256 research outputs found
Multi-frequency based location search algorithm of small electromagnetic inhomogeneities embedded in two-layered medium
In this paper, we consider a problem for finding the locations of
electromagnetic inhomogeneities completely embedded in homogeneous two layered
medium. For this purpose, we present a filter function operated at several
frequencies and design an algorithm for finding the locations of such
inhomogeneities. It is based on the fact that the collected Multi-Static
Response (MSR) matrix can be modeled via a rigorous asymptotic expansion
formula of the scattering amplitude due to the presence of such
inhomogeneities. In order to show the effectiveness, we compare the proposed
algorithm with traditional MUltiple SIgnal Classification (MUSIC) algorithm and
Kirchhoff migration. Various numerical results demonstrate that the proposed
algorithm is robust with respect to random noise and yields more accurate
location than the MUSIC algorithm and Kirchhoff migration.Comment: 21 pages, 25 figure
Detection of Electromagnetic Inclusions using Topological Sensitivity
In this article a topological sensitivity framework for far field detection
of a diametrically small electromagnetic inclusion is established. The cases of
single and multiple measurements of the electric far field scattering amplitude
at a fixed frequency are taken into account. The performance of the algorithm
is analyzed theoretically in terms of its resolution and sensitivity for
locating an inclusion. The stability of the framework with respect to
measurement and medium noises is discussed. Moreover, the quantitative results
for signal-to-noise ratio are presented. A few numerical results are presented
to illustrate the detection capabilities of the proposed framework with single
and multiple measurements.Comment: 31 pages, 5 figure
Digital Image Processing
Newspapers and the popular scientific press today publish many examples of highly impressive images. These images range, for example, from those showing regions of star birth in the distant Universe to the extent of the stratospheric ozone depletion over Antarctica in springtime, and to those regions of the human brain affected by Alzheimerâs disease. Processed digitally to generate spectacular images, often in false colour, they all make an immediate and deep impact on the viewerâs imagination and understanding.
Professor Jonathan Blackledgeâs erudite but very useful new treatise Digital Image Processing: Mathematical and Computational Methods explains both the underlying theory and the techniques used to produce such images in considerable detail. It also provides many valuable example problems - and their solutions - so that the reader can test his/her grasp of the physical, mathematical and numerical aspects of the particular topics and methods discussed. As such, this magnum opus complements the authorâs earlier work Digital Signal Processing. Both books are a wonderful resource for students who wish to make their careers in this fascinating and rapidly developing field which has an ever increasing number of areas of application.
The strengths of this large book lie in: ⢠excellent explanatory introduction to the subject; ⢠thorough treatment of the theoretical foundations, dealing with both electromagnetic and acoustic wave scattering and allied techniques; ⢠comprehensive discussion of all the basic principles, the mathematical transforms (e.g. the Fourier and Radon transforms), their interrelationships and, in particular, Born scattering theory and its application to imaging systems modelling; discussion in detail - including the assumptions and limitations - of optical imaging, seismic imaging, medical imaging (using ultrasound), X-ray computer aided tomography, tomography when the wavelength of the probing radiation is of the same order as the dimensions of the scatterer, Synthetic Aperture Radar (airborne or spaceborne), digital watermarking and holography; detail devoted to the methods of implementation of the analytical schemes in various case studies and also as numerical packages (especially in C/C++); ⢠coverage of deconvolution, de-blurring (or sharpening) an image, maximum entropy techniques, Bayesian estimators, techniques for enhancing the dynamic range of an image, methods of filtering images and techniques for noise reduction; ⢠discussion of thresholding, techniques for detecting edges in an image and for contrast stretching, stochastic scattering (random walk models) and models for characterizing an image statistically; ⢠investigation of fractal images, fractal dimension segmentation, image texture, the coding and storing of large quantities of data, and image compression such as JPEG; ⢠valuable summary of the important results obtained in each Chapter given at its end; ⢠suggestions for further reading at the end of each Chapter. I warmly commend this text to all readers, and trust that they will find it to be invaluable.
Professor Michael J Rycroft Visiting Professor at the International Space University, Strasbourg, France, and at Cranfield University, England
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