2.2.1. MODIS BRDF/Albedo Products

Based on the three-parameter RossThick–LiSparse–Reciprocal (RTLSR) model, the MODIS bi-directional reflectance distribution function and albedo (BRDF/albedo) products (MCD43A) provide a collection of 500-m, daily resolution data [14]. Clear-sky and atmospherically-corrected surface reflectances from Terra satellite and Aqua satellite, within a 16-day window, were used to retrieve the BRDF parameters. MCD43A1 provides the 3 BRDF parameters (isotropic, volumetric and geometric) for each of the MODIS bands 1–7, and the visible, near infrared and shortwave bands. The related quality assurance (QA) data are stored in MCD43A2. Based on the retrieved weighting parameters (isotropic, volumetric, and geometric), MCD43A3 derives both DHR (black sky albedo) and BHR (white sky albedo) 500-m data for the corresponding bands. In this study, the 500-m shortwave DHR and BHR from 2012 to 2016, covering the 19 tower sites (except for the SPO), were directly extracted from the MCD43A3 products. For the sites (e.g., the US-BRW and AU-CPR) where there were missing values in the MCD43A3, the DHR and BHR were calculated from the MCD43A1 BRDF parameters. A cross-check was performed to ensure consistency between the two.

#### 2.2.2. Copernicus Global Land Service

The European Union CGLS operates a "a multi-purpose service component" that produces a series of qualified bio-geophysical products on the status and evolution of the land surface at global scale (https://land.copernicus.eu/global/). The land surface parameters produced from the CGLS include the leaf area index (LAI), the fraction of absorbed photosynthetically active radiation (FAPAR) absorbed by the vegetation, the surface albedo, the land surface temperature, the soil moisture, etc. The CGLS albedo products are solely derived from the VEGETATION instrument up until 2014, and since then from the PROBA-V sensors. They are updated every 10 days using a 30-day window. The DHR and BHR are projected onto a regular latitude/longitude grid with a resolution of 1/112◦ (approx. 1 km at the equator) covering the area from 180◦E to 180◦W and from 75◦N to 60◦S. In this study, 1-km CGLS shortwave DHR and BHR products from 2012 to 2016 covering the 19 tower sites were used (no CGLS data over the SPO).
