Guide to Predictive Modelling for Environmental Noise Assessment This guide has been prepared for all parties who commission, undertake or use environmental noise predictions for commercial or industrial operations, of whatever type or scale, for which an environmental noise assessment may be required. It provides: Introductory information on environmental noise modelling Guidance on risks associated with the use of environmental noise modelling for decision-making An account of sound propagation theory A guide to standards, regulations and other guidance in this area A decision procedure for the design and use of environmental noise models Contents Introduction Environmental Noise Modelling: Introduction What is environmental noise modelling? What are environmental noise models used for? What information is needed to construct a noise model? Models in general use and their intrinsic limitations and risks How reliable is environmental noise modelling? Are there standardised methods of modelling? Risk in Environmental Noise Assessment: Risk, variability and uncertainty Factors affecting risk in environmental noise predictions Input data Algorithms for outdoor sound propagation Propriety software Other factors related to the ways in which models are used in practice Sound propagation theoryStandards, regulations and guidance notes Designing environmental noise models - decision procedure: Review the requirement for predictions Preliminary screening study Detailed model design Physical environment Sources Propagation Algorithm Execute calculations Analyse and report GlossaryLinks 1. Introduction 1.1Authorship This guide has been prepared on behalf of the Department of Trade Industry (DTI) under the National Measurement Systems Acoustics Programme 2004-2007, managed by the National Physical Laboratory. Whilst this material has been prepared in consultation with the DTI, the views and judgements expressed in this guide are those of the authors and do not necessarily represent those of the DTI and NPL. The document on which this guide is closely based has been prepared by Hoare Lea Acoustics. The material contained herein has been approved and guided by a Project Board, with the following attendees: Acoustics Group, National Physical LaboratoryAcSoft Casella Stanger (now Bureau Veritas) DTI (now BERR) Environment Agency Environmental acoustics Hoare Lea Institute of Acoustics 1.2Purpose This guide has been prepared for all parties who commission, undertake or use environmental noise predictions for commercial or industrial operations, of whatever type or scale, for which an environmental noise assessment may be required. The guidance is directly relevant to predictive studies carried out in support of the following types of assessment: Pollution Prevention and Control (PPC) permitting BS 4142 and BS 9142 based investigations Planning condition compliance Development of site specific noise mitigation methodologies The guide is intended to: Raise awareness of the utility of environmental noise prediction studies Raise awareness of the inherent variability of environmental noise fields, and the subsequent risk of incorrect assessment outcome that may result when attempting to utilise any objective rating method Provide an understanding of the types of potentially significant risks involved in using environmental noise predictions to inform decision making processes Promote the management of such risks from the outset of an investigation by adopting a structured approach to the design of prediction studies that recognises the relationship between variability, uncertainty and risk Raise awareness of the unavoidable practical, technical, and commercial limitations that prevail in all methods of noise assessment, and of the conclusion that limited assessment resources are best focussed on reduction of risk rather than of uncertainty Assist users to balance the risks arising from a restricted predictive study against other constraints and considerations, and thus identify instances where alternative assessment methods may need to be considered Whilst this guide primarily addresses issues surrounding situation specific modelling for industrial and commercial noise immissions, the principles contained in it also have relevance for broader applications of environmental noise modelling. 1.3Other sources of guidance The uncertainties and challenges involved in large scale noise modelling have received considerable attention under European Union Directives that establish requirements for strategic noise modelling of transportation and industrial noise sources. However, this attention has been primarily focussed on the consideration of harmonised methodologies for strategic applications. In contrast, localised industrial and commercial noise issues require modelling techniques driven by different information requirements and constraints. The principles contained in the guide share important synergies with BS 9142 (available from IEMA Publications) and the guidance produced under the NMS project on managing risks associated with environmental noise measurements (see Hoare Lea's project web page). An understanding of the guidance provided by these documents will be of assistance when the use of environmental noise predictions is being considered.

Other published sources of information on environmental noise prediction are listed in the document bibliography. The advice contained in this guide should be read in conjunction with any other standards or codes of practice directly applicable to a given assessment. The advice is not intended to conflict with any existing standards, regulations or guidelines concerned with environmental noise assessment, and where any such conflict is found to exist, then users of this guidance should note that existing regulations take precedence. In the case of conflict with standards and guidelines, users will have to decide for themselves how best to proceed, but they should also provide a clear justification for any decisions made. It is permissible to deviate from non-statutory standards and guidelines where deviation can be justified by reference to the facts of any particular case. .Environmental Noise Modelling 2.1 Introduction risks associated with using noise predictions requires clear e an overview of environmental noise modelling to address tal Noise Modelling? s of theoretically estimating noise will be a fixed stimating noise for a specific set of , or sources, for which associated s ons ironment, to the receiver location or region of interest 2Management of the communication of the relevant issues between practitioners and the end users of the information. It is therefore necessary for all parties involved to have some appreciation of what is involved when producing environmental noise models and thrange of approaches that can be adopted. In particular, what it is that a noise model will represent, for which types of applications do models offer useful information, and what are the relative benefits and limitations of modelling compared to other types of objective assessment? The following providesthese types of questions, and thus provide a basis on which non-technical parties can engage with practitioners. 2.2 What is EnvironmenEnvironmental noise modelling describes the proceslevels within a region of interest under a specific set of conditions. The specific set of conditions for which the noise is being estimatedrepresentation or 'snapshot' of a physical environment of interest. However, in practice the physical environment will usually not be fixed, but will be characterisedby constantly varying conditions. These variations in real world conditions will subsequently cause the actual sound field to vary in time and space. Thus it is important to recognise that the output of an environmental noise model will onlyrepresent an estimate for a snapshot of the range of actual environmental noise levels that could occur in time and space. Recognising that modelling is a means of econditions, attention is now directed to defining what these conditions are. The key conditions that a noise model relates to are: An approximation of the noise sourceenvironmental noise levels are of interest An approximation of the physical environment through which noise willtransmit from the noise source(s) to the location or region of interest. Thiincludes the ground terrain, the built environment, and atmospheric conditi(e.g. wind, temperature, humidity) An approximation of the way in which sound will travel from the input noise source(s) via the input physical env Thus, producing an environmental noise model involves defining a series of noise sources to be investigated, describing acoustically significant features of the nvironment through which sound will propagate to the receiver, and then applying a se below ecalculation method that accounts for these descriptions to produce an estimated noilevel at a location or region of interest. To demonstrate this concept, Figure 1provides a schematic illustration of the simplest type of environmental noise model, involving a single sound source, radiating sound via a single transmission path, to a single location in the surrounding space: Figure 1:The simplest type of model practice, environmental noise models will often be more complex, involving a multiple complex transmission paths, to ultiple locations of interest.e, via each transmission path to each and every ceiver location. The total sound level at each position is then calculated by summing f equal estimated noise level nd depict trends in the spatial pattern of the sound field: Inmultiple sound sources, transmitting vim In these more complex scenarios, the environmental noise model is repetitiously calculated for each sound sourcrethe contribution of each source and transmission path. Application of these calculations to each point on a uniformly distributed grid enables a noise contour map to be developed to depict regions oa Figure 2:Example contour map produced from an environmental noise model

2.3What are environmental noise models used for? Environmental noise predictions are used in an increasing range of decision-making applications. The most common application is for assessments where a decision is to be made regarding some future change to an environmental noise field. However, given the practical and technical challenges to noise measurement strategies, there are an increasing number of situations in which predictions complement or substitute for measurement-based noise assessment techniques. Common uses of predictions for practical noise assessment purposes are as follows: Forecasting the impacts or benefits of proposed changes to an environmental noise field such as introduction, change or removal of a commercial/industrial ment that affect noise propagation, such as the construction or removal of barriers or enclosures. Assessment of existing commercial/industrial installations where the needs to be evaluated. ed variability in measurement installation, or modification of significant features in the physical environeffectiveness of different noise mitigation strategiesPredictions can be used to rank the relative contributions of individual component sources of an installation comprising multiple complex sources. These rankings can then be used to focus noise mitigation resources on to the component sources whose treatment will enable the greatest reduction in total noise levels. Investigating the results of a measurement study to better understand the causes of the measured levels. For example, predictions may be used to assist the investigation of observed but unexplainresults. Alternatively, predictions may be used to provide an estimate of the extent to which a particular source, or group of sources, may have influenced the total noise level measured from all sources affecting the environment in question. Complementing the results of measurement studies to investigate a wider range of locations, time periods or noise sources than could be directly investigated with measurements. Assisting the design of measurement studies by using predictions to understand the possible criticality of the situation before committing to expensive measurement studies. The predictions can be used to identify situations that are most critical to the assessment outcome, such as locations where noise levels might be expected to be similar to some threshold value where the assessment outcome significantly differs. This knowledge can then be used to design the measurement study in a way that focuses the available resources on the most effective strategy. A further benefit of predictions used in this way is the reference it provides when conducting post measurement analysis to judge the validity of a set of measurements, and whether there are any aspects of the results that differ from original expectations and subsequently warrant specific explanation or further investigation.

