SGP/SIRS/E21 - Shadowband Misalignment

Solar tracker stopped functioning on 7/17. Tracker power cycled on 
              07/24 and returned to normal tracking but failed again 7/25.  Power
              was cycled again 8/6 and tracker performance was sustained thereafter.

• Raw data stream - documentation not supported(Raw data stream - documentation not supported)

• Instantaneous Direct Normal Shortwave Irradiance, Pyrheliometer Thermopile
  Voltage(inst_direct_normal)
• Instantaneous Uncorrected Downwelling Shortwave Diffuse, Shaded Pyranometer
  Thermopile Voltage(inst_diffuse)
• Instantaneous Downwelling Pyrgeometer Thermopile Voltage, Shaded Pyrgeometer(inst_down_long_hemisp_shaded_tp)

• Downwelling Shortwave Diffuse Hemispheric Irradiance, Ventilated Pyranometer,
  Standard Deviation(down_short_diffuse_hemisp_std)
• Downwelling Longwave Hemispheric Irradiance, Shaded Pyrgeometer, Minima(down_long_hemisp_shaded_min)
• Shortwave Direct Normal Irradiance, Pyrheliometer, Maxima(short_direct_normal_max)
• Downwelling Longwave Hemispheric Irradiance, Shaded Pyrgeometer, Maxima(down_long_hemisp_shaded_max)
• Downwelling Shortwave Diffuse Hemispheric Irradiance, Ventilated Pyranometer(down_short_diffuse_hemisp)
• Downwelling Longwave Hemispheric Net Infrared(down_long_netir)
• Downwelling Longwave Hemispheric Irradiance, Shaded Pyrgeometer, Standard
  Deviation(down_long_hemisp_shaded_std)
• Downwelling Shortwave Diffuse Hemispheric Irradiance, Ventilated Pyranometer,
  Maxima(down_short_diffuse_hemisp_max)
• Shortwave Direct Normal Irradiance, Pyrheliometer(short_direct_normal)
• Downwelling Longwave Hemispheric Irradiance, Shaded Pyrgeometer(down_long_hemisp_shaded)
• Downwelling Shortwave Diffuse Hemispheric Irradiance, Ventilated Pyranometer,
  Minima(down_short_diffuse_hemisp_min)
• Shortwave Direct Normal Irradiance, Pyrheliometer, Standard Deviation(short_direct_normal_std)
• Shortwave Direct Normal Irradiance, Pyrheliometer, Minima(short_direct_normal_min)

SGP/SIRS/E21 - Reprocess: Incorrect PIR/UIR Calibration Coefficient

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

• Raw data stream - documentation not supported(Raw data stream - documentation not supported)

• Upwelling (10 meter) Longwave Hemispheric Irradiance, Ventilated Pyrgeometer(up_long_hemisp)
• Upwelling (10 meter) Longwave Hemispheric Irradiance, Ventilated Pyrgeometer,
  Minima(up_long_hemisp_min)
• Upwelling (10 meter) Longwave Hemispheric Irradiance, Ventilated Pyrgeometer,
  Maxima(up_long_hemisp_max)
• Upwelling (10 meter) Longwave Hemispheric Irradiance, Ventilated Pyrgeometer,
  Standard Deviation(up_long_hemisp_std)
• Upwelling Longwave Hemispheric Net Infrared(up_long_netir)

SGP/SIRS/E21 - False signal

During clear-sky conditions, downwelling shortwave values spike downward approximately 50 
to 200 W/m^2 around 22:15 UTC for about 15 minutes. This problem occurs at about the same 
time for the same duration each day during the indicated period of the year.  This 
effect is due to a shadow from the Rotating Bird Deterrent (RBD) installed earlier in the year 
to prevent extensive bird droppings at the site.  The RBD is installed at such a 
location that it will partially shade the downwelling shortwave PSP from 19 October to 23 
February of the year.

• Raw data stream - documentation not supported(Raw data stream - documentation not supported)

• Instantaneous Downwelling Hemispheric Shortwave, Unshaded Pyranometer Thermopile
  Voltage(inst_global)

• Downwelling Shortwave Hemispheric Irradiance, Ventilated Pyrgeometer, Maxima(down_short_hemisp_max)
• Downwelling Shortwave Hemispheric Irradiance, Ventilated Pyrgeometer, Minima(down_short_hemisp_min)
• Downwelling Shortwave Hemispheric Irradiance, Ventilated Pyrgeometer(down_short_hemisp)
• Downwelling Shortwave Hemispheric Irradiance, Ventilated Pyrgeometer, Standard
  Deviation(down_short_hemisp_std)

SGP/SIRS/E21 - Shadowband Misalignment

The NIP reported values close to zero and downwelling shortwave global and diffuse were 
equivalent due to tracker failure.  

