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  MADIS Satellite Wind Quality Control

MADIS Satellite Wind Quality Control


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

Automated Quality Control

At this time, only level 1 QC checks are applied to satellite wind variables. The following table lists the variables that are QC'ed, and the checks that are used:


  MADIS Satellite Wind Variables with QC
  ---------------------------------------------------------------------------
  Code       Name                                    Max     Level | Level 1: 
                                                   Possible        |          
                                                   QC Level        | Validity 
                                                                   |          
  ---------------------------------------------------------------------------
  
  All Wind Products                                               
  -----------------
  
  DD        wind direction                           1                  X
  FF        wind speed                               1                  X
  U         u wind component                         1                  X
  V         v wind component                         1                  X
  
  Infrared Cloud-Drift                               
  --------------------
  
  DDIR      wind direction                           1                  X
  FFIR      wind speed                               1                  X
  UIR       u wind component                         1                  X
  VIR       v wind component                         1                  X
  
  Visible Cloud-Drift                                
  -------------------
  
  DDVIS     wind direction                           1                  X
  FFVIS     wind speed                               1                  X
  UVIS      u wind component                         1                  X
  VVIS      v wind component                         1                  X
  
  Water Vapor Motion                                  
  ------------------
  
  DDWV      wind direction                           1                  X
  FFWV      wind speed                               1                  X
  UWV       u wind component                         1                  X
  VWV       v wind component                         1                  X
  
  Sounder Channel 10 (7.4 um) Water Vapor Motion      
  ----------------------------------------------
  
  DDS10     wind direction                           1                  X
  FFS10     wind speed                               1                  X
  US10      u wind component                         1                  X
  VS10      v wind component                         1                  X
  
  Sounder Channel 11 (7.0 um) Water Vapor Motion      
  ----------------------------------------------
  
  DDS11     wind direction                           1                  X
  FFS11     wind speed                               1                  X
  US11      u wind component                         1                  X
  VS11      v wind component                         1                  X

The level 1 validity checks restrict each observation to falling within a TSP-specified set of tolerance limits. Observations not falling within the limits are flagged as failing the check. The tolerances are specified as a function of pressure level, and are listed in the following table:


  ---------------------------------------------------
  Validity Checks

                    Max Wind
  Level(mb)         Speed(Kts)
  ---------------------------------------------------
  1000                  70
   850                  90
   700                 120
   500                 200
   400                 250
   300                 300
   250                 300
   200                 300
   150                 200
   100                 200
    70                 200
    50                 200
    30                 200
    20                 200
    10                 200       
   <10                 200       

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 satellites and wind product types that will be labeled as bad, regardless of the outcome of the QC checks; the accept list is the corresponding list of satellites and wind product types 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 - Satellite Wind
  -------------------------------------

  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 = N/A
             level 3 = N/A

  Subjective intervention:

   G - Subjective good
   B - Subjective bad

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

   Bit       QC Check                      Decimal Value
   ---       --------                      -------------
    1        Master Check                        1
    2        Validity Check                      2
    3        Reserved                            4
    4        Reserved                            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 3 should be interpreted as 1 + 2, meaning the validity check was applied (and the "master check" as well).


References

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