8 March 2006 12:00 UTC, dust outbreak over the Sahara.

The desert surface is characterized by very low emissivity at IR8.7μm, we can see it appear darker on the image:

If we make the difference between 8.7μm and 10.8μm we are able to separate the clear-sky regions from the regions with aerosols:

In order to make a reference image with the surface contribution we estimate the surface emissivity from the clear-sky observations: