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Articles de revues sur le sujet "NCF (Noise Correlation Function)"
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Peng, Hanshu, Zhongliang Wu et Changsheng Jiang. « Pre-seismic changes of noise correlation function (NCF) before the Wenchuan earthquake ? » Concurrency and Computation : Practice and Experience 22, no 12 (25 septembre 2009) : 1774–83. http://dx.doi.org/10.1002/cpe.1517.
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Kuponiyi, Ayodeji Paul, et Honn Kao. « Temporal Variation in Cultural Seismic Noise and Noise Correlation Functions during COVID-19 Lockdown in Canada ». Seismological Research Letters 92, no 5 (28 avril 2021) : 3024–34. http://dx.doi.org/10.1785/0220200330.
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Abstract The COVID-19 pandemic of 2020 led to a widespread lockdown that restricted human activities, particularly land, air, and maritime traffic. The “quietness” on land and ocean that followed presents an opportunity to measure an unprecedented reduction in human-related seismic activities and study its effect on the short-period range of ambient noise cross-correlation functions (NCFs). We document the variations in seismic power levels and signal quality of short-period NCFs measured by four seismographs located near Canadian cities across the pandemic-defined timeline. Significant drops in seismic power levels are observed at all the locations around mid-March. These drops coincide with lockdown announcements by the various Canadian provinces where the stations are located. Mean seismic power reductions of ∼24% and ∼17% are observed near Montreal and Ottawa, respectively, in eastern Canada. Similar reductions of ∼27% and 17% are recorded in western Canada near Victoria and Sidney, respectively. None of the locations show full recovery in seismic power back to the pre-lockdown levels by the end of June, when the provinces moved into gradual reopening. The overall levels of seismic noise during lockdown are a factor of 5–10 lower at our study locations in western Canada, relative to the east. Signal quality of NCF measured in the secondary microseism frequency band for the station pair in western Canada is maximum before lockdown (late February–early March), minimum during lockdown (mid–late March), and increased to intermediate levels in the reopening phase (late May). A similar pattern is observed for the signal quality of the eastern Canada station pair, except for a jump in levels at similar periods during the lockdown phase. The signal quality of NCF within the secondary microseism band is further shown to be the lowest for the western Canada station pair during the 2020 lockdown phase, when compared with similar time windows in 2018 and 2019.
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Hawkins, Rhys, et Malcolm Sambridge. « An Adjoint Technique for Estimation of Interstation Phase and Group Dispersion from Ambient Noise Cross Correlations ». Bulletin of the Seismological Society of America 109, no 5 (16 juillet 2019) : 1716–28. http://dx.doi.org/10.1785/0120190060.
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Abstract A method of extracting group and phase velocity dispersions jointly for Love‐ and Rayleigh‐wave observations is presented. This method uses a spectral element representation of a path average Earth model parameterized with density, shear‐wave velocity, radial anisotropy, and VP/VS ratio. An initial dispersion curve is automatically estimated using a heuristic approach to prevent misidentification of the phase. A second step then more accurately fits the observed noise correlation function (NCF) between interstation pairs in the frequency domain. For good quality cross correlations with reasonable signal‐to‐noise ratio, we are able to very accurately fit the spectrum of NCFs and hence obtain reliable estimates of both phase and group velocity jointly for Love and Rayleigh surface waves. In addition, we also show how uncertainties can be estimated with linearized approximations from the Jacobians and subsequently used in tomographic inversions.
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Jiang, Changsheng, et Zhongliang Wu. « Temporal variation of noise correlation function (NCF) in Beijing and surroundings : Its relation with climate events and implications ». Earthquake Science 22, no 1 (février 2009) : 75–81. http://dx.doi.org/10.1007/s11589-009-0075-5.
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Ragland, John, et Shima Abadi. « Exploring surface source distributions for ocean ambient noise interferometry with airgun shots ». Journal of the Acoustical Society of America 151, no 4 (avril 2022) : A190. http://dx.doi.org/10.1121/10.0011063.
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Ambient noise interferometry utilizes the cross-correlations of ambient sound to estimate the time domain Green’s function (TDGF). We have previously shown that ambient noise interferometry can resolve multi-path arrivals between two bottom-mounted hydrophones separated by 3.2 km, at a depth of 1500 m, and located 470 km off the Oregon coast. In 2019, a seismic reflection survey was conducted directly over the two hydrophones for 28 days covering a 763 km2 area. The airgun shots occurred every 37.5 m while the ship moved at a speed of ∼4.5 knots, equivalent to a shooting interval of 16 s. The hydrophone recordings during this survey provide the unique opportunity to understand the effects of the surface source distribution on the noise cross correlation function (NCCF). In this talk, we show the sensitivity of the NCCF to the surface source locations using simulated and experimental data. Then, we use the image source method to analytically define the location of the sound sources that contribute to different delay times in the NCCF. [Work supported by ONR.]
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Steinmann, René, Céline Hadziioannou et Eric Larose. « Effect of centimetric freezing of the near subsurface on Rayleigh and Love wave velocity in ambient seismic noise correlations ». Geophysical Journal International 224, no 1 (28 août 2020) : 626–36. http://dx.doi.org/10.1093/gji/ggaa406.
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SUMMARY About a decade ago, noise-based monitoring became a key tool in seismology. One of the tools is passive image interferometry (PII), which uses noise correlation functions (NCF) to retrieve seismic velocity variations. Most studies apply PII to vertical components recording oceanic low-frequent ambient noise ( < 1 Hz). In this work, PII is applied to high-frequent urban ambient noise ( > 1 Hz) on three three-component sensors. With environmental sensors inside the subsurface and in the air, we are able to connect observed velocity variations with environmental parameters. Temperatures below 0 °C correlate well with strong shear wave velocity increases. The temperature sensors inside the ground suggest that a frozen layer of less than 5 cm thickness causes apparent velocity increases above 2 % , depending on the channel pair. The observations indicate that the different velocity variation retrieved from the different channel pairs are due to different surface wave responses inherent in the channel pairs. With dispersion curve modelling in a 1-D medium we can verify that surfaces waves of several tens of metres wavelength experience a velocity increase of several percent due to a centimetres thick frozen layer. Moreover, the model verifies that Love waves show larger velocity increases than Rayleigh waves. The findings of this study provide new insights for monitoring with PII. A few days with temperature below 0 °C can already mask other potential targets (e.g. faults or storage sites). Here, we suggest to use vertical components, which is less sensitive to the frozen layer at the surface. If the target is the seasonal freezing, like in permafrost studies, we suggest to use three-component sensors in order to retrieve the Love wave response. This opens the possibility to study other small-scale processes at the shallow subsurface with surface wave responses.
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Tian, Jinyu, Jian Lin, Fan Zhang, Min Xu, Yayun Zhang, Laiyin Guo et Xin Zeng. « Time Correction of Ocean-Bottom Seismometers Using Improved Ambient Noise Cross Correlation of Multicomponents and Dual-Frequency Bands ». Seismological Research Letters 92, no 3 (13 janvier 2021) : 2004–14. http://dx.doi.org/10.1785/0220200358.
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Abstract An effective approach was developed for identifying and correcting ocean-bottom seismometer (OBS) time errors through improving ambient noise cross-correlation function (NCCF) analysis and combination with other methods. Significant improvements were illustrated through analyzing data from a passive-source seismic experiment in the southwestern sub-basin of the South China Sea. A novel method was first developed that can effectively identify errors in the sampling frequency of the OBS instruments. The traditional NCCF method was then expanded by increasing the analyzed data spectrum from a single-frequency band to dual-frequency band pairs, thus doubling the number of available data points and substantially improving the time correction quality. For data with relatively low signal-to-noise ratios, the average time errors were reduced from the original average values of 60–80 ms by the conventional methods to <40 ms using the improved approaches. The new multistep procedure developed in this study has general applicability to analysis of other OBS experiments. The demonstrated significant improvements in the data quality are critical for advancing seismic tomography and other modern marine geophysical studies that require high accuracy in the OBS data.
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Cheng, Wei, Lintao Liu et Guocheng Wang. « A new method for estimating the correlation of seismic waveforms based on the NTFT ». Geophysical Journal International 226, no 1 (1 avril 2021) : 368–76. http://dx.doi.org/10.1093/gji/ggab047.
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SUMMARY We propose a new correlation function called the similarity coefficient (SC) based on the normal time–frequency transform (NTFT) to evaluate the similarity between two non-stationary seismic signals as a function of the delay time. The SC is defined in the time–frequency spectrum of the NTFT, and the instantaneous phase and amplitude of each frequency component in a signal are used to calculate the SC. Our simulation experiments demonstrate that the SC method can effectively recognize similar signals compared to the conventional normalized cross-correlation coefficient (NCC) under high background noise conditions. The SC presents good robustness in identifying similar signals and performs well in the case of an extremely low signal-to-noise ratio (SNR), which makes it suitable for detecting weak seismic signals concealed by noise. As a real application case, we use the SC method to detect quasi-Love (QL) surface waves. QL waves are scattered Love waves and are important indicators for lateral anisotropic gradients in the upper mantle. We detect the QL waves at 21 stations deployed across Japan after the 23 December 2004 Mw 8.1 Macquarie earthquake by using the SC method. Obvious QL waves are observed at 19 stations, and we locate the Love-to-Rayleigh scatterers by applying the delay times between the QL and main Love waves. Our results show that the QL wave scatterers were mostly generated in two areas: Mariana subduction and Papua New Guinea. The observations of QL waves suggest the presence of lateral gradients in anisotropy beneath those two areas. The spatial distribution of the 13 scatterers in the Mariana subduction zone agrees well with the Mariana Island Arc, and we infer that the Mariana slab may have melted and coupled with the surrounding mantle at depth.
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Wang, Jian, Xiaolei Lv, Zenghui Huang et Xikai Fu. « An Epipolar HS-NCC Flow Algorithm for DSM Generation Using GaoFen-3 Stereo SAR Images ». Remote Sensing 15, no 1 (26 décembre 2022) : 129. http://dx.doi.org/10.3390/rs15010129.
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Radargrammetry is a widely used methodology to generate the large-scale Digital Surface Model (DSM). Stereo matching is the most challenging step in radargrammetry due to the significant geometric differences and the inherent speckle noise. The speckle noise results in significant grayscale differences of the same feature points, which makes the traditional Horn–Schunck (HS) flow or multi-window zero-mean normalized cross-correlation (ZNCC) methods degrade. Therefore, this paper proposes an algorithm named Epipolar HS-NCC Flow (EHNF) for dense stereo matching, which is an improved HS flow method with normalized cross-correction constraint based on epipolar stereo images. First, the epipolar geometry is applied to resample the image to realize the coarse stereo matching. Subsequently, the EHNF method forms a global energy function to achieve fine stereo matching. The EHNF method constructs a local normalized cross-correlation constraint term to compensate for the grayscale invariance constraint, especially for the SAR stereo images. Additionally, two assessment methods are proposed to calculate the optimal cross-correlation parameter and smoothness parameter according to the refined matched point pairs. Two GaoFen-3 (GF-3) image pairs from ascending and descending orbits and the open Light Detection and Ranging (LiDAR) data are utilized to fully evaluate the proposed method. The results demonstrate that the EHNF algorithm improves the DSM elevation accuracy by 9.6% and 27.0% compared with the HS flow and multi-window ZNCC methods, respectively.
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Perez-Cham, Oscar E., Cesar Puente, Carlos Soubervielle-Montalvo, Gustavo Olague, Carlos A. Aguirre-Salado et Alberto S. Nuñez-Varela. « Parallelization of the Honeybee Search Algorithm for Object Tracking ». Applied Sciences 10, no 6 (20 mars 2020) : 2122. http://dx.doi.org/10.3390/app10062122.
