DQRID : D000711.64
Start DateStart TimeEnd DateEnd Time Data Quality Metric
10/11/1996000011/30/19972359Suspect
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Subject:
TWP/GNDRAD/C1 - Net Radiometer: Correction for negative net fluxes
DataStreams:twpgndrad60sC1.b1, twpgndrad60sC1.a1
Description:
The Net radiometer seems to have a calibration problem and a poor
cosine response.  The Net radiometer consistently measures low
relative to Net surface irradiance calculated from the SKYRAD and
GNDRAD Eppleys around local noon.  The relative discrepancy changes
rapidly with sun angle and the two streams typically cross in
mid-morning and mid-afternoon beyond which the Net radiometer reads
high relative to the Eppleys.

The net radiometer typically reports postive values for the net flux
during the day and negative values at night.  There are actually
different calibration coefficients that must be applied for positive
and negative fluxes.  Currently, all data are processed by applying the
positive flux coefficient.  Consequently, the negative values are in
error.  The net flux, F, is obtained by simply applying the formula F =
C*V where V is the measured voltage and C is the calibration factor.
Therefore, negative fluxes can be corrected by multiplying the
fluxes by the ratio of the negative calibration factor, C_neg to the
postive factor C_pos, so the corrected flux for negative values is
equal to F_neg = F*C_neg/C_pos where F is the flux value reported in
the data files.  Through 970227, the values for these calibration
factors are F_pos = 9.26 and F_neg = 11.43.  After 970227, the
calibration factors are F_pos = 9.33 and F_neg = 11.6.
Suggestions: 
Measurements:twpgndrad60sC1.b1:
  • net_min
  • net_sd
  • net_max
  • net_mean
more
twpgndrad60sC1.a1:
  • net_max
  • net_min
  • net_mean
  • net_sd
more

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