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This thesis presents theoretical and experimental investigations of atmospheric refraction and diffraction of sound over curved surfaces. The main contributions of this work are as follows: The development of an alternative method for calculating the influence of wind on sound propagation in the presence of a ground of finite impedance. The development of numerical models to calculate sound propagation due to monopole and dipole sources over cylindrical or spherical convex and concave surfaces of finite impedance. Laboratory measurements of sound propagation over curved surfaces and comparisons with the proposed theoretical and numerical models. The exploration of the theory for surface wave contributions in an upward refracting atmosphere in the light of obtained experimental data and observation of the surface waves above a convex surface. Experimental and theoretical investigations of the effectiveness of a barrier in the presence of sound speed gradients.

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A model for predicting the response of a system composed of a fluid halfspace, overlying a porous ground layer, resting on an elastic halfspace, to incident plane waves, is developed to include further porous elastic layers within the ground. The dynamic properties of the porous elastic layers are modelled using a modified Biot formulation. Using the same boundary conditions a Fast Field algorithm for Layered Air Ground Systems (FFLAGS) is formulated to predict acoustic propagation and acoustic-seismic coupling in the model layered system due to a point source in a horizontally stratified atmosphere. This is a full wave solution. Results are compared to those of existing propagation prediction methods. FFLAGS has been used to predict (i) the effects of temperature gradients on short range propagation over an asphalt like surface, (ii) sensitivity of received sound pressure levels to ground parameters for various atmospheric conditions, and (iii) the influence of ground parameters on acoustic-seismic coupling. Predictions of acoustic surface waves in the presence of an upward refracting atmosphere using Creeping wave theory and the FFP method have been shown to agree. Dispersion equation based predictions of surface wave types have been assessed. It has been shown that the high velocity surface waves predicted by dispersion equation solutions on porous and elastic ground surfaces are not predicted to be excited by a point source. However several other surface wave modes have been predicted in layered systems, similar to those predicted in visco-elastic media. The influence of ground elasticity on received sound pressure levels is examined. Measurable effects of elasticity of the surface are predicted for low density materials, and measured over a low density polyester foam. Controlled experiments have been performed to study the effect of soil wetting on acoustic to seismic coupling. It is found that the observed effects can be modelled using FFLAGS.

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Ocean environments with sloped seafloors can give rise to sound paths that do not remain in a constant plane of propagation. Numerical modelling of sound fields in such environments requires the use of computer models that fully account for out-of-plane sound propagation effects. The inclusion of these three-dimensional effects can be computationally intensive and the effects are often neglected in computer sound propagation codes. The current state-of-the art in sound propagation modelling has seen the development of models that can fully account for out-of-plane sound propagation. Such a model has been implemented in this research to provide acoustic consultants JASCO Applied Sciences with an important tool for environmental noise impact assessment in complicated marine environments. The model is described and validation results are shown for benchmark test cases. The model is also applied to study three-dimensional propagation effects in measured data from a realistic ocean environment. Particular analysis techniques assist in the interpretation of the modelled sound field for this physical test environment providing new insight into the characteristics of the test environment. / Graduate

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.

Die vorgestellte Methode der akustischen Tomographie (Simultane Iterative Rekonstruktionstechnik) und ein spezieller Auswertungsalgorithmus können flächengemittelte Werte meteorologischer Größen direkt bereitstellen. Somit werden zur Validierung numerischer mikroskaliger Atmosphärenmodelle weitgehend konsistente Daten geliefert. Das Verfahren verwendet die horizontale Ausbreitung von Schallstrahlen in der atmosphärischen Bodenschicht. Um einen allgemeinen Überblick zur Schallausbreitung unter verschiedenen atmosphärischen Bedingungen zu erhalten, wird ein zweidimensionales Schallausbreitungsmodell genutzt. Von Messungen der akustischen Laufzeit zwischen Sendern und Empfängern an verschiedenen Punkten in einem Meßfeld kann der Zustand der durchquerten Atmosphäre abgeschätzt werden. Die Ableitung flächengemittelter Werte für die Schallgeschwindigkeit und der daraus deduzierten Lufttemperatur resultiert aus der Inversion der Laufzeitwerte für alle möglichen Schallwege. Das angewandte zweidimensionale Tomographiemodell mit geradliniger Schallstrahlapproximation stellt dabei geringe Computeranforderungen und ist auch während des online-Betriebes einfach zu handhaben. / The presented method of acoustic tomography (Simultaneous Iterative Reconstruction Technique) and a special algorithm of analysis can directly provide area averaged values of meteorological quantities. As a result rather consistent data will be delivered for validation of numerical atmospheric rnicro-scale models. The procedure uses the horizontal propagation of sound waves in the atmospheric surface layer. To obtain a general overview of the sound propagation under various atmospheric conditions a two-dimensional ray-tracing model is used. The state of the crossed atmosphere can be estimated from measurements of acoustic travel time between sources and receivers on different points in an tomographic array. Derivation of area averaged values of the sound speed and furthermore of air temperature results from the inversion of travel time values for all possible acoustic paths. Thereby, the applied straight-ray two-dimensional tomographic model is characterised as a method with small computational requirements and simple handling, especially, during online working.