2.4What information is needed to construct a noise model? Approaches to environmental noise modelling vary in terms of the complexity wwhich each element of the model is described and analysed. However, irrespective ofthe chosen approach, the key information to all predictive studies is the systematic representation of the noise sources to be investigated, and theith physical environment rough which noise will transmit to the receivers. Once these are defined, an estimate o thof the way in which noise will travel from the noise sources to the receivers is alsrequired. Table 1 shows the requirements for specifying a noisy environment: StageMinimum requirementsOther information that may be requiredThe noise sources to be investigated Number of sound sources Total sound power output of each source Directional characteristics of each source Height of each source Frequency characteristics of each source Time variations of emissions Information to determine which value or range of values best correlates to the conditions for which the assessment will apply. For example, a worst-case assessment would imply the use of the highest possible value irrespective of how frequently it may occur, whilst an assessment which related to 'typical' conditions could necessitate the use of an averaged value or some typically recurring upper value The physical environment through which noise will transmit to the receivers Separating distances between all relevant noise sources and receivers Reflecting/obstructing structures Height(s) of receiver(s) Ground terrain profile Characteristics of the ground cover Meteorological conditions relevant to the intentions of the assessment (e.g. worst case such as downwind propagation, or generally recurring long term conditions). These may include wind direction and speed, variations with wind and temperature with height above ground, temperature, and humidity Table 1:Requirem To estimate the way in which noise will travela range of sound propagation methodologies m ods vary widely in their complexity and the scope of applications for which they can offer meaningful ents of the specification of a noisy environment from the noise sources to the receivers,ay be employed. Methpredictions. The most basic spherical' spreaas a sound wave front sprfor ation methodolo'hemi-din co ity are For common types of noise sources in relativelcase where separating distances are relatively sstructures to impede noise propagation, this typvironmental noise levels. These methods rely on a combination of of noise through the atmosphere ht rce and a receiver location ulti-source industrial/commercial t is instances where there is a large margin m of propag gy is described as 'spherical' orunts for the reduction in sound intensa.y simple environments, as may be the mall and there are no intervening e of method is often sufficient for g. This method simply aceads over a larger estimation purposes. In instances where the noise sources are more complex and/or account must be made of the influence of significant features of the physical environment, more robust and detailed information is needed to describe the propagation of noise. In most types of practical applications, engineering methods will provide the most viable basis for predicting enacoustic principles and empirical knowledge to provide a means of estimating the influence of a range of phenomena, including: The absorption associated with the passageThe change in noise level that occurs as a result of interactions between the sound wave travelling directly to the receiver and those reflected from the ground, accounting for influence of the ground cover type The attenuation offered by obstacles that fully or partly obstruct line of sigbetween a souThe influence of atmospheric conditions that can change the direction of an advancing sound wave front by refracting the wave at points where there are significant changes in wind speed and/or temperature The influence of reflecting surfaces that re-direct an advancing sound wave front Engineering methods can therefore take account of a wide range of factors that fluence noise propagation, and their use for m ininstallations can become complex when all relevant paths of sound transmission are taken into account. Whilst these methods provide a robust way of describing sound propagation in many general applications, it must be recognised that there will be more complex situations where their description does not properly account for whawill actually happen in practice. Example situations include assessments relating to noise sources with very distinct frequency characteristics and, in particular, situationswhere the influence of different aspects of the physical environment cannot be considered in isolation. erefore important that they are used with proper regard t It is th o their limitations. Thmay mean that their descriptions are only relied upon for very broad value estimatesof the noise where feasible to do so (e.g. inbetween the predicted value and the decision threshold). Alternatively, it may be a case of correcting the predicted values where the limitations can be quantified. In some instances though, it may be necessary to discard the results provided by engineering methods, and either refer to more advanced analytical methods or seek analternative to predictions as a basis for informing the assessments. The limitations ofengineering methods, and possible alternative approaches, are discussed further in subsequent sections. cal effects, these methods allow a better tracking of the fluence of specific meteorological conditions on noise levels, such as upwind or thods within ed user-specified tmospheric conditions. The BEM includes the effects of sound diffraction due to Perhaps the mostpowerful current the ontally stratified medium. The method provides an exact solution of the elmholtz equation, except within a wavelength or so of the source, but is restricted ed atmosphere and a homogeneous ground surface. Therefore, ns. a tems with a layered tmosphere and a homogeneous ground surface. The PE method, Euler-type finite- 2.5Models in general use and their intrinsic limitations and risks Practical engineering methods: The technique adopted by these models involves the calculation of noise levels by adding the separate contributions that each sound attenuation factor has on noise propagation. The common factor in all these models is that they are mainly based onempirical results. In general, they are simple and easy-to-use. Approximate semi-analytical methods: These methods retain the same practical structure as engineering methods, but are based on simplified analytical solutions of the acoustic wave equation rather than empirical results. While the practical engineering methods only take into account averaged meteorologiindownwind situations. Simple ray tracing models are the most popular methis category. Numerical methods: This group includes methods such as the Fast Field Program (FFP), the Parabolic Equation (PE) and the Boundary Element Method (BEM). These methods are bason the numerical solution of the wave equation. The FFP and BE allow the calculationof sound propagation over non-complex level terrain with any alarge obstacles and more complex terrains.outdoor sound propagation numerical models are Euler-type finite-difference time-domain models (see, e.g., D Heimann, A linearized Euler finite-difference time-domain sound propagation model with terrain-following coordinates, Journal of Acoustical Society of America, vol. 119, issue 6, p. 3813, 2006). The FFP (or "wave number integration method") gives the full wave solution for the field in a horizHto systems with a layersystems with a range-dependent terrain (either in terms of ground impedance or terrain shape), or with a range-dependent atmospheric environment (variable sound speed profile with range) cannot be modelled with the FFP method. This makes the model inappropriate for use over long distances or with mixed ground conditioFurthermore, the computing time is often considerable. FFP is not so efficient sincethe ground has to be flat and homogeneous, and the atmosphere is described by succession of horizontal layers (no range-dependency). In contrast to the FFP method, the Parabolic Equation (PE) method, which is based on an approximate form of the wave-equation, is not restricted to sysadifference time-domain models and the Lagrangian sound particle model are theonlycurrents technique that can handle environmental range-dependent variations. There are three limitations to the PE method: PE algorithms only give accurate rein a region limited by a maximum elevation angle, ranging from 10 to 70 or even higher depending on the angle approximation used in the derivation of the parabolic equation; the computing time for a complete spectrum is often considerable, particularly for to the calculation of frequencies above 600 Hz; scattering by sound speed gradients in the direction back to the source is neglected. In other words, a parabolic equation is a one-way wave equation, taking insults to account only sound waves avelling in the direction from the source to the receiver. As the sound speed is on ffects for individual frequencies in certain conditions, they provide the basis for the mber trusually a smooth function of position in the atmosphere, the one-way wave propagation approximation is usually a good one, but, when turbulence is to be taken into account, this limitation must be considered. Since hybrid methods can provide highly accurate representations of propagatie'reference model' used to validate the engineering method produced by HARMONOISE, an EU project which has produced methods for the prediction of environmental noise levels caused by road and railway traffic. These methods are intended to become the harmonized methods for noise mapping in all EU MeStates. The methods are developed to predict the noise levels in terms of Lden and Lnight, which are the harmonised noise indicators according to the EnvironmentalNoise Directive 2002/49/EC. Since the techniques are computationally intense they are most commonly only employed for 2D prediction. Furthermore, the methodsnot widely available within common commercial software. In summary, numerical methods have many stren are