[CF-metadata] Quality flag values for missing data

andrew walsh awalsh at metoc.gov.au
Fri Aug 24 01:27:29 MDT 2012


Randy,

The oceanographic community uses a set of integer QC flags (0 to 9)
See document http://www.nodc.noaa.gov/GTSPP/document/qcmans/MG22rev1.pdf
and section 2 'Quality Flagging'.

One of the flags is for a 'missing value' = 9. Would that suit your fill value 
case?

A netCDF sample in CDL is:

 double TEMP(TIME, DEPTH, LATITUDE, LONGITUDE) ;
  TEMP:standard_name = "sea_water_temperature" ;
  TEMP:units = "Celsius" ;
  TEMP:_FillValue = -99.99 ;
  TEMP:valid_min = -2. ;
  TEMP:valid_max = 40. ;
  TEMP:quality_control_set = 1. ;
  TEMP:ancillary_variables = "TEMP_quality_control" ;
 byte TEMP_quality_control(TIME, DEPTH, LATITUDE, LONGITUDE) ;
  TEMP_quality_control:long_name = "quality control flag for temperature" ;
  TEMP_quality_control:standard_name = "sea_water_temperature status_flag" ;
  TEMP_quality_control:quality_control_convention = "IMOS standard using IODE 
flags" ;
  TEMP_quality_control:_FillValue = -9b ;
  TEMP_quality_control:valid_min = 0 ;
  TEMP_quality_control:valid_max = 9 ;
  TEMP_quality_control:flag_values = 0b, 1b, 2b, 3b, 4b, 5b, 6b, 7b, 8b, 9b ;
  TEMP_quality_control:flag_meanings = "no_qc_performed good_data 
probably_good_data bad_data_that_are_potentially_correctable bad_data 
value_changed not_used not_used interpolated_values missing_values" ;

HTH,

Andrew Walsh

----- Original Message ----- 
From: "Randy Horne" <rhorne at excaliburlabs.com>
To: <cf-metadata at cgd.ucar.edu>
Cc: <aschut01 at harris.com>; <rhorne99 at harris.com>; <ekennell at aer.com>
Sent: Friday, August 24, 2012 4:37 AM
Subject: [CF-metadata] Quality flag values for missing data


>
> What is the "generally accepted" approach for how a specific quality flag 
> value should be assigned for a corresponding data value (in the corresponding 
> data variable) that has a _FillValue ?
>
> Is it sufficient that, because the data variable value is _FillValue, the 
> corresponding quality flag value can be undefined ?
>
>
>
> ..............End of Message ...............................-->
>
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