Dissertations / Theses on the topic 'Signals attenuation'

Low frequency volcanic earthquakes, characterised by slowly decaying harmonic codas of 0.5-5Hz, have been observed on many volcanoes and are considered key tools in monitoring and eruption forecasting. The common element in a variety of models proposed for the origin of these earthquakes is resonance of a fluid body within a volcanic edifice. The source of the resonance is believed to consist of dispersive interface waves, trapped at the fluid-solid boundaries. The amplitude decay or attenuation of these earthquake signals can be decomposed into radiative and intrinsic components, and in this way yield information about both the geometry and fluid properties of the resonating source body. This thesis presents a study of the attenuation of low-frequency volcanic earthquakes, with particular emphasis on quantitatively linking seismic signals to magmatic processes and properties. The effect of the intrinsic attenuation of the fluid on the amplitude decay of low-frequency volcanic earthquakes is examined using a viscoelastic finite-difference model of seismic wave propagation. It is shown that the viscosity of the fluid contributes 23.6±2.26% less than previously thought to the apparent attenuation, and that its effect may have been substantially overestimated in previous studies. A physical explanation for this lies in understanding the fundamental differences between acoustic and interface waves. An analytical approach demonstrates that, for a set of realistic volcanic parameters, interface waves can be attenuated less than acoustic waves in a pure melt, if the longitudinal viscosity is at least 107 Pas. These results widen the set of possible resonators and imply that resonating volcanic conduits filled with high viscosity magma are viable sources for low-frequency seismicity. An automated method to measure the apparent attenuation of seismic signals is developed, tested, and applied to a dataset of low-frequency earthquakes from Soufri`ere Hills Volcano, Montserrat. Temporal trends in attenuation are observed and quantitatively interpreted as changes in magma viscosity. An estimate of the magma shear viscosity of 2.3 ± 2 × 105 Pas is obtained, demonstrating the ability of seismological data to place constraints on the magma properties.

International Telemetering Conference Proceedings / October 28-31, 1996 / Town and Country Hotel and Convention Center, San Diego, California
This paper presents the interim results of an effort to corroborate analytic model predictions of the effects of rocket motor plume on telemetry signal RF propagation. When space is available, telemetry receiving stations are purposely positioned to be outside the region of a rocket motor's plume interaction with the RF path; therefore, little historical data has been available to corroborate model predictions for specific rocket motor types and altitudes. RF signal strength data was collected during the flight of HERA target missile by White Sands Missile Range (WSMR) using a transportable telemetry receiving site specifically positioned to be within the rocket plume region of influence at intermediate altitudes. The collected data was analyzed and compared to an RF plume attenuation model developed for pre-mission predictions. This work was directed by the US Army Kwajalein Atoll (USAKA)/ Kwajalein Missile Range (KMR) Safety Division.

Les ondes acoustiques subissent peu de dispersion dans le milieu marin, comparé au milieu aérien. Certaines espèces de cétacés communiquent ainsi à grande distance, d'autres utilisent leurs émissions sonores pour s'orienter. La bioacoustique consiste à étudier ces espèces à partir de l'analyse de leurs sons, c'est-à-dire à les détecter, classer, localiser. Cela peut se faire via un réseau d'hydrophones au déploiement fastidieux. Afin de contribuer au passage à l'échelle de la bioacoustique, cette thèse propose des modèles originaux mono-hydrophone pour l'analyse de ces signaux stationnaires ou transitoires. Premièrement, nous dérivons un nouveau modèle d'estimation de la distance entre une source impulsive (ex. biosonar) et un hydrophone. Notre modèle théorique, l'Intra Spectral ATténuation(ISAT), dérive des lois acoustiques de déformation spectrale du signal transitoire induite par l'atténuation durant sa propagation. Ce modèle relie les rapports énergétiques des bandes de fréquences pondérés par un modèle de perte par atténuation fréquentielle (Thorp ou Leroy) à la distance de propagation. Nous approximons aussi ISAT par un modèle neuromimétique. Ces deux modèles sont validés sur le sonar du cachalot (Physeter macrocephalus) enregistré avec notre bouée acoustique autonome BOMBYX et notre système d'acquisition DECAV en collaboration avec le Parc National de Port-Cros et le sanctuaire Pelagos pour la protection des mammifères marins en Méditerranée. Les mesures d'erreur (RMSE) d'environ 500 mètres sur nos références du centre d'essai OTAN aux Bahamas présentent un intérêt opérationnel. Deuxièmement, nous proposons une analyse originale de l'évolution des voisements de cétacé par codage parcimonieux. Notre encodage des cepstres par apprentissage non supervisé d'un dictionnaire met en évidence l'évolution temporelle des bigrammes des chants que les baleines à bosse mâles émettent durant la période de reproduction. Nous validons ce modèle sur nos enregistrements du canal de Sainte-Marie à Madagascar entre 2008 et 2014, via notre réseau d'hydrophones BAOBAB qui constitue une première dans l'Océan Indien. Nos modèles s'inscrivent dans le projet Scaled Bioacoustics (SABIOD, MI CNRS) et ouvrent de nouvelles perspectives pour les passages à l'échelle temporelle et spatiale de la bioacoustique
Acoustic waves show low dispersion due to the underwater propagation, compared to the propagation in the air. Some species of cetaceans communicate at long distance, others use their sound production for orientation. The goal of the scientic area called bioacoustics is to study animal species based on the analysis of their emitted sound. Their sounds can be used to detect, to classify and to locate the cetaceans. Recordings can be done with an passive acoustic array of multiple hydrophones, but this method is expensive and difficult to deploy. Thus, in order to scale this approach, we propose in this Phd thesis several original single hydrophone models to analyze these stationary or transient signals.Firstly, we provide a new theoretical model to estimate the distance between the impulsive source (ex. biosonar of the cetacean) and the hydrophone. Our model, the Intra Spectral ATtenuation (ISAT), is based on the spectral signal alteration due to the underwater acoustic propagation, especially the differences in different frequency bands. We also approximated ISAT by an artificial neural network. Both models are validated on clicks emitted by sperm whales (Physeter macrocephalus) recorded by our sonobuoy BOMBYX and our data-acquisition system DECAV developed incollaboration with the National Park of Port-Cros (France) and the Pelagos sanctuary for the protection of marine mammals in the Mediterranean sea (France). The error (RMSE) measures on the recordings of the NATO test center in the Bahamas are about500 meters, promising further real applications. Secondly, we worked on the variations of the cetacean vocalizations using the sparse coding method. The encoding of thecepstrums by unsupervised learning of a dictionary shows bigrammic time changes of the songs of humpback whales (Megaptera novaeangliae). We validate this model on signals recorded in the Ste Marie Channel (Madagascar) between 2008 and 2014, through our network of hydrophones BAOBAB which is the first passive acoustic array deployed in the Indian Ocean.Our models are part of the Saled Bioacoustics project (SABIOD, MI CNRS) and open perspectives for temporal and spatial scaling of bioacoustics