gths, mainly in accuracy, and eaknesses, mainly in practical application. None of the methods is capable on its on method must ic gation under specific eteorological conditions. The problem is that they yield results for only those evels. n merically-derived methods is used for complex situations. The eneral principle of these methods is to solve the wave equation or Helmholtz lytic Helmholtz equation, therefore it is necessary to use wown of handling all possible environmental conditions, frequencies and transmissiranges of interest in practical applications. One method will be more appropriate thananother for a particular problem scenario, and thus selection of the best be situation specific. For information on the PE, see K E Gilbert, M J White, Application of the parabolequation to sound propagation in a refracting. atmosphere, J. A. S. A. 85, pp.630-637, 1989. Details of the BEM are given in S N Chandler-Wilde, The boundary element method in outdoor noise propagation, Proceedings of the Institute of Acoustics 19(8), 27-50, 1997. These methods are extremely useful for analysing the propamspecific conditions and give little indication of statistical mean values of sound lAlso, the user must provide substantial amounts of information. This information cabe difficult to generate, such as complete profiles of wind and temperature.. Hybrid models: A group of hybrid, nugequation to deduce the sound field. The procedure for solving the wave equation is generally difficult to implement due to the complexity of the atmospheric-acoustic environment. In fact, except for the very simplest boundary conditions and uniformmedia (which rarely occur in reality), it is not possible to obtain a complete anasolution for either the wave or numerical methods. Several different types of solution for the sound field have evolved over the past few decades: ray tracing provides a visual representation ofield, the FFP is accurate but computationally intensive and the PE is an approximation to the wave equation that has been solved using explicit and implicit finite different schemes. f the els are fast to compute and providing a pictorial representation, in t by , s, and ome by Sachs and Silbiger describe a caustic correction (Sachs, D. ., Silbiger, A., "Focusing and refraction of harmonic sound and transient pulses in n ver used due to their otably a Attenborough, Keith, Ground parameter information for propagation Ray-tracing modthe form of ray diagrams, of the sound field. Further advantages of ray tracing are thathe directionality of the source and receiver can be fairly easily accommodated,introducing appropriate launch- and arrival-angle weighting factors; and rays can betraced through range-dependent sound speed profiles. Ray-tracing models are limited in capability only as a consequence of the approximation leading to the ional equation. This imposes restrictions on the physicswhich in turn limit the applicability of ray theory. Two major anomalies can arise from these limitations: predictions of infinite intensity in regions around causticpredictions of zero intensity in shadow areas (where in reality sound energy will be present through diffraction and scattering). Such difficulties can be overcintroducing different modifications, accounting to some extent for caustics and diffraction. For instance, Astratified media" J. Acoust. Soc. Am. 49, pp. 824-840, 1971) and Jensen et al explaina way to deal with shadow areas based on considering complex take-off angles (Jensen, F. B., Kuperman, W. A., Porter, M. B., Schmidt, H., "Computational OceaAcoustics" American Institute of Physics Press, New York, p 605). However, in practical applications, such modifications are almost necomplexity. Simplified variants of ray tracing have also been developed, ntechnique for tracing Gaussian beams ("fuzzy rays") is described by Porter and Bucker (Porter, M. B., Bucker, H.P., "Gaussian beam tracing for computing oceanacoustic fields" J. Acoust. Am. 82, pp. 1349-1359, 1987). However, this technique presents problems when applied to propagation over an irregular terrain in an inhomogeneous atmosphere. The Lagrangian sound particle model is another approach which considers complex terrain and meteorological fields which are consistent with that terrain (Heimann D., de Franceschi M., Emeis S., Lercher P., Seibert P. (Eds.), 2007: Air Pollution, Traffic Noise and Related Health Effects in the Alpine Space A Guide for Authorities and Consulters. ALPNAP comprehensive report. Universit degli Studi di Trento, Dipartimento di Ingegneria Civile e Ambientale, Trento, Italy, 335 pp) For more background information on propagation effects, see: J.E. Piercy, T.F.W. Embleton and L.C. Sutherland : Review of noise propagation in the atmosphere. J.A.S.A. 61, pp1403-1418, 1977 (general effects) modelling , The Journal of the Acoustical Society of America, Volume 92, Issue 1, pp.418-427, July 1992 (ground impedance effects) Ingard, Uno "A Review of the Influence of Meteorological Conditions on Sound Propagation," Journal of the Acoustical Society of America, 25, p. 405, 1953 (meteorological effects) able 2 summarises and supplements the above. For comparison purposes the practica For details of the CNPE and GFPE, see ACTA ACUSTICA UNITED WITH ACUSTICA, Vol. 93 (2007) 213 227, Outdoor Sound Propagation Reference Model Tl engineering method ISO 9613 has also been included. Developed in the European Harmonoise Project Defrance et al. Hybrid modelling methods Engineering Approximatesemi-analytic Numerical Characteristic ISO 9613Ray tracingFFP CrankNicholson Parabolic Equation (CNPE) Generalised Fokker-Planck Equation (GFPE) Computing timeFastFastSlowSlowMedium AccuracyPoorMediumExact Very goodGood Optimum frequency range AllHighLowLow Low and middle Meteorological conditions? NoNoNoYesYes Shadows and caustics? YesYesYesYesYes Elevated sourcesNoYesYesNoYes Table 2:Characteristics of commonly used environmen ode odstal noise m lling meth ironmental noise modelling? environmental noise modelling is a very important question, but one en a ssed by potentially misleading statements abou uracy' in he clos sured andict ues. repre a snapsh ti s will be ssed he following section, environmental noise fields tend to be inherently me and space. This variability introduces a difficulty in defining the practice. 2.6How reliable is envThe reliability of that is all too oftthe sense of tddreeness between t 'accmea pred ed val A noise modelfurther in tsents an estim te of a ' ot' inme. Adiscuvariable in both tiaccuracy of a model, as it is a function of the relationship between a constant predicted value and a potentially widely varying noise level that could be measured in The value of a model cannot be measured by accuracy perjudgement of its reliability as a tool in decision making, and this judgemse, but rather on a ent should be upon which a ng reliable information that is fit for the purpose of the decision making n s exactly hen or how environmental noise modelling should be used. Approaches to how made according to the specific application and situation under consideration. Providing that modelling studies are used with an awareness of the relative benefits nd limitations of predictions when compared to other possible bases adecision could be made, such studies can provide a reliable basis for decision makipurposes. In other words, a reliable model is one that is fit for purpose. It is the purpose of this guide to assist all parties involved in these types of studies to identify those situations where predictions can offer a reliable decision making tool, and subsequently design case specific approaches to modelling that is focussed on roducing pexercise. The requirement of fit for purpose information establishes an onus opractitioners to deliver the outputs of predictive studies with accompanying contextual information that enables decision makers to understand how such information can be sed.u 2.7Are there standardised methods of modelling? At present, there is no ratified methodology within the UK that describewenvironmental noise models are developed and presented is largely dependent on individual practitioner judgement and experience. The purpose of this document is topromote a greater level of transparency and consistency to this process. Introduction n important factor in the consideration of site specific noise modelling is the strong fluence of commercial and practical constraints which are more prevalent than in strategic mapping. In these instances, the commissioning party with ultimate sponsibility for allocating timescale and budget resources may not be aware of the oices, nor appreciate the varying risks of different approaches. Given the degree of flexibility and interpretation permitted by relevant assessment criteria that ay drive the requirement for predictive studies, industry expectations of what may be involved in conducting a predictive study are understandably wide ranging. These 3. Risk in Environmental Noise Assessment 3.1 Ainreavailable chmfactors will often lead to a situation where the scope of a compromised without proper regard to the consequential study will be limited or trade off in terms of the risk and significance of an incorrect assessment outcome. the context set out above, the challenge for practitioners is to raise the end users al or ude forming the decision). This type of approach provides the opportunity to focus e levels t here worst case approaches re frequently relied upon to address the challenges and limitations that apply to Inappreciation of the potential decision risk associated with different approaches, and todevelop tailored assessment strategies that strike an appropriate balance between thescale of resources required for a predictive study and the costs (social, financiotherwise) and likelihood of an incorrect decision resulting from a compromised study. To achieve such a balance requires the assessment design to 'begin at the end'; that is, prior to developing an assessment strategy, consider the nature and scale of the decision to be made, and how predicted noise data could be used to inform the decision. In some cases, designing the assessment strategy in this way may lead to a number of possible approaches to conducting predictions, or may ultimately