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Littérature scientifique sur le sujet « Coherence technique »

Auteur : Grafiati

Publié le 21 décembre 2024

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Articles de revues sur le sujet "Coherence technique"

Palato, Samuel, Hélène Seiler, Parmeet Nijjar, Oleg Prezhdo et Patanjali Kambhampati. « Atomic fluctuations in electronic materials revealed by dephasing ». Proceedings of the National Academy of Sciences 117, n^o 22 (14 mai 2020) : 11940–46. http://dx.doi.org/10.1073/pnas.1916792117.

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The microscopic origin and timescale of the fluctuations of the energies of electronic states has a significant impact on the properties of interest of electronic materials, with implication in fields ranging from photovoltaic devices to quantum information processing. Spectroscopic investigations of coherent dynamics provide a direct measurement of electronic fluctuations. Modern multidimensional spectroscopy techniques allow the mapping of coherent processes along multiple time or frequency axes and thus allow unprecedented discrimination between different sources of electronic dephasing. Exploiting modern abilities in coherence mapping in both amplitude and phase, we unravel dissipative processes of electronic coherences in the model system of CdSe quantum dots (QDs). The method allows the assignment of the nature of the observed coherence as vibrational or electronic. The expected coherence maps are obtained for the coherent longitudinal optical (LO) phonon, which serves as an internal standard and confirms the sensitivity of the technique. Fast dephasing is observed between the first two exciton states, despite their shared electron state and common environment. This result is contrary to predictions of the standard effective mass model for these materials, in which the exciton levels are strongly correlated through a common size dependence. In contrast, the experiment is in agreement with ab initio molecular dynamics of a single QD. Electronic dephasing in these materials is thus dominated by the realistic electronic structure arising from fluctuations at the atomic level rather than static size distribution. The analysis of electronic dephasing thereby uniquely enables the study of electronic fluctuations in complex materials.

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McNutt, Marcia. « Basis of the coherence technique ». Nature 343, n^o 6259 (février 1990) : 596. http://dx.doi.org/10.1038/343596b0.

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YAKOVLEV, D. R., A. GREILICH, M. BAYER et I. A. YUGOVA. « ELECTRON SPIN COHERENCE IN SINGLY CHARGED QUANTUM DOTS ». International Journal of Modern Physics B 23, n^o 12n13 (20 mai 2009) : 2813–25. http://dx.doi.org/10.1142/s0217979209062396.

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Electron spin coherence is examined experimentally and theoretically in singly charged ( In , Ga ) As / GaAs quantum dots. Time-resolved pump-probe Faraday rotation technique is used to examine fine structure and Zeeman splitting of excitons and resident electrons. Spin dephasing and spin coherence times of resident electrons have been measured in the regime of mode-locking of spin coherency.

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Qin, Lei, Frank L. Vernon, Christopher W. Johnson et Yehuda Ben‐Zion. « Spectral Characteristics of Daily to Seasonal Ground Motion at the Piñon Flats Observatory from Coherence of Seismic Data ». Bulletin of the Seismological Society of America 109, n^o 5 (27 août 2019) : 1948–67. http://dx.doi.org/10.1785/0120190070.

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Abstract We investigate coherences of seismic data recorded during three years (2015–2017) at the Piñon Flats Observatory (PY) array and a collocated 148 m deep borehole station B084, along with oceanic data from a buoy southwest of the PY array. Seismic and barometric recordings at PY stations are analyzed with a multitaper spectral technique. The coherence of signals from seismic sources is >0.6 at 0.05–8 Hz between closely spaced (<65 m) surface stations and decreases to ∼0.2 in frequency bands in which the wavelengths are smaller than interstation distances. There are several local coherence increases at 1–8 Hz between nearby (<65 m) surface stations, whereas large coherence values between a surface and 148 m deep borehole stations are only present at the secondary microseism (∼0.14 Hz). These points to significant modification of seismic recordings in the top crust, and those continual near‐surface failures might produce shallow rapidly attenuating signals at surface stations. Incoherent local atmospheric effects induce incoherent seismic signals in low‐ and high‐frequency ranges through different coupling mechanisms. Between 0.003 and 0.05 Hz, atmospheric loadings generate ground tilts that contaminate the two horizontal seismic recordings and decrease their coherence, whereas the vertical component is less affected. At 1–8 Hz, coupling of atmospheric pressure with surface structures transmits incoherent signals into the ground, degrading the seismic coherence in all three components. The two horizontal coherences show seasonal variations with extended coherent frequency bands in winter and spring, likely to be produced by seasonal variations in microseisms and local ground tilts. The coherences also contain high anomalies between 2 and 4 Hz resulting from anthropogenic activities. The results provide useful information on instrument characteristics and variations in the shallow crustal response to earthquakes, seasonal and ambient sources of seismic energy, along with atmospheric pressure–temperature changes and anthropogenic activities.

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DOLAN, KEVIN T. « SURROGATE ANALYSIS OF MULTICHANNEL DATA WITH FREQUENCY DEPENDANT TIME LAG ». Fluctuation and Noise Letters 04, n^o 01 (mars 2004) : L75—L81. http://dx.doi.org/10.1142/s0219477504001677.

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Recently a new technique for generating linear surrogates of multichannel data was introduced. This technique, referred to as the coherent digitally filtered surrogate method, preserves both the individual power spectra, and the coherence function, of the original data. This method is somewhat limited in that it can only be applied to multichannel data in which the cross-spectrum is real. We present here an alteration to this algorithm that can be used to test any linear-correlation model, with arbitrary complex cross-spectra. This is of particular interest for experiments in which two channels are coupled with some time lag, and it is necessary to determine if the coupling is linear. We also demonstrate that this algorithm can be used along with the synchronization to provide a much better estimate for the degree of phase-locking between two signals than the coherence analysis techniques traditionally used in neuroscience.

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Lokhande, Prakash. « A NEW AND MODERN DIGNOSTIC TECHNIQUE : SWEPT-SOURCE OPTICAL COHERENCE TOMOGRAPHY (SS-OCT) ». CODS Journal of Dentistry 5, n^o 2 (2013) : 31–33. http://dx.doi.org/10.5005/cods-5-2-31.

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ABSTRACT Innovative technique has been introduced in the field of dentistry for the purpose of diagnosis and treatment. Technologies like laser, composite curing techniques, optical imaging have been utilized in the field of dentistry. OCT(optical coherence tomography) is a recent. technique which creates cross-sectional high resolution images. SS-OCT(Swept -Source optical coherence tomography) is a variant of optical coherence tomography, which provides instant imaging with high resolution, non-invasive and ease of handling. This article provides a overview of Swept -Source OCT and its application in the field of dentistry.

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Abdushkour, Hesham, Toufique A. Soomro, Ahmed Ali, Fayyaz Ali Jandan, Herbert Jelinek, Farida Memon, Faisal Althobiani, Saleh Mohammed Ghonaim et Muhammad Irfan. « Enhancing fine retinal vessel segmentation : Morphological reconstruction and double thresholds filtering strategy ». PLOS ONE 18, n^o 7 (19 juillet 2023) : e0288792. http://dx.doi.org/10.1371/journal.pone.0288792.

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Eye diseases such as diabetic retinopathy are progressive with various changes in the retinal vessels, and it is difficult to analyze the disease for future treatment. There are many computerized algorithms implemented for retinal vessel segmentation, but the tiny vessels drop off, impacting the performance of the overall algorithms. This research work contains the new image processing techniques such as enhancement filters, coherence filters and binary thresholding techniques to handle the different color retinal fundus image problems to achieve a vessel image that is well-segmented, and the proposed algorithm has improved performance over existing work. Our developed technique incorporates morphological techniques to address the center light reflex issue. Additionally, to effectively resolve the problem of insufficient and varying contrast, our developed technique employs homomorphic methods and Wiener filtering. Coherent filters are used to address the coherence issue of the retina vessels, and then a double thresholding technique is applied with image reconstruction to achieve a correctly segmented vessel image. The results of our developed technique were evaluated using the STARE and DRIVE datasets and it achieves an accuracy of about 0.96 and a sensitivity of 0.81. The performance obtained from our proposed method proved the capability of the method which can be used by ophthalmology experts to diagnose ocular abnormalities and recommended for further treatment.

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Bennett, Michael, et Simon Christie. « Application of a Doppler optical coherence technique to boundary layer sounding ». Meteorologische Zeitschrift 16, n^o 5 (26 octobre 2007) : 469–77. http://dx.doi.org/10.1127/0941-2948/2007/0219.

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Li, Yandong, Wenkai Lu, Huanqin Xiao, Shanwen Zhang et Yanda Li. « Dip-scanning coherence algorithm using eigenstructure analysis and supertrace technique ». GEOPHYSICS 71, n^o 3 (mai 2006) : V61—V66. http://dx.doi.org/10.1190/1.2194899.

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The eigenstructure-based coherence algorithms are robust to noise and able to produce enhanced coherence images. However, the original eigenstructure coherence algorithm does not implement dip scanning; therefore, it produces less satisfactory results in areas with strong structural dips. The supertrace technique also improves the coherence algorithms’ robustness by concatenating multiple seismic traces to form a supertrace. In addition, the supertrace data cube preserves the structural-dip information that is contained in the original seismic data cube; thus, dip scanning can be performed effectively using a number of adjacent supertraces. We combine the eigenstructure analysis and the dip-scanning supertrace technique to obtain a new coherence-estimation algorithm. Application to the real data set shows that the new algorithm provides good coherence estimates in areas with strong structural dips. Furthermore, the algorithm is computationally efficient because of the small covariance matrix [Formula: see text] used for the eigenstructure analysis.

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Nagpal, Manish, et Gujarat India. « Optical Coherence Tomography Angiography ». US Ophthalmic Review 11, n^o 2 (2018) : 91. http://dx.doi.org/10.17925/usor.2018.11.2.91.

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Optical coherence tomography angiography (OCTA) is a new revolutionary non-invasive imaging modality, built on the platform of optical coherence tomography (OCT). This technique works on the principle of ‘decorrelation’ and is still a nascent technology in its infancy with tremendous potential applicability for diagnosing retinal and choroidal vascular diseases. Its non-invasive nature, and the ability to generate images of retinal and choroidal vasculature, allows it to replace and/or supplement the current angiographic gold standards, fluorescein angiography (FA) and indocyanine green angiography (ICGA), if not in all but certainly in most retinal and choroidal pathologies. Still, there exists a major challenge in terms of its wide-scale availability, equipment and processing techniques, presence of artifacts, limitations of imaging capability, and lack of common vocabulary among retinal specialists for interpretation. In this review we intend to describe this novel technique by highlighting its key features, and comparing it with FA and ICGA. We will also discuss its applicability in various clinical scenarios such as diabetic retinopathy, age-related macular degeneration, retinal venous occlusion, choroiditis, and in routine practice. Further studies are needed to more definitively determine OCTA’s utility in the clinical setting and to establish if this technology may offer a non-invasive option of visualizing the retinal vasculature in detail.

