Long-term omni-directional ambient noise was collected at several sites in the Gulf of Mexico during 2004 and 2005. The Naval Oceanographic Office deployed bottom moored Environmental Acoustic Recording System (EARS) buoys approximately 159 nautical miles south of Panama City, Florida, in water depths of 3200 meters. The hydrophone of each buoy was 265 meters above the bottom. The data duration ranged from 10-14 months. The buoys were located near a major shipping lane, with an estimated 1.5 to 4.5 ships per day passing nearby. The data were sampled at 2500 Hz and have a bandwidth of 10-1000 Hz. Data are processed in eight 1/3-octave frequency bands, centered from 25 to 950 Hz, and monthly values of the following statistical quantities are computed from the resulting eight time series of noise spectral level: mean, median, standard deviation, skewness, kurtosis and coherence time. Four hurricanes were recorded during the summer of 2004 and they have a major impact on all of the noise statistics. Noise levels at higher frequencies (400-950 Hz) peak during extremely windy months (summer hurricanes and winter storms). Standard deviation is least in the region 100-200 Hz but increases at higher frequencies, especially during periods of high wind variability (summer hurricanes). Skewness is positive from 25-400 Hz and negative from 630-950 Hz. Skewness and kurtosis are greatest near 100 Hz. Coherence time is low in shipping bands and high in weather bands, and it peaks during hurricanes. The noise coherence is also analyzed. The 14-month time series in each 1/3- octave band is highly correlated with other 1/3-octave band time series ranging from 2 octaves below to 2 octaves above the band's center frequency. Spatial coherence between hydrophones is also analyzed for hydrophone separations of 2.29, 2.56 and 4.84 km over a 10-month period. The noise field is highly coherent out to the maximum distance studied, 4.84 km. Additionally, fluctuations of each time series are analyzed to determine time scales of greatest variability. The 14-month data show clearly that variability occurs primarily over three time scales: 7-22 hours (shipping-related), 56-282 hours (2-12 days, weather-related) and over an 8-12 month period.

Les travaux présentés dans ce manuscrit sont basés sur des études précédentes réalisées à l’Institut d’Électronique de Microélectronique et de Nanotechnologie (IEMN) de l’Université de Valenciennes et du Hainaut Cambrésis (UVHC). Ils concernent le développement d’un système de surveillance embarqué destiné au contrôle des matériaux et des structures utilisés dans différents domaines de transport (fluidique, tubulaire, aéronautique, ferroviaire…). Il s’agit du principe de Contrôle Santé Intégré CSI (ou SHM en anglais pour Structural Health Monitoring). L’idée est d’intégrer des capteurs sur les surfaces des structures à contrôler pour aboutir à un système de contrôle non destructif de ces dernières durant la totalité de leurs fonctionnements. Tout d’abord, les travaux réalisés à l’IEMN dans ce domaine sont illustrés, quelques définitions comme celles des ondes ultrasonores, du Contrôle Non Destructif et du Contrôle Santé Intégré sont rappelées, avant d’aborder l’explication du passage d’un contrôle actif à un contrôle passif. Dans un deuxième temps, un algorithme de comparaison d’images basé sur les minimums locaux présents dans ces images a été proposé et testé sur des images simples de seize pixels, et a permis de tester le degré de ressemblance entre elles. L’explication de l’algorithme développé est divisée en deux grandes parties. Dans la première nous expliquons comment extraire les minimums locaux d’une image. La deuxième partie expose la procédure pour déterminer le taux de ressemblance entre les images. La simulation de la propagation d’un signal dans une plaque réverbérante et l’obtention des images temps-fréquence correspondantes à des corrélations filtrées (autocorrélation) ont été décrites. L’algorithme proposé a été validé sur ces images, permettant ainsi la localisation d’une position inconnue de la source. / The works presented in this manuscript are based on previous studies conducted at the Institute of Electronics Microelectronics and Nanotechnology of the University of Valenciennes and Hainaut Cambrésis. They concern the development of an embedded monitoring system for the control of materials and structures used in different transport domains (pipeline, aerospace, railway ...). This is the Structural Health-Monitoring principle. The idea is to integrate sensors into the surfaces of the controlled structures in order to achieve a non-destructive control system for the control of the latter during their entire lifetime. First the work done at the laboratory in this domain, are illustrated, some definitions such as ultrasonic waves, the Non Destructive Testing and the Structural Health Monitoring are recalled, to switch later to the explanation of the passage from an active control to a passive control. In a second step, an images comparison algorithm based on the local minima present in these images has been proposed and tested on simple images of sixteen pixels and was used to test the degree of resemblance between them. The explanation of the developed algorithm is divided into two parts. In the first one, we explain how to extract the local minima of an image. The second part describes the procedure for determining the rate of resemblance between the images. The simulation of the propagation of a signal in a reverberant plate and the obtaining of the frequency time images corresponding to filtered correlation (autocorrelation) has been described. The algorithm was validated on those images allowing the localization of an unknown source position.

