scholarly journals A Through-the-Wall Imaging Approach Based on a TSVD/Variable-Exponent Lebesgue-Space Method

2021 ◽  
Vol 13 (11) ◽  
pp. 2028
Author(s):  
Andrea Randazzo ◽  
Cristina Ponti ◽  
Alessandro Fedeli ◽  
Claudio Estatico ◽  
Paolo D’Atanasio ◽  
...  
Keyword(s):  
Variable Exponent ◽  
Scattering Problem ◽  
Inverse Scattering Problem ◽  
Source Spectrum ◽  
Computationally Efficient ◽  
Geometrical Properties ◽  
Singular Value Decomposition Method ◽  
The Time Domain ◽  
Value Decomposition ◽  
Wall Imaging

A hybrid inversion scheme for through-the-wall imaging is proposed in this paper. The approach is based on a linearized model of the inverse-scattering problem, employing the Green’s function developed for a layered background. The reconstruction is obtained by means of a Landweber-like iterative method performing a regularization in the framework of variable-exponent Lebesgue spaces. Thanks to the non-conventional geometrical properties of such spaces, it is possible to enhance the reconstruction capabilities, e.g., by promoting sparseness and reducing over-smoothing. The exponent function defining the specific space adopted in the inversion procedure is adaptively obtained directly from the measured data, through a truncated-singular value decomposition method. In this way, it is possible to precompute and reuse in both steps, for a given scenario, all the matrices necessary in the inversion process, thus leading to a computationally efficient solving strategy. The effectiveness of the approach is evaluated by using experimental data obtained with a commercial GPR apparatus employing a pulsed source field. A fast Fourier transform is applied to the time-domain measurements to extract frequency-domain data at a set of frequencies in the source spectrum, which are fed in input to the imaging scheme. Very good reconstruction capabilities are obtained both with a single metallic target, as well as in a challenging two targets layout including both a metallic object and a low-permittivity target.

The Effect of Inlet Grooves and Swirl on the Dynamics of Long Annular Seals in Centrifugal Pumps

1993 ◽  
Author(s):  
Mohamed Ismail ◽  
R. David Brown ◽  
David France
Keyword(s):  
Rolling Element Bearings ◽  
Rigid Rotor ◽  
Centrifugal Pumps ◽  
Test Rig ◽  
Singular Value Decomposition Method ◽  
Forcing Function ◽  
Rolling Element ◽  
The Time Domain ◽  
Value Decomposition ◽  
Annular Seals

Abstract This paper describes additional results from a continuing research program which aims to identify the dynamics of long annular seals in centrifugal pumps. A seal test rig designed to experimentally identify dynamic coefficients using a least-squares technique based on the singular value decomposition method. The analysis is carried out in the time domain using a multifrequency forcing function. The experimental method relies on the forced excitation of a flexibly supported stator by two hydraulic shakers. A rigid rotor supported in rolling element bearings runs through the stator. The only physical connection between shaft and stator is a pair of annular gaps filled with pressurised water discharged axially. The experimental coefficients obtained from the tests are compared with theoretical values.

Identification of the Dynamic Characteristics of Long Annular Seals Using a Time Domain Technique

1998 ◽  
Vol 120 (3) ◽  
pp. 705-712 ◽  
Author(s):  
M. Ismail ◽  
R. D. Brown
Keyword(s):  
Dynamic Characteristics ◽  
Time Domain ◽  
Theoretical Models ◽  
Rotational Frequency ◽  
Singular Value Decomposition Method ◽  
Damping Coefficients ◽  
Theoretical Predictions ◽  
The Time Domain ◽  
Value Decomposition ◽  
Annular Seals

This paper describes experimental results from a research program aimed at a study of the static and dynamic characteristics of liquid long annular seals. A seal test rig permits the identification in the time domain of mass, stiffness, and damping coefficients using a least-squares technique based on the singular value decomposition method. The experimental method relies on the forced excitation of a flexibly supported stator by two hydraulic shakers. The forcing signal is composed from a small number of frequencies which are not related to the rotational frequency of the rigid shaft rotating inside the stator. The test data consisting of two inertia, four stiffness, and four damping coefficients is compared with theoretical predictions based on two theoretical models: (i) the model of Black et al. (1971 and 1981) and (ii) the model of Childs and Kim (1985).

scholarly journals Down-Looking Airborne Radar Imaging Performance: The Multi-Line and Multi-Frequency

2021 ◽  
Vol 13 (23) ◽  
pp. 4897
Author(s):  
Ilaria Catapano ◽  
Carlo Noviello ◽  
Francesco Soldovieri
Keyword(s):  
Analytical Study ◽  
Scattering Problem ◽  
Inverse Scattering Problem ◽  
Radar Imaging ◽  
Airborne Radar ◽  
Sampled Data ◽  
Constant Depth ◽  
Practical Usefulness ◽  
Value Decomposition ◽  
Imaging Performance

The paper proposes an analytical study regarding airborne radar imaging performances and accounts for a down-looking radar system moving along parallel lines far, in terms of probing wavelength, from the investigated domain and collecting multi-frequency and multi-monostatic data. The imaging problem is formulated in a constant depth plane by exploiting the Born approximation. Hence, a linear inverse scattering problem is faced by considering both the Adjoint and the Truncated Singular Value Decomposition reconstruction schemes. Analytical and simulated results are provided to state how the achievable performances depend on the measurement configuration. These results are of practical usefulness because, in operative conditions, it is unfeasible to plan a flight grid made up by a high number of closely (in terms of probing wavelength) spaced lines. Hence, the understanding of how the availability of under-sampled data affects the radar imaging allows for a trade-off between operative data collection constrains and reliable reconstructions of the scenario under test.

An Efficient Image Preprocessing Technique for Land Use Analysis by Using Remote Sensing Images

2021 ◽  
Vol 10 (1) ◽  
pp. 316-320
Keyword(s):  
Singular Values ◽  
Ease Of Use ◽  
Basic Knowledge ◽  
New Technique ◽  
Computationally Efficient ◽  
Singular Value Decomposition Method ◽  
Block Based ◽  
Use Of Social Media ◽  
Preprocessing Technique ◽  
Value Decomposition

With the widespread availability of image manipulating software and with ease of use, anyone with basic knowledge can modify the image without leaving any traces in the image. People believe in whatever they see in an image, but it is not necessary that the content has to be real. With the wide use of social media people with malicious intent share images that are modified and make you believe that they are real and by doing so they can influence people’s opinion which is a grave danger for society.In copy paste attack a part of the image is copied and pasted on to a different region of the same image, this pasted region can be detected by using the block-based method, but when the copied region is rotated orthogonally or if it is flipped before pasting on to the destination, such pasted regions are impossible to detect with the block-based approach.In this paper we are proposing a new technique to detect rotated or flipped pasted regions in an image and the performance of this new technique is compared with the SVD (Singular Value Decomposition) method used for the same purpose. The proposed new technique overcomes the rounding off errors in singular values of SVD method and computationally efficient than SVD and also computes the angle of rotation

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