Abstract
The Copernicus Climate Change Service (C3S) includes estimates of Essential Climate Variables (ECVs) as a series of Climate Data Records (CDRs) derived from satellite data. The C3S Surface Albedo (SA) v1.0 CDR is composed of observations from National Oceanic and Atmospheric Administration (NOAA) Very High Resolution Radiometers (AVHRR) (1981–2005), and VEGETATION sensors onboard Satellites for the Observation of the Earth (SPOT/VGT) (1998–2014) and Project for Onboard Autonomy satellite (PROBA-V) (2014–2020), and will continue with Sentinel-3 (from 2020 onwards). The goal of this study is to assess the uncertainties associated with the C3S PROBA-V SA v1.0 product, with a focus on the transition from SPOT/VGT to PROBA-V. The methodology followed the good practices recommended by the Land Product Validation sub-group (LPV) of the Working Group on Calibration and Validation (WGCV) of the Committee on Earth Observing Satellites (CEOS) for the validation of satellite-derived global albedo products. Several performance criteria were evaluated, including an intercomparison with National Aeronautics and Space Agency (NASA) MCD43A3 C6 products. C3S PROBA-V SA v1.0 and MCD43A3 C6 showed similar completeness but had higher fractions of missing data than C3S SPOT/VGT SA v1.0. C3S PROBA-V SA v1.0 showed similar precision (~1%) to MCD43A3 C6, improving the results of SPOT/VGT SA v1.0 (2–3%), but C3S PROBA-V SA v1.0 provided residual noise in the near-infrared (NIR). Good spatio-temporal continuity between C3S PROBA-V and SPOT/VGT SA v1.0 products was found with a mean bias between ±2%. The comparison with MCD43A3 C6 showed positive mean biases (5%, 8%, and 12% for visible, NIR and total shortwave, respectively). The accuracy assessment with ground measurements showed a median error of 18.4% with systematic overestimation (positive bias of 11.5%). The percentage of PROBA-V retrievals complying with the C3S target requirements was 28.6%.
Highlights
The land surface albedo, which is defined as the ratio of the radiant flux reflected from the Earth’s land surface to the incident flux, is a key forcing parameter controlling the planetary radiative energy budget and the partitioning of the radiative energy between the atmosphere and surface
Our analysis focuses on the consistency during the 6-month overlap period between PROBA-V Surface Albedo (SA) v1.0 and SPOT/VGT SA v1.0, whereas the intercomparison with MCD43A3 Collection 6 (C6) was conducted using one year (2014) of data
Better completeness was found for SPOT/VGT SA v1.0 with almost no missing data during the months from March to May and a percentage up to 10% in wintertime in the northern hemisphere
Summary
The land surface albedo, which is defined as the ratio of the radiant flux reflected from the Earth’s land surface to the incident flux, is a key forcing parameter controlling the planetary radiative energy budget and the partitioning of the radiative energy between the atmosphere and surface. In C3S, the PROBA-V SA v1.0 products are generated with the aim to extend the CDRs based on AVHRR and VGT observations over time The algorithms for these C3S SA products were designed by Meteo-France based on previous research conducted within the Satellite Application Facility for Land Surface Analysis (LSA SAF) program of EUMETSAT [4,5]. [6,7,8,9] based on MSG/SEVIRI and MetOp/AVHRR within the EUMETSAT LSA SAF program, and were later adapted to these other sensors in C3S and Copernicus Global Land Service (CGLS) [10] These products are generated by the processing line infrastructure implemented by VITO and openly distributed through the C3S Climate Data Store (CDS) [11]
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