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 |