DQRID : D940820.1
Start DateStart TimeEnd DateEnd Time Data Quality Metric
01/01/1994000008/16/19942359Does not affect quality
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Subject:
SGP/MWR/C1 - IRT rain lid removal
DataStreams:sgpmwrlosC1.b1, sgpmwrlosC1.a1
Description:
The IR thermometer (or IRT) was deployed at the SGP central facility in
January 1994 with an automatic mechanism which closed a protective lid
over the zenith-viewing lens when a moisture detector indicated
condensation or precipitation.

Since that time the 120 VAC-to-12 VAC transformer in the lid mechanism
has failed 5 times with an average downtime of two weeks.  In addition,
the collar by which the (normally open) lid is attached to the lens
barrel of the IRT has made it difficult for site operations personnel
to observe the condition of the IRT lens.  As a result, dirt and
insects have been able to accumulate on the lens.  This has resulted in
long periods of invalid data.

To alleviate these problems the lid mechanism was removed from service
on 16 August at my recommendation.

It is anticipated that condensation and precipitation will result in
invalid data.  However, these events should be readily detectable
because the observed IR temperature will closely match the ambient
temperature (e.g. the temperature of the moisture on the lens) which is
usually much greater than the sky or cloud base temperature normally
measured.  I believe that this will not result in a large increase in
invalid data because these data would have been invalid anyway when the
lid was closed.  (This situation is now the same as for the other 
radiometers at the site.)

In addition, removing the attaching collar from the lens barrel will
prevent insects from nesting in it, and will permit site operations
personnel easy access to the lens so that they may more easily maintain
it in a clean condition.

A summary of the quality of the IR thermometer data in general,
including notes on the performance of the protective lid, follows:

JANUARY 1994
 19-JAN:  Operational.  No IR data collected.

FEBRUARY 1994
  2-FEB:  Failure of lid reported.  Transformer burned out.
 15-FEB:  IRT returned to service.    
 24-FEB:  Valid data begin.

MARCH 1994
  3-MAR:  Failure of lid reported. Transformer burned out.
  8-MAR:  IRT returned to service.
  8-MAR:  Cable problems reported.
 17-MAR:  Cable problems resolved.  IRT returned to service.
 17-27-MAR:  Comparison with AERI indicates IRT 1-10 deg C higher; 
          increasing error with decreasing temperatures.  Probably  
          due to dirt/debris on lens.  Also, IRT calibration not valid
          below -50 deg C (223 K).
 21-MAR:  Problems with O-ring on lid sticking reported/repaired.

APRIL 1994
 Data values below -50 deg C (223 K) not valid - below range of 
 calibration.  Otherwise data within 2-3 degrees of AERI.
 24-APR: Large (10-20 Deg C) offset between IRT and AERI develops.

MAY 1994
  7-MAY: Mentor visits site, observes spider's nest and dead insects
         inside collar attaching lid to lens barrel in optical path of
         instrument. Probably the source of the offset between IRT and
         AERI during late and April.
  9-MAY: Insects removed, lens cleaned by site operations personnel.
         Agreement between IRT and AERI within 1 deg C.
 23-MAY: Failure of lid reported.  Transformer burned out.

JUNE 1994
 22-JUN: Rebuilt/redesigned lid mechanism put in service; data collection
         computer fails same day.

JULY 1994
 11-JUL: Computer returned to service.  
         Agreement between IRT and AERI within 1 deg C.
 22-JUL: Failure of lid reported.  Transformer burned out.

AUGUST 1994
  3-AUG: IRT returned to service.
 12-AUG: Failure of lid reported.  Transformer burned out.
 16-AUG: Lid mechanism abandoned.
Suggestions: 
Measurements:sgpmwrlosC1.a1:
  • sky_ir_temp
more
sgpmwrlosC1.b1:
  • sky_ir_temp
more

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