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Quality management, calibration, testing and comparison of instruments and observing
systems
M. Leroy,
CIMO ET on SBII&CM
Quality management, some aspects
Explicit identification of uncertainty objectives Representativeness of observations Calibration and maintenance Selecting instruments : knowing their characteristics
– Testing– Intercomparisons
Composite observing systems Value analysis ISO 9001-2000 is an international frame
Quality management process
Setting and documenting objectives Defining associated indicators Regular survey of indicators Regular survey of users’ (customers) needs and
satisfaction. Correcting and improving
Identification of uncertainty objectives
Identification of users of observation data– Forecasters and climatologists– Few direct users of observation : special case is aeronautic
users, with needs clearly defined in Annex 3 of ICAO.
Getting the users’ needs is not always easy– They are not always aware of the possible uncertainty and
associated cost. – A value analysis is necessary to get a good compromise.
The CIMO guide (WMO doc n° 8) is a guide.– Annex 1B indicates users’ needs and achievable measurements
(best state of the art).
The measurement uncertainty must be demonstrated. So realistic choices must be done.
An example
For his proprietary Radome network, mainly dedicated for real-time observation, Météo-France has set up the following objectives; some are less ambitious than the achievable measurement uncertainty stated by the CIMO guide.– 0.5 hPa for pressure– 6% for relative humidity– 0.5°C for air temperature– 10% for wind speed– 5-10% for precipitation amount– 5% for daily amount of solar radiation.
For other objectives, additional care can be necessary
Example : US Climate Reference Network – Redundancy and cross check of measurements.– 3 independent air temperature measurements.– Dual fence rain gauge.– Associated measurement of wind speed.
Such efforts cannot be made in each station of a climatological cooperative network.
Quality indicators
Availability of data in the (final) data base– Within a given limit of time : example 95% of expected surface
observations available within 10 minutes.– Availability of data in the climatological data base : example 98%
for the Radome network. Measurement uncertainty
– % of sensors calibrated in a stated delay : example 12 months nominal, 15 months maximum, objective is more than 90%.
– % of sensors found outside an Acceptable User Limit : example hygrometers found with one (or more) control point more than 5% from the reference. These sensors are flagged as having drifted.
– % of sensors for which the periodicity of preventive maintenance is respected.
– % of large errors when compared to numerical models (monitoring)
Some examples
Knowing the characteristics of an instrument
Technological survey : reading publications, participating to conference and instrument exhibitions.
Testing of instruments : please, publish results and make them available.
Intercomparisons, WMO intercomparisons. Read the manufacturers’ technical
documentation, having in mind the common characteristics of instruments, for example, thru the CIMO guide.
Recent WMO intercomparisons
Radiosonde intercomparisons WMO Laboratory Intercomparison of Rainfall
Intensity gauges WMO Field Intercomparison of RI gauges : May
2007-May 2008, Vigna di Valle, Italy WMO Intercomparison of Thermometer
Screens/Shields in conjunction with Humidity Measurements : 2007, Ghardaïa, Algeria
WMO Field Intercomparison of Rainfall Intensity Instruments
The laboratory Intercomparison was a first step, easier to handle than a field test.
Not all instrument types available on the market were tested in laboratory.
Looking for a possible site, Vigna di Valle, Italy (Italian Meteorological Service, ReSMA) was selected.
August 2007 August 2008
Field Intercomparison
Call for instruments (March 2006) 24 instruments of different measuring principles were selected (54
proposed !). Reference based on a set of high quality devices, inserted in a pit
gauge. Draft Rec. 4.2/2 : Procedure and reference instruments for field
rainfall intensity intercomparisons
WMO Combined Intercomparison of Thermometer Screens/Shields, in conjunction with Humidity Measuring Instruments
Looking for a possible site in harsh conditions, Ghardaïa, Algeria was selected.
Desert region Jan. 2007 Jan. 2008 Instruments’ calibration before and after
Screens & Hygrometers Intercomparison
Call for instruments (March 2006) 16 screens/shields’ types (29 proposed) and 11 hygrometers’
types(17 proposed) were selected. Reference : Thygan Data analysis :
– International Organizing Committee
– ISO standard 17714 (draft)
Conclusion
There are many other subjects and actions concerning quality measurement :– Quality control directly at the level of the measurement systems.– Quality control using spatial and temporal cross-check.– Representativeness of observations, due to the nearby
environment of the measuring site.– …
Quality management and ISO 9001-2000 certification force us to explicit the objectives of observing networks and the proofs demonstrating their achievement.