A 3D Unstructured Mesh FDTD Scheme for EM Modelling

The Yee finite difference time domain (FDTD) algorithm is widely used in computational electromagnetics because of its simplicity, low computational costs and divergence free nature. The standard method uses a pair of staggered orthogonal cartesian meshes. However, accuracy losses result when it is used for modelling electromagnetic interactions with objects of arbitrary shape, because of the staircased representation of curved interfaces. For the solution of such problems, we generalise the approach and adopt an unstructured mesh FDTD method. This co-volume method is based upon the use of a Delaunay primal mesh and its high quality Voronoi dual. Computational efficiency is improved by employing a hybrid primal mesh, consisting of tetrahedral elements in the vicinity of curved interfaces and hexahedral elements elsewhere. Difficulties associated with ensuring the necessary quality of the generated meshes will be discussed. The power of the proposed solution approach is demonstrated by considering a range of scattering and/or transmission problems involving perfect electric conductors and isotropic lossy, anisotropic lossy and isotropic frequency dependent chiral materials

Triangulation of multistation camera data to locate a curved line in space

A method is described for finding the location of a curved line in space from local azimuth as a function of elevation data obtained at several observation sites. A least-squares criterion is used to insure the best fit to the data. The method is applicable to the triangulation of an object having no identifiable structural features, provided its width is very small compared with its length so as to approximate a line in space. The method was implemented with a digital computer program and was successfully applied to data obtained from photographs of a barium ion cloud which traced out the earth's magnetic field line at very high altitudes

Microwave and submillimeter wave scattering of oriented ice particles

Microwave (1-300GHz) dual-polarization measurements above 100GHz are so far sparse, but they consistently show polarized scattering signals of ice clouds. Existing scattering databases of realistically shaped ice crystals for microwaves and submillimeter waves (> 300GHz) typically assume total random orientation, which cannot explain the polarized signals. Conceptual models show that the polarization signals are caused by oriented ice particles. Only a few works that consider oriented ice crystals exist, but they are limited to microwaves only. Assuming azimuthally randomly oriented ice particles with a fixed but arbitrary tilt angle, we produced scattering data for two particle habits (51 hexagonal plates and 18 plate aggregates), 35 frequencies between 1 and 864GHz, and 3 temperatures (190, 230 and 270K). In general, the scattering data of azimuthally randomly oriented particles depend on the incidence angle and two scattering angles, in contrast to total random orientation, which depends on a single angle. The additional tilt angle further increases the complexity. The simulations are based on the discrete dipole approximation in combination with a self-developed orientation averaging approach. The scattering data are publicly available from Zenodo (https://doi.org/10.5281/zenodo.3463003). This effort is also an essential part of preparing for the upcoming Ice Cloud Imager (ICI) that will perform polarized observations at 243 and 664GHz. Using our scattering data radiative transfer simulations with two liquid hydrometeor species and four frozen hydrometeor species of polarized Global Precipitation Measurement (GPM) Microwave Imager (GMI) observations at 166GHz were conducted. The simulations recreate the observed polarization patterns. For slightly fluttering snow and ice particles, the simulations show polarization differences up to 11K using plate aggregates for snow, hexagonal plates for cloud ice and totally randomly oriented particles for the remaining species. Simulations using strongly fluttering hexagonal plates for snow and ice show similar polarization signals. Orientation, shape and the hydrometeor composition affect the polarization. Ignoring orientation can cause a negative bias for vertically polarized observations and a positive bias for horizontally polarized observations

