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Showing 31 to 38 of 38 (0.058 seconds)Spelling suggestions: "subject:"polarimetrie"" "subject:"polarimetrien""
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Shape-temperature relationship of ice crystals in mixed-phase cloudsbased on observations with polarimetric cloud radar: Shape-temperature relationship of ice crystals in mixed-phase cloudsbased on observations with polarimetric cloud radarMyagkov, Alexander 04 January 2017 (has links)
This thesis is devoted to the experimental quantitative characterization of the shape and orientation distribution of ice particles in clouds. The characterization is based on measured and modeled elevation dependencies of the polarimetric parameters differential reflectivity and correlation coefficient. The polarimetric data is obtained using a newly developed 35-GHz cloud radar MIRA-35 with hybrid polarimetric configuration and scanning capabilities. The full procedure chain of the technical implementation and the realization of the setup of the hybrid-mode cloud radar for the shape determination are presented. This includes the description of phase adjustments in the transmitting paths, the introduction of the general data processing scheme, correction of the data for the differences of amplifications and electrical path lengths in the transmitting and receiving channels, the rotation of the polarization basis by 45°, the correction of antenna effects on polarimetric measurements, the determination of spectral polarimetric variables, and the formulation of a scheme to increase the signal-to-noise ratio. Modeling of the polarimetric variables is based on existing backscattering models assuming the spheroidal representation of cloud scatterers. The parameters retrieved from the model are polarizability ratio and degree of orientation, which can be assigned to certain particle orientations and shapes.
In the thesis the first quantitative estimations of ice particle shape at the top of liquid-topped clouds are presented. Analyzed ice particles were formed in the presence of supercooled water and in the temperature range from -20 °C to -3 °C. The estimation is based on polarizability ratios of ice particles measured by the MIRA-35 with hybrid polarimetric configuration, manufactured by METEK GmbH. For the study, 22 cases observed during the ACCEPT (Analysis of the Composition of Clouds with Extended Polarization Techniques) field campaign were used. Polarizability ratios retrieved for cloud layers with cloud-top temperatures of about -5, -8, -15, and -20 °C were 1.6, 0.9, 0.6, and 0.9, respectively. Such values correspond to prolate, quasi-isotropic, oblate, and quasi-isotropic particles, respectively. Data from a free-fall chamber were used for the comparison. A good agreement of detected shapes with well-known shape{temperature dependencies observed in laboratories was found.:1 Introduction
2 Formation and development of ice particles: Laboratory studies and remote observations
2.1 Heterogeneous ice formation in the atmosphere
2.2 Laboratory investigations of ice crystal development
2.3 Polarimetric radar observations of ice microphysics
2.3.1 Polarimetry in weather radar networks
2.3.2 Polarimetry in cloud radars
2.3.3 Polarization coupling
2.4 Aims and scientific questions
3 Effects of antenna patterns on cloud radar polarimetric measurements
3.1 Measurements of complex antenna patterns
3.1.1 Problem definition
3.1.2 Measurement description
3.1.3 Results of antenna pattern measurements
3.2 Correction of LDR measurements
3.3 Discrimination between insects and clouds
4 Cloud radar MIRA-35 with hybrid mode
4.1 Implementation and phase adjustment
4.2 Processing of the coherency matrix
4.3 Correction of the coherency matrix for differences of channels
4.4 The coherency matrix in the slanted basis
4.5 Correction for the antenna coupling
4.6 Spectral polarimetric variables
4.7 Sensitivity issue
5 Shape and orientation retrieval
5.1 Backscattering model
5.2 Retrieval technique
5.3 Case study
6 Shape-temperature relationship of pristine ice crystals
6.1 Instrumentation and data set
6.2 Examples of the shape retrieval
6.2.1 Case 1: 12 October 2014, 15:00-16:00 UTC
6.2.2 Case 2: 18 October 2014, 01:00-02:00 UTC
6.2.3 Case 3: 20 October 2014, 18:00-19:00 UTC
6.2.4 Case 4: 10 November 2014, 02:00-03:00 UTC
6.2.5 Case 5: 7 November 2014, 20:00-21:00 UTC
6.3 Comparison of shape with laboratory studies
6.4 Orientation of pristine ice crystals
7 Summary and outlook
Bibliography
List of Abbreviations
List of Symbols
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Struktur und Dynamik kleinskaliger Magnetfelder der Sonnenatmosphäre / Ergebnisse hochaufgelöster Polarimetrie und Bildrekonstruktion / Structure and Dynamics of small scale magnetic fields in the solar atmosphere / Results of high resolution polarimetry and image reconstructionJanßen, Katja 02 July 2003 (has links)
No description available.
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Observations and modeling of polar faculae on the Sun / Beobachtungen und numerische Simulationen polarer Fackeln der Sonne.Okunev, Oleg 16 September 2004 (has links)
No description available.
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Využití polarimetrie a refraktometrie ke stanovení koncentrace invertního cukru v invertních sirupech / Use of polarimetry and refractometry for determination of invert sugar concentration in invert syrupsMrůzková, Karolína January 2021 (has links)
Invert syrup is a liquid sweetener, which is produced by sucrose hydrolysis to form fructose and glucose. Important qualitative parameter of invert syrup is the sucrose inversion – weight percentage of invert sugar (sum of fructose and glucose) in invert syrup dry mass. This diploma thesis presents a possibility of sucrose inversion determination by polarimetry in combination with refractometry in invert syrups of 70–78 % dry mass produced at 80 °C and pH 2,4. New relationship describing the sucrose inversion as a function of polarization and refractometric dry mass was determined. The results of sucrose inversion determined using this new relationship were compared to results obtained by HPLC/RI, which was used as a reference method. The difference between these 2 determination methods was 0,1 ± 0,5 %. The new relationship was detemined with reference to the fact, that under the processing conditions, more glucose than fructose is formed. The fructose : glucose concentration ratio formed under processing conditions was observed to be equal 0,96 ± 0,02.
