Surface Albedo Retrieval from 40-Years of Earth Observations through the EUMETSAT/LSA SAF and EU/C3S Programmes: The Versatile Algorithm of PYALUS

Abstract

Land surface albedo quantifies the fraction of the sunlight reflected by the surface of the Earth. This article presents the algorithm concepts for the remote sensing of this variable based on the heritage of several developments which were performed at Méteo France over the last decade and described in several papers by Carrer et al. The scientific algorithm comprises four steps: an atmospheric correction, a sensor harmonisation (optional), a BRDF (Bidirectional Reflectance Distribution Function) inversion, and the albedo calculation. At the time being, the method has been applied to 11 sensors in the framework of two European initiatives (Satellite Application Facility on Land Surface Analysis—LSA SAF, and Copernicus Climate Change Service—C3S): NOAA-7-9-11-14-16-17/AVHRR2-3, SPOT/VGT1-2, Metop/AVHRR-3, PROBA-V, and MSG/SEVIRI. This work leads to a consistent archive of almost 40 years of satellite-derived albedo data (available in 2020). From a single sensor, up to three different albedo products with different characteristics have been developed to address the requirements of both, near real-time (NRT) (weather prediction with a demand of timeliness of 1 h) and climate communities. The evaluation of the algorithm applied to different platforms was recently made by Lellouch et al. and Sánchez Zapero et al. in 2020 which can be considered as companion papers. After a summary of the method for the retrieval of these surface albedos, this article describes the specificities of each retrieval, lists the differences, and discusses the limitations. The plan of continuity with the next European satellite missions and perspectives of improvements are introduced. For example, Metop/AVHRR-3 albedo will soon become the medium resolution sensor product with the longest NRT data record, since MODIS is approaching the end of its life-cycle. Additionally, Metop-SG/METimage will ensure its continuity thanks to consistent production of data sets guaranteed till 2050 by the member states of the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT). In the end, the common strategy which we proposed through the different programmes may offer an unprecedented opportunity to study the temporal trends affecting surface properties and to analyse human-induced climate change. Finally, the access to the source code (called PYALUS) is provided through an open access platform in order to share with the community the expertise on the satellite retrieval of this variable.

Comparison of Long-Term Albedo Products against Spatially Representative Stations over Snow

“…The Copernicus Climate Change Service (C3S) produces a 10-daily multi-sensor surface albedo product that spans from 1981 to 2020 using NOAA- [7,9,11,14,16,17]/AVHRR- [2,3], SPOT- [4,5]/VGT- [1,2], and PROBA-V observations [36]. The parameters provided are 10-day spectral and broadband white and black sky albedo with a spatial resolution of 1/30 • ∼4 km (AVHRR) and 1/112 • ∼1 km (SPOT/VGT and PROBA-V).…”

Comment on gi-2022-6

“…Updated narrow-to broadband conversion coefficients. The narrow-to broadband conversion in the MDAL retrieval algorithm involves a set of conversion coefficients which are calculated based on regression analysis using synthetic spectral reflectances of different surface types (generated from Advanced Spaceborne Thermal Emission Reflection Radiometer, ASTER, data), fitted by the SAIL (Scattering by Arbitrary Inclined Leaves) radiative transfer model (for more details see section 2.5.2 in Carrer et al, 2021). The database of synthetic spectral reflectances has been updated to A2).…”

Climate cooling benefits of cellulosic bioenergy crops from elevated albedo

“…Albedo is a vital indicator of energy partitioning because it reflects solar energy absorbed by a land surface (e.g., grasslands, forest, or urban lands) and then converted to heat, versus the amount reflected back to space with no warming impact (Ollinger et al, 2008). Theoretically, if more solar radiation is reflected back to space, the global climate is cooled-raising the potential for contributing to climate change mitigation through land surface management (Bright et al, 2012;Carrer et al, 2018Carrer et al, , 2021Muñoz & Kravchenko, 2011;Ouyang et al, 2022). Spatial and temporal changes in albedo have been closely explored, as albedo not only directly affects climate warming and cooling (Campbell & Norman, 2012) but also indirectly affects changes in evaporation and transpiration, and also local climate through its impact on surface energy fluxes and the hydrologic cycle (Akbari et al, 2009;Cherubini et al, 2012;Pachauri et al, 2014).…”