Thesis (MScEng)--University of Stellenbosch, 2001,
ENGLISH ABSTRACT: A frequency domain Power Line Carrier (PLC) simulation program, with the ability to simulate signal attenuation including the coupling equipment, was developed. This simulation program was put to the test against the independent program of Professor L.M. Wedepohl and against practical field measurements. The predictions of the two programs were in precise agreement for a wide range of input parameters. Results from the field tests and predictions also showed close agreement. Further investigations, applying the simulation program, explained how ground conductors and soil resistivity influences PLC signal propagation. An experiment, which was developed to monitor PLC signal attenuation, was installed on the PLC system between Koeberg power station and Acacia substation, both near Cape Town. Data logged continuously over 28 days, indicated measurable and deterministic PLC signal attenuation variations with typical time constants of a few hours. Simulations of the PLC system indicated that the signal amplitude variations were influenced by changes in the height above the ground plane of the phase conductor. This significant finding creates the possibility to obtain real time knowledge of the sag of an Over Head Transmission Line (OHTL) by exploiting an operational PLC system. The knowledge about real time sag can be used in economical dynamic ampacity control systems. The practical and financial benefits to the electricity supply and distribution industry can be significant.
AFRIKAANSE OPSOMMING: 'n Frekwensie gebied "Power Line Carrier" (PLC) simulasie program wat die sein verswakking en die koppeling verliese kan naboots, is ontwikkel. Die program is getoets teen die onafhanklike program van Professor L.M. Wedepohl asook praktiese metings in die veld. Die vooruitskatings van beide programme is presies die selfde vir 'n wye reeks van parameters. Metings en nabootsings het ook noue ooreenstemming getoon. Verdere ondersoek, m. b. v. die program, is gedoen ten einde te verduidelik hoe grond-geleiers en grond weerstand die PLC sein se voortplanting beïnvloed. 'n Eksperiment om die PLC sein se verswakking mee te monitor is ontwerp. Die eksperiment was geïnstalleer in die PLC stelsel tussen Koeberg kernkragstasie en Acacia substasie, naby Kaapstad. Die eksperiment was vir 28 dae geaktiveer en die data wat die eksperiment opgelewer het toon meetbare PLC sein verswakking met tyd konstantes van 'n paar uur. Verdere nabootsings het gewys dat die veranderende verswakking in die PLC seinsterkte toegeskryf kan word aan die wisseling in hoogte van die fase geleiers bo die grondvlak. Hierdie bevinding is van besondere belang aangesien dit die moontlikheid oopmaak om die gemiddelde sak van kraglyne in reële tyd en onder bedryfs toestande te kan meet. Die informasie van die reële sak van kraglyne kan gebruik word in effektiewe stroomdrae-vermoë beheer stelsels. Die praktiese en finansiële voordele wat krag voorsieners en verspreiders hieruit kan put kan aansienlik wees.

This Master´s thesis focuses on design and implementation of programmable attenuator. The main aim of this thesis is to create an electronical device that provide continuous setting of attenuation value in the range between 0–150 dB. Setting a value from the range can be performed using buttons and set values are shown on display. For this thesis an attenuator with working frequency between 0–6 GHz was chosen and four–layer printed circuit board was designed. As a result the device is fitted with an 8bit microcontroller ATmega328P–PU using five 6bit digital attenuators connected in series with manual and program settings of attenuation from 0–157,5 dB with step of 0,5 dB. Data are shown on a build–in display. The application for remote settings and value reading over integrated USB (Universal Serial Bus) interface, was created in C#. In conclusion of this thesis there is a measurement evaluation of attenuation measurement performed on the device.

In this study, the weather impact on lidar signals has been researched. A lidar system was placed with a target at approximately 90 m and has together with a weather station collected data for about a year before this study. By using the raw detector data from the lidar, the full waveform can be obtained and the amplitude of the return pulse can be calculated. Atmospheric attenuation of lidar signals is often modeled using the lidar equation, which predicts an exponential decrease in energy over the distance. The factor in the exponent is referred to as the extinction coefficient and it is the main property studied in this thesis. By utilizing models for the extinction coefficient under different weather conditions, it is possible to simulate the performance of the lidar.  The extinction coefficient was calculated using different empirical models. The empirical models investigated in this thesis are the Kim and Kruse models for known visibility, the Al Naboulsi model for different types of fog with known visibility, the Carbonneau model for known precipitation amount in rainy conditions, and a similar model for snowy conditions. For the case of rain, a physical model was also used, which is derived through Mie theory. The physical model requires a particle size distribution, which is the number of particles of a certain radius per unit volume. A particle size distribution for rain was generated using the Ulbrich raindrop size distribution, using the precipitation amount recorded by the weather station. Particle size distributions for radiation and advection fog were also simulated.  The measured attenuation in lidar signals was compared to the predicted attenuation that was calculated using different models for the extinction coefficient in the lidar equation. Generally, the models tend to underestimate the amplitude of the return pulse. This can partially be explained by the assumptions used to derive the lidar equation, which neglects all augmentation of the beam. The visibility models gave more accurate results compared to the precipitation models. This was expected, since visibility is defined as a measure of attenuation and precipitation amount is not.  When a lidar signal is emitted, the light will be reflected from optical surfaces within the lidar and cause a pulse to be detected. This pulse is referred to as the zeropulse. In the first couple of meters of the transmission, we expect to see some backscattered light from adverse weather, since the detector has a larger solid angle at shorter distances. This returned light will be combined with the zeropulse and cause it to expand in width. By examining the zeropulse, it was possible to observe a difference between the average zeropulse under some different weather conditions. This leads to the conclusion that it may be possible to extract some information about current weather conditions from the zeropulse data, given that there is little ambient light and snowy weather conditions.  By integrating the zeropulse, variations in the shape of the zeropulse could be described by a single value. Then by separating the data into low and high visibility populations, the zeropulse integral could be used to predict the visibility. The conclusion was that the zeropulse integral can accurately predict whether visibility is above or below a threshold value, given that there is little ambient light and the visibility is known to be below 19950 m.

Engineering advancement over the last decade has significantly benefited the medical field, facilitating personalised and accessible healthcare. Various portable systems have been developed to obtain diagnostic parameters without the necessity for sedation or immobilisation of the patient, and even their presence at the medical facility. This can be especially important for populations that are at greater medical risk and are unable to undergo sedation, as well as for overall screening of the underlying conditions by continuous monitoring. This thesis provides engineering solutions aimed at improving the reliability of one of the modern medical diagnostic techniques – Wireless Capsule Endoscopy (WCE). It is a non-invasive approach for gastrointestinal (GI) tract examination that involves the natural propagation of a capsule through the entire tract of the patient while recording images of the lining. The video data are transmitted to a receiving unit outside the body, which is then accessed by medical practitioners for appropriate diagnostics. The Wireless Body Area Network (WBAN) technology describes the acquisition and transmission of the signal. One of the major challenges associated with WCE is the accurate localisation of the capsule due to the transit time being different for each individual. Localisation methods based on various physical principles are still under investigation by researchers. In this study, radiofrequency (RF) signal propagation analysis was used to provide accurate received signal strength (RSSI)-based localisation of the wireless endoscopy capsule. RSSI-based methods are widely used in indoor and outdoor positioning systems, allowing the estimation of the radial distance between reference sensors and an unknown transmitter position. Due to the significantly different electromagnetic (EM) properties of the human body as a propagation medium compared to air, one of the main objectives of this work was to develop an appropriate path loss propagation model. The advantage of the proposed solution is that it is based on an analytical approach and includes the attenuation constant defined by the EM properties of the soft tissues in the abdominal area. The theoretical basis of the developed attenuation path loss model (APLM) can be used to generalise and implement it for various In-to-On-Body communication systems at different operational frequencies. The APLM was numerically validated using CST Studio Software©, as well as by experiments on ex-vivo porcine tissues and in-vivo measurements on anesthetised living pigs. The experiments also served as the iii performance validation of a receiving inward cavity-backed slot antenna designed specifically for In-to-On-Body communications at 2.45 GHz, ISM band. In-vivo trials included implanting a wireless transmitter at several abdominal positions, which were then used for the 2-D and 3-D localisation accuracy assessment. Two trials were conducted separately at the medical facilities of The University of Southern Denmark (Odense, Denmark) and at the Herston Medical Research Centre, The University of Queensland (Brisbane, QLD, Australia). The research presents new knowledge for WBAN channel modelling for propagation media similar to the human body; confirms the reliability of the slot antenna performance for surface field measurements in WCE applications at 2.45 GHz; validates the application of the attenuation path loss model for In-to-On-Body communication channels; and it demonstrates high localisation accuracy when the proposed attenuation path loss model is used as an inverse solution for finding radial distances between the reference sensor and the unknown implant position.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Eng & Built Env
Science, Environment, Engineering and Technology
Full Text

