Star-forming compact dwarf galaxies (CDGs) resemble the expected pristine conditions of the first galaxies in the Universe and are the best systems to test models on primordial galaxy formation and evolution. Here, we report on one of such CDGs, Tololo 1214-277, which presents a broad, single peaked, highly symmetric Ly alpha emission line that had evaded theoretical interpretation so far. In this paper, we reproduce for the first time these line features with two different physically motivated kinematic models: an interstellar medium composed by outflowing clumps with random motions and an homogeneous gaseous sphere undergoing solid body rotation. The multiphase model requires a clump velocity dispersion of 54.3 +/- 0.6 km s(-1) with outflows of 54.3 +/- 5.1 km s(-1), while the bulk rotation velocity is constrained to be 348(-48)(+75) km s(-1). We argue that the results from the multiphase model provide a correct interpretation of the data. In that case, the clump velocity dispersion implies a dynamical mass of 2 x 10(9) M-circle dot, 10 times its baryonic mass. If future kinematic maps of Tololo 1214-277 confirm the velocities suggested by the multiphase model, it would provide additional support to expect such kinematic state in primordial galaxies, opening the opportunity to use the models and methods presented in this paper to constrain the physics of star formation and feedback in the early generation of Ly alpha - emitting galaxies.

The Infrared Atmospheric Sounding Interferometer (IASI) provides atmospheric observations with high spectral resolution and its data have been shown to have a significant positive impact on global Numerical Weather Prediction (NWP) and trace gas retrievals. A fundamental component of the retrieval of atmospheric composition is the radiative transfer model used to simulate the observations. An accurate representation of the expected emission spectrum measured by the satellite is essential given that differences in the reproduced atmospheric spectra propagate through a retrieval procedure and produce an altered estimate of the atmospheric state. The importance of the assumptions within the forward model are discussed and it is established that in the simulation of spectra from satellite-borne instruments the choice of the model parameters can have a large impact upon the resulting output. These assumptions are explored in the context of the Reference Forward Model (RFM), which is further configured to optimise its output for simulating the IASI spectrum in the troposphere. In order to ascertain the consistency of different radiative transfer models, comparisons are carried out between the RFM and the Radiative Transfer model for TOVS (RTTOV) in order to quantify any discrepancies in the reproduction of IASI measurements. Good agreement is shown across the majority of the spectrum, with exceptions caused by CO₂ line mixing effects and the H₂O continuum. Alongside model comparisons, the RFM is validated against real IASI measurements. Being a Fourier Transform Spectrometer, there are a large number of channels available from the IASI instrument, which leads to a very large quantity of data. However, this can lead to problems within retrievals and data assimilation. Choosing an optimal subset of the channels is an established method to reduce the amount of data; maintaining the information contained within it whilst eliminating spectral regions with large uncertainties. The method currently used at the UK Met Office to select their spectral channels is re-assessed and a modified method is presented that improves upon the modelling of spectrally correlated errors.

Les travaux présentés dans ce manuscrit sont consacrés à l'étudie du un petit instrument sophistiqué de mesure d'épaisseur optique : ODS (Optical Depth Sensor) a été conçu pour étudier l'atmosphère martienne et terrestre. L'une de ses principales missions consiste à fournir des mesures journalières de l'épaisseur optique des aérosols (AOD: Aerosol Optical Depth) et de détecter et caractériser les nuages optiquement minces à l'aube et au crépuscule. Les méthodes d'analyses sont basées sur l'utilisation de tables d'intensité reproduisant les signaux observés ODS en fonction de différents paramètres clés. Ces tables ont été réalisées à l'aide d'un code de transfert radiatif dans une géométrie en plans parallèles pour l'estimation de l'opacité des poussières, tandis que les propriétés des nuages sont issues d'un modèle de type Monte-Carlo en géométrie sphérique. Le premier objectif de ce travail a consisté à développer les algorithmes d'analyses nécessaires à l'étude du signal d'ODS. / The work presented in this manuscript is devoted to the development of reliable retrieval procedures for a lightweight and sophisticated optical depth sensor (ODS) which measures alternatively scattered flux at zenith and the sum of the direct flux and the scattered flux in the blue and red wavelength ranges. The ODS sensor is dedicated to Mars and Earth atmosphere and its principal goals are perform measurements of the daily mean aerosol optical depth (AOD) and retrieve the altitude and optical depth of high altitude clouds at twilight. The retrieval procedure is based on the use of look-up tables of intensities reproducing the signals that should be observed by ODS, as a function of different key parameters. For the estimation of AOD, the look-up tables are obtained by using a plane-parallel radiative transfer code, while for the study of cloud properties a Monte-Carlo radiative transfer code in spherical geometry is used.

The work conducted in this thesis examines the nature of circumstellar discs by investigating irradiance and polarization of scattered light. Two circumstellar discs are investigated. Firstly, H-band high contrast imaging data on the transitional disc of the Herbig Ae/Be star HD169142 are presented. The images were obtained through the polarimetric differential imaging (PDI) technique on the Very Large Telescope (VLT) using the adaptive optics system NACO. Our observations use longer exposure times, allowing us to examine the edges of the disc. Analysis of the observations shows distinct signs of polarization due to circumstellar material, but due to excessive saturation and adaptive optics errors further information on the disc could not be inferred. The HD169142 disc is then modelled using the 3D radiative transfer code Hyperion. Initial models were constructed using a two disc structure, however recent PDI has shown the existence of an annular gap. In addition to this, the annular gap is found not to be devoid of dust. This then led to the construction of a four-component disc structure. Estimates of the mass of dust in the gap (2:10x10⁻⁶ M⊙) are made as well as for the planet (≈1:53 x 10⁻⁵ M⊙ (0.016MJupiter)) suspected to be responsible for causing the gap. The predicted polarization was also estimated for the disc, peaking at 14 percent. The use of realistic dust grains (ballistic aggregate particles) in Monte Carlo code is also examined. The fortran code DDSCAT is used to calculate the scattering properties for aggregates which are used to replace the spherical grain models used by the radiative transfer code Hyperion. Currently, Hyperion uses four independent elements to de ne the scattering matrix, therefore the use of rotational averaging and a 50/50 percent population of grains and their enantiomers were explored to reduce the number of contributing scattering elements from DDSCAT. A python script was created to extract the scattering data from the DDSCAT output les and to apply a size distribution to the data. The second circumstellar disc investigated is the debris disc of the M dwarf star AU Mic. The disc was modelled, using the radiative transfer code Hyperion, based on F606W (HST) and JHK0-band (Keck II) scattered light observations and F606Wband polarized light observations. Initially, the disc is modelled as a two component structure using two grain types: compact silicate grains and porous dirty ice water. Both models are able to reproduce the observed SED and the F606W and H-band surface brightness pro les, but are unable to t the observed F606W degree of polarization. Therefore, a more complex/realistic grain model was examined (ballistic aggregate particles). In addition, recent millimetre observations suggest the existence of a planetesimal belt < 3 AU from the central star. This belt is included in the BAM2 model and was successful in fitting the observed SED, F606W and H-band surface brightness and F606W polarization. These results demonstrate the limitations of spherical grain models and indicate the importance of modelling more realistic dust grains.

