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>Magister Scientiae - MSc / There have been increasing calls to monitor Groundwater-Dependent Ecosystems (GDEs) more effectively, since they are biodiversity hotspots that provide several ecosystem services. The accurate monitoring of GDEs is an indispensable under Sustainable Development Goal (SDG) 15, because it promotes the existence of phreatophytes. It is imperative to monitoring GDEs, since their ecological significance (e.g., as biodiversity hotspots) is not well understood in most environments they exist. For example, vegetation diversity in GDEs requires routine monitoring, to conserve their biodiversity status and to preserve the ecosystem services in these environments. Such monitoring requires robust measures and techniques, particularly in arid environments threatened by groundwater over–abstraction, landcover and climate change. Although in–situ methods are reliable, they are challenging to use in extensive transboundary groundwater resources such as the Khakea-Bray Transboundary Aquifer.

For elliptic operators on manifolds with boundary, we define spectral boundary value problems, which generalize the Atiyah-Patodi-Singer problem to the case of nonhomogeneous boundary conditions, operators of arbitrary order, and nonself-adjoint conormal symbols. The Fredholm property is proved and equivalence with certain elliptic equations on manifolds with conical singularities is established.

The Intergovernmental Panel on Climate Change (IPCC) found in their 2007 report that aerosol radiative forcing contributed larger uncertainties to estimates affecting future climate change than any other radiative forcing factor. Lidar is a tool with which this uncertainty can be reduced, increasing our understanding of the impact of aerosols on climate change. Lidar, or laser radar, is a monostatic active remote sensing technique used to measure aerosols and particulates in the atmosphere, with accuracies comparable to in-situ measurements (Russell 2002). High Spectral Resolution Lidar (HSRL) systems use a narrow band filter to spectrally separate Doppler broadened aerosol and molecular back-scattered return signals, which allows for range resolved profiles of aerosol extinction and backscatter. The narrow band filter is a key component, for which two novel approaches are currently being used: NASA Langley Research Center has implemented a wide-angle Michelson interferometer in the second version of their airborne HSRL, and Montana State University is using a spherical Fabry-Perot interferometer in a ground based HSRL. In this research, a comprehensive comparative analysis of these two interferometric filters is performed, the result of which is a methodology for the design of narrow band filters for HSRL systems. The techniques presented identify the critical components and analyze the performance of each filter based on the spectral and angular properties, as well as the efficiency.

