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Output Feedback Stabilization for a Class of Multi-Variable Bilinear Stochastic Systems with Stochastic Coupling AttenuationZhang, Qichun, Zhou, J., Wang, H., Chai, T. 03 October 2019 (has links)
Yes / In this technical note, stochastic coupling attenuation is investigated for a class of multi-variable bilinear stochastic systems and a novel output feedback m-block backstepping controller with linear estimator is designed, where gradient descent optimization is used to tune the design parameters of the controller. It has been shown that the trajectories of the closed-loop stochastic systems are bounded in probability sense and the stochastic coupling of the system outputs can be effectively attenuated by the proposed control algorithm. Moreover, the stability of the stochastic systems is analyzed and the effectiveness of the proposed method has been demonstrated using a simulated example.
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Les galaxies observées de l'ultraviolet à l'infrarouge. Les résultats du télescope spatial HerschelGiovannoli, Elodie 09 November 2011 (has links)
Ma thèse s'inscrit dans l'étude de la physique extragalactique. Pendant mes trois années de thèse j'ai travaillé sur les méthodes d'ajustement de la distribution d'énergie spectrale des galaxies (ou SED fitting) en effectuant un bilan énergétique entre l'émission en ultraviolet et l'émission en infrarouge. A cet effet j'ai très largement utilisé le code CIGALE (Burgarella et al. 2005, Noll et al. 2009) qui permet d'estimer les paramètres physiques des galaxies à partir de l'analyse de leur émission dans des bandes larges et intermédiares de l'ultraviolet au submillimétrique. J'ai procédé pendant ma thèse à des améliorations de ce code en rajoutant des paramètres d'extinction en sortie et j'ai implémenté plusieurs modèles d'émission de noyaux actifs de galaxies pour compléter les modèles existants.En parallèle de l'étude de la méthode de SED fitting avec des données en bandes larges et intermédiaires, j'ai développé la construction originale d'un catalogue de galaxies artificielles, dont le but est de déterminer la fiabilité des paramètres de sortie du code CIGALE et des codes de SED fitting en général. La technique du SED fitting m'a permis d'analyser plusieurs échantillons de galaxies dans l'univers proche et dans l'univers lointain possédant des données multi longueurs d'onde. Pratiquement j'ai travaillé avec des données allant de l'ultraviolet (GALEX) à l'infrarouge lointain avec les téléscopes spatiaux AKARI et Herschel. Les données AKARI couplées à des données ancillaires ont été à la base d'une étude de galaxies de l'univers local pour lesquelles j'ai pu déterminer la quantité d'atténuation.J'ai également travaillé avec les données Herschel en tant que membre des consortiums HerMES et GOODS-H. Dans le cadre du projet GOODS-H j'ai participé à la mise en évidence et à l'étude du "bump" à 2175 A d'un échantillon de galaxies distantes ainsi qu'à la formulation d'une loi d'atténuation pour ces objets. Dans le cadre d'un groupe de travail sur le SED fitting au sein d'HerMES j'ai participé à l'étude d'un échantillon de galaxies avec 0<z<3 afin de déterminer la fiabilité des paramètres physiques estimés par différents codes de SED fitting.Une partie de ma thèse a été consacrée à l'étude de galaxies distantes et lumineuses en infrarouge et à la détermination des caractéristiques physiques de ces objets grâce au code CIGALE. L'étude des paramètres de formation stellaire et d'atténuation ont fait l'objet d'un article, Giovannoli et al. (2011) paru dans la revue scientifique A&A. Toujours dans le cadre du projet HerMES j'ai pu avoir accès aux données du télescope spatial Herschel pour ces objets et donc poursuivre mon étude afin de déterminer l'importance des données infrarouges et submillimétriques pour l'étude des galaxies à haut redshift. / My PhD thesis takes part of extragalactic physics. During three years I have worked on the fit of the spectral energy distribution (SED fitting) of galaxies by doing an energetic budget between the emission at ultraviolet wavelengths and the one at infrared wavelengths. I have extensively used the code CIGALE (Burgarella et al. 2005, Noll et al. 2009) allowing to estimate the physical parameters of galaxies from their broad bands and intermediate bands emission from ultraviolet wavelengths to submillimetric wavelengths. During my thesis I have improved this code by adding output parameters and several templates of active galactic nuclei to those already available.While I have studied the SED fitting technics I have also built original mock catalogues of galaxies to determine the reliability of the output parameters of CIGALE and, more generally, the reliability of parameters estimated by SED fitting codes.I have used the SED fitting method to analyse several samples of galaxies from low redshift to high redshift, with multi wavelength detections. I have used data from the ultraviolet (GALEX) to the far infrared using data from AKARI and Herschel space observatory. I