Stars on the asymptotic giant branch (AGB) lose a significant fraction of their mass to their surroundings through stellar winds. As a result, they are surrounded by circumstellar shells of gas and dust. This stellar mass loss replenishes and enriches the interstellar medium (ISM) with the products of stellar nucleosynthesis, progressively increasing its metallicity and thereby driving galactic chemical evolution. In this thesis I present a comprehensive study of oxygen-rich (O-rich) AGB stars and red supergiants (RSG) observed with the Spitzer Infrared Spectrograph and Infrared Space Observatory Short Wavelength Spectrometer in the Milky Way, the Large and Small Magellanic Clouds, and Galactic globular clusters; focusing on the composition of the dust in the circumstellar envelopes surrounding these stars. Combining spectroscopic and photometric observations with the GRAMS grid of radiative transfer models to derive (dust) mass-loss rates, I detect crystalline silicates in stars with dust mass-loss rates which span over a factor of 1000, down to rates of ~10^{-9} Msun/yr. Detections of crystalline silicates are more prevalent in higher mass-loss rate objects, and our results indicate that the dust mass-loss rate has a greater influence on the crystalline fraction than the gas mass-loss rate, suggesting that thermal annealing of amorphous silicate grains is the primary formation mechanism of crystalline silicates in such environments rather than the direct condensation of crystalline silicates from the gas phase. I also find that metallicity influences the composition of crystalline silicates, with enstatite seen increasingly at low metallicity, while forsterite becomes depleted at these metallicities due to the different chemical composition of the gas. To trace the evolution of alumina and silicate dust along the AGB, I present an alternative grid of MODUST radiative transfer-models for a range of dust compositions, mass-loss rates, dust shell inner radii and stellar parameters. Our analysis shows that the AKARI [11]-[15] versus [3.2]-[7] colour is a robust indicator of the fractional abundance of alumina in O-rich AGB stars. From the modelling, I show that a grain mixture consisting primarily of amorphous silicates, with contributions from amorphous alumina and metallic iron provides a good fit to the observed spectra of O-rich AGB stars in the LMC. In agreement with previous studies, we find a correlation between the dust composition and mass-loss rate; the lower the mass-loss rate the higher the percentage of alumina in the shell. Finally, I present mid-infrared observations of the Local Group dwarf elliptical galaxy M32; where I find a large population of dust-enshrouded stars. These observations will act as a pathfinder for future observations with the JWST and SPICA.

Evolved stars and planetary nebulae are rich and varied sites of molecule and dust formation. These objects undergo dramatic mass loss which ultimately enriches the interstellar medium. In this thesis, a number of studies, outlined below, have been undertaken to better understand the chemical and physical properties of these diverse objects. A molecular line survey of a sample of evolved stars and planetary nebulae has been carried out using the Mopra radio telescope, Australia. Transitions with hyperfine structure have been fitted to constrain optical depths. The population diagram method was applied to determine the rotation temperatures of molecules which had multiple transitions available. Column densities have been calculated for all detected species and isotopic ratios measured where possible. The results include the corroboration of the classification of II Lup as a J-type star. The 89.087 GHz HCN maser was detected in IRAS 15082-4808 for the first time from the aforementioned survey, bringing the total number of detections of this maser to ten. The velocity shift of this maser has been measured at −2.0+/-0.9 km/s. Drawing on literature data in addition to the survey data, the variation of maser intensity with pulsation phase has been investigated across all sources for the first time. Comparing these masers with model atmospheres constrains the formation region to between 2 and 4 stellar radii. CO in the circumstellar envelope of II Lup has been modelled using the radiative transfer codes GASTRoNOoM, and ComboCode. The models have demonstrated that a ‘standard’ smooth model does not satisfactorily reproduce the combined CO observations of PACS, JCMT, Mopra and APEX. Two potential solutions are proposed: a discontinuous temperature model, requiring the presence of an efficient cooling molecule that is most effective in the region 75-200 R*, or a variable mass loss model that requires a factor of ten increase inmass loss in the same region. Zinc abundances, a proxy for iron abundances, have been determined for a sample of Galactic planetary nebulae using the [Zn IV] 3.625 μm line. O++/O has been shown to be a reliable ionisation correction factor for Zn3+ from Cloudy photoionisation models. The majority of the sample are sub-solar in [Zn/H] and enriched in [O/Zn]. Zinc abundances as functions of Galactocentric distance have also been investigated and no evidence for a trend has been found.

