No description available.

Zugl.: Aachen, Techn. Hochsch., Diss., 2009.

Universiẗat, Diss., 1999--Hamburg.

This thesis presents the design and development of an accelerated signal-level radar simulator with an emphasis on space debris monitoring in the Low Earth Orbit. Space surveillance represents a major topic of concern to astronomers as the threat of space debris and orbital overpopulation looms – particularly due to the lack of effective mitigation techniques and the limitations of modern space-monitoring sensors. This work thus aimed to investigate and design possible tools that could be used for training, testing and research purposes, and thereby aid further study in the field. At present, there exist no three-dimensional, ray-traced, signal-level radar simulators available for public use. As such, this thesis proposes an open-source, ray-traced radar simulator that models the interactions between spaceborne targets and terrestrial radar systems. This utilises a ray-tracing algorithm to simulate the effects of debris size, shape, orientation, and material properties when computing radar signals in a typical simulation. The generated received signals, produced at the output of the simulator, were also verified against systems theory, and validated with an existing, well-established simulator. The developed software was designed to aid astronomers and researchers in space situational awareness applications through the simulation of radar designs for orbital surveillance experiments. Due to its open-source nature, it is also expected to be used in training and research environments involving the testing of space-monitoring systems under various simulation conditions. The software offers native support for measured Two-Line Element datasets and the Simplified General Perturbations #4 orbit propagation model, enabling the accurate modelling of targets and the dynamic orbital forces acting upon them. As a result, the software has aptly been named the Space Object Astrodynamics and Radar Simulator – or SOARS. SOARS was built upon the foundations of a general-purpose radar simulator known as the Flexible Extensible Radar Simulator – or FERS – which provided integrated radar models for propagation loss, antenna shapes, Doppler and phase shifts, Radar Cross Section modelling, pulse waveforms, high-accuracy clock mechanisms, and interpolation algorithms. While FERS lacked various features required for space-monitoring applications, many of its implementations were used in SOARS to minimise simulation limits and maximise signal rendering accuracy by supporting an arbitrary number of transmitters, receivers, and targets. The goal was thus to have the simulator limited only by the end-user's system, and to specialise the operation of the software towards space surveillance by integrating additional features – such as built-in models for environmental and system noise, multiscatter effects, and target modelling using meshes comprised of triangular primitives. After completing the software's development, the ray-traced simulator was compared against a more streamlined version of SOARS that made use of point-model approximations for quick-look simulations, and the trade-offs between both simulators (including software runtime, memory utilisation and simulation accuracy) were investigated and evaluated. This assessed the value of implementing ray tracing in a radar simulator operating primarily within space contexts and evaluated the results of both simulators using detection processing as a demonstrated application of the system. And while the use of ray tracing resulted in significant costs in speed and memory, the investigation found that the ray-traced simulator generated more reliable results relative to the point-model version – providing various advantages in test scenarios involving shadowing and multiscatter. The design of the SOARS software, as well as its point-model “baseline” alternative and the investigation into each simulator's advantages and disadvantages, are thus presented in this thesis. The developed programs were released as open-source tools under the GNU General Public Licence and are freely available for public use, modification, and distribution.

A three-by-three polarization ray tracing matrix method is developed to calculate the polarization transformations associated with ray paths through optical systems. The relationship between the three-by-three polarization ray tracing matrix P method and the Jones calculus is shown in Chapter 2. The diattenuation, polarization dependent transmittance, is calculated via a singular value decomposition of the P matrix and presented in Chapter 3. In Chapter 4 the concept of retardance is critically analyzed for ray paths through optical systems. Algorithms are presented to separate the effects of retardance from geometric transformations. The parallel transport of vectors is associated with non-polarizing propagation through an optical system. A parallel transport matrix Q establishes a proper relationship between sets of local coordinates along the ray path, a sequence of ray segments. The proper retardance is calculated by removing this geometric transformation from the three-by-three polarization ray trace matrix. Polarization aberration is wavelength and spatial dependent polarization change that occurs as wavefrontspropagate through an optical system. Diattenuation and retardance of interfaces and anisotropic elements are common sources of polarizationaberrations. Two representations of polarization aberrationusing the Jones pupil and a polarization ray tracing matrix pupil, are presentedin Chapter 5. In Chapter 6 a new class of aberration, skew aberration is defined, as a component of polarization aberration. Skew aberration is an intrinsic rotation of polarization states due to the geometric transformation of local coordinates; skew aberration occurs independent of coatings and interface polarization. Skew aberration in a radially symmetric system primarily has the form of a tilt plus circular retardance coma aberration. Skew aberration causes an undesired polarization distribution in the exit pupil. A principal retardance is often defined within (-π, + π] range. In Chapter 7 an algorithm which calculates the principal retardance, horizontal retardance component, 45° retardance component, and circular retardance component for given retarder Jones matrices is presented. A concept of retarder space is introduced to understand apparent discontinuities in phase unwrapped retardance. Dispersion properties of retarders for polychromatic light is used to phase unwrap the principal retardance. Homogeneous and inhomogeneous compound retarder systems are analyzed and examples of multi-order retardance are calculated for thick birefringent plates. Mathematical description of the polarization properties of light and incoherent addition of light is presented in Chapter 8, using a coherence matrix. A three-by-three-by-three-by-three polarization ray tracing tensor method is defined in order to ray trace incoherent light through optical systems with depolarizing surfaces. The polarization ray tracing tensor relates the incident light’s three-by-three coherence matrix to the exiting light’s three-by-three coherence matrix. This tensor method is applicable to illumination systems and polarized stray light calculations where rays at an imaging surface pixel have optical path lengths which vary over many wavelengths. In Chapter 9 3D Stokes parameters are defined by expanding the coherence matrix with Gell-Mann matrices as a basis. The definition of nine-by-nine 3D Mueller matrix is presented. The 3D Mueller matrix relates the incident 3D Stokes parameters to the exiting 3D Stokes parameters. Both the polarization ray tracing tensor and 3D Mueller matrix are defined in global coordinates. In Chapter 10 a summary of my work and future work are presented followed by a conclusion.

