Documentation of surface observation. Classification for siting and performance characteristics

1. Documentation of surface observation. Classification for siting and performance characteristics Michel Leroy, Météo-France

2. 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

3. 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.

4. 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.

5. 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.

6. 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.

7. 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

8. 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).

9. 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.

10. 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.

11. Other parameters • Pressure • Amount of precipitation • Wind • Visibility • Temperature above ground • Soil temperature

12. 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

13. Status of the cooperative network • Air temperature (liquid in glass thermometers) : Class C • Amount of precipitation : Class B

14. 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

15. 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°.

16. 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.