Le sondeur hyperspectral infrarouge IASI, dont le premier modèle vole depuis 2006 sur le satellite défilant météorologique Metop-A, a déjà conduit a des retombées scientifiques très spectaculaires, en prévision météorologie et pour l’étude de la composition atmosphérique et du climat. Les mesures du sondeurs sont toutefois largement sous exploitées en grande partie du a la présence des nuages dans l’atmosphère. Ces derniers interagissent avec le rayonnement incident de façon hautement non-linéaire rendant le traitement de la mesure du sondeur bien plus complexe, voire parfois rédhibitoire pour accéder depuis l’espace aux propriétés des couches atmosphériques situées au-dessus du nuage, mais également en dessous dans le cas de semi-transparence. Cependant, au vue de la quantité d’informations potentielles qu’offre les sondeurs, la communauté scientifique s’intéresse de près a l’exploitation des radiances nuageuse, c’est dans ce cadre que s’inscrivent les travaux de recherche de cette thèse. Nous proposons d’étudier deux schémas nuageux radicalement différents : la clarification nuageuse et un schéma permettant de simuler la radiance nuageuse en utilisant les propriétés optique et microphysique des nuages. La première de ces méthodes, initiée par Smith et al. (1968), permet sous certaines conditions, de faire abstraction du nuage dans le pixel IASI. La méthode est basée sur l’algorithme du logiciel Scenes Heterogenes du CNES. Apres une première étape de validation, les performances de la méthode sont évaluées a travers la quantité d’information indépendante qu’offre la clarification par rapport a une chaine de traitement des radiances nuageuses mise en place au CMS. Les résultats sont favorables à la méthode testée permettant de traiter les couches atmosphériques situées sous le nuage, possédant donc une quantité plus importante. Cependant la clarification repose a la fois sur une hypothèse forte d’homogénéité atmosphérique et ne s’applique qu’à 15% des situations nuageuses. La seconde méthode est une simulation de la radiance nuageuse par des modèles de transfert radiatif rapides utilisant les propriétés optique et microphysique du nuage. Cette méthode présente l’avantage majeur d’utiliser les mêmes profils nuageux que ceux produits par les modèles de prévision numérique, laissant entrevoir l’assimilation de ces profils à partir de la mesure IASI. Cependant, l’utilisation de ces modèles de transfert radiatif rapide dans le cadre d’une assimilation de données n’en est encore qu’à ces prémices, très peu d’études ont été menées sur ce sujet. Nous proposons une étude en trois étapes permettant une utilisation en opérationnel de ces modèles de transfert radiatif. La première étape est une compréhension des modèles et de leur validité en réalisant quelques études de cas s’appuyant sur la campagne de mesures de Lindenberg. Ensuite, dans le cadre de la campagne ConcordIasi, une statistique est réalisée mettant en place des filtrage pour sélectionner uniquement les profils nuageux cohérent avec l’observation IASI. La dernière étape est une application en global, les statistiques révèlent une nette amélioration des écarts a l’ébauche grâce aux filtres, passant de 8K a 2K. Nous proposons tout au long de l’étude une discussion sur les modèles utilises (RTTOV et HISCRTM), leurs points forts et leurs défaillances. Enfin l’ultime étape, permet d’évaluer les performances des profils nuageux issus des modèles de prévision numérique. / The IASI hyperspectral infrared sounding interferometer, the first model of which has been flown on board the meteorological polar orbiting satellite MetOp-A since 2006, has already led to spectacular scientific breakthroughs in both weather forecasting and research into atmospheric composition and the climate. Measurements from the sounders are however largely underutilised, mainly because of the presence of clouds in the atmosphere. The highly non-linear way in which the clouds interact with incident radiation makes analysis of the readings much more complex, and can sometimes even prohibit access from space to the properties of not only the atmospheric layers located above the cloud, but also below them in the case of semi-transparency. However, in view of the potential amount of information offered by the sounders, the scientific community is very interested in exploiting cloud radiance. The research for this thesis stems from this interest. We plan to study two radically different cloud schemes: cloud clarification and a scheme which allows for simulation of cloud radiance by using the optical and microphysical properties of clouds. The first of these methods, initiated by Smith et al. (1968), allows us under certain conditions to disregard the cloud in the IASI pixel. This method is based on the CNES Heterogeneous Scenes software algorithm. After a first validation step, method performance is evaluated by the amount of independent information offered by the clarification, compared to a cloud radiance process chain established at CMS. The results are favorable to the tested method allowing us to deal with atmospheric layers under the cloud, which have therefore larger quantities. However clarification is based on a strong assumption of atmospheric homogeneity and only applies to 15% of cloud situations. The second method is a simulation of cloud radiance by fast radiative transfer models using the optical and microphysical properties of the cloud. The major advantage of this method is that it uses the same cloud profiles as those produced by numerical weather prediction models, allowing assimilation of these profiles from the IASI measurement. However, the use of these fast radiative transfer models in the context of data assimilation is still in the early stages, very few studies have been conducted on this topic. We are proposing a three-phase study which will allow for an operational use of these radiative transfer models. The first step is validation. This is done by conducting several case studies based on Lindenberg’s measurement campaign. Then, within the framework of the ConcordIasi campaign, a statistical analysis will be carried out by introducing filtering, to select cloud profiles which are consistent with the IASI observations. The last step is an overall application, the statistics showing a clear improvement in deviation from the draft thanks to the filters, going from 8K to 2K. Throughout the study we will discuss the models used (RTTOV and HISCRTM), their strengths and weaknesses. Finally the last step allows us to evaluate the performance of the cloud profiles obtained by the digital forecasting models

The influence of spectral resolution on land cover classification in Krkonoše Mts. tundra Abstract The aim of this diploma thesis was to specify the spectral resolution requirements for classification and to identify the most important spectral bands to discriminate classes of the predefined legend. Aerial hyperspectral data acquired by AisaDUAL sensor were used. The method applied for the selection of the important bands was discriminant analysis performed in IBM SPSS Statistics. The most discriminative bands were found in intervals 1500-1750 nm (beginning of SWIR), 1100- 1300 nm (longer wavelengths of NIR), 670-760 (red-edge) and 500-600 nm (green light). The classification of the selected bands was realized in ENVI 5.4 using the Support Vector Machine classifier, achieving overall accuracy of 80,54 %, Kappa coefficient 0,7755. The suitability of available satellite data for the classification of tundra vegetation in Krkonoše mountains based on spectral resolution was evaluated as well. Keywords: tundra, Krkonoše, classification, spectral resolution, class separability, discriminant analysis, hyperspectral data

