Optimal estimation retrieval is a nonlinear regression scheme to determine the conditions statistically most-likely to produce a given measurement, weighted against any a priori knowledge. The technique is applied to three problems within the field of lidar data analysis. A retrieval of the aerosol backscatter and either the extinction or lidar ratio from two-channel Raman lidar data is developed using the lidar equations as a forward model. It produces profiles consistent with existing techniques at a resolution of 10-1000 m and uncertainty of 5-20%, dependent on the quality of data. It is effective even when applied to noisy, daytime data but performs poorly in the presence of cloud. Two of the most significant sources of uncertainty in that retrieval are the nonlinearity of the detectors and the instrument's calibration (known as the dead time and overlap function). Attempts to retrieve a nonlinear correction from a pair of lidar profiles, one attenuated by a neutral density filter, are not successful as uncertainties in the forward model eliminate any information content in the measurements. The technique of Whiteman et al. [1992] is found to be the most accurate. More successful is a retrieval of the overlap function of a Raman channel using a forward model combining an idealised extinction profile and an adaptation of the equations presented in Halldórsson and Langerholc [1978]. After refinement, the retrieval is shown to be at least as accurate, and often superior to, existing methods of calibration from routine measurements, presenting uncertainties of 5-15%. These techniques are then applied to observations of ash over southern England from the Eyjafjallajökull eruption of April 2010. Lidar ratios of 50-60 sr were observed when the plume first appeared, which reduced to 20-30 sr after several days within the planetary boundary layer, indicating an alteration of the particles over time.

A cobertura de nuvens e os aerossóis são os dois principais fatores que modulam a energia solar que atinge a superfície e é absorvida pela atmosfera. Esses dois fatores, portanto, têm um papel essencial no clima do planeta. Há atualmente um interesse nos efeitos radiativos dos aerossóis, particularmente por causa da atividade antrópica, que aumenta sua concentração na atmosfera, e por sua íntima relação com a formação de nuvens. Partículas que podem ser ativadas e ganhar água para se tornarem nevoeiro ou gotas de nuvens, na presença de supersaturação de vapor de água, são chamadas de Núcleo de Condensação de Nuvens. O estudo das partículas que aumentam de tamanho com o ganho de água conforme aumenta a umidade relativa (higroscopicidade) torna-se então de fundamental importância no entendimento da contribuição dos aerossóis na regulação do clima do planeta. O LIDAR é um instrumento promissor no estudo da higroscopicidade dos aerossóis atmosféricos, porque pode operar em ambiente não perturbado e em condições muito próximas da saturação. O LIDAR Raman apresenta a vantagem de poder obter o perfil de vapor de água e retroespalhamento de aerossóis no mesmo volume atmosférico e sem nenhuma suposição a priori a respeito da razão LIDAR Este trabalho objetiva avaliar o crescimento higroscópico do material particulado urbano em São Paulo, Brasil, e em Washington, D.C, Estados Unidos durante a campanha NASA-Discover-AQ com o uso da técnica LIDAR Raman, obtendo o fator de crescimento por higroscopicidade. Apesar da metodologia que se baseia na determinação de uma atmosfera bem misturada com o uso de radiossondagem já ter sido utilizada na literatura, este trabalho acrescenta importantes informações, já que não se tem notícias de outros estudos extensos com múltiplos casos feitos com o LIDAR Raman para avaliação de higroscopicidade nos Estados Unidos, bem como é a primeira vez que este estudo é feito em São Paulo, como resultado de três anos de aquisição de dados. Os resultados mostram que é possível identificar o crescimento higroscópico dos aerossóis em ambas os ambientes de estudo, cuja detecção depende de condições atmosféricas que estão raramente presentes, tornando o estudo da higroscopicidade com o LIDAR um desafio que exige uma extensa coleta de dados. Mostram ainda que a determinação da origem e o estudo conjugado das propriedades químicas da população de aerossóis são informações que auxiliariam no entendimento do comportamento higroscópico, aprofundamentos estes que podem ser derivados deste trabalho. / The cloud cover and aerosols are two main factors that modulate the solar energy that reaches the surface and is absorbed by the atmosphere. These two factors therefore have a key role in global climate. There is currently an interest in the radiative effects of aerosols, particularly because of human activity, increasing its concentration in the atmosphere, and its close relationship with cloud formation Particles that can be activated and gain water to form fog or cloud droplets in the presence of