SGP/SIRS/C1 - NIP sensor failure

The short_direct_normal data are missing due to an instrument failure (NIP pyhrheliometer) 
likely due to a nearby lightning strike near the time of initial failure.

The short_direct_normal data are not recoverable during this time period.  However, direct 
normal data can be reconstructed from the down_short_diffuse_hemisp and 
down_short_hemisp using the following relationship for each data point:
short_direct_normal = (down_short_hemisp - down_short_diffuse_hemisp)/cos(zenith angle)

• 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)
• Shortwave direct normal irradiance, pyrheliometer(short_direct_normal)

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