Investigation of atmospheric effects on retrieval of sun-induced fluorescence using hyperspectral imagery

Significant research progress has recently been made in estimating fluorescence in the oxygen absorption bands, however, quantitative retrieval of fluorescence data is still affected by factors such as atmospheric effects. In this paper, top-of-atmosphere (TOA) radiance is generated by the MODTRAN 4 and SCOPE models. Based on simulated data, sensitivity analysis is conducted to assess the sensitivities of four indicators—depth_absorption_band, depth_nofs-depth_withfs, radiance and Fs/radiance—to atmospheric parameters (sun zenith angle (SZA), sensor height, elevation, visibility (VIS) and water content) in the oxygen absorption bands. The results indicate that the SZA and sensor height are the most sensitive parameters and that variations in these two parameters result in large variations calculated as the variation value/the base value in the oxygen absorption depth in the O2-A and O2-B bands (111.4% and 77.1% in the O2-A band; and 27.5% and 32.6% in the O2-B band, respectively). A comparison of fluorescence retrieval using three methods (Damm method, Braun method and DOAS) and SCOPE Fs indicates that the Damm method yields good results and that atmospheric correction can improve the accuracy of fluorescence retrieval. Damm method is the improved 3FLD method but considering atmospheric effects. Finally, hyperspectral airborne images combined with other parameters (SZA, VIS and water content) are exploited to estimate fluorescence using the Damm method and 3FLD method. The retrieval fluorescence is compared with the field measured fluorescence, yielding good results (R2 = 0.91 for Damm vs. SCOPE SIF; R2 = 0.65 for 3FLD vs. SCOPE SIF). Five types of vegetation, including ailanthus, elm, mountain peach, willow and Chinese ash, exhibit consistent associations between the retrieved fluorescence and field measured fluorescence

RÔLE DE L'OCCUPATION DU SOL VIS À VIS DE LA MODÉLISATION DES FLUX ENERGÉTIQUES ET HYDRIQUES EN MILIEU URBAIN ET PÉRIURBAIN

National audienceLe projet Rosenhy vise à étudier l’impact de l’occupation du sol sur la modélisation météorologique et hydrologique en termes de flux énergétiques et hydriques, en milieu urbain et périurbain. Trois sites appartenant aux observatoires français OTHU et ONEVU sont au centre de ce projet. Le quartier urbain hétérogène du Pin sec (Nantes), imperméabilisé à environ 45%, a fait l’objet d’une campagne expérimentale durant le mois de juin 2012, visant à estimer les flux de chaleur sensible et latente avec une haute résolution spatiale et temporelle par rapport aux mesures réalisées en continu sur ce site depuis 5 ans. Deux bassins versant périurbains (La Chézine à Nantes et l’Yzeron à Lyon), avec un taux d’imperméabilisation moins important (environ 10%) mais grandissant depuis plusieurs décennies, sont aussi étudiés. Ces deux derniers sites bénéficient d’un suivi hydrométéorologique depuis 10 ans pour la Chézine et 15 ans pour l’Yzeron. Sur ces trois sites, différentes sources de données d’occupation du sol à différentes résolutions sont disponibles :différentes bases de données géographiques communément utilisées par la communauté scientifique et les collectivités et des données télédétectées (multispectrales et hyperspectrales). L’utilisation de ces données en entrée de différents modèles météorologiques et hydrologiques implique un travail d’analyse et de classification pour adapter les informations aux besoins des modèles. Dans ce projet, les différents modèles adaptés au milieu urbain ou périrubain sont évalués et améliorés. Ainsi, les modèles hydrologiques périrubains sont en développement pour prendre en compte les différentes pratiques de gestion des eaux pluviales existantes (noues, toitures végétalisées, ...). L’utilisation conjointe des données simulées par les différents modèles aidera à déterminer le rôle de la part des surfaces naturelles et artificielles sur les bilans énergétique et hydrique en milieu plus ou moins urbanisé. Le milieu périurbain étant en évolution, le projet s’intéressera aussi à des scénarios d’urbanisation prospectifs en regardant d’une part l’impact de la densification sur les scénarios construits pour l’Yzeron lors du projet AVuPUR (ANR-VMCS, 2008-2011) et d’autre part, en réfléchissant conjointement avec Nantes Métropole, aux possibles voies d’évolution sur le bassin de la Chézine

Correction for the Impact of the Surface Characteristics on the Estimation of the Effective Emissivity at Fine Resolution in Urban Areas

