In der folgenden Ausarbeitung soll der Einfluss der vertikalen Auflösung der Eingangsprofile auf die Schallausbreitungsrechnungen eines Schallstrahlenmodells näher untersucht werden. Der Grund hierfür liegt in dem Auftreten eines „Schichtenproblems“ bei der Arbeit mit einem solchen Modell. Das bedeutet, dass je größer die vertikale Auflösung der Eingangsprofile ist, desto mehr weicht die mit dem Computermodell bestimmte Lösung von der analytischen ab. Im folgenden Beitrag werden verschiedene vertikale Auflösungen untersucht und es wird gezeigt, dass eine höhere Auflösung dieses Problem lösen kann. Die Berechnungen erfolgen mit dem Schallstrahlenmodell SMART. Dieses Modell basiert auf der Berechnung des Weges, den der Schall in einer geschichteten Atmosphäre zurücklegt. Die Berechnungsgrundlage für das Strahlenmodell bilden dabei aus Radiosondendaten interpolierte, sowie klimatologisch klassifizierte Temperatur- und Windprofile. Diese Untersuchungen stellen eine notwendige Grundlage bei der Analyse und Interpretation der durch ein Strahlenmodell gewonnenen Dämpfungsberechnungen dar. / In the following article, effects of the vertical resolution of input data on numerical sound attenuation simulations are investigated. The reason for this lies in the occurrence of a „layer problem“ during work with such a model. That means, even larger the vertical resolution of the input profiles is, so much more the calculated answer deviates from the analytic. Therefore, different vertical resolutions are examined. The analyzed results show that a higher resolution can solve this problem. Calculations are carried out using the sound ray model SMART which considers the dependency of sound ray propagation on stratified atmosphere. As a basis for calculating the sound ray paths interpolated and climatologically classified profiles of temperature and wind obtained from radiosonde data are utilized. These investigations provide a basis for the analysis and interpretation of attenuation calculations derived from a sound ray model.

A key aspect of immersive audio is realistic acoustics. To get plausible acoustics for an environment the impulse response can be generated using acoustic simulations and should ideally be updated in real-time for interactive applications. In this thesis the listening experience of sound generated with an interactive sound propagation engine was explored and compared to spatial sound produced with a static impulse response. The aim was to evaluate the sound experience for applications outside of virtual reality, with computational cost in consideration. This was done by conducting a user study where the participants got to interact and compare the two sound methods in different environments. The study was performed using a custom developed application integrated with a pre-existing sound propagation engine. The results from the user study showed no obvious perceptive difference between the two sound rendering methods that could justify the extra computations. Overall there was even a slight preference for the stereo method that used a static impulse response. However, there were qualities to both sound rendering methods that were preferred depending on the environment. Another thing that was investigated in the work of this thesis was how the varying accuracy of localization of sound in different directions can be used in acoustic ray tracing algorithms. An alternative sampling method was developed that uses a biased distribution based on spatial resolution of human hearing instead of traditional uniform sampling. The computation time of the random sampling phase increases, but could potentially reduce the number of ray samples needed. / <p>Examensarbetet är utfört vid Institutionen för teknik och naturvetenskap (ITN) vid Tekniska fakulteten, Linköpings universitet</p>