water vapor supersaturation, are called Cloud Condensation Nucleus. The study of particles that increase in size because of the uptake of water under increasing relative humidity conditions (hygroscopicity) then becomes of fundamental importance in understanding the contribution of aerosols in regulating the global climate. The LIDAR is a promising tool in the study of hygroscopic properties of atmospheric aerosols, because it can operate in undisturbed environment and much close to saturation conditions. The Raman LIDAR has the advantage of being able to obtain the profile of water vapor and aerosol backscatter at the same atmospheric volume and no a priori assumption of the LIDAR ratio. This study aims to evaluate the hygroscopic growth of urban particulate matter in Sao Paulo, Brazil, and Washington, DC, United States during the NASA-Discover-AQ campaign using the technique Raman LIDAR, getting the growth factor by hygroscopicity . Although the methodology - which is based on determination of a well-mixed atmosphere using radiosonde - have already been described in the literature, this work adds important information, since they do not have other news with multiple cases extensive studies made with the LIDAR Raman hygroscopicity for evaluation in the United States, and is the first time that this study is done in São Paulo, as a result of three years of data acquisition. The results show that it is possible to identify the hygroscopic growth of aerosol in both environments, whose detection depends on atmospheric conditions that are rarely present, making the study of hygroscopic properties with LIDAR a challenge that requires extensive data collection. Also, show that the determination of origin and the combined study of chemical properties of the population of aerosols would assist in the understanding of hygroscopic behavior.

A cobertura de nuvens e os aerossóis são os dois principais fatores que modulam a energia solar que atinge a superfície e é absorvida pela atmosfera. Esses dois fatores, portanto, têm um papel essencial no clima do planeta. Há atualmente um interesse nos efeitos radiativos dos aerossóis, particularmente por causa da atividade antrópica, que aumenta sua concentração na atmosfera, e por sua íntima relação com a formação de nuvens. Partículas que podem ser ativadas e ganhar água para se tornarem nevoeiro ou gotas de nuvens, na presença de supersaturação de vapor de água, são chamadas de Núcleo de Condensação de Nuvens. O estudo das partículas que aumentam de tamanho com o ganho de água conforme aumenta a umidade relativa (higroscopicidade) torna-se então de fundamental importância no entendimento da contribuição dos aerossóis na regulação do clima do planeta. O LIDAR é um instrumento promissor no estudo da higroscopicidade dos aerossóis atmosféricos, porque pode operar em ambiente não perturbado e em condições muito próximas da saturação. O LIDAR Raman apresenta a vantagem de poder obter o perfil de vapor de água e retroespalhamento de aerossóis no mesmo volume atmosférico e sem nenhuma suposição a priori a respeito da razão LIDAR Este trabalho objetiva avaliar o crescimento higroscópico do material particulado urbano em São Paulo, Brasil, e em Washington, D.C, Estados Unidos durante a campanha NASA-Discover-AQ com o uso da técnica LIDAR Raman, obtendo o fator de crescimento por higroscopicidade. Apesar da metodologia que se baseia na determinação de uma atmosfera bem misturada com o uso de radiossondagem já ter sido utilizada na literatura, este trabalho acrescenta importantes informações, já que não se tem notícias de outros estudos extensos com múltiplos casos feitos com o LIDAR Raman para avaliação de higroscopicidade nos Estados Unidos, bem como é a primeira vez que este estudo é feito em São Paulo, como resultado de três anos de aquisição de dados. Os resultados mostram que é possível identificar o crescimento higroscópico dos aerossóis em ambas os ambientes de estudo, cuja detecção depende de condições atmosféricas que estão raramente presentes, tornando o estudo da higroscopicidade com o LIDAR um desafio que exige uma extensa coleta de dados. Mostram ainda que a determinação da origem e o estudo conjugado das propriedades químicas da população de aerossóis são informações que auxiliariam no entendimento do comportamento higroscópico, aprofundamentos estes que podem ser derivados deste trabalho. / The cloud cover and aerosols are two main factors that modulate the solar energy that reaches the surface and is absorbed by the atmosphere. These two factors therefore have a key role in global climate. There is currently an interest in the radiative effects of aerosols, particularly because of human activity, increasing its concentration in the atmosphere, and its close relationship with cloud formation Particles that can be activated and gain water to form fog or cloud droplets in the presence of water vapor supersaturation, are called Cloud Condensation Nucleus. The