Dans ce travail, nous nous intéressons à la spectroscopie optique par réflexion d’une vapeur diluée de césium infiltrée dans des opales artificielles Langmuir-Blodgett. Après une étude microscopique de la structure des opales, nous rapportons des expériences de réflexion, transmission et diffraction (sans atomes) effectuées sur diverses opales, dans le but d’explorer la propagation du champ lumineux dans ces milieux. En effectuant des expériences de réflexion sélective, nous observons que pour une polarisation TM, le signal atomique s’annule à 45° et à l’angle de Brewster, et entre ces deux zéros le signe du signal est inversé. Cet effet était prédit théoriquement mais n’avait jamais été observé. Nous rapportons aussi les expériences de spectroscopie par réflexion d’une vapeur infiltrée dans diverses opales et pour différentes longueurs d’onde. Sur des opales multicouches, nous observons des spectres sub-Doppler en incidence oblique, dont la forme est sensible à l’incidence, la polarisation et la longueur d’onde. Ces spectres ont été interprétés comme une signature d’un confinement tridimensionnel. Les expériences sur une opale multizone montre que sur une opale monocouche, nous observons aussi un signal sub-Doppler où il n’y a pas de confinement tridimensionnel. / In this work, we are interested in reflection optical spectroscopy of diluted cesium vapor infiltrated in Langmuir-Blodgett artificial opals. After a microscopic study of the structure of opals, we report experiments of reflection, transmission and diffraction (without atoms) carried out on various opals, with the aim of exploring the propagation of the light field in these media. By carrying out selective reflection experiments, we observe that for a TM polarization the atomic signal vanishes at 45° and the Brewster angle, and between these two zeros the sign of the signal is reversed. This effect was predicted theoretically but had never been observed. We also report the experiments of reflection spectroscopy of a vapor infiltrated in various opals and for different wavelengths. On multi-layered opals, we observe sub-Doppler spectra in oblique incidence, the shape of wich in sensitive to incidence, polarization and wavelength. These spectra were interpreted as a signature of a three-dimensional confinement. Experiments on a multi-zone opal show that on a monolayer opal, we also observe a sub-Doppler signal where there is no three-dimensional confinement.

<p>The University of Massachusetts S-band frequency-modulated, continuous-wave radar (UMass FMCW) was deployed to monitor the growth of the convective boundary layer over northern Alabama during the Verification of the Origins of Rotation in Tornadoes Experiment-Southeast (VORTEX-SE). The Doppler spectra collected in 2016 from the vertically-pointing UMass FMCW contain “spurs”, or spurious spectral peaks, caused by high-voltage switching power supplies in the traveling wave tube amplifier. In the original data processing scheme for this radar, a median filtering method was used to eliminate most of the spurs, but the largest ones persisted, which significantly degraded the quality of derived radar moments (e.g., reflectivity, Doppler velocity, and spectrum width) and hindered further analysis of these data (e.g., boundary layer height tracking). </p><p><br></p><p>In this study, a novel “in-painting” image processing technique was applied to remove the spurs in the Doppler spectra. We hypothesized the in-painting method would exhibit superior performance to the median filter at removing large spectral peaks, and also improve downstream radar products derived from the spectra. First, a Laplacian filter identified and masked spikes in the spectra that were characteristic of the spurs in shape and amplitude. The in-painting method then filled in masked areas based on surrounding data. Via a histogram analysis, the in-painting method was found to be more effective than the median filter at removing the large spurs from the Doppler spectra. The radar moments were then recomputed using a coherent power (CP) technique, resulting in cleaner reflectivity, Doppler velocity, and spectrum width data. Improvement was also found downstream when a boundary layer height detection algorithm was applied to the moments generated from the in- painted spectra. Output from the boundary layer height detection algorithm was then used to verify forecast boundary layer height from the Advanced Regional Prediction System (ARPS) model for the 31 March 2016 VORTEX-SE tornadic case study. </p>

