Pixel Flagging
This process consists of pixel flagging, indicating land, water, cloud cover, ice/snow and cloud shadows (individual flags are listed in the table below). The quality flags and the land-water mask result from flags present in the SYNERGY collocated data.
| FLAG MASK | FLAG VALUE | FLAG MEANING | DESCRIPTION |
| 3 | 0 | clear | Indicates cloud-free pixels. |
| 3 | 1 | shadow | Indicates pixels shadowed by clouds. |
| 3 | 2 | uncertain | Indicates uncertain cloud detection. |
| 3 | 3 | cloud | Indicates cloudy pixels. |
| 4 | 4 | ice_or_snow | Indicates ice or snow. |
| 8 | 8 | land | Indicates land. |
| 16 | 16 | MIR_good | Quality of MIR measurement is good. |
| 32 | 32 | B3_good | Quality of B3 measurement is good. |
| 64 | 64 | B2_good | Quality of B2 measurement is good. |
| 128 | 128 | B0_good | Quality of B0 measurement is good. |
The algorithm's detection of clouds, ice/snow is based on SYNERGY Level 2 cloud flags (computed through IDEPIX approach). Each 300m SYNERGY pixel contributing to a VGT Plate carrée pixel is associated with a coefficient. This coefficient is itself depending on the distance between the center of Plate carrée pixel and the 300m SYNERGY pixel.
All coefficients associated with contributing cloudy pixels are summed. If the result is higher than a certain threshold, the Plate carrée pixel will be then flagged as cloudy. Thresholds have been defined to be consistent with the ones used in PROBA-V processing.
Same approach is performed for snow flag.
Detection of cloud shadows should be added to the SYNERGY processing during the second half of 2020.