Cloud Coverage Metadata

Hello, Everyone!

In the S2L2A metadata we can find for example:


<Image_Content_QI>
      <CLOUDY_PIXEL_PERCENTAGE>16.875117</CLOUDY_PIXEL_PERCENTAGE>
      <CLOUDY_PIXEL_OVER_LAND_PERCENTAGE>16.897722</CLOUDY_PIXEL_OVER_LAND_PERCENTAGE>
      <DEGRADED_MSI_DATA_PERCENTAGE>0.010200</DEGRADED_MSI_DATA_PERCENTAGE>
      <NODATA_PIXEL_PERCENTAGE>26.354271</NODATA_PIXEL_PERCENTAGE>

Initially, I thought that the cloudy_pixel_percentage is the clouds covering the portion of the scene that constitutes part of the scene with clouds as compared to the area of the actually captured by the sensor image part, excluding any no-data regions.

Now that the cloudy_pixel_over_land_percentageis greater than the cloudy_pixel_percentage I am not any more sure about that…

Could anyone help me understand the difference between those attributes.

Thank you for your time helping me to properly understand these quality indicators!

Hello @ssh,

This question might be better suited for the STEP Forum since you are asking about the Sentinel-2 L2A Product Quality Indicators. Sentinel Hub is a platform that provides this data but the data itself comes from ESA.

But from my understanding, the CLOUDY_PIXEL_PERCENTATGE is the the percentage of cloud cover over the entire tile, where as the CLOUDY_PIXEL_OVER_LAND_PERCENTAGE is the percentage of cloud cover over just the land pixels. So in case there are water bodies within the tile you are interested in, and there are more clouds over these water bodies as as compared to land, then the CLOUDY_PIXEL_OVER_LAND_PERCENTAGE would be lower than CLOUDY_PIXEL_PERCENTATGE.

But please refer to the documentation and the STEP Forum for more accurate explanations.

Kind regards,
Megha

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Hi, @megha.devaraju ,

I did some more investigation and according to the documentation on Sentinel-2 Product Specification:

CLOUDY_PIXEL_PERCENTAGE
is Local cloud coverage indicator: A percentage of cloud coverage is computed for each Level-0 Granule (for the area covered by a reference band).

CLOUD_PIXEL_OVER_LAND_PERCENTAGE
is the Percentage of land cloud coverage provided for each Tile.
ed for each Tile.

I did test few scenes and I found out that CLOUDY_PIXEL_PERCENTAGE is derived from SCL classes for medium and high probability clouds and cirrus clouds for DATA pixels - the one acquired by the sensor).

For the CLOUD_PIXEL_OVER_LAND_PERCENTAGE I am still puzzled how it is assessed.