DQRID : D120419.4
Start DateStart TimeEnd DateEnd Time Data Quality Metric
07/23/2003133008/08/20031650Suspect
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Subject:
SGP/QCRAD/E21 - Reprocess: Incorrect PIR/UIR Calibration Coefficient
DataStreams:sgpqcrad1longE21.s2, sgpqcrad1longE21.s1, sgpqcrad1longE21.c1, sgpqcrad1longE21.c2
Description:
Problem documented in instrument DQR D031009.2:

Incorrect coefficients were applied to the upwelling longwave radiation
measurement instrument (i.e. pyrgeometer, SIRS acroynm "UIR") during
this time period.

For a PIR mounted in an upwelling measurement orientation (UIR), the
thermopile output is extremely low compared to a downwelling PIR (DIR).
In addition, the UIR case and dome temperature differences are much
smaller than a DIR.  This results in the pyrgeometer receiver radiation 
term, Wr (NREL/Hickey equation) or Wc (Albrecht/Cox equation), dominating
all other terms of the infrared radiant flux equation.

Since the receiver radiation term uses coefficients in both forms of
the pyrgeometer equations nearly equal to 1.0 +- <1% the result is a
measurement of incoming longwave radiant flux relatively insensitive 
to the installed instrument - so long as it is an Eppley PIR.
		
Evaluation of the problem data shows the expected error of the data
(before correction) will be within 1% - less than the uncertainty of 
the instrument (Eppley PIR greater of 5% or 5 W/m2)
		
To correct the one minute data found in the a1 or b1 datastream follow
this procedure:
1) Obtain the following variables from the b1 datafile:
	 inst_up_long_dome_temp
	 inst_up_long_case_temp
	 up_long_netir

2) For each one minute data entry in b1
     tpUIR[uV] = up_long_netir[uV]/0.2523876[W/m2/uV]

3) Apply for each one minute data entry:

WinUIR(W/m2)=k*V+ Sigma*Tc^4 -4*Sigma*(Td^4 - Tc^4)
	    =[0.28902*tpUIR]+[Sigma*inst_up_long_case_temp^4]
	      -[4*Sigma*(inst_up_long_dome_temp^4-inst_up_long_case^4)]

where, Sigma =	5.6697E-8 (Stefan-Boltzman Const)
		
Other datastream corrections that use the UIR measurements will require
similar corrections.


See the following web site for additional information on the pyrgeometer
equations, specifically sections 2.1(Single Calibration Factor Approach)
and 2.2 (Four Coefficient Calibration Approach)

      http://www.arm.gov/docs/instruments/static/pyrg.html
Suggestions: 
Correct data as described
Measurements:sgpqcrad1longE21.s2:
  • up_long_hemisp
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sgpqcrad1longE21.c2:
  • up_long_hemisp
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sgpqcrad1longE21.c1:
  • up_long_hemisp
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sgpqcrad1longE21.s1:
  • up_long_hemisp
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