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Object tracking refers to the relocation of specific objects in consecutive frames of a video sequence. Presently, this visual task is still considered an open research issue, and the computer science community attempted solutions from the standpoint of methodologies, algorithms, criteria, benchmarks, and so on. This article introduces a GPU-parallelized swarm algorithm, called the Honeybee Search Algorithm (HSA), which is a hybrid algorithm combining swarm intelligence and evolutionary algorithm principles, and was previously designed for three-dimensional reconstruction. This heuristic inspired by the search for food of honeybees, and here adapted to the problem of object tracking using GPU parallel computing, is extended from the original proposal of HSA towards video processing. In this work, the normalized cross-correlation (NCC) criteria is used as the fitness function. Experiments using 314 video sequences of the ALOV benchmark provides evidence about the quality regarding tracking accuracy and processing time. Also, according to these experiments, the proposed methodology is robust to high levels of Gaussian noise added to the image frames, and this confirms that the accuracy of the original NCC is preserved with the advantage of acceleration, offering the possibility of accelerating latest trackers using this methodology.
Thèses sur le sujet "NCF (Noise Correlation Function)"
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Hejazi, Nooghabi Aida. « Green's function retrieval from noise correlation in multiple scattering media ». Electronic Thesis or Diss., Sorbonne université, 2018. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2018SORUS609.pdf.
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L'interférométrie de bruit ambiant est une approche pour estimer la réponse impulsionnelle entre deux récepteurs sans source active. Cette thèse contribue à l'évaluation de la robustesse et de la précision de la reconstruction de la fonction de Green par la corrélation du bruit ambiant dans les milieux réverbérants. Plus précisément, on distingue les rôles respectifs de la partie balistique et coda des signaux dans les corrélations. Ensuite, nous nous concentrons sur un milieu réverbérant incluant un diffuseur. Nous estimons de manière passive la force du diffuseur en utilisant l'interférométrie du bruit ambiant. Dans la dernière partie de ce travail, nous nous concentrons sur un milieu réverbérant contenant les inclusions résonantes. Notre but est d'évaluer le comportement de la corrélation dans ce type de milieu. Nous avons construit un de ces matériaux au laboratoire qui est constitué des tiges verticales à la surface d'une plaque mince élastique. Nous trouvons que les différents comportements sont bien cohérents avec les régimes qui correspondent à la bande de propagation ou interdite. Comme la partie sismique, nous appliquons la technique de corrélation aux données réelles récupérées lors de l'expérience METAFORET. Nos résultats sont sont en accord avec le comportement diffusant des arbres dans les gammes de fréquence correspondanteAmbient-noise interferometry is an approach to estimate the transient response between two receivers without an active source. The method consists of cross-correlating recordings of ambient vibrations at a pair of passive instruments that act only as receivers. This dissertation contributes to evaluating the robustness and accuracy of Green's function reconstruction by cross-correlation of noise, disentangling the respective roles of ballistic and reverberated ('coda') signals. We focus our study on a strongly reverberating medium. We conduct a suite of experiments on a highly reverberating thin duralumin plate. We find that the coda of the arrivals contribute the most to retrieval of the Green's function. We also develop an analytical model that predicts the dependence of symmetry of the cross-correlations on the number of sources. Next, we focus on a reverberating medium with a scatterer. We passively estimate the scattering strength of the scatterer by implementing ambient-noise interferometry. In the last part, we focus on a reverberating medium with locally resonant scatterers which acts as a metamaterial. Our objective is to assess the behaviour of the cross-correlation in such a medium. We build an example of such materials in the laboratory by attaching an array of rods, arranged in a sub-wavelength order, to the surface of a thin elastic plate. We find different behaviours which are consistent with the regimes that correspond to propagation band and bandgap. We next apply the cross-correlation technique to the real data obtained in METAFORET experiment. Our findings are consistent with the resonating behaviour of trees at the corresponding frequency bands
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Spitz, Nicolas. « Prediction of Trailing Edge Noise from Two-Point Velocity Correlations ». Thesis, Virginia Tech, 2005. http://hdl.handle.net/10919/32637.
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This thesis presents the implementation and validation of a new methodology developed by Glegg et al. (2004) for solving the trailing edge noise problem. This method is based on the premises that the noise produced by a surface can be computed by the integral of the cross product between the velocity and vorticity fields, of the boundary layer and shed vorticity (Howe (1978)). To extract the source terms, proper orthogonal decomposition is applied to the velocity cross spectrum to extract modes of the unsteady velocity and vorticity.
The new formulation of the trailing edge noise problem by Glegg et al. (2004) is attractive because it applies to the high frequencies of interest but does not require an excessive computational effort. Also, the nature of the formulation permits the identification of the modes producing the noise and their associated velocity fluctuations as well as the regions of the boundary layer responsible for the noise production.
The source terms were obtained using the direct numerical simulation of a turbulent channel flow by Moser et al. (1998). Two-point velocity and vorticity statistics of this data set were obtained by averaging 41 instantaneous fields. For comparisons purposes, experimental boundary layer data by Adrian et al. (2000) was chosen. Statistical reduction of 50 velocity fields obtained by particle image velocimetry was performed and analysis of the two-point correlation function showed features similar to the DNS data case. Also, proper orthogonal decomposition revealed identical dominant modes and eddy structures in the flow, therefore justifying considering the channel flow as an external boundary layer for noise calculations.
Comparison of noise predictions with experimental data from Brooks et al. (1989) showed realistic results with the largest discrepancies, on the order of 5 dB, occurring at the lowest frequencies. The DNS results are least applicable at these frequencies, since these correspond to the longest streamwise lengthscales, which are the most affected by the periodicity conditions used in the DNS and also are the least representative of the turbulence in an external boundary layer flow. Most of the noise was shown to be produced by low-frequency streamwise velocity modes in the bottom 10% of the boundary layer and locations closest to the wall. Only 6 modes were required to obtain noise levels within 1 dB of the total noise.