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Surface Parameter Estimation using Bistatic Polarimetric X-band MeasurementsBen Khadhra, Kais 31 January 2008 (has links)
To date only very few bistatic measurements (airborne or in controlled laboratories) have been reported. Therefore most of the current remote sensing methods are still focused on monostatic (backscatter) measurements. These methods, based on theoretical, empirical or semi-empirical models, enable the estimation of soil roughness and the soil humidity (dielectric constant). For the bistatic case only theoretical methods have been developed and tested with monostatic data. Hence, there still remains a vital need to gain of experience and knowledge about bistatic methods and data. The main purpose of this thesis is to estimate the soil moisture and the soil roughness by using full polarimetric bistatic measurements. In the experimental part, bistatic X-band measurements, which have been recorded in the Bistatic Measurement Facility (BMF) at the DLR Oberpfaffenhofen, Microwaves and Radar Institute, will be presented. The bistatic measurement sets are composed of soils with different statistical roughness and different moistures controlled by a TDR (Time Domain Reflectivity) system. The BMF has been calibrated using the Isolated Antenna Calibration Technique (IACT). The validation of the calibration was achieved by measuring the reflectivity of fresh water. In the second part, bistatic surface scattering analyses of the calibrated data set were discussed. Then, the specular algorithm was used to estimate the soil moisture of two surface roughnesses (rough and smooth) has been reported. A new technique using the coherent term of the Integral Equation Method (IEM) to estimate the soil roughness was presented. Also, the sensitivity of phase and reflectivity with regard to moisture variation in the specular direction was evaluated. Finally, the first results and validations of bistatic radar polarimetry for the specular case of surface scattering have been introduced. / Aktuell sind nur sehr wenige Messungen mit bistatischem Radar durchgeführt worden, sei es von Flugzeuggetragenen Systemen oder durch spezielle Aufbauten im Labor. Deshalb basieren die meisten der bekannten Methoden zur Fernerkundung mit Radar auf monostatis-chen Messungen der Rückstreuung des Radarsignals. Diese Methoden, die auf theoretischen, empirischen oder halb-empirischen Modellen basieren, ermöglichen die Schätzung der Oberfächenrauhigkeit und die Bodenfeuchtigkeit (Dielektrizitätskonstante). Im bistatischen Fall wurden bisher nur theoretische Modelle entworfen, die mittels monostatischer Messungen getestet wurden. Aus diesem Grund ist es von großer Bedeutung, Erfahrung und Wissen über die physikalischen Effekte in bistatischen Konfigurationen zu sammeln. Das Hauptziel der vorliegenden Dissertation ist es, anhand vollpolarimetrischer, bistatischer Radarmessungen die Oberfächenrauhigkeit und Bodenfeuchtigkeit zu bestimmen. Im experimentellen Teil der Arbeit werden die Ergebnisse bistatischer Messungen präsentiert, die in der Bistatic Measurement Facility (BMF) des DLR Oberpfaffenhofen aufgenommen wurden. Die Datensätze umfassen Messungen von Böden unterschiedlicher statistischer Rauhigkeit und Feuchtigkeit, die mittels eines Time Domain Reflectivity (TDR) Systems bestimmt werden. Zur Kalibration des BMF wurde die Isolated Antenna Calibration Technique (IACT) verwendet und anhand der Messung der Reflektivität von Wasser überprüft. Im zweiten Teil der vorliegenden Arbeit wird anhand der kalibrierten Daten eine Analyse der Oberflächenstreuung in bistatischen Konfigurationen vorgenommen. Im Anschluss daran wird mittels des Specular Algorithm eine Schätzung der Bodenfeuchte zweier Proben unter- schiedlicher Rauhigkeit (rau und fein) durchgeführt. Ein neues Verfahren zur Schätzung der Oberfächenrauhigkeit, das auf dem kohärenten Term der Integral Equation Method (IEM) basiert, wurde eingeführt. Daneben wird die Empfindlichkeit der Phase sowie der Reflektivität des vorwärtsgestreuten Signals gegenüber Veränderungen der Bodenfeuchtigkeit analysiert. Schließlich werden erste Ergebnisse und Validierungen bistatischer Radarpolarimetrie für den Fall der Vorwärtsstreuung präsentiert.
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Zeeman tomography of magnetic white dwarfs / Zeeman-Tomographie magnetischer Weißer ZwergeEuchner, Fabian 16 May 2006 (has links)
No description available.
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Kleinskalige Magnetfelder der Sonne und ihr Einfluß auf Chromosphäre, Übergangszone und Korona / Small-Scale Solar Magnetic Fields and their Influence upon Chromosphere, Transition Region and CoronaWilken, Volker 28 June 2001 (has links)
No description available.
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Spektroskopie und Polarimetrie kleinskaliger magnetischer Strukturen der Sonnenoberfläche mit Methoden der Bildrekonstruktion / Spectroscopy and polarimetry of small-scale magnetic structures on the solar surface with image restoration techniquesKoschinsky, Markus 03 May 2001 (has links)
No description available.
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