have matched the AKARI data to ancillary data at other wavelengths to study nearby galaxies and determine their dust attenuation quantity. I have used Herschel data as part of HerMES and GOODS-H consortium members. In the framework of the GOODS-H project I have worked on the determination and the study of the so-called ultraviolet bump at 2175 A for a sample of high-redshift galaxies, and on the formulation of an attenuation law for these objects. In the framework of HerMES I have worked with the SED fitting working group to study a sample of galaxies with 0<z<3 to determine the reliability of the physical parameters of these objects estimated with differents SED fitting codes.A part of my thesis was devoted to the study of a sample of distant galaxies, luminous at infrared wavelengths. I have determined the physical parameters of these objects thanks to the code CIGALE. The study of the star formation parameters and the attenuation parameters has been published in Giovannoli et al. (2011), in the scientific journal A&A. With the HerMES project I could have access to Herschel data for these luminous galaxies and pursue my study to determine the importance of far infrared data to study high-redshift galaxies.determine the importance of far infrared data to study high-z galaxies.
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Estimating attenuation properties of bentonite layer in Cut Bank oil field, Glacier County, MontanaKarakurt, Necdet 12 April 2006 (has links)
Acquisition and interpretation of 3-D seismic data led DeAngelo and Hardage (2001)
to describe the channel system in the south central Cut Bank area in Glacier County,
Montana. The presence of a low velocity layer called Bentonite was also discovered
in the area with the help of well-logs. Bentonite is a volcanic ash, which lies on both
sides of the channel system and is absent within the channel. DeAngelo and Hardage
(2001) shot a vertical seismic profiling (VSP) survey at well # 54-8 to analyze the
formation structure in depth, since seismic signals around the reservoir area were
unclear in the 3-D survey.
This research attempts to estimate the attenuation properties of the Bentonite
layer in the Cut Bank oil field. VSP data is processed for velocity information and
estimation of seismic Q using the spectral ratios method (SRM). The SRM theoretically
assumes that the propagating signal is a plane seismic wave traveling vertically
from one point to another in a homogeneous model. The amplitudes at the start
and end points are known and relate to each other with the attenuation coefficient in
a frequency range. The relation between the seismic amplitudes at z distance from
each other can be expressed as a linear function of frequency after a few modifications.
SRM uses the linearity of the logarithmic ratio of the seismic amplitudes over
a frequency range. In theory, ratios plotted against a frequency range must produce
a flat line. However, in practice, the logarithmic ratios are expected to draw an approximate
line (curve), where some of the data points deviate from the origin of the
line. Thus fitting a line to the ratios curve and calculating the slope of this curve are
necessary. Slope of the curve relates to the seismic attenuation coefficient and further
to the seismic Q.
The SRM results suggest that Bentonite may have a Q value as low as 5. This
highly attenuative and thin (20 to 40 feet throughout the south central Cut Bank
Unit) layer alters seismic signals propagating through it. A thorough analysis of
the amplitude spectra suggests that seismic signals dramatically lose their energy
when they pass through Bentonite. Low energy content of the signals below the Bentonite layer highlights that the recovery of the seismic energy is less likely despite
the presence of multiples, which are known to affect the seismic signals constructively.
Therefore, separation of reflected events is a greater challenge for the thin reservoir
sand units lying underneath the Bentonite layer. Thus the Bentonite layer in the
Cut Bank oil field has to be taken seriously and data processing should be done
accordingly for better accuracy.
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In situ bioremediation and natural attenuation of dinitrotoluenes and trinitrotolueneHan, Sungsoo 09 June 2008 (has links)
Contamination of soils and groundwater with nitroaromatic compounds such as 2,4,6-trinitrotoluene (TNT) and dinitrotoluenes (DNTs) has drawn considerable attention due to widely distributed contamination sites and substantial efforts for cleanup. Two isomers of DNT, specifically 2,6-dinitrotoluene (2,6-DNT) and 2,4-dinitrotoluene (2,4-DNT), occur as soil and groundwater contaminants at former TNT production sites. The discovery of bacteria that use DNT isomers as electron donors has encouraged bioremediation at contaminated sites. Current work is extending the existing engineered bioremediation to naturally occurring in situ biodegradation and focuses on the application of natural attenuation (NA) as a remediation strategy for residual DNT at contaminated sites.