L’objectif de cette étude est d’évaluer la faisabilité de la reconstitution des champs de précipitations dans les zones urbaines à l’aide de liaisons hyper - fréquence commerciales. Dans un cadre de simulations appliquées à une étude de cas réaliste, une attention particulière est portée au réseau de téléphonie mobile et à la ville de Nantes en France. Comme base, nous utilisons un ensemble de données composé de 207 images radar météo enregistrées par Météo - France (bande C) à haute résolution spatiale (250m x 250m) et temporelle (5 min). Nous avons généré des données d’atténuation de pluie le long de ces liaisons qui sont utilisés pour représenter le signal réel. Ces données d’atténuation peuvent être enregistrées dans les stations d’antenne à hyper - fréquence. Deux algorithmes de reconstitution, à savoir l’algorithme inverse et la tomographie, sont proposés pour reconstruire des champ s de pluie sur la base des données d ’atténuation de pluie générées. Pour valider les performances de la méthode, nous réalisons des séries de tests de reconstitution de pluie pour des pluies légères, des averses, des orages organisés et non organisés avec des variabilités spatiales et temporelles. Les comparaisons entre les algorithmes inverse et tomographique sont réalisées également pour plus de 40 champs de précipitations et les 4 types d’événements afin de définir les limites et les capacités des deux algorithmes
The objective in this study is to assess the feasibility of retrieval of rainfa ll fields in urban areas using commercial microwave links, with a special focus given on cellular network, in a simulation framework applied to a realistic case study. The study domain is the city of Nantes, France. As a basis, we use a data set consisting of 207 weather radar images recorded by Météo - France C band at high spatial (250m x 250m) and temporal (5 min) resolutions. We generated rain attenuation data along those links that are used to represent real signal attenuation data that can be recorded a t microwave antenna stations. Two retrieval algorithms, namely inverse and tomography, are proposed to retrieve rainfall fields based on the generated rain attenuation data. To validate the system performance, we carry out series of rain retrieval tests in light rain, shower, organized and unorganized storm events with high spatial and temporal variability. The comparisons between the inverse and the tomographic algorithms are also made over 40 rainfall fields in 4 events in order to define limitations and capabilities of both algorithms

Short description of new ground radiometric complex, working on 40 GHz and 94 GHz frequencies and providing remote continuous measurements of full vertical atmosphere attenuation, effective temperature values and liquid-water content of clouds, integral content of vaporous moisture in atmosphere. The feature of the complex is the availability of digital signal processing of detected signals mode.

Thesis deals with the analysis of the sliding contact in the ring mill. It focuses on the assessment of the effect of the current load on the sliding contact, the assessment of the signal transmission quality from the static to the rotara part of the ring contact slide contact.

The growth in the number of wireless devices and applications underscores the need for characterizing and mitigating interference induced problems such as distortion and blocking. A typical interference scenario involves the detection of a small amplitude signal of interest (SOI) in the presence of a large amplitude interfering signal; it is desirable to attenuate the interfering signal while preserving the integrity of SOI and an appropriate dynamic range. If the frequency of the interfering signal varies or is unknown, an adaptive notch function must be applied in order to maintain adequate attenuation. This work explores the performance space of a phase cancellation technique used in implementing the desired notch function for communication systems in the 1-3 GHz frequency range. A system level model constructed with MATLAB and related simulation results assist in building the theoretical foundation for setting performance bounds on the implemented solution and deriving hardware specifications for the RF notch subsystem devices. Simulations and measurements are presented for a Low Noise Amplifer (LNA), voltage variable attenuators, bandpass filters and phase shifters. Ultimately, full system tests provide a measure of merit for this work as well as invaluable lessons learned. The emphasis of this project is the on-wafer LNA measurements, dependence of IC system performance on mismatches and overall system performance tests. Where possible, predictions are plotted alongside measured data. The reasonable match between the two validates system and component models and more than compensates for the painstaking modeling efforts. Most importantly, using the signal to interferer ratio (SIR) as a figure of merit, experimental results demonstrate up to 58 dB of SIR improvement. This number represents a remarkable advancement in interference rejection at RF or microwave frequencies.

Na barreira regressiva da Pinheira, são reconhecidos quatro ambientes deposicionais costeiros, caracterizados por parâmetros geológicos como a análise de litofácies, estruturas sedimentares, grau de compactação e conteúdo de moluscos. Informações que são analisadas em conjunto com imagens de dados geofísicos obtidas com o método do Radar de Penetração no Solo (GPR – Ground Penetrating Radar) para determinar esses ambientes. O presente trabalho visa a caracterização destes ambientes deposicionais através da análise da amplitude do sinal em traços de antenas com frequências centrais de 80, 100, 200 e 400 MHz em conjunto com os dados de compactação e litológicos de um furo de sondagem. E também mostra o comportamento da atenuação do sinal em relação a umidade presente no ambiente. A análise dos traços permitiu a identificação dos contatos entre os ambientes já descritos para barreiras regressivas, mostrando variação no valor das amplitudes (decréscimo ou aumento) em conjunto com a variação no grau de compactação, que evidenciam em subsuperfície a mudança entre os ambientes de cordões litorâneos, backshore/foreshore e shoreface superior e inferior. A interferência da umidade na atenuação do sinal nos dados analisados pode ser observada apenas nos primeiros 0,5 m. Demonstrando que a pluviosidade não é um fator de relevância para atenuação do sinal em ambientes arenosos onde o nível da água é próximo a superfície. A análise dos radargramas para todas as antenas, permitiu a identificação dos padrões de refletores já descritos para os ambientes da área de estudo e a antena com frequência central de 200 MHz apresentou maior resolução para a definição de todos os ambientes.
In the Pinheira regressive barrier, four coastal depositional environments are recognized, characterized by geological parameters such as lithofacies analysis, sedimentary structures, compaction degree and set of mollusks. Information that is analyzed together with images of geophysical data obtained with the Ground Penetrating Radar (GPR) method to determine these environments. The present work aims to characterize these depositional environments by analyzing the signal amplitude in traces with central frequencies antennas of 80, 100, 200 and 400 MHz in conjunction with the compaction and lithological data of a drill hole. It also shows the behavior of signal attenuation in relation to the humidity present in the environment. The analysis of the traces allowed the identification of the contacts between the environments already described for regressive barriers, showing variation in the value of the amplitudes (decrease or increase), together with the variation in the degree of compaction, which evidences in subsurface the change between the environments of foredune ridges, backshore/foreshore and upper and lower shoreface. The interference of humidity in attenuation of the signal in the studied data can be observed only in the first 0.5 m. Rainfall was not relevant for signal attenuation in the studied sandy deposits with water level close to the surface. The analysis of the radargrams for all the antennas allowed the identification of the patterns of reflectors already described for the environments of the study area and the central frequency antenna of 200 MHz showed the highest resolution for the definition of all the environments.