Finally, the method for predicting spatial velocity correlation from Reynolds stress data in wake flows, originally developed by Devenport et al. (1999, 2001) and Devenport and Glegg (2001), was adapted to boundary-layer type flows. This method, using Reynolds stresses and the prescription of a lengthscale to extrapolate the full two-point correlation, was shown to produce best results for a lengthscale prescribed as proportional to the turbulent macroscale.
Noise predictions using modeled two-point statistics showed good agreement with the DNS inferred data in all but frequency magnitude, a probable consequence of the modeling of the correlation function in the streamwise direction. Other quantities associated to noise were seen to be similar to the ones obtained using the DNS.Master of Science
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Starkloff, Hans-Jörg, et Ralf Wunderlich. « Stationary solutions of linear ODEs with a randomly perturbed system matrix and additive noise ». Universitätsbibliothek Chemnitz, 2005. http://nbn-resolving.de/urn:nbn:de:swb:ch1-200501335.
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The paper considers systems of linear first-order ODEs with a randomly perturbed system matrix and stationary additive noise. For the description of the
long-term behavior of such systems it is necessary to study their stationary solutions. We deal with conditions for the existence of stationary solutions as well as
with their representations and the computation of their moment functions.
Assuming small perturbations of the system matrix we apply perturbation techniques to find series representations of the stationary solutions and give asymptotic
expansions for their first- and second-order moment functions. We illustrate the findings with a numerical example of a scalar ODE, for which the moment functions of
the stationary solution still can be computed explicitly. This allows the assessment
of the goodness of the approximations found from the derived asymptotic expansions.
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Dias, Fábio Luiz. « Estudo da Camada de Basalto em Bebedouro, Bacia do Paraná, com Função do Receptor - Implicações para a Sismicidade Induzida por Poços Profundos ». Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/14/14132/tde-12062018-172635/.
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Este trabalho consiste no estudo da estrutura sedimentar da Bacia do Paraná da região de Bebedouro utilizando função do receptor, ondas de superfície e sísmica de refração. Funções do Receptor (FR) mostram a resposta da estrutura geológica abaixo de uma estação sismográfica. Para diminuir a não unicidade na inversão do traço de uma FR, foram usadas curvas de dispersão de ondas de superfície como vínculos adicionais. Ondas de superfície foram também obtidas com a correlação cruzada de ruído sísmico ambiental. Esse método passivo permite a obtenção de dispersão em períodos intermediários entre os dados de telessismos e os dados de sísmica rasa auxiliando na determinação estruturas sedimentares. Foi utilizada a inversão conjunta de FR de alta e baixa frequência, dispersão de fase e grupo de períodos menores que 2 s e dispersão de ondas Love e Rayleigh continentais (períodos entre 10 e 100 s). Na inversão conjunta, foram usados vários modelos iniciais diferentes para garantir melhor cobertura do espaço de soluções possíveis. Os resultados mostram uma camada de basalto com uma espessura entre 200 e 400 m, sob uma camada superficial de arenito de 50 a 100m. O embasamento da bacia está torno de 2.5 3.0 km. A espessura e razão Vp/Vs crustal da região foi estimada em 40.0 (1.0) km e 1.78 (0.02). Foi possível identificar zonas de baixa velocidade dentro do pacote de basalto, possivelmente relacionadas a zonas de fraturas ou camadas de basalto alterado. Estas camadas de baixa velocidade estão na parte sul, próximas à área de maior sismicidade induzida e também relativamente mais perto dos poços profundos de maior vazão. Isto corrobora com a hipótese de que a sismicidade local está associada à exploração de poços e estrutura de falhas pré -existentes.A study of the seismic structure of the Paraná Basin in Bebedouro, SP, was carried out with Receiver Functions (RF). Both low frequency (with ~0.5 Hz low pass filter) and high-frequency (~10Hz) RFs were jointly inverted with surface wave dispersion curves. Surface-wave data included: long-period group velocities of Rayleigh and Love waves from continental-scale tomography in the period range 10-100 s (useful to control crustal scale structure and Moho depth), intermediate period group velocities near 1s period obtained from cross-correlation of ambient noise (useful to control sedimentary structure), phase velocities near 0.2-1.0 s obtained from local earthquakes, and phase velocities of Rayleigh waves from shallow seismic refraction data near ~0.1 s period (useful to control shallow layers). Joint inversion was obtained with several different initial models to better cover all possible solutions. The results indicate that the basalt layer is 200 to 400m thick, beneath sandstones of about 50 100m thick. The Basin basement was detected between 2.5 3.0 km depth, consistent with expected values from regional bore-hole data in the Paraná Basin. Beneath several stations a low-velocity zone was detected in the middle of the basalt pack which is interpreted as a zone of fractured or altered basalt. This anomalous low-velocity layer was detected near the most seismically active zone in the Andes district. It is also relatively close to the deep wells with larger outflow. The existence of this low-velocity zone in the middle of the basalt layer is consistent with the model proposed for the water-well induced seismicity.
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Mahmoud, Ali. « Analyseur de spectre à haute résolution : Apllication à la mesure des oscillateurs ultrastables ». Besançon, 1989. http://www.theses.fr/1989BESA2004.
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Une methode de mesure par intercorrelation utilisant l'intercomparaison de trois oscillateurs deux a deux, permet de mesurer les fluctuations de phase ou de frequence des oscillateurs ultrastables. Nous presentons l'etude et la realisation d'un analyseur de spectre par correlation. Cet appareil permet d'analyser la fonction de correlation ou de calculer la densite spectrale de puissance du bruit de phase de l'oscillateur a mesurer
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Hourany, Karl. « Contribution à l'exploitation du bruit ambiant pour le contrôle santé intégré passif des barres et des tubes ». Thesis, Valenciennes, 2015. http://www.theses.fr/2015VALE0039/document.
