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Updated: 2010 / 04 / 20 |
Environmental
acoustics: The LCPC's permanent experimental site at Saint-Berthevin
(Western France)
The Long-Term Monitoring Site (LTMS) was set up to better
understand the physical phenomena inherent in the field
of environmental acoustics; though noise annoyance can
stem from a variety of sources (road and railway traffic, airplanes, industrial noise), they all display similar
characteristics with respect to the physical phenomena
involved in long-range acoustic propagation. This research
topic still encounters some major scientific obstacles
despite the interest shown by the international scientific
community and despite the resources allocated in this research domain over the
past several decades.
At the same time, regulatory and standards organizations
are severely constrained due to public pressure. The
number of Europeans exposed to noise-related nuisances
from roads, railways and industries is continuously
on the rise; this has spurred
the need to improve the reliability of numerical and
experimental tools for estimating acoustic levels within
the soundscape.
Measured and/or modelled sound levels depend on a wide
array of physical phenomena: diffraction, diffusion,
reflection, etc. In particular, the combined influence
of micrometeorological effects and ground effects leads
to great sound dispersion as the distance to a sound
source increases. Such effects differ over highly-variable
time scales and their relative influence on the acoustic
field depends significantly on both the geometric configuration
and propagation conditions: average
vertical wind and temperature gradients, atmospheric
turbulence.
The benefit of setting up such a continuous monitoring
site for a long observation period (10 years) lies in
quantifying the influence of micrometeorological conditions
on acoustic field variability at the local scale (i.e.
site scale), in contrast with the regional scale (i.e.
Météo-France weather stations). These
research efforts focus on spatial aspects (site effects)
as well as temporal aspects (short vs. long term), in
the aim of deriving an estimation of space-time variability
of critical sound pressure levels (SPL) on any site over the short-,
medium- and long-term periods.
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The LCPC's Saint-Berthevin experimental site - General
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This LCPC-backed Development Project was initiated in
1999 and has been running since 2001, with a planned period
of operations covering 10 years. Its activities fall within
the scope of LCPC Research Project 11M041: "Outdoor sound propagation in heterogeneous medium" (2004-2007).
Although LTMS experimental data are primarily intended
to feed into the third topic studied
in this Research Project, they obviously will also be
used to advance on other topics. Thus, after recording, the
raw data must be processed, validated and analysed to
produce a statistical characterisation of the site (from
both a micrometeorological and acoustic standpoint); this
step enables determining the most influential parameters
behind acoustic propagation on such complex sites and
estimating the precision and representativeness of a given
measurement, especially over the "long-term periods"
(topic 2). Moreover, post-processed data also serve
the purpose of validating the acoustic and micrometeorological
numerical models developed by LCPC and/or associated research
institutes (topic 1).
These data furnish a permanent acquisition
(monitoring) over a 10-year period (sampling
interval: 10 sec) of the sound pressure levels
(global “A” -SPL- , 1/1 octave, etc.) and micrometeorological
characteristics (wind speed and direction, air and
ground temperature, rainfall, solar insolation,
etc.) at several points on the site via: five
5-m high acoustic masts (with 2 sensor heights),
two 25-m high meteorological towers (3 sensor
heights), and two 10-m high meteorological towers
(2 sensor heights). In conjunction with this
equipment, an onsite traffic counting station
is operational 24 hours a day 365 days a year.
Ground characteristics measurements are also performed regularly
(once a month) at 12 points on the site (optimised spatial sampling) to yield the sound
energy absorbed by the ground (acoustic impedance).
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The daily database set generated (approx. 10 megabytes/day) is next preprocessed,
synchronised, concatenated packed and then transferred
to a Web host site (with an FTP protocol).
Before each use, these data first undergo detailed validation
post-processing (using filters) in order to detect: sensor
malfunctions, parasitic noise events, etc. The various
tasks required for system hardware and software maintenance,
preventive and remedial monitoring, acquisition, data
preprocessing and post-processing are allocated considerable
human and technical resources by the Scientific and Technical
Network (STN) of the national ministry, with contributions coming mainly from LCPC, CETE-Western
Office and CETE-Normandy-Centre Office. In addition, the
metrological tracking of all site sensors (which entails
introducing sensor enhancements) is conducted every 2
to 3 years by Project Team member laboratories (see "Project
Team" composition below). This metrological tracking
consists of doubling the site's acoustic and micrometeorological
sensors with (calibrated) reference sensors of the same
type, followed by a comparative analysis to identify eventual
LTMS sensor malfunctions. Experimental data are next analysed
in collaboration with LCPC-affiliated research institutes,
including EDF R&D, SNCF, INRA, ECL, ECN, ENSMP, etc..