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Thèses sur le sujet "Coherence technique"

Chau, Alexandra H. (Alexandra Hung) 1980. « Elastography using optical coherence tomography : development and validation of a novel technique ». Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/91380.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2004.
Includes bibliographical references (p. 161-167).
Atherosclerosis is an inflammatory disease characterized by an accumulation of lipid and fibrous tissue in the arterial wall. Postmortem studies have characterized rupture-prone atherosclerotic plaques by the presence of a large lipid-rich core covered by a thin fibrous cap. Studies employing finite element analysis (FEA) based on ex vivo plaque geometry have found that most plaques rupture at sites of high circumferential stress, thus diagnosis of plaque vulnerability may be enhanced by probing the mechanical behavior of individual plaques. Elastography is a method of strain imaging in which an image sequence of the artery undergoing deformation is acquired, pixel motion is estimated between each frame, and the resulting velocity field is used to calculate strain. In this thesis, optical coherence tomography (OCT), a high-resolution optical imaging modality, is investigated as a basis for FEA and elastography of atherosclerotic plaques. FEA was performed using plaque geometries derived from both histology and OCT images of the same plaque. Patterns of mechanical stress and strain distributions computed from OCT-based models were compared with those from histology-based models, the current gold standard for FEA. The results indicate that the vascular structure and composition determined by OCT provides an adequate basis for investigating the biomechanical factors relevant to atherosclerosis. A new variational algorithm was developed for OCT elastography that improves upon the conventional algorithm by incorporating strain smoothness and incompressibility constraints into the estimation algorithm.
(cont.) In simulated OCT images, the variational algorithm offers significant improvement in velocity and strain accuracy over the conventional algorithm, particularly in the presence of image noise. Polyvinyl alcohol (PVA) phantoms of homogeneous and heterogeneous elastic modulus distribution were developed for further testing of the variational algorithm. Testing with the phantoms indicated that motion- and strain-induced decorrelation between images presents a practical challenge to the implementation of OCT elastography. Analysis of the experimental results led to the identification of potential improvements to the elastography algorithm that may increase accuracy. These improvements may include relaxation of the strain smoothness constraint to incorporate strain discontinuities at boundaries of elastic modulus in heterogeneous regions, and enforcement of geometry compatibility to prevent the estimation of non-physical velocity fields.
by Alexandra H. Chau.
S.M.

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Kinnunen, M. (Matti). « Comparison of optical coherence tomography, the pulsed photoacoustic technique, and the time-of-flight technique in glucose measurements in vitro ». Doctoral thesis, University of Oulu, 2006. http://urn.fi/urn:isbn:9514281462.

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Abstract The development of a non-invasive glucose monitoring technique is very important because it would tremendously diminish the need to puncture the skin when taking blood samples and help diabetic patients in controlling their blood glucose levels and in treating Diabetes Mellitus. The focus of this thesis is on measuring the effect of glucose on the light scattering properties of a tissue-simulating phantom and biological tissues in vitro. Optical coherence tomography (OCT), the pulsed photoacoustic (PA) technique, and the time-of-flight (TOF) technique are used in the measurements and their capabilities for detecting changes in the scattering properties are evaluated and compared with each other. The theoretical background of the techniques, light propagation and PA wave generation are briefly explained. The glucose-induced changes in light scattering are also reviewed. The measurement results with the OCT and the PA technique from Intralipid, pig whole blood, and mouse skin tissue samples show that the glucose-induced changes are larger in the biological tissues than in the Intralipid phantom. The PA measurements show that although the PA signals are stronger at a wavelength of 532 nm than at 1064 nm, the glucose-induced change in the peak-to-peak value of the PA signal measured from pig whole blood is larger at a wavelength of 1064 nm than at 532 nm. The TOF measurements with a streak camera show that the scattering-related changes in the registered pulse shapes occur mainly in the rising part of the pulses. The utilization of fiber-optic measurement heads enabled the detection of back-scattered photons at different distances from the emitting fiber. Although all the techniques are able to detect changes induced by large glucose concentrations (0–5000 mg/dl) in Intralipid, the effect of glucose on the scattering properties of Intralipid is so weak that the techniques failed to detect changes with lower (50–500 mg/dl) concentrations. The measurements of biological samples with the PA technique and with the OCT also demonstrate capabilities to measure glucose concentrations in the physiologically relevant range (18–450 mg/dl) as well. The results compare well with earlier literature and also confirm some earlier findings.

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Hollington, Barnaby Paul. « Chordal roots, Klangverwandtschaft, euphony and coherence : an approach to ostensibly 'atonal', 'non-tonal' or 'post-tonal' harmonic technique ». Thesis, University of Sussex, 2018. http://sro.sussex.ac.uk/id/eprint/75394/.

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My harmonic approach is founded on two premises, pertaining especially to chordal spacing. First, that for each of the 4,096 possible sets of pitch-classes within equal temperament, without exception, certain spacing principles and techniques, if consistently applied, will generate clear, or relatively clear chordal roots. Typically, the resulting sonorities will possess more than one root – that is, be heard as polychords. Second, that one may control the level of inherent sensory dissonance of any given set of pitch-classes, presented as a chord, through register. These two factors combine to induce both harmonic coherence and euphony. For most listeners, rightly or wrongly, these are not qualities normally associated with music written using the 4,096 – that is, ostensibly ‘atonal', ‘non-tonal' or ‘post-tonal' music. Through my harmonic method, since chordal roots are consistently clarified, one may compose progressions of chordal roots – an asset on which the coherence of diatonic tonality also fundamentally depends. Within a non-diatonic context, the expressive and technical consequences are far-reaching. The following textual commentary demonstrates all of the above, supported by analyses of numerous musical extracts. These are drawn primarily from four of the compositions included in the portfolio – Madame de Meuron, The Art of Thinking Clearly, Velvet Revolution and Nevermore.

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Pfeffer, Nathalie. « Connaissances expertes, propagation de contraintes et maintien de coherence pour l'aide a la conception. Application a la conception d'equipements electroniques de satellites : le systeme smack ». Paris 11, 1992. http://www.theses.fr/1992PA112278.