The ability to perceive speech is related to the listener's ability to differentiate among frequencies (i.e. spectral resolution). Cochlear implant users exhibit variable speech perception and spectral resolution abilities, which can be attributed at least in part to electrode interactions at the periphery (i.e. spatial resolution). However, electrophysiological measures of peripheral spatial resolution have not been found to correlate with speech perception. The purpose of this study was to systematically evaluate auditory processing from the periphery to the cortex using both simple and spectrally complex stimuli in order to better understanding the underlying processes affecting spatial and spectral resolution and speech perception. Eleven adult cochlear implant users participated in this study. Peripheral spatial resolution was assessed using the electrically evoked compound action potential (ECAP) to measure channel interaction functions for thirteen probe electrodes. We evaluated central processing using the auditory change complex (ACC), a cortical response, elicited with both spatial (electrode pairs) and spectral (rippled noise) stimulus changes. Speech perception included a vowel-discrimination task and the BKB-SIN test of keyword recognition in noise. We varied the likelihood of electrode interactions within each participant by creating three experimental programs, or MAPs, using a subset of seven electrodes and varying the spacing between activated electrodes. Linear mixed model analysis was used to account for repeated measures within an individual, allowing for a within-subject interpretation. We also performed regression analysis to evaluate the relationships across participants. Both peripheral and central processing abilities contributed to the variability in performance observed across CI users. The spectral ACC was the strongest predictor of speech perception abilities across participants. When spatial resolution was varied within a person, all electrophysiological measures were significantly correlated with each other and with speech perception. However, the ECAP measures were the best single predictor of speech perception for the within-subject analysis, followed by the spectral ACC. Our results indicate that electrophysiological measures of spatial and spectral resolution can provide valuable information about perception. All three of the electrophysiological measures used in this study, including the ECAP channel interaction functions, demonstrated potential for clinical utility.

For cochlear implant (CI) listeners, poorer than normal speech recognition abilities are typically attributed to degraded spectral acuity. However, estimates of spectral acuity have most often been obtained using simple (tonal) stimuli, presented directly to the implanted electrodes, rather than through the speech processor as occurs in everyday listening. Further, little is known about spectral acuity for dynamic stimuli, as compared to static stimuli, even though the perception of dynamic spectral cues is important for speech perception. The primary goal of the current study was to examine spectral acuity in CI listeners, and a comparison group of normal hearing (NH) listeners, for both static and dynamic stimuli presented through the speech processor. In addition to measuring static and dynamic spectral acuity for simple stimuli (pure tones) in Experiment 1, spectral acuity was measured for complex stimuli (synthetic vowels) in Experiment 2, because measures obtained with speech-like stimuli are more likely to reflect listeners’ ability to make use of spectral cues in naturally-produced speech. Sixteen postlingually-deaf, adult CI users and sixteen NH listeners served as subjects in both experiments. In Experiment 1, frequency discrimination limens (FDLs) were obtained for 1.5 kHz reference tones, and frequency glide discrimination limens (FGDLs) were obtained for pure-tone frequency glides centered on 1.5 kHz. Glide direction identification thresholds (GDITs) were also measured, in order to determine the amount of frequency change required to identify glide direction. All three measures were obtained for stimuli having both longer (150 ms) and shorter (50 ms) durations. Spectral acuity for dynamic stimuli (FGDLs, GDITs) was poorer than spectral acuity for static stimuli (FDLs) for both listener groups at both stimulus durations. Stimulus duration had a significant effect on thresholds in NH listeners, for all three measures, but had no significant effect on thresholds in CI listeners for any measure. Regression analyses revealed no systematic relationship between FDLs and FGDLs in NH listeners at either stimulus duration. For CI listeners, the relationship between FDLs and FGDLs was significant at both stimulus durations, suggesting that, for tonal signals, the factors that determine spectral acuity for static stimuli also largely determine spectral acuity for dynamic stimuli. In Experiment 2, estimates of static and dynamic spectral acuity were obtained using three-formant synthetic vowels, modeled after the vowel /^/. Formant discrimination thresholds (FDTs) were measured for changes in static F2 frequency, whereas formant transition discrimination thresholds (FTDTs) were measured for stimuli that varied in the extent of F2 frequency change. FDTs were measured with 150-ms stimuli, and FTDTs were measured with both 150-ms and 50-ms stimuli. For both listener groups, FTDTs were similar for the longer and shorter stimulus durations, and FTDTs were larger than FDTs at the common duration of 150 ms. Measures from Experiment 2 were compared to analogous measures from Experiment 1 in order to examine the effect of stimulus context (simple versus complex) on estimates of spectral acuity. For NH listeners, measures obtained with complex stimuli (FDTs, FTDTs) were consistently larger than the corresponding measures obtained with simple stimuli (FDLs, FGDLs). For CI listeners, the relationship between simple and complex measures differed across two subgroups of subjects. For one subgroup, thresholds obtained with complex stimuli were smaller than those obtained with simple stimuli; for another subgroup the pattern was reversed. On the basis of these findings, it was concluded that estimates of spectral acuity obtained with simple stimuli cannot accurately predict estimates of spectral acuity obtained with complex (speech-like) stimuli in CI listeners. However, a significant relationship was observed between FDTs and FTDTs. Thus, similar to the measures obtained with pure-tone stimuli in Experiment 1 (FDLs and FGDLs), estimates of static spectral acuity (FDTs) appear to predict estimates of dynamic spectral acuity (FTDTs) when both measures are obtained with stimuli of similar complexity in CI listeners. Taken together, findings from Experiments 1 and 2 support the following conclusions: (1) Dynamic spectral acuity is poorer than static spectral acuity for both simple and complex stimuli. This outcome was true for both NH and CI listeners, despite the fact that absolute thresholds were substantially larger, on average, for the CI group. (2) For stimuli having the same level of complexity (i.e., tonal or speech-like), dynamic spectral acuity in CI listeners appears to be determined by the same factors that determine spectral acuity for static stimuli. (3) For CI listeners, no systematic relationship was observed between analogous measures of spectral acuity obtained with simple, as compared to complex, stimuli. (4) It is expected that measures of spectral acuity based on complex stimuli would provide a better indication of CI users’ ability to make use of spectral cues in speech; therefore, it may be advisable for studies attempting to examine the relationship between spectral acuity and speech perception in this population to measure spectral acuity using complex, rather than simple, stimuli. (5) Findings from the current study are consistent with recent vowel identification studies suggesting that some poorer-performing CI users have little or no access to dynamic spectral cues, while access to such cues may be relatively good in some better-performing CI users. However, additional research is needed to examine relationship between estimates of spectral acuity obtained here for speech-like stimuli (FDTs, FTDTs) and individual CI users’ perception of static and dynamic spectral cues in naturally-produced speech.