Les protubérances solaires sont de fascinantes structures magnétiques à grande échelle dans l'atmosphère solaire. Elles sont l'objet de recherches depuis des dizaines d'années mais des questions comme leur formation, leur stabilité et leur éruption ne sont toujours pas bien comprises. De grands progrès ont été obtenus dans ce domaine et celui des éruptions en particulier avec une combinaison d'observations synoptiques et continues depuis l'espace (voir SoHO/EIT, STEREO/SECCHI/EUVI, et SDO/AIA) et en spectro-imagerie multilongueurs d'onde. Depuis le lancement du satellite IRIS en 2013, beaucoup de résultats d'observations et de modélisations ont été obtenus grâce à la très haute résolution spectrale et spatiale d'IRIS tant en spectroscopie qu'en imagerie. Dans cette thèse, nous nous focalisons sur les signatures observationnelles des processus mis en avant pour expliquer les éruptions de protubérances. Nous essayons aussi de déterminer les variations de conditions physiques d'une protubérance éruptive et d'estimer à la fois les masses de matière qui quittent le Soleil et celles qui retournent au Soleil pendant une éruption. En ce qui concerne les vitesses, nous parvenons à construire le vecteur vitesse en chaque pixel de la protubérance observée, grâce à la combinaison d'une méthode de "flot optique" appliquée aux images AIA 304 et IRIS Mg II h&k ce qui donne accès aux vitesses dans le plan du ciel, d'une part, et grâce à la technique Doppler appliquée aux profils IRIS Mg II h&k ce qui permet de calculer les vitesses le long de la ligne de visée, d'autre part. En ce qui concerne les densités et températures, nous comparons les intensités absolues observées avec les valeurs déduites de calculs de transfert radiatif Hors-Equilibre Thermodynamique Local, ce qui nous permet de construire des cartes de ces quantités. Les densités électroniques ainsi déduites sont dans la gamme 1.3E9 - 7.0E10 cm⁻³ et les densités totales d'hydrogène dans la gamme 1.5E9 – 3.6E11 cm⁻³ dans les diverses régions de la protubérance. La température moyenne est d'environ 1.1E4 K une valeur plus élevée que dans les protubérances quiescentes. Le degré d'ionisation varie entre 0.1 et 10. Les flux de masse à l'intérieur de la protubérance et leurs variations temporelles ont pu ainsi être calculés. La masse totale ainsi déduite est dans la gamme 1.3E14 - 3.2E14 g. La perte totale de masse de la protubérance vers la surface solaire évaluée sur la durée d'observation avec IRIS est d'un ordre de grandeur plus faible que la masse totale de la protubérance. Nous explorons aussi les corrélations entre indices spectraux observables dans les raies h et k de Mg II et des quantités physiques comme la densité et la mesure d'émission (ME). Nous avons choisi de calculer des modèles uni-dimensionnels (1D) isothermes et isobares en utilisant le code PRODOP_Mg NLTE disponible à MEDOC (IAS) et en procédant au calcul exact du rayonnement incident. Nous en déduisons des corrélations entre les intensités émergentes dans les raies h et k d'une part, et les densités et les ME d'autre part. Moyennant quelques hypothèses sur la température, nous établissons une relation entre les intensités k (et h) et la ME, une relation qui devrait être utile pour déterminer les densités d'hydrogène et d'électrons aussi bien que l'épaisseur effective d'une protubérance observée. Ainsi donc, l'évolution des propriétés morphologiques et thermodynamiques d'une protubérance éruptive ont été étudiées de dans cette thèse. Ces travaux conduisent à une meilleure compréhension de quelques aspects des protubérances (éruptives), tels la distribution et l'évolution des densités, de la température, des vitesses et du degré d'ionisation. Nous avons ainsi fourni des contraintes utiles à la modélisation des protubérances. Dans notre conclusion, nous résumons nos résultats et proposons quelques suggestions pour de futures analyses et observations et pour des capacités instrumentales optimisées. / Solar prominences are fascinating, large-scale magnetic structures in the solar atmosphere. They have been investigated for many decades, but the issues of their formation, stability, and eruption are still not well understood. Much progress has been made in our knowledge of prominences and their eruptions with both synoptic measurements from space (with SoHO/EIT, STEREO/SECCHI/EUVI, and SDO/AIA) and multiwavelength spectro-imaging. Since the launch of IRIS in 2013, a lot of results have been obtained in both observational and modeling domains with IRIS high spectral and spatial resolution imaging and spectroscopy. In this thesis, we focus on the observational signatures of the processes which have been put forward for explaining eruptive prominences. We also try to figure out the variations of physical conditions of the eruptive prominence and estimate the masses leaving the Sun vs. the masses returning to the Sun during the eruption. As far as velocities are concerned, we derive a full velocity vector for each