SGP/SIRS/E16 - Questionable downwelling SW hemisp

There was an abnormal difference between downwelling shortwave hemispheric data and 
derived downwelling shortwave hemispheric data 7/16 - 7/24 between ~16:00-20:00 GMT. 

Data review indicates that the derived downwelling shortwave hemispheric 
(down_short_hemisp) data and possibly the shortwave direct normal (short_direct_normal) data were slightly 
lower (up to 50W/m2) than usual at these times. Either the downwelling shortwave 
instrument dome or the short direct normal instrument window may have been dirty during this 
time.  The downwelling shortwave instrument (PSP) is most likely to blame.  After recorded 
precipitation on 7/24 and 7/25 the problem resolved.  Ops visit on 7/26 recorded no 
observable contamination.  The instrument mentors guesses that the precipitation event 
effectively cleaned the instruments.

No recurrence has been observed since 7/24.

Suspect data are not recoverable or correctable

• Instantaneous direct normal shortwave irradiance, pyrheliometer thermopile
  voltage(inst_direct_normal)
• Instantaneous Downwelling Hemispheric Shortwave, Pyranometer Thermopile Voltage(inst_global)

• Shortwave direct normal irradiance, pyrheliometer, minima(short_direct_normal_min)
• Down-welling unshaded pyranometer voltage(down_short_hemisp)
• Downwelling Shortwave Hemispheric Irradiance, Pyranometer, Minima(down_short_hemisp_min)
• Downwelling Shortwave Hemispheric Irradiance, Ventilated Pyrgeometer, Standard
  Deviation(down_short_hemisp_std)
• Downwelling shortwave hemispheric irradiance, pyranometer, maxima(down_short_hemisp_max)
• Shortwave direct normal irradiance, pyrheliometer(short_direct_normal)
• Shortwave Direct Normal Irradiance, Pyrheliometer, Maxima(short_direct_normal_max)
• Shortwave Direct Normal Irradiance, Pyrgeometer, Standard Deviation(short_direct_normal_std)