DQRID : D050215.3
Start DateStart TimeEnd DateEnd Time Data Quality Metric
12/07/1998000008/31/20092357Does not affect quality
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Subject:
NSA/MPL/C1 - Frost on Viewport Window
DataStreams:nsamplsmask1clothC1.c1, nsamplcmask1clothC1.c1
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.
Suggestions: 
Being virtually indistinguishable from low ground-level ice fog or blizzard 

conditions of blowing snow, this condition is very difficult to definitively identify exclusively 
from the MPL datastream.  It is not flagged in the lowest level "a1" datastream at all.  
In subsequent processing it is typically flagged generally as a "beam-blocked" condition 
but it is not distinguished from blocking by atmospheric phenomenon such as fog or 
blizzard conditions.  

It may be possible for the user manually identify frost-covered episodes in the presence of cold clear skies by observing brightness temperatures from the AERI or IRT.  (Cold clear skies will present very low brightness temperatures while fog and blizzard conditions will not.)  Alternatively, the user may use the co-located ceilometer as an alternate indication of cloud base.  If the ceilometer does not report a beam-blocked condition or obscuration but the MPL does, it is likely that the MPL window is significantly obscured.

Being virtually indistinguishable from low ground-level ice fog or blizzard 
cond
itions of blowing snow, this condition is very difficult to definitively identify exclusively 
from the MPL datastream.  It is not flagged in the lowest level "a1" datastream at all.  
In subsequent processing it is typically flagged generally as a "beam-blocked" condition 
but it is not distinguished from blocking by atmospheric phenomenon such as fog or 
blizzard conditions.  

It may be possible for the user manually identify frost-covered episodes in the presence of cold clear skies by observing brightness temperatures from the AERI or IRT.  (Cold clear skies will present very low brightness temperatures while fog and blizzard conditions will not.)  Alternatively, the user may use the co-located ceilometer as an alternate indication of cloud base.  If the ceilometer does not report a beam-blocked condition or obscuration but the MPL does, it is likely that the MPL window is significantly obscured.
Measurements:nsamplcmask1clothC1.c1:
  • CloudMaskMplCloth
  • Heights
more
nsamplsmask1clothC1.c1:
  • Heights
  • SigniMaskMplCloth
more

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