Status of automatic observation on aerodrome and ongoing

improvements in France

M. Leroy, Météo-France

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.

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

Advantages

Continuous observation 24 hours a day Reproducible measurements Staff savings Local reports updated every minute

Minimum set of instruments

Basic measurements : pressure, temperature, humidity, wind

Ceilometer(s)

Present Weather Sensor Forward scatter meter (transmissometer/forward scatter meter for

RVR)

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.

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.

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.

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.

An example : 30-Jul-2002 12h00

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.

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

CB/TCU coding

TS/VCTS coding

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.

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

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.