Project team (Team leader: B. Gauvreau -
LCPC Nantes):
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> LCPC Nantes (B. Gauvreau,
Ph. L'hermite, V. Gary): Lead "LTMS"
Development Project participant and team coordinator,
Administrative and financial management, Hardware
and software upgrades, Processing and analysis
of the experimental data, Communication and publications.
> CECP Angers (F. Lauzin,
C. Berlin, H. Poirier): Hardware and software
development and maintenance of LTMS systems, Feasibility
studies and operational implementation.
> LRPC Blois (B. Bonhomme,
H. Boutefol): Preventive and remedial maintenance,
On-site functions, technical management and regular maintenance,
Data archiving and processing.
> LRPC Clermont-Ferrand
(H. Lefèvre): Metrological tracking of
the LTMS.
> LRPC Lille (J.P. Deparis):
Metrological tracking of the LTMS.
> LRPC Strasbourg (D. Ecotière,
S. Doisy): Metrological tracking of the LTMS.
> CETE Western Office (C. Brochard):
Preventive and remedial maintenance of the "SIREDO"-type
road traffic counting station
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Unit responsible for station operations:
ESAR Division
Sector of activity:
Environment (Programme Committee
M)
Contacts
:
- Road
Maintenance, Safety and Acoustics Division
(ESAR)
- Road
and Urban Acoustics Unit (ARU)
-
Benoit
Gauvreau
A remarkable application example:
As a certified "Research Facility",
this experimental site has not been designed to
directly generate studies, but rather to enhance scientific knowledge in the field
of outdoor acoustic propagation,
by making use of the extensive experimental LTMS database to pursue:
numerical model validation (both acoustic and
micrometeorological) and (geo)statistical data
analysis (see the PDF summary presentation brochure).
This site has been selected for contribution to
the European "HARMONOISE"
project (6 th R&D Framework Programme), in
which LCPC had been involved (Workpackage 4) over
the period 2002-2004; furthermore, a number of
LCPC scientific publications have been intimately
associated:
> Articles published in journals with
an editorial board
- M. Bérengier, B. Gauvreau, Ph. Blanc-Benon,
D. Juvé, (2003), "Outdoor sound
propagation: A short review on analytical and
numerical approaches", Acustica united
with Acta Acustica, Volume 86(9)
- B. Lihoreau, B. Gauvreau, M. Bérengier,
Ph. Blanc-Benon, I. Calmet, (2006), "Outdoor
sound propagation modeling modeling in realistic
environments: A application of coupled parabolic
and atmospheric models", J. Acoust. Soc.
Amer., Accepté pour publication
> Books and papers submitted at conferences
with proceedings
- B. Gauvreau, M. Bérengier, Ph. Blanc-Benon,
N. Blairon, (2003), "Modelling of the propagation
in an atmospheric or topographic shadow zone
using the parabolic equation: comparisons with
in situ measurements", invited paper to
Euronoise 2003, Naples, Italie, mai 2003
- B. Lihoreau, B. Gauvreau, T. Pénelon,
I. Calmet, M. Bérengier, Ph. Blanc-Benon,
(2004), "Outdoor sound propagation modelling
in complex environments : A new PE code coupled
with a micrometeorological code", CFA/DAGA
2004, Strasbourg, mars 2004
- D. Ecotière, B. Gauvreau, Y. Brunet,
(2004), "Meteorological effects on long-range
sound propagation : evaluation of the long
term sound level using statistical analysis",
CFA/DAGA 2004, Strasbourg, mars 2004
- O. Baume, B. Gauvreau, M. Bérengier,
F. Junker, F. Lauzin, (2004), "Long term
monitoring site at Saint-Berthevin (France-53) :
a tool for traffic noise characterization using
space and time statistical variability of acoustical
and meteorological events", CFA/DAGA 2004,
Strasbourg, mars 2004
- Ph. Blanc-Benon, B. Lihoreau, T. Pénelon,
B. Gauvreau, I. Calmet, M. Bérengier
(2004), "Outdoor sound propagation modelling
in complex environments : A new PE code
coupled with a micrometeorological code",
LRSP 2004, Penn State, Juin 2004
- B. Gauvreau, B. Lihoreau, M. Bérengier,
Ph. Blanc-Benon, I. Calmet, (2005), "A
coupling method for SPL predictions in complex
