Underwater acoustic modelling is an important aspect of Synthetic Aperture Sonar (SAS) system design and algorithm development. Sea-trials are an expensive and time-consuming exercise and simulations provide an efficient and economic alternative. However, there are few simulators (in the open literature) that can efficiently provide realistic SAS data for large, complicated scenes. Conventional side-scan sonar simulators are not suitable for SAS data simulation. These simulators utilise narrow-beam and narrow-band approximations; typical SAS systems are wide-beam and wide-band and these approximations are invalid. Moreover, conventional side-scan sonar is a non-coherent imaging technique and SAS processing relies on the phase. Existing SAS simulators are capable of modelling very simple scenes only. They utilise a decomposition of the scene into point or smooth facet primitives, which is very inefficient. Many primitives are required and this imposes a severe restriction on scene complexity and size. This thesis presents a rigorous mathematical framework for the modelling of SAS imagery. A novel acoustic scattering model is developed and its implementation in a wide-beam and wide-band, multiple-receiver Interferometric SAS (InSAS) simulator is detailed. The scattering model utilises a decomposition of the scene into rough (rather than smooth) facet primitives. The use of rough facet primitives provides a significant increase in computational efficiency since scenes are decomposed into fewer primitives. This facilitates the simulation of larger and more complicated scenes. Each rough facet is characterised by its far-field beampattern. The statistics of the beampattern are related to the facet shape and roughness statistics using the Kirchhoff approximation. The beampattern is realised from its first and second-order statistics. The SAS imagery is obtained using a coherent sum of the facet responses and occlusions and multiple-scattering are resolved by ray-tracing. The simulator is implemented for use on a parallel computing cluster. The simulator is shown to provide realistic SAS data that is qualitatively and quantitatively similar to real data. The simulated results are considered, in many ways, superior to the simulated results in the literature.

High-resolution seismic images of lithospheric structures allow us to infer the tectonics that modified the lithosphere. We apply such methods to understand Cenozoic modification of the lithosphere by tectonic and magmatic processes in the tectonically active western United States. Using USArray Transportable and Flexible Array data, we present high-resolution images for three regions in this thesis. (1) In the Mendocino triple junction, we use a joint inversion of Rayleigh-wave dispersion data and receiver functions to obtain a new crust and upper Vs model to ~150km depth. The model shows four distinct, young lithosphere-asthenosphere boundary systems. A low-Vs anomaly beneath the Great Valley-Sierra Nevada reconciles existing slab window models with the mantle-wedge geochemical signatures in Coast Range volcanics, and explains the ~3 Myr delay of the onset of volcanism after slab removal. Uppermost mantle low velocities provide evidence for forearc mantle serpentinization extending along the Cascadia margin. (2) In the Colorado Plateau, a Rayleigh wave tomography model sheds light on the volcanism along the margins and plateau uplift. Strong upper mantle heterogeneity across the plateau edge results from the combined effect of a ~200-400 K temperature difference and ~1% partial melt. A ring of low velocities under the plateau periphery suggests that the rehydrated Proterozoic lithosphere is progressively removed by convective processes. Particularly, a high-Vs anomaly imaged beneath the western plateau adds evidence for a downwelling/delamination hypothesis [Levander et al., 2011]. Thermo-chemical edge-driven convection causing localized lithospheric downwelling provides uplift along the margins and magmatic encroachment into the plateau center. (3) In the final study, we developed a 3-D teleseismic scattering wave imaging technique based on the Kirchhoff approximation and 3-D inverse Generalized Radon Transform. Synthetic tests demonstrate higher resolution imaging for continuous, irregular interfaces or localized scatterers, in comparison to conventional methods. Applied to the High Lava Plains dataset, the transmission coefficient structure shows a deepening Moho near 117.6°W and three negative events that correlate well with the Rayleigh wave low-Vs zones. Images made with the Mendocino data clearly show rapidly decreasing lithosphere-asthenosphere boundary depths from the subduction to transform regime.

