Minimize 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 SYN collocated data after pixel classification.

 

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.
VGT status flags

The algorithm's detection of clouds, ice/snow and cloud shadows is essentially the same as for SPOT VGT. The detection of clouds, ice or snow are based on several threshold tests. Detection of cloud shadows uses geometry to find potential shadow pixels, detects changes in radiometry for calculating cloud height, and uses geometry again for calculating the shadow mask from the cloud mask.

Note:  in the frame of coming evolutions, the cloud detection will be improved following the recommendations raised during investigation phase.