situations using acoustic and micrometeorological
numerical codes", Forum Acusticum 2005,
Budapest (H), Aout 2005
- O. Baume, B. Gauvreau, M. Bérengier,
F. Junker, H. Wackernagel, J.P. Chilès,
(2005), "Statistical exploration of small-scale
variation in acoustic time series taking into
account micro-meteorological stability conditions",
Forum Acusticum 2005, Budapest (H), Aout 2005
- B. Gauvreau, B. Lihoreau, M. Bérengier,
Ph. Blanc-Benon, I. Calmet, (2005), "Estimating
long-term representative SPL in complex environments
using a coupling method based on acoustic (MW-WAPE)
and micrometeorological (SUBMESO) numerical
predictions", Internoise 2005, Rio (B),
Septembre 2005
- B. Gauvreau, B. Bonhomme, H. Lefèvre,
F. Lauzin, (2006), "Un outil expérimental
pour l’analyse statistique et la validation
des modèles numériques :
la Station de Long-Terme du LCPC à Saint-Berthevin
(France-53)", Congrès Français
d’Acoustique 2006, Tours (F), Avril 2006
- O. Baume, B. Gauvreau, M. Bérengier,
F. Junker, H. Wackernagel, J.P. Chilès,
(2006), "Exploration statistique de fluctuations
temporelles à petite échelle des
grandeurs acoustiques et micrométéorologiques
", Congrès Français d’Acoustique
2006, Tours (F), Avril 2006
- B. Gauvreau, B. Lihoreau, M. Bérengier,
Ph. Blanc-Benon, I. Calmet, (2006), "Une
méthode de couplage de modèles
acoustique et micrométéorologique
pour la prévision des niveaux sonores
de long-terme en situation complexe", Congrès
Français d’Acoustique 2006, Tours
(F), Avril 2006
> Research reports, including reports
on contracted research work
- B. Gauvreau & M. Bérengier, HARMONOISE
european research project - WP4 -
LCPC final report, 2004
- V. Zouboff, B. Gauvreau, Y. Brunet, M. Bérengier,
(2005), " Méthode de reconstitution
d’un niveau sonore de long terme -
Principe et applications ", Coll. Études
et Recherches des Laboratoires des Ponts et
Chaussées, Ref CR36, mars 2005
Technical characteristics:
The Saint-Berthevin site was selected in accordance
with a set of specifications that established
the primary characteristics:
- A complex topography: valley without any
major obstacles (unbuilt), and a flat and unobstructed
landform beyond the valley;
- A roadway crossing the valley on a viaduct
with a traffic volume in excess of 15,000 vehicles
per day;
- A relatively homogeneous ground composition
in terms of acoustic impedance (pastureland, cropland);
- No significant modifications planned over
the next 10 years (e.g. no approved real estate
development, infrastructure);
- Proximity to a regional Météo-France
weather station; and
- Secondary noise source (SNCF railway) in the
vicinity, easily identifiable and not parasitic.
The acoustic masts and meteorological towers were located
to enable studying the influence of topography: valley
floor, halfway up the slope, at the slope break
and on the plateau. For each of these positions,
an acoustic mast was installed 280 m from the
edge of the A81 highway. This distance satisfies
the criterion adopted in Article 6 of the May
5, 1995 ordinance with respect to road infrastructure
noise, which makes it mandatory to conduct acoustic
impact studies that incorporate meteorological
effects for sites at distances beyond 250 m. Each
acoustic mast corresponds with a meteorological
tower, except for the mid-slope position: the acoustic
mast was moved onto the opposite slope to serve
as a reference at the railway noise source (SNCF
line). A reference acoustic mast was also installed
near the highway, close to a road traffic counting
station. All data collected is relayed by means
of a fixed network crossing the site via an RS485-type
series connection leading to a central computing
unit set up inside an air-conditioned bungalow
on the valley floor. At midnight GMT, the database
is concatenated and the radio clock queried to
reset all 10 stations to the right time. Data
acquisition for the following day begins by automatically
calibrating the 9 acoustic measurement sequences
programmed to commence 20 seconds after midnight.
