DQRID : D940804.1
Start DateStart TimeEnd DateEnd Time Data Quality Metric
07/13/1994113108/03/19941430Suspect
more
Subject:
Possible error in humidity ground check
DataStreams:sgpsondewrpnC1.a1, sgpsondewrpnC1.a0
Description:
DQR No:                               Platform:  sgpsondewrpnC1

Subject:   Possible error in humidity ground check

Date Submitted:  8/3/94
Submitted By:    Barry Lesht          _X_  Instrument Mentor
                                      ___  EST Member
                                      ___  Science Team Member
                                      ___  Other _____________________________
 
For questions or problems, please contact the ARM Experiment Center at
509-375-6898 or via email at dqr@arm.gov.

Platform/Measurement:
	What level data: (raw,a0,a1,b1,c1 etc): raw, a0, a1

    What location was the data collected at: CF
 
    Period of time in question
 	Begin Date   7/13/94   Time   11:31    (GMT)
 	End Date     8/ 3/94   Time   14:30    (GMT)

 Data should be labeled:
 _X_  questionable                      ___  All data fields affected
 ___  incorrect                         _X_  Only some data fields affected
 ___  wrong calibration
 ___  others 
 
 Discussion of Problem:

We suspect that the dessicant in the bbss ground check set (located 
only at the central facility) has become saturated and is no longer
providing a 0 %RH environment against which to check the sonde RH sensor.
This would result in a bias in the correction for humidity for 
those soundings that were done during the time the dessicant was bad.  
Examination of the data suggests that the potential errors are small, 
(on the order of a few percent RH), but sufficiently different from previous 
corrections to warrant temporary suspension of the ground check procedure.

A review of the data collected since the beginning of the year shows no
trend in humidity correction until July 13, 1994.  The last positive
humidity correction was recorded on July 12, 1994 and since then has been
noticably (though slightly) downward.

The humidity correction is applied linearly.  That is, U = U' + (Uo - Uo')
where U is the humidity with the ground check applied (this is the RH
value in our data stream), U' is the humidity measured at the sonde before
correction, Uo is the reference humidity (assumed to be 0%), and Uo' is
is the humidity measured by the sonde in the ground check set.  Users
can recover the RH measured at the sonde by subtracing the global attribute
"humidity-correction" from the RH values in the data set.  Based on our
experience with the ground check data, we expect the RH values measured
at the sonde to be accurate within +/-2% RH.  

 
Other observations/measurements impacted by this problem:  

Any measurement derived from the sonde RH measurement, for example
dew point temperature, water vapor mixing ratio).


Suggested Corrections of the Problem: (e.g. change calibration factor and
recompute, flag data with this comment, etc.)

Flag data warning user that RH may be biased high by an unknown amount,
probably not exceeding 2% RH.


Data Processing Notes                Date
Suggestions: 
Measurements:sgpsondewrpnC1.a0:
  • wspd
  • rh
  • time_offset
  • lon
  • deg
  • asc
  • base_time
  • wstat
  • pres
  • tdry
  • lat
  • dp
  • alt
more
sgpsondewrpnC1.a1:
  • v_wind
  • wstat
  • lat
  • base_time
  • alt
  • asc
  • rh
  • wspd
  • time_offset
  • dp
  • tdry
  • lon
  • deg
  • u_wind
  • pres
more

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