NSA/SKYRAD/C1 - Direct and Diffuse incorrect

The short_direct_normal (NIP) instrument and cable were damaged by tracker rewind 
malfunction. Tracker and NIP replaced on 4/22 2200GMT but tracker not operational until 4/23 
1815GMT.  Thus, down_short_diffuse_hemisp (8-48) was not shaded 4/22 to 4/23.

Do not use 8-48 data from 4/22 to 4/23. NIP data is not recoverable during entire time but 
can be estimated using component sum for each 1 minute data: Direct = (global - 
diffuse)/cos(zenith angle)

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

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