This calibration may also be performed manually
using a conventional calibrator through an RA0009-type
adaptor.
Acoustics: All acoustic masts
are installed at a distance of 280 m from the
source and feature two measurement heights: 2
m and 5 m. The mast located at the highway edge
only takes measurements at a height of 2 m above
the roadway. The data acquisition units for the
5 acoustic masts store the following equivalent
continuous energetic levels every 10 sec:
- Leq10s for each octave bandwidth,
in dB,
- Leq10s for the global level, in dB(A)
- 01dB-Stell acquisition units of the
"SALTO" type ("Symphonie"
module connected to a local computing
unit installed in the case contained on
each mast).
- GRASS microphone sensors, G-41CM model:
"External microphone unit, 90°,
land-based noise"
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Micrometeorology: two
25 m high towers are positioned on the valley floor and
on the plateau. Wind speed, wind direction and
temperature are recorded at heights of 3, 10 and
25 m. Two 10-m high meteorological towers are placed
at the mid-slope and slope break on the plateau
border. These towers measure wind speed, wind direction
and temperature at heights of 3 and 10 m. In addition,
the LTMS provides ground temperature measurements
at depths of 2, 5, 10, 20 and 100 cm along with
a relative humidity reading 3 m above ground level.
The plateau tower also features a solarimeter and
pluviometer. The characteristics of these sensors
are summarized as below:
- M1: "CAMPBELL Scientific" sensors
(3 measurement heights: 3 m, 10 m and 25 m)
- Wind direction: Vectors Instruments W200P
probe
- Wind speed: Vectors Instruments A100L2
probe
- Air (ventilated) temperature: Vectors
Instruments T302 probe
- Data acquisition system: CR23X
- M2: "CAMPBELL Scientific" sensors
(3 measurement heights: 3 m, 10 m and 25 m)
- Wind direction: Vectors Instruments W200P
probe
- Wind speed: Vectors Instruments A100L2
probe
- Air (ventilated) temperature: Vectors
Instruments T302 probe
- Data acquisition system: CR23X
- M3: "CAMPBELL Scientific" sensors
(3 measurement heights: 3 m, 10 m and 25 m)
- Wind direction: Vectors Instruments W200P
probe
- Wind speed: Vectors Instruments A100L2
probe
- Air (ventilated) temperature: Vectors
Instruments T302 probe
- Data acquisition system: CR23X
- M4: "CAMPBELL Scientific" sensors
(3 measurement heights: 3 m, 10 m and 25 m)
- Wind direction: Vectors Instruments W200P
probe
- Wind speed: Vectors Instruments A100L2
probe
- Air (ventilated) temperature: Vectors
Instruments T302 probe
- Data acquisition system: CR23X
- Relative humidity: Rotronic MP100A probe
- Pluviometer (heat-free RM): Young 52203
probe
- Solarimeter - pyranometer: Kipp &
Zonen SP-LITE probe
- Ground temperature (depths: -2 cm, -5
cm, -10 cm, -20 cm and -1 m): Thermistance
107 probes
Road traffic: The "SIREDO"-type
road traffic counting station was adapted to this particular
context. By means of two loops and one piezoelectric
sensor per roadway, a measurement sequence yields
the following possibilities:
- discriminating among 14 vehicle types (weight,
length, number of axles)
- indicating a given vehicle's lane assignment
- associating a precise timestamp with each
vehicle
- providing the exact speed of each vehicle
Upcoming trends
Hardware upgrades (three-dimensional sonic anemometers,
cloud cover and humidification sensors, etc.)
and software upgrades (transition to 1/3 octave
for acoustics, computations of atmospheric turbulence
parameters, etc.) are scheduled over 2006 and
2007. Plans also call for developing and implementing
a permanent system for monitoring ground characteristics
at any point onsite (impedance), independently
of measurement locations targeted by regular campaigns
with optimised spatial sampling (12 measurement
points).
For further information:
> Road
Maintenance, Safety and Acoustics Division
(ESAR)
>
Ongoing research project entitled: "Outdoor sound propagation in heterogeneous medium"
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Summary
presentation of the LTMS 
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