Une perte auditive neurosensorielle est généralement associée à uneréduction de l’intelligibilité de la parole, et ce tout particulièrement dans le bruit.Les contributions respectives d’une réduction de l'audibilité et de déficitssupraliminaires sont encore débattues.L'objectif principal de cette thèse était d'évaluer l'effet spécifique desdéficits supraliminaires sur l’intelligibilité de la parole. L'effet de l'audibilité étaitcontrôlé en mesurant l’intelligibilité de signaux de parole sans signification filtrésdans les régions basses et moyennes fréquences au sein desquelles la détection desons purs était normale chez des auditeurs malentendants présentant par ailleursune perte auditive en hautes fréquences. Dans ces régions fréquentielles oùl’audibilité est supposée normale, des déficits d'intelligibilité de la parole légers àsévères ont été observés dans le silence comme dans le bruit chez les auditeursmalentendants. Les déficits étaient similaires dans les bruits masquantstationnaires et fluctuants. Ces résultats démontrent l’influence des déficitsauditifs supraliminaires sur l’intelligibilité de la parole.Le second objectif de cette thèse était d'étudier l'origine de ces déficitssupraliminaires. Les résultats indiquent qu’une réduction de la sélectivitéfréquentielle cochléaire ne peut pas expliquer entièrement les déficitsd’intelligibilité de la parole des auditeurs malentendants. L'influence de lasensibilité à la structure temporelle fine reste incertaine / Speech intelligibility is reduced for listeners with sensorineural hearingloss, especially for speech in noise. The extent to which this reduction is due toreduced audibility or to supra-threshold deficits is still debated.The main goal of this PhD work was to investigate the specific influenceof supra-threshold deficits on speech intelligibility. The effect of audibility wascontrolled for by measuring speech intelligibility for hearing-impaired listenersusing nonsense speech signals filtered in low- and mid-frequency regions wherepure-tone sensitivity was normal. Hearing-impaired listeners with hearing loss inhigh-frequency regions showed mild to severe intelligibility deficits for speechboth in quiet and in noise in these frequency regions of normal audibility. Similardeficits were obtained for speech in steady and fluctuating masking noises. Thisprovides additional evidence that speech intelligibility may be strongly influencedby supra-threshold auditory deficits.The second aim of this PhD work was to investigate the origin of thesesupra-threshold deficits. Results showed that reduced frequency selectivity cannotentirely explain the speech intelligibility deficits of the hearing-impaired listeners.The influence of temporal fine structure sensitivity remained unclear

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