CSU Quality Control (QC) procedure for Version 1 sonde products 

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1) Data is put into a common 5 mb ASCII format. Temperature and dew point
   are interpolated to 5 mb level. Winds are averaged in 5 mb layers. A
   1-2-1 filter is applied to the 5 mb wind data to remove unrealistic
   high-frequency vertical noise.  

2) Time mean and standard deviation (sigma) of each field is computed at
   each 5 mb level. These statistics are computed a second time not using
   any data that are more than 4*sigma from the mean. These stats are 
   saved to file and used in gross limit checks (see step 3). 

3) Objective QC: 
   Perform a gross limit check flagging all data as questionable that
   is more that 3*sigma from the mean and as bad if data is more than
   6*sigma from the mean. Hydrostatic (pressure decreasing with height, 
   height increasing with decreasing pressure) and vertical consistency 
   checks (excessive lapse rates or vertical shears) are performed and 
   flagged accordingly.

4) Subjective QC:
   Visually QC all sondes at a given site from the surface up to 100 mb. 
   By viewing consecutive skew-Ts in time, large temporal changes in a 
   field can be noted and flagged if suspicious looking.

5) Linearly interpolate (in log pressure) missing data in the vertical if
   the layer of missing data is 200 mb or less. Interpolated data is flagged
   accordingly.

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The idea of using QC flags is to never change a data value, but rather to 
provide data flags to quide the user. In this approach, it is up to the data 
user to decide whether or not to use a given data value. 

QC FLAGS     flag meaning 

  1  	     parameter good
  2 	     parameter questionable
  3          parameter "visually" questionable
  4          parameter bad
  5 	     parameter "visually" bad
  6 	     parameter interpolated
  7 	     parameter estimated
  8 	     parameter unchecked
  9 	     parameter missing  

Value used for missing data is -999.0

Notes:

Sonde data from the ISS sites were provided in 1 sec format. The raw soundings
are first run through the ATD APSPEN processing system which performs 
smoothing and removes suspect data points. The soundings are then visually
evaluated by ATD for outliers, or any other obvious problems. There is
no record of the changes made to the data by ATD. 

The bottom point in the sondes at the ISS sites is from surface met station. 
Surface met station at Loreto failed so bottom point is from sonde measurement
and human estimated winds. During its first cruise the R/V Altair did not
report a surface wind.  

Any problems with the data should be reported to Paul Ciesielski 
(paulc@atmos.colostate.edu).