La technologie à ultrasons constitue un moyen abordable de mettre en œuvre des solutions non invasives pour évaluer de manière diagnostique les caractéristiques mécaniques de l'os. Dans cette thèse nous introduisons la poursuite orthogonale (OMP) pour obtenir une reconstruction robuste de la forme d'onde de chaque écho après rebond sur les faces externe et interne de l'os cortical. Le temps de vol et les fréquences centrales des échos sont utilisés pour calculer l'atténuation normalisée à large bande (nBUA). Des mesure in vivo ont été effectuées avec succès en mode écho et des données de référence ont été obtenues à partir de mesures HR-pQCT (épaisseur corticale, vBMD). Il est ainsi apparu que Ct.Th et nBUA étaient fortement corrélés aux valeurs d'épaisseur de référence (r2=0,90), respectivement. La deuxième contribution principale de ces travaux consiste en l'utilisation de la méthode TDTE (Time Domain Topological Energy) et de la migration dans l'imagerie de l'os cortical. L'approche TDTE montre de bonnes performances dans l'imagerie de la structure de l'os cortical (faces interne et externe de l'os, ainsi que la structure poreuse à l'intérieur de l'os). La migration quant à elle peut fournir une distribution quantitative approximative de la densité, de la vitesse de compression et de la vitesse de cisaillement
Ultrasound technology provides an affordable means to implement non-invasive solutions to diagnostically assess the mechanical characteristics of the bone. In this thesis we introduce Orthogonal Matching Pursuit (OMP) to obtain a robust reconstruction of the waveform of each echo bouncing off the cortical bone surfaces. Echoes' time-of-flight and central frequencies are used to calculate Ct.Th and normalized broadband attenuation (nBUA). In vivo measurements have been successfully performed with pulse-echo ultrasound and reference data wase obtained with HR-pQCT (cortical thickness, vBMD). Ct.Th and nBUA were highly correlated to reference thickness values (r2=0.90) and vBMD (r2=0,90), respectively. The second main contribution is that we introduce Time Domain Topological Energy (TDTE) method and migration into cortical bone imaging. TDTE shows well performance in extracting the structure of cortical bone, including the external, internal boundary of cortical bone and porous structure inside the cortical bone. Migration can provide a rough quantitative distribution of density, compression wave speed, and shear wave speed

Orientador: Martin Tygel
Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Matemática Estatística e Computação Cientifica
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Resumo: As reflexões de ondas sísmicas na subsuperfície terrestre podem ser colocadas em duas categorias disjuntas: reflexões primárias e múltiplas. Reflexões primárias carregam informações pontuais sobre um refletor específico, enquanto reflexões múltiplas carregam informações sobre interfaces e pontos de reflexão variados. Consequentemente é usual tentar atenuar reflexões múltiplas e trabalhar somente com reflexões primárias. Neste trabalho, a teoria de ondas acústicas é desenvolvida somente a partir da equação da onda. Um resultado que demonstra como a propagação de ondas acústicas pode ser descrita somente com uma única multiplicação por matriz é exposta. Este resultado permite que um algoritmo seja desenvolvido que, em teoria, pode ser usado para remover todas as reflexões múltiplas que refletiram na superfície pelo menos uma vez. Uma implementação prática deste algoritmo é mostrada. Por conseguinte, a teoria de análise de componentes independentes é apresentada. Suas considerações teóricas e práticas são abordadas. Finalmente, ela é usada em conjunção com o método de eliminação de múltiplas de superfície para atenuar múltiplas de quatro dados diferentes. Estes resultados são então analisados e a eficácia do método é avaliada
Abstract: The reflections of seismic waves in the subsurface of the Earth can be placed under two disjoint categories: primary and multiple reflections. Primary reflections carry pointwise information about a specific reflector while multiple reflections carry informations about various interfaces and reflection points. Consequently, it is customary to attempt to attenuate multiple reflections and work solely with primary reflections. In this work, the theory of acoustic waves is developed solely from the wave equation. A result that shows how acoustic wave propagation can be described as a single matrix multiplication is exposed. This result enables one to develop an algorithm that, in theory, can be used to remove all multiple reflections that have reflected on the surface at least once. The practical implementation of this algorithm is shown. Thereafter, the theory of independent component analysis is presented. Its theoretical and practical considerations are addressed. Finally, it is used in conjunction with the surface-related multiple elimination method to attenuate multiples in four different datasets. These results are then analyzed and the efficacy of the method is evaluated
Mestrado
Matematica Aplicada
Mestre em Matemática Aplicada

Sensors based on radio waves are used for inline moisture determination in the sawn wood industry. Placed at the final sorting line such a device can be invaluable, giving the operators real time information on the moisture content of the boards passing through. Information that can then be used to improve process control both upstream and downstream. The equipment must first be trained to correlate radio wave attenuation and phase shift to water conten

Ce travail de thèse porte sur l'analyse et le traitement des signaux ultrasonores pour la caractérisation de l'os cortical. La première partie est dédiée à l'analyse des signaux acquis par un prototype de sonde de transmission axiale à 1 MHz. Nous montrons qu'une contribution arrivant après le premier signal présente un intérêt pour la caractérisation ultrasonore de l'os cortical. En effet, cette contribution évaluée sur des radius humains in vitro est associée à une onde de flexion propagée dans l'os qui est dépendante de l'épaisseur corticale. L'analyse de cette contribution a nécessité le développement d'une technique de séparation d'ondes. Cette contribution étant plus basse fréquence que le premier signal et associée à un mode de propagation différent, nous montrons ainsi qu'une analyse plus poussée du signal peut permettre une approche multi-modes/multi-fréquences. Dans une seconde partie, nous montrons l'intérêt de l'évaluation de l'atténuation ultrasonore pour la caractérisation de l'os cortical. Lors d'une étude expérimentale in vitro sur des échantillons corticaux bovins, nous montrons la dépendance d'un paramètre d'atténuation aux propriétés osseuses et à la micro-structure. De plus, ce paramètre semble plus sensible aux propriétés osseuses que ne l'est la vitesse de l'onde longitudinale. Ainsi, l'atténuation évaluée en complément de la vitesse pourrait permettre de caractériser de manière plus complète l'os cortical

Objective assessment for the effect of hearing protectors, background noise levels, and backup alarm acoustic features on listeners' abilities to localize backup alarm signals in the horizontal dimension, as well as on their ability to detect backup alarm signals in the distance dimension, is lacking in the acoustics and safety literature. Accordingly, two research experiments were conducted for this dissertation. In the first experiment, the effect of seven hearing protectors, two background pink noise levels (60 dBA and 90 dBA), and two backup alarm signals (standard and spectrally-modified) on the ability of normal hearing listeners to localize backup alarm signals in the horizontal dimension was investigated. Results indicated that a diotic sound transmission earmuff significantly degraded localization accuracy as compared to all other hearing protectors and the open ear condition. In addition, no significant difference existed between the open ear condition and the other hearing protectors in localization accuracy in most of the conditions tested. However, the E-A-R/3M HiFiTM earplug was advantageous in localization performance since it provided a significantly higher percentage correct localization than the Moldex foam earplug, the diotic earmuff, and the dichotic earmuff in 90 dBA pink noise. As for main effects of the other independent variables, the 90 dBA pink noise significantly degraded localization performance as compared to the quiet condition of 60 dBA, and a spectrally-modified backup alarm significantly improved localization performance as compared to the standard (narrowband) backup alarm. Potential application of these results includes the revision of backup alarm standards. In addition, these results provide clear advice for safety professionals to avoid the application of diotic sound transmission earmuffs for workers if localizing backup alarms is important. In the first experiment, listeners' feeling of comfort for each hearing protector was assessed subjectively by using a comfort rating scale. In addition, a subjective assessment for listeners' confidence in their localization decisions was established. Results indicated no significant difference between the hearing protectors in terms of comfort. However, in terms of listeners' confidence in localization decisions, their confidence was significantly degraded when they were fitted with the diotic earmuff. By contrast, they showed significantly more confidence in their localization decisions when they were fitted with the E-A-R/3M HiFi™ earplug as compared to when they were fitted with the Moldex foam earplug, the E-A-R/3M Ultrafit™ earplug, and the Bilsom passive earmuff. In the second experiment, listeners' performance in detecting a stationary backup alarm signal, including both a standard (narrowband) and broadband (pulsed white noise) alarm, was determined while they were equipped with various passive and electronic hearing protection devices. Listeners' performance was quantified by detection distance, which was defined as the distance between the stationary backup alarm device and the position where the listener detected the backup alarm signal. The resultant data demonstrated that normal hearing listeners detected a standard (narrowband) backup alarm signal at significantly longer distances as compared to the broadband (Brigade™) backup alarm signal, thus indicating the earlier forewarning by the standard alarm. In addition, passive hearing protection devices characterized with high attenuation significantly reduced the detection distance. These results may be applied to assist safety professionals in selecting hearing protectors and backup alarm signals that provide on-foot workers with ample time to react to an approaching backing vehicle, thus improving their safety.
Ph. D.

