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Continental scale hotspot observations of Australia at sub-degree angular resolution from POLDER / F. Grant in International Journal of Remote Sensing IJRS, vol 25 n° 18 (September 2004)  

Public [article]  inInternational Journal of Remote Sensing IJRS > vol 25 n° 18 (September 2004) . - pp 3625 - 3636 Titre : Continental scale hotspot observations of Australia at sub-degree angular resolution from POLDER Type de document : Article/Communication Auteurs : F. Grant, Auteur ; C. Heyraud, Auteur ; François-Marie Bréon, Auteur Année de publication : 2004 Article en page(s) : pp 3625 - 3636 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Traitement d'image [Termes IGN] analyse comparative [Termes IGN] Australie [Termes IGN] bande spectrale [Termes IGN] carte de la végétation [Termes IGN] image ADEOS-POLDER [Termes IGN] réflectance végétale [Termes IGN] tâche claire Résumé : (Auteur) Angular signatures of the innermost few degrees of the hotspot are retrieved on Australian land surfaces with an angular resolution better than 0.5° and a spatial resolution of around 150 km, using data from the Polarization and Directionality of the Earth's Reflectances (POLDER) instrument on the Advanced Earth Observing Satellite (ADEOS). These constitute the first comprehensive hotspot measurements at the scale of a continent. The retrieval technique requires that the hotspot characteristics at small angular scales are approximately invariant over a region of about 50km in extent, but accommodates pixel-to-pixel variations in the other characteristics, of the angular signature. Continental maps of the amplitude and half-width of the hotspot, in two spectral bands, are presented for two 41-day orbit cycles in different seasons and compared with a vegetation map. The half-widths are predominantly in the range 0.5°-1.5°, with no systematic difference between the 670 nm and 865 nm bands, and show little spatial structure. The maps of hotspot amplitude display significant spatial structure that corresponds closely to the vegetation map. Generally, areas of trees and tall shrubs are characterized by low hotspot amplitudes, while cropland, grassland and areas of low shrubs have high hotspot amplitudes. The evergreen broadleaf eucalypt forests are notable in that the amplitude is low at 670 nm and high at 865 nm. Numéro de notice : A2004-354 Affiliation des auteurs : non IGN Thématique : FORET/IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1080/01431160310001648000 En ligne : https://doi.org/10.1080/01431160310001648000 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=26881 [article]

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Bidirectional reflectance of Earth targets: evaluation of analytical models using a large set of spaceborne measurements with emphasis on the Hot Spot / F. Maignan in Remote sensing of environment, vol 90 n° 2 (30/03/2004)  

Public [article]  inRemote sensing of environment > vol 90 n° 2 (30/03/2004) . - pp 210 - 220 Titre : Bidirectional reflectance of Earth targets: evaluation of analytical models using a large set of spaceborne measurements with emphasis on the Hot Spot Type de document : Article/Communication Auteurs : F. Maignan, Auteur ; François-Marie Bréon, Auteur ; R. Lacaze, Auteur Année de publication : 2004 Article en page(s) : pp 210 - 220 Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Rayonnement électromagnétique [Termes IGN] albedo [Termes IGN] distribution du coefficient de réflexion bidirectionnelle BRDF [Termes IGN] image ADEOS-POLDER [Termes IGN] réflectance [Termes IGN] rétrodiffusion [Termes IGN] tâche claire [Termes IGN] transfert radiatif Résumé : (Auteur) Multidirectional observation from the spacebome POLDER (Polarization and Directionality of the Earth Reflectance) instrument makes it possible to measure the bidirectional reflectance of a large variety of Earth targets. A careful selection of cloud-free measurements with a large directional coverage lead to about 22,000 sets of measured Bidirectional Reflectance Distribution Functions (BRDFs). This data set is used to evaluate the ability of analytical models to reproduce the observed directional signatures. Among those evaluated, the best models appear to be the three-parameter linear Ross-Li model, and the nonlinear Rahman-Pinty-Verstraete (RPV) model. On the other hand, all models fail to accurately reproduce the sharp reflectance increase (hot spot) close to the backscattering direction. Based on physical considerations, we suggest a modification of the Ross-Li model, without adding a free parameter, to account for the complex radiative transfer within the canopy that leads to the hot spot signature. The modified linear model performs better than all others, including the RPV nonlinear model. Although the correction modifies the retrieved directional signature parameters, it does not change significantly the surface albedo estimates. Numéro de notice : A2004-142 Affiliation des auteurs : non IGN Thématique : IMAGERIE Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1016/j.rse.2003.12.006 En ligne : https://doi.org/10.1016/j.rse.2003.12.006 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=26669 [article]