DQRID : D040322.1
Start DateStart TimeEnd DateEnd Time
03/18/2004150006/10/20042000
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Subject:
SGP/SIRS/C1 - Discrepancy between measured and derived downwelling shortwave hemispheric
DataStreams:sgpsirsC1.b1, sgpsirs20sC1.a0
Description:
Measured values of downwelling hemispheric shortwave radiation were up to 40 W/m^2 higher 
than derived values during the afternoon hours.

Analysis reveals that this is likely an artifact of the cosine response of the particular 
installed PSP coupled with typical uncertainties of this set of installed radiometers.   
That is, this particular instrument cluster seems to be producing cumulative errors on 
the high side of accepted values.

The PSP contains the most uncertainty in measurement at this station. Users should use a 
derived value for the downwelling shortwave hemispheric irradiance (DS). Where DS = 
diffuse component + direct normal * cos(SZA) component described in the SIRS handbook Sec 7.2 
available at: http://www.arm.gov/publications/tech_reports/handbooks/sirs_handbook.pdf
Suggestions: 
Measurements:sgpsirsC1.b1:
  • Downwelling Shortwave Diffuse Hemispheric Irradiance, Ventilated Pyranometer(down_short_diffuse_hemisp)
  • Shortwave direct normal irradiance, pyrheliometer, minima(short_direct_normal_min)
  • Down-welling unshaded pyranometer voltage(down_short_hemisp)
  • Downwelling Shortwave Diffuse Hemispheric Irradiance, Pyrgeometer, Minima(down_short_diffuse_hemisp_min)
  • Downwelling Shortwave Hemispheric Irradiance, Pyranometer, Minima(down_short_hemisp_min)
  • Shortwave Direct Normal Irradiance, Pyrgeometer, Standard Deviation(short_direct_normal_std)
  • Shortwave Direct Normal Irradiance, Pyrheliometer, Maxima(short_direct_normal_max)
  • Downwelling Shortwave Diffuse Hemispheric Irradiance, Pyranometer, Standard
    Deviation(down_short_diffuse_hemisp_std)
  • Downwelling Shortwave Hemispheric Irradiance, Ventilated Pyrgeometer, Standard
    Deviation(down_short_hemisp_std)
  • Downwelling shortwave hemispheric irradiance, pyranometer, maxima(down_short_hemisp_max)
  • Downwelling shortwave diffuse hemispheric irradiance, pyranometer, maxima(down_short_diffuse_hemisp_max)
  • Shortwave direct normal irradiance, pyrheliometer(short_direct_normal)
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sgpsirs20sC1.a0:
  • Instantaneous direct normal shortwave irradiance, pyrheliometer thermopile
    voltage(inst_direct_normal)
  • Instantaneous uncorrected downwelling shortwave diffuse, shaded pyranometer
    thermopile voltage(inst_diffuse)
  • Instantaneous Downwelling Hemispheric Shortwave, Pyranometer Thermopile Voltage(inst_global)
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