Previously used standardized calculation methods for sound propagation contain the influence of meteorological parameters just in a very simplified way. But the propagation of acoustic signals over a distance of several kilometers is essentially dependent on the distribution of temperature and wind. The sound level attenuation maps shown in this work have been calculated with the use of the sound ray model SMART (Sound propagation Model of the Atmosphere using Ray-Tracing). They demonstrate the meteorological influence on the sound attenuation in a distance of up to 15 km from the sound source. SMART takes the current or the predicted state of the atmosphere into account to depict the distribution of sound attenuation near the ground surface. Therefore it is an instrument which is able to estimate sound immission for a current or future moment (sound weather). Applied to meteorological data of longer time periods typical mean sound immissions for individual regions can be derived, which is referred as sound climate. On the one hand these attenuation maps firstly clarify the difference between these two terms. On the other hand they show the dependence of sound propagation on atmospheric conditions on several timescales. Radiosonde data from the years 1990 – 2009 were used for this analysis. A second part of this study deals with the question whether observational data (radiosonde) can be replaced by model data (COSMO-EU). For this purpose data of the station of Bergen was used for the year 2009. / Bisher verwendete standardisierte Berechnungsverfahren für die Schallausbreitung beinhalten meteorologische Einflüsse nur in stark vereinfachter Weise. Die Ausbreitung akustischer Signale über mehrere Kilometer Entfernung hängt jedoch wesentlich von der Temperatur- und Windverteilung im Gebiet des Emissionsortes ab. In der Umgebung einer Schallquelle bis hin zu einer Entfernung von 15 km wird in dieser Studie der meteorologische Einfluss auf Schallpegeldämpfungskarten dargestellt, die mit Hilfe des Schallstrahlenmodells SMART (Sound propagation Model of the Atmosphere using Ray-Tracing) berechnet wurden. Das Modell SMART bezieht dabei die beobachteten bzw. prognostizierten meteorologischen Verhältnisse in die Darstellung der bodennahen Schalldämpfungsverteilung ein. Es ist damit ein Instrument für die Abschätzung der Schallimmission zu einem aktuellen oder zukünftigen Zeitpunkt (Schallwetter). Angewendet auf meteorologische Daten aus längeren Zeitabschnitten sind mittlere, für einzelne Regionen typische Schallimmissionsaussagen ableitbar, was hier als Schallklima bezeichnet wird. Diese Dämpfungskarten sollen zum einen den Unterschied dieser beiden Begriffe verdeutlichen, auf der anderen Seite aber auch die Abhängigkeit beider Zeitrahmen von der Meteorologie aufzeigen. In die Auswertungen gehen Radiosondenbeobachtungen aus den Jahren 1990 – 2009 ein. Ein zweiter Teil dieser Arbeit befasst sich mit der Frage der Ersetzbarkeit von Beobachtungsdaten (Radiosonde) durch Modelldaten (COSMO-EU). Diese Analyse erfolgt beispielhaft für die Station Bergen für das Jahr 2009.

Die Schallausbreitung in der Atmosphäre wird durch vertikale Gradienten meteorologischer Größen, insbesondere Lufttemperatur und Windvektor, maßgeblich beeinflusst. Ziel dieser Studie ist die Abschätzung des Einflusses einer Schallstrahlenrefraktion infolge von Temperatur- und Windgradienten auf die Laufzeit akustischer Signale zwischen Sendern und Empfängern. Mit Hilfe des hier vorgestellten Schallstrahlenmodells SMART (Sound propagation model of the atmosphere using ray-tracing) wird die Differenz der Laufzeiten entlang des gekrümmten Schallweges (mit Refraktion) und entlang der geraden Verbindungslinie (ohne Refraktion) zwischen einem Sender und einem Empfänger berechnet. Je größer die Sender-Empfänger-Entfernung und je größer der Unterschied zwischen Sender- und Empfängerhöhe sind, desto größer sind auch die Beträge der Laufzeitunterschiede. Der gekoppelte Einfluss von Temperatur- und Windprofil auf die Schallstrahlenrefraktion lässt zum großen Teil jedoch keine pauschalen Abschätzungen der Laufzeitdifferenz zu. Die erzielten Untersuchungsergebnisse werden insbesondere für eine Einschätzung der Anwendbarkeit einer Schallstrahlapproximation (geradlinige Schallstrahlen) bei der akustischen Laufzeittomographie benötigt. / Sound propagation inside the atmosphere is mainly influenced by vertical gradients of meteorological quantities, in particular air temperature and wind vector. The aim of this study is to estimate the influence of the sound ray refraction on the travel time of acoustic signals between transmitters and receivers due to temperature and wind gradients. The difference of the travel times along the curved sound ray (with refraction) and along the straight line (without refraction) between the transmitter and the receiver is calculated by means of the presented sound-ray model SMART (Sound propagation model of the atmosphere using ray-tracing). The greater the transmitter-receiver-distances, and the greater the height-level differences of transmitter and receiver, the greater are the travel-time differences. However, the coupled influence of temperature and wind profiles on the sound-ray refraction does mostly not allow an universal estimation of the travel-time difference. The obtained results are necessary to validate the sound-ray approximation (straight-line approximation) applied by the acoustic tomography.

