SGP/SIRS/E16 - Direct normal instrument failure

The short_direct_normal/NIP data spiked a few times and then completely failed resulting 
in missing values (-9999) for this time period.  

The short_direct_normal data during this time period is not recoverable. However, it can 
be reconstructed using the following shortwave instrument relationship for each minute of 
data:

short_direct_normal = (down_short_hemisp - down_short_diffuse)/cos(zenith angle).

• inst_direct_normal

• short_direct_normal_min
• short_direct_normal
• short_direct_normal_max
• short_direct_normal_std