Light Scattering by Non-Spherical Particles

Nicht-sphärische Teilchen sind in der Natur sowie in verfahrenstechnischen Anwendungen sehr häufig anzutreffen. Insbesondere die Detektion von Eiskristallen während des Fluges durch Verkehrsflugzeuge ist ein Problem, dass in den vergangenen Jahren vermehrt Aufmerksamkeit erhalten hat. Während das Problem der Streuung einer ebenen elektromagnetischen Welle durch ein homogenes und isotropes sphärisches Teilchen, wie z.B. einen Regentropfen als vollständig gelöst anzusehen ist, ist dies bei nicht-sphärischen Partikeln nicht der Fall. Hier existiert nach wie vor ein Fokus der Forschung und Entwicklung sowohl auf theoretischer, numerischer, als auch experimenteller Seite, aufgrund einer Vielzahl an unterschiedlichen Schwierigkeiten. Diese Arbeit beschreibt verschiedene numerische und semianalytische Verfahren, die auf das Streuproblem angewandt werden können und dabei die gesamte Reichweite des maßgeblichen Mie-Größenparameters abdecken. Diese Methoden werden auf die Kalibration und Interpretation der Messergebnisse des PHIPS-Messinstruments angewandt, welches in einer HALO Kampagne zur Charakterisierung von atmosphärischen Eiskristallen erprobt wurde. Die Berechnungsmethoden im Einzelnen beinhalten zwei Derivate der geometrischen Optik, anwendbar auf beliebige Partikel-Geometrien mit homogenem, als auch inhomogenem Brechungsindex, das numerisch exakte Verfahren der Finiten Integration der Maxwell-Gleichungen, sowie die in der Lichtstreuung und Quantenmechanik häufig verwendete Transitionsoperator-Methode. Diese Berechnungsmethoden werden auf eine Reihe von Beispiel- Geometrien angewandt und der Einfluss von Polarisation und gemittelter Partikel-Orientierung werden untersucht. Zusätzlich wurde ein Verfahren implementiert, dass das Strahlprofil eines Laserstrahls auf die gestreute Lichtintensität berücksichtigt, welches beispielsweise in der Anwendung bei Time-Shift Messungen eine zentrale Rolle spielt. Die Grenzen der Anwendbarkeit der verschiedenen Berechnungsmethoden werden in der Arbeit erläutert. Des Weiteren werden mehrere moderne Messverfahren auf ihre Anwendbarkeit im Hinblick auf nicht-sphärische Teilchen hin überprüft. Dies beinhaltet unter anderem das Time-Shift Messverfahren, sowie interferometrische bildgebende Verfahren. Die Analyse der Anwendbarkeit der verschiedenen Messmethoden ist im experimentellen Abschnitt der Arbeit dokumentiert. Messungen der Streulicht-Phasenfunktionen von natürlichen Eiskristallen wurden ebenfalls durchgeführt und die spezifischen Vorbereitungen für die Untersuchungen von Eiskristallen in einem optischen Experiment werden in dieser Arbeit ebenfalls erläutert. Als gemeinsame Problematik konnte bei vielen Verfahren der limitierte Dynamikbereich der verwendeten Detektoren identifiziert werden. Ein abschließender wichtiger Aspekt in dieser Arbeit ist die Produktion und Aufbewahrung von Eiskristallen mit möglichst natürlichen optischen Eigenschaften in einer Laborumgebung. Hierfür wurde eine kompakte Wolkenkammer entwickelt, die die geforderten Eigenschaften an Produktionsmenge und Qualität von Eiskristallen erfüllt. Auslegung, Konstruktion und Betrieb des Apparates werden im letzten Kapitel der Dissertation detailliert wiedergegeben

The deep space network, volume 7

The objectives, functions, and organization of the Deep Space Network are summarized. The Deep Space Instrumentation Facility, the Ground Communications Facility, and the Space Flight Operations Facility are described

Polarization studies in electromagnetic scattering by small Solar-system particles