conclthat predictions do not represent a viable decision making tool (requiring either the available resources to be re-considered, or evaluation of alternative methods of ininevitably limited resources on the most critical elements of a study that influence thdecision for which the assessment is intended to inform. The above considerations highlight the need for noise predictions to be used in a waythat appropriately manages the risk of incorrect assessment outcomes. It is worth emphasising that there are two main risks when considering the implication of an incorrect assessment outcome. The first and perhaps most commonly recognised risk is that of an outcome where a prediction fails to represent the full scale of noisethat occur in practice, leading to a situation where environmental noise levels breach acceptable levels with associated social and financial consequences. However, the second and perhaps most frequently underestimated risk is that of the unnecessary development costs (direct costs as well as those associated with lost developmenopportunities) of incorrect assessments arising from a prediction study that overestimates noise levels experienced in practice. The latter risk is an important consideration within the current assessment framework wapractical environmental noise studies. of s and This section of the guidelines commences with a discussion of environmental noise variability and the challenges it presents to any attempt to objectively rate a noise 3.2Risk, Variability and Uncertainty Appreciating from the previous section how environmental noise models are constructed and used, the next stage is to discuss the challenges associated with usethe modelling in environmental noise assessment and identify how these challengemay translate into assessment risk. It is essential that the users have an appreciation of variability in environmental noise and equally important to recognise the distinction between variability, uncertaintyrisk. fiof factors that a noise modelling exercise eld. Understanding variability in this way provides a basis for identifying the types should take into account. ted to to the use of models is the fact that it is necessary be realised in practice. Since the variation of output values with input condition , tions relies ce are with variability in two distinct sound fields. The section then concludes with a discussion of the compounding factors relathe use of predictions that can introduce a further risk of incorrect assessment outcome if not properly understood. y far the most important limitationBin exercising them to make some selection of the environmental parameters. Often, a model will be required to output a single figure and it is crucial to realise that this figure is dependent on assumptions about, for example, weather conditions that will arelyrvalues is so large, a model may very well therefore give an answer far different to what is experienced in reality. Environmental noise fields exhibit very large variability in space and time. In the UKnvironmental noise assessment of commercial or industrial installa eheavily on comparisons between the specific noise (the noise attributable to the installation in question) and the background noise (the underlying noise in the absenof influence from the installation in question). Thus, these forms of assessmenturdened by the challenges of dealing bIn terms of both the background and specific noise, changing source and propagation conditions will give rise to changes in both predicted and actual sound fields. The reflection of these changes in predictions or measurements is thus a representation of real trends exhibited in the sound field. Table 3 gives examples of how background and specific noise levels can vary: ComponentExamples of component variations SourceBackground noise Changing natural sound source contributions e.g. diurnal and seasonal variations in the composition of natural sound sources such as streams and wind disturbed vegetation Changing traffic sound e.g. hourly, daily, and seasonal changes in the general traffic flow volume and composition, as well short term (wet or dry) and long term (road surface degradation) changes in road condition. Specific noise Operational characteristics, e.g. continuous or intermittent operation, cyclical operations, load settings, personnel dependent effects, demand-driven operational intensity Seasonal effects for sources enclosed in buildings, such as open windows in summer Directionally varying sound characteristics Varying sound characteristics and features such as tones and impact sound TransmissionPosition dependent sound propagation, e.g. varying separation distances due to sound source movement, varying degrees of sound path screening according to source and receiver location, and localised regions affected by reflections Seasonal effects such as varying ground cover conditions (e.g. grass or ice) that affect absorption of propagating sound, or open windows in summer for indoor assessment locations Topographical changes that increase or reduce obstructions to sound propagation, e.g. construction of a building structure that will shield otherwise 'exposed' areas Varying atmospheric conditions, e.g. wind speed/direction, temperature changes with increasing height above ground, pressure, and humidity Table 3:Significant causes of variation in environmental noise sound fields The variabilityany attempt to rating of a sou ay relate to those occurring in other conditions. Furconsideration tdegree of varia n fact undermine the validity of an assessmeinfluence the dcharacterised by identical average noise levels could invoke very different assessment outcomes if on t with the average value,maximum levels substantially above the average at certain times. This highlights the d by the only ield may vary. Importantly, when evaluating appropriate conditions for hich an assessment should take account of, it is necessary to identify any of environmental noise fields presents the most critical challenge to rate the field by prediction. It raises the question of how an objective nd field in one set of conditions mther, the variation patterns of a sound field may be a very important o the assessment. The use of well-intended measures to suppress the bility exhibited in objective ratings may int finding by failing to recognise how actual sound variability may ecision making process. For example, two separate sound fields each e of the fields was characterised by constant levels consisten whilst the other field was characterised by widely varying levels withimportance of understanding the relative timing of the highs and lows exhibiteackground and specific noise sources, e.g. does the highest background noise boccur when the highest specific noise occurs? This is an important consideration forobjective sound field ratings that are often produced for downwind atmospheric conditions that favour sound propagation from the source in question. Such an assessment condition cannot always be assumed to be the condition in which the greatest difference between specific and background noise levels occurs if the controlling background noise sources are also affected by atmospheric propagation conditions. Whether the specific noise of the installation in question is being compared against a background related limit or fixed value limit, unidentified or misunderstood variability can create significant uncertainty as to whether an objective sound field rating produced for one set of conditions will provide a complete representation of thesound field. Subsequently, if unknown variability or uncertainty overlaps some threshold value at which different assessment outcomes are triggered, there is a significant risk of an incorrect assessment being made. A related issue is that available prediction methods are limited in the range of conditions which they can model: for example, some engineering methods only enable the calculation of noise levels which occur under downwind conditions. Given the reliance on knowledge of the background and specific noise for the assessment of commercial or industrial installations, it is important to recognise howach sound f ewrelationships that may exist between the variabilities of the background and specific noise fields. The importance of such relationships can be seen from Figure 3. This demonstrates how the combined effects of variability in both sound fields can lead to critical regions where the ability to discern the causes of variability becomes significant.this example assessment, where the priority is to determ In ine if the specific noise xceeds the background noise, the critical region occurs when the range of specific f the xtent one, ct ially high vels of variability, rstandecific p ratin sounund n olimeand background noise levels overlap. The situation therefore arises as a result ocombination of two factors; the relative magnitudes of the sound levels and the eto which each may vary. An important consequence is that, outside the critical zthe specific and/or background noise levels may exhibit even higher degrees ofvariability but, due to the increased relative difference between background and specific noise levels, this increased variability may have no impact on the assessmentoutcome. In summary, outside of the critical zone, there is no risk of incorreassessment outcome despite potentleeven if the sources of this variability are not known. However, within the critical zone the risk of incorrect assessment outcome becomes significant as long as the sources of variability remain unknown. Figure 3:Indicative sound level versus distance chart depicting increasing variabilitywith distance fromsource It is important to emphasise the importance of undebackground and spoccur when the highest sobjective sound fieldconditions that favourassessment condition cagreatest difference betwcontrolling backgroconditions.ing the relative timing of the highs and lows exhibited by the noise sources, e.g. does the highest background noise only ecific noise occurs? This is an important consideration for gs that are often produced for downwind atmospheric nd propagation from the source in question. Such an not always be assumed to be the condition in which the een specific and background noise levels occurs