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L'activite de conception donne naissance a tous les objets qui nous entourent: les voitures, les batiments, les ordinateurs. . . Cette these vise l'automatisation du processus de conception preliminaire d'objets industriels (artefacts). Le modele computationnel de conception par assemblage que nous avons elabore s'execute en trois phases. La premiere analyse l'ensemble des specifications pour y detecter les points delicats et completer les valeurs manquantes. La seconde phase applique un modele de decomposition/combinaison pour construire un artefact de performances proches des specifications. La troisieme phase applique un modele de reconception transformationnelle pour l'ameliorer en vue d'obtenir un artefact repondant aux specifications. Nous proposons dans cette these de combiner trois types de techniques d'intelligence artificielle: (1) un systeme expert pour conseiller des pistes de solution, (2) un systeme de propagation de contraintes pour expliciter leurs consequences afin d'anticiper les conflits et de tirer parti d'interactions entre parties de la solution, et (3) un systeme de maintien de coherence pour resoudre les conflits au sein de la solution dus a l'incoherence et/ou incompletude des connaissances expertes. Ces principes sont mis en uvre dans le systeme smack d'aide a la conception preliminaire d'equipements electroniques de satellites

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Gerges, Awad Samir. « Novel fibre-optic-based interferometric sensors exploiting coherent and low-coherence signal processing techniques ». Thesis, University of Kent, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.236854.

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Wu, Jigang Yang Changhuei Yang Changhuei. « Coherence domain optical imaging techniques / ». Diss., Pasadena, Calif. : Caltech, 2009. http://resolver.caltech.edu/CaltechETD:etd-12112008-102138.

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Albezzawy, Muhammad Nabil Mustafa. « Advanced signal processing methods for source identification using references ». Electronic Thesis or Diss., Lyon, INSA, 2024. http://www.theses.fr/2024ISAL0074.

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Les techniques de référence à rang réduit sont couramment employées pour résoudre les problèmes d’extraction de source et de resynchronisation de champs physiques, lorsque le nombre de références dépasse celui des sources incohérentes. Dans ce cas, la matrice croisée-spectrale devient mal conditionnée, rendant la solution des moindres carrés invalide. Bien que la décomposition en valeurs singulières tronquée (DVST) soit utilisée pour résoudre ce problème, elle n'est valable que pour un bruit scalaire sur les références. De plus, il est difficile de définir un seuil de troncature lorsque les valeurs singulières diminuent progressivement. Cette thèse propose une solution nommée technique de référence maximale-coherent (RMC), basée sur la recherche d’un ensemble de références virtuelles maximales correlées avec les mesures de champ. Cette technique est optimale, surtout en présence d’un bruit corrélé sur la référence. Cependant, elle nécessite également une troncature des valeurs propres, exigeant la connaissance ou l’estimation préalable du nombre de sources incohérentes, un problème inverse mal posé et peu étudié. La thèse présente trois méthodes d’énumération de sources applicables à toutes les techniques de référence : un test du rapport de vraisemblance contre le modèle saturé, une technique de bootstrap paramétrique et une approche de validation croisée. Une étude comparative basée sur des données numériques et expérimentales montre deux résultats importants. D'abord, le nombre de fenêtres spectrales utilisées affecte grandement la performance des trois méthodes, qui se comportent différemment selon ce nombre. Ensuite, le bootstrap paramétrique s’avère être la meilleure méthode en termes de précision et de robustesse par rapport au nombre de fenêtres utilisées. Enfin, la technique RMC accompagnée de bootstrap a été utilisée pour l’extraction de source et la resynchronisation de données réelles provenant d’expériences en laboratoire et d’un moteur électrique, fournissant de meilleurs résultats que la solution des moindres carrés et la DVST dans les mêmes conditions
Rank-reduced reference/coherence techniques based on the use of references, i.e. fixed sensors, are widely used to solve the two equivalent problems of source extraction and resynchronization encountered during remote sensing of physical fields, when the number of references surpasses the number of incoherent sources. In such case, the cross-spectral matrix (CSM) becomes ill-conditioned, resulting in the invalidity of the least squares LS solution. Although the truncated singular value decomposition (TSVD) was successfully applied in the literature to solve this problem, its validity is limited only to the case of scalar noise on the references. It is also very difficult to define a threshold, for truncation, when the singular values are gradually decreasing. This thesis proposes a solution based on finding a set of virtual references that is maximally correlated with the field measurements, named the maximally-coherent reference (MCR) Technique. This solution is optimal, especially, in the case of correlated noise on the reference, where TSVD fails. However the technique also includes an eigenvalue truncation step, similar to the one required for the TSVD, which necessitates a priori knowledge or the estimation of the number of incoherent sources, i.e. source enumeration, which is an ill-posed inverse problem, insufficiently investigated in the literature within the framework of reference techniques. In this thesis, after providing a unified formalism for all the reference techniques in the literature, three alternative source enumeration methods, applicable to all the reference techniques, were presented namely; a direct likelihood ratio test (LRT) against the saturated model, a parametric bootstrap technique and a cross-validation approach. A comparative study is performed among the three methods, based on simulated numerical data, real sound experimental data, and real electrical motor data. The results showed two important outcomes. The first is that the number of snapshots (spectral windows), used in the spectral analysis, greatly affects the performance of the three methods, and that, they behave differently for the same number of used snapshots. The second is that parametric bootstrapping turned out to be the best method in terms of both estimation accuracy and robustness with regard to the used number of snapshots. Finally, the MCR technique accompanied with bootstrapping was employed for source extraction and resynchronization of real data from laboratory experiments, and an e-motor, and it returned better results than the LS solution and the TSVD when employed for the same purpose

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Zhu, Kai. « Coherent and non-coherent techniques for cooperative communications ». Thesis, University of York, 2014. http://etheses.whiterose.ac.uk/6852/.