More specifically this research evaluated factors influencing in situ bioremediation of DNTs and TNT in surface soils, vadose zones, and saturated medium. Applications involving surface soils and vadose zones investigated the potential of water infiltration to promote in situ bioremediation. Studies in saturated media were more applicable to NA. Factors that were also considered in studies conduced included: 1) the presence and distribution of degrading microbes in field soils (Barksdale, WI); 2) the dissolution and bioavailability of contaminants in historically contaminated soils; and 3) the effect of mixtures of contaminants (i.e., DNTs and TNT) on biodegradation processes.
This research provided information useful for practitioners considering an in situ bioremediation NA as a remedial solution for contaminated sites. Under the condition simulating downflow of surface waters or rainwater, the rapid rate of DNT degradation could be facilitated by the availability of oxygen in the soil gas without concern of toxicity (i.e., nitrite evolution and pH drop) and addition of nutrients. As a result, in situ bioremediation or NA should be strongly considered as a remedial option for Barksdale soils and similar sites where relatively low concentrations of DNT isomers are present as contaminants. At TNT contaminated sites TNT was not mineralized by indigenous microorganisms despite oxidative biotransformation, and mixed culture capable of growth on DNT also could not develop the mineralization of TNT during DNT degradation. This suggests that the mixtures of contamination did not improve the potential for in situ TNT bioremediation.
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[en] DYNAMIC ANALYSIS OF RAIN ATTENUATION IN TROPICAL REGIONS / [pt] ANÁLISE DA DINÂMICA DA ATENUAÇÃO POR CHUVAS EM REGIÕES TROPICAISMARIA CRISTINA QUESNEL DE FLAINVILLE RAMOS 09 July 2008 (has links)
[pt] O principal efeito causador de indisponibilidade em sistemas de rádio comunicações com freqüências superiores a 10 GHz é a atenuação por chuvas, especificamente a chuva convectiva, que é predominante em climas tropicais. Nesta tese será realizado o estudo e modelagem do comportamento dinâmico da atenuação por chuvas em enlaces terrestres e via satélite, com base em medidas realizadas no Brasil.
Os aspectos dinâmicos da atenuação relacionam-se com as funções de distribuição de probabilidade de três variáveis aleatórias: a taxa de variação da atenuação com o tempo, o número de eventos em que um certo nível de atenuação é excedido e as durações individuais destes eventos. Em outras palavras, trata-se de
problema de cruzamento de níveis aplicado à série temporal da atenuação. Ao contrário da distribuição cumulativa da atenuação, da qual informação que pode ser efetivamente retirada é limitada, a análise estatística de cada nível de atenuação, em separado, provê uma completa caracterização do fenômeno da atenuação servindo de base para aplicações tais como a construção de técnicas adaptativas de controle de ganho, metodologias de adaptação do sinal por códigos, modulações ou taxas de bits e a elaboração de esquemas de diversidade de rotas, espaço, sítio ou tempo. Utilizando o banco de dados de medidas de
atenuação por chuvas em regiões tropicais e equatoriais brasileiras, obtido em medidas realizadas em seis localidades, tanto em enlaces terrestres como via satélite, foram analisados neste trabalho os comportamentos estatísticos da taxa de variação temporal da atenuação e da duração de eventos. Foi tratado, ainda, o problema do cruzamento de níveis aplicado ao conceito de disponibilidade. A informação obtida a partir dos resultados da análise dinâmica pode ser usada, como já mencionado, no tratamento de
vários problemas fundamentais do projeto de sistemas de comunicações. A tese tem, também, como objetivo, contribuir para o aumento da base mundial de dados da análise da dinâmica da atenuação, principalmente em climas tropicais e equatoriais, onde tais dados são bastante escassos. / [en] The main effect causing non-availability in radio
communication systems
operating in frequencies above 10GHz, is the rain
attenuation, particularly the heavy
convective rain that is predominant in tropical regions.
This thesis presents a detailed
study and modelling of the dynamics of rain attenuation in
terrestrial links and earthspace
links, based on data obtained in long-term experimental
measurements in Brazil.