if the oise sources are also affected by atmospheric propagation ise of the installation in question is being compared against a it or fixed value limit, unidentified or misunderstood ificant uncertainty as to whether an objective sound field Whether the specific nbackground related variability can create signrating produced for one set of conditions will provide a complete representation of the sound field. Subsequently, if unknown variability or uncertainty overlaps some threshold value at which different assessment outcomes are triggered, there is a significant risk of an incorrect assessment being made. ely rate an ttention is now directed to the challenges s: n ally to environmental noise predictions there will often be less information to quantify the full range of variability that may be expected in practice. Also, there is often a restricted range of conditions for which the available prediction le, some engineering methods only enable the calculation of noise levels which occur sical of the , ships ccording to the type of equipment under consideration and some aspect of its may er of a 3.3Factors Affecting Risk in Environmental Noise Predictions The preceding section sets out the challenges facing any attempt to objectivnvironmental noise field. In this section a eand risks specifically relating to objective ratings derived from predictions. The origins of this risk can be described by two broad categories described as follow Assessment Conditions: The inherent variability of environmental noise levels presents the challenge of determining which source and propagatioconditions should be used for the assessment. This challenge applies equmeasurement and prediction based studies. However, in the case of methodologies can offer meaningful representations For exampunder downwind conditions, whilst in some cases, upwind conditions may be equally or more important. Prediction Quality: The accuracy with which the prediction model determines the noise level that would occur in practice for the exact phyconditions that the model is attempting to represent. These inaccuracies relate to the limitations of the input data and to the ability of the chosen sound propagation algorithm to represent actual transmission conditions. In both of these two broad categories, the limits of application and accuracy of practical prediction techniques represent important considerations. These limits are discussed below in the context of the input data used to construct the models, available calculation models, proprietary software packages that implement these calculations, and the practical constraints typically encountered in dealing with these challenges. 3.3.1Input Data The key input information to most noise prediction studies is a representationsound emission level and character of the sources to be investigated. Where availablesuch information might comprise a test emission level deduced from measurements made in relatively controlled environmental and operational conditions. In other instances, emission characteristics may be deduced from empirical relationaperformance rating. In cases where no such information is available, an estimatebe acquired from field measurements of an installed item of plant. In all cases, the data will be a relatively simple representation of the total emission and charactvery complex sound-compgenerating mechanism. The total emission of a machinewill comprise many contributions from individual components which have their own sound emiss ion characteristics. This complexity introduces some important factors to bear in mind when considering the representation provided by sound emission data: ity: Many types of noise sources have directional rces irectivity, e e ing t n Source directivcharacteristics such that the noise level observed at a constant distance from the machine will vary according to the orientation of the machine. These characteristics are often not evident in sound emission data, and it is usually very difficult to establish the extent to which the emission in a particular direction may vary from the average quoted value. Source geometry: The distribution of the individual component noise souassociated with a complex machine will affect the pattern of the noise field that emanates from it. This is relevant to the source directivity as described above, but also has an important relationship to how the sources sound field will interact with the surrounding environment. For example, a large piece of equipment may be almost entirely visually obstructed from a receiver location of interest by a solid screen; the question as to whether sound levels at the receiver location will be significantly reduced by the obstruction will be highly dependent on whether or not the exposed portion of the machine is a significant source of the machines total sound emission. As with dthe distribution of sound sources about a complex machine will often be verydifficult to establish from the available emission data. Source input versus actual emission level and character: the actual emission level and character of the item of plant being modelled may vary from the input representation for a wide variety of reasons including manufacturing variations between the tested and installed item of plant, sensitivity of the installed plant item to mounting conditions and variations in the operational duty of the installed machine. Representation of the physical environment: An accurate representation of the physical dimensions of all acoustically significant features of a potentially large assessment area can be very problematic. The additional challenge is then the assignment of acoustical properties to surfaces that absorb, impede and reflect sound to varying degrees. Accounting for the complexities of thterrain and built environment generally requires simplifying assumptions to bmade in order that they can be included in a noise model. Subtle factors and variations not represented in the estimation can lead to differences between predicted and actual noise levels, particularly where the influence of certain environmental features have interdependencies (e.g. the effect of screenand wind conditions cannot be considered in isolation from each other). The complexity further extends to the atmosphere through which the sound muspropagate. This is discussed in further detail in the following section. 3.3.2Algorithms for Outdoor Sound Propagation The ability of mathematical algorithms to accurately represent sound propagation has been the focus of considerable research, particularly given the role of noise predictioas an integral assessment tool in the fulfilment of the European Noise Directive (i.e. EU Directive 2002/49/EC, which requires member states to produce noise maps and action plans for urban areas and major transport infrastructures, including roads, railways and airports). Predictive algorithms vary widely in sophistication from commonly employed engineering methods (empirically based) through to more complex scientific methods that are mostly employed for specialist research applications. Engineering methods offer the benefit of robust and practical computation, but are generally limited to the prediction of longer term average A-eighted noise levels, and exhibit increasing uncertainty when attempting to evaluate nd curacy for omplex situations, but generally only for very specific and limited scenarios, and are iability as a practical ssessment tool. o r of sources over extensive areas, proprietary software packages are s ese software packages will often implement efficiency algorithms that enable users d calculation time. clearly beneficial for practical on available to the user to understand ciency techniques may compromise the predicted value. mplemented packages has indicated that variations n potentially amount to significant variations in calculated outputs. At present, there are no international or British Standards that n en wnoise fields with complex sources and/or propagation conditions. At the opposite eof the spectrum, scientific methods can provide significantly greater acccomputationally intensive to an extent that limits their va The complexity of atmospheric conditions and the impracticability of measuring all the relevant environmental parameters throughout the sound propagation path, requirethat several assumptions and simplifications in the models are adopted. This set of assumptions and approximations has led to the existence of a variety of methods tmathematically represent sound propagation. Generally, all these methods can beclassified as one of the following three categories: Practical engineering methods Approximate semi-analytical methods Numerical methods 3.3.3Proprietary Software Given the practical complexity of applying predictive algorithms to the computation f a large numbe omost commonly employed to generate predictive noise models. These packages provide an efficient and organised approach to the collection of input data, and then provide the option to execute various predictive algorithms to generate calculated noise levels over a wide range of receiver locations. The development of these software packages involves the translation of standard predictive algorithms (such aISO 9613) into computational code. In order to achieve practical computation times, thto strike a balance between likely computational accuracy anWhilst such aspects of proprietary packages ares limited informati assessment purposes, there ithe extent to which such effiExperience of several commonly iin the approach to efficiency caprovide a user with any certification of a proprietary packages accuracy in applying agiven predictive algorithm, and the credibility of a particular package will therefore often derive from brand recognition. This contrasts with objective studies based omeasurements that require that any sound level meter used for such an exercise to becalibrated and demonstrated to achieve agreement with set reference conditions whtested in a laboratory scenario. Furthermore, a common feature of most software packages is the assignment of standard atmospheric conditions which are then applied to the calculation of propagation from all sources. Wind direction related sound propagation effects isimportant example of a factor for which such an assumption can be a source of in the calculation. For example, industrial sites may be sufficiently large that some sources at the site are upwind of a calculation position at the same time as other sources at the site are downwind of the calculation, with potentially significant implications for the total received noise level in practice. 