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  MADIS Radiometer Quality Control

MADIS Radiometer Quality Control


This page provides a detailed description of the quality control (QC) processing and data structures for the radiometer dataset. For a general overview of MADIS quality control, click here.

Automated Quality Control

Level 1 QC checks are considered the least sophisticated, level 2 the most sophisticated checks. The following table lists the radiometer variables* that are QC'ed, and the checks that are used:


  MADIS Radiometer Variables with QC
  -------------------------------------------------------------------------------------
  Code       Name                                Max     Level | Level 1: | Level 2:          
                                               Possible        |          |                           
                                               QC Level        | Validity |  Internal    
                                                               |          | Consistency  
  -------------------------------------------------------------------------------------
  
  Profiles          
  --------
  
  T         air temperature                      2                  X            X
  TV        virtual temperature                  2                  X            X
  TD        dewpoint temperature                 2                               X
  RH        relative humidity                    2                               X
  Q         specific humidity                    2                               X
  DPD       dewpoint depression                  2                               X
  AH        absolute humidity                    2                               X
  CLD       cloud liquid density                 2                               X
  
  Single-level Observations
  -------------------------
  
  CBH       cloud base height                    2                               X
  CBT       infrared cloud base temperature      2                               X
  ILW       integrated liquid water              2                               X
  PWV       integrated water vapor               2                               X
  
  Internal Consistency Checks
  ---------------------------
  
    1   Rain contamination check 
    2   Integrated liquid check (ILW > 1.5 mm)

The level 1 validity check restrict observations to falling within a TSP-specified set of tolerance limits. Temperatures not falling within the limits are flagged as failing the QC check. The tolerances are specified as a function of pressure level, and the radiometer heights are converted into pressure using the U.S. standard atmosphere calculation. The following table lists the tolerance limits:


  ------------------------
  Validity Check

                 Temp.(C) 
  Level(mb)      Low  High
  ------------------------
  1000           -65    60
   850           -50    45
   700           -50    30
   500           -57     5
   400           -66   -10
   300           -72   -20
   250           -76   -25
   200           -78   -30
   150           -85   -30
   100           -95   -30
    70           -95   -25
    50           -95   -15
    30           -95    -5
    20           -95     5
    10           -95    15
   <10           -95    15

The level 2 internal consistency checks include two separate checks that look for contamination of the data from various phenomena. The rain contamination check indicates that retrievals may be degraded as a result of the presence of rain on the radome, and failure of the integrated liquid check indicates degradation due to scattering effects that occur when the integrated liquid retrieval is larger than 1.5 mm.

*It should be noted that while the QC checks discussed here are generally applied to the form of the variable stored in the database, the QC results will also be applied to any forms of the variable that are requested by the user and are derived from the primary variable. For example, virtual temperature will get the QC results from the checks applied to air temperature.

Subjective Intervention

Two text files, a "reject" and an "accept" list provide the capability to subjectively override the results of the automated QC checks. The reject list is a list of stations and associated input observations that will be labeled as bad, regardless of the outcome of the QC checks; the accept list is the corresponding list of stations that will be labeled as good, regardless of the outcome of the QC checks.

Here are the current subjective intervention lists in use:

QC Data Structures

The MADIS QC information available for each variable includes the following QC structures: a single-character "data descriptor", intended to define an overall opinion of the quality of each observation by combining the information from the various QC checks, and for users desiring detailed information, a "QC applied" bitmap indicating which QC checks were applied to each observation, and a "QC results" bitmap indicating the results of the various QC checks.

The following table provides a complete list of the data descriptors and the bits used in the bitmaps:

  ---------------------------------
  MADIS QC Information - Radiometer
  ---------------------------------

  QC Data Descriptor Values
  -------------------------

  No QC available:

   Z - Preliminary, no QC

  Automated QC checks:

   C - Coarse pass, passed level 1
   S - Screened, passed levels 1 and 2
   V - Verified, passed levels 1, 2, and 3
   X - Rejected/erroneous, failed level 1
   Q - Questioned, passed level 1, failed 2 or 3

       where level 1 = validity
             level 2 = internal consistency
             level 3 = N/A

  Subjective intervention:

   G - Subjective good
   B - Subjective bad

  Interpolated/Corrected observations:

   T - Virtual temperature could not be calculated, air temperature passing all QC 
       checks has been returned

  Bitmask for QC Applied and QC Results
  -------------------------------------

   Bit       QC Check                      Decimal Value
   ---       --------                      -------------
    1        Master Check                        1
    2        Validity Check                      2
    3        Reserved                            4
    4        Internal Consistency Check          8
    5        Reserved                           16
    6        Reserved                           32
    7        Reserved                           64
    8        Reserved                          128
    9        Reserved                          256
   10        Reserved                          512

The QC bitmask is used in the QC applied and QC result "words" returned along with the QC data descriptor. By examining the individual bits, the user can determine which checks were actually applied, and the pass/fail status of each check that was applied.

In the QC applied word, a bit value of 1 means the corresponding check was applied, a bit value of 0 indicates the check wasn't applied.

In the QC results word, a bit value of 1 means the corresponding check was applied and failed, a bit value of 0 indicates the check passed (given that the check was applied).

The "Master Check" is used to summarize all of the checks in a single bit. If any check at all was applied, this bit will be set in the QC applied word. If the observation failed any QC check, it will be set in the QC results word.

When read as decimal numbers, the different bits that are set in the bitmask are summed together. For example, a QC applied value of 131 should be interpreted as 1 + 2 + 128, meaning the validity and super-adiabatic lapse rate checks were applied.


References

DiMego, G.J, P.A. Phoebus, and J.E. McDonnel, 1985: Data Processing and Quality Control for Optimum Interpolation Analysis at the National Meteorological Center. NMC Office Note 306, NOAA, U.S. Dept. of Commerce, 38 pp.

Technique Specification Package 88-21-R2 For AWIPS-90 RFP Appendix G Requirements Numbers: Quality Control Incoming Data, 1994. AWIPS Document Number TSP-032-1992R2, NOAA, National Weather Service, Office of Systems Development.


Last updated 16 June 2016