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Retrieval and validation of forest background reflectivity from daily Moderate Resolution Imaging Spectroradiometer (MODIS) bidirectional reflectance distribution function (BRDF) data across European forests
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Orientador(es)
Resumo(s)
Information about forest background reflectance
is needed for accurate biophysical parameter retrieval from
forest canopies (overstory) with remote sensing. Separating
under- and overstory signals would enable more accurate
modeling of forest carbon and energy fluxes. We retrieved
values of the normalized difference vegetation index (NDVI)
of the forest understory with the multi-angular Moderate
Resolution Imaging Spectroradiometer (MODIS) bidirectional
reflectance distribution function (BRDF)/albedo data
(gridded 500m daily Collection 6 product), using a method
originally developed for boreal forests. The forest floor background
reflectance estimates from the MODIS data were
compared with in situ understory reflectance measurements
carried out at an extensive set of forest ecosystem experimental
sites across Europe. The reflectance estimates from
MODIS data were, hence, tested across diverse forest conditions
and phenological phases during the growing season
to examine their applicability for ecosystems other than boreal
forests. Here we report that the method can deliver good
retrievals, especially over different forest types with open
canopies (low foliage cover). The performance of the method
was found to be limited over forests with closed canopies
(high foliage cover), where the signal from understory becomes
too attenuated. The spatial heterogeneity of individual
field sites and the limitations and documented quality of
the MODIS BRDF product are shown to be important for the
correct assessment and validation of the retrievals obtained
with remote sensing.
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Citação
Pisek, Jan and Erb, Angela and Korhonen, Lauri and Biermann, Tobias and Carrara, Arnaud and Cremonese, Edoardo and Cuntz, Matthias and Fares, Silvano and Gerosa, Giacomo and Gruenwald, Thomas and Hase, Niklas and Heliasz, Michal and Ibrom, Andreas and Knohl, Alexander and Kobler, Johannes and Kruijt, Bart and Lange, Holger and Leppänen, Leena and Limousin, Jean-Marc and Lopez Serrano, Francisco Ramo and Loustau, Denis and Lukeš, Petr and Lundin, Lars and Marzuoli, Riccardo and Mölder, Meelis and Montagnani, Leonardo and Neirynck, Johannes and Peichl, Matthias and Rebmann, Corinna and Rubio, Eva and Santos-Reis, Margarida and Schaaf, Crystal and Schmidt, Marius and Simioni, Guillaume and Soudani, Kamel and Vincke, Caroline (2021). Retrieval and validation of forest background reflectivity from daily MODIS bidirectional reflectance distribution function (BRDF) data across European forests. Biogeosciences. 18 , 621–635
Editora
Copernicus Publications