study of particles that increase in size because of the uptake of water under increasing relative humidity conditions (hygroscopicity) then becomes of fundamental importance in understanding the contribution of aerosols in regulating the global climate. The LIDAR is a promising tool in the study of hygroscopic properties of atmospheric aerosols, because it can operate in undisturbed environment and much close to saturation conditions. The Raman LIDAR has the advantage of being able to obtain the profile of water vapor and aerosol backscatter at the same atmospheric volume and no a priori assumption of the LIDAR ratio. This study aims to evaluate the hygroscopic growth of urban particulate matter in Sao Paulo, Brazil, and Washington, DC, United States during the NASA-Discover-AQ campaign using the technique Raman LIDAR, getting the growth factor by hygroscopicity . Although the methodology - which is based on determination of a well-mixed atmosphere using radiosonde - have already been described in the literature, this work adds important information, since they do not have other news with multiple cases extensive studies made with the LIDAR Raman hygroscopicity for evaluation in the United States, and is the first time that this study is done in São Paulo, as a result of three years of data acquisition. The results show that it is possible to identify the hygroscopic growth of aerosol in both environments, whose detection depends on atmospheric conditions that are rarely present, making the study of hygroscopic properties with LIDAR a challenge that requires extensive data collection. Also, show that the determination of origin and the combined study of chemical properties of the population of aerosols would assist in the understanding of hygroscopic behavior.

This thesis presents a development to the technique of rotational Raman lidar by, incorporating an imaging spectrometer in conjunction with a clocking CCD detection system. This allowed the rotational Raman spectra of nitrogen and oxygen to be simultaneously recorded as a function of altitude. The rotational Raman spectra were uses to calculate temperature profiles. Recording the complete band envelopes of the rotational Raman spectra removed the need for an external reference, such as a radiosonde. Results are presented from measurements made in Cambridge in chapter 4 and Ny-Alesund in chapter 6. Chapter 7 presents some conventional lidar backscatter measurements made using a PMT in Birmingham during the winter part of the pollution in the Urban Midlands Area (PUMA) campaign. These measurements were used to determine the cloud base and the planetarty boundary layer height. Two automated algorithms were tested at retrieving the PBL height, the inflection point method and the centroid method.

Développé initialement pour la correction du retard humide des signaux GPS, le lidar Raman vapeur d’eau de l’Institut National de l’information Géographique et forestière (IGN) pourrait aujourd’hui servir pour d’autres applications telles que la climatologie et la météorologie. Cependant, quelle que soit l’application visée, il est primordial d’assurer une très bonne précision de la mesure. Un étalonnage fiable et stable de l’instrument est alors requis. Lors de la dernière campagne de mesures (Démévap) qui consistait à inter-comparer différentes techniques d’étalonnage, une dérive du coefficient d’étalonnage du lidar a été observée. Ce travail revient alors sur cette dérive et explore, dans un premier temps, les signaux enregistrés durant cette campagne. En découle alors un inventaire de sources d’erreurs et de variations pouvant expliquer ces résultats. Trois sources majeures de variations seront ensuite étudiées de manière approfondie : la dépendance en température des sections efficaces Raman induite par l’usage de filtres étroits, l’impact du choix des optiques de transmission et détection du signal et les problèmes liés à l’électronique de détection. À l’aide de simulations numériques, modélisations et tests en laboratoire, on s’est efforcés de mettre en évidence et de quantifier les variations. Des solutions permettant de minimiser ces instabilités ont aussi été proposées et testées. Finalement, le système lidar a été remonté entièrement et une campagne de validation des améliorations a été menée à Saint-Mandé. Sur une période de cinq mois, on a pu contrôler la stabilité instrumentale et étudier l’étalonnage du lidar à l’aide de capteurs d’humidité placés au sol. / The IGN (Franch Mapping Institut) water vapor Raman lidar has been developed in order to correct the wet delay of GPS signals. Today, the goal is to open up to other applications such as meteorology and climatology. Regardless the applications, high accuracy is and will be completed with a reliable calibration of the instrument. The latest campaign, during which the IGN Raman was experimented, was Demevap. Several lidar calibration techniques were compared, and results showed