Transportation is the main source of environmental noise in Europe, with an estimated 125 million people affected by excessive noise levels from road traffic, causing a burden of noise related diseases and having a substantial economic impact on society. In order to reduce exposure to high levels of traffic noise, two approaches are the topic of extensive research: preventing sound from propagating from roads and railways using for example noise barriers, and reducing the sources of noise themselves. The second solution, which addresses directly the cause of the problem, requires improved design methods, with a more systematic resort to multi-functional design. Addressing cross-functions simultaneously reduces the number of design iterations and the high cost of prototyping. The work presented in this thesis aims at developing methods that can be used to design quieter vehicle concepts within a multi-functional approach, and is articulated around two main axis of research, aerodynamic sound generation and sound propagation. The first axis aims at performing an aeroacoustic analysis to predict aerodynamic sound sources. A hybrid method is used on the example of a type of submerged air inlet called a NACA duct, where the near-field flow is solved through detached eddy simulation (DES) and where the far-field acoustics is computed using the Ffowcs Williams and Hawkings integral. Results for the flow for various operating conditions are presented and validated against experimental data from the literature, with very good agreement. Far-field acoustic results are shown, exhibiting levels and components that are strongly dependent on the operating conditions. This analysis gives a framework for future aeroacoustic analysis in the project, and sets the path for the development of air inlets with improved aerodynamic and aeroacoustic characteristics. The second axis focuses on the propagation of sound from a given source, moving in an urban environment. An approximate boundary method is presented, which relies on the Kirchhoff approximation applied to the Kirchhoff-Helmholtz integral equation. Using this approximation speeds up the computational time compared to using a regular boundary element method. The resulting expression is extended to account for multiple scattering through consecutive updates of the surface pressures, and for moving sources through the introduction of a retarded time and of a Doppler shift. Validation tests for this method are presented, from simple scatterers to a more realistic configuration, showing good agreement with analytical, experimental and simulated work. / Fordon är den främsta källan till bullerexponering i Europa med uppskattningsvis 125 miljoner människor som är utsatta för höga ljudnivåer från vägtrafik, vilket kan orsaka bullerrelaterade häsloproblem samt har en betydande ekonomisk effekt på samhället. För att minska exponeringen för höga ljudnivåer från fordon, finns det två angreppssätt som båda idag är ämne för omfattande forskning: att förhindra ljudutbredning från vägar och järnvägar (till exempel med hjälp av bullerskydd), samt att minska ljudnivån från olika bullerkällor. Den sistnämnda, som direkt riktar sig till problemets orsak, kräver förbättrade designmetoder med mer systematisk användning av multifunktionell design. Att hantera flera funktioner hos fordonet samtidigt minskar antalet designiterationer och den höga kostnaden för prototyper. Arbetet som presenteras i denna avhandling syftar till att utveckla metoder som kan användas för att utforma tystare fordonskoncept inom ramen för en multifunktionell strategi och fokuserar på två spår i forskningen: aerodynamisk ljudalstring och ljudutbredning från rörliga källor. Det första spåret i forskningen syftar till att utföra en aeroakustisk undersökning för att modellera aerodynamiska ljudkällor. En hybridmetod tillämpas på ett typ av nedsänkt luftintag, kallat NACA-intag, där källområdet i strömningen löses genom detached eddy simulation (DES) och akustiken i fjärrfältet beräknas enligt Ffowcs Williams och Hawkings integral. Resultat för strömningen för olika driftförhållanden presenteras och valideras mot experimentella data från litteraturen, med mycket god överensstämmelse. Resultat för det akustika fjärrfältet visas, vilket uppvisar nivåer och komponenter som är starkt beroende av driftförhållandena. Denna analys ger en ram för kommande analyser av aeroakustik inom projektet och visar vägen för utvecklingen av luftintag med förbättrade aerodynamiska och aeroakustika egenskaper. Det andra spåret i forskningsprojektet är inriktat på ljudets utbredning från en given källa som rör sig i en urban miljö. En approximativ randvärdesmetod presenteras som bygger på Kirchhoff approximation tillämpad på Kirchhoff-Helmholtz integralekvation. Med hjälp av denna approximation minskas beräkningstiden jämfort med vanlig boundary element method (BEM). Modellen utvecklas sedan för att kunna hantera flera reflektioner genom att det akustiska trycket på ytorna uppdateras för varje reflektion samt för att kunna hantera rörliga källor genom att introducera tidsfördröjningar och Dopplerförskjutning. Validering för denna modell presenteras, från enkla spridare till en mer realistisk urban konfiguration, som visar god överensstämmelse med analytiskt, experimentellt och simulerat data. / <p>QC 20151002</p>

