DQRID : D000518.1
Start DateStart TimeEnd DateEnd Time Data Quality Metric
03/25/1996220004/03/19961630Suspect
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Subject:
SGP/TWR/C1 - 25m Problems with RH probe
DataStreams:sgp1twr25mC1.a0, sgp1440twr25mC1.a0, sgp30twr25mC1.a1
Description:
Site Operations replaced the 25m RH probe on 25 March 1996.

I have reviewed the T/RH data from the 25 meter level and find that the RH sensor was 
working, but that the 25m RH did not compare favorably with the 60m RH, or EBBR RH data.  An 
error in the sensitivity of the 25m RH can be seen for 
the whole range of RH.

A comparison of data showed that 25m RH was 19% too low for RH < 80%, 18% too low for RH 
between 80% and 85%, and 17% too low for RH > 85%.  Thus calculated vapor pressures were 
also too low.  With this information, adjustments can be made (by the user) in the data 
from March 25 through 2 April.

On April 2 and 3, 1996, I was assisted by Chris Martin in testing the 25m RH probe.  We 
lowered the 25 and 60 meter tower carriages to the surface.  The RH data from 2 April at 
1607 to 2240 GMT for both 25 and 60m levels was taken at about 2 to 3 meters above the 
surface.  Furthermore, much of the T/RH/Aspirator data is corrupted because of tests; data 
from this period is incorrect.

A multiplier of 1.04 was applied to the 25 meter RH data for the period 2 April at 2240 
GMT to 3 April at 1700 GMT; therefore, for this short period, a different adjustment by the 
data user is needed (multiply 25m RH by 1.144 for RH < 80%, by 1.135 for RH between 80% 
and 85%, and by 1.125 for RH > 85%).

On April 3, 1996 at 1700 GMT I increased the 25m RH multiplier to 1.19. Thereafter, the 
25m RH values must be decreased by 1% for RH between 80% and 85%, and decreased 2% for RH > 
85%.  The slight non-linearity of this type of RH probe at greater than 80% RH is 
exaggerated for this probe by it not being properly electronically calibrated.  Using the 
information above, the RH values above 80% can be adjusted to within 1% of the accuracy that 
would be obtained from a factory calibration.
Suggestions: 
Measurements:sgp1twr25mC1.a0:
  • rh
more
sgp30twr25mC1.a1:
  • rh
  • sd_rh
more
sgp1440twr25mC1.a0:
  • min_rh
  • max_rh
more

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