MADIS Satellite Sounding Quality Control Checks
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 QC check. The following table lists the tolerance limits:
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Validity Checks
Air and Dewpoint Temperature (C)
Level(mb) Low High
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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 enforce reasonable, meteorological relationships among observations measured at a single location. In this case, the dewpoint temperature must not exceed the temperature observation. If it does, the dewpoint is flagged as failing the internal consistency check.
*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, specific humidity will get the QC results from the checks applied to dewpoint 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 satellites 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 satellites that will be labeled as good, regardless of the outcome of the QC checks. In both cases, observations associated with the satellites in the lists can be individually flagged. For example, moisture observations at a particular satellite may be added to the reject list, but not the temperature observations.
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:
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MADIS QC Information - Satellite Sounding
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QC Data Descriptor Values
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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
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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 11 should be interpreted as 1 + 2 + 8, meaning the validity and internal consistency checks were applied.
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 March 2017