a common drift all along the campaign. The work presented here starts with a detailed investigation of the Demavap absolute signals. This first step allowed listing different likely sources of errors and instabilities in the system which lead to fluctuations of the calibration coefficient. Among them, we chose to study thoroughly three subsystems which appear to have a major influence on the calibration coefficient variations: the temperature dependence of the Raman cross sections induced by the use of narrowband interference filters, the effect of the optical configuration of the detection part of the lidar and problems linked to the electronic part of the detection. We strive to highlight and quantify the variations by means of numerical simulations, models and laboratory experiments. Furthermore, we proposed theoretical, empirical and instrumental solutions for the mitigation of these variations. Eventually, long term calibration coefficient stability of the overall system will be assessed with regular water vapor profile recordings and calibration measurements spread over several months.

For the first time, vertical water vapour profiles were measured in the Central Arctic North of 85°N during the MOSAiC campaign (Multidisciplinary drifting Observatory for the Study of Arctic Climate). Continuous measurements of the Raman lidar PollyXT are used to retrieve high-resolved vertical profiles of the water vapour mixing ratio (WVMR) during the polar night. The collected data are calibrated and evaluated by use of selected clear-sky profiles between 25 October 2019 and 29 February 2020. Three different calibration methods are applied using reference data from radiosonde launches or microwave radiometer (MWR) measurements, respectively. The calibration with the least error results from a linear fit between collocated radiosonde and lidar measurements and delivers a final calibration constant of 15.96 ± 0.37 g/kg for the period from 25 Oct 2019 to 29 Feb 2020. The calibrated WVMR profiles are analysed regarding the vertical distribution of water vapour in the Arctic, its impact on the downward thermal-infrared radiation (DTIR) at the surface, and its relation to the Arctic Oscillation (AO) index as a measure for the general atmospheric circulation. The Arctic atmosphere is very dry during the winter time with WVMR values below 2 g/kg. The vertical water vapour distribution is strongly related to the temperature profile. Layers with higher WVMR values are often capped by temperature inversions. Layers with higher integrated water vapour values (IWV) are located either close to the surface (coupled) or in an elevated layer (decoupled), related to local or advective processes, respectively. The impact of the vertical distributed water vapour on the clear-sky DTIR at the surface was investigated by evaluating the evolution of the air mass at the measurement location over several hours for seven clear-sky cases. The relation between the measured DTIR at the surface and the lidar IWV shows a linear correlation for each case, but with a shift in the radiation values depending on the temperature of the vertical distributed water vapour. The impact of the IWV on the DTIR is determined to be 9.33 − 15.03 W/kg from the example cases. Beside, a linear correlation is found between the temperature of the vertical distributed water vapour and the radiation temperature of the sky, which is derived from the Stefan-Boltzmann’s Law. Both results depict the high impact of the atmospheric water vapour profile on the surface energy budget during clear-sky winter conditions. The influence of the atmospheric circulation on the vertical water vapour distribution in the Arctic is investigated by use of the AO index. While very stable conditions with a weak exchange with lower latitudes are expected during the positive phase of the AO, a stronger meridional transport is related to the negative phase of the AO. The evaluation of 71 randomly selected clear-sky profiles shows differences in the amount and the vertical structure of each WVMR profile between the two phases. Higher WVMR values and layers with higher IWV are observed during the negative AO phase. Nonetheless, a high variability between dry and humid cases is seen during all phases of the AO due to synoptic events. Two main sources for water vapour in the Eastern Central Arctic are identified independent of the AO. These are cyclones on the one hand and the occurrence of a main wind direction from the seas north of Siberia namely Laptev, Kara and Barents Sea on the other hand. In summary, the thesis discusses different calibration methods for the derivation of WVMR profiles from Raman lidar measurements in its first part. In the second part, the thesis gives an overview over the vertical water vapour distribution in the Central Arctic winter and its complex relation to temperature profiles, radiation measurements at the surface and the atmospheric circulation.

