A review of current A review of current debates on noise-debates on noise-

mappingmapping

Professor Jian KangProfessor Jian Kang

康健康健School of Architecture, University of School of Architecture, University of

SheffieldSheffield United KingdomUnited Kingdom

5th UK CARE Annual General MeetingCambridge, 2005

Important to predict urban noise Important to predict urban noise contributioncontribution

While noise-mapping widely used, While noise-mapping widely used, especially in the EU, there are still especially in the EU, there are still serious debates about the validity. serious debates about the validity.

ResearchersResearchersMicro-scale modelling for urban sound Micro-scale modelling for urban sound

propagationpropagation Theories and models:Theories and models:

Image source method, with or without interferencesImage source method, with or without interferences Ray tracingRay tracing RadiosityRadiosity Acoustic particle transport theoryAcoustic particle transport theory Wave-based modelsWave-based models

finite element method (FEM) finite element method (FEM) boundary element method (BEM)boundary element method (BEM) equivalent sources method (ESM)equivalent sources method (ESM) finite difference – time domain method (FDTD)finite difference – time domain method (FDTD) parabolic equation (PE) methodparabolic equation (PE) method

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20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95

接受点位置 (米)

声压

级( 分

贝)

street

square

Special issues of <Applied Acoustics>, and European Journal of Acoustics

Can be used for very large urban area (whole Can be used for very large urban area (whole city)city)

Over 10 software packages developedOver 10 software packages developed Consider various sources, various Consider various sources, various

configurationsconfigurations Attractive outputAttractive output With GIS, predict affected population …With GIS, predict affected population … Every EU city is mapping, now also UK - Every EU city is mapping, now also UK -

London doneLondon done But, based on algorithms from standards, But, based on algorithms from standards,

30 years old, calculator based …30 years old, calculator based …

PractitionersPractitionersMacro-scale modelling for urban sound: Macro-scale modelling for urban sound:

noise mappingnoise mapping

Sheffield centre

M1 outside Sheffield

Hong Kong

Debates: Debates: againstagainst A letter in <Acoustics Bulletin> from Professor B. Shield A letter in <Acoustics Bulletin> from Professor B. Shield

((researcherresearcher)) ‘‘very worried by the way in which noise mapping has been very worried by the way in which noise mapping has been

accepted, apparently without question, by the acoustics accepted, apparently without question, by the acoustics community in the country’ community in the country’

AccuracyAccuracy - very few were concerned about accuracy and no proofs - very few were concerned about accuracy and no proofs were achieved to substantiate the claim that ‘the predictions are were achieved to substantiate the claim that ‘the predictions are within 2 or 3 dB of measured levels’.within 2 or 3 dB of measured levels’.

Cost Cost - the acquisition and input of data with the production of a noise - the acquisition and input of data with the production of a noise map ‘would take many weeks or months of a person’s time’.map ‘would take many weeks or months of a person’s time’.

Necessity of noise mappingNecessity of noise mapping - the maps only mapped traffic on major - the maps only mapped traffic on major urban roads, but ‘most experienced noise consultants could produce urban roads, but ‘most experienced noise consultants could produce an accurate noise map if given a street map and a red pen’.an accurate noise map if given a street map and a red pen’.

PolicymakingPolicymaking - policy is currently being driven by noise mapping - - policy is currently being driven by noise mapping - should be developed independently of noise mapping.should be developed independently of noise mapping.

Supported by letters from Jopson and Maning (consultants) with some other points• Need more budget• Input from experienced people• A ‘transportation noise strategy’ rather than a national strategy to deal with all sources – ‘too wild a dream’

Debates: Debates: forforTompsett (Tompsett (software developersoftware developer) ) AccuracyAccuracy – –

software developers were always ‘intensely’ interested in software developers were always ‘intensely’ interested in accuracy and had spent much time on it accuracy and had spent much time on it

often with a standard error of ±2 dB (A). often with a standard error of ±2 dB (A). since the calculation is usually compared with a measurement since the calculation is usually compared with a measurement

rather than the ’real answer’, ‘a clear definition of accuracy is rather than the ’real answer’, ‘a clear definition of accuracy is not obvious’. not obvious’.

CostCost - £13m for a national noise map seems very modest - £13m for a national noise map seems very modest compared with some typical budgets for Highways Agency.compared with some typical budgets for Highways Agency.

Necessity of noise mappingNecessity of noise mapping - the presentation of noise - the presentation of noise mapping can make politicians and the public better mapping can make politicians and the public better understand and treat the noise as a serious issue. understand and treat the noise as a serious issue.

Turner (Equipment/consultancy) and Hinton (EC Working Group/ Birmingham City) • EU tendency• DEFRA is carrying out a wide-ranging study regarding the modelling process • a platform for further refinement and development

London results still not published…

Debates: Debates: forfor

Actual measurements can only be a small sample of the sound Actual measurements can only be a small sample of the sound environment over much longer periods of time. Since the environment over much longer periods of time. Since the actual sound levels tend to vary considerably, due to the actual sound levels tend to vary considerably, due to the source variation, temperature and wind conditions, for source variation, temperature and wind conditions, for example, short-term measurements could be rather example, short-term measurements could be rather unrepresentative.unrepresentative.

Comparing sample measurements taken under different Comparing sample measurements taken under different meteorological conditions between two different sites might meteorological conditions between two different sites might be unreasonable.be unreasonable.

In a calculated map, any differences in the outputs are then In a calculated map, any differences in the outputs are then solely due to the differences in the input data that are taken solely due to the differences in the input data that are taken into account by the computation. into account by the computation.

Noise mapping useful for relative comparison

Either calculated or measured specific noise levels can be compared Either calculated or measured specific noise levels can be compared before and after development (change), against the context set by the before and after development (change), against the context set by the pre-existing background noise - pre-existing background noise - Noise mapping needs only to be as Noise mapping needs only to be as complex as is actually required for the purpose for which the noise complex as is actually required for the purpose for which the noise map is intendedmap is intended

Noise mapping useful for relative effectiveness of a treatment/change

So?So? Not accurate?Not accurate? Many advantagesMany advantages No alternative wayNo alternative way A process which cannot be stopped!A process which cannot be stopped!

Integrate micro-scale techniques to Integrate micro-scale techniques to noise mappingnoise mapping

Improve the accuracyImprove the accuracy Strategic applicationStrategic applicationA bridge between researchers and A bridge between researchers and

practitionerspractitionersSome of our work …

CASE STUDIESCASE STUDIES

Acceptable accuracy with busy urban areas where the direct sound is generally dominant.

Less so for situations where reflection and diffraction more important.

COMPARISON WITH IMAGE SOURCE COMPARISON WITH IMAGE SOURCE

METHODMETHOD

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Source-receiver distance (m)

SP

L d

iffe

renc

e (d

B)

R=1

R=3

R=5

R=10

R=20

SPL difference of the noise mapping calculation with

reference to the image source model

SIMPLIFICATION OF ROOF FORMSIMPLIFICATION OF ROOF FORM

GAPS BETWEEN BUILDINGSGAPS BETWEEN BUILDINGS