## 2 Remote Sensing Surface Albedo Products
### Evaluated Dataset: C3S SA v1.0 Based on PROBA-V Data  
PROBA-V has operated since May 2013 at an altitude of 820 km in a sun-synchronous orbit with a local overpass time at launch of 10:45 a.m. However, because the satellite has no onboard propellant, this local overpass time gradually differs from the at-launch value [3]. The payload consists of three identical cameras, which are equipped with a very compact Three Mirror Anastigmat telescope. Each camera has two focal planes, one for the short-wave infrared (SWIR) and one for the visible and near-infrared (VNIR) bands, with a slightly different off-nadir along track viewing direction. PROBA-V observes four spectral bands: Blue (called B0: centered at 0.463 \(\upmu\)m), Red (B1: 0.655 \(\upmu\)m), NIR (B2: 0.845 \(\upmu\)m), and SWIR (MIR: 1.600 \(\upmu\)m). The target on the ground is imaged at different times and with different viewing angles. This specific technical concept makes the angular configurations of the observations in the VNIR and SWIR bands different, and hence, different angular information is provided. Observations are taken at resolutions from 100 to 180 m at nadir and up to 350 m and 660 m at the swath extremes for the VNIR and SWIR channels, respectively [38]. The final PROBA-V data [39], disseminated by the PROBA-V Ground Segment at 100 m, 300 m and 1 km resolutions, have been available on [40] since the end of 2013. \begin{table}
\begin{tabular}{c} **Width** \\ **(nm)** \\ \end{tabular} \\ \hline
**Blue** & B0 & 463 & 46 & B0 & 458 & 37 & Band3 & 489 & 20 \\ \hline
**Red** & B2 & 655 & 79 & B2 & 653 & 74 & Band1 & 645 & 50 \\ \hline
**NIR** & B3 & 845 & 144 & B3 & 838 & 109 & Band2 & 858.5 & 35 \\ \hline
**SWIR** & MIR & 1600 & 73 & MIR & 1635 & 101 & Band6 & 1639 & 24 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Spectral characteristics of PROBA-V, and its equivalent channels in the VGT-2 and MODIS sensors. \begin{table}
\begin{tabular}{c c} \hline \hline
**Product** & **Quality Control Used to Discard Pixels** \\ \hline \multirow{4}{*}{**C3S PROBA-V SA v1.0**} & Sea (bit 1) \\  & Input status out of range or invalid (bit 6) \\  & B2 saturated (bit 10) \\  & B0 saturated (bit 11) \\ \hline \multirow{4}{*}{**C3S SPOT/VGT SA v1.0**} & Sea and continental water (bits 0-1 of QFLAG) \\  & Algorithm Failed (bit 6 of QFLAG) \\  & ERR \textgreater{} 0.2 \\  & AGE \textgreater{} 20 \\ \hline \multirow{4}{*}{**MCD43A2 C6**} & BRDF\_Albedo\_Band\_Quality\_Band1-7: \\  & Magnitude inversion (number of observations lower than 7) \\ \cline{1-1} \cline{2-6}  & \multicolumn{1}{c}{} & & \\ \end{tabular}
\end{table} 
Table 3: Quality flag (QFLAG) information used to filter pixels flagged as ’low-quality’. The C3S PROBA-V SA v1.0 products (example in Figure 1) are freely available in the C3S CDS[11]. They also provide Directional-Hemispherical albedos (AL-DH)--also called Black-Sky Albedo (BSA)--and the Bi-Hemispherical albedos (AL-BH)--also called White-Sky Albedo (WSA)--in three broadband spectral domains (visible [VI: 0.4-0.7 \(\upmu\)m], NIR [NI: 0.7-4 \(\upmu\)m] and total shortwave [BB: 0.3-4 \(\upmu\)m]). These broadband albedos are taken from the CGLS [10]. In addition, the spectral AL-DH and AL-BH albedos in the four spectral channels (see Table 2) are made available in the C3S. These products have been produced every 10 days from the end of 2013 onwards, with the production dates on the 3 rd, 13 th, and 23 rd of each month and delivered with a 12 day lag in near real-time. The spatial resolution of the grid is 1/112\({}^{\circ}\), resulting in a pixel size of approximately 1 km at the equator. Apart from the layers corresponding to albedo retrievals, the ancillary layers corresponding to their respective errors (ERRs), the associated quality flag (QFLAG) and the number of valid observations during the synthesis period (NMOD) are provided. The information of each layer is described in the Product User Guide and Specification (PUGS) document [41].