Eine wichtige Aufgabe des Umweltschutzes besteht in der Überwachung von Geräuschimmissionen. Die Grenzen der bisher verwendeten, operationellen Verfahren zeigen sich vor allem darin, dass der Einfluss der Atmosphäre auf die Schallausbreitung nur unzureichend berücksichtigt wird. In dieser Studie wird deshalb ein Modell aus dem Bereich der geometrischen Akustik zur Einbeziehung des Atmosphärenzustandes in die Schallprognose vorgestellt. Das Modell SMART (Sound propagation model of the atmosphere using ray-tracing) bestimmt die durch Schallstrahlenrefraktion modifizierten Schallausbreitungsbedingungen für ein Gebiet entsprechend der vorgegebenen thermischen Atmosphärenschichtung und den Vertikalprofilen von Windgeschwindigkeit und –richtung. Ein wichtiger Schritt bei der Weiterentwicklung von SMART war die Implementierung eines Refraktionsgesetzes, welches die Schallstrahlenbrechung an Schichtgrenzen in einem zweidimensional geschichteten, bewegten Medium exakt beschreibt. Die Unterschiede in der Schallstrahlenberechnung zwischen diesem Modell und früheren Simulationen machen sich insbesondere für Entfernungen von der Schallquelle zwischen 1 und 3 km bemerkbar. Da in diesem Bereich eine verstärkte Lärmbelastung gegenüber vorangegangenen Simulationen auftritt, wird die Verwendung des physikalisch exakten Refraktionsgesetzes für eine bewegte Atmosphäre im Rahmen von Lärmschutzuntersuchungen empfohlen. / An important problem regarding the environmental protection is the immission control of noise. The applicability of currently operational methods is limited because the influence of the atmosphere on the sound propagation is only insufficiently taken into account. Thus, a geometrical sound propagation model is presented in this study to include the state of the atmosphere into the forecast of noise immission. The model SMART (Sound propagation model of the atmosphere using ray-tracing) calculates the modified sound propagation conditions due to sound-ray refraction for an area according to the given thermal stratification of the atmosphere and the vertical profiles of wind speed and wind direction. An important step during the further development of the model SMART was the implementation of a refraction law, that is exactly valid for the sound-ray refraction at the boundary between two layers with different properties inside a twodimensional, stratified moving medium. Maximal differences between simulations with this model and former investigations occur at a distance of 1-3 km away from the sound source. A stronger noise immission is also notable in this area. Because of this result it is recommended to use the presented physically more exact refraction law for a moving atmosphere within the scope of noise immission control.

Mit dem Schallstrahlenmodell SMART (Sound propagation model of the atmosphere using ray-tracing) werden die Auswirkungen der Schallstrahlenrefraktion in der Atmosphäre und der Schallstrahlenreflexion am schallharten Boden auf die Schallimmission untersucht. Die gekoppelte Wirkung von Temperatur-, Windgeschwindigkeits- und Windrichtungsprofilen auf die Lärmbelastung an einem Ort über einer schallharten Oberfläche wird für eine große Anzahl möglicher Atmosphärenzustände simuliert und mit Schallausbreitungsrechnungen für eine absorbierende Bodenschicht verglichen. Ein Drittel der Bildpunkte der resultierenden Schalldämpfungskarten unterscheiden sich im Mittel signifikant voneinander. Die größten Unterschiede ergeben sich bei Temperaturinversionen. Hier treten für die Simulationen mit Bodenreflexionen geringere Schalldämpfungen gegenüber dem Fall ohne Bodenreflexionen auf. Diese kritischen Situationen mit einer verstärkten Lärmbelastung sind bei einer Überarbeitung von Lärmschutzrichtlinien besonders zu beachten. / Effects of sound-ray refraction in the atmosphere and sound-ray reflection at the sound-hard surface on the sound immission are investigated using the sound-ray model SMART (Sound propagation model of the atmosphere using ray-tracing). The coupled effect of temperature, wind velocity and wind direction profiles on the noise immission at one location over a sound-hard surface is simulated for a great number of possible states of the atmosphere. The results are compared with sound propagation simulations over a sound-absorbing soil layer. One third of the pixels of the resulting sound attenuation maps are significantly different from each other on the average. The greatest differences appear in cases of temperature inversion. Thereby, the simulations with reflections at the surface lead to smaller sound attenuation in comparison to the case without reflections at the surface. Such critical situations with an amplified noise immission have to be especially considered during the improvement process of noise immission control.