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Les travaux présentés dans ce manuscrit sont basés sur des études précédentes réalisées à l’Institut d’Électronique de Microélectronique et de Nanotechnologie (IEMN) de l’Université de Valenciennes et du Hainaut Cambrésis (UVHC). Ils concernent le développement d’un système de surveillance embarqué destiné au contrôle des matériaux et des structures utilisés dans différents domaines de transport (fluidique, tubulaire, aéronautique, ferroviaire…). Il s’agit du principe de Contrôle Santé Intégré CSI (ou SHM en anglais pour Structural Health Monitoring). L’idée est d’intégrer des capteurs sur les surfaces des structures à contrôler pour aboutir à un système de contrôle non destructif de ces dernières durant la totalité de leurs fonctionnements. Tout d’abord, les travaux réalisés à l’IEMN dans ce domaine sont illustrés, quelques définitions comme celles des ondes ultrasonores, du Contrôle Non Destructif et du Contrôle Santé Intégré sont rappelées, avant d’aborder l’explication du passage d’un contrôle actif à un contrôle passif. Dans un deuxième temps, un algorithme de comparaison d’images basé sur les minimums locaux présents dans ces images a été proposé et testé sur des images simples de seize pixels, et a permis de tester le degré de ressemblance entre elles. L’explication de l’algorithme développé est divisée en deux grandes parties. Dans la première nous expliquons comment extraire les minimums locaux d’une image. La deuxième partie expose la procédure pour déterminer le taux de ressemblance entre les images. La simulation de la propagation d’un signal dans une plaque réverbérante et l’obtention des images temps-fréquence correspondantes à des corrélations filtrées (autocorrélation) ont été décrites. L’algorithme proposé a été validé sur ces images, permettant ainsi la localisation d’une position inconnue de la sourceThe works presented in this manuscript are based on previous studies conducted at the Institute of Electronics Microelectronics and Nanotechnology of the University of Valenciennes and Hainaut Cambrésis. They concern the development of an embedded monitoring system for the control of materials and structures used in different transport domains (pipeline, aerospace, railway ...). This is the Structural Health-Monitoring principle. The idea is to integrate sensors into the surfaces of the controlled structures in order to achieve a non-destructive control system for the control of the latter during their entire lifetime. First the work done at the laboratory in this domain, are illustrated, some definitions such as ultrasonic waves, the Non Destructive Testing and the Structural Health Monitoring are recalled, to switch later to the explanation of the passage from an active control to a passive control. In a second step, an images comparison algorithm based on the local minima present in these images has been proposed and tested on simple images of sixteen pixels and was used to test the degree of resemblance between them. The explanation of the developed algorithm is divided into two parts. In the first one, we explain how to extract the local minima of an image. The second part describes the procedure for determining the rate of resemblance between the images. The simulation of the propagation of a signal in a reverberant plate and the obtaining of the frequency time images corresponding to filtered correlation (autocorrelation) has been described. The algorithm was validated on those images allowing the localization of an unknown source position
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Silva, Erick Rodrigues. « Simetrias de paridade e de reversão temporal no Efeito Hanbury Broen-Twiss ». Universidade Federal da Paraíba, 2015. http://tede.biblioteca.ufpb.br:8080/handle/tede/8164.
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Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq
The Hanbury Brown-Twiss experiment is very well established in quantum optics literature, so we devoted this dissertation in order to embed the parity and temporal reversal symmetry in the former experiment. Therefore, we developed the scattering matrix formalism which allow us use some techniques such as the scattering matrices' concatenation of di erent sections in terms of one matrix and the scattering problem of a parity and temporal reverse symmetric system. In this manner, we could derive the scattering matrix of a parity and temporal reverse symmetric Hanbury Brown- Twiss experiment(HBT-PT). With the possession of this matrix, we proposed a theoretical model which provides how to measure the symmetry of this system, which we called correlation functions formalism. In order to stablish the former formalism, we studied B uttiker formalism, which we veri ed how the correlation between 2 incident particles in a system relates to the noise due transport of this particles and what kind of noise we are treating in a given regime which the system is operating. Then, we found the input states in terms of the output states of two particles inciding in a multiterminal system, which we used it's scattering matrix to stablish the relation between the states. Thereat, we derived all the possibles correlations(therefore, the noise) of two incident particles in the former system. Thereby, we analysed the extreme cases of a barrier coupled to the HBT-PT experiment for the purpose of stablish which regime the experiment is symmetric adjusted, so, demonstrating the Hanbury Brown-Twiss E ect with parity and temporal reverse symmetries.
Sendo o experimento Hanbury Brown-Twiss bem estabelecido na literatura da otica quântica, dedicamos esta dissertação a embutir no mesmo experimento a questão da simetria por paridade e reversão temporal. Para tanto, abrimos mão do formalismo da matriz de espalhamento que permitiu nos utilizar tecnicas como a concatenação de matrizes de espalhamento de sec ções diferentes em termos de apenas uma matriz e o problema do espalhamento em um sistema simétrico por paridade e reversão temporal. Dessa forma, pudemos derivar a matriz de espalhamento para o experimento Hanbury Brown-Twiss com simetria de paridade e revers~ao temporal(HBT-PT). De posse dessa matriz, propusemos um modelo teórico que propicia a medição experimental a simetria desse sistema, o qual chamamos de formalismo das fun c~oes de correla c~ao. Para estabelecermos o formalismo supracitado, estudamos o formalismo de Buttiker, onde veri case como a correlaçãao entre 2 partículas incidentes em um sistema relaciona-se com o ru do devido ao transporte dessas part culas e que tipo de ru do estamos tratando, dado o regime em que o sistema está operando. Em seguida, encontramos os estados de entrada em termos dos estados de saída de 2 partículas incidindo em um sistema multiterminal, onde utilizamos a sua matriz de espalhamento para estabelecer a rela c~ao entre os estados. Com isso, derivamos todas as possíveis correlações (e, por conseguinte, o ruído) de 2 partículas incidentes nesse sistema. Assim, analisamos os casos extremos de uma barreira acoplada ao experimento HBT-PT, a m de estabelecer o regime em que o experimento está simetricamente ajustado e demonstramos o Efeito Hanbury Brown-Twiss por paridade e reversão temporal.
