Direct Deconvolution Method Research Articles

Maximum Likelihood Deconvolution of Beamforming Images with Signal-Dependent Speckle Fluctuations

Ocean Acoustic Waveguide Remote Sensing (OAWRS) typically utilizes large-aperture linear arrays combined with coherent beamforming to estimate the spatial distribution of acoustic scattering echoes. The conventional maximum likelihood deconvolution (DCV) method uses a likelihood model that is inaccurate in the presence of multiple adjacent targets with significant intensity differences. In this study, we propose a deconvolution algorithm based on a modified likelihood model of beamformed intensities (M-DCV) for estimation of the spatial intensity distribution. The simulated annealing iterative scheme is used to obtain the maximum likelihood estimation. An approximate expression based on the generalized negative binomial (GNB) distribution is introduced to calculate the conditional probability distribution of the beamformed intensity. The deconvolution algorithm is further simplified with an approximate likelihood model (AM-DCV) that can reduce the computational complexity for each iteration. We employ a direct deconvolution method based on the Fourier transform to enhance the initial solution, thereby reducing the number of iterations required for convergence. The M-DCV and AM-DCV algorithms are validated using synthetic and experimental data, demonstrating a maximum improvement of 73% in angular resolution and a sidelobe suppression of 15 dB. Experimental examples demonstrate that the imaging performance of the deconvolution algorithm based on a linear small-aperture array consisting of 16 array elements is comparable to that obtained through conventional beamforming using a linear large-aperture array consisting of 96 array elements. The proposed algorithm is applicable for Ocean Acoustic Waveguide Remote Sensing (OAWRS) and other sensing applications using linear arrays.

Advancing the temporal direct deconvolution method with spatial regularization

This study continues the exploration of temporal large-eddy simulation, particularly the extension of the temporal direct deconvolution method (TDDM) with a regularization term based on spatial dissipation. Furthermore, we aim to put insight stemming from previous work to test. Specifically, the hypothesis is that the temporal residual-stress leads to a reduction of the required artificial dissipation in under-resolved simulations. Moreover, this work seeks corroborate earlier discoveries with a posteriori results. We perform a numerical examination of two different spatial regularization terms in conjunction with TDDM: a spatial variant of selective frequency damping, functioning as a relaxation term that gradually drifts the velocity toward the filtered velocity, and the dynamic Smagorinsky model incorporating a prefactor. We test various cases, including the Taylor–Green vortex flow with a Reynolds number of Re = 3000, forced homogeneous isotropic turbulence with Reλ=200, turbulent channel flow at Reτ=590, and the flow over a periodic hill with Re = 10 935. Additionally, we also analyze the various dissipation contributions in TDDM as well as their interrelations. We also discuss grid artifacts and energy budget errors using these to compare the different models. Our results confirm the hypothesis that residual-stress dissipation reduces the necessary artificial dissipation. Because of the numerical ill-conditioning of deconvolution, whether temporal or spatial, there are practical limitations in the size of the filter width. Due to these limitations, the impact remains relatively minor. The a posteriori results of the new spatial regularization term show it to be effective in eliminating energy from the high wavenumber range.

Wellbore storage removal in pressure transient analysis for gas wells

Wellbore storage (WBS) occurs due to fluid loading/unloading in the wellbore, when a well starts production or is shut-in. This phenomenon creates variable sandface rate and time lag between the surface production rate and the stable sandface rate. Wellbore storage effects can sometimes conceal important information and complicate well test analysis and interpretation. In well tests that suffer from long WBS, removal of WBS effects can usually recover important features in the reservoir signal and lead to significant improvement in identifying the reservoir model and calculating reservoir parameters. Until recently, WBS removal relied on direct deconvolution techniques that require accurate well test data. Presence of noise in the pressure and rate data usually makes direct deconvolution methods unstable. Well test pressure and rate data usually suffer from some noise, and therefore, application of direct deconvolution methods may not work.