Cette thèse porte sur l’application de la technique de corrélation de bruit sismologique ambiant pour l'imagerie et le suivi des réservoirs géothermiques de Rittershoffen (ECOGI) et de Soultz-sous-Forêts (GEIE-EMC). La forte variabilité spatio-temporelle des sources du bruit de fond sismologique dans la gamme de période 0.2-7s limite la reconstruction des fonctions de Green. Cela induit des erreurs dans la construction des modèles de vitesse. Deux approches sont proposées pour s’affranchir des effets de la non-uniformité spatiale du bruit. Par ailleurs, la variabilité temporelle des sources de bruit est un facteur limitant pour le suivi du réservoir. On estime que les perturbations de vitesse doivent être de l’ordre de 0.1% à 1% pour pouvoir être détectées par les réseaux disponibles. Ce seuil n’a pas été franchi lors de la construction du site Rittershoffen mais une modification probable des propriétés diffractantes du milieu a été observée à la suite d’une stimulation. / This work focuses on the application of the ambient seismic noise correlation technique for the imaging and monitoring of deep geothermal reservoirs near Rittershoffen (ECOGI) and Soultz-sous-Forêts (GEIE-EMC). The strong spatial and temporal variability of the noise sources in the period range 0.2-7s limits the reconstruction of the Green’s functions. This results in significant errors in the velocity models. Two approaches are proposed to overcome the spatial non-uniformity of the noise and to improve the quality of the velocity models. Besides that, the temporal variability of the noise sources is a limiting factor for monitoring purposes. We estimate that the speed variations should be larger than 0.1% to 1% to be detected by the available networks. This threshold was not reached at Rittershoffen during the drillings or the stimulations. However, a probable change of the diffracting properties of the medium was observed following a hydraulic stimulation.

Nightclubs and restaurant bars have become major sources of noise pollution particularly in areas close to residential dwellings. The purpose of this study was to investigate the impact of noise emanating from nightclubs and restaurant bars on the community of Melville, Johannesburg. This study followed both qualitative and quantitative research methods. A total of 100 respondents were randomly sampled within the study area. Qualitative data was collected using a structured questionnaire. A calibrated sound level meter was used to measure environmental noise levels at 10 different measuring points. The research finding revealed that about:  87% of noise levels measured with the sound level meter did not comply with officially acceptable levels of 40dB at night.  69% of respondents indicated that the main source of noise is pollution is nightclubs.  78% of respondents described noise as annoying, disturbing and unwanted.  57% of respondents indicated that members of their household have suffered from sleeping disorders due to noise activities at night disrupting their sleep patterns and resulting in irritability and fatigue. The noise measurements were taken on weekends and public holidays during the day from 10h00 to 14h30 and at night from 22h00 to 02h30. The research findings revealed that the residents of Melville experienced high level of noise at night with nightclub as major source of noise and as a result the majority of the sampled population complained about irritability, fatigue and sleeping disorders due to exposure to noise. The outcome of this research indicated the need of health education on the adverse effects of noise pollution and the need of sound insulation at places of entertainment. Implementation of a noise management policy is needed in order to effectively control and manage the noise pollution in its area of jurisdiction and regular noise level monitoring by constantly taking noise measurements by law enforcements officers. / Department of Environmental Sciences / M. Sc. (Environmental Management)