In the manufacturing process of mineral wool insulation plates, defects arise, such as unmelted base minerals and uncured binder which gets embedded within the plates. To be able to sort out these defective plates from a manufacturing line, a reliable quality assessment is needed. The aim is to find an ultrasonic non-destructive testing method that can identify the embedded defects. This was achieved through experiments on defective insulation plates using three different ultrasonic non-destructive testing methods that were of interest. These methods were higher harmonics, pulse-echo and through transmission. Of these three, the through transmission method showed the most promising results in finding the defects that were sought after. The through transmission method utilizes two aligned transducers, one acting as a transmitter and one as a receiver. When the defective area passes through the sound beam between the transducers the intensity of the beam drops, indicating that a defect is present. The weakened intensity is due to the signal attenuation, mainly caused by the higher density of the defects compared to the base material in the surrounding insulation plate. The method is well suited for being implemented in a production line since it’s a fast method and, therefore, suited for moving objects. More measurements are needed to establish a reliable reference value to consistently distinguish the defects from the surrounding plate. The method was only evaluated in a small scale experimental environment so further experiments on a larger scale are needed to mimic and evaluate the reliability in the real case scenario of the production lines.
I tillverkningsprocessen av isolerskivor i stenull uppstår inneboende defekter i isolerskivorna, dessa defekter består av osmälta basmineraler och ohärdat bindemedel. För att kunna sortera bort dessa skadade skivor från tillverkningslinjen behövs en pålitlig metod för kvalitetsbedömning. Avsikten med det här arbetet är att hitta en oförstörande provningsmetod baserad på ultraljud som kan identifiera de inneboende defekterna. Detta genomfördes genom experiment på defekta isolerskivor med tre olika oförstörande provningsmetoder baserade på ultraljud. Dessa metoderna var, higher harmonics, pitch-echo och through transmission. Through transmission visade lovande resultat i att identifiera de båda typerna av skador. Metoden är baserad på att en sändare sänder ut ultraljud till en mottagare placerad i linje med sändaren. När ett defekt område passerar ultraljudsvågen mellan sändaren och mottagaren försvagas intensiteten av signalen. Försvagningen av signalen beror mestadels på att densiteten är högre hos defekterna än hos basmaterialet i isolerskivan. Denna försvagning indikerar att en defekt befinner sig i mätområdet. Metoden är väl implementerbar i en tillverkningslinje, då det är en snabb metod vilket den behöver vara då objektet är i rörelse. Mer mätningar behövs för att fastställa ett pålitligt referensvärde för att konsekvent kunna sortera ut de defekta isolerskivorna. Metoden är endast utvärderad i en småskalig laborationsmiljö och det behövs fler tester i en större skala undersöka pålitligheten i det verkliga scenariot med tillverkningslinjen.

The aim of this thesis is to study a free space optics and its application in communication technologies. It describes possible interrupting impacts on the beamed optical signal, which are signal noise, attenuation of the atmosphere and atmospheric turbulence. The basis of the thesis is to describe the impact of the atmospheric turbulences on the optical beam. Fluctuation of optical intensity in the optical beam has been measured and index of refraction structure parameter calculated. With its assistance, turbulence rate has been determined.

Le géoradar, ou Ground Penetrating Radar (GPR) en anglais, est une méthode non destructive couramment utilisée pour l'auscultation des ouvrages en béton. L'intérêt de cette méthode réside sur sa capacité à ausculter rapidement des très grandes surfaces, elle est de plus en plus employée en Génie Civil. Habituellement, cette méthode est utilisée en Génie Civil pour la localisation les aciers de renforcements, ou bien pour l'estimation de l'épaisseur d'enrobage du béton. Toutefois, la méthode GPR peut aussi être utilisée pour l'auscultation du béton. En effet, le béton est un matériau diélectrique poreux qui peut modifier la propagation des ondes électromagnétiques (EM). Les résultats les plus récents présentent la capacité du GPR à évaluer la teneur en eau. Cependant, le GPR pourrait très bien aussi être utilisé pour la détection des ions chlorure présents dans la solution interstitielle du béton, car comme les chlorures modifient la conductivité du béton ils sont susceptibles d'atténuer les ondes électromagnétiques. Néanmoins, seulement quelques études ont été menées dans ce domaine. Par conséquent, dans cette étude, nous proposons d'utiliser les ondes EM du géoradar pour estimer conjointement la teneur en eau et la teneur en chlorure du béton pour différents corps d'épreuves. Pour cela, plusieurs séries de corps d'épreuves sont utilisées avec des modes de contaminations par les chlorures différents. Une procédure de mesure de la vitesse à partir de l'analyse des signaux réfléchis est proposée. On démontre que la vitesse des ondes EM est essentiellement affectée par la teneur en eau alors que l'atténuation est sensible à la fois à la teneur en eau et à la teneur en chlorures. Ensuite, dans un second temps, nous testons différents modèles de permittivité pour prédire les mesures de constante diélectrique et du facteur de pertes évalués à partir des mesures par GPR ou de résistivité électrique
Ground Penetrating Radar (GPR) is an usual nondestructive testing method for the assessment of concrete structures. The benefit of this method lies within its ability to assess quickly a large scale of concrete surface. Generally, GPR is used for the localization of reinforcements or for the thickness measurements. However, GPR can be also used for the diagnosis of concrete because concrete is a porous dielectric material which can modify the propagation of the electromagnetic (EM) waves. Most common results present the ability of GPR to assess moisture. But, GPR could be also used to detect the presence of chlorides into the interstitial concrete solution as chlorides can modify the concrete conductivity and altered the electromagnetic signal waves. However, only few studies have been carry-out on that field. Therefore, in this study, we propose to use GPR electromagnetic waves to evaluate both the water content and the chloride content inside the interstitial concrete solution of several tests concrete samples. So, several groups of concrete samples with the same formulation will be conditioned for different chloride contamination modes. Thereafter, a velocity measurement process will be proposed from the reflected signal wave analysis. In that process, we will show that the velocity is only affected by the water content while the attenuation strongly affected by both the water content and the chloride content. Furthermore, we will test several permittivity models to predict the dielectric permittivity and the loss factor estimated from the concrete samples measurements with the GPR device and the electrical resistivity device