New technique revives direct deconvolution methods for Wellbore storage removal in pressure transient analysis

Eliminating wellbore storage (WBS) effects inherent in pressure transient data is one of the challenges in well test analysis. The available WBS-removal techniques are either direct or time-consuming approaches. The direct methods are mostly unstable and require accurate data with almost no noise. However, well test data often have noise in both rate and pressure measurements.This work discusses the development of a stable technique to overcome the shortcomings in the available WBS-removal methods. The technique presented here takes advantage of the recently developed stable deconvolution algorithms (e.g. von Schroeter algorithm) to achieve a stable WBS-removal process. The developed approach provides longer WBS-free reservoir response signal (extended over the entire test duration) than the previous methods. In addition, the approach introduced here can remove WBS-effects in noisy data and does not require sandface rate measurements.Different simulated and field examples were used to validate the proposed approach. The examples included data with different levels of rate and pressure measurement errors and covered wide variety of well/reservoir models. The available approaches were implemented to the same examples. A comparison of the results shows the superiority of the approach presented in this paper.

Robust defocus blur identification in the context of blind image quality assessment

A defocus blur metric for use in blind image quality assessment is proposed. Blind image deconvolution methods are used to determine the metric. Existing direct deconvolution methods based on the cepstrum, bicepstrum and on a spectral subtraction technique are compared across 210 images. A variation of the spectral subtraction method, based on a power spectrum surface of revolution, is proposed and is found to compare favourably with existing direct deconvolution methods for defocus blur identification. The method is found to be especially useful when distinguishing between in-focus and out-of-focus images.

Lifetime extraction from delayed-coincidence experiments by a direct deconvolution method

A direct deconvolution method has been developed to extract lifetimes from delayed-coincidence curves. After it has been checked on a Monte-Carlo simulation, it has been applied to the lifetime of the 260.5 keV level in 187 Pt . In combination with the standard re-convolution method it gives an estimate of the systematic error, and could be helpful when only approximately matched prompt curves are available.

Removal of Tracking Error with Image Restoration

In this paper, image restoration is presented as a way to remove the influence of tracking error in astrometric CCD images, based on the characteristics of spatially invariant tracking error within a CCD frame. The direct deconvolution method was used in the process of image restoration. The results of reduction using practical data show improved precision in the images of star centers, including those of closely spaced stars. In particular, close binaries can be separated easily after image restoration.

Spectral restoration in HREELS

The spectral resolution of HREELS is determined by both instrumental and sample-related factors. Despite substantial progress in electron optic design, these factors are still a limitation in assigning the vibrational modes of complex molecules and in determining linewidths. To the extent that all spectral features are broadened in the same way and within signal to noise limitations, currently available spectral restoration methods may provide a reliable solution. In principle, the measured elastic peak provides a template for deconvolution of these factors from the observed lineshapes. We compare results of a direct deconvolution method, in which division in the Fourier domain is followed by a linearised maximum entropy filter, with iterative methods based on maximum likelihood, maximum entropy and Bayesian principles involving only multiplication (i.e. convolution) in the Fourier domain. These methods are applicable both to spectra of modest resolution (intrinsic linewidths > > instrumental linewidth) and to high resolution spectra (linewidths ≈ instrumental resolution) in which spectral lineshapes are measurably different. The asymmetry and tailing of the elastic peak, which are critical to restoration of low frequency features, are determined by a number of processes such as multiple scattering, the thermal population of vibrational states, and low energy continuum excitations (e–h pairs, phonons) of the substrate. These factors, as well as practical considerations, are discussed in relation to measuring data for optimal spectral restoration.