The dynamic aspects of rain attenuation can be described by
probability distribution
functions of three variables: the rate of change of the
attenuation with time (fade slope),
the number of events of a certain level of attenuation to
be exceeded and the individual
duration of these events. In other words, the level
crossing applied to the attenuation
time series. In contrast to the cumulative distribution of
the attenuation, from which
limited information can effectively be obtained, the
separate statistical analysis of each
level of attenuation can provide a complete understanding
of the phenomenon, allowing
the development of adaptive power control techniques,
methods for signal adaptation
using codes, modulation or bits rate and the design of
spacial, routing, site and time
diversity strategies. The work is based on rain attenuation
data measured in terrestrial
and earth-space links operating at frequencies above 10 GHz
in 6 Brazilian locations.
The study includes the analysis and modelling of the
statistical behaviour of the rate of
variation of the attenuation with time and the event
durations. Also considered, is the
level crossing problem applied to the availability concept.
As mentioned, the
information obtained from the dynamic analysis results and
modelling can be used for
the treatment of various fundamental problems in the radio
communication system
project. A contribution to increase the database of dynamic
attenuation mainly in
tropical and equatorial climates, where data is scarce, is
also a result of this thesis.
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Nouvelle approche de la correction de l'atténuation mammaire en tomoscintigraphie de perfusion myocardique / New approch of breast attenuation correction in SPECT myocardial perfusion imagingChamouine, Saïd Omar 12 December 2011 (has links)
Nous proposons dans le cadre de cette thèse une nouvelle approche permettant de s'affranchir de l'atténuation mammaire en tomographie par émission monophotonique (TEMP) de perfusion myocardique. Elle est constituée de deux parties : - la première consiste à rendre les projections acquises consistantes. - la deuxième consiste à pondérer ces même les projections corrigées durant la reconstruction. Nous avons effectué l'étude de validité de nos méthodes sur quelques exemples de simulation TEMP de perfusion myocardique simulant l'atténuation mammaire et sur quelques exemples d'études patients réelles notamment : des cas d'atténuation mammaire, d'infarctus inférieure, d'infarctus apical, d'infarctus antérieur, d'ischémie antérieure et inférieure. Les résultats semblent encourageants. Il s'agit dans le proche avenir de mener une étude de validation chez les patients versus un gold standard (coronarographie, coroscanner) / We propose in this thesis a new approach to correct the breast attenuation in SPECT myocardial perfusion imaging. It consists of two parts: -The first is to make the acquired projections consistent with each other. - The second is to weight the corrected attenuated projection during the reconstruction. We conducted a validation of our methods on some examples of myocardial perfusion SPECT imaging simulating the breast attenuation and some examples of real patient studies including: breast attenuation, anterior myocardial infarction, inferior myocardial infarction, anterior myocardial ischemia and inferior myocardial ischemia. The obtained results are encouraging. At this step, it is interesting in the near future to conduct a validation study in patients versus a gold standard (angiography, coroscan).Key words: SPECT, tomographic reconstruction, breast attenuation, Iterative reconstruction, attenuation correction, myocardial perfusion imaging, nuclear medicine
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[en] COVERAGE PLANNING OF BROADBAND ACCESS NETWORKS OPERATING AT FREQUENCIES ABOVE 20 GHZ / [pt] PLANEJAMENTO DE COBERTURA DE SISTEMAS DE RÁDIO ACESSO EM BANDA LARGA OPERANDO ACIMA DE 20 GHZGUSTAVO PINHEIRO MACHADO 19 February 2004 (has links)
[pt] Os sistemas de rádio acesso em banda larga em freqüências
superiores a 20 GHz oferecem soluções de alta velocidade,
vídeo, áudio e multimídia sendo, portanto, alternativas aos
sistemas cabeados para acesso à última milha. Nestas
faixas de freqüências, os sistemas de rádio acesso em banda
larga utilizam enlaces do tipo ponto-multiponto na direção
de descida e ponto-a-ponto na subida, com configurações
semelhantes às encontradas nas redes celulares. Entretanto,
devido as altas freqüências utilizadas, os enlaces operam
apenas em visibilidade e o principal problema de propagação
encontrado é a atenuação por chuvas, que afeta fortemente o
nível do sinal recebido reduzindo a cobertura e o
desempenho do sistema. Neste trabalho é desenvolvida uma
ferramenta computacional com a finalidade de simular
o cálculo de cobertura, de capacidade e da disponibilidade
de sistemas de rádio acesso em banda larga utilizando os
modelos de previsão de atenuação por chuvas do ITU-R e do
CETUC, incluindo também efeitos de atenuação diferencial. A
inclusão deste último efeito permite tratar de forma
completa o problema da atenuação por chuvas em enlaces
convergentes e determinar a degradação total na relação
sinal-interferência do sistema. / [en] Broadband wireless access systems in frequencies above 20
GHz can provide a simple and effective solution for high
speed, video, audio and multimedia service providers being
an excellent alternative to cable systems for the last
mile. At these frequencies bands, the broadband radio
access system uses point to multipoint link in the downlink
direction and point to point in the uplink. The
configuration is similar to those of cellular networks.