3.3.4Other factors related to the ways in which models are used in practice There are many other factors which influence the accuracy and usefulness of models in practice, including the following: bsence of nationally standardi an error sed requirements for the verification and quality g to nties Many environmental noise assessment projects are won through a competitive s to be undertaken than the bidder would commend under less competitive circumstances, and those commissioning y uential loss associated in e relationship between the practitioner, the party Aassurance of commercial software which implement engineering methods, leadina very wide range of performance and suitability for purpose. In the absence of clearly defined assessment requirements, the conditions that should be included in prediction models are often selected in a somewhat arbitrary manner. There is no defined system for generating traceable accounts of a model outputs development/construction. There is varied industry understanding of modelling limitations. There is an absence of guidance on how to deal with the limitations and uncertaiof predictions. Noise modelling studies are generally constrained to fall short of the ideal, due to budget restrictions. tendering process, so bidders are often obliged to limit their scope to one which allows for less rigorous investigationreprediction studies understandably seek the lowest cost options without necessarilunderstanding the potential trade-off between decreasing study cost and increasing outcome uncertainty. For example, the increased risk of conseqwith increased uncertainty is not always appreciated. There may also be limited access to information: due either to limited resources to collect information, or as often occurs, due to the confidentiality surrounding certainformation depending on thcommissioning the study, and the noise producer. 4. Designing environmental sound models - decision procedure Many of the risks associated with the production of environmental noise are intriand cannot be specifically mitigated economically. Hence in general the best waymanage risks is as part of the whole process of using models. The following guis a suggested approach. The guidance of this section is broken into the several key constituent elements thatmake up any environmental noise prediction programme, as represented in the following flowchart: nsic to idance Commission brief for assessment Client consultation 1.Review the requirement for predictions 2.Preliminary screening study 3.Detailed model design 4.Execute calculations 5.Analyse and report Evaluate potential risk sources Consider alternative methods of informing the decision process that may be of lower risk Figure 4:Generalised approach to environmental noise measurements ll stages are shown w Athith a return path to client consultation and brief, since progress rough the investigation will yield information about the noise environment that y not have be tset re-evaluation of strategy. An important point is that environmental noise predictions may not always be able to inform the assessment to an acce , so another approach may be required. The realisation that a modi pproach may be more appropriate ut the course of the itial review ri oueither contradicts earlier assumptions or that mof the study and so may necessitatea en available at the outhe forward investigation ptable level of riskfied amay arise at any point throughobecomes available, from the ininvestigation as new information ght thr gh to the post-analysis phase of the study. irement for predictions o have a any parison against known benchmark). Relative difference values (which may between sources or locations), where menting the design or findings of a ld Stage 1:Review the requ Whenever environmental noise predictions are proposed, it is necessary tlear understanding of the reasons for the predictions, the significance of cdecisions to be made on the basis of them, any variable characteristics of the sound field in question that may represent sources of uncertainty (including longer term sources of variability or change, as may be related to seasonal effects or future imminent development that may passively or directly change the noise environment), and the likely feasibility of conducting predictions. It is at this point that consideration must be given to the type of noise data that the assessment calls for, under the following categories: Absolute values, where the specific numeric value of the calculation is important (e.g. comdeveloping attenuation strategies or complemeasurement study. The relevance and reliability of any existing assessment data that is available shoube evaluated to determine whether this may negate the need for further assessments.The limitations of any available existing data will need to be considered against the difficulties that may face any attempt to develop new prediction data. Finally, it is important at this point to identify any well-defined threshold values that trigger significantly different assessment outcomes. The knowledge of such resholds, in conjunction with estimates of what predicted values that might be modelling exercises. thexpected from the study (see following screening exercise) is critical to determiningthe requirement for, and scope of, subsequent detailed sment locations. These studies are relatively brief, and aluable for defining the scope of any future work. They proceed as follows: Identify the assessment (receiving) locations. ding. In some instances, gathering information about the sound sources may be roblematic. In these cases, it may be possible to consider the separation between the se this information to work back to the agnitude of sound emission levels that would be needed to trigger differing No further studies are required, since the output information is already ould lable information suggests that further detailed studies can be averted . The findings may nnot Stage 2:Preliminary screening study Preliminary screening prediction studies provide a means of gauging the potential criticality of the prediction outcomes, and identifying critical source elements, transmission paths, and assesv 1Clearly define any thresholds at which differing assessment outcomes are triggered. This might take the form of a threshold defined in a planning conditionor contract. 23Gather preliminary sound source type and position data. 4Apply a very simple propagation assumption such as hemispherical sprea5Produce very rough estimates of the expected noise levels at the identified assessment locations for comparison with the thresholds or limit values. psource and assessment locations, and umassessment outcomes. Screening studies then lead to one of the following outcomes: sufficient to enable a decision to be made, and further detailed studies wnot provide any benefit to the study. The avaiby a revised screening study. A refined sound propagation model must be designedprovide guidance as to the areas on which to focus. Predictions with a risk level commensurate with project requirements cabe made and a different approach must be sought. f ining a hat is suitable for every application. The process of developing detailed model design will often consist in a gradual refinement of the predictions of ill often prevent the eal modelling approach from being pursued, the detailed design must identify the most effective refinements that strike the best compromise between the resources required to construct the model and the reliability of the outcome for decision-making Stage 3:Detailed model design Given the wide variety of uses of noise modelling, as well as the wide variety ofactors that influence environmental noise levels, there is no procedure for defdetailed model design tathe screening study. Since practical and technical constraints widpurposes. Reaching this compromise will need consideration of the criticality afinancial impact of the decision that depends on the assessment outcome. nd ect on the calculated noise levels. These hysical Environment vironment to be defined is the scale of the tailed model needs to be developed. This will be ing ignificantly reduced under such conditions. methods to calculate the influence of o be recognised that the validity of the methods is often uch as f the preliminary screening study it should be possible to es that may together result in total noise levels similar to, or er ses of tively small such that ground and The detailed model design will define the features of the sources and environment whose description will have a significant efffeatures will often determine the type of algorithm required. The following sections discuss the types of technical factor that should be consideredin developing the detailed model design. PThe first aspect of the physical enssessment area for which the de abased on the assessment locations identified in the screening study. The positional accuracy required decreases with increasing separating distance: a 10% change in separating distance equates in general to less than a 1 dB change in the calculated noise level. The other aspects of the environment to be defined relate to the presence of screenand reflecting surfaces, the location and extent of any absorptive ground coverings, and the atmospheric conditions. The level of information required depends on the sophistication of the propagation algorithm to be used. In some instances, a decision that the assessment should consider atmospheric conditions that are favourable to the propagation of sound will reduce the required precision of details of screening structures and ground cover as their influences are sThe importance of precisely defining such attributes must be considered in the contextof the importance of small changes in calculated noise level to the assessment utcome. However, when using engineeringothese features, it must alsrestricted to general characterisations, particularly