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  MADIS Hydrological Surface Quality Control

MADIS Hydrological Surface Quality Control


This page provides a detailed description of the quality control (QC) processing and data structures for the hydrological surface 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 hydrological surface variables. The following table lists the variables that are QC'ed, and the checks that are used:

  MADIS Hydro Variables with QC
  --------------------------------------------------------------
  Code       Name                      Max     Level | Level 1: 
                                     Possible        |          
                                     QC Level        | Validity 
                                                     |          
  --------------------------------------------------------------
  PCP5M     accumulated precip - 5m    1                  X
  PCP1H     accumulated precip - 1h    1                  X
  PCP3H     accumulated precip - 3h    1                  X
  PCP6H     accumulated precip - 6h    1                  X
  PCP12H    accumulated precip - 12h   1                  X
  PCP24H    accumulated precip - 24h   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 following table lists the tolerance limits:


  -----------------------------------------
  Validity Checks
  -----------------------------------------
  Accumulated precip - [all]   0 -   44  in

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 - Hydro
  ----------------------------

  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 29 October 2014