The potential for high spatio-temporal resolution microwave measurements has urged the adoption of the signals of opportunity (SoOp) passive radar technique for use in remote sensing. Recent trends in particular target highly complex remote sensing problems such as root-zone soil moisture and snow water equivalent. This dissertation explores the continued open-sourcing of the SoOp coherent bistatic scattering model (SCoBi) and its use in soil moisture sensing applications. Starting from ground-based applications, the feasibility of root-zone soil moisture remote sensing is assessed using available SoOp resources below L-band. A modularized, spaceborne model is then developed to simulate land-surface scattering and delay-Doppler maps over the available spectrum of SoOp resources. The simulation tools are intended to provide insights for future spaceborne modeling pursuits.

Le sujet porte sur l'étude de systèmes SAS (Synthetic Aperture Sonar) multistatiques. Ces systèmes permettent d'obtenir des images de cibles mieux résolues qu'avec un sonar classique à partir d'ondes acoustiques. Le SAS est largement exploité en configuration monostatique mais il existe très peu d'études à ce jour en SAS multistatique. Le travail consiste donc à évaluer les performances en configuration bistatique et multistatique et à les comparer à celles connues en configuration monostatique. Une méthode de calcul utilisée en radar a donc été mise en oeuvre en sonar de façon à expliciter la résolution en configuration bistatique, ce qui est un résultat original de ce travail. L'algorithme classiquement utilisé pour reconstruire des images repose sur l'hypothèse que la cible est une somme de points brillants. Cette hypothèse n'est pas bien adaptée en acoustique sous-marine. Un nouvel algorithme a donc été développé dans le but de se rapprocher des phénomènes de diffraction présents à l'interface entre l'eau et la cible. Le modèle de champ diffracté est obtenu par la combinaison d'équations intégrales de frontière avec l'approximation de Kirchhoff. Une méthode de reconstruction d'images par transformée de Fourier 2D de ce modèle a été implémentée et testée sur des données simulées, puis sur des données obtenues lors d'essais en cuve. Le nouvel algorithme montre une meilleure précision de la reconstruction et la capacité de pouvoir extraire de l'information quantitative de la cible. L'intérêt des configurations multistatiques pour la reconnaissance de cibles a également été démontré dans ces travaux de thèse. / This study deals with multistatic SAS (Synthetic Aperture Sonar) systems. SAS are high resolution imaging systems compared to classical sonar ones. The SAS technique is largly exploited in the monostatic configuration but few studies already exist in multistatic SAS. Thus, the work consists in evaluating resolution and detection performances in bistatic and multistatic configurations. Then, the objective is to compare these performances to monostatic ones. A radar method has been adapted to sonar to compute bistatic performances and this is an original result of this work.The classical algorithm to reconstruct images from acoustical waves lies on the hypothesis that the target is a sum of point scatterers. This hypothesis is not really well adapted to underwater acoustics that is why a new algogorithm has been developped in this study. The new algorithm would be better adapted to scattering diffraction phenomena at the interface between water and target than the classical one. The scattered field model of the target is obtained by combinating boundary integral equations and the Kirchhoff Approximation. An imaging reconstruction method by 2D Fourier Transform of this model has been implemented and tested on numerical and experimental datas. The new algorithm allow a better reconstruction accurency and is able to give quantitative information on targets. The interest of multistatic configurations for target identification has also been demonstrated in this PhD work.