when describing features sacoustically soft ground covers. It therefore does not follow that continually increasing the precision with which the physical environment is described will ecessarily translate to any increased precision of calculated noise levels.n Sources Based on the findings oentify all sound sourc idhigher than, the prevailing decision threshold or limit at the assessment locations. The contribution of relatively low-power unscreened sources should not be neglected if the model includes screening effects, as these may become significant if higher powsources are screened. A range of source attributes may need to be defined in more detail for the purpothe detailed model design. Consideration of the extent and nature of the physical environment can simplify this definition. For example, in instances where there is noscreening and the separating distances are relaatmospheric effects are minimal, the calculation of total levels may not require any information about the frequency profiles of the emission sources. Attention must also be given to the range of emission levels that a source may produce and the time span over which its emissions may vary. Correspondingly, the relevant assessment time period must be clearly defined and related to the oppatterns of the sources. For example, the standard most frequently used for ratinindustrial noise in the UK defines time periods of 1 hour and 5 minutes forerating g ssessments made during the day and night respectively. Therefore, sources with an or pattern of time variation significantly less than the assessment period will ould e hen favourable propagation conditions occur?). gs encies at the ceiver location and therefore potentially more disturbing than a wide-frequency rder that rge industrial etrochemical) sites, but is now widely used in a range of environmental scenarios. s . The ucing e the eteorological conditions (e.g. ISO 9613 does not provide a method of alculating noise levels that occur upwind of a source). In situations where the noise aon-timeneed to be directly factored into the emission rating. Conversely, sources which cdisplay differing emission levels in different assessment time periods will need to berationalised according to whether the assessment relates to average, typical upper, or worst case conditions, as well as considering how the pattern of variations may relatto that of other assessment sources or atmospheric conditions (e.g. is the highest noise level likely to occur w Other important source characteristics such as frequency and directivity may also need to be defined, depending on the likelihood of those characteristics being significant to the assessment at the receiver location. For example, frequency information may be important in terms of calculating the effect of ground coverinor screening, as well as being a material consideration to the impact the noise may have at the location (i.e. is the noise dominated by individual frequresource?). In situations where barrier effects are to be factored into the calculation, careful consideration must be given to the assignment of representative source heights for large pieces of machinery. Conservative decisions may need to be made in ounrealistic screening benefits are not factored into the calculation. However this will need to be balanced against the need for refinement of the calculation and may warrant closer inspection of the sound radiation properties of the source. Propagation Algorithm In most practical assessments, environmental noise propagation calculations will be performed using standard engineering methods such as ISO 9613 or CONCAWE. The CONCAWE method was originally developed for noise impact from la(pFor an example of its use, click here. In the future, the newly developed procedureformulated under the EU HARMONOISE and IMAGINE projects may be useduse of these engineering methods provides a relatively efficient means of prodestimated noise levels that account for a significant level of detail. It must however brecognised that these methods validated application is for the calculation of overalltotal averaged noise levels under specified meteorological conditions. Not all of engineering methods are able to directly estimate noise levels that may occur in differing mcmodel is to account for sources with very prominent and narrow frequency components, or where the variations which occur for different meteorological conditions are of interest, engineering methods should be used with a high level of caution. In some cases, the complexity of the situation may warrant the use of more intensive scientific methods or, ultimately, abandonment of predictions. To makinformed decisions about the appropriate algorithm to adopt requires backe ground nowledge in the principles of sound propagation and an overview of the relative e various procedures. kmerits and limitations of th Stage 4:Execute calculations The initial phase of the calculation is an extension of the detailed model design, in thform of a review of the decisions made concerning the input information, through testing elements of the calculation to gauge the sensitivity of the outputs to the precischoice of input value, and thus identify where the quality of input information may need to be revisited for further refinement. Engineering methods can be implemented for many situations, but for large numof source and receiver locations and/or complex propagation paths dedicated softwbecomes practically essential. In particular, the use of such software enables the rapidexploration of different scenarios that may be relevant to the assessment. Fusuch software often enables visualisations of the input data to be produced in othat a user can readily check the plausibility of the input data. However, the use of such software requires users to be fully aware of the manner in which it implements aparticular procedure and in particular what assumptions are being made. Additionathe documented descriptions of engineering methods are sometimes subject to a degree of interpretation as to the correct procedure, and this is a source of variationbetween different software packages. These consie e bers are rther, rder lly, derations are such that proprietary odelling software should not be used in the absence of a working knowledge of the calculation routines. t the outset of any calculation, the input data should be checked to confirm the ularly where the latter are within close proximity to a k mAplausibility of the results, particdecision threshold or limit value. It is also essential to compare the predicted values with the simple calculated values estimated during the screening study, and to checthe ranking of reported contributions attributable to each source against expectations. tage 5:Analyse and reportSThorough reporting of environmental noise modelling is essential for users of the outputs to understand the reliability of the information as a basis for decision-making purposes. Important elements that the reporting must address are: The assessment conditions that have been chosen as the basis for the assessment and the reasoning behind the selection of these conditions. The input information used to describe the sources, physical environment, and propagation conditions, and how this input information relates to the chosen assessment conditions. Any uncertainties in the input information used for the model, how these uncertainties have been rationalised in the modelling, and the significance of their effect on the calculated values. The choice of algorithm used to predict noise levels and the reasoning forchoice, as well as any known limits associated with the method and assumptions incorporated in the package that implements the algorithm. A discussion of the output findings in comparison to any prevailing decision thresholds or limit values, including references to the propensity for varied its input data or calculation uncertainties to alter this comparison, and thus the assessment outcome, as well as reporting of the potential changes in noise for ent conditions (as may be judged by prediction, n data for decision-making purposes. other possible assessmknowledge of algorithm limitations, or measurement data). Any recommendations for further work that could be carried out to address any residual risks associated with reliance on the calculatio een weighed by filters to produce a reading that ironmental noise The underlying level of residual noise remaining when specific noises have been moved. The background noise level is often quantified by using the LA90 sound is the A-weighted sound pressure level that is exceeded for 90% of a given me interval, T, measured using time weighting, F. hat must determined from a set of easured sound levels in order to provide a basis for decision-making. on which specifies travel times to points on an acoustic wavefront. It can us be used to represent the development of a wavefront over time. Glossary A-Weighted Noise Level: A measured noise level which has bcorresponds approximately to what we hear. Acoustic Wave Equation: An equation which describes the propagation of a sound wave through a specified medium. Ambient Sound: The totally encompassing sound in a given situation at a given time usually being composed of sound from many sources near and far. Assessment: Any decision making process that uses objective evaluations of envfields. Background Noise Level:relevel. Thisti Derived Value: A derived value is the assessment parameter tm Eikonal Equation: An equatith Receiver Site: The place for which a noise assessment is required. Risk: The likelihood of an incorrect assessment outcome resulting from uncertainty. Note, however, that uncertainty does not automatically imply risk. o pecific Noise: he ambient noise that can be attributed to a specific source. he inherent changes in environmental noise levels that occur with changing location dentified or misunderstood variability is the prime source of ser: ody having an interest in the prescription, commissioning, nts. Sound and Noise: Sound is pressure fluctuations in the air, or other supporting medium, that can be detected by the ear or by a microphone. Noise is sound which is loud or perceived tbe unpleasant in a given situation and thus causes disturbance.

