| Description: | During my recent trip to the SGP I noticed that the IRT was reading
too high (about 250 K for clear sky with less than 2 cm PWV). The
anti-reflective coating on the lens appeared to have deteriorated
significantly. Because I observed no change in the measurements
after cleaning the lens, I replaced it with the original lens which
had been saved as a spare.
The measured sky temperature fell to 232 K, which appeared more reasonable.
The next morning I realized that I had forgotten to clean the lens
after replacing it. After cleaning the IR temperature fell from 219
to 213 K with about 1.2 cm PWV. This appeared to be in agreement
with Martin Platt's radiometer which measures the same passband
(10 micrometers.)
Upon returning to Ames, I compared the IRT with AERI for April 1998.
It appears that at least as far back as 1 April the IRT data are bad. |