SGP/SIRS/E8 - Ventilator Fan Failure

At the start time specified the PSP (down_short_hemisp) ventilator fan failed. PM replaced 
the fan 7/8/2008 1750.  Ventilator failure does adversely affect radiometer measurements 
but the extent has not been quantified.  Mentor suggests using component sum method 
detailed in SIRS instrument handbook where down_short_hemisp = down_short_diffuse + 
short_direct_normal * cos (zenith angle) for each time record.

Use down_short_hemisp with descretion or apply component sum method.

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

• (Raw data stream - documentation not supported)

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