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Article

Validation of Space-Based Albedo Products from Upscaled Tower-Based Measurements Over Heterogeneous and Homogeneous Landscapes

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Imaging Group, Mullard Space Science Laboratory, Department of Space & Climate Physics, University College London, Holmbury St Mary, Surrey RH56NT, UK
2
NCEO, Department of Geography, University College London, Gower Street, London WC1E 6BT, UK
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CSIRO, Black Mountain, Building 801, Canberra 2601, Australia
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Research Center of Excellence PLECO, Department of Biology, University of Antwerp, Universiteitsplein 1, B-2610 Wilrijk, Belgium
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Joint Research Centre, European Commission, Via Enrico Fermi 2749, 21027 Ispra, Italy
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TerRésultats de recherche TERN - Terrestrial Ecosystem Research Network (TERN), School of Biological Sciences, The University of Adelaide, Adelaide 5005, Australia
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AgroParisTech, INRAE, UMR Silva, Université de Lorraine, 54000 Nancy, France
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AgroParisTech, INRAE, UMR EcoFoG, Cirad, CNRS, Université des Antilles, Université de Guyane, 97310 Kourou, France
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Bioclimatology, Faculty of Forest Sciences and Forest Ecology, University of Goettingen, 37077 Goettingen, Germany
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Institut National de Recherche Agronomique (INRA), Université Paris-Saclay, 78850 Saint-Aubin, France
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Faculty of Science and Technology, Free University of Bozen-Bolzano, 39100 Bolzano, Italy
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Forest Services, Autonomous Province of Bolzano, 39100 Bolzano, Italy
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ACRI-ST, 260 Route de Pin Montard, BP 234, 06904 Sophia Antipolis, France
*
Author to whom correspondence should be addressed.
Remote Sens. 2020, 12(5), 833; https://doi.org/10.3390/rs12050833
Received: 21 December 2019 / Revised: 26 February 2020 / Accepted: 26 February 2020 / Published: 4 March 2020
Surface albedo is a fundamental radiative parameter as it controls the Earth’s energy budget and directly affects the Earth’s climate. Satellite observations have long been used to capture the temporal and spatial variations of surface albedo because of their continuous global coverage. However, space-based albedo products are often affected by errors in the atmospheric correction, multi-angular bi-directional reflectance distribution function (BRDF) modelling, as well as spectral conversions. To validate space-based albedo products, an in situ tower albedometer is often used to provide continuous “ground truth” measurements of surface albedo over an extended area. Since space-based albedo and tower-measured albedo are produced at different spatial scales, they can be directly compared only for specific homogeneous land surfaces. However, most land surfaces are inherently heterogeneous with surface properties that vary over a wide range of spatial scales. In this work, tower-measured albedo products, including both directional hemispherical reflectance (DHR) and bi-hemispherical reflectance (BHR), are upscaled to coarse satellite spatial resolutions using a new method. This strategy uses high-resolution satellite derived surface albedos to fill the gaps between the albedometer’s field-of-view (FoV) and coarse satellite scales. The high-resolution surface albedo is generated from a combination of surface reflectance retrieved from high-resolution Earth Observation (HR-EO) data and moderate resolution imaging spectroradiometer (MODIS) BRDF climatology over a larger area. We implemented a recently developed atmospheric correction method, the Sensor Invariant Atmospheric Correction (SIAC), to retrieve surface reflectance from HR-EO (e.g., Sentinel-2 and Landsat-8) top-of-atmosphere (TOA) reflectance measurements. This SIAC processing provides an estimated uncertainty for the retrieved surface spectral reflectance at the HR-EO pixel level and shows excellent agreement with the standard Landsat 8 Surface Reflectance Code (LaSRC) in retrieving Landsat-8 surface reflectance. Atmospheric correction of Sentinel-2 data is vastly improved by SIAC when compared against the use of in situ AErosol RObotic NETwork (AERONET) data. Based on this, we can trace the uncertainty of tower-measured albedo during its propagation through high-resolution EO measurements up to coarse satellite scales. These upscaled albedo products can then be compared with space-based albedo products over heterogeneous land surfaces. In this study, both tower-measured albedo and upscaled albedo products are examined at Ground Based Observation for Validation (GbOV) stations (https://land.copernicus.eu/global/gbov/), and used to compare with satellite observations, including Copernicus Global Land Service (CGLS) based on ProbaV and VEGETATION 2 data, MODIS and multi-angle imaging spectroradiometer (MISR). View Full-Text
Keywords: surface albedo; directional hemispherical reflectance; bi-hemispherical reflectance; upscaling; CGLS; ProbaV; vegetation; MODIS; MISR surface albedo; directional hemispherical reflectance; bi-hemispherical reflectance; upscaling; CGLS; ProbaV; vegetation; MODIS; MISR
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MDPI and ACS Style

Song, R.; Muller, J.-P.; Kharbouche, S.; Yin, F.; Woodgate, W.; Kitchen, M.; Roland, M.; Arriga, N.; Meyer, W.; Koerber, G.; Bonal, D.; Burban, B.; Knohl, A.; Siebicke, L.; Buysse, P.; Loubet, B.; Leonardo, M.; Lerebourg, C.; Gobron, N. Validation of Space-Based Albedo Products from Upscaled Tower-Based Measurements Over Heterogeneous and Homogeneous Landscapes. Remote Sens. 2020, 12, 833. https://doi.org/10.3390/rs12050833

AMA Style

Song R, Muller J-P, Kharbouche S, Yin F, Woodgate W, Kitchen M, Roland M, Arriga N, Meyer W, Koerber G, Bonal D, Burban B, Knohl A, Siebicke L, Buysse P, Loubet B, Leonardo M, Lerebourg C, Gobron N. Validation of Space-Based Albedo Products from Upscaled Tower-Based Measurements Over Heterogeneous and Homogeneous Landscapes. Remote Sensing. 2020; 12(5):833. https://doi.org/10.3390/rs12050833

Chicago/Turabian Style

Song, Rui, Jan-Peter Muller, Said Kharbouche, Feng Yin, William Woodgate, Mark Kitchen, Marilyn Roland, Nicola Arriga, Wayne Meyer, Georgia Koerber, Damien Bonal, Benoit Burban, Alexander Knohl, Lukas Siebicke, Pauline Buysse, Benjamin Loubet, Montagnani Leonardo, Christophe Lerebourg, and Nadine Gobron. 2020. "Validation of Space-Based Albedo Products from Upscaled Tower-Based Measurements Over Heterogeneous and Homogeneous Landscapes" Remote Sensing 12, no. 5: 833. https://doi.org/10.3390/rs12050833

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