pixel of the observed prominence by combining an optical flow method on the AIA 304Å and IRIS Mg II h&k images in order to derive the plane-of-sky velocities and a Doppler technique on the IRIS Mg II h&k profiles to compute the line-of-sight velocities. As far as densities and temperatures are concerned, we compare the absolute observed intensities with values derived from Non-Local Thermodynamic Equilibrium (NLTE) radiative transfer computations to build maps of these quantities. The derived electron densities range from 1.3E9 to 7.0E10 cm⁻³ and the derived total Hydrogen densities range from 1.5E9 to 3.6E11 cm⁻³ in different regions of the prominence. The mean temperature is around 1.1E4 K which is higher than in quiescent prominences. The ionization degree is in the range of 0.1 to 10. The mass flows in the prominence and their variations with time are consequently computed. The total mass is 1.3E14 to 3.2E14 g. The total mass drainage from the prominence to the solar surface during the observation of IRIS is about one order of magnitude smaller than the total mass of prominence. We also explore the correlations between the observable spectral features in h and k lines of Mg II to physical quantities such as the density and the Emission Measure (EM). We choose to compute one-dimensional (1D) isothermal and isobaric models using the PRODOP_Mg NLTE code available at MEDOC (IAS) with the exact computation of the incident radiation. Then we derive correlations between the k and h emergent intensities on one hand and the densities and EM on the other hand. With some assumptions on the temperature, we obtain a unique relation between the k (and h) intensities and the EM that should be useful for deriving either the hydrogen and electron densities or the effective thickness of an observed prominence. Thus, the evolution of the morphology and thermodynamic properties of an erupting prominence have been studied in the thesis. These investigations lead to our understanding in some aspects of prominences, e.g., the distribution and evolution of densities, temperatures, velocities and ionization degree. These could be useful constraints for theoretical prominence models. In the conclusion, we summarize our results and provide some suggestions for future analysis, observations and ideal observing capabilities.

Les recherches de SNe ont commencé il y a plus de 100 ans. Depuis, il a été possible de collecter beaucoup de données d'observations astronomiques. Les astronomes ont développé une classification détaillée et ont abouti un relatif consensus sur la nature physique de ces événements très différents. Néanmoins, beaucoup de questions restent sans réponse. En résumé, les supernovæ de type II (riche en hydrogène) résultent de l'éjection l'enveloppe des supergéantes rouges (SGR). Les principales sources de connaissance sur ces objets sont l'évolution de leur luminosité en fonction du temps (`courbes de lumière') et leurs spectres observés à différentes époques. La méthode la plus utilisée pour extraire les informations des données d'observation est la modélisation des courbes de lumières et des spectres des supernovæ. Dans le Chapitre 1 (Introduction), nous présentons successivement l’évolution stellaire, la physique des explosions et l’évolution des éjectas. Nous décrivons aussi les différents types de supernova ; l’état actuel des connaissances sur les CCSNe ainsi que ces limitations. Nous discutons de la théorie de l'évolution stellaire. Nous décrivons notre approche numérique au Chapitre 2 (Supernova modelling). Elle consiste en trois étapes principales : la modélisation de l'évolution stellaire, l'explosion de l'étoile SGR résultante, et la modélisation de l'évolution des éjectas. Nous présentons la structure modélisée des étoiles SGR ; ces modèles et techniques de calcul sont similaires aux modèles utilisés dans les chapitres suivants. Nous discutons notre méthode d'explosion d'un progéniteur quand son noyau dégénéré commence à s'effondrer. Dans le Chapitre 3 (Observational properties), nous discutons les propriétés observées en photométrie et spectroscopie des CCSNe. Nous extrayons les propriétés statistiques de l'échantillon existant. En utilisant la technique présentée, nous avons effectué une étude détaillée de SN 2008bk, une supernova bien observée (Chapitre 4). Nous pouvons contraindre les propriétés du progéniteur et des paramètres d'explosion. Notre modélisation nous permet de comparer non seulement les propriétés de base telles que la luminosité, mais aussi à analyser en détail les caractéristiques spectrales, telles que la présence de certaines raies spectrales ainsi que leur morphologie. Nous montrons qu'une étoile de 12M⊙ sur la séquence principale est un bon candidat au progéniteur de SN 2008bk. Aussi, nous discutons de la forme asymétrique de la raie Hα et concluons qu'elle provient du chevauchement avec la raie forte du Ba II 6596.9 Å. SN 2008bk, avec quelques dizaines d'autres objets, forme une sous-classe