<p>Biodynamic imaging (BDI) is a high-content optical imaging technology based on Fourier-domain digital holography and Doppler spectroscopy of intracellular dynamics. There are three main functions of the BDI technique, which are optical coherence imaging (OCI), motility contrast imaging (MCI) and tissue dynamics spectroscopy (TDS). OCI is related to <em>en face</em> optical coherence tomography (OCT) using partially coherent speckle generated by broad-area illumination with coherence detection through digital holography. MCI provides noninvasive functional imaging by treating intracellular motility as an endogenous dynamic imaging contrast agent. TDS produces broad-band Doppler fluctuation power spectra that contain the ensemble of all intracellular motions by collecting and extracting depth-resolved quasi-elastic dynamic light scattering from inside multicellular living tissue. This thesis presents the development and applications of BDI systems. Doppler spectral clustering analysis is demonstrated when comparing fresh canine lymphoma biopsies and their corresponding flash-Frozen samples. Doppler spectral phenotyping analysis is used to identify a non-predictive phenotype of TDS that shows a systemic red-shift of frequencies. Doppler spectral shift analysis is used to monitor bacterial infection of living tissue. </p>

Im Rahmen dieser Studie wurden Beobachtungen eines bodengebundenen, scannenden, polarimetrischen Wolken-Doppler-Radars genutzt, um Vertikalprofile der Form und Ausrichtung von bis zu 5 Hydrometeor-Typen in Mischphasenwolken abzuleiten. Voraussetzung für die neue Methodik war ein bestehender Ansatz, der Elevationsscans (Range-Height-Indikator, RHI) der differentiellen Reflektivität ZDR und des Korrelationskoeffizienten RHV nutzt, die von einem 35-GHz (Ka-Band) Wolken-Doppler-Radar beobachtet wurden. ZDR und RHV am Ort des maximalen Signals in den beobachteten Dopplerspektren werden anschließend mit entsprechenden simulierten Elevationsabhängigkeiten von ZDR und RHV verglichen. Das Ergebnis des Retrievals, das mittels eines Fits der simulierten und beobachteten ZDR und RHV Werte erhalten wird, ist ein Paar des polarizability ratio (dichtegewichtetes Achsenverhältnis) und dem degree of orientation, einem Maß für die bevorzugte Ausrichtung der Teilchen. Diese Arbeit widmet sich der Erweiterung der ursprünglichen Ansatzes der Form- und Ausrichtungsbestimmung. Die Methode nutzt die vollständigen beobachteten Dopplerspektren von ZDR und RHV für alle Elevationswinkel der vom 35-GHz Wolkenradar durchgeführten RHI-Scans. Die Aufteilung der Doppler-Spektren in 5 Teile ermöglicht die Ermittlung von Vertikalprofilen der Hydrometeor-Verteilung. In dieser Arbeit wird zunächst der ursprüngliche Ansatz zur Bestimmung der Form und Ausrichtung von Hydrometeors rekapituliert. Anschließend werden das Splitting-Verfahren und die Schritte der Datenanalysekette vorgestellt. Insbesondere auf die Korrektur von Horizontalwindeffekten auf die Doppler-Spektren wird eingegangen. Die Anwendbarkeit des neuen, erweiterten Ansatzes wird anhand von vier Fallstudien demonstriert. Ein Fall diskutiert die Identifizierung von Variationen der Form- und Ausrichtung innerhalb einer Hydrometeor-Population, die vollständig der gleichen primären Form-klasse angehört. Zwei Fallstudien zeigen die Anwendung des Algorithmus in Umgebungen mit mehreren Hydrometeortypen, einschließlich der Identifizierung von sekundärer Eisbildung. In der vierten Fallstudie wurde