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Evaluation of different methods to retrieve the hemispherical downwelling irradiance in the thermal infrared region for field measurements / Vicente Garcia-Santos in IEEE Transactions on geoscience and remote sensing, vol 51 n° 4 Tome 2 (April 2013)  

Public [article]  inIEEE Transactions on geoscience and remote sensing > vol 51 n° 4 Tome 2 (April 2013) . - pp 2155 - 2165 Titre : Evaluation of different methods to retrieve the hemispherical downwelling irradiance in the thermal infrared region for field measurements Type de document : Article/Communication Auteurs : Vicente Garcia-Santos, Auteur ; Enric Valor, Auteur ; et al., Auteur Année de publication : 2013 Article en page(s) : pp 2155 - 2165 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Acquisition d'image(s) et de donnée(s) [Termes IGN] analyse comparative [Termes IGN] données de terrain [Termes IGN] éclairement énergétique [Termes IGN] effet atmosphérique [Termes IGN] emissivité [Termes IGN] nébulosité [Termes IGN] nuage [Termes IGN] radiomètre [Termes IGN] rayonnement infrarouge thermique [Termes IGN] réflectance spectrale [Termes IGN] réflexion diffuse [Termes IGN] température de surface Résumé : (Auteur) The thermal infrared hemispherical downwelling irradiance (HDI) emitted by the atmosphere and surrounding elements contributes through reflection to the signal measured over an observed surface by remote sensing. This irradiance must be estimated in order to obtain accurate values of land-surface temperature (LST). There are some fast methods to measure the HDI with a single measurement pointing to the sky at a specified viewing direction, but these methods require completely cloud-free or cloudy skies, and they do not account for the radiative contribution of surrounding elements. Another method is the use of a diffuse reflectance panel (usually, a rough gold-coated surface) with near-Lambertian behavior. This method considers the radiative contribution of surrounding elements and can be used under any sky condition. A third possibility is the use of atmospheric profiles and a radiative transfer code (RTC) in order to simulate the atmospheric signal and to calculate the HDI by integration. This study compares the HDI estimations with these approaches, using measurements made on four different days with a completely clear sky and two days with a partially cloudy sky. The measurements were made with a four-channel CIMEL Electronique radiometer working in the 8–14-u spectral range. The HDI was also estimated by means of National Centers for Environmental Prediction atmospheric profiles introduced in the MODTRAN RTC. Additionally, the measurements were made at two different places with very different environments to quantify the effect of the contributing surroundings. Results showed that, for a clear-sky day with a minimal contribution of the surroundings, all methods differed from each other between 5% and 11%, depending on the spectral range, and any of them could be used to estimate HDI in these conditions. However, in the case of making surface measurements in an area with significant surrounding elements (buildings, trees, etc.), HDI values retrieved from the panel present an increase of +3 W . m-2 . um-1} compared with the other methods; this increase, if ignored, implies to make an error in LST ranging from +0.5°C to +1.5°C, depending on the spectral range and on surface emissivity and temperature. Comparison under heterogeneous skies with changing cloud coverage showed also large differences between the use of panel and the other methods, reaching a maximum difference of +4.6W . m-2 . um-1, which implies to make an error on LST of +2.2°C. In these cases, the use of the diffuse reflectance panel is proposed, since it is the unique way to capture the contribution of the surroundings and also to adequately measure HDI for sky changing conditions. Numéro de notice : A2013-221 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1109/TGRS.2012.2209891 En ligne : https://doi.org/10.1109/TGRS.2012.2209891 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=32359 [article]

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Diffuse and specular characteristics of leaf reflectance / L. Grant in Remote sensing of environment, vol 22 n° 2 (01/07/1987)  

Public [article]  inRemote sensing of environment > vol 22 n° 2 (01/07/1987) . - pp 309 - 322 Titre : Diffuse and specular characteristics of leaf reflectance Type de document : Article/Communication Auteurs : L. Grant, Auteur Année de publication : 1987 Article en page(s) : pp 309 - 322 Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Télédétection [Termes IGN] polarisation [Termes IGN] réflectance végétale [Termes IGN] réflexion diffuse [Termes IGN] réflexion spéculaire Numéro de notice : A1987-338 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1016/0034-4257(87)90064-2 En ligne : https://doi.org/10.1016/0034-4257(87)90064-2 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=24415 [article]