Field and greenhouse studies were conducted in 1986 and 1987 to determine the impact of disturbance of microphytic soil crust on emergence of two warm season grass species. In the greenhouse, emergence of seedlings sown on the top of undisturbed crust, under the crust, on disturbed crust, and on bare soil was studied. The mean number of seedlings of "Cochise" lovegrass (Eragrostis lehmanniana x Eragrostis tricophora) and Kleingrass (Panicum coloratum) was higher on disturbed field plots than undisturbed plots. Disturbance reduced the microphytic crust cover, and the crust did not recover throughout the growing season. Presence of seedlings in samples of litter washed off the plots and observation on ants showed that all the seeds sown did not remain on the plots during the growing season. In greenhouse flats the emergence of seedlings of both species was greater on disturbed microphytic crust and bare soil than when seeded on top of or under an intact crust. Undisturbed crust restricted penetration of roots and shoots when seeds were placed on or under the crust.

Aircraft operators demand an ever increasing availability of their fleets with constant reduction of their operational costs. With the age of many fleets measured in decades, the options to face these challenges are limited. Integrated Vehicle Health Management (IVHM) uses data gathered through sensors in the aircraft to assess the condition of components to detect and isolate faults or even estimate their Remaining Useful Life (RUL). This information can then be used to improve the planning of maintenance operations and even logistics and operational planning, resulting in shorter maintenance stops and lower cost. Retrofitting health monitoring technology onto legacy aircraft has the capability to deliver what operators and maintainers demand, but working on aging platforms presents numerous challenges. This thesis presents a novel methodology to select the combination of diagnostic and prognostic tools for legacy aircraft that best suits the stakeholders’ needs based on economic return and financial risk. The methodology is comprised of different steps in which a series of quantitative analyses are carried out to reach an objective solution. Beginning with the identification of which components could bring higher reduction of maintenance cost and time if monitored, the methodology also provides a method to define the requirements for diagnostic and prognostic tools capable of monitoring these components. It then continues to analyse how combining these tools affects the economic return and financial risk. Each possible combination is analysed to identify which of them should be retrofitted. Whilst computer models of maintenance operations can be used to analyse the effect of retrofitting IVHM technology on a legacy fleet, the number of possible combinations of diagnostic and prognostic tools is too big for this approach to be practicable. Nevertheless, computer models can go beyond the economic analysis performed thus far and simulations are used as part of the methodology to get an insight of other effects or retrofitting the chosen toolset.

The propagation of intense picosecond laser pulses in air in the presence of strong nonlinear self-action effects and air ionization is investigated experimentally and numerically. The model used for numerical analysis is based on the nonlinear propagator for the optical field coupled to the rate equations for the production of various ionic species and plasma temperature. Our results show that the phenomenon of plasma-driven intensity clamping, which has been paramount in femtosecond laser filamentation, holds for picosecond pulses. Furthermore, the temporal pulse distortions in the picosecond regime are limited and the pulse fluence is also clamped. In focused propagation geometry, a unique feature of picosecond filamentation is the production of a broad, fully ionized air channel, continuous both longitudinally and transversely, which may be instrumental for many applications including laser-guided electrical breakdown of air, channeling microwave beams and air lasing.

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.

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.

Acoustic source localization (ASL) is pinpointing an acoustic source. ASL can reveal the point of impact of a foreign object or the point of crack initiation in a structure. ASL is necessary for continuous health monitoring of a structure. ASL in an anisotropic plate is a challenging task. This dissertation aims to investigate techniques that are currently being used to precisely determine an acoustic source location in an anisotropic plate without knowing its material properties. A new technique is developed and presented here to overcome the existing shortcomings of the acoustic source localization in anisotropic plates. It is done by changing the analysis perspective from the angular dependent group velocity of the wave and its straight line propagation to the wave front shapes and their geometric properties when a non-circular wave front is generated. Especially, 'rhombic wave front' and 'elliptical wave front' are dealt with because they are readily observed in highly anisotropic composite plates. Once each proposed technique meets the requirements of measurement, four sensor clusters in three different quadrants (recorded by 12 sensors) for the rhombus and at least three sensor clusters (recorded by 9 sensors) for the ellipse, accurate Acoustic Source Localization is obtained. It has been successfully demonstrated in the numerical simulations. In addition, a series of experimental tests demonstrate reliable and robust prediction performance of the developed new acoustic source localization technique.

Das Schallstrahlenmodell SMART (Sound Propagation Model for the Atmosphere using Ray Tracing) simuliert die Schallausbreitung in der Atmosphäre unter der Berücksichtigung der Einflüsse der frequenzabhängigen Schallabsorption in der Luft, des frequenzabhängigen Bodeneinflusses und der Refraktion durch vertikale Gradienten im Wind- und Temperaturfeld. Die Ergebnisse des Modells werden zum Beispiel auf Truppenübungsplätzen zur Schallortung und zur Einschätzung der allgemeinen Schallausbreitungssituation verwendet. Des Weiteren wurde eine Untersuchung einer Regionalisierung von Schallausbreitungsverhältnissen durchgeführt. Daraus ergab sich eine Einteilung Deutschlands in verschiedene Gebiete mit unterschiedlichen mittleren Schallausbreitungsbedingungen. Die Schallquellenhöhe befand sich für diese Untersuchungen am Boden. SMART ist aber auch in der Lage die Schallausbreitung für weitaus höherliegende Schallquellen zu simulieren. So wurden Simulationen für die Emissionshöhe von 140 m durchgeführt. Es zeigten sich große Unterschiede zu einer bodennahen Schallausbreitung. / The sound propagation model SMART (Sound Propagation Model for the Atmosphere using Ray Tracing) simulates the sound propagation in a stratified atmosphere. In addition to the geometrical spreading and the stratification of the atmosphere, the properties of the ground also strongly affect the sound propagation. Further the absorption in the air is dependent for the frequency of the sound signal. The results of the model are used on drill grounds of the German Federal Armed Forces, on the one side for a locating of sound sources and on the other side for an estimation of the conditions of the sound propagation. Furthermore, there was a study to find regional differences in the model results. This leads to a classification of Germany in different areas with the same mean conditions for sound propagation. The sound source for this study was positioned at the ground surface. SMART also can be used for the simulation of a sound propagation with a high-placed sound source. So there was a study for an emission height of 140 meter. There were shown great differences to a sound propagation near the ground.

The purpose of the present study is to present research data on the propagation of the southern spotted channel catfish.