der Einfluss der Kristallmorphologie und -orientierung auf die Lichtstreuung in einer Mischphasenwolke charakterisiert. Die spektral aufgelöste Form- und Orientierungsbestimmung zeigt, dass vertikal ausgedehnte Mischphasenwolken praktisch immer eine Mischung verschiedener Hydrometeorarten oder eine beträchtliche Variation einer einzigen Hydrometeorart enthalten. Diese Information ist insofern von Bedeutung, als dass viele bestehende Fernerkundungsdaten auf der Annahme beruhen, dass nur eine einzige Hydrometeor-Population vorhanden ist.:1 Introduction 2 Introduction to mixed-phase clouds and ice crystals 2.1 Introduction to mixed–phase clouds 2.2 Ice formation 2.3 Morphology of ice crystals 2.4 Ice crystal growth and secondary ice formation processes 2.4.1 Riming: interaction between supercooled liquid droplets and ice crystals 2.4.2 Aggregation: interaction between ice crystals 2.4.3 Secondary ice production 2.5 Relation between fall speed and shape of ice particles 3 Simulating backscattering by hydrometeors in the microwave regime 3.1 Overview of scattering approaches 3.2 Spheroidal scattering approach 4 Radar observations of atmospheric hydrometeors 4.1 Polarimetric cloud radars 4.1.1 Radar reflectivity 4.1.2 Differential reflectivity 4.1.3 Correlation coefficient 4.1.4 Linear depolarization ratio 4.1.5 Doppler capability 4.2 Retrieving hydrometeor shape and orientation 4.2.1 Modeling part 4.2.2 Observational part 4.2.3 Comparing modeling and observational parts 5 Instrumentation and Dataset 5.1 Hybrid-mode cloud radar Mira-35 5.2 ACCEPT campaign 5.3 Retrieval of shape and orientation of the main hydrometeor population from STSR cloud radar observations 5.3.1 Toward extension of the main-peak approach 6 Doppler-spectra separation method for retrieving shape and orientation of multiple hydrometeor populations 6.1 Spectrally resolved approach 6.2 The influence of air motion on the Doppler spectra observed by a scanning cloud radar 6.2.1 Retrieval of horizontal wind from PPI scans 6.2.2 Aliasing problem and Doppler shift correction 6.2.3 An illustrative example showcasing the correction of horizontal wind effects 6.3 Application of spectrally resolved approach on the case study from 07 Nov 2014, 09:15 – 09:30UTC 7 Results: Application of the spectrally resolved approach on Analysis of the Composition of Cloud with Extended Polarization Techniques (ACCEPT) data 7.1 Case study 10 Nov 2014, 01:15 – 01:30: Shape variability within a deep mixed-phase cloud 7.2 Case study 03 Nov 2014, 20:30 – 20:45: Secondary ice formation 7.3 Case study 18 Nov 2014, 01:15 – 01:30: Impact of crystal morphology on light scattering in a mixed-phase cloud 7.3.1 Relationship between lidar depolarization ratio and ice crystal morphology 7.3.2 Investigation of particle shape and orientation of a low-depolarization cloud layer 8 Summary & Conclusion List of Abbreviations and Acronyms List of Symbols Bibliography / In the framework of this study ground-based scanning polarimetric cloud Doppler radar observations were utilized to derive vertical profiles of the shape and orientation of up to 5 different hydrometeor types in mixed-phase clouds. Prerequisite for the new methodology was an existing approach that uses elevation (range-height indicator, RHI) scans of differential reflectivity ZDR and correlation coefficient RHV observed by a 35-GHz (Ka-band) cloud Doppler radar as well as simulations of the latter. ZDR and RHV from the location of the maximum signal in the observed Doppler spectra are compared with corresponding simulated elevation dependencies of ZDR and RHV. The retrieval output, which is obtained by a fit of simulated and observed ZDR and RHV, is then a pair of the polarizability ratio (density-weighted axis ratio) and the degree of orientation, a measure of the preferable orientation of the particles. This thesis is dedicated to an extension of the original shape and orientation retrieval. The method utilizes the entire observed Doppler spectra of ZDR and RHV from all