SGP/SIRS/E21 - Roosting birds in field of view

The RBDD (Rotating Bird Deterrent Device) installed at E21 to prevent turkey vultures from 
roosting on the instrument boom failed resulting in noisy NIP (Short Direct Normal) and 
PSP (Short Global Hemispheric) data and a spike occurring around 2230 UTC everyday due to 
obstruction of the field of view.

Problem is intermittant due to moving birds.  Use data with discretion.  Follow ARM 
(DQMS3) flag recommendations for QC flags 02 or 03 found in section 5.1.4 of the SIRS handbook:
http://www.arm.gov/publications/tech_reports/handbooks/sirs_handbook.pdf

Use data with discretion

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

• (Raw data stream - documentation not supported)

• Down-welling unshaded pyranometer voltage(down_short_hemisp)
• Shortwave direct normal irradiance, pyrheliometer(short_direct_normal)
• 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)
• Shortwave Direct Normal Irradiance, Pyrgeometer, Standard Deviation(short_direct_normal_std)
• Shortwave Direct Normal Irradiance, Pyrheliometer, Maxima(short_direct_normal_max)
• Shortwave direct normal irradiance, pyrheliometer, minima(short_direct_normal_min)