Le projet Cigéo, mené par l’ANDRA, vise à permettre à l’horizon 2030 le stockage géologique des déchets les plus radioactifs du parc nucléaire français. Ces déchets, qui seraient placés dans des alvéoles souterraines de plusieurs centaines de mètres, sont susceptibles de relâcher de l’hydrogène gazeux (H2), un gaz inflammable dans l’air lorsque sa concentration dépasse 4%. Pour la sécurité des installations, il est indispensable de s’assurer que la concentration de H2 dans les alvéoles de stockage reste inférieure à sa limite de dangerosité. L’objectif de cette thèse, menée à l’ONERA, est de concevoir et réaliser un Lidar permettant de profiler à distance la concentration de H2 (0-4%), sur plusieurs centaines de mètres, avec une forte résolution spatiale (< 3 m), et de proposer ainsi un moyen non intrusif de détection et de prévention du risque lié à l’hydrogène. Le principe retenu est celui d’un Lidar Raman vibrationnel dans le domaine ultra-violet (355 – 420 nm). Pour sa conception, nous avons pris en compte les conditions particulières prévues dans les alvéoles de stockage. Une chaine de détection très sensible à comptage de photons a été choisie et mise en oeuvre, basée sur des détecteurs SiPM (Silicium Photomultiplier). La nécessité d’employer une voie de mesure de la vapeur d’eau, simultanément à l’hydrogène, a été mise en évidence et est liée au recouvrement partiel des spectres de diffusion Raman de H2 et H2O. Un analyseur spectral à trois voies de mesure (H2, H2O, et N2 utilisé comme référence) a été conçu et mis en place. Une méthode de traitement de signal en temps réel a enfin été réalisée pour visualiser les profils de concentrations de H2 et H2O. L’ensemble du système lidar a pu être testé dans une scène de portée réduite (100 m) permettant des relâchements d’hydrogène. Des mesures simultanées de profils de vapeur d’eau naturelle et de dihydrogène (0-2%) ont pu être démontrées avec succès à 85 m, avec une résolution spatiale et temporelle de 1 mètre et 1 minute respectivement, pour une détectivité de 600 ppm. / The CIGEO project, led by the ANDRA agency, aims at enabling future deep geological disposal of french nuclear waste packages. Those packages could be stored in hundred-meters long underground galleries, and may release hydrogen gas (H2), which is explosive at concentrations above 4% in the air. For safety concerns, it is important to ensure that H2 concentration remains well below the lower explosive limit. The objective of this thesis work, conducted at the ONERA agency, is to design and build a lidar which enable high-resolution (3 m) remote profiling of H2 concentration (0-4%) over hundreds of meters. Such a lidar could perform nonintrusive H2 detection and then prevent H2-related explosion risks. This lidar measures vibrational Raman scattering in the UV domain (355 – 420 nm). Its design takes into account the specific conditions expected in storage galleries. A highspeed and sensitive detection stage has been chosen, based on SiPM (Silicium Photomultiplier) technology in photon counting mode. Due to a spectral overlap between molecular hydrogen and water vapor Raman spectra, the need of a H2O measurement channel has been demonstrated. A three-channel spectral analyzer (H2, H2O and N2 used as reference) has been designed and implemented. Signal processing in real time has been developed to display H2 and H2O concentration profiles. This lidar has been tested in a reduced range scene (100 m) enabling hydrogen gas releases. Simultaneous measurements of concentration profiles of natural water vapor and hydrogen gas (0-2%) have been performed at 85 m with 1-meter and 1-minute resolution and a 600 ppm detectivity.