Most of the methods used to retrieve land surface temperature (LST) from thermal infrared (TIR) satellite data in urban areas do not take into account the complexity of the surface. Cities are characterized by high surface roughness and one of the main constraints to estimate LST over those areas is the difficulty to define an effective emissivity for a given pixel at a given scale. When working with mixed pixels, the emissivity used to estimate the LST is an effective emissivity composed of the emissivities of each basic element constituting the pixel. In urban areas, the surface geometry has a strong impact on this effective emissivity. Its estimation from TIR satellite data must be carried out considering multiple surface reflections and diffusions within the urban canopy in order to retrieve accurate LST values. The objective of this study is then to evaluate the impact of the surface geometry within the pixel on effective emissivity estimation and to propose a method to derive an effective emissivity corrected for those effects. Emissivity can be derived at 90 m of spatial resolution from the TIR data acquired by ASTER. To evaluate the impact of the geometry at the scale of an ASTER pixel, several urban canyon configurations are designed to develop and test the correction method. The basic principle behind the method is to accurately estimate the downwelling TIR radiation received by a pixel integrating contributions from both the atmosphere and the scene inside this pixel and then derive the corrected effective emissivity from ASTER data using the TES (temperature emissivity separation) algorithm. First, the total downwelling TIR radiation is estimated from the geometric characteristics of the scene, using morphological indicators and integrating the non-isothermal behavior of the pixel thanks to 3D thermo-radiative model simulations. The validation of those estimations for each canyon configuration provides a maximum RMSE (Root Mean Square Error) value of 2.2 W·m−2. The validation performed over a district extracted from the 3D numerical model of Strasbourg (France) shows a RMSE of 2.5 W·m−2. Once the method to estimate the total downwelling TIR radiation is validated, LSE and LST maps are retrieved from an ASTER image over three districts of Strasbourg, showing that accounting for the surface geometry highlights thermal behavior differences inside districts, and that the impact of the geometry seems more influenced by building height than street width or building density

Correction for the Impact of the Surface Characteristics on the Estimation of the Effective Emissivity at Fine Resolution in Urban Areas

Most of the methods used to retrieve land surface temperature (LST) from thermal infrared (TIR) satellite data in urban areas do not take into account the complexity of the surface. Cities are characterized by high surface roughness and one of the main constraints to estimate LST over those areas is the difficulty to define an effective emissivity for a given pixel at a given scale. When working with mixed pixels, the emissivity used to estimate the LST is an effective emissivity composed of the emissivities of each basic element constituting the pixel. In urban areas, the surface geometry has a strong impact on this effective emissivity. Its estimation from TIR satellite data must be carried out considering multiple surface reflections and diffusions within the urban canopy in order to retrieve accurate LST values. The objective of this study is then to evaluate the impact of the surface geometry within the pixel on effective emissivity estimation and to propose a method to derive an effective emissivity corrected for those effects. Emissivity can be derived at 90 m of spatial resolution from the TIR data acquired by ASTER. To evaluate the impact of the geometry at the scale of an ASTER pixel, several urban canyon configurations are designed to develop and test the correction method. The basic principle behind the method is to accurately estimate the downwelling TIR radiation received by a pixel integrating contributions from both the atmosphere and the scene inside this pixel and then derive the corrected effective emissivity from ASTER data using the TES (temperature emissivity separation) algorithm. First, the total downwelling TIR radiation is estimated from the geometric characteristics of the scene, using morphological indicators and integrating the non-isothermal behavior of the pixel thanks to 3D thermo-radiative model simulations. The validation of those estimations for each canyon configuration provides a maximum RMSE (Root Mean Square Error) value of 2.2 W·m−2. The validation performed over a district extracted from the 3D numerical model of Strasbourg (France) shows a RMSE of 2.5 W·m−2. Once the method to estimate the total downwelling TIR radiation is validated, LSE and LST maps are retrieved from an ASTER image over three districts of Strasbourg, showing that accounting for the surface geometry highlights thermal behavior differences inside districts, and that the impact of the geometry seems more influenced by building height than street width or building density

Radiométrie infrarouge (Développement et validation de méthodes utilisant la bande [3-5um] pour la détermination des paramètres de surface à haute résolution spatiale)

STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Suivi de la végétation à travers l'étude de séries temporelles de NDVI et LST à partir de bases de données historiques