Maintenance replaced tracker 2/27, but couldn't replace instruments until 03/02 2000 GMT 
due to bird poop contamination.

• Raw data stream - documentation not supported(Raw data stream - documentation not supported)

• Instantaneous Uncorrected Downwelling Shortwave Diffuse, Shaded Pyranometer
  Thermopile Voltage(inst_diffuse)
• Instantaneous Direct Normal Shortwave Irradiance, Pyrheliometer Thermopile
  Voltage(inst_direct_normal)

• Downwelling Shortwave Diffuse Hemispheric Irradiance, Ventilated Pyranometer,
  Maxima(down_short_diffuse_hemisp_max)
• Shortwave Direct Normal Irradiance, Pyrheliometer(short_direct_normal)
• Downwelling Shortwave Diffuse Hemispheric Irradiance, Ventilated Pyranometer,
  Standard Deviation(down_short_diffuse_hemisp_std)
• Downwelling Shortwave Diffuse Hemispheric Irradiance, Ventilated Pyranometer,
  Minima(down_short_diffuse_hemisp_min)
• Shortwave Direct Normal Irradiance, Pyrheliometer, Standard Deviation(short_direct_normal_std)
• Shortwave Direct Normal Irradiance, Pyrheliometer, Maxima(short_direct_normal_max)
• Downwelling Shortwave Diffuse Hemispheric Irradiance, Ventilated Pyranometer(down_short_diffuse_hemisp)
• Shortwave Direct Normal Irradiance, Pyrheliometer, Minima(short_direct_normal_min)

SGP/SIRS/E21 - Dirt on dome

Measured downwelling shortwave values differed from calculated 
              (direct + diffuse) by +/-100 W/m^2 in the afternoon.  Pattern of
              differences is indicative of a dirty downwelling shortwave dome.
              Maintenance on 6/9 cleaned water spots on the dome.  Other 
              downwelling instruments may have also been dirty during this 
              period.

• Raw data stream - documentation not supported(Raw data stream - documentation not supported)

• 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, Unshaded Pyranometer Thermopile
  Voltage(inst_global)

• Downwelling Shortwave Hemispheric Irradiance, Ventilated Pyrgeometer, Maxima(down_short_hemisp_max)
• Downwelling Shortwave Diffuse Hemispheric Irradiance, Ventilated Pyranometer,
  Standard Deviation(down_short_diffuse_hemisp_std)
• Downwelling Shortwave Hemispheric Irradiance, Ventilated Pyrgeometer, Minima(down_short_hemisp_min)
• Downwelling Shortwave Hemispheric Irradiance, Ventilated Pyrgeometer(down_short_hemisp)
• Shortwave Direct Normal Irradiance, Pyrheliometer, Maxima(short_direct_normal_max)
• Downwelling Shortwave Hemispheric Irradiance, Ventilated Pyrgeometer, Standard
  Deviation(down_short_hemisp_std)
• Downwelling Shortwave Diffuse Hemispheric Irradiance, Ventilated Pyranometer(down_short_diffuse_hemisp)
• Downwelling Shortwave Diffuse Hemispheric Irradiance, Ventilated Pyranometer,
  Maxima(down_short_diffuse_hemisp_max)
• Shortwave Direct Normal Irradiance, Pyrheliometer(short_direct_normal)
• Downwelling Shortwave Diffuse Hemispheric Irradiance, Ventilated Pyranometer,
  Minima(down_short_diffuse_hemisp_min)
• Shortwave Direct Normal Irradiance, Pyrheliometer, Standard Deviation(short_direct_normal_std)
• Shortwave Direct Normal Irradiance, Pyrheliometer, Minima(short_direct_normal_min)

SGP/SIRS/E21 - Reprocess: Longwave Calibration error

Modified pyrgeometer calibration procedures were implemented beginning in December 2003.  
These modified procedures introduced a calibration bias in the longwave data.  The 
previous procedures were re-implemented at all sites between December 2005 and February 2006 to 
restore proper calibrations.                                                             
                The data collected while the incorrect procedures were in place are 
being reprocessing to remove the calibration bias.  Note, this also affected standard 
deviation, maximum and minimum data fields.

• Downwelling Longwave Hemispheric Net Infrared(down_long_netir)
• Upwelling (10 meter) Longwave Hemispheric Irradiance, Ventilated Pyrgeometer(up_long_hemisp)
• Downwelling Longwave Hemispheric Irradiance, Shaded Pyrgeometer(down_long_hemisp_shaded)
• Upwelling Longwave Hemispheric Net Infrared(up_long_netir)