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Noise Measurement System

The noise monitoring system detects, identifies and analyses the noise produced by arriving and departing aircrafts.

The system was supplied by Lochard which already installed more than 120 systems all over the world, including 59 in Europe.

System architecture

Architecture du système

The architecture includes:

  1. The noise monitoring system (NMS)t
  2. The peripherals needed to analyse the measured noise.

Monitoring system components

The noise monitoring system is composed by:

  • 5 fixed monitoring stations known as EMU (Environmental Monitoring Unit)
  • One central processing system comprising:
    • The Comms (Communication Server)
    • The Gems server (Global Environmental Monitoring System)
  • 3 workstations for maintenance purposes, consulting and updating the databases.

The NMS measures aircraft noise according to defined criteria. The first step of the system is the collection of the detected aircraft noise, the second the attribution of the noise to a specific aircraft movement. To perform the correlation of the noise to the aircraft, other information described below are necessary.

Peripheral components

The data captured by the noise measurement sensors (EMU) are not sufficient to perform a correlation of a noise event with an aircraft. For correlation the system needs the information of the following equipments:

  • RADAR system
  • Flight Plan Processing System (FDPS)
  • GPS clock system

Description of the measurement system components

EMU - Environmental Monitoring UnitEMU - station de mesure de bruit

The EMU consists of

  • a digital microphone for noise measurement,,
  • a local unit for data backup and
  • a modem for transmitting data to the central processing system.

During system installation, it is important to choose sites equipped with an electric power supply and a data transmission equipment.


Sites of noise monitoring

Sites of noise monitoring





Central station

at 4520 m from threshold of runway 06



at 1050 m from threshol of runwaye 06


Middle of the runway

 at -1570 m from threshold of runway 06


Threshold of runway 24

at 980 m from threshold of runway 24



at 6100 m from threshold of runway 24

Sites of the 5 EMUs

Microphone unit

L´unité microphoniqueEach unit is mounted at the end of a mast and equipped with a digital microphone, an anti-wind and bird guard and a lightning arrestor.

The microphone captures the analogue noise signal and performs the critical conversion of the signal immediately at the microphone head, and transmits the noise data in digital form to the EMU’s electronics.

The immediate conversion to a digital signal provides a higher immunity to interference.

The unit guarantees an omni directional detection of noise with high reception qualities.

(unit is mounted at the end of a mast)

A manual calibration is performed every 4 months with an high precision source by the CNS department operators.


(Procédure manuelle de calibrage d´une unité microphonique)

Manual calibration of a microphone

Local unit

The noise events detected by the microphone are sent via modem to the central unit and stored in the local unit. The storage capacity is seven days.

The 5 local units are synchronised two times a day by the central system GPS clock.

Central processing system

All the data collected via network or modem from the airport radar, the flight plan processing system and the EMUs are put through to the central processing system which consists of:

  • Comms  (Communication Server)
  • GEMS     (Global Environment Monitoring System)

The Comms server collects:

  • the noise events of the five EMUs,
  • the radar aircraft tracks,
  • the flight plans from FDP (Flight Data Processor),
  • the GPS (Global Positioning System) to guarantee the synchronisation of the noise monitoring system.

The Gems processes and correlates the data acquired by the Comms server in order to identify an aircraft that produced a noise event.

The essential processing in Gems consists of:

  • correlating the real time data from the Comms server,
  • archiving the acquired data,
  • generating reports about individual events, daily, monthly or annual summaries.


Sound/noise events

A noise generated by an aircraft and identified as such is called a noise event.

Generally, a distinction can be made between three different types of noise:

  • aircraft noise,
  • road traffic noise, and
  • train noise.

The various noise curves are characteristic for each type of noise and, by their very specific nature, allow identifying clearly the noise events linked to air traffic, through their highly specific signature.

Evénements sonores  

Identification of the noise event

The EMU continuously analyses the incoming noise signal to identify the source of noise. By using various detection algorithms it is possible to identify noise generated by an aircraft flying past, known as event.

The process of identifying a noise event is based on threshold and time change criteria.

The standard noise event detection works on a template defined to pick out the required type of noise envelope:


Identification d´un événement sonore

Threshold criterion

All information below a primary threshold is ignored. By exceeding the first threshold T1 the subsequent noise data is validated as a possible noise event. The event continues while the noise level passes Lmax and remains above the secondary threshold T2 for a given duration D.

When the noise signal moves below the threshold T2 it must remain below for a given termination time at which the noise event is closed.

Duration criterion

For the final validation of a sound event, the event duration D, between the thresholds T1 and T2 , must equal or exceed the minimum duration time for the event otherwise the event is discarded.

After an event has been identified, the EMU sends the data via modem to the Comms server.



Threshold 1= Threshold 2

Background noise

Minimum duration



65 dB(A)

40 dB(A)

5 s


Seuil de piste 24

65 dB(A)

48 dB(A)

5 s


Milieu de piste

75 dB(A)

49 dB(A)

5 s



66 dB(A

58 dB(A)

5 s


Gare centrale

64 dB(A)

62 dB(A)

5 s

The background noise is the ever-present noise and is recorded all during day and night.

The threshold values represented in the table are put individually for each site in order to avoid that an EMU checks every single noise sound if it is a possible noise event or not. In fact an EMU can only handle one event at the time.


Creating a noise event as described beforehand doesn't permit to attribute this event to a specific aircraft movement. To be able to identify a noise event the system needs to correlate the event data with further data from peripheral systems.

A distinction is made between:

  • real time correation done in the Comms server;
  • non real time correlation done in GEMS server;

The incoming data :

  • noise events,
  • airraft flight plans,
  • Radar information,
  • date and time,

    are stored in three different database tables.

Principe de corrélation

Principle of correlation

The correlation algorithm permanently scans these tables for uncorrelated data and allows the following correlation modes:

  1. Track to flight plan correlation
    This correlation associates a radar flight track to a specific flight plan by mean SSR (Secondary Surveillance Radar) code.
  2. Track to noise correlation or distance based correlation
    The distance based correlation is performed in real time. Each sound event is correlated to the nearest flight track at the time of the Lmax of the noise event.
  3. Time based correlation
    For flights without flight tracks, noise events may be correlated to the flight plan based on travel time to the EMUs.
  4. Manual correlation
    The noise system operator is able to correlate manually a noise event after in-depth data analysis.

Measurement availability

Considering that the system is based entirely on automatic event correlation, in case of failure of one of the following equipment:

  • Noise monitoring station,
  • Gems server,
  • Comms server,
  • Radar system (no SSR code attribution possible),
  • FDP (flight plan processing) system (no call sign attribution possible),

there is no automatic correlation possible.


Data evaluation and report publication

The Administration publishes monthly reports on the Internet and that may be downloaded from this site in PDF format.

For any additional information, please contact us via e-mail at: