SGP/SIRS/E18 - Dirt on dome

It appears that the PSP dome was dirty.  There was a noticeable dip in down_short_hemisp 
values from 13:53 to 14:31 UTC every day after 09/26. 

This facility was decommissioned and maintenance efforts ceased 10/1/2009.  The instrument 
was removed from service 11/17/2009.

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

• Down-welling unshaded pyranometer voltage(down_short_hemisp)
• Downwelling Shortwave Hemispheric Irradiance, Ventilated Pyrgeometer, Standard
  Deviation(down_short_hemisp_std)
• Downwelling shortwave hemispheric irradiance, pyranometer, maxima(down_short_hemisp_max)
• Downwelling Shortwave Hemispheric Irradiance, Pyranometer, Minima(down_short_hemisp_min)