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Future wireless network may consist of a cluster of low-complexity battery-powered nodes or mobile stations (MS). Information is propagated from one location in the network to another by cooperation and relaying. Due to the channel fading or node failure, one or more relaying links could become unreliable during multiple-hop relaying. Inspired by conventional multiple-input multiple-output (MIMO) techniques exploiting multiple co-located transmit antennas to introduce temporal and spatial diversity, the error performance and robustness against channel fading of a multiple-hop cooperative network could be significantly improved by creating a virtual antenna array (VAA) with various distributed MIMO techniques. In this thesis, we concentrate on the low-complexity distributed MIMO designed for both coherent and non-coherent diversity signal reception at the destination node. Further improvement on the network throughput as well as spectral efficiency could be achieved by extending the concept of unidirectional relaying to bidirectional cooperative communication. Physical-layer network coding (PLNC) assisted distributed space-time block coding (STBC) scheme as well as non-coherent PLNC aided distributed differential STBC system are proposed. It is confirmed by the theoretical analysis that both approaches have the potential for offering full spatial diversity gain. 　　 Furthermore, differential encoding and non-coherent detection techniques are generally associated with performance degradation due to the doubled noise variance. More importantly, conventional differential schemes suffer from the incapability of recovering the source information in time-varying channels owing to the assumption of static channel model used in the derivation of non-coherent detection algorithm. Several low-complexity solutions are proposed and studied in this thesis, which are able to compensate the performance loss caused by non-coherent detection and guarantee the reliable recovery of information in applications with high mobility. A substantial amount of iteration gain is achieved by combining the differential encoding with error-correction code and sufficient interleaving, which allows iterative possessing at the receiver.

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Dunsby, Christopher William. « Wide-field coherence-gated imaging techniques including photorefractive holography ». Thesis, Imperial College London, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.407465.

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Méteau, Jérémy. « Instrumentation optique pour la caractérisation des tissus : analyse de la complémentarité et des limites techniques de fluorescence hyperspectrale et de Tomographie Optique Cohérente en vue de leur intégration multimodale ». Thesis, Besançon, 2014. http://www.theses.fr/2014BESA2041/document.

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L'objectif de ce travail de recherche est le développement d'un système fibré d'imagerie point par point d'auto fluorescence multi-excitation, de tissus biologiques en utilisant la technique de fluorescence hyperspectrale et l'étude d'un système de tomographie optique cohérente comme possible modalité supplémentaire. La première partie de ce rapport présente les propriétés optique des tissus biologiques et les fluorophores pertinents pour la détection de tumeurs cancéreuses. La deuxième partie présente l'instrumentation du système d'imagerie de fluorescence et l'analyse hyperspectrale des résultats obtenus in vitro.Il est démontré la pertinence de ce type d'analyse qui permet de déterminer la concentration de certains fluorophores. La troisième partie présente le système de tomographie optique cohérente appelé "scan free" OCT car il permet de réaliser des images sans déplacement d'éléments optiques. Ce système est caractérisé et présente des fonctionnalités intéressantes comme la compensation de la dispersion dépendante de la profondeur. Les divers résultats obtenus montrent que ces deux techniques sont complémentaires car elles apportent des informations de nature différentes. La première technique donne de se informations sur la composition biochimique des tissus, la seconde donne des information sur la structure
The aim of this activity is the development of a mono point imaging fiber system which uses hyperspectral multi-excitation auto fluorescence technique for biological tissues and the study of an Optical Coherence Tomography system like another modality. At first, this report presents the optical properties of biological tissues and the relevant fluorophores for cancerous tumors detection. Secondly, the fluorescence imaging system instrumentation and hyperspectral analysis are presented with in vitro results. The third part presents the "scan free" optical coherence tomography system which is able to image without optical displacement. It's characterized and have interesting functionality like depth dependant dispersion compensation. These both techniques are complementary because they get different kind of information. The information of the first one is about biochemical composition of the tissues and the information of the second one is about the stucture

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Livres sur le sujet "Coherence technique"

Wolfgang, Drexler, Society of Photo-optical Instrumentation Engineers., Optical Society of America, European Physical Society et European Conference on Biomedical Optics (2003 : Munich, Germany), dir. Optical coherence tomography and coherence techniques : 22-24 June 2003, Munich, Germany. Bellingham, Wash., USA : SPIE, 2003.

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Leitgeb, Rainer A. Optical coherence tomography and coherence techniques V : 24-26 May 2011, Munich, Germany. Bellingham, Wash : SPIE, 2011.

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Andersen, Peter E., et Brett E. Bouma. Optical coherence tomography and coherence techniques IV : 14-17 June 2009, Munich, Germany. Sous la direction de Optical Society of America, SPIE (Society), German Biophotonics Research Program, Photonics4Life (Group) et United States. Air Force. Office of Scientific Research. Bellingham, Wash : SPIE, 2009.

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Andersen, Peter E. Optical coherence tomography and coherence techniques III : 17-19 June 2007, Munich, Germany. Sous la direction de SPIE (Society), Optical Society of America, European Optical Society, Wissenschaftliche Gesellschaft Lasertechnik et Deutsche Gesellschaft für Lasermedizin. Bellingham, Wash : SPIE, 2007.

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F, Steinert Roger, et Huang David, dir. Anterior segment optical coherence tomography. Thorofare, NJ : SLACK, 2008.

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F, Steinert Roger, et Huang David, dir. Anterior segment optical coherence tomography. Thorofare, NJ : SLACK, 2008.

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Agarwal, Amar. Diagnostic and imaging techniques in ophthalmology. Panamá, Rep. of Panamá : Jaypee-Highlights Medical Publishers, 2009.

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1937-, Meischner P. (Peter), et Chandra Madhukar, dir. Coherent polarimetric radar techniques for microwave propagation and cloud physics research. Köln : DFVLR, 1988.

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David, Huang, dir. Imaging the eye from front to back with RTVue Fourier-domain optical coherence tomography. Thorofare, NJ : SLACK, 2010.

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Götz, Alexander. Coherent Time Difference of Arrival Estimation Techniques for Frequency Hopping GSM Mobile Radio Signals. München : Oldenbourg Wissenschaftsverlag Verlag, 2013. http://dx.doi.org/10.1524/9783486748628.

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Chapitres de livres sur le sujet "Coherence technique"

Brun, G., I. Verrier, K. Ben Houcine, C. Veillas et J. P. Goure. « Low Coherence Interferometric Technique ». Dans Waves and Imaging through Complex Media, 243–50. Dordrecht : Springer Netherlands, 2001. http://dx.doi.org/10.1007/978-94-010-0975-1_11.

