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Status of automatic observation on aerodrome and ongoing
improvements in France
M. Leroy, Météo-France
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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.
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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
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Advantages
Continuous observation 24 hours a day Reproducible measurements Staff savings Local reports updated every minute
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Minimum set of instruments
Basic measurements : pressure, temperature, humidity, wind
Ceilometer(s)
Present Weather Sensor Forward scatter meter (transmissometer/forward scatter meter for
RVR)
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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.
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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.
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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.
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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.
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An example : 30-Jul-2002 12h00
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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.
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CB/TCU, TS/VCTS detection
Lightning
Lightning impact(s) in an
area of 8 km around the aerodrome
Lightning impact(s) in an
area from 8 km to 16km
around the aerodrome
Lightning impact(s) in
area from 16 km to 30 km around
the aerodrome
No lightning impact
No data
Reflectivity of 5 closely pixels >41 dBZ
CB TS
CB VCTS
CB CB CB No
information 33 ? Reflectivity of 5 closely pixels <41 dBZ
CB TS
CB VCTS
CB TCU
TCU No
information Reflectivity of 5 closely pixels ? 33 dBZ
CB TS
CB VCTS
CB
No
information
Lev
el o
f ra
dar
refle
ctiv
ity
in a
n ar
ea o
f 30k
m a
roun
d th
e ae
rodr
ome
No data CB TS
CB VCTS
CB No informati
on
No information
No information
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CB/TCU coding
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TS/VCTS coding
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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.
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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
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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.