second series of simulations is used to select among them the tightest one to the empirical one. The results are useful, e.g., for determining the necessary antenna calibration accuracy to achieve a target performance. © 2008 IEEE.
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| 32. |
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| 33. |
- Ferreol, A., et al.
(författare)
-
Statistical Analysis of the MUSIC Algorithm in the Presence of Modeling Errors, Taking Into Account the Resolution Probability
- 2010
-
Ingår i: IEEE Transactions on Signal Processing. - 1941-0476 .- 1053-587X. ; 58:8, s. 4156-4166
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Tidskriftsartikel (refereegranskat)abstract
- This paper considers the statistical performance of the MUSIC method under the condition that two closely spaced sources impinging on an array of sensors are effectively resolved, i.e., the spectrum exhibits two peaks in the neighborhood of the true directions-of-arrival (DOA). The MUSIC algorithm is known to have an infinite resolution power in theory. However, in the presence of modeling errors, sources can not be resolved with certainty, even if the array correlation matrix is perfectly known. The focus of this paper is to predict the bias and variance of the DOA estimates taking into account the possible resolution failure of MUSIC. This performance prediction, based on our recent mathematical investigation, is new to the best of our knowledge. A general mathematical framework to derive closed form expressions of the bias and variance versus the model mismatch, conditioned on a general statistical resolution test is proposed. In order to illustrate our mathematical approach, statistical tests with one and two conditions, respectively, are investigated. The accuracy of the performance prediction is illustrated in a simulation study. It is found that the proposed approach outperforms the "classical" technique, which ignores the possible resolution failure of the MUSIC algorithm. Therefore, our results provide better tools for determining the necessary antenna calibration accuracy to achieve some targeted specifications on the estimator performance.
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| 34. |
- Ghaemi, Hirad, 1980, et al.
(författare)
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CLEAN technique in strip-map SAR for high-quality imaging
- 2009
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Ingår i: IEEE Aerospace Conference Proceedings. - 1095-323X. - 9781424426225 ; , s. Art. no. 4839474-
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Konferensbidrag (refereegranskat)abstract
- The maximum obtainable resolution of a strip-map synthetic aperture radar (SAR) system can be retained by simply avoiding weighting, or tapering, data samples in the along-track compression process. However, this will lead to hazardous artifacts caused by strong sidelobes of the corresponding adjacent scatterers whose interference might severely weaken the desired targets or even introduce false targets. On the other hand, some residual artifacts, even after tapering process, may still deteriorate the quality (contrast) of the SAR image. These issues can be remedied by applying the so-called CLEAN technique, which can mitigate these ill-effects in strip-map SAR imagery while maintaining the maximum resolution. This, indeed, is carried out as a post processing step, i.e., after the azimuth compression is accomplished, in the SAR system. The objective of this paper is to extend the CLEAN technique to strip-map SAR system to produce high-quality images with a very good along-track resolution. The algorithm is then applied to data from a ground-based circular SAR (CSAR) system to verify its implementation as well as this new application of the CLEAN technique.
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| 35. |
- Ghaemi, Hirad, 1980, et al.
(författare)
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RELAX-based autofocus algorithm for high-resolution strip-map SAR
- 2009
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Ingår i: IEEE National Radar Conference - Proceedings. - 1097-5659. - 9781424428717 ; , s. 1 - 6
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Konferensbidrag (refereegranskat)abstract
- This paper addresses the non-iterative quality phase gradient autofocus (QPGA) technique which was originally proposed to remove one-dimensional phase errors in spotlight-mode synthetic aperture radar (SAR) imagery. By enriching the source pool, the method is modified in a way suitable for autofocus in stripmap-mode SAR system with the advantage of being independent of any priori assumptions. Unlike the QPGA the potential candidates, i.e., dominant scatterers located along azimuth in each specific range bin, are automatically selected by exploiting the one-dimensional RELAX algorithm. Furthermore, RELAX is capable of estimating the size of blur window which is, in fact, associated with the Doppler spread of signal spectrum. The corresponding model includes four parameters i.e., complex amplitude, delay, Doppler center and spectral width. The proposed method has been applied to data extracted by a ground-based rotating coherent Doppler radar operating in strip-mapping mode SAR, with the aim of high-resolution clutter detection.
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| 36. |
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| 37. |
- Hashemzadeh, Parham, 1976, et al.
(författare)
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Analysis of 3-D shape estimation using bistatic multi-channel radar systems
- 2008
-
Ingår i: SAM 2008 - 5th IEEE Sensor Array and Multichannel Signal Processing Workshop; Darmstadt; Germany; 21 July 2008 through 23 July 2008. - 9781424422418 ; , s. 463-467
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Konferensbidrag (refereegranskat)abstract
- We estimate the radius of a perfect electric conductor (PEC) half-sphere placed on a ground plane, given six bi-conical antennas that suffer from manufacturing errors. The results are complemented by an analytical model of the sensor system and the scatterer. The analytical model includes the front-end electronics in combination with the antenna radiation impedance and the radiation field function.
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| 38. |
- Holdfeldt, Peter, 1976, et al.
(författare)
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A Dynamic Programming Inspired Method for Boundary Detection in Ultrasound Image Sequences with Application to Brachial Artery Flow-Mediated Dilation (FMD) Studies
- 2009
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This paper describes a new method for boundary detection in ultrasound image sequences with specific application to brachial artery flow-mediated dilation (FMD) studies. The method represents an extension to conventional two-dimensional dynamic programming to be applied in a three-dimensional (spatio-temporal) context. A total of 42 digital image sequences, each of which contained 240 frames, were analyzed. The majority (34) of these sequences were analyzed successfully, and a few (8) partly successful. Following automated boundary detection, vessel diameter extrema (minima and maxima) could easily be computed and used for FMD calculations. It was concluded that the new method, although optimality when moving from two to three dimensions cannot be guaranteed, outperforms conventional dynamic programming.
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| 39. |
- Holdfeldt, Peter, 1976, et al.
(författare)
-
A New Method Based on Dynamic Programming for Boundary Detection in Ultrasound Image Sequences
- 2008
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Ingår i: Engineering in Medicine and Biology Society, 2008. EMBS 2008. 30th Annual International Conference of the IEEE. EMBC 2008, August 20-24, Vancouver, Canada. - 9781424418145 ; , s. 3072-3074
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Konferensbidrag (refereegranskat)abstract
- Dynamic programming has previously been used when measuring Lumen Diameter (LD) and Intima-Media Thickness (IMT) in single frame ultrasound carotid artery images [1]. An extension to multiframe detection of that procedure is proposed in this paper. Our new method transforms a three dimensional problem into multiple two dimensional problems that can again be solved by dynamic programming. First, several “candidate boundaries” are detected in each image. Then, one boundary from each image in the sequence is selected in such a way that the sequence of boundaries is optimal among the considered possibilities. A model of the movements of the boundaries is used in the second step. Our proposed method shows promising performance on both synthetic and real ultrasound data.
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| 40. |
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