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Friberg, Ari T., et Anna Thaning. « Inverse diffractive optics : asymptotic technique for light of any state of coherence ». Dans Coherence and Quantum Optics VIII, 415–16. Boston, MA : Springer US, 2003. http://dx.doi.org/10.1007/978-1-4419-8907-9_96.

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Filho, Jozue Vieira, Fabricio Guimarães Baptista et Daniel J. Inman. « A PZT-Based Technique for SHM Using the Coherence Function ». Dans Advanced Aerospace Applications, Volume 1, 111–18. New York, NY : Springer New York, 2011. http://dx.doi.org/10.1007/978-1-4419-9302-1_10.

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Nawrocki, Jerzy, et Zofia Michalewska. « Swept Source OCT for Macular Hole Treated with the Inverted Internal Limiting Membrane Flap Technique ». Dans Atlas of Swept Source Optical Coherence Tomography, 97–113. Cham : Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-49840-9_11.

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Cuche, E., P. Poscio et Ch Depeursinge. « Three-Dimensional Microscopy with a Numerical Optical Low-Coherence Holographic Technique ». Dans Optical Technologies in the Humanities, 83–85. Berlin, Heidelberg : Springer Berlin Heidelberg, 1997. http://dx.doi.org/10.1007/978-3-642-60872-8_8.

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Xu, Min, Jing Luo, Hong Liang, Rong-rong Yang, Ying Deng, Fan Yang, Yue-zong Zhou et Li-feng Gao. « Application of Prestack Wide-Azimuth Coherence Technique in Complex Fault Area ». Dans Proceedings of the 2021 International Petroleum and Petrochemical Technology Conference, 3–12. Singapore : Springer Singapore, 2022. http://dx.doi.org/10.1007/978-981-16-9427-1_1.

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Maingonnat, Igor, Gilles Tissot et Noé Lahaye. « Correlated Structures in a Balanced Motion Interacting with an Internal Wave ». Dans Mathematics of Planet Earth, 207–22. Cham : Springer Nature Switzerland, 2023. http://dx.doi.org/10.1007/978-3-031-40094-0_9.

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AbstractCharacterizing the loss of coherence of an internal tide propagating through mesoscale turbulence has been a major challenge in oceanography, particularly due to its implications for the interpretation of satellite data. In this paper, we intend to study the correlations between a balanced motion and the incoherent part of a wave in an idealised configuration. We introduce a new modal decomposition technique, named broad-band proper orthogonal decomposition (BBPOD), which consists in performing a proper orthogonal decomposition (POD) on complex demodulated variables. After connecting BBPOD to the standard SPOD, we show that BBPOD, coupled with the extended POD technique enables us to associate the principal components of the incoherent field to the slow flow structures responsible of this loss of coherence through triadic interactions with the incident wave.

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Panta, Prashanth, Chih-Wei Lu, Piyush Kumar, Tuan-Shu Ho, Sheng-Lung Huang, Pawan Kumar, C. Murali Krishna, K. Divakar Rao et Renu John. « Optical Coherence Tomography : Emerging In Vivo Optical Biopsy Technique for Oral Cancers ». Dans Oral Cancer Detection, 217–37. Cham : Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-61255-3_11.

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Rhodes, Michael L., Yu-Ming Kuo, Alex T. Pang et Stephen L. G. Rothman. « An Image Coherence Technique for Ray Traced Three-Dimensional Presentations in Clinical Radiology ». Dans CAR ’87 Computer Assisted Radiology, 615–18. Berlin, Heidelberg : Springer Berlin Heidelberg, 1987. http://dx.doi.org/10.1007/978-3-642-95530-3_90.

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Harrison, C. H. « The Influence of Noise and Coherence Fluctuations on a New Geo-Acoustic Inversion Technique ». Dans Impact of Littoral Environmental Variability of Acoustic Predictions and Sonar Performance, 139–46. Dordrecht : Springer Netherlands, 2002. http://dx.doi.org/10.1007/978-94-010-0626-2_18.

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Actes de conférences sur le sujet "Coherence technique"

Nugent, K. A., et J. E. Trebes. « Measurement technique for the spatial coherence of x-ray sources ». Dans OSA Annual Meeting. Washington, D.C. : Optica Publishing Group, 1991. http://dx.doi.org/10.1364/oam.1991.mp1.

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This paper proposes and analyzes a technique that will allow the spatial coherence properties of short-wavelength radiation sources to be measured. The technique is based on the analysis of the partially coherent diffraction patterns produced by a uniformly redundant array. The technique is particularly suited to short pulse sources and allows, assuming a Schell model for the mutual intensity function, a complete determination of the complex coherence factor for the radiation. Some measurements of the spatial coherence of the Se soft x-ray laser at the Lawrence Livermore National Laboratory are presented.

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Chan, Kin Pui, Makoto Yamada et Humio Inaba. « Imaging through biological tissues by use of optical low-coherence heterodyne detection technique ». Dans Advances in Optical Imaging and Photon Migration. Washington, D.C. : Optica Publishing Group, 1996. http://dx.doi.org/10.1364/aoipm.1996.cit250.

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A coherent detection imaging system has been modified to employ a super-luminescent diode as low-coherence optical source for optical imaging through strongly scattering media such as biological tissues. By appropriately fixing the coherence gating, the system is able to selectively detect the coherent components of transmitted light. Using this system we have demonstrated the feasibility of optical heterodyne detection method in discriminating against the diffuse photons. The unique applications of low-coherence heterodyne detection in transillumination imaging that may potentially yield useful diagnostic information on tissue structures are also presented.

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Sinescu, Cosmin, Adrian G. Podoleanu, Souman Barua, Florin Ionel Topala, Alin Gabor, Cristian Zaharia, Adrian Bradu, Meda-Lavinia NEGRUTIU et Virgil F. Duma. « Dental impression technique using optoelectronic devices ». Dans Second Canterbury Conference on Optical Coherence Tomography, sous la direction de Ole Bang et Adrian Podoleanu. SPIE, 2018. http://dx.doi.org/10.1117/12.2281775.

