Carmen García Izquierdo Centro Español de Metrología

1. Traceability of ground-based Meteorological surface temperature measurements Carmen García Izquierdo Centro Español de Metrología

2. European Metrology Research Program (EMRP) MeteoMet Project (October 2011) WP3. Traceable measurements methods and protocols for ground based meteorological observations. 16 partners from different European countries Objectives: 1.- Improve the reliability of the weather stations measurements 2.- Assure traceability of the weather stations measurements to National Standards

3. Climate change: 1. Robustness the climate measurements and its uncertainties 2. Metrological traceability of the measurements Today: Conventional calibrations of the weather stations: By comparison Calibration of 1 parameter at a time Limitations: 1.- The mutual influences of several parameters systematic error 2.- There aren’t accurate methods for in-situ calibrations of weather stations (mostly are sort of checks)

4. 1. Influences between parameters Weather stations: sensors T, rh, p, v Reliable uncertainties calculation Study the influence of quantities

5. ( 0%, 95%) rh (700, 1150) hPa (-40, 50) ºC (0 %, 95 %) rh ( -40, 50) ºC (700, 1150) hPa 1.1. Mutual influence of the parameters. (T, rh, p→T, Rh, p) Performance of the most common sensors of T, rh and p, simulating ≠ T, rh and altitude conditions. T rh p Behaviour with fast changes → Response time of each sensor Stability test

6. 1 m/s ≤ v ≤ 40 m/s ≠ wind directions fast changes T rh p 1.2.1 Influence of the parameters. (wind speed →T, rh, p) • T = f1(v), rh = f2(v), p = f3(v) • f1, f2, f3→ Correction model + uncertainty Uncertainty Tests in 3 wind tunnels

7. Danish Technological Institute 1.2.1 Influence of the parameters. (wind speed →T, p, rh) Wind tunnel built at the Mars Simulation Laboratory (AU) Aim: Use this facility for testing, calibration and comparison of meteorological sensors under a wide range of terrestrial conditions REG 3 Researcher: “Mars simulator” → adapt to earth conditions Extensive modifications of the control system, sensor systems and mechanical design of the facility Characterization of the wind tunnel before its use as chamber for testing the meteorological sensors v T rh p T rh p

8. 1.2.2. Influence of the parameters. (salinity →T, rh, p) It’s not only a cause of malfunctioning It’s also a source of uncertainty Ageing of the sensors in salinity chamber with periodical control calibrations T rh → Stability p Sensors will be cleaned and checked to understand the limits of the possible recovery

9. 1.2.3. Influence of the parameters. (solar radiation →T, rh, p) Protection shield for rain and direct sun radiation - is heated under direct solar radiation - avoids the free movement of fresh air sensor environment ≠ real environment systematic errors Aim: Evaluate the effect of the solar radiation in weather measurements

10. 1.2.3. Mutual influence of the parameters. (solar radiation →T, rh, p) Reference radiation shield has been designed and built -Forced mechanical ventilation -A simulation was performed to make sure that the aspirated air is leaving the shield straight out instead of out downwards -One reference shield will be white and the other one black -Some tests and a comparison with other types of housing (real situation or sun simulator) A comparison (1 year) of different housings with reference shield will be done in Spain and Sweden - Same kind of sensors - Continuous readings of T, v, radiation Aging of the shield - Analysis of temperature error data - Development of a temperature model, f( v, radiation, shield ageing, type of housing ) - Proposal of procedures to measure in a harmonizing way with different shields

11. 1.3. Mutual influence of the parameters. (T, rh, p → wind speed) Anemometers (cup, propeller or ultrasonic) Calibration alone in a laboratory reliable measurements - Strongly dependence on the surrounding environment (local geography and /or buildings) Calibration in situ - Influence of seeding, rain and ice mainly in ultrasonic anemometers

12. v1(40 m) v2(10 m) 1.3. Mutual influence of the parameters. (T, rh, p→ wind speed) Laser based measurement technique : v2 = f (v1) -take several days in places with difficult holography -establish a rough relation more reliable and traceable measurements Calibration in-situ: Mathematical model effect of seeding, rain and ice -tested with experimental measurements in wind tunnel controlling seeding, ice growth or rain - tested with experimental measurements in real conditions Danish Technological Institute Calibration ≠ kinds of wind speed anemometers T (10, 40) ºC rh up 90% v (1, 40) m/s ≠ wind directions

13. 2. Accurate methods for weather station calibration Calibration of weather station usually in situ by comparison weak point[1] Construction of two new chambers specifically designed for the calibration of weather stations • Laboratory facility • Primary climate chamber for traceable in-situ calibrations [1] G. Lopardo, D. Marengo, A. Meda, A. Merlone, F. Moro, F. R. Pennecchi, M. Sardi, “Traceability and online publication of weather station measurements of temperature, pressure, and humidity” Int J Thermophys, (2012) DOI 10.1007/s10765-012-1175-3 The standards, used in in-situ calibration, usually are calibrated in a laboratory without taking into account the influence of the other meteorological quantities. behaviour in laboratory ≠ behaviour in the calibration site.

14. 2. Accurate methods for weather station calibration. Laboratory chamber -Chamber can host different types of weather stations and sensors -Separated and independent control of T, rh,p control within: 0,05 ºC , -40 ºC ≤ T ≤ 50 ºC 100 Pa, 75 kPa ≤ p ≤ 110 kPa accuracy (0,3 % rh, 0,7% rh) (5, 98) % rh, (0, 50) ºC -Will also include a wind generator (0, 30) m/s -Will be designed to contain a solar radiation generator Combined and simultaneous calibration of T, rh and p sensors Study the impact of the interfering quantities on individual calibration curves (T, rh, p)

15. 2. Accurate methods for weather station calibration. Chamber in-situ calibration -Smaller than the laboratory chamber. REG1 Researcher: it will be used at the base of Everest Mount -Separated and Independent control of T, rh,p within: 0,05 ºC , -20 ºC ≤ T ≤ 50 ºC 100 Pa, 50 kPa ≤ p ≤ 110 kPa uncertainty 1.5 % (5, 98) % rh, T (0, 50) ºC -Measurements of T, rh and p, with instruments directly calibrated against primary standards -June 2012 the first prototype was used in a campaign of calibration of meteorological sensors in-situ (Italy). -Final prototype was ended in August 2012 and now is under characterization

16. Conclusions • The activities of the WP3 of the project are focus on the improving the reliability of the measurements of the ground-based meteorological weather stations. • The mutual influence of the meteorological quantities is going to be studied. • A reference shield has been designed, built and characterized to analyze the impact of the solar radiation to the sensors of surface ground based instruments. A comparison is going to run at two very different meteorological sites to see the influence of the aging shield 4. The influence of the salinity in meteorological measurements is going to be analyzed 5. A new in-situ calibration method of anemometers will be developed, where the local holography is taken into account. A new mathematical model will tell us the influence the seeding, rain and ice in wind speed measurements performed by ultrasonic anemometers 6. Two new chambers, specifically designed for the calibration of weather stations and sensors, are under construction. One of them is a laboratory facility and the other one is for in-situ calibrations. The use of both chambers, will increase the reliability of the measurements by means of weather stations