NSA/MFRSR/C1 - Channel 673 failure

A problem developed in channel 673.  The issue was typically seen between about 1800 UTC 
to about 0300 UTC the following day.  Though the channel appears to be fine at other times 
of the day, the mentor suggest avoiding it altogether.

The instrument has been pulled for winter maintenance and will be repaired before 
re-installation.

Use the co-located NIMFR data

• log(irradiance) for the Direct Narrowband Filter4(barnard_lnI_filter4)
• log(irradiance) for the Direct Narrowband Filter4, Michalsky(michalsky_lnI_filter4)

• Angstrom exponent(barnard_angstrom_exponent)
• optical depth for the Direct Narrowband Filter4(michalsky_optical_depth_filter4)
• Angstrom exponent(michalsky_angstrom_exponent)
• optical depth for the Direct Narrowband Filter4(barnard_optical_depth_filter4)

• Alltime Narrowband Hemispheric Irradiance, Filter 4(alltime_hemisp_narrowband_filter4)
• Diffuse Narrowband Hemispheric Irradiance, Filter 4(diffuse_hemisp_narrowband_filter4)
• Ratio of direct_normal_filter4 to diffuse_hemisp_filter4(direct_diffuse_ratio_filter4)
• Direct normal narrowband irradiance, filter 4, offset corrected(direct_normal_narrowband_filter4)
• Narrowband hemispheric irradiance, filter 4, offset and cosine corrected(hemisp_narrowband_filter4)
• Narrowband Direct Horizontal Irradiance, Filter 4, cosine corrected(direct_horizontal_narrowband_filter4)

• Diffuse Narrowband Hemispheric Irradiance, Filter 4(diffuse_hemisp_narrowband_filter4)
• Diffuse narrowband hemispheric irradiance, filter 4(diffuse_hemisp_narrowband_filter4_raw)
• Alltime Narrowband Hemispheric Irradiance, Filter 4(alltime_hemisp_narrowband_filter4)