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 50 km 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.
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Document Type: Research Article
CSIRO Atmospheric Research PMB 1, Aspendale VIC 3195 Australia, Email: [email protected]
Atmosphére Basse et Moyenne, Centre d'etude des Environnements Terrestre et Planétaires, IUT de Vélizy 10-12, avenue de l'Europe 78140 Vélizy France, Email: [email protected]
Laboratoire des Sciences du Climat et de l'Environnement Commissariat à l'Energie Atomique 91191 Gif sur Yvette France, Email: [email protected]
Publication date: 2004-09-01
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