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LOTTI, ALESSIA. « Investigation of a rockslide from its local seismic response - Analisi di una frana in roccia dalla sua risposta sismica locale ». Doctoral thesis, 2016. http://hdl.handle.net/2158/1043751.
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Il presente lavoro consiste in un esperimento pilota per valutare l'efficacia dell'applicazione di reti micro-sismiche a piccola scala in sistemi di early-warning per il monitoraggio di versanti rocciosi instabili e la prospezione in passivo di aree di frana. Il lavoro si articola in tre parti principali: a.) analisi del dato sismico per la caratterizzazione del corpo di frana e dell'area in esame; b.) analisi del dato sismico continuo per la valutazione di eventuali modifiche nei parametri di analisi capaci di rivelare variazioni interne al corpo di frana, e c.) analisi dei transienti, discriminazione e classificazione. Un ulteriore sezione è dedicata al confronto con i dati indipendenti disponibili derivati dalla rete di monitoraggio già presente al sito di acquisizione.
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Chen, Ying-Nien, et 陳映年. « On the noise level of the ambient noise cross-correlation function and its applications ». Thesis, 2014. http://ndltd.ncl.edu.tw/handle/20177172834406515417.
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博士國立臺灣大學
海洋研究所
103
Retrieving the Empirical Greens function (EGF) between two receivers by cross-correlating continuous records is now a well-recognized technique and the derived EGFs have been applied to various fields of seismology. However, little attention has been given to a more quantitative description on the noise behavior of the noise-derived cross-correlation functions (CCF), for its signal-to-noise ratio (SNR) can be improved easily by increasing the total correlation time. In this thesis, we propose a method to measure the noises within the CCFs and demonstrate the relationship between noises and the corresponding sources properties. We evaluate the original noise level (ONL) for CCFs in Taiwan and Korea. With the measured ONL, we can estimate data quality for any portion of the CCF in the time domain. Moreover, since the ONL is closely related to the noise source population and EGF’s amplitude is sensitive to the excitation strength, combination of both measurements allows us to put better constraints to the noise sources. Using the approach, we conclude that (1) The dominant microseisms of period 5~10 sec observed in Taiwan and Korea are mostly contributed by Primary microseisms (PM), rather than long period secondary microseisms (LPSM) proposed by previous studies; (2) The high short period secondary microseisms (SPSM) level in Taiwan Strait is mainly caused by the bathymetry effect; (3) The low ONL in the SPSM band implies that sources for these dominant signals in CCFs are likely confined in the near-coast region; (4) The expected high source population of PM around Taiwan is well demonstrated by the strong ONL in the period ~6-9 seconds, although the PM signals are not present in the CCF records or the background seismic noises.
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Koubek, Antonín. « Bodové procesy v čase a prostoru ». Master's thesis, 2013. http://www.nusl.cz/ntk/nusl-320988.
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In this work we present an introduction to the theory of point processes in space and time with focus on space--time shot--noise Cox process. Further from theoretical point of view we study its simulation, space--time separability, kernel estimate of intensity function and non--parametric estimation of some summary statistics using edge corrections. For two ambit models and one space--time separable model we do numerical calculations using the presented theory and software Wolfram Mathematica 9.0. For these three models we do simulations, we select the best bandwidth for kernel estimate of the intensity function and we also calculate some theoretical summary statistics including the pair correlation function. Powered by TCPDF (www.tcpdf.org)
Livres sur le sujet "NCF (Noise Correlation Function)"
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National Aeronautics and Space Administration (NASA) Staff. Separating Direct and Indirect Turbofan Engine Combustion Noise While Estimating Post-Combustion (Post-Flame) Residence Time Using the Correlation Function. Independently Published, 2019.
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Berber, Stevan. Discrete Communication Systems. Oxford University Press, 2021. http://dx.doi.org/10.1093/oso/9780198860792.001.0001.
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The book present essential theory and practice of the discrete communication systems design, based on the theory of discrete time stochastic processes, and their relation to the existing theory of digital communication systems. Using the notion of stochastic linear time invariant systems, in addition to the orhogonality principles, a general structure of the discrete communication system is constructed in terms of mathematical operators. Based on this structure, the MPSK, MFSK, QAM, OFDM and CDMA systems, using discrete modulation methods, are deduced as special cases. The signals are processed in the time and frequency domain, which requires precise derivatives of their amplitude spectral density functions, correlation functions and related energy and pover spectral densities. The book is self-sufficient, because it uses the unified notation both in the main ten chapters explaining communications systems theory and nine supplementary chapters dealing with the continuous and discrete time signal processing for both the deterministic and stochastic signals. In this context, the indexing of vital signals and finctions makes obvious distinction beteween them. Having in mind the controversial nature of the continuous time white Gaussian noise process, a separate chapter is dedicated to the noise discretisation by introducing notions of noise entropy and trauncated Gaussian density function to avoid limitations in applying the Nyquist criterion. The text of the book is acompained by the solutions of problems for all chapters and a set of deign projects with the defined projects’ topics and tasks and offered solutions.
Chapitres de livres sur le sujet "NCF (Noise Correlation Function)"
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Orlowitz, Esben, et Anders Brandt. « Influence of Noise in Correlation Function Estimates for Operational Modal Analysis ». Dans Topics in Modal Analysis & ; Testing, Volume 9, 55–64. Cham : Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-74700-2_6.