No description available.

No description available.

In RF communications with a rotorcraft such as a helicopter, the rotor blades can impart a modulation onto the received signal called Rotor Blade Modulation (RBM). This modulation is caused by the reflection of a signal off the rotating blades. The reflected signal is Doppler shifted based on where the signal is reflected along the length of the blade as well as the angle between the axis of rotation and the emitter. RBM is known to degrade the performance of RF communications on rotorcraft and can be used in radar applications to detect and classify aircraft, but there is little on its usefulness in other areas. This thesis looks at the ability to utilize the RBM phenomenon on the rotorcraft itself to geo-locate and track a signal emitter on the ground. To do this a 3D RF ray tracing program was developed in C++ to produce simulations of RBM signals. The developed program is based on optical ray tracing algorithms with modified physical propagation effects for RF signals, and swapping lights and cameras for RF transmitters and receivers respectively. The ray tracer was then run over a realistic set of physical parameters to determine their effects on the received signal; this includes transmitter azimuth and elevation angle, receiver position, blade pitch, etc. along with their combinations. The simulations of the azimuth and elevation angle produce predictable modulations on the received signal. Based on the trends in the signal's modulation, a DSP algorithm was distilled down that accurately determines the azimuth and elevation angle of the transmitter from simulated signal data.

This work does not limit itself to its title and touches on a number of related topics beyond it. Starting with the title, Polarization Aberrations of Optical Coatings, the immediate question that comes to mind is: what coatings? All coatings? Not all coatings, but just enough that a third person could take this information and apply it anywhere: to all coatings. The computational work-flow required to break-down the aberrations caused by polarizing events (3D vector forms of reflection and refraction) in dielectric and absorbing materials and for thick and thin films is presented. Therefore, it is completely general and of interest to the wide optics community. The example system is a Ritchey-Chrétien telescope. It looks very similar to a Cassegrain, but it is not. It has hyperbolic surfaces, which allows for more optical aberration corrections. A few modern systems that use this configuration are the Hubble Space Telescope and the Keck telescopes. This particular system is a follow-up on this publication, where an example Cassegrain with aluminum coatings is characterized, and I was asked to simply evaluate it at another wavelength. To my surprise, I found a number of issues which lead me to write a completely new, one-of-its-kind 3D polarization ray-tracing code. It can do purely geometrical ray-tracing with add-on the polarization analysis capability, and more importantly: it keeps your data at your fingertips while offering all the outstanding facilities of Mathematica. The ray-tracing code and its extensive library, which can do several advanced computations, is documented in the appendix. The coatings of the Ritchey-Chrétien induce a number of aberrations, primarily, but not limited to: tilt, defocus, astigmatism, and coma. I found those forms to exist in both aluminum and with a reflectance-enhancing dielectric quarter-wave multilayer coating over aluminum. The thickness of the film stack varies as function of position to present a quarter-wave of optical thickness to oblique rays. Most commercial optical software that I know cannot compute this. And the results are impressive: the scalar transmission, which is a measure of ray efficiency, was raised from 78% to 95%. This means that only 5% of the incident light is lost, assuming ideal coating interfaces. This is very advantageous, considering the application: coronagraphs for exoplanet detection. Exoplanets are very far away, and therefore efficient use of light is essential. I also created a ray! I call it Huygens' twin ray. It is credited to Christiaan Huygens, who postulated that points on a wavefront can be considered as a sources of secondary spherical wavelets. This concept normally belongs to physical optics. The twin ray is emitted from the exact same object point but traced in a slightly different direction, which can be assumed by invoking Huygens's principle, and defined in a special way that consistently prevents vignetting. This requires high-precision ray-tracing, which is introduced along with this thesis work as part of the appendix. The application of this concept is exemplified in finding the exit pupil of the Ritchey-Chrétien telescope. It can be modified to work in a plurality of cases and find the precise image location in three-dimensions, making it completely general and useful. Mastering the ray-tracing documented here depends on how much optics the user knows, but tracing a single ray is something that can be learned in minutes. I welcome you to freely use it and make it your own. If your goal is to learn to ray-trace in Mathematica, the reader is directed to the appendix, especially to the four-port polarimeter example, as it is a 3D system that contains both reflection and refraction through thin films, thick films, retarders, and a single surface is traced at a time!

Student Number : 0006329K - MSc(Eng) Dissertation - School of Electrical and Information Engineering - Faculty of Engineering and the Built Environment / Geometric optimisations are presented for the UTD in SuperNEC which is a commercial electromagnetic software package. Path finding optimisations rapidly find propagation paths of electromagnetic waves by using back face culling to determine the visible plates of polyhedral structures and by using reflection and diffraction zones which use image theory and the law of diffraction to determine illuminated spatial regions. An octree reduces the number of intersections during the shadow tests. Numerical results show that overall the optimisations halve the run time of the software for models which consist of plates and cylinders. The path finding optimisations do not scale with model size, are limited to plates and introduce errors. The mean absolute error due to the path finding optimisations is on average 0:02 dB for first order rays and 0:17 dB for second order rays. The octree optimisation scales with model size, can be used with any geometry and any type of ray and does not cause errors.