In der vorliegenden Arbeit wird ein zweistufiger Algorithmus, das sogenannte Retrieval, zur Ableitung von Wasserdampfprofilen aus einer Kombination von Ramanlidar und Mikrowellenradiometer zur operationellen Anwendung vorgestellt. Beide Instrumente kamen während einer groß angelegten Kampagne nahe Jülich im Frühjahr 2013 zum Einsatz (HOPE). Ziel der Arbeit ist es, kontinuierliche Zeitreihen der vertikalen Wasserdampfverteilung abzuleiten. Dies erfordert eine Kalibrierung des Ramanlidars. Im Rahmen dieser Arbeit wurde ein automatisches Kalibrierschema entwickelt, welches auf dem integrierten Wasserdampfgehalt abgeleitet aus Mikrowellenradiometermessungen basiert. Die Methode zeigt eine gute Übereinstimmung mit herkömmlichen Ansätzen, welche auf Radiosondenaufstiegen beruhen. Der Kalibrierfaktor ist sehr stabil mit einer relativen Abweichung von 5 %. Diese Stabilität bietet den Vorteil, das Lidar auch unter bewölkten Bedingungen zu kalibrieren. Hierfür wird der Kalibrierfaktor des letzten wolkenfreien Zeitraums herangezogen. Dies ermöglicht die kontinuierliche Messung von Wasserdampfprofilen bis zu einer möglichen Wolkenbasis. Um verlässliche Wasserdampfinformationen innerhalb und oberhalb einer Wolke zu erhalten, wird ein zweistufiger Algorithmus angewandt. Der erste Schritt ist ein Kalman Filter, der die an der Wolkenbasis abgeschnittenen Wasserdampfprofile vom Ramanlidar mittels eines vorherigen Profils zu einem kompletten Profil (bis zu 10 km) kombiniert. Das komplette Wasserdampfprofil dient dann als Input für die eindimensionale variationelle (1D- VAR) Methode, auch als optimale Schätzung bekannt. Für dieses Profil werden die Helligkeitstemperaturen simuliert, die das Mikrowellenradiometer in der gegebenen Atmosphäre messen würde und anschließend mit den tatsächlich gemessenen verglichen. Das Profil wird dann iterativ entsprechend seiner Fehlerbalken so lange modifiziert, bis die modellierten mit den gemessenen Helligkeitstemperaturen hinreichend übereinstimmen. Die Funktionsweise des Retrievals wird mit Hilfe von Fallstudien unter verschiedenen Bedingungen detailliert beleuchtet. Eine statistische Analyse zeigt, dass die Verfügbarkeit von Ramanlidardaten (nachts) die Genauigkeit der abgeleiteten Profile verbessert. Tagsüber resultiert das Fehlen der Lidarinformationen in größeren Unterschieden zu Referenzradiosonden. Die Datenabdeckung der kompletten Lidarprofile von 17 % während der zweimonatigen Kampagne wird durch Anwendung des Retrievals auf 60 % signifikant erhöht. Da die relative Feuchte oft mals ein nützliches Maß für die Beschreibung von Wolkenbildung und Aerosolwachstum ist, wird die Bestimmung der relativen Feuchte aus den abgeleiteten Profilen unter verschiedenen Temperaturannahmen behandelt. Die Annahme eines Temperaturprofils vom Mikrowellenradiometer resultiert in einem absoluten Bias von 4.7 g/kg . Weiterhin wird in der Arbeit die flexible und vielfältige Anwendung des Retrievals an verschiedenen Messstationen in Jülich, Lindenberg und auf dem Forschungsschiff Polarstern sowie unterschiedlichen Ramanlidargeräten und Mikrowellenradiometern präsentiert. Ein besonders hervorzuhebender positiver Aspekt der Arbeit ist die Implementierung des Retrievals in die Cloudnet-Prozessierung, welche die Untersuchung von Wolken und Niederschlag bereichert. Die gewonnenen Profile werden außerdem für eine Evaluierung des Klima- und Vorhersagemodells ICON verwendet.