В роботі було розроблено методологію підвищення ефективності стільникових мереж зв’язку, яка полягає у використанні удосконалено методу планування мережі стільникового зв’язку для розгортання стільникових мереж нового покоління, методу оцінки ключових показників функціонування мережі стільникового оператора з метою безперервної оптимізації мережі оператора шляхом використання методу оптимізації підсистеми базових станцій розгорнутої мережі стільникового оператора, удосконаленого методу розвантаження радіо інтерфейсу мережі стільникового оператора із використанням підмережі Wi-Fi (Wireless Fidelity), методу оптимізації багаторівневого транспортного сегменту стільникової мереж, удосконаленого методу маршрутизації із резервуванням ресурсів та балансуванням навантаження транспортної мережі стільникового оператора, методу оцінки ефективності програмно-конфігурованої мережі та методу мережецентричного моніторингу та реагування на кіберінциденти в мережі оператора стільникового зв’язку. За допомогою розробленої методології операторам стільникового зв’язку вдається підвищити ефективність функціонування своїх мереж за рахунок збільшення радіусу зон обслуговування абонентів стільникових мереж, мінімізації необхідної кількості базових станцій для побудови мережі, збільшення вдвічі кількості активних абонентів, які обслуговуються в стільнику та забезпечення балансування навантаження в радіопідмережі, підвищення економічної ефективності транспортної мережі, підвищення рівня надійності мережі, оптимізації утилізації транспортних каналів, проведення більш гнучкого та оперативного розширення мережі, запровадження нових сервісів, підвищення оперативності доставки даних для ієрархічної структури рівня управління. Отримані наукові результати доцільно використовувати під час планування безпроводових мереж стандарту LTE та 5G, розробки обладнання та програмного забезпечення для систем передачі даних, а також в навчальному процесі.
Диссертация посвящена вопросам разработки методологии повышения эфективности сотовых сетей связи. В работе был проведен анализ качества обслуживания абонентов сотовых сетей в Украине с целью определения их эффективности. Было установлено, что заявленные требования к сетям четвертого поколения не достигаются ни в одной из реализованных сетей, а фактическое качество обслуживания абонентов находится на достаточно низком уровне, что свидетельствует о низкой эффективности существующих методов планирования радиосетей, транспортных подсистем и методов управления. В работе были предложены альтернативные стратегии развития операторов сотовой связи в Украине. В работе впервые разработана методология повышения эффективности сотовых сетей связи, заключающаяся в использовании усовершенствованного метода планирования сети LTE для развертывания сотовых сетей нового поколения, метода оценки ключевых показателей функционирования сети сотового оператора с целью непрерывного оп-тимизации сети оператора путем использования метода оптимизации подсистемы базо вых станций развернутой сети сотового оператора, усовершенствованного метода рас-погрузки радио интерфейса сети сотового оператора с использованием подмел-режиме Wi-Fi, метода оптимизации многоуровневого транспортного сегмента сотовой сетей, метода резервирования ресурсов и балансировки нагрузки транспортной ме-режи сотового оператора и метода оценки эффективности программно-конфигурируемых сети. С помощью разработанной методологии операторам сотовой связи удается повысить эффективность своих сетей за счет увеличения радиус зон обслуживания абонентов сотовых сетей, минимизации необходимого количества базовых станций для построения сети, увеличение вдвое количества активных абонентов, обслугвуються в базовой и обеспечения балансировки нагрузки в радиопидмережи, повышение економинои эффективности транспортной сети, повышение уровня надежности сети, оптимизацией утилизации транспортных каналов, проведение более гибкого и оперативного расширения сети, внедрение новых сервисов, повышения оперативности доставки данных для иерархической структуры уровня управления.
The amount of traffic carried over wireless networks is growing rapidly and is being driven by many factors. Chief among them is the tremendous growth in multimedia applications on mobile devices – streaming music and video, two-way video conferencing and social networking to name a few. The telecoms industry is undergoing a major transformation towards 5G networks in order to fulfil the needs of existing and emerging use cases. The 5G architecture should seamlessly support both fixed and mobile access technologies under a fully converged end-to-end system in order to deliver future service requirements for some of the deployment scenarios that could be supported. This technologies in nearest future have come to Ukraine too. That’s why in this dissertation an analysis of the quality of service of subscribers of cellular networks in Ukraine was conducted in order to determine the efficiency of their operation and security. An analysis of the quality of customer service in the implemented projects of LTE networks in the world and 4G networks in Ukraine has established that the claimed requirements for fourth generation networks are not achieved in any of the implemented networks, and the actual quality of customer service (target efficiency) is at a rather low level which indicates the low efficiency of existing radio network planning methods, transport subsystems, control and cybersecurity management methods. This made it possible to determine the directions by which it is necessary to increase the efficiency of the operation of cellular networks. In this dissertation were developed several methods to improve network efficiency. The method of planning of the network of the cellular operator enables cellular operators to more accurately assess the coverage of radio coverage areas, choose key indicators of service quality, more efficient frequency planning and capital cost calculation, which in turn allows us to assess the feasibility of constructing a cellular network option. On the basis of this advanced method, a training software (web-application) was developed to evaluate radio coverage zones of LTE network base stations. The method for evaluating key indicators of service quality, the level of information security and the efficiency of cellular networks makes it possible to assess the most important indicators of the quality of functioning and security of the cellular network network in order to continuously monitor and optimize them when introducing new services during customer service. The method for optimizing the subsystem of base stations allows to increase the radius of subscriber service areas of cellular networks, which allows minimizing the number of base stations for network construction, and therefore reduce the cost of the cellular operator to build the subsystem of the base stations, that is, increase the economic efficiency of the network. Improved method of the radio interface off-loading using a non-3GPP standard subnet allow to reduce the load on the radio interface of the network of the cellular network to an acceptable level, double the number of active subscribers, which are served in the cell, and provide load balancing and increase the efficiency of the radio subnetwork. The method of optimization of a multi-level transport segment of a cellular network has been developed, which allows to improve the structure of the transport network during the transition to new generations networks, providing the necessary capacity and increasing and improving the efficiency of the transport network. The method of routing with resource reservation and balancing of the traffic of a cellular operator with the consideration of information security requirements allows to increase the efficiency of the transport channels usage. The method for evaluating the effectiveness of a software-configured network allows for a more flexible and operational expansion of the network, the introduction of new services, increasing the efficiency of data delivery for the hierarchical structure. The method of network-centric monitoring and response to cyber incidents in the network of the cellular network allows real-time monitoring of the state of cyber security, its level and, consequently, the efficiency of the cellular network. On the base of these methods in this dissertation was developed cellular networks efficiency improving methodology, which is using the improved method of LTE network planning, the key method for assessing performance of the cellular operator for the purpose of continuous operator network optimizing using the method of base station subsystem optimization, improved method of radio interface of the cellular operator offloading using Wi-Fi, the method of optimization of multi-vehicle segment of the cellular network, the method of roating with resource reservation and load balancing of mobile operator and method of SDN network effectiveness evaluation. Using the developed methodology mobile operators can improve the efficiency of their networks by increasing the radius of the service areas, minimizing the required number of base stations for the construction of the network, doubling the number of active subscribers in the cell and provide load balancing in transport and radio network, increase transport network efficiency, enhance network reliability, optimize utilization of transport channels for a more flexible and rapid network expansion, introduction of new services and improved data delivery in the hierarchical structure of SDN. It is advisable to use the obtained scientific results when planning LTE and 5G wireless networks, developing equipment and software for data transmission systems, as well as in the learning process.

碩士
國立成功大學
醫學資訊研究所
103
The Nakagami statistical distribution of ultrasonic backscattering signals has shown it is capable of characterizing the variations of density and arrangement of scatterers in biological tissues. This analysis of ultrasound signals has also found with less dependency on the effect of attenuation and the estimated statistical parameter can be affected by the board-band attenuation in the tissues and distortion of acquired echo signals. Accordingly, as the employed ultrasound frequency and pulse duration, namely operational mode, were increased, several additional factors could come into play and further affect the precise estimation of the statistical parameters. To further investigate the addressed issues, experiments were arranged and performed using 3.5, 7.5, and 10MHz focused transducer in vitro porcine liver tissues and using 30, 50MHz focused transducer in vivo rat liver tissues. The porcine liver tissues were obtained with either healthy (N=10) or pathological fibrosis (N=10) were obtained from a local slaughter house, and rat liver tissues from 10-week-old male Sprague Dawley (SD) rat liver tissues (N=5). Various excitation cycles, including 1, 3, 5, and 10, of tone bursts at pulse repetition frequency corresponding to ultrasound frequencies of 3.5, 7.5, 10, 30 and 50 MHz were adjusted for driving the transducers. Various thickness of attenuated phantoms with the attenuation coefficient of 1.62 dB/mm．MHz were placed on the surface of tissue to be measured. The Nakagami statistical model, which includes the shape parameter (Nakagami-m), was implemented to assess variations of the probability density function (PDF) estimated from the acquired ultrasonic backscattering signals. Eventually, the histological analysis, using the H＆E staining, not only detect the pathological fibrosis liver status but also measure the number of scatterers in the resolution cell, it’s corresponds to a volume of ultrasound signals within transducer pulse length and the lateral profile beamwidths. Results of in vitro porcine liver tissues indicated that the attenuation could significantly vary the shape of PDF of backscattered envelopes. Results of in vivo rat liver tissues indicated that the Nakagami-m increased with the increasing ultrasound frequencies and bandwidth, and that those associated PDFs were nearly pre-Rayleigh distributed. Results of histological analysis are shown the stronger scatterers distributed in the tissues, the characterization of tissues both describe to pre-Rayleigh distribution. All the results consistently demonstrated that the use of 3 cycles tone bursts may achieve the most appropriate performance to accommodate a trade-off between attenuation effect and image resolution. Current study also verified that the operational modes of incident ultrasound need to be properly assured before that the statistical model may be further applied to parametric imaging and clinical applications.

