Documentation of surface observation. Classification for siting and performance characteristics

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Documentation of surface observation.
Classification for siting and performance
characteristics

• Michel Leroy, Météo-France

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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

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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.

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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.

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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 (gt 3000)
• The intrinsic performances, maintenance and
  calibration procedures are not the same.

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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,
  Météo-France was forced to increase his knowledge
  of the various networks characteristics.

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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

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Air temperature

• Class A Overall uncertainty of 0.1C. Therefore,
  the uncertainty of the temperature probe lower
  than 0.1C and use of a perfect artificially
  ventilated screen. Achievable measurement
  uncertainty is 0.2C.
• Class B Pt100 (or Pt1000) temperature probe of
  class A (? 0.25C). Acquisition uncertainty lt
  0.15C. Radiation screen with known
  characteristics and over-estimation of Tx (daily
  max. temperature) lt 0.15C in 95 of cases.
  Laboratory calibration of the temperature probe
  every 5 years.
• Class C Temperature probe with uncertainty lt
  0.4C. Acquisition uncertainty lt 0.3C. Radiation
  screen with known characteristics and
  over-estimation of Tx lt 0.3C 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 gt 0.7C in 5 of cases).

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Relative humidity

• Class A Overall uncertainty of 1! Achievable
  2.
• Class B Sensor specified for ? 6, over a
  temperature range of 20C to 40C. Acquisition
  uncertainty lt 1. Calibration every year, in an
  accredited laboratory.
• Class C Sensor specified for ? 10, over a
  temperature range of 20C to 40C. Acquisition
  uncertainty lt 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.

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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.

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Other parameters

• Pressure
• Amount of precipitation
• Wind
• Visibility
• Temperature above ground
• Soil temperature

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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

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Status of the cooperative network

• Air temperature (liquid in glass thermometers)
  Class C
• Amount of precipitation Class B

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Status of non-Météo-France additional networks

• 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

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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.

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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.