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8.6.3 Validation Procedures All
necessary supporting material, such as audit reports and any site logs,
should be readily available for the level 1 validation. Access to a daily
weather archive should be provided for use in relating suspect data with to
local and regional meteorological conditions. Any problem data, such as data
flagged in an audit, should be corrected prior to the level 1 data
validation. The validation procedures described in the following include
screening, manual review, and comparison.
Table 8-3
Suggested quality control (QC)
codes for meteorological data
Code Meaning Description |
| Code | Meaning | Description |
| 0 | Valid |
Observations that were judged accurate within the performance limits
of the instrument
Observations that required additional processing because the
original values were suspect, invalid, or missing.
|
| 1 | Estimated | Estimated data may be
computed from patterns or trends in the data (e.g., via
interpolation), or they may be based on the meteorological judgment
of the reviewer.
|
| 2 | Calibration
applied | Observations that were
corrected using a known, measured quantity (e.g., instrument
offsets measured during audits)
|
| 3 | Unassigned | Reserved for future use
|
| 4 | Unassigned | Reserved for future use
|
| 5 | Unassigned | Reserved for future use
|
| 6 | Failed
automatic QC check | Observations that
were flagged with this QC code did not pass screening criteria set
in automatic QC software.
|
| 7 | Suspect | Observations that, in the
judgment of the reviewer, were in error because their values
violated reasonable physical criteria or did not exhibit reasonable
consistency, but a specific cause of the problem was not identified
(e.g., excessive wind shear in an adiabatic boundary layer).
Additional review using other, independent data sets (Level 2
validation) should be performed to determine the final validity of
suspect observations.
|
| 8 | Invalid | Observations that
were judged inaccurate or in error, and the cause
of the inaccuracy or error was known (e.g., wind contaminated by ground
clutter or a temperature lapse rate that exceeded the auto convective
lapse rate). Besides the QC flag signifying invalid data, the data
values themselves should be assigned invalid indicators.
|
| 9 | Missing | Observations data were not
collected. |
Data
Screening Screening
procedures generally include comparisons of measured values to upper and
lower limits; these may be physical limits, such as an instrument threshold,
or may be established based on experience or historical data. Other types of
procedures employed in screening include assessments based on the rate of
change of a variable (in these data that change too rapidly or not at all
are flagged as suspect) and assessments based on known physical principles
relating two or more variables (e.g., the dew point should never exceed the
dry-bulb temperature). Screening
may be regarded as an iterative process in which range checks and other
screening criteria are revised as necessary based on experience. For
example, an initial QA pass of a data set using default criteria may flag
values which upon further investigation are determined to be valid for the
particular site. In such cases, one or more follow-up QA passes using
revised criteria may be necessary to clearly segregate valid and invalid
data. Suggested screening criteria are listed in Table 8-4. Data which fail
the screening test should be flagged for further investigation. Manual
Review The
manual review should result in a decision to accept or reject data flagged
by the screening process. In addition, manual review may help to identify
outliers that were missed by screening. This review should be performed by
someone with the necessary training in meteorological monitoring. In
the typical manual review, data should be scanned to determine if the
reported values are reasonable and in the proper format. Periods of missing
data should be noted and investigated. Data should also be evaluated for
temporal consistency. This is particularly useful for identifying outliers
in hourly data. Outliers should be reviewed with reference to local
meteorological conditions. Data are considered to be at Level 1 validation
following the manual review and can be used for modeling and analysis. Comparison
Program After
the data have passed through the screening program, they should be evaluated
in a comparison program. Randomly selected values should be manually
compared with other available, reliable data (such as, data obtained from
the nearest National Weather Service observing station). At least one hour
out of every 10 days should be randomly selected. To account for
hour-to-hour variability and the spatial displacement of the NWS station, a
block of several hours may be more desirable. All data selected should be
checked against corresponding measurements at the nearby station(s). In
addition, monthly average values should be compared with climatological
normals, as determined by the National Weather Service from records over a
30-year period. If discrepancies are found which can not be explained by the
geographic difference in the measurement locations or by regional climatic
variations, the data should be flagged as questionable.
Table 8-4
Suggested Data Screening Criteria |
| Variable | Screening
Criteria: flag data if the value |
| Wind Speed | - is less than
zero or greater than 25 m/s
- does not vary by more than 0.1 m/s for 3 consecutive
hours
- does not vary by more than 0.5 m/s for 12
consecutive
hours
|
| Wind Direction | - is less than
zero or greater than 360
- is less tan zero or greater than 1 degree for more than
3
consecutive hours
- does not vary by more than 10 degrees for 18 consecutive
hours
|
| Temperature | - is greater
than the local record high
- is less than the local record low
(The above limit could be applied on a monthly basis)
- is greater than a 5 °C change from the previous hour
- does not vary by more than 0.5 °C form 12 consecutive
hours
|
| Temperature
Difference | - is greater
than 0.1 °C/m during the daytime
- is less than -0.1 °C/m during the night time
- is greater than 5.0 °C or less tan -3.0 °C
|
| Dew Point
Temperature | - is greater
than the ambient temperature for the given time
period
- is greater than a 5 °C change form the previous hour
- does not vary by more than 0.5 °C for 12 consecutive hours
- equals the ambeint temperature for 12 consecutive hours
|
| Precipitation | - is greater
than 25 mm in one hour
- is greater than 100 mm in 24 hours
- is less than 50 mm in three moths
(The above values can be adjusted based on local climate)
|
| Pressure | - is greater
than 1060 mb (sea level)
- is less than 940 mb (sea level)
(The above values should be adjusted for elevations other
than sea level.)
- changes by more than 6 mb in three hours
|
| Radiation | - is greater
than zero at night
- is greater than the maximum possible for th date and
latitude. |
Further
Evaluations Any
data which are flagged by the screening program or the comparison program
should be evaluated by personnel with meteorological expertise. Decisions
must be made to either accept the flagged data, or discard and replace it
with back-up or interpolated data, or data from a nearby representative
monitoring station (see Section 1). Any changes in the data due to the
validation process should be documented as to the reasons for the change. If
problems in the monitoring system are identified, corrective actions should
also be documented. Any edited data should continue to be flagged so that
its reliability can be considered in the interpretation of the results of
any modeling analysis which employs the data. 8. QUALITY ASSURANCE AND QUALITY CONTROL
8.1 Instrument Procurement
8.1.1 Wind Speed
8.1.2 Wind Direction
8.1.3 Temperature and Temperature Difference
8.1.4 Dew Point Temperature
8.1.5 Precipitation
8.1.6 Pressure
8.1.7 Radiation
8.2 Installation and Acceptance Testing
8.2.1 Wind Speed
8.2.2 Wind Direction
8.2.3 Temperature and Temperature Difference
8.2.4 Dew Point Temperature
8.2.5 Precipitation
8.2.6 Pressure
8.2.7 Radiation
8.3 Routine Calibrations
8.3.1 Sensor Check
8.3.2 Signal Conditioner and Recorder Check
8.3.3 Calibration Data Logs
8.3.4 Calibration Report
8.3.5 Calibration Schedule/Frequency
8.3.6 Data Correction Based on Calibration Results
8.4 Audits
8.4.1 Audit Schedule and Frequency
8.4.2 Audit Procedure
8.4.3 Corrective Action and Reporting
8.5 Routine and Preventive Maintenance
8.5.1 Standard Operating Procedures
8.5.2 Preventive Maintenance
8.6 Data Validation and Reporting
8.6.1 Preparatory Steps
8.6.2 Levels of Validation
8.6.3 Validation Procedures
8.6.4 Schedule and Reporting
8.7 Recommendations
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