In remote-sensing studies, particles that are comparable to the wavelength exhibit characteristic features in electromagnetic scattering, especially in the degree of linear polarization. These features vary with the physical properties of the particles, such as shape, size, refractive index, and orientation. In the thesis, the direct problem of computing the unknown scattered quantities using the known properties of the particles and the incident radiation is solved at both optical and radar spectral regions in a unique way. The internal electromagnetic fields of wavelength-scale particles are analyzed by using both novel and established methods to show how the internal fields are related to the scattered fields in the far zone. This is achieved by using the tools and methods that were developed specifically to reveal the internal field structure of particles and to study the mechanisms that relate the structure to the scattering characteristics of those particles. It is shown that, for spherical particles, the internal field is a combination of a forward propagating wave with the apparent wavelength determined by the refractive index of the particle, and a standing wave pattern with the apparent wavelength the same as for the incident wave. Due to the surface curvature and dielectric nature of the particle, the incident wave front undergoes a phase shift, and the resulting internal wave is focused mostly at the forward part of the particle similar to an optical lens. This focusing is also seen for irregular particles. It is concluded that, for both spherical and nonspherical particles, the interference at the far field between the partial waves that originate from these concentrated areas in the particle interior, is responsible for the specific polarization features that are common for wavelength-scale particles, such as negative values and local extrema in the degree of linear polarization, asymmetry of the phase function, and enhancement of intensity near the backscattering direction. The papers presented in this thesis solve the direct problem for particles with both simple and irregular shapes to demonstrate that these interference mechanisms are common for all dielectric wavelength-scale particles. Furthermore, it is shown that these mechanisms can be applied to both regolith particles in the optical wavelengths and hydrometeors at microwave frequencies. An advantage from this kind of study is that it does not matter whether the observation is active (e.g., polarimetric radar) or passive (e.g., optical telescope). In both cases, the internal field is computed for two mutually perpendicular incident polarizations, so that the polarization characteristics can then be analyzed according to the relation between these fields and the scattered far field.Kaukokartoitustutkimuksissa aallonpituusluokkaa olevat hiukkaset aiheuttavat niille luonteenomaisia piirteitä sähkömagnettisessa säteilyssä, varsinkin lineaarisen polarisaation asteessa. Nämä piirteet vaihtelevat hiukkasen fyysisten ominaisuuksien, kuten muodon, koon, taitekertoimen ja orientaation myötä. Tässä väitöskirjassa ratkaistaan sähkömagneettisen sironnan suora ongelma uudella tavalla, samalla kun hiukkasten ominaisuudet oletetaan tunnetuiksi. Aallonpituusluokkaa olevien hiukkasten sisäisiä sähkökenttiä analysoidaan sekä uusilla että vakiintuneilla menetelmillä, jotta voidaan osoittaa, mikä on sisäisten kenttien suhde sironneisiin kenttiin kauko-alueessa. Tämä on saavutettu käyttämällä työkaluja ja menetelmiä, jotka on kehitetty paljastamaan sirottajien sisäisen kentän rakenne ja joilla voidaan tutkia mekanismeja, jotka liittävät näiden sirottajien rakenteen niiden sirontaominaisuuksiin. Tutkimuksessa näytetään, että pallomaisten hiukkasten sisäinen kenttä on yhdistelmä eteenpäin etenevää aaltoa, jonka allonpituus määräytyy hiukkasen taitekertoimen mukaan, ja seisovaa aaltoa, jonka aallonpituus on sama kuin tulevan aallon. Koska hiukkanen on eriste ja sen pinta on kaareva, tuleva aaltorintama kokee vaihesiirron ja tuloksena oleva sisäinen aalto fokusoituu pääasiassa hiukkasen etupuolelle optisen linssin tavoin. Tämä fokusointi havaitaan myös epäsäännöllisillä hiukkasilla. Johtopäätöksenä on, sekä pallomaisille että ei-pallomaisille hiukkasille, että kaukokentässä tapahtuva interferenssi osittaisten aaltojen välillä, jotka ovat peräisin näistä fokusoituneista alueista hiukkasen sisällä, on vastuussa tietyistä, aallonpituusluokkaa oleville hiukkasille ominaisista piirteistä lineaarisessa polarisaatiossa, kuten negatiiviset arvot ja paikalliset maksimit, vaihefunktion asymmetria, ja intensiteetin kasvaminen lähellä takaisinsirontasuuntaa. Tässä väitöskirjassa esitellyt paperit ratkaisevat suoran ongelman, sekä yksinkertaisille, että epäsäännöllisille hiukkasille osoittaakseen, että nämä interferenssimekanismit ovat yhteisiä kaikille aallonpituusluokkaa oleville, eristäville sirottajille. Lisäksi näytetään, että näitä mekanismeja voidaan soveltaa sekä regoliittihiukkasille näkyvän valon alueella että hydrometeoriiteille mikroaaltoalueessa. Yksi tällaisen tutkimuksen eduista on, että ei ole merkitystä, onko havaitsija aktiivinen (esim. polarisaatiotutka) vai passiivinen (esim. optinen teleskooppi). Molemmissa tapauksissa sisäinen kenttä lasketaan kahdelle keskenään kohtisuorasti polarisoituneelle tulevalle kentälle, jotta polarisaatiossa havaitut piirteet voidaan analysoida näiden kenttien ja sironneen kentän suhteen avulla

Accurate characterization of winter precipitation using multi-angle snowflake camera, visual hull, advanced scattering methods and polarimetric radar

Includes bibliographical references (pages 28-31).This article proposes and presents a novel approach to the characterization of winter precipitation and modeling of radar observables through a synergistic use of advanced optical disdrometers for microphysical and geometrical measurements of ice and snow particles (in particular, a multi-angle snowflake camera-MASC), image processing methodology, advanced method-of-moments scattering computations, and state-of-the-art polarimetric radars. The article also describes the newly built and established MASCRAD (MASC + Radar) in-situ measurement site, under the umbrella of CSU-CHILL Radar, as well as the MASCRAD project and 2014/2015 winter campaign. We apply a visual hull method to reconstruct 3D shapes of ice particles based on high-resolution MASC images, and perform "particle-by-particle" scattering computations to obtain polarimetric radar observables. The article also presents and discusses selected illustrative observation data, results, and analyses for three cases with widely-differing meteorological settings that involve contrasting hydrometeor forms. Illustrative results of scattering calculations based on MASC images captured during these events, in comparison with radar data, as well as selected comparative studies of snow habits from MASC, 2D video-disdrometer, and CHILL radar data, are presented, along with the analysis of microphysical characteristics of particles. In the longer term, this work has potential to significantly improve the radar-based quantitative winter-precipitation estimation.Published with support from the Colorado State University Libraries Open Access Research and Scholarship Fund

Acceleration hodograph analysis techniques for powered orbital trajectories, phase 3 Final report

Hodographic equations of motion for powered orbital trajectories in acceleration vector spac

Near-Field Radiative Heat Transfer in Linear Chains of Multilayered Spheres

Thermal radiation is ubiquitous to all matter at finite temperature and controlling the radiative nature of that matter has been a key enabling factor in the development of several recent technologies, such as thermal diodes, thermal antennae, thermophotovoltaics, heat-assisted magnetic recording, and contactless cooling in microelectromechanical systems. At the micro/nano-scale, thermal radiation does not reliably behave in the way Planck's blackbody law predicts, due to near-field effects such as the diffraction, interference, and tunneling of light. In fact, the so-called blackbody limit can routinely be broken by several orders of magnitude when objects of dimensions or separation distances much smaller than the peak thermal wavelength (approximately 10 \si{\micro\meter} at room temperature) exchange thermal radiation. A deeper theory is required to understand near-field thermal radiation: Maxwell's equations. Maxwell's equations allow for a direct connection between the thermally induced current fluctuations and radiative transfer. In this dissertation, I investigate radiative transfer among spherical bodies aligned in a linear chain. The chain may be composed of any number of spheres, and the spheres themselves may be composed of any linear isotropic material, may be of any size and separation distance, and may each have any number of spherically symmetric layers. Using a dyadic Green's function formalism, I derive numerically exact formulas for heat transfer between pairs of spheres in the chain and between any sphere in the chain and its environment. My work clearly demonstrates that adding coatings to spherical objects can drastically impact the spectrum of radiative transfer, enhancing or diminishing it in various cases. This degree of tailoring makes coated spheres a flexible, yet unexplored, platform for future experiments in near-field radiative heat transfer. My work also demonstrates that, in an experiment measuring the distance dependent heat transfer between two spheres, heat transfer from the spheres to their environment can also have a strong distance dependence, which must be considered carefully when designing an experiment and analyzing its results. This demonstrates a cautious but optimistic outlook for the near-field radiative heat transfer community moving beyond traditional plane-plane and sphere-plane experimental configurations