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Ossowski, Pawel, Maciej Wojtkowski et Peter R. T. Munro. « Characterization of flowing blood cells using a novel OCT technique : rigorous three-dimensional computational study (Conference Presentation) ». Dans Optical Coherence Tomography and Coherence Domain Optical Methods in Biomedicine XXI, sous la direction de Joseph A. Izatt, James G. Fujimoto et Valery V. Tuchin. SPIE, 2017. http://dx.doi.org/10.1117/12.2254800.

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Chathanathil, Jabir, Gengyuan Liu et Svetlana Malinovskaya. « Remote detection using maximal coherence control technique in coherent anti-Stokes Raman spectroscopy ». Dans Laser Applications to Chemical, Security and Environmental Analysis. Washington, D.C. : Optica Publishing Group, 2022. http://dx.doi.org/10.1364/lacsea.2022.lm3b.5.

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A theoretical framework for the remote detection of molecules is presented in which a quantum control technique, determined to maximize the vibrational coherence in coherent anti-Stokes Raman spectroscopy, is used to optimize the backscattered signal from a cloud of molecules.

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Kou, Ge, Wanrong Gao, ChunKan Tao et Luguo Hao. « Low-coherence tomography technique in biological tissues ». Dans Photonics China '98, sous la direction de Junheng Li et James A. Harrington. SPIE, 1998. http://dx.doi.org/10.1117/12.317852.

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Fuhr, Peter L., et Betty Lise Anderson. « Twin-fiber technique for measuring spatial coherence ». Dans OSA Annual Meeting. Washington, D.C. : Optica Publishing Group, 1989. http://dx.doi.org/10.1364/oam.1989.wl40.

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The traditional method for measuring spatial coherence is to use Young's double slit arrangement or some similar variant. Although quick and easy, this technique has some drawbacks, particularly in replacing and realigning successive sets of apertures. A new method is described using single-mode optical fibers to sample the beam, and a γ-coupler to combine the light from the two points. As one fiber end is translated along the fiber axis (perpendicular to the wavefront), fringes are observed at the output. This method has the added advantage of being able to compare any two arbitrarily chosen points on the wavefront, and symmetry does not have to be assumed. Spatial coherence functions for several different lasers have been measured and compared with results using the classical method. Visibility is measured as a function of aperture spacing and of bias current (for laser diodes). No fringes are observed for below lasing threshold operation of laser diodes or for a light emitting diode (LED).

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Karnowski, Karol, Jadwiga Milkiewicz, Ewa Mączyńska-Walkowiak, Patryk Młyniuk, Onur Cetinkaya, Bartłomiej J. Kałużny, Andrea Curatolo, Ireneusz Grulkowski et Maciej Wojtkowski. « OCT-based, multi-spot assessment of corneal biomechanical asymmetries – clinical results ». Dans Optical Coherence Tomography. Washington, D.C. : Optica Publishing Group, 2024. http://dx.doi.org/10.1364/oct.2024.cm1e.4.

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In clinical settings, precise biomechanical assessments of the cornea are crucial for early detection of keratoconus. Our study introduces the clinical application of a breakthrough multi-meridian technique that enables simultaneous 3-D deformation measurements, enhancing the diagnostic capabilities of standard air-puff swept-source OCT systems. By implementing a spatial-depth-encoded multiplexing approach, we achieved a detailed 9-spot measurement of dynamic corneal deformations. The system's efficacy was rigorously evaluated through comprehensive ex vivo trials on porcine eyes and corroborated with in vivo experiments on human subjects. This innovative method has shown significant potential in identifying biomechanical asymmetries associated with keratoconus. Our findings indicate great capabilities in detecting biomechanical discrepancies indicative of keratoconus, positioning this technique as a promising diagnosis and monitoring tool for corneal pathologies.

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Izatt, Joseph A., Michael R. Hee, Gary Tearney, Gabrielle M. Owen, Eric Swanson et James G. Fujimoto. « Optical Coherence Microscopy ». Dans Advances in Optical Imaging and Photon Migration. Washington, D.C. : Optica Publishing Group, 2022. http://dx.doi.org/10.1364/aoipm.1994.ci.249.

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Confocal microscopy has become a standard technique for high resolution optical imaging in many fields1,2. Confocal imaging is conventionally limited to relatively transparent specimens, since image contrast is degraded by light scattering in turbid samples. We have developed a new method for coherent confocal microsopy which uses low-coherence interferometry to enhance optical sectioning in highly scattering media. In optical coherence microscopy (OCM), improved confocal imaging is achieved through high detection sensitivity and high contrast rejection of out-of-focus light. OCM is an adaptation of optical coherence tomography (OCT), which has recently been demonstrated for noninvasive, ten-micron-scale resolution imaging in the eye and other biological tissues3-5. The extension of this technique to confocal microscopy offers the potential for micron-resolution imaging deep into highly scattering media such as skin and endoscopically accessible tissues, and may make possible the development of a new form of noninvasive "optical biopsy."

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Wright, Kevin C., L. Suzanne Leslie et Nicholas P. Bigelow. « Angular Momentum Transfer to BEC by a Two-Photon Stimulated Raman Technique ». Dans Conference on Coherence and Quantum Optics. Washington, D.C. : OSA, 2007. http://dx.doi.org/10.1364/cqo.2007.cmi54.

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Rapports d'organisations sur le sujet "Coherence technique"

Chang, Chang. Coherence techniques at extreme ultraviolet wavelengths. Office of Scientific and Technical Information (OSTI), janvier 2002. http://dx.doi.org/10.2172/810486.

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Doss, Hani. Statistical Inference for Coherent Systems from Partial Information and in Resampling Techniques in Survival Analysis. Fort Belvoir, VA : Defense Technical Information Center, septembre 1993. http://dx.doi.org/10.21236/ada277382.

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Lora, Eduardo, et Andrew Powell. A New Way of Monitoring the Quality of Urban Life. Inter-American Development Bank, novembre 2011. http://dx.doi.org/10.18235/0011346.