importante de CCSNe — supernovae à faible luminosité. Nous avons consacré une attention particulière à cette classe d'objets, dont l'uniformité et les données d'observation nous permet de tirer des conclusions importantes. Au Chapitre 5, nous étudions l'échantillon de 17 SNe de faible luminosité et analysons la possibilité que ces événements résultent d'explosions de progéniteurs de petite ou de grande masse. Il n'y a pas d'accord solide dans la communauté astronomique sur les progéniteurs possibles des explosions de SNe à faible luminosité. Notre analyse montre que les étoiles massives de masse inférieure (~12 M⊙) sont de bons candidats pour les progéniteurs de cette sous-classe de SNe. De plus, nos simulations d'étoiles de masse élevée (25 et 27 M⊙) montrent qu'une explosion ayant une luminosité aussi faible aurait des propriétés d’observation remarquables qui ne sont pas présentes dans les données. Dans le Chapitre 6, nous étendons notre étude sur toutes les CCSNe, en utilisant des modèles plus énergétiques que dans les Chapitres 4 et 5. Nous fournissons des preuves que ce qui différencie la diversité de SNe II est l'énergie d'explosion plutôt que la masse des éjectas (ou plus précisément la masse de l'enveloppe riche en H de progéniteur). / Dedicated SN searches started over 100 years ago. Over that time, astronomers have collected large sets of observational data. They have developed detailed classification and achieved general agreement on the nature of these events. Nevertheless, a lot of questions remain unanswered. In short, most Type II SNe (hydrogen-rich SNe) are terminal explosions of red supergiant (RSG) stars. The main source of knowledge about these objects are the way their luminosity changes with time (`light curves') and how their radiation is distributed in wavelength. One of the widely used methods to extract the information from the observational data is computer modelling. The largest part of our work lays in the numerical simulations. In Chapter 1 (Introduction), we present succinctly the necessary theory which includes stellar evolution, explosion physics and ejecta evolution. We discuss different types of SNe; the modern knowledge on CCSNe and its problems. We discuss stellar evolution theory. We describe the nucleosynthesis that takes place in the cores of massive stars and gives rise to their final chemical stratification. We describe our numerical approach in Chapter 2 (Supernova modelling). It includes three major steps: stellar evolution modelling, explosion of the resulting RSG star, and ejecta evolution modelling. We present modelled structure of RSG stars; these models and computational techniques are similar to models used in subsequent chapters. We then discuss our numerical methods of exploding a SN once its degenerate core starts collapsing. We discuss explosive nucleosynthesis and its impact on the progenitor composition, production of unstable isotopes and the basic physics of radioactive decay. In Chapter 3 (Observational properties), we discuss the photometric and spectral observational properties of core-collapse SNe. We extract statistical properties of the existing sample. Using the presented technique, we performed a detailed study of the well observed object SN 2008bk (Chapter 4). We are able to constrain its progenitor and explosion properties. Our modelling allows us to compare not only the basic properties such as luminosity, but also to analyze in detail the spectral features, such as line identification and morphology. We show that a 12 M⊙ star on the main sequence is a good candidate for the progenitor of SN 2008bk. Also we discuss the asymmetric shape of the Hα line and conclude that it stems from the overlap with the strong Ba II 6596.9 Å line. SN 2008bk, together with about 20 objects, form a subclass of low-luminosity CCSNe Type II. We devoted a particular attention to this class of objects, whose uniformity and observational data allows us to draw important conclusions. In Chapter 5 (Low-luminosity Type II-P SNe), we study the sample of 17 low-luminosity SNe and analyze the possibility that these events are the result of explosions of low- and high-mass progenitors. There is no solid agreement in the astronomical community on the possible progenitors of the low-luminosity explosions of Type II SNe. Our analysis shows that lower-mass massive stars (~12 M⊙) are good candidates for the progenitors of this subclass of SNe. Moreover, our simulations of high-mass stars (25 and 27 M⊙) show that such low brightness of the explosion of such a massive object would have notable observational properties which are not present in the data. In Chapter 6 (Kinetic energy variation), we extend our study further on the whole class of hydrogen-rich core-collapse SN, using more energetic models than in Chapters 4 and 5. We provide evidences that what differentiates the diversity of SNe II is the explosion energy rather than the ejecta mass (or H-rich envelope mass of the progenitor).

