Transcript Documentation of surface observation. Classification for siting and performance characteristics Michel Leroy, Météo-France Quality factors of a measurement  The intrinsic characteristics of sensors or measurement.

Documentation of surface
observation. Classification for
siting and performance
characteristics
Michel Leroy, Météo-France
Quality factors of a measurement
 The intrinsic characteristics of sensors or
measurement methods
 The maintenance and calibration needed
to maintain the system in nominal
conditions.
 The site representativeness
Site representativeness
 Exposure rules from CIMO recommendations.
 But not always followed and not always possible to
follow, depending on the geographical situation.
 In 1997, Météo-France defined a site classification for
some basic surface variables.
– Class 1 is for a site following WMO recommendations
– Class 5 is for a site which should be absolutely avoided for large
scale or meso-scale applications.
– Class 2, 3 and 4 are intermediate
 This classification has been presented during TECO98
in Casablanca.
Classification of stations
 Between 2000 and 2006, 400 AWS have been installed
for the Radome network.
 The objective was class 1 for each parameter (Temp,
RH, wind, precip., solar radiation).
 But class 2 or class 3 were accepted when class 1 not
possible.
 Météo-France is now classifying al the surface observing
stations, including the climatological cooperative
network: ~4300 sites, before the end of 2008.
 Update at least every 5 years.
Other quality factors
 Intrinsic performances
 Maintenance and calibration
 Within a homogeneous network, these factors are known
and generally the same. But Météo-France is using data
from various networks:
– Radome (554)
– Non-proprietary AWS (~800)
– Climatological cooperative network (> 3000)
 The intrinsic performances, maintenance and calibration
procedures are not the same.
Several reasons
 The objectives may be different.
 But some uncertainty objectives are sometimes (often)
unknown !
– To get cheap measurements ?
 The maintenance and/or the calibration are not always
organized !
 Within the ISO 9001-2000 certification process, MétéoFrance was forced to increase his knowledge of the
various networks’ characteristics.
Another classification !
 After site classification (1 to 5), definition of an additional
classification, to cover the two quality factors :
– Intrinsic performances
– Maintenance and calibration
 4 levels were defined :
– Class A : WMO/CIMO recommendations (Annex 1B of CIMO guide)
– Class B : Lower specs, but more realistic or affordable : “good”
performances and “good” maintenance and calibration. RADOME
specs.
– Class C: Lower performances and maintenance, but
maintenance/calibration organized.
– Class D : Unknown performances and/or no maintenance/calibration
organized.
 This classification is called : Maintained performance classification
Air temperature
 Class A: Overall uncertainty of 0.1°C. Therefore, the uncertainty of
the temperature probe lower than 0.1°C and use of a “perfect”
artificially ventilated screen. Achievable measurement uncertainty is
0.2°C.
 Class B: Pt100 (or Pt1000) temperature probe of class A ( 0.25°C).
Acquisition uncertainty < 0.15°C. Radiation screen with known
characteristics and over-estimation of Tx (daily max. temperature) <
0.15°C in 95% of cases. Laboratory calibration of the temperature
probe every 5 years.
 Class C: Temperature probe with uncertainty < 0.4°C. Acquisition
uncertainty < 0.3°C. Radiation screen with known characteristics
and over-estimation of Tx < 0.3°C in 95% of cases.
 Class D: Temperature probe and/or acquisition system uncertainty
lower than for class C or unknown. Unknown radiation screen or
with “unacceptable” characteristics (for example, over-estimation of
Tx > 0.7°C in 5% of cases).
Relative humidity
 Class A: Overall uncertainty of 1%! Achievable 2%.
 Class B: Sensor specified for  6%, over a temperature
range of –20°C to +40°C. Acquisition uncertainty < 1%.
Calibration every year, in an accredited laboratory.
 Class C: Sensor specified for  10%, over a temperature
range of –20°C to +40°C. Acquisition uncertainty < 1%.
Calibration every two years in an accredited laboratory,
or calibration every year in a non-accredited laboratory.
 Class D: Sensor with unknown performances or
specifications worst than  10% over the common
temperature conditions. Unknown calibration or
calibration not organized.
Global solar radiation
 Class A: Pyranometer of ISO class 1. Uncertainty of 5%
for daily total. Ventilated sensor. Calibration every two
years. Regular cleaning of the sensor (at least weekly).
 Class B: Pyranometer of ISO class 1. No ventilation.
Calibration every two years. No regular cleaning of the
sensor.
 Class C: Pyranometer of ISO class 2. No ventilation.
Calibration every five years. No regular cleaning of the
sensor.
 Class D: Sensor with unknown performances or sensor
not using a thermopile. Unknown calibration or
calibration not organized.
Other parameters
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Pressure
Amount of precipitation
Wind
Visibility
Temperature above ground
Soil temperature
Status of the RADOME network
 Air temperature : Class B
 RH : Class B
 Amount of precipitation : Class B or Class C, depending
on the rain gauge used.
 Wind : Class A
 Global solar radiation : Class A for manned station, class
B for isolated sites.
 Ground temperatures : Class B
 Pressure : Class B
 Visibility (automatic) : Class B
Status of the cooperative network
 Air temperature (liquid in glass thermometers) : Class C
 Amount of precipitation : Class B
Status of non-Météo-France additional
networks
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Air temperature : Class B to D
RH : Class B to D
Amount of precipitation : Class B to C
Wind : Class B to D
Global solar radiation : Class B to D
Ground temperature : Class B to C
Pressure : Class B to D
Metadata
 These classification for each site are meta data, part of
the climatological database.
 Site classification is on going.
 Maintained performance classification has been defined
this year and is in a test phase : is it possible to “easily”
classify the additional networks.
 With these two classifications, a measurement on a site
can be given a short description.
– Example : C3 for global solar radiation is for a class 2
pyranometer without ventilation, calibrated every 2 years,
installed on a site with direct obstructions, but below 7°.
Conclusion
 These classifications are intended to describe the real
world of measuring networks, which is sometimes far
form the WMO/CIMO recommendations.
 The possible interest of such classifications within CIMO
could be considered.