SGP/SIRS/E15 - NIP failure

The short_direct_normal (NIP instrument) cable failed during this time period.  Data are 
not recoverable.

Users can derive an estimate of direct normal values using the following formula:
short_direct_normal = (down_short_hemisp - down_short_diffuse_hemisp)/cos(zenith angle)

• Instantaneous direct normal shortwave irradiance, pyrheliometer thermopile
  voltage(inst_direct_normal)

• Shortwave direct normal irradiance, pyrheliometer(short_direct_normal)
• Shortwave Direct Normal Irradiance, Pyrheliometer, Maxima(short_direct_normal_max)
• Shortwave direct normal irradiance, pyrheliometer, minima(short_direct_normal_min)
• Shortwave Direct Normal Irradiance, Pyrgeometer, Standard Deviation(short_direct_normal_std)