| Description: | During periods of extremely cold outside temperatures (-30 C or below), the MPL may suffer
from reduced sensitivity due to obscuration of its viewport window with frost or
condensation.
During the winter of 1998-1999, on-site observers noted frost or condensation obscuring
part or all of the viewport window. A fan providing blowing heated air on the viewport had
failed. Although replacement of this fan reduced the degree of obscuration, the problem
was not entirely eliminated. During the summer of 1999 a more robust forced-air system
was installed and the problem was essentially solved except for during isolated cases of
extremely cold weather. Under these extreme conditions partial or complete obscuration
of the window is still possible with the result that cloud detection sensitivity will be
reduced depending on the fraction of the window surface obscured. Even with significant
obscuration, the MPL may still detect clouds and the cloud base heights of detected
clouds will be reported correctly. This problem is one of detection sensitivity only and does
not affect the range scale in any way. |