This diploma thesis deals with a spatial imaging of targets using time-domain radar responses on the max(t,0) pulse. The problem is formulated for both perfectly electrically conductive and dielectric objects. The main aim of the thesis includes a code implementation calculating the profile functions of an unknown object from the mentioned time responses and a code for the subsequent reconstruction of an object in the MATLAB environment. A graphical user interface was created for testing purposes. The 3D probability function technique was used for the final reconstruction. The implemented technique achieves interesting results, which are presented in the final part of this thesis.

This dissertation focuses on the scattering phenomena by well-polished optical mirror surfaces. Specifically, predicting image degradation by surface scatter from rough mirror surfaces for a two-mirror telescope operating at extremely short wavelengths (9nm~30nm) is performed. To evaluate image quality, surface scatter is predicted from the surface metrology data and the point spread function in the presence of both surface scatter and aberrations is calculated. For predicting the scattering intensity distribution, both numerical and analytic methods are considered. Among the numerous analytic methods, the small perturbation method (classical Rayleigh-Rice surface scatter theory), the Kirchhoff approximation method (classical BeckmanKirchhoff surface scatter theory), and the generalized Harvey-Shack surface scatter theory are adopted. As a numerical method, the integral equation method (method of moments) known as a rigorous solution is discussed. Since the numerical method is computationally too intensive to obtain the scattering prediction directly for the two mirror telescope, it is used for validating the three analytic approximate methods in special cases. In our numerical comparison work, among the three approximate methods, the generalized Harvey-Shack model shows excellent agreement to the rigorous solution and it is used to predict surface scattering from the mirror surfaces. Regarding image degradation due to surface scatter in the presence of aberrations, it is shown that the composite point spread function is obtained in explicit form in terms of convolutions of the geometrical point spread function and scaled bidirectional scattering distribution functions of the individual surfaces of the imaging system. The approximations and assumptions in this iv formulation are discussed. The result is compared to the irradiance distribution obtained using commercial non-sequential ray tracing software for the case of a two-mirror telescope operating at the extreme ultra-violet wavelengths and the two results are virtually identical. Finally, the image degradation due to the surface scatter from the mirror surfaces and the aberration of the telescope is evaluated in terms of the fractional ensquared energy (for different wavelengths and field angles) which is commonly used as an image quality requirement on many NASA astronomy programs.

In a society where environmental noise is becoming a major health and economical concern, sound emissions are an increasingly critical design factor for vehicle manufacturers. With about a quarter of the European population living close to roads with heavy traffic, traffic noise in urban landscapes has to be addressed first. The current introduction of electric vehicles on the market and the need for sound systems to alert their presence is causing a shift in mentalities requiring engineering methods that will have to treat noise management problems from a broader perspective. That in which noise emissions need not only be considered as a by-product of the design but as an integrated part of it. Developing more sustainable ground transportation will require a better understanding of the sound field emitted in various realistic operating conditions, beyond the current requirements set by the standard pass-by test, which is performed in a free-field. A key aspect to improve this understanding is the development of efficient numerical tools to predict the generation and propagation of sound from moving vehicles. In the present thesis, a methodology is proposed aimed at evaluating the pass-by sound field generated by vehicle acoustic sources in a simplified urban environment, with a focus on flow sound sources. Although it can be argued that the aerodynamic noise is still a minor component