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A review of current debates on noise-mapping

5th UK CARE Annual General Meeting Cambridge, 2005. A review of current debates on noise-mapping. Professor Jian Kang 康健 School of Architecture, University of Sheffield United Kingdom. I mportant to predict urban noise contribution

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A review of current debates on noise-mapping

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  1. 5th UK CARE Annual General Meeting Cambridge, 2005 A review of current debates on noise-mapping Professor Jian Kang 康健 School of Architecture, University of SheffieldUnited Kingdom

  2. Important to predict urban noise contribution • While noise-mapping widely used, especially in the EU, there are still serious debates about the validity.

  3. ResearchersMicro-scale modelling for urban sound propagation • Theories and models: • Image source method, with or without interferences • Ray tracing • Radiosity • Acoustic particle transport theory • Wave-based models • finite element method (FEM) • boundary element method (BEM) • equivalent sources method (ESM) • finite difference – time domain method (FDTD) • parabolic equation (PE) method square street Special issues of <Applied Acoustics>, and European Journal of Acoustics

  4. PractitionersMacro-scale modelling for urban sound: noise mapping • Can be used for very large urban area (whole city) • Over 10 software packages developed • Consider various sources, various configurations • Attractive output • With GIS, predict affected population … • Every EU city is mapping, now also UK - London done • But, based on algorithms from standards, 30 years old, calculator based … Hong Kong M1 outside Sheffield Sheffield centre

  5. Debates: against • A letter in <Acoustics Bulletin> from Professor B. Shield (researcher) • ‘very worried by the way in which noise mapping has been accepted, apparently without question, by the acoustics community in the country’ • Accuracy - very few were concerned about accuracy and no proofs were achieved to substantiate the claim that ‘the predictions are within 2 or 3 dB of measured levels’. • Cost - the acquisition and input of data with the production of a noise map ‘would take many weeks or months of a person’s time’. • Necessity of noise mapping - the maps only mapped traffic on major urban roads, but ‘most experienced noise consultants could produce an accurate noise map if given a street map and a red pen’. • Policymaking - policy is currently being driven by 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’

  6. Debates: for Tompsett (software developer) • Accuracy – • software developers were always ‘intensely’ interested in accuracy and had spent much time on it • often with a standard error of ±2 dB (A). • since the calculation is usually compared with a measurement rather than the ’real answer’, ‘a clear definition of accuracy is not obvious’. • Cost - £13m for a national noise map seems very modest compared with some typical budgets for Highways Agency. • Necessity of noise mapping - the presentation of noise mapping can make politicians and the public better understand and treat the noise as a serious issue. London results still not published… • 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

  7. Debates: for Noise mapping useful for relative comparison • Actual measurements can only be a small sample of the sound environment over much longer periods of time. Since the actual sound levels tend to vary considerably, due to the source variation, temperature and wind conditions, for example, short-term measurements could be rather unrepresentative. • Comparing sample measurements taken under different meteorological conditions between two different sites might be unreasonable. • In a calculated map, any differences in the outputs are then solely due to the differences in the input data that are taken into account by the computation. Noise mapping useful for relative effectiveness of a treatment/change Either calculated or measured specific noise levels can be compared before and after development (change), against the context set by the pre-existing background noise - Noise mapping needs only to be as complex as is actually required for the purpose for which the noise map is intended

  8. So? • Not accurate? • Many advantages • No alternative way • A process which cannot be stopped! • Integrate micro-scale techniques to noise mapping • Improve the accuracy • Strategic application A bridge between researchers and practitioners Some of our work …

  9. CASE STUDIES Acceptable accuracy with busy urban areas where the direct sound is generally dominant. Less so for situations where reflection and diffraction more important.

  10. COMPARISON WITH IMAGE SOURCE METHOD SPL difference of the noise mapping calculation with reference to the image source model

  11. SIMPLIFICATION OF ROOF FORM

  12. GAPS BETWEEN BUILDINGS

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