Cloud cover fraction As additional service to interpret the SO2
vertical column densities, the web pages that show images of the
SO2 data also show an image of the cloud cover fraction for the
same region, taken from the same instrument. Note that currently
there is no cloud screening performed on the data: all SO2 slant
column retrieval results are shown as-is. The same cloud
fraction is also used to determine the air-mass factor (AMF)
when taking the AMF from look-up tables made with a radiative
transfer model in order to compute the SO2 vertical column
density. Note that the AMF and thus the vertical column cannot
be calculated of the cloud cover fraction is missing. For the
daily data at orbit (like the image shown here) and at grid
coordinates the cloud cover fraction is presented in the same
way and available in the accompanying data files. Monthly
averages if the cloud fraction are not made: there is no cloud
screening method applied to the SO2 data, so that a monthly
average cloud fraction does not pr