L observation de la Terre a commencé avec l apparition de la photographie au XIXe siècle, même si son développement a dû attendre jusqu aux années 70 les débuts de l ère spatiale pour atteindre les proportions qu elle a aujourd hui. Le travail de thèse présenté ici s inscrit dans le cadre de l observation de la Terre, plus spécialement de la végétation, incluant dans le terme végétation les différents états de surface des terres émergées de notre planète (forêts, cultures, savanes, toundra, mais aussi déserts, étendues glacées, etc.). Ce travail, réalisé principalement au sein de l Unité de Changement Global de l Université de Valence (Espagne), consiste en l exploitation extensive de bases de données historiques d images satellite pour l observation de la végétation, à travers deux paramètres, que sont la température de surface (LST pour sa traduction à l anglais) et un indice de végétation (NDVI, voire Rouse et al., 1973). Jusqu ici, l observation de la végétation s est limitée à l utilisation des indices de végétation, et l insertion du paramètre de température de surface représente le principal aspect novateur de ce travail de doctorat. Ce mémoire est constitué de 5 chapitres, compilant les aspects théoriques et pratiques du travail réalisé. Le chapitre 1 s attache à réaliser un état de l art, d un point de vue théorique et bibliographique, des thèmes abordés par ce doctorat. Les différents paramètres utilisés dans ce mémoire sont décrits dans le chapitre 2, ainsi que les différentes bases de données par lesquelles ces données ont été obtenues. Le chapitre 3 décrit en détail les algorithmes appliqués à ces données, afin d obtenir les paramètres de NDVI et LST nécessaires à l étude de la végétation. Les méthodes et résultats obtenus par l étude temporelle du NDVI sont présentés chapitre 4. Finalement, le chapitre 5 décrit les avancées réalisées dans l étude conjointe de la végétation à l aide du NDVI et de la LST...[etc.]Earth observation began with the apparition of photography during 19th century, even though its development really started during the 1970 s with the coming of the Space Age, to reach the dimensions it has today. The PhD dissertation presented here falls into the Earth Observation field, specifically vegetation monitoring, and includes different states of the exposed surface of our planet (forests, cultures, savannahs, tundra, as well as deserts, ice, etc.). This work, carried out mainly within the Global Change Unit of the University of Valencia (Spain), consists of the extensive exploitation of historical databases of satellite images for vegetation monitoring through two parameters, which are the land surface temperature (LST) and a vegetation index (NDVI, see Rouse et al., 1973). Up to now, vegetation monitoring has been limited to the use of vegetation indices, so the addition of the land surface temperature parameter represents the main innovative character of this PhD study. This dissertation is divided into 5 chapters, including the theoretical and experimental aspects of the work carried out. In chapter 1, an overview of the state of the various issues addressed in this study is realized from a theoretical and a bibliographical point of view. The different parameters used in this dissertation are described in chapter 2, along with a description of the databases through which these data were retrieved. The algorithms applied to the data to obtain the NDVI and LST parameters needed for vegetation monitoring are described in chapter 3. The methods and results obtained through NDVI temporal analysis are presented in chapter 4. Finally, chapter 5 describes the advances realized in the simultaneous study of the vegetation through NDVI and LST parameters...[etc.]STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Estimation of Daily Solar Radiation Budget at Kilometer Resolution over the Tibetan Plateau by Integrating MODIS Data Products and a DEM

Considering large and complex areas like the Tibetan Plateau, an analysis of the spatial distribution of the solar radiative budget over time not only requires the use of satellite remote sensing data, but also of an algorithm that accounts for strong variations of topography. Therefore, this research aims at developing a method to produce time series of solar radiative fluxes at high temporal and spatial resolution based on observed surface and atmosphere properties and topography. The objective is to account for the heterogeneity of the land surface using multiple land surface and atmospheric MODIS data products combined with a digital elevation model to produce estimations daily at the kilometric level. The developed approach led to the production of a three-year time series (2008–2010) of daily solar radiation budget at one kilometer spatial resolution across the Tibetan Plateau. The validation showed that the main improvement from the proposed method is a higher spatial and temporal resolution as compared to existing products. However, even if the solar radiation estimates are satisfying on clear sky conditions, the algorithm is less reliable under cloudy sky condition and the albedo product used here has a too coarse temporal resolution and is not accurate enough over rugged terrain

A new thermal infrared channel configuration for accurate land surface temperature retrieval from satellite data

International audienc

Land Surface Temperature and Emissivity Retrieval from Field-Measured Hyperspectral Thermal Infrared Data Using Wavelet Transform

International audienc