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Charles Liberman, M., L. W. Dodds et D. A. Learson. « Structure-Function Correlation in Noise-Damaged Ears : A Light and Electron-Microscopic Study ». Dans Basic and Applied Aspects of Noise-Induced Hearing Loss, 163–77. Boston, MA : Springer US, 1986. http://dx.doi.org/10.1007/978-1-4684-5176-4_12.
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Oswald, Julie N., Christine Erbe, William L. Gannon, Shyam Madhusudhana et Jeanette A. Thomas. « Detection and Classification Methods for Animal Sounds ». Dans Exploring Animal Behavior Through Sound : Volume 1, 269–317. Cham : Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-030-97540-1_8.
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AbstractClassification of the acoustic repertoires of animals into sound types is a useful tool for taxonomic studies, behavioral studies, and for documenting the occurrence of animals. Classification of acoustic repertoires enables the identification of species, age, gender, and individual identity, correlations between sound types and behavior, the identification of changes in vocal behavior over time or in response to anthropogenic noise, comparisons between the repertoires of populations living in different geographic regions and environments, and the development of software tools for automated signal processing. Techniques for classification have evolved over time as technical capabilities have expanded. Initially, researchers applied qualitative methods, such as listening and visually discerning sounds in spectrograms. Advances in computer technology and the development of software for the automatic detection and classification of sounds have allowed bioacousticians to quickly find sounds in recordings, thus significantly reducing analysis time and enabling the analysis of larger datasets. In this chapter, we present software algorithms for automated signal detection (based on energy, Teager–Kaiser energy, spectral entropy, matched filtering, and spectrogram cross-correlation) as well as for signal classification (e.g., parametric clustering, principal component analysis, discriminant function analysis, classification trees, artificial neural networks, random forests, Gaussian mixture models, support vector machines, dynamic time-warping, and hidden Markov models). Methods for evaluating the performance of automated tools are presented (i.e., receiver operating characteristics and precision-recall) and challenges with classifying animal sounds are discussed.
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Wu, Xin, Lin Liu et Shu Li. « Correlation output analysis based on variance and power spectrum function of noise signal for random noise radar ». Dans Electronics, Communications and Networks IV, 1213–18. CRC Press, 2015. http://dx.doi.org/10.1201/b18592-218.
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Khan, Bilal Muhammad, et Rabia Bilal. « Blind Signal Detection Techniques for Spectrum Sensing in Satellite Communication ». Dans Handbook of Research on Recent Developments in Intelligent Communication Application, 1–48. IGI Global, 2017. http://dx.doi.org/10.4018/978-1-5225-1785-6.ch001.
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Modulated signals used in communication systems exhibits cyclic periodicity. This is primarily due to sinusoidal product modulators, repeating preambles, coding and multiplexing in modern communication. This property of signals can be analyzed using cyclostationary analysis. SCF (Spectral correlation function) of cyclic autocorrelation (CAF) has unique features for different modulated signals and noise. Different techniques are applied to SCF for extracting features on the basis of which decision of detecting a signal or noise is made. In this chapter, study and analysis of different modulated signals used in satellite communication is presented using SCF. Also comparison of several signal detection techniques is provided on the basis of utilizing unique feature exhibit by a normalized vector calculated on SCF along frequency axis. Moreover a signal detection technique is also proposed which identifies the presence of a signal or noise in the analyzed data within the defined threshold limits.
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Pérez-Mercade, Juan. « Coarse-Graining, Scaling, and Hierarchies ». Dans Nonextensive Entropy. Oxford University Press, 2004. http://dx.doi.org/10.1093/oso/9780195159769.003.0026.
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We present a scenario that is useful for describing hierarchies within classes of many-component systems. Although this scenario may be quite general, it will be illustrated in the case of many-body systems whose space-time evolution can be described by a class of stochastic parabolic nonlinear partial differential equations. The stochastic component we will consider is in the form of additive noise, but other forms of noise such as multiplicative noise may also be incorporated. It will turn out that hierarchical behavior is only one of a class of asymptotic behaviors that can emerge when an out-of-equilibrium system is coarse grained. This phenomenology can be analyzed and described using the renormalization group (RG) [6, 15]. It corresponds to the existence of complex fixed points for the parameters characterizing the system. As is well known (see, for example, Hochberg and Perez-Mercader [8] and Onuki [12] and the references cited there), parameters such as viscosities, noise couplings, and masses evolve with scale. In other words, their values depend on the scale of resolution at which the system is observed (examined). These scaledependent parameters are called effective parameters. The evolutionary changes due to coarse graining or, equivalently, changes in system size, are analyzed using the RG and translate into differential equations for the probability distribution function [8] of the many-body system, or the n-point correlation functions and the effective parameters. Under certain conditions and for systems away from equilibrium, some of the fixed points of the equations describing the scale dependence of the effective parameters can be complex; this translates into complex anomalous dimensions for the stochastic fields and, therefore, the correlation functions of the field develop a complex piece. We will see that basic requirements such as reality of probabilities and maximal correlation lead, in the case of complex fixed points, to hierarchical behavior. This is a first step for the generalization of extensive behavior as described by real power laws to the case of complex exponents and the study of hierarchical behavior.
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A. Guinee, Richard. « Novel Application of Fast Simulated Annealing Method in Brushless Motor Drive (BLMD) Dynamical Parameter Identification for Electric Vehicle Propulsion ». Dans Self-driving Vehicles and Enabling Technologies [Working Title]. IntechOpen, 2021. http://dx.doi.org/10.5772/intechopen.97370.