However, at these high frequencies the links are line-of-
sight and the main problem is rain attenuation, that
seriously affects the received signal level reducing
coverage and system performance. In this work a
computational tool is developed with the purpose of simula-
ting coverage prediction, capacity and system availability
calculations using models for rain attenuation prediction
developed by ITU-R and CETUC. Also considered is the effect
of differential attenuation, what allows a complete
treatment of rain effects in point to multipoint links and
the calculation of the total degradation in the signal to
interference ratio.
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L'atténuation sismique dans le manteau terrestre / Seismis attenuation in the Earth's mantleDurand, Stéphanie 26 October 2012 (has links)
Cette thèse s’intéresse à divers aspects de l’atténuation sismique dans le manteau terrestre et aux implications de celle-ci quant à la structure de ce dernier. L’enjeu est de mieux comprendre les mécanismes d’atténuation ainsi que les mesures que l’on peut effectuer afin d’améliorer les modèles radiaux d’atténuation dont on dispose et in fine l’interprétation des modèles de tomographie. Je me suis concentrée sur deux exemples de mécanismes d’atténuation, appartenant à deux grands types d’atténuation : l’atténuation intrinsèque, liée à l’absorption par le milieu d’une partie de l’énergie sismique dissipée irréversiblement sous forme de chaleur, et l’atténuation extrinsèque, liée à la dispersion de cette énergie par le milieu. Dans le premier cas, j'ai regardé l’effet des transitions de phase sur l’atténuation des ondes sismiques. En appliquant un modèle thermomécanique développé par Ricard et al., 2009, pour prédire l’atténuation des ondes sismiques liée à la transition de phase uniquement et en comparant les valeurs obtenues aux mesures dont on dispose, j'ai pu contraindre la cinétique d’une transition de phase mantellique. Dans le second cas, j'ai testé l’effet de l’anisotropie comme mécanisme d'atténuation apparente, le but étant de trouver une distribution statistique d’orientation d’anisotropie pouvant reproduire la quasi-constance du facteur de qualité Q avec la fréquence, observée en sismologie et lors d’expériences de laboratoire (Knopoff, 1964), et aujourd’hui expliquée par un modèle ad-hoc seulement (Liu, 1976).Enfin, je me intéressée à mesurer cette atténuation sismique sur des enregistrements réels. Après avoir testé la méthode dite de la fréquence instantanée (Ford et al., 2012), je me suis concentrée sur deux régions, l’Amérique centrale et l’Alaska pour l'appliquer. Ces mesures sont ensuite interprétées en termes de modèle radial d’atténuation révélant un manteau inférieur hétérogène atténuant. Je montre aussi qu’une origine compositionnelle est la plus probable pour expliquer ces anomalies d’atténuation. / This thesis is devoted to various aspects of seismic attenuation in the Earth's mantle and the consequences on the mantle structure. The challenge is to better understand the attenuation mechanisms, as well as the measurements that can be done, in order to improve the published radial profiles of attenuation and in fine the interpretation of tomographic models.I focus on two examples of attenuation mechanisms, belonging to two kinds of attenuation: the intrinsic attenuation related to the absorption by the medium of a part of the seismic energy then irreversibly dissipated as heat, and the extrinsic attenuation related to the dispersion of the seismic energy by the medium. In the first case, I investigate the effect of phase transitions upon seismic attenuation. Applying the thermo-mechanical model developped by Ricard et al., 2012, to calculate the attenuation of seismic waves due to the phase transition only and comparing the obtained values to published measurements, I succeed in constraining the kinetics of a mantle phase transition. In the second case, I test the seismic anisotropy as a mechanism of extrinsic attenuation, the aim being to find a statistical distribution of anisotropy orientation and layer thicknesses that can reproduce the observed quasi-frequency independence of Q in seismology and laboratory experiments (Knopoff, 1964), and which is, today, only explained by an ad-hoc model (Liu, 1976).Finally, I was interested in measuring the seismic attenuation on real seismograms. After having tested the method of the instantaneous frequency (Ford et al., 2012), I applied it to seismic records sampling the mantle below Central America and Alaska. These measurements are then inverted for a radial profile of shear attenuation which reveals the existence of an attenuating zone in the lower mantle. I also show that these attenuation anomalies are likely to be of chemical origin.