elevation angles of the RHI scans performed by the 35-GHz cloud radar. The split- up of the Doppler spectra into 5 parts enables the retrieval of vertical profiles of the hydrometeor distribution. Within the thesis, the original shape retrieval approach is recapitulated. Subsequently, the splitting procedure and required preparatory steps in the data analysis chain are introduced. Specifically, a correction of horizontal wind effects on the Doppler spectra had to be implemented. The remainder of the thesis is dedicated to demonstrate the applicability of the new spectrally shape and orientation retrieval approach by means of four case studies. One case demonstrates the detection of variabilities in shape and orientation within a hydrometeor population belonging entirely to the same primary shape class. Two case studies were selected to evaluate the application of the spectrally resolved approach in an environment of multiple hydrometeor types, including its utilization for identification of secondary ice production. In the fourth case study the characterization of the impact of crystal morphology and orientation on light scattering in a mixed-phase cloud was performed. The spectrally resolved shape and orientation retrieval demonstrates that vertically extensive mixed-phase clouds contain virtually always a mix of different hydrometeor types or a considerable variation of a single hydrometeor type. This information holds relevant as many existing remote sensing retrievals rely on the assumption of the presence of a single hydrometeor population, only.:1 Introduction 2 Introduction to mixed-phase clouds and ice crystals 2.1 Introduction to mixed–phase clouds 2.2 Ice formation 2.3 Morphology of ice crystals 2.4 Ice crystal growth and secondary ice formation processes 2.4.1 Riming: interaction between supercooled liquid droplets and ice crystals 2.4.2 Aggregation: interaction between ice crystals 2.4.3 Secondary ice production 2.5 Relation between fall speed and shape of ice particles 3 Simulating backscattering by hydrometeors in the microwave regime 3.1 Overview of scattering approaches 3.2 Spheroidal scattering approach 4 Radar observations of atmospheric hydrometeors 4.1 Polarimetric cloud radars 4.1.1 Radar reflectivity 4.1.2 Differential reflectivity 4.1.3 Correlation coefficient 4.1.4 Linear depolarization ratio 4.1.5 Doppler capability 4.2 Retrieving hydrometeor shape and orientation 4.2.1 Modeling part 4.2.2 Observational part 4.2.3 Comparing modeling and observational parts 5 Instrumentation and Dataset 5.1 Hybrid-mode cloud radar Mira-35 5.2 ACCEPT campaign 5.3 Retrieval of shape and orientation of the main hydrometeor population from STSR cloud radar observations 5.3.1 Toward extension of the main-peak approach 6 Doppler-spectra separation method for retrieving shape and orientation of multiple hydrometeor populations 6.1 Spectrally resolved approach 6.2 The influence of air motion on the Doppler spectra observed by a scanning cloud radar 6.2.1 Retrieval of horizontal wind from PPI scans 6.2.2 Aliasing problem and Doppler shift correction 6.2.3 An illustrative example showcasing the correction of horizontal wind effects 6.3 Application of spectrally resolved approach on the case study from 07 Nov 2014, 09:15 – 09:30UTC 7 Results: Application of the spectrally resolved approach on Analysis of the Composition of Cloud with Extended Polarization Techniques (ACCEPT) data 7.1 Case study 10 Nov 2014, 01:15 – 01:30: Shape variability within a deep mixed-phase cloud 7.2 Case study 03 Nov 2014, 20:30 – 20:45: Secondary ice formation 7.3 Case study 18 Nov 2014, 01:15 – 01:30: Impact of crystal morphology on light scattering in a mixed-phase cloud 7.3.1 Relationship between lidar depolarization ratio and ice crystal morphology 7.3.2 Investigation of particle shape and orientation of a low-depolarization cloud layer 8 Summary & Conclusion List of Abbreviations and Acronyms List of Symbols Bibliography

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