The simplified approach of a turbid medium is commonly applied in theory of radiative transfer for vegetation media. Oriented planar model leaves are assumed whose normals are always confined to the upper half space. These orientations are described with the help of so-called leaf normal distribution functions (LNDFs) so that, within the scope of the turbid theory, a radiative transfer equation can be derived in which the so called Ross-Nilson function G occurs explicitly. This function, as introduced by J. Ross, is based on geometrical considerations and is therefore called geometry function, or shortly G-function (GF). To solve the latter equation G must be known. GF is calculated from the LNDF and was originally derived in an explicit and analytical form for strongly simplified LNDFs only. We demonstrated in a previous work that GF can be calculated also for other standard LNDFs. Based on the latter LNDFs we introduce here a generalised trigonometric LNDF and present the respective formula for G. / Die vereinfachte Annahme eines turbiden Mediums findet in der Theorie des Strahlungstransfers für Vegetationsmedien breite Anwendung. Darin werden orientierte ebene Modellblätter angenommen, deren Normalen stets in den oberen Halbraum weisen. Diese Orientierungen werden mittels sogenannter Blattnormalenverteilungen (BNV) beschrieben, so dass sich im Rahmen der turbiden Theorie eine Strahlungstransfergleichung ableiten lässt, in der die sogenannte Ross-Nilson-Funktion G explizit auftritt. Diese von J. Ross eingeführte Funktion basiert auf geometrischen Betrachtungen und wird daher auch Geometriefunktion genannt oder kurz G-Funktion. G muss zur Lösung der vorigen Gleichung bekannt sein. Es leitet sich aus der BNV ab und konnte in expliziter sowie analytischer Form bislang lediglich für stark vereinfachte BNV hergeleitet werden. Wie wir an dieser Stelle in einem früheren Beitrag gezeigt haben, lässt sich G darüber hinaus für andere standardisierte BNV berechnen. Auf letzteren aufbauend führen wir jetzt eine verallgemeinerte trigonometrische BNV ein und präsentieren die entsprechende Formel für G.

Profiles of broadband terrestrial radiation from airborne pyrgeometer measurements aboard research aircraft Polar 5 obtained during the VERDI campaign in 2012 were used to derive vertical temperature profiles. The retrievals were performed utilizing radiative transfer simulations by libRadtran (Mayer and Kylling, 2005). Manually changing the temperature of the input file for the simulations resulting calculated profiles of terrestrial irradiance were compared with measured profiles and iterated until best agreement. The selected test case shows the possibility of this technique and reveals several possible improvements. The algorithm has to be optimized to adapt the modelling temperature profile automatically using least-square error minimization between measured and modelled irradiance profiles. Additionally the vertical resolution has to be increased to consider small-scale variations. Using humidity and pressure profiles from ground-based observations and nearby radiosoundings significantly improves the retrieved temperature profiles. / Vertikalprofile der breitbandigen terrestrischen Strahlung von flugzeuggetragenen Pyrgeometermessungen an Bord des Forschungsflugzeuges Polar 5 während der VERDI Kampagne in 2012 wurden genutzt, um Vertikalprofile der Temperatur abzuleiten. Das Retrieval erfolgte mit Hilfe von Strahlungstransfersimulationen unter der Verwendungung von libRadtran (Mayer and Kylling, 2005). Dazu wurde die Temperatur der Modellatmosphäre variert, bis eine bestmögliche Übereinstimmung von gemessenem und modellierten Irradianzprofil erzielt wurde. Der ausgesuchte Testfall zeigt das Potential dieser Technik und mögliche Verbessungsansätze. So muss der verwendete Algorithmus automatisiert werden, indem das modellierte Strahlungsprofil mit Hilfe eines Iterationsverfahrens und der Methode der kleinsten Fehlerquadrate an das gemessene Profil angepasst wird. Zusätzlich ist eine Erhöhung der vertikalen Auflösung von 50 m auf 10 m Schritte nötig, um kleinskalige Fluktuationen zu berücksichtigen. Die Verwendung von bodengebundenen Beobachtungen und nahegelegenen Radiosondenaufstiegen in der Modellatmosphäre führt zu einer weiteren signifikanten Verbesserung der abgeleiteten Temperaturprofile.