Discussion of the Paper by Vardi and Lee

Discussion of the Paper by Vardi and Lee

地震観測に基づく観測点特性と径路減衰特性の評価

Estimation of site factor and propagation characteristics is an important work in order to evaluate strong-motion characteristics. This paper gives a review of methods used for the estimation of these two factors. The usual evaluation of site factor is based on the records obtained by means of downhloe array observation. Several methods which are independent of downhole array recordings have appeared in the last decade in order to evaluate the site factor. Most methods have essentially an inversion scheme, and are applicable to the separation of site factor, propagation characteristics and source factor, simultaneously. In this review, coda normalization method, method by using a spectral decay parameter and direct deconvolution method are given as such methods.

Oxide formation on Fe and Ti thin films and on Fe thin films modified with ultrathin layers of Ti

AbstractReactions of O2 and H2O to from thin oxides on Fe, Ti and Ti‐modified Fe thin films have been studied by XPS, following O2 and H2O exposure in the range 0‐600 L, to form oxides with thicknesses of < 40 Å. XPS Iineshape analysis is used, utilizing a special combination of reflection electron energy‐loss spectroscopy (REELS) and nonlinear least‐squares fitting routines to model the intrinsic and extrinsic energy losses that accompany potoemission for the Ti and Fe 2p lines. During the formation of the thinnest oxides, this approach yields a unique picture of the composition of the oxide, while for the thicker layers, there is little significant difference between this fitting approach and (1) fitting approaches using an integral background approach or (2) direct deconvolution methods using the REELS data. Both Fe and Ti are quite reactive to O2, yielding a surface oxide that is apparently an FeO‐dominated FeO/Fe3O4 bilayer on Fe surface oxide that is predominantly TiO2 on the Ti surface. Pure Fe and Ti surfaces are unreactive to H2O. Predosing of thewse surfaces with low levels of O2 (5 L) does not increase the reactivity appreciably toward H2O. Ti dispersed on the Fe surface as an adatom layer, with an equivalent thickness of 3 Å, greatly suppresses the reactivity of Fe toward O2, while the Ti is oxidized primarily to TiO2, In contrast to the pure Ti layers, these Ti adatom layers are quite reactive toward H2O, yielding oxides (no evidence for hydroxide) in a uniform distribution of oxidation states (Ti+2, Ti+3 and Ti+4).

Deconvolution with partially known kernel of nonnegative signals

This paper extends the Bayesian direct deconvolution method to the case in which the convolution kernel depends on few unknown nuisance parameters. Moreover, an acceleration procedure is proposed that drastically reduces the computational burden. Finally, the implementation of the method by means of the fast Fourier transform is fully discussed in the multidimensional case.

Another look at a Bayesian direct deconvolution method

The paper points out that a certain iterative method of direct deconvolution is a particular manifestation of the so-called Expectation-Maximisation (EM) algorithm. Recognition of this leads to the establishment of general convergence results by reference to existing work.

Comparaison de precédures d'evaluation des distortions et de la taille des cristallites par analyse des raies de diffraction des rayons X

A procedure based on successive convolution operations is developed and associated with the Warren–Averbach method. Applications to cold-worked lithium fluoride samples are presented. The microstrain results are compared with those obtained in the classical way including the use of the direct deconvolution method. It is shown experimentally that the difficulties involved in the deconvolution operation have no significant effect on the evaluation of microstrains by the classical X-ray line-profile analysis.

X-Ray Small Angle Scattering: A New Deconvolution Method for Evaluating Electron Density Distributions from Small Angle Scattering Diagrams

The direct determination of the electron density distributions of multilayered specimens with a small number of unit cells from X-ray small angle scattering experiments via the Q-function method of Hosemann and Bagchi includes the deconvolution of the so-called Q(o)-function, the generalized Patterson function of one unit cell. In this paper a new and direct deconvolution method on the basis of Fourier series is presented which is suitable for one-dimensional centrosymmetrical (or antisymmetrical) density distributions. A FORTRAN-program has been written which has an execution time of ca. 20 s on an UNIVAC 1106-computer. The procedure has been successfully tested on some convolution functions generated by membrane-type electron density distributions.