Start Date | Start Time | End Date | End Time | Data Quality Metric |
---|---|---|---|---|
07/23/2003 | 1330 | 08/08/2003 | 1650 | Suspect |
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: more
sgpqcrad1longE21.c2: more sgpqcrad1longE21.c1: more sgpqcrad1longE21.s1: more |