Wind power is a rapidly increasing resource of electrical power world-wide. With the increasing number of wind turbines installed one major concern is the noise they generate. Sometimes already built wind turbines have to be put down or down-regulated, when certain noise levels are exceeded, resulting in economical and environmental losses. Therefore, accurate sound propagation calculations would be beneficial already in a planning stage of a wind farm. A model that can account for varying wind speeds and complex terrains could therefore be of great importance when future wind farms are planned. In this report an extended version of the classical wave equation that allows for variations in wind speed and terrain is derived which can be used to solve complex terrain and wind settings. The equation are solved with the use of Fourier transforms and Chebyshev polynomials and a numerical code is developed. The numerical code is evaluated against test cases where analytical and simple solutions exist. Tests with no wind for both totally free propagation and with a ground surface is evaluated in both 2D and 3D settings. For these simple cases the developed code shows good agreement to analytical solutions if the computational domain is sufficiently large. More advanced test cases with wind and terrain is not evaluated in this report and needs further validation. If the sound pressure needs to be calculated for a large area, and if the frequency is high, the developed model has problems regarding computational time and memory. These problems could be solved by further development of the numerical code or by using other solution methods.

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The payload environment of a rocket is random and dynamic during liftoff and flight, with acoustic noise, vibration, and acceleration falling under its definition. Characterization of this environment is important to finalize payload design requirements and insure mission completion. This report will focus on the study and measurement of acoustic noise using a low-cost microphone. Various spectral analysis techniques were utilized to characterize acoustic intensities and frequency content. Effects of vibration and acceleration, ground reflection, atmospheric absorption, and nonlinear propagation were investigated. Noise data were obtained from a rocket launch and several vertical, staticired hybrid motors. The propulsion system acoustic loads were compared to prediction methods from NASA SP-8072.

Prediction of the sound field in large urban environments has been limited thus far by the heavy computational requirements of conventional numerical methods such as boundary element (BE), finite-difference time-domain (FDTD), or ray-tracing methods. Recently, a considerable amount of work has been devoted to developing energy-based methods for this application, and results have shown the potential to compete with conventional methods. However, these developments have been limited to two-dimensional (2-D) studies (along street axes), and no real description of the phenomena at issue has been exposed (e.g., diffraction effects on the predictions). The main objectives of the present work were (i) to evaluate the feasibility of an energy-based method, the diffusion model (DM), for sound-field predictions in large, 3-D complex urban environments, (ii) to propose a numerical hybrid method that could improve the accuracy and computational time of these predictions, and (iii) to verify the proposed hybrid method against conventional numerical methods. The proposed numerical hybrid method consists of a full-wave model coupled with an energy-based model. The full-wave model is used for predicting sound propagation (i) near the source, where constructive and destructive interactions between waves are substantial, and (ii) outside the cluttered environment, where free-field-like conditions apply. The energy-based model is used in regions where diffusion conditions are met. The hybrid approach, as implemented in this work, is a combination of FDTD and DM models. Results from this work show the role played by diffraction near buildings edges close to the source and near the exterior boundaries of the computational domain, and its impact on the predictions. A wrong modeling of the diffraction effects in the environment leads to significant under or overpredictions of the sound levels in some regions, as compared to conventional numerical methods (in these regions, some differences are as high as 10 dB). The implementation of the hybrid method, verified against a full FDTD model, shows a significant improvement of the predictions. The mean error thus obtained inside the cluttered region of the environment is 1.5 dB. / Master of Science