SGP/SIRS/E15 - Tracker misaligned

During this time the tracker was misaligned due to an internal mechanical failure. Tracker 
was repaired and returned to service on 12/13/2012 at 18:00 UTC. Affected data are 
short_direct_normal and down_short_diffuse_hemisp. 

Generally, data are not recoverable. However, there are periods when the tracker was 
shading properly each day. The sgpqcrad1long vap datastream adequately finds periods of good 
data and the user is directed to using that datastream for quality checked diffuse and 
direct data.

Use sgpqcrad1longE15.c1 data

• Instantaneous direct normal shortwave irradiance, pyrheliometer thermopile
  voltage(inst_direct_normal)
• Instantaneous uncorrected downwelling shortwave diffuse, shaded pyranometer
  thermopile voltage(inst_diffuse)

• Shortwave direct normal irradiance, pyrheliometer(short_direct_normal)
• Downwelling Shortwave Diffuse Hemispheric Irradiance, Ventilated Pyranometer(down_short_diffuse_hemisp)
• Downwelling Shortwave Diffuse Hemispheric Irradiance, Pyranometer, Standard
  Deviation(down_short_diffuse_hemisp_std)
• Shortwave Direct Normal Irradiance, Pyrheliometer, Maxima(short_direct_normal_max)
• Downwelling shortwave diffuse hemispheric irradiance, pyranometer, maxima(down_short_diffuse_hemisp_max)
• Shortwave direct normal irradiance, pyrheliometer, minima(short_direct_normal_min)
• Shortwave Direct Normal Irradiance, Pyrgeometer, Standard Deviation(short_direct_normal_std)
• Downwelling Shortwave Diffuse Hemispheric Irradiance, Pyrgeometer, Minima(down_short_diffuse_hemisp_min)