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Factors influencing natural attenuation of dinitrotoluenes in surface soils: Badger Army Ammunition Plant a case studyTulsiani, Urvi Kotak 18 July 2005 (has links)
Factors influencing natural attenuation of dinitrotoluenes (DNT) in surface soils and the application of monitored natural attenuation (MNA) as a remediation strategy were examined using contaminated soils from Badger Army Ammunition Plant (BAAP). Based on the previous research involving contaminated media obtained from locations at BAAP, and the fact that groundwater at the site is not contaminated, it seemed likely that aerobic biodegradation of DNT is active without intervention, and that natural attenuation may be an effective strategy for managing the contamination that exists at BAAP. Microcosms showed that microbes indigenous to soils are capable of 2,4-DNT mineralization and that DNT will adsorb reversibly and become bioavailable. In column studies 2,4-DNT biodegradation was observed and the nitrite evolved during DNT degradation was presumably removed due to oxidation by nitrite oxidizers. The use of simulated rainwater as influent with no nutrient amendments suggests that nutrients do not limit the biodegradation of low concentrations of DNT in the soil tested. In the chemostat study carried out to study effect lowering of temperature (22㬠15㬠10㬠7.5㠡nd 4㩠on biodegradation of DNT at hydraulic retention time of 2.5 days, no sustained change in the DNT substrate removal was observed with change in temperature, but it had a large effect on the nitrite oxidizers. This suggests that the seasonal fluctuations in temperature will have minimal effect on the DNT removal via biodegradation at temperatures above 0㮠Nitrite oxidizers were active at 22㬠their activity decreased at 15㠡nd ceased at temperatures 10㠡nd lower. Nitrite is generally taken as a line of evidence for biodegradation of DNT. The results from the soil column study and chemostat showed that nitrite measurement should not be always taken as a conclusive indicator of DNT degradation. It should be taken into consideration that absence of nitrite does not necessarily mean absence of DNT biodegradation (probably at high temperatures).
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Array-Based Measurements of Surface Wave Dispersion and Attenuation Using Frequency-Wavenumber AnalysisYoon, Sungsoo 20 July 2005 (has links)
Surface wave methods have been used to determine dynamic properties of near-surface soils in geotechnical engineering for the past 50 years. Although the capabilities of engineering surface wave methods have improved in recent years due to several advances, several issues including (1) near-field effects, (2) combined active and passive measurements, and (3) accurate measurements of surface wave attenuation still require study to further improve the capabilities of modern surface wave methods.
Near-field effects have been studied for traditional surface wave methods with two receivers and several filtering criteria to mitigate the effects have been recommended. However, these filtering criteria are not applicable to surface wave methods with multiple receivers. Moreover, the criteria are not quantitatively based and do not account for different types of soil profiles, which strongly influence near-field effects. A new study of near-field effects on surface wave methods with multiple receivers was conducted with numerical and experimental methods. Two normalized parameters were developed to capture near-field effects. Quantitatively based near-field effect criteria for an ideal homogeneous half-space and three typical soil profiles are presented.
Combining active and passive surface wave measurements allows developing a shear wave velocity profile to greater depth without sacrificing the near-surface resolution offered by active measurements. Generally, active and passive measurements overlap in the frequency range from approximately 4 to 10 Hz, and there are often systematic differences between the two measurements. The systematic errors in active and passive surface wave methods were explored to explain and resolve the differences, allowing for a more accurate composite dispersion curve.
The accuracy of measured surface wave attenuation is improved by properly accounting for (1) geometric spreading, (2) near-field effects, and (3) ambient noise. In this study, a traditional estimation method and a frequency-wavenumber method utilizing sub-arrays were investigated using displacement data from numerical simulations, focusing on near-field and ambient noise effects. Detailed procedures for the frequency-wavenumber estimation method are developed based on a study of the primary factors affecting attenuation estimates. The two methods are also evaluated using experimental displacement data obtained from surface wave field measurements with three different arrays.
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