SA component of t Variability: Tand time period. Unimeasurement uncertainty and risk in practical environmental noise assessment.

UAny person or bexecution, or use of environmental noise measureme Standards, regulations and guidance notes ISO 9613-2, Part 2: General method of calculation BS 4142, Method for rating industrial noise affecting mixed residential and industrial areas BS 5228-2, Noise and vibration control on construction 2: Guide demolition including road construction and maintenance BS 7445, Description and measurement of environmental noise Acoustics Attenuation of sound during propagation outdoors and open sites Part to noise and vibration control legislation for construction and 3 Horizontal Noise Guidance. Part 1 Regulation and Permitting and Calculation of Railway Noise 1995. Department of Transport The CAA Aircraft Noise Contour Model: ANCON Version 1. DORA Report oise. Department of the Environment 1994. TAN11 (Wales); PAN56 (Scotland) BS 9142: 2006 Assessment methods for environmental noise Guide, : horities and Consulters. ALPNAP comprehensive report. IPPC HPart 2 'Noise Assessment and Control' Calculation of Road Traffic Noise 1988, Department of Transport, Welsh Office 9120, Civil Aviation Authority 1992 PPG 24 Planning Policy Guidance: Planning and N2003/01534 12 July 2006 Other relevant texts: Heimann D., de Franceschi M., Emeis S., Lercher P., Seibert P. (Eds.), 2007Air Pollution, Traffic Noise and Related Health Effects in the Alpine Space A Guide for AutUniversit degli Studi di Trento, Dipartimento di Ingegneria Civile e Ambientale, Trento, Italy, 335 pp. K Attenborough et al, Benchmark cases for outdoor sound propagation, J. ands, 2001 above a snow of the revision of planning guidance. FINAL REPORT MARCH 2004, DEFRA Ref. NANR 5 Bernard F Berry, Berry l Ltd in association with Nicole Porter Independent Consultant Imagine Improved Method for the Assessment of Generic Impact of Noise in 005 Task 2.4, Choice of basic sound 2002 project, HAR29TR-041118-TNO10.doc, 22 chnical Report - Deliverable 18, Harmonoise WP 3 ONOISE, Validation of the Harmonoise models, Deliverable 21, ssment of Exposure to Noise apping ework OF EU f earch Acoust. Soc. Am. 97, 173-191, 1995 K Attenborough, K, Ming Li & K. Horoshenkov, Predicting Outdoor Sound, Taylor & Francis, London, 2006 E M Salomons, Computational Atmospheric Acoustics, Kluwer, The NetherlD G Albert, Observation of acoustic surface waves propagatingcover, Proc. Fifth Symposium on Long Range Sound Propagation, 10-16, 1992 A Beginner's Guide to Uncertainty in Measurement. GPG(011), Bell S. National Physical Laboratory, August 1999 Review and analysis of published research into the adverse effects of industrial noise, in supportEnvironmentathe Environment. State of art review, Deliverable 2 of the Imagine Project, Document identity: IMA10TR-040423-AEATNL32, 14 October 2004 HARMONOISE, FINAL TECHNICAL REPORT Final public version. Document identity: (HAR7TR041213AEAT04public.doc), 1 March 2HARMONOISE Reference Model propagation models. Deliverable 14 of the Harmonoise project, HAR24-TR021018-TNO10.doc. 12 DecemberHARMONOISE Reference Model, Description of the Reference model Deliverable 16 of the HarmonoiseDecember 2004 HARMONOISE TeEngineering method for road traffic and railway noise after validation and fine-tuning, HAR32TR-040922-DGMR20, 20 January 2005 HARMHAR28TR-041109-TNO11.doc, 24 February 2005 European Commission Working Group Asse(WG-AEN), Position Paper, Good Practice Guide for Strategic Noise Mand the Production of Associated Data on Noise Exposure, Version 1, 5 December 2003 FINAL REPORT ON DEFRA RESEARCH PROJECT NOISE MAPPING INDUSTRIAL SOURCES TECHNICAL REPORT NO: AT 5414/2 REV 1, S J STEPHENSON, B C POSTLETHWAITE, 13TH OCTOBER 2003 NordTest Method NT Acou 107 Approved 2001-05. Acoustics: A Framfor the Verification of Environmental Noise Calculation Software ADAPTATION AND REVISION OF INTERIM COMPUTATION METHODS AND QA OF NOISE MAPPING FOR THE PURPOSESTRATEGIC NOISE MAPPING, E Wetzel Wlfel, Eupen(B), Institute oAcoustics Conference Paper WG-AENs Good Practice Guide and the Implications for Accuracy, ResProject NANR 93: Final Report: The Department for Environment, Food and Rural Affairs (DEFRA), Document Code: HAL 3188.3/10/2 DGMR V.2004.1300.00.R014.1, May 2005 Attenuation of Environmental Noise: Comparing the Predictions of ISO 9613-oise st, a based on acoustic (MW-WAPE) and micrometeorological ra , Ale GLOBEVNIK 2 and Lilijana KUHELJ3, tion ited, Newman. M, Campus Marine A.S, Institute of ional Measurement System Policy Unit, Department of Trade is n Ulrich Donner, ACCON GmbH 2 and theoretical models. Gilles A. Daigle and Michael R. Stinson, Intern2005 How to Evaluate the Quality of Noise Prediction Software. Wolfgang ProbInternoise 2005 Estimating long-term representative SPL in complex environments usingcoupling method (SUBMESO) numerical predictions. Benoit GAUVREAU, Bertrand LIHOREAU, Michel BERENGIER, Philippe BLANC-BENON, Isabelle CALMET, Internoise 2005 Qualitative and quantitative study on relative influence of physical parameters affecting long-range sound propagation. Fabrice JUNKER, Benoit GAUVREAU, Michel BERENGIER, Philippe BLANC-BENON, CoCREMEZI-CHARLET, Internoise 2005 UNCERTAINTY IN NOISE MAPPING OF INDUSTRIAL SOUND SOURCES. Igor ROZMAN 1Internoise 2006 AIRCRAFT NOISE MODEL VALIDATION HOW ACCURATE DO WE NEED TO BE? Jopson. I, Rhodes. D. Dr, Havelock. P, UK Civil AviaAuthority VARIATION OF ISO 9613, CONCAWE AND THE JOINT NORDIC METHODS OF PROPAGATION CALCULATION, Richards. J M.W.Kellogg LimAcoustics Conference Paper, Vol. 25. Pt 3. 2003 Report to the Natand Industry From the Software Support for Metrology Programme, TestingAlgorithms in Standards and METROS By R M Barker, M G Cox, P M Harrand I M Smith, March 2003 The Uncertainty of Sound Pressure Levels calculated with Noise PredictioPrograms, Wolfgang Probst, Sound propagation theory "Sound propagation theory and methodologies" - download PDF file (615 KB) ound urbine Links DEFRA noise site European Union noise site Hoare Lea Acoustics site NPL Acoustic Technical Guides: These includes a number of environmental noise-related calculators (Speed of Sin Humid Air, Calculation of Atmospheric Absorption (ISO9613), Wind TNoise Model, Calculation of Road Traffic Noise (CRTN) Model)