SGP/AERI/C1 - Fault within the channel 2 (InSb) detector

On 10 Sep 2009, an "event" happened at the SGP site which impacted the AERI instrument.  
This event has been documented in DQPR 2258.  This event had a tremendous impact on the 
radiance, and in particular the noise level, in the channel 2 data (which uses the InSb 
detector).  After much effort by the site operators and mentors, it appeared that the system 
was "fixed" on 5 October 2009.  However, there were some weird irregularities in the 
dataset that were bothersome, and necessitated a more complete analysis.

We (the instrument mentor team) have concluded that the fault suffered on Sept 10 affected 
the grounding of the InSb detector.  The symptoms included a 'wandering' of the phase of 
the interferogram, which results in errors in calibration, as well as increased noise in 
the data.  We have attempted to correct the data for a few days by hand, as phase errors 
typically can be accounted for; however, in these cases we were unable to do this 
satisfactorily with significant amounts of atmospheric signal remaining in the imaginary 
spectrum and low-frequency biases remaining in the real spectrum.  [If the data are properly 
calibrated, then the real spectrum is what is used for science and has all of the 
atmospheric signal, while the imaginary spectrum should be all random noise.]

Therefore, we have concluded that all radiance data from the channel 2 detector of this 
system, including all downstream data products that make use of these data, should be 
classified as INCORRECT / BAD.  The channel 1 data (which is from a different detector) 
appears to be fine and properly calibrated.  The system will be replaced with the spare AERI.

Users should NOT use the channel 2 radiance data from this system.

• Difference between the sky view\'s radiance variance and the hot black body
  view\'s variance(standard_dev_mean_rad)
• Mean of radiance spectra ensemble(mean_rad)

• Interpolated water vapor mixing ratio(waterVaporMixingRatio)
• Interpolated dewpoint temperature(dewpointTemperature)
• CPL retrieval of ambient temperature(CPL_ambientTemp)
• Total precipitable water vapor, from Microwave Radiometer(totalPrecipitalWater)
• Temperature used for calculation(temperature)
• CPL retrieval of water vapor mixing ratio(CPL_waterVaporMixingRatio)
• CPL retrieval of dewpoint temperature(CPL_dewpointTemp)

• Total precipitable water vapor, from Microwave Radiometer(totalPrecipitalWater)
• CPL retrieval of dewpoint temperature(CPL_dewpointTemp)
• Temperature used for calculation(temperature)
• Interpolated dewpoint temperature(dewpointTemperature)
• Interpolated water vapor mixing ratio(waterVaporMixingRatio)
• CPL retrieval of ambient temperature(CPL_ambientTemp)
• CPL retrieval of water vapor mixing ratio(CPL_waterVaporMixingRatio)

• Difference between the sky view\'s radiance variance and the hot black body
  view\'s variance(standard_dev_mean_rad)
• Mean of radiance spectra ensemble(mean_rad)