Clouds with Copernicus Sentinel-3 SLSTR over Amazonia

RGB picture from Copernicus Sentinel-3 SLSTR-A over Amazonia on 30.11.2020. SWIR (1.6 um) in Red, and Visible (675 & 550 nm) in Blue & Green. Credit Picture from the SNAP tool box ESA/Brockmann Consult.

There is not only one type of clouds, but many of them, with diverse properties leading to various ways to visualize them when looking at our satellite measurements. Here an example with the Copernicus Sentinel-3 (S3) A Sea & Land Surface Temperature Radiometer (SLSTR) over Amazonia.

The Red-Green-Blue (RGB) picture below, of 30.11.2020 over Amazonia, combines the ShortWave InfraRed (SWIR) 1.6 um and the visible (674 & 550 nm). Water clouds with small droplets largely reflect at all channels & appear white. Snow & ice clouds strongly absorbs SWIR & appear cyan.

What about their altitude?

SLSTR has a special channel at 1.3 um in which water vapor (H2O) so much absorbs that no signal at the top of the atmosphere may be measured. Unless clouds at a very high altitude are present, shielding then a large fraction of the H2O column in the atmosphere. Consequently, a bright signal spikes up and elevated clouds shine!

Radiance at 1.3 um from Copenicus Sentinel-3 SLSTR-A over Amazonia on 30.11.2020. Credit Picture from the SNAP tool box ESA/Brockmann Consult.

From the picture above, snow & ice clouds are primary the highest one! Anything else lower, such as surface and fractional low clouds, seems “invisible”. They cannot be “seen”.

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