Analysis of thermal infrared directional anisotropy over different surface types
| Autor: | Lagouarde, Jean-Pierre, Irvine, Mark Rankin, Dayau, Sylvia, Kurz, Britta, Ogée, Jérôme, Moreau, Patrick, Guyon, Dominique, Champion, Isabelle |
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| Přispěvatelé: | Écologie fonctionnelle et physique de l'environnement (EPHYSE), Institut National de la Recherche Agronomique (INRA) |
| Jazyk: | angličtina |
| Rok vydání: | 2006 |
| Předmět: | |
| Zdroj: | 1. Workshop on Remote Sensing and Modeling of Surface Properties, Paris, FRA, 2006-06-20-2006-06-22 1. Workshop on Remote Sensing and Modeling of Surface Properties 1. Workshop on Remote Sensing and Modeling of Surface Properties, Jun 2006, Paris, France. 1 p. + 29 pl |
| Popis: | National audience; Measurements of surface temperature performed in the thermal infrared (TIR) domain display important directional anisotropy and significant 'hot spot' effects during daytime. These depend (1) on the surface structure which governs the temperature profiles inside the canopy via the coupled energy-radiative transfers simultaneously to the spatial distribution of the facets seen by the sensor, and (2) on the solar position. Characterizing the TIR directional anisotropy is important for several purposes : (1) access to the surface temperature of the different canopy layers for improving sensible heat flux estimates, (2) assimilation of multi-angular remotely sensed data in the surface models, (3) correction and normalization of large swath satellite sensors with the scope of analyzing temporal or spatial variability, and (4) definition of optimal viewing configurations and recommendations for future TIR spatial systems. Several experiments based on airborne measurements have been performed to characterize the TIR directional anisotropy over different types of surfaces: pine forests, vineyards, urban areas. The protocol is based on the use of a TIR camera equipped with wide-angle lenses and installed aboard a small aircraft flying different directions. It allows retrieving directional anisotropy (differences between oblique and nadir viewing temperatures) in a range of zenithal viewing angles up to 60° and in all azimutal directions. The possible sources of errors related to the instruments and the atmosphere are analysed and corrections proposed. Experimental results reveal significant directional anisotropy whatever the surface type. Measurements performed at different times of day and at different periods of the year show systematic hot spots in relation with the sun position. The impact of the surface structure is also illustrated. Over maritime pine stands it is shown that the size of the hot spot directly depends on the stand structure (i.e. size, geometry and spacing of trees on the stand), with values reaching ±2 K in the principal plane. Results obtained over vineyards reveal that anisotropy results from the combination of a 'macro structure' effect (orientation of rows) with a 'micro-structure' effect (hot spot of bare stony soil). The strong contrasts between dry bare soil and vegetation walls explain huge directional variations from -12 to 4 K in the principal plane. The impact of the size of buildings, the built-up ratio, and the vegetation ratio on the TIR anisotropy over urban areas is also illustrated from results obtained in the framework of the ESCOMPTE experiment performed at Marseille in 2001 which show ranges of variation between -5 K up to 7 K. An example of application for the correction of two temporal series of NOAA 14 and NOAA 16 data over the city is given. Finally we discuss the difficulty of assessing the contribution of angular variations in surface emissivity to the overall thermal anisotropy, and we briefly present a directional anisotropy modelling approach of surface temperature based on combining 3D canopy models with surface models. |
| Databáze: | OpenAIRE |
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