of the total emitted noise in urban driving conditions, this share will certainly increase in the near future with the introduction of quiet electric engines and more noise-efficient tyres on the market. This work presents a complete modelling of the problem from sound generation to sound propagation and pass-by analysis in three steps. Firstly, computation of the flow around the geometry of interest; secondly, extraction of the sound sources generated by the flow, and thirdly, propagation of the sound generated by the moving sources to observers including reflections and scattering by nearby surfaces. In the first step, the flow is solved using compressible detached-eddy simulations. The identification of the sound sources in the second step is performed using direct numerical beamforming with linear programming deconvolution, with the phased array pressure data being extracted from the flow simulations. The outcome of this step is a set of uncorrelated monopole sources. Step three uses this set as input to a propagation method based on a point-to-point moving source Green's function and a modified Kirchhoff integral under the Kirchhoff approximation to compute reflections on built surfaces. The methodology is demonstrated on the example of the aeroacoustic noise generated by a NACA air inlet moving in a simplified urban setting. Using this methodology gives insights on the sound generating mechanisms, on the source characteristics and on the sound field generated by the sources when moving in a simplified urban environment. / I ett samhälle där buller håller på att bli ett stort hälsoproblem och en ekonomisk belastning, är ljudutsläpp en allt viktigare aspekt för fordonstillverkare. Då ungefär en fjärdedel av den europeiska befolkningen bor nära vägar med tung trafik, är åtgärder för minskat trafikbuller i stadsmiljö en hög prioritet. Introduktionen av elfordon på marknaden och behovet av ljudsystem för att varna omgivningen kräver också ett nytt synsätt och tekniska angreppssätt som behandlar bullerproblemen ur ett bredare perspektiv. Buller bör inte längre betraktas som en biprodukt av konstruktionen, utan som en integrerad del av den. Att utveckla mer hållbara marktransporter kommer att kräva en bättre förståelse av det utstrålade ljudfältet vid olika realistiska driftsförhållanden, utöver de nuvarande standardiserade kraven för förbifartstest som utförs i ett fritt fält. En viktig aspekt för att förbättra denna förståelse är utvecklingen av effektiva numeriska verktyg för att beräkna ljudalstring och ljudutbredning från fordon i rörelse. I denna avhandling föreslås en metodik som syftar till att utvärdera förbifartsljud som alstras av fordons akustiska källor i en förenklad stadsmiljö, här med fokus på strömningsgenererat ljud. Även om det aerodynamiska bullret är fortfarande en liten del av de totala bullret från vägfordon i urbana miljöer, kommer denna andel säkerligen att öka inom en snar framtid med införandet av tysta elektriska motorer och de bullerreducerande däck som introduceras på marknaden. I detta arbete presenteras en komplett modellering av problemet från ljudalstring till ljudutbredning och förbifartsanalys i tre steg. Utgångspunkten är beräkningar av strömningen kring geometrin av intresse; det andra steget är identifiering av ljudkällorna som genereras av strömningen, och det tredje steget rör ljudutbredning från rörliga källor till observatörer, inklusive effekten av reflektioner och spridning från närliggande ytor. I det första steget löses flödet genom detached-eddy simulation (DES) för kompressibel strömning. Identifiering av ljudkällor i det andra steget görs med direkt numerisk lobformning med avfaltning med hjälp av linjärprogrammering, där källdata extraheras från flödessimuleringarna. Resultatet av detta steg är en uppsättning av okorrelerade akustiska monopolkällor. Steg tre utnyttjar dessa källor som indata till en ljudutbredningsmodel baserad på beräkningar punkt-till-punkt med Greensfunktioner för rörliga källor, och med en modifierad Kirchhoff-integral under Kirchhoffapproximationen för att beräkna reflektioner mot byggda ytor. Metodiken demonstreras med exemplet med det aeroakustiska ljud som genereras av ett NACA-luftintag som rör sig i en förenklad urban miljö. Med hjälp av denna metod kan man få insikter om ljudalstringsmekanismer, om källegenskaper och om ljudfältet som genereras av källor när de rör sig i en förenklad stadsmiljö. / <p>QC 20170425</p>