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This paper proposes a methodology to resolve the problems that result from using a combination of objective and subjective information in evaluating urban quality of life. The paper further suggests techniques to identify and rank issues of potential importance for urban dwellers. In order to combine objective and subjective information in a coherent manner and focus on the most relevant dimensions of the quality of life in a city or neighborhood, the paper attempts to exploit the complementary nature of two approaches: the "hedonic" approach, which employs market prices for housing, and the "life satisfaction" approach, which addresses subjective well-being. Results using both approaches in selected Latin American cities are discussed and compared. The paper concludes with a discussion of potential uses of the two-pronged methodology for policy analysis.

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Dudley, J. P., et S. V. Samsonov. SAR interferometry with the RADARSAT Constellation Mission. Natural Resources Canada/CMSS/Information Management, 2022. http://dx.doi.org/10.4095/329396.

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The RADARSAT Constellation Mission (RCM) is Canada's latest system of C-band Synthetic Aperture Radar (SAR) Earth observation satellites. The system of three satellites, spaced equally in a common orbit, allows for a rapid four-day repeat interval. The RCM has been designed with a selection of stripmap, spotlight, and ScanSAR beam modes which offer varied combinations of spatial resolution and coverage. Using Differential Interferometric Synthetic Aperture Radar (DInSAR) techniques, the growing archive of SAR data gathered by RCM can be used for change detection and ground deformation monitoring for diverse applications in Canada and around the world. In partnership with the Canadian Space Agency (CSA), the Canada Centre for Mapping and Earth Observation (CCMEO) has developed an automated system for generating standard and advanced deformation products and change detection from SAR data acquired by RCM and RADARSAT-2 satellites using DInSAR processing methodology. Using this system, this paper investigates four key interferometric properties of the RCM system which were not available on the RADARSAT-1 or RADARSAT-2 missions: The impact of the high temporal resolution of the four-day repeat cycle of the RCM on temporal decorrelation trends is tested and fitted against simple temporal decay models. The effect of the normalization and the precision of the radiometric calibration on interferometric spatial coherence is investigated. The performance of the RCM ScanSAR mode for wide area interferometric analysis is tested. The performance of the novel RCM Compact-polarization (CP) mode for interferometric analysis is also investigated.

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Deschamps, Robert et Henschel. PR-420-133721-R01 Comparison of Radar Satellite Methods for Observation of Stability. Chantilly, Virginia : Pipeline Research Council International, Inc. (PRCI), juillet 2015. http://dx.doi.org/10.55274/r0010840.

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This report discusses the use of Synthetic Aperture Radar (SAR) satellites for monitoring above ground pipelines and buried pipeline Rights-Of-Way (ROWs) using Interferometric Synthetic Aperture Radar (InSAR) techniques. The main thrust of the research was to evaluate the suitability of above-ground pipeline support members as InSAR measurement points, and to adapt existing techniques to allow for precise monitoring of jacking and subsidence caused by permafrost degradation and dynamics. The study site at Prudhoe Bay, Alaska includes more than 60,000 horizontal pipeline supports. The known locations of supports were used to identify and isolate supports in the radar imagery, and the phase and intensity of supports were analyzed to determine their ability to provide reliable estimates of deformation. An additional component of this research was the comparison of two satellites operating at different frequencies, RADARSAT-2 operating at C-band and TerraSAR-X operating at X-band. One year of data was acquired with both sensors in similar acquisition geometries and resolutions, at 24-day intervals for RADARSAT-2 and 11-day intervals for TerraSAR-X. Recommendations are made on the choice of wavelength and concerning future work in this area. A list of technical requirements is also provided. The technologies for obtaining ground deformation estimates from natural targets, coherent targets and homogeneous and distributed targets are explained and supported by three operational case-studies in different environments. The work should provide above-ground pipeline operators working in permafrost areas with a clear view of the current state of research towards the operationalization of InSAR monitoring, but also of current operational capabilities in other pipeline applications, including ROW geohazard monitoring and monitoring of buried pipelines crossing Enhanced Oil Recovery (EOR) fields.

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Letcher, Theodore, Julie Parno, Zoe Courville, Lauren Farnsworth et Jason Olivier. A generalized photon-tracking approach to simulate spectral snow albedo and transmittance using X-ray microtomography and geometric optics. Engineer Research and Development Center (U.S.), juin 2023. http://dx.doi.org/10.21079/11681/47122.

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A majority of snow radiative transfer models (RTMs) treat snow as a collection of idealized grains rather than an organized ice–air matrix. Here we present a generalized multi-layer photon-tracking RTM that simulates light reflectance and transmittance of snow based on X-ray micro- tomography images, treating snow as a coherent 3D structure rather than a collection of grains. The model uses a blended approach to expand ray-tracing techniques applied to sub-1 cm3 snow samples to snowpacks of arbitrary depths. While this framework has many potential applications, this study’s effort is focused on simulating reflectance and transmittance in the visible and near infrared (NIR) through thin snow- packs as this is relevant for surface energy balance and remote sensing applications. We demonstrate that this framework fits well within the context of previous work and capably reproduces many known optical properties of a snow surface, including the dependence of spectral reflectance on the snow specific surface area and incident zenith angle as well as the surface bidirectional reflectance distribution function (BRDF). To evaluate the model, we compare it against reflectance data collected with a spectroradiometer at a field site in east-central Vermont. In this experiment, painted panels were inserted at various depths beneath the snow to emulate thin snow. The model compares remarkably well against the reflectance measured with a spectroradiometer, with an average RMSE of 0.03 in the 400–1600 nm range. Sensitivity simulations using this model indicate that snow transmittance is greatest in the visible wavelengths, limiting light penetration to the top 6 cm of the snowpack for fine-grain snow but increasing to 12 cm for coarse-grain snow. These results suggest that the 5% transmission depth in snow can vary by over 6 cm according to the snow type.

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