Intrabody communication (IBC) is a new physical layer defined in the recently ratified wireless body area network (WBAN) IEEE 802.15.6 standard. The cable-free IBC technology uses body tissue as a propagation medium instead of air. While recent studies have shown a degradation of transmission signal for IBC between limb segments, these degradations have yet to be quantified with respect to relative limb positions. The current thesis investigates the influence of human movement on signal attenuation during IBC considering limb joint effects within the transmission frequency range 0.3-200 MHz. In-vivo experiments are conducted to determine the effects of size, situations (flexed or extended), and locations (lower or upper limb) of joints on the IBC. Results show that the presence of joints along the transmission path causes high signal attenuation (up to 6.0 dB), the flexed limb exhibits 4.0 dB less attenuation compared with extended one, and the lower limb joints (knee) shows higher attenuation (2.0 dB) than upper limb joints, below 60 MHz. We propose a new IBC circuit model explaining elbow joint effects. The presented model not only takes the limb joint effects of the body into account but also considers the influence of measurement equipment in higher frequency band thus predicting signal attenuation behavior over wider frequency ranges. Results from the model simulation reveal that the presence of limb joint within the signal transmission path causes an additional 1.0 to 5.2 dB loss at frequencies below 60 MHz for on-body channel length of 20 cm. The simulation results suggest that the measurement equipment effects are negligible, below 60 MHz. Finally, this work proposes transmitter and receiver architectures for intrabody communication. A carrier-free scheme based on impulse radio (IR) for the IBC (IR-IBC) is implemented on a FPGA. Results demonstrate data rates of up to 1.56 Mbps achievable for the galvanic coupling IBC method.

碩士
國立臺灣科技大學
工程技術研究所
81
Distribution-Line-Carrier (DLC) can serve as a meduim of two- way communication for load management and distribution automation. Attenuation analysis of DLC signal along complicated distribution systems network is indispensable to achieving an acceptable level of reliability to satisfy two-way communication requirements on DLC communication system. In this thesis, emphasis has been placed on analyzing the DLC from calculation of the distributed parameters of overhead line and underground cable in distribution systems to the derivation of their equivalent PI models. In addition, the distribution transformer models of various connection configurations are derived in detail. A general computer program coded in C language has been developed for analyzing the distribution-line- carrier signal of the distribution systems. Finally, the Carolina power and light company's distribution test site and the Tai-power two-way communication demonstration system will be taken as illustrative examples to carry out the comparison of computer simulation with field test data.

碩士
國立彰化師範大學
電機工程學系
107
This thesis uses the loop diagnostic method (Web Base LDM) developed by the telecommunications service provider to perform image recognition for the ultra-high-speed digital data rate (VDSL) and the inner loop signal attenuation response map (HLog). First, the system uses the Unicom labeling method to mark the position of the desired image, and then use the color separation and graphic redraw to convert the original image into a MATLAB coordinate map. First, it uses rule of thumb to find out the graphic characteristics of common obstacles, and then determine the cause of the obstacles on the coordinate map after redrawing of the graphs. Finally, the system compares them with the situation at the scene. If there is any difference, the data should be recorded to make the basis for interpretation by identifying its characteristic. The experimental results can be used to help the interpretation of obstacles for newcomers and the people who are not familiar with the Web Base LDM system.

碩士
國立中央大學
太空科學研究所
85
The ROCSAT-1 with the missions of space research, earth- space communication and remote sensing is about to be launchedin the end of 1998 or at the begin of 1999. By the specifica-tions of the original desigins, the freqrncy for the earth- earthcommunication of the ROCSAT-1 is ranged in the Ka band ( 30GHz for uplink, 20 GHz for downlink). While millimeter wavespropagate through the atmospheric chanel, the degradation ofpropagation may take place, such as the attenuation and thedepolarization by raindrops, the absorption by oxygen andwater vapor, and the scintillation by atmospheric turbulance. Taiwan, for the understanding of the propagation propertiesat Ka band. In the whole context, the attenuation by rain iscalculated under differert latitude through the analyzation ofrainy data from Central Weather Bureau.

Seismic attenuation is a fundamental parameter on the comprehension of the viscoelastic real behavior of the medium. Characterization of the ability of materials to transmit and dissipate seismic waves is even important for petrophysical descriptions of reservoir rocks. The purpose of this work is to investigate the reliability of the rise-time and the spectral ratio methods for estimation in a seismic downhole campaign, to obtain accurate profiles. In this study, we applied two different methods to estimate attenuation. We used a standard spectral ratio technique to obtain the frequency independent and then compared the results to obtained in the time domain from rise-time measurements. Most of the borehole attenuation studies presented in literature are carried out for hydrocarbon exploration. The main contribution of the present work is to apply the two most used attenuation estimation methods to near-surface data. They include two techniques to determine the material damping ratio of the soil based on the downhole (DHT) test, and other two for attenuation and dispersion curves from MASW testing

Seismic attenuation is a fundamental parameter on the comprehension of the viscoelastic real behavior of the medium. Characterization of the ability of materials to transmit and dissipate seismic waves is even important for petrophysical descriptions of reservoir rocks. The purpose of this work is to investigate the reliability of the rise-time and the spectral ratio methods for estimation in a seismic downhole campaign, to obtain accurate profiles. In this study, we applied two different methods to estimate attenuation. We used a standard spectral ratio technique to obtain the frequency independent and then compared the results to obtained in the time domain from rise-time measurements. Most of the borehole attenuation studies presented in literature are carried out for hydrocarbon exploration. The main contribution of the present work is to apply the two most used attenuation estimation methods to near-surface data. They include two techniques to determine the material damping ratio of the soil based on the downhole (DHT) test, and other two for attenuation and dispersion curves from MASW testing.

This thesis outlines the procedure and theory used to calibrate the UMass eXperimental X-band Radar (UMAXX) for the purpose of monitoring meteorological events in the Pioneer Valley region. Due to the complex topography of the area, lower tilt angles are subject to partial or full beam blockage as well as ground clutter observed through the main beam or sidelobes. Additionally, there are biases internal and external to the system that impact the reflectivity and differential reflectivity measurements. These biases and corrections are addressed in this work. As the radar has been operational since September of 2018, there is ample data available to diag-nose and to perform the necessary corrections to the system. A variety of methods are employed to validate these corrections including comparing intersecting scan volumes between the UMAXX and nearby WSR-88Ds of the NEXRAD network as well as the use of membership functions. Key results of this work are: Ground clutter is principally identified through differential phase and secondarily through velocity and co-polar correlation Partial beam blockage is best estimated assuming a 1.67◦, 2-way beamwidth with an 8dB cutoff System differential phase and Differential Reflectivity bias are functions of az-imuth due to the radome panels. A linear relation between wet radome attenuation and rain rate is found Using an attenuation factor of a = .28 to determine path integrated attenuation improves correlation of reflectivity measurements between UMAXX and NEXRAD network. Ultimately, the goal is to establish UMAXX as a reliable and well understood benchmark with which to calibrate Raytheon’s dual-polarized phased array radar. The two radars operate in sufficiently close frequencies within X-band and collected data simultaneously while colocated. While phased arrays show great promise and potential in meteorologic observations, they come with many challenges that neces-sitate the use of a trustworthy baseline with which to validate its measurements. Additionally, UMAXX’s data is to be streamed to serve as a source to fill any gaps present in the National Weather Service’s network in the region.