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Permanent magnet brushless motor drives (BLMD) are extensively used in electric vehicle (EV) propulsion systems because of their high power and torque to weight ratio, virtually maintenance free operation with precision control of torque, speed and position. An accurate dynamical parameter identification strategy is an essential feature in the adaptive control of such BLMD-EV systems where sensorless current feedback is employed for reliable torque control, with multi-modal penalty cost surfaces, in EV high performance tracking and target ranging. Application of the classical Powell Conjugate Direction optimization method is first discussed and its inaccuracy in dynamical parameter identification is illustrated for multimodal cost surfaces. This is used for comparison with the more accurate Fast Simulated Annealing/Diffusion (FSD) method, presented here, in terms of the returned parameter estimates. Details of the FSD development and application to the BLMD parameter estimation problem based on the minimum quantized parameter step sizes from noise considerations are provided. The accuracy of global parameter convergence estimates returned, cost function evaluation and the algorithm run time are presented. Validation of the FSD identification strategy is provided by excellent correlation of BLMD model simulation trace coherence with experimental test data at the optimal estimates and from cost surface simulation.
Actes de conférences sur le sujet "NCF (Noise Correlation Function)"
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Blanchet, Denis, Luca Alimonti et Anton Golota. « Applying Complex Turbulent Cross-Correlation Function to an SEA Side Glass to Predict Interior Wind Noise ». Dans 9th International Styrian Noise, Vibration & Harshness Congress : The European Automotive Noise Conference. 400 Commonwealth Drive, Warrendale, PA, United States : SAE International, 2016. http://dx.doi.org/10.4271/2016-01-1830.
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Miles, Jeffrey. « Separating Direct and Indirect Turbofan Engine Combustion Noise Using the Correlation Function ». Dans 48th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition. Reston, Virigina : American Institute of Aeronautics and Astronautics, 2010. http://dx.doi.org/10.2514/6.2010-19.
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Artyushenko, Vladimir Mikhaylovich, et Vladimir Ivanovich Volovach. « Correlation Functions of the Noise Modulation Function under the Influence of Stationary and Slow Multiplicative Noise ». Dans 2022 International Siberian Conference on Control and Communications (SIBCON). IEEE, 2022. http://dx.doi.org/10.1109/sibcon56144.2022.10003012.
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Pesquera, L., J. M. Noriega et M. A. Rodríguez. « Decay of the Intensity Correlation Function for Dye Lasers with White Gain Noise ». Dans Nonlinear Dynamics in Optical Systems. Washington, D.C. : Optica Publishing Group, 1990. http://dx.doi.org/10.1364/nldos.1990.ndd433.
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We consider a single-mode dye laser model incorporating pump white noise through gain-parameter fluctuations. The relaxation function C(t) is analyzed with the use of a method based on the combination of the low and high frequency expansions of the Laplace transform of C(t). The correlation function is approximated by a superposition of two decaying exponentials. It is found that the intensity correlation function does not show two separated time scales as observed experimentally.
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Zhang, Guangmin, et Yue Song. « Novel imaging method based on cross-correlation function for suppressing the interference of noise ». Dans 2016 IEEE International Conference on Signal and Image Processing (ICSIP). IEEE, 2016. http://dx.doi.org/10.1109/siprocess.2016.7888262.
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Shul’man, A. Ya. « Effect Of Non-Equilibrium Term In Two-Particle Correlation Function On Electron-Phonon Collision Integrals ». Dans UNSOLVED PROBLEMS OF NOISE AND FLUCTUATIONS : UPoN 2005 : Fourth International Conference on Unsolved Problems of Noise and Fluctuations in Physics, Biology, and High Technology. AIP, 2005. http://dx.doi.org/10.1063/1.2138661.
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Alejos, Ana Vazques, et Muhammad Dawood. « Information retrieval and cross-correlation function analysis of random noise radar signal through dispersive media ». Dans SPIE Defense, Security, and Sensing, sous la direction de Kenneth I. Ranney et Armin W. Doerry. SPIE, 2012. http://dx.doi.org/10.1117/12.918775.
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Pralgauskaite, S., J. Matukas, V. Palenskis, E. Sermuksnis et J. Vysniauskas. « Correlation Function Method for Semiconductor Laser Optical Noise Investigation and Fluctuations of Directivity Diagram of Laser Radiation ». Dans 2006 International Conference on Microwaves, Radar & Wireless Communications. IEEE, 2006. http://dx.doi.org/10.1109/mikon.2006.4345134.
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Mann, J. Adin. « Some Fundamentals of Surface Fluctuation Spectroscopy ». Dans Photon Correlation and Scattering. Washington, D.C. : Optica Publishing Group, 1996. http://dx.doi.org/10.1364/pcs.1996.saa.4.
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The technology of surface light scattering spectroscopy1 involves hardware issues in measuring accurately the surface elevation ζq(t), autocorrelation function Rq(t)def¯¯ζ q *(0)ζ q (t) or the corresponding spectrum, G q (ω)=F^ς* q (0)ς q (t)[ω] where q is the wave number of the capillary wave spectrum and ω the frequency. Major issues include the optimization of the optical signal to noise, minimization of environmental noise and deconvolution of Rq(t) from the instrument function. This last issue is of special interest when measuring scattering from small patches wherein qσ < 20, σ is the Gaussian beam width parameter, as is the case when used with Brewster angle microscopy in overlapping footprints.
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Phillips, Ronald L., et Larry C. Andrews. « K-distributed noise from a space-time random process ». Dans OSA Annual Meeting. Washington, D.C. : Optica Publishing Group, 1986. http://dx.doi.org/10.1364/oam.1986.fa4.
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The perturbation of both the spatial and temporal behavior of an optical wave propagating through a random medium is modeled as a Gaussian fluctuating process. We assume the wave has a space-time separable correlation function. We then expand the spatial fluctuations as an orthonormal series over the receiver aperture. Each term of the series represents a single spatial mode. Each of the spatial modes can be expanded as a temporal orthonormal series over the Integration time of the detector. Since the fluctuations of the entire wave are taken to be Gaussian, the coefficients of each term in the space-time series are also Gaussian. If each function within the two series expansions is an eigenfunction of its respective correlation function, the random Gaussian coefficients of the functions are independent.