GRW/SKYRAD/M1 - Possible dirty dome

The difference between downwelling shortwave hemispheric irradiance and derived 
downwelling shortwave hemispheric irradiance was larger than normal (>50W/m2) and was most 
noticeable at lower zenith angles.  The problem spontaneously resolved itself on 7/16 without any 
specific callouts by the GRW cleaning personnel on their reports.  Short_direct_normal 
datastream is suspected to be low due to potentially dirty NIP instrument window during 
this time period.  The commencement of this problem corresponds with a rain event early 
7/12. The possibility of other radiometers affected by dirty domes is also possible. 
Longwave instruments are typically immune to this level of contamination.

• inst_global
• inst_diffuse
• inst_direct_normal

• Downwelling Shortwave Hemispheric Irradiance, Ventilated Pyranometer, Minima(down_short_hemisp_min)
• Downwelling Shortwave Hemispheric Irradiance, Ventilated Pyranometer, Maxima(down_short_hemisp_max)
• Downwelling Shortwave Diffuse Hemisp. Irrad., Ventilated Pyranometer, Maxima(down_short_diffuse_hemisp_max)
• down_short_hemisp_std
• down_short_diffuse_hemisp_std
• short_direct_normal_std
• Downwelling Shortwave Diffuse Hemisp. Irrad., Ventilated Pyranometer, Minima(down_short_diffuse_hemisp_min)
• Radiation, shortwave, downwelling diffuse hemispheric irradiance, 1-min avg(down_short_diffuse_hemisp)
• Radiation, shortwave, direct normal irradiance, 1-min avg(short_direct_normal)
• Shortwave Direct Normal Irradiance, Pyrheliometer, Minima(short_direct_normal_min)
• Shortwave Direct Normal Irradiance, Pyrheliometer, Maxima(short_direct_normal_max)
• Radiation, shortwave, downwelling total hemispheric irradiance, 1-min avg(down_short_hemisp)

GRW/SKYRAD/M1 - Daily brief instrument shading

Due to the persistent cloudy conditions at this site this shading of the NIP and PSP is 
rarely evident in the data. But from approximately 1745 to 1810 GMT from 8/26 to 10/23 and 
from 3/01 to 4/18 during the AMF deployment years 2009 and 2010, the NIP and PSP are 
shaded by the 10m met tower to the SE of the Skystand. 

Data review indicates that the NIP (short_direct_normal) and PSP (down_short_hemisp) are 
shaded by a single tower pole and possibly other tower mounted objects.  The data are not 
correctable but the azimuth and zenith windows to avoid are:
short_direct_normal (NIP instrument)
	     Zenith angle > 62 deg
  254 deg < Azimuth angle < 262 deg
primary obstruction at 255 deg Az

down_short_diffuse(PSP instrument)
	     Zenith angle > 59 deg
  246 deg < Azimuth angle < 257 deg
primary obstruction at 251.5 deg Az


Date ranges this problem will exist for are:
20090301-20090418 (pre-official deployment, data exist)
20090826-20091023
20100301-20100418
20100826-20101023

The QCrad VAP should flag bad data points via its QC logic.  Users should either exclude 
the data within the windows above or review data for outliers in these zenith, azimuth 
angles.

• inst_direct_normal
• inst_global

• Downwelling Shortwave Hemispheric Irradiance, Ventilated Pyranometer, Minima(down_short_hemisp_min)
• Downwelling Shortwave Hemispheric Irradiance, Ventilated Pyranometer, Maxima(down_short_hemisp_max)
• Radiation, shortwave, direct normal irradiance, 1-min avg(short_direct_normal)
• Shortwave Direct Normal Irradiance, Pyrheliometer, Minima(short_direct_normal_min)
• Shortwave Direct Normal Irradiance, Pyrheliometer, Maxima(short_direct_normal_max)
• down_short_hemisp_std
• short_direct_normal_std
• Radiation, shortwave, downwelling total hemispheric irradiance, 1-min avg(down_short_hemisp)

GRW/SKYRAD/M1 - AOS tower Obstruction

Due to the persistent cloudy conditions at this site the shading is rarely evident in the 
data. But at approximately 1010GMT everyday during from approximately 12/2/2009 to 
1/11/2010 the NIP is shaded by the AOS tower.  Data review indicates that only the NIP 
(short_direct_normal) is obstructed when the sun is at 130 to 132 deg azimuth during the time 
period specified.

NIP data are not recoverable.  However, short_direct_normal can be reconstructed by 
applying the following formula:

Short_direct_normal = (down_short_hemisp-down_short_diffuse_hemisp)/cos(Zenith angle)

• inst_direct_normal

• Radiation, shortwave, direct normal irradiance, 1-min avg(short_direct_normal)
• Shortwave Direct Normal Irradiance, Pyrheliometer, Minima(short_direct_normal_min)
• Shortwave Direct Normal Irradiance, Pyrheliometer, Maxima(short_direct_normal_max)
• short_direct_normal_std

GRW/SKYRAD/M1 - Short direct normal questionable

Starting on 05/08/2010 values of short_direct_normal from the NIP instrument were reading 
low (up to 50W/m2).  This was most apparent during sunny/partly sunny periods.  The 
values spontaneously returned to normal on 5/14 with no Ops intervention.  Data system checks 
after that date revealed no apparent problems with instruments or datalogger. The problem 
has not recurred.

Only the short_direct_normal values during this time period are suspect.  If direct normal 
values are needed they can be re-constructed using the following relationship for each 
minute of data:
down_short_hemisp = short_direct_normal * cos(zenith angle) + down_short_diffuse_hemisp

• inst_direct_normal

• Radiation, shortwave, direct normal irradiance, 1-min avg(short_direct_normal)
• Shortwave Direct Normal Irradiance, Pyrheliometer, Minima(short_direct_normal_min)
• Shortwave Direct Normal Irradiance, Pyrheliometer, Maxima(short_direct_normal_max)
• short_direct_normal_std