碩士
國立臺北科技大學
電腦與通訊研究所
99
In recent years, the rapid development of wireless sensor networks (WSNs) is obvious. It will change interactive mode between humans and the objectives. Numerous sensor nodes are deployed in object areas, which can realize tasks of complex large-range monitoring and tracking. However, for most of applications, the data ,which are collected by the sensor, is meaningless unless the location information. In this thesis, we design a local centralized positioning scheme for indoor wireless sensor networks. The proposed method combines the advantages of centralized positioning and decentralized positioning scheme, and based on signal attenuation difference of arrival to improve the location accuracy. It utilizes recursive weighted interpolation method to compute the target location. In addition, the life time and bandwidth efficiencies of whole WSNs are accomplished because of the sensed data are processed in the user’s handheld and need not be transmitted to the sever. The simulation results show that our method has better location performance then other positioning schemes.

The advantages offered by Super High Frequency (SHF) and Extremely High Frequency (EHF) bands such as large bandwidth, small antenna size, and easy installation or deployment have motivated the interest of researchers to study those factors that prevent optimum utilization of these bands. Under precipitation conditions, factors such as clouds, hail, fog, snow, ice crystals and rain degrade link performance. Rain fade, however, remains the dominant factor in the signal loss or signal fading over satellite and terrestrial links especially in the tropical and sub-tropical regions within which South Africa falls. At millimetre-wave frequencies the signal wavelength approaches the size of the raindrops, adversely impacting on radio links through signal scattering and absorption. In this work factors that may hinder the effective use of the super high frequency and extremely high frequency bands in the Southern African region are investigated. Rainfall constitutes the most serious impairment to short wavelength signal propagation in the region under study. In order to quantify the degree of impairment that may arise as a result of signal propagation through rain, the raindrops scattering amplitude functions were calculated by assuming the falling raindrops to be oblate spheroidal in shape. A comparison is made between the performance of the models that assume raindrops to be oblate spheroidal and those that assume them to be spherical. Raindrops sizes are measured using the Joss-Waldvogel RD-80 Distrometer. The study then proposes various expressions for models of raindrops size distributions for four types of rainfall in the Southern Africa region. Rainfall rates in the provinces in South Africa are measured and the result of the cumulative distribution of the rainfall rates is presented. Using the information obtained from the above, an extensive calculation of specific attenuation and phase shift in the region of Southern Africa is carried out. The results obtained are compared with the ITU-R and those obtained from earlier campaigns in the West African sub region. Finally, this work also attempts to determine and characterize the scattering process and micro-physical properties of raindrops for sub-tropical regions like South Africa. Data collected through a raindrop size measurement campaign in Durban is used to compare and validate the developed models.
Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2014.

Бартиш А. А. Дослідження волоконно-оптичної системи передачі інформації та розробка фотоприймального пристрою : кваліфікаційна робота магістра спеціальності 153 "Мікро- та наносистемна техніка" / наук. керівник О. Ю. Небеснюк. Запоріжжя : ЗНУ, 2020. 87 с.
UA : Розроблено фізичну модель фотоприймального пристрою для волоконно-оптичної системи передачі інформації, що дозволяє зменшити вплив шумів на спотворення електричного сигналу у інтерфейсному обладнанні.
EN : A physical model of a photodetector device for a fiber-optic information transmission system has been developed, which allows to reduce the influence of noise on the distortion of the electrical signal in the interface equipment.

Wissenschaftliche Untersuchungen von terrestrischen und aquatischen Ökosystemen erfordern präzise Informationen über die dreidimensionale Struktur des ökologischen Systems. Full-waveform Flugzeuglaserscannerdaten eignen sich hervorragend zur Charakterisierung von Ökosystemen und bilden eine ideale Basis für die vollständige volumetrische Repräsentation der Vegetations- und Gewässerstruktur in einem Voxelraum. Die Voxelattribute werden dabei aus der digitalisierten Wellenform abgeleitet. Jeder emittierte Laserpuls wird von Dämpfungseffekten beeinflusst, die durch Teilreflexionen auf seinem Weg durch die unterschiedlichen Vegetations- oder Wasserschichten entstehen. Dadurch ist die Struktur im unteren Bereich der empfangenen Rohsignale unterrepräsentiert. Die im Rahmen dieser Arbeit entwickelten innovativen Methoden zur Analyse von full-waveform Daten ermöglichen die Generierung einer radiometrisch korrigierten Voxelraumrepräsentation. Voraussetzung dafür ist die numerisch stabile Rekonstruktion des effektiven differentiellen Rückstreuquerschnitts mit geeigneten Entfaltungs- und Regularisierungsverfahren. Das Kernstück der Analyse bildet die Beschreibung der Signaldämpfung mit Hilfe geeigneter Modelle. Auf Grundlage dieser Modelle wurden neuartige Korrekturverfahren zur Kompensation der Signaldämpfung erarbeitet, wobei der Korrekturterm direkt aus dem differentiellen Rückstreuquerschnitt abgeleitet wird. Die Grundidee der entwickelten Methode ist das schrittweise Anheben der Signalintensität in Abhängigkeit von der individuellen Historie jedes Laserpulses. Die Resultate der vorliegenden Arbeit tragen dazu bei, die in full-waveform Daten enthaltenen Informationen über die Vegetations- und Gewässerstruktur zugänglich zu machen. Weiterhin zeigen die hier präsentierten Ergebnisse, dass die Limitierungen bestehender Auswertemethoden, welche weitgehend auf die Extraktion diskreter Maxima und die Erzeugung volumetrischer Repräsentationen aus diskreten 3D Punktwolken beschränkt sind, überwunden werden können.
The scientific investigation of terrestrial and aquatic ecosystems requires precise information on the three-dimensional structure of the ecologic system. Full-waveform airborne laser scanner data are an ideal basis for the complete volumetric representation of vegetation and water structure in a voxel space. Due to attenuation effects, caused by partial reflections during the laser pulse propagation through the vegetation or water column, each individual laser pulse echo is significantly modified. As a result, the structure in the lower parts of the vegetation or water column is underrepresented in the digitized waveform. Within this research, novel and innovative methods were developed, which enable the generation of a radiometrically correct voxel space representation. Therefore, a numerically stable reconstruction of the effective differential backscattering cross section utilizing appropriate deconvolution and regularization techniques is required. The essential element of the analysis is the description of the signal attenuation using applicable mathematical models. For this purpose, novel correction methods compensating the signal attenuation based on these models were developed. The correction term is directly derived from the differential backscatter cross section. The basic idea is a gradually increase of the signal amplitudes depending on the individual history of each laser pulse. The results gained in this work contribute to an improved access to the information on vegetation and water structure, contained in full-waveform laser scanner data. Furthermore, it is possible to overcome limitations of existing approaches, which are mainly based on the extraction of discrete maxima.

Intrabody communications (IBC) is a novel physical layer outlined in the recently ratified IEEE 802.15.6 Wireless Body Area Network (WBAN) standard. This data communication method uses the human body itself as the signal propagation medium.