Final Report Summary - IMAGINE (Improved Methods for the Assessment of the Generic Impact of Noise in the Environment)
The IMAGINE project aimed to extend the existing HARMONOISE project source databases for road and rail and to use the HARMONOISE methodology to develop prediction methods for aircraft and industrial noise sources. This required the setting up of industry and aircraft source models together with such modifications to the propagation models as was necessary to account for high sources (aircraft), large sources (industry) and diffraction by vertical barriers (industry).
The overall objective of both projects was therefore to provide a model which meets the requirements of a common assessment method and which eventually can be adopted for use for strategic mapping as defined by the Environmental Noise Directive.
The main technical objectives of IMAGINE were:
1. to provide practical guidelines for data management and information technology aspects of noise mapping (work package (WP) 1);
2. to provide guidelines and examples for an efficient link between traffic flow management on the one hand and noise mapping and noise action planning on the other hand (WP 2);
3. to provide guidelines and examples of how and when noise measurements can add to the credibility and reliability of assessed noise levels (WP 3);
4. to provide a harmonised, accepted and reliable method for the assessment of environmental noise levels from airports, which links well within the methods for noise propagation description developed in HARMONOISE and - at the same time - has a large acceptance in the field of future users and other stakeholders (WP 4);
5. to provide default databases for the source description of road noise, i.e. vehicle category and road surface type, for a typical fleet of European road traffic, and provide guidelines on how to deal with situations deviating from the default value (WP 5);
6. to provide databases for the source description of rail noise, i.e. vehicle category and track type, for an example sample of the European rail traffic fleet, as well as default data sets, and provide guidelines on how to deal with situations deviating from the typical (WP 6);
7. to provide a harmonised, accepted and reliable method for the assessment of environmental noise levels from industrial sites and plants, which links well within the methods for noise propagation description developed in HARMONOISE, in combination with methods for source description by measurements based on the existing set of standards and guidelines, together with a default database for typical sound production for a limited but representative number of industrial activities (WP 7);
8. to provide for acceptance and easy and quick implementation of the above deliverables and those from the HARMONOISE projects, in order to allow a smooth and harmonised process of noise mapping and noise action planning in all member states (WP 8).
The HARMONOISE propagation method has been extended in IMAGINE for practical use and for the calculation of Lden at the receiver. The points which have been added and improved are:
- use of external GIS data in the noise modelling;
- adaptation of the propagation model to industrial noise sources;
- adaptation of the propagation model to aircraft noise;
- estimation of populations exposed to noise;
- determination of Lden and Lnight as long term averaged quantities;
- pre-processing of meteorological data to calculate the Lden and Lnight.
In the HARMONOISE project, it was shown how noise levels are influenced by meteorological conditions such as wind speed, wind direction and thermal inversion effects. For the determination of long term averaged noise levels by means of measurement or calculations, short term levels, valid under specific meteorological conditions, must be weighted according to their frequency of occurrence. The step by step method to define the occurrence of meteorological conditions is an output of IMAGINE.
The road noise source method represents the noise emission of the average European road vehicle. It is more suitable for noise mapping purposes than currently used methods because:
- it is based on extensive and recent measurement sets from the most important European regions, and therefore is truly representative of the European average heavy duty vehicles (trucks) and powered two-wheelers (mopeds, motorcycles) have received special attention and are now supported with extensive measurement data;
- it provides correction factors to adapt for local variations in road surfaces and vehicle fleet.
With the guidelines given in deliverable 7 (Guidelines for the use of traffic models in noise mapping and noise action planning), more accurate traffic flow data can be produced when using a traffic model. The purpose of the report is to assist authorities and consultants in using traffic models to produce road traffic data for noise mapping and noise action planning. Separate guidelines are given for noise mapping and noise action planning. For noise mapping, a further distinction is made between noise mapping for main roads and agglomerations, and between macroscopic and microscopic traffic models.
In the HARMONOISE / IMAGINE rail model the combined roughness of the wheels and the rails is a key parameter for rolling noise. The inclusion of the combined roughness leads to a major improvement in modelling accuracy, especially because local track roughness can cause rolling noise to vary over a range of up to 20 dB. At present, most national rail noise models include overall rolling noise data (i.e. vehicle and track contributions combined) that have been acquired from pass-by measurements on track that is not excessively rough or corrugated.
In the HARMONOISE / IMAGINE model, rolling noise is split into the vehicle and track contribution. In addition, the rail model takes into account all other potential noise sources, such as traction elements (exhaust, fans, and compressors), braking noise (including brake squeal), curve squeal and aerodynamic noise. The level of detail of these extra sources is significantly greater than is the case with other available mapping models.
This complete separation allows a detailed apportionment of the rolling noise sub-sources and it allows an evaluation of the effects of noise mitigation applied to sub-sources. This is a valuable tool in action planning, and is also useful for identifying whether vehicles or track are the prime emitters of noise, helping with such considerations as track access charging or determining responsibility when levels are exceeded.
The source term database and associated procedures for acquiring and storing data provide a standardised and efficient method both for accessing appropriate data and for adding new data. In its delivered form it holds example data from France, the Netherlands, Sweden, Hungary and the United Kingdom