Status of automatic observation on aerodrome and ongoing improvements in France

1. Status of automatic observation on aerodrome and ongoing improvements in France M. Leroy, Météo-France

2. Introduction • About 15 years ago, a new aerodrome was set up in the Estearn part of France (LFJL) • Equiped for cat III operations. • But, no observer from Météo-France. • Observation made by local fire fighters • Operational test of METAR AUTO started in 2001.

3. Documentation of the possibilities and limitations of automatic observation • Spatial representativeness of visibility observation • Validity of cloud layers, calculated from ceilometer(s) measurements (ASOS algorithm). • No identification of CB and TCU • Limited list of Present Weather codes and reliability of PW detection and identification. • SPECI criteria : no SPECI AUTO with with 30 min. METAR AUTO

4. Advantages • Continuous observation 24 hours a day • Reproducible measurements • Staff savings • Local reports updated every minute

5. Minimum set of instruments • Basic measurements : pressure, temperature, humidity, wind • Ceilometer(s) • Present Weather Sensor • Forward scatter meter • (transmissometer/forward scatter meter for RVR)

6. First feed-back • Good experience and users’ feed back for METAR AUTO in LFJL. • No degradation of the quality of TAF messages. • No major limiting meteorological conditions missed. • Meteorologists more reluctant than users ! • One reason may be the fact that observations are used for many purposes, not only aeronautic.

7. Levels of service • Defined with the French civil aeronautic agency (DGAC) • METOBS1 : METAR with human observation 24h/day, except 3 hours during night (AUTO), with possible reactivation of human observation. • METOBS2 : METAR AUTO when staff is off duty • METOBS3 : METAR AUTO every 30 minutes. • METOBS4 : Occasional METAR, no SPECI : to be stopped.

8. Actual status in France • List of 69 aerodrome with a defined level of service (METOBS1 .. METOBS3). • 52 aerodromes with METAR AUTO (target is 63 in 6 months). • Users are satisfied. • Improvements are on going.

9. Improvement : Convective information • Use of the Météo-France lightning network and weather radar network. • Study over one year to check the correlation between human observation of CB/TCU (from METAR) and radar observation: • Above a given threshold of reflectivity. • For a minimum size of cell (adjacent pixels). • Within a given distance.

10. An example : 30-Jul-2002 12h00

11. Results of the study • Best correlation with human observation : 41 dBz (CB), 33 dbZ (TCU), 30 km max. distance. • But significant differences, mainly coming from the “definition” of CB • Human : visual detection of clouds or lightning stroke. No maximum distance defined. • Radar : High level of reflectivity. Max. distance defined. Very good correlation with behaviour of pilots avoiding high reflectivity area.

12. CB/TCU, TS/VCTS detection

13. CB/TCU coding

14. TS/VCTS coding

15. Operational system • Timing for the construction of diagnostics (CB/TCU, TS/VCTS) in Toulouse. • Getting the value in each aerodrome where METAR AUTO and local reports are constructed. • Adding the information in messages • 28 operational sites • 99% availability of information in messages.

16. Improving the detection and identification of freezing precipitation. • Addition of a state of ground sensor : • Measurement of reflected light and back scatter light. • Difference between snow and rain/drizzle/ice. • Detection of humid and wet surface • Use of “ground” temperature and air temperature

18. Conclusion • METAR AUTO well accepted in France. • Small aerodrome are interested in automatic observation, to improve their level of services. • ICAO is recognizing the automatic observation.