AATSR Visible Channel Update Information
Studies of the long term stability of the AATSR visible channel
calibration have shown that the drift does not follow a linear trend.
A further correction is therefore needed to compensate for the deviation
from the expected trend. Inspection of the data suggests that the
calibration drift may be due to the gradual build up of a thin
contaminant film on the optical surfaces of the visible calibration
system, rather than by the gradual degradation of the exposed optics.
A simple thin film model has been applied to the data that appears to
confirm this hypothesis. A new drift correction based on this model is
proposed, along with a guide to applying the new correction, in the
AATSR Technical Note: Visible Channel Update, D. Smith, January 2006.