DQRID : D050815.1
Start DateStart TimeEnd DateEnd Time
08/11/2005164808/16/20052230
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Subject:
TWP/GNDRAD/C2 - IRT power supply failed
DataStreams:twpgndradC2.00, twpgndrad60sC2.b1
Description:
The IRT output dropped to its minimum output of 223 K (0 volts).  It was determined the 24 
V DC converter had failed.  The converter was replaced on 16 August and the instrument 
began reporting normally again.  The IRT data are unusable during the five day period when 
the DC converter was faulty.

The GNDRAD (down-looking) IRT is used primarily for surface temperature.  The PIR can be 
used for this purpose by inverting the IR flux equation, Flux = sigma*temperature^4 where 
sigma = 5.67x10-8 W/m^2K^4.  But, unlike the IRT, the PIR measurement is strongly 
effected by the air temperature in addition to the surface temperature.  At night, when the air 
temperature approaches the surface temperature, the PIR provides a good estimate of the 
surface temperature.  During the day, however, the PIR tends to underestimate the ground 
temperature,  particularly on sunny days.  The magnitude of the underestimate can be 
estimated by evaluating periods when both instruments are operating but is typically on the 
order of 5-10C.
Suggestions: 
Measurements:twpgndrad60sC2.b1:
  • IRT1 standard deviation(irt1_sd)
  • IRT1 mean(irt1_mean)
  • IRT1 maximum(irt1_max)
  • IRT1 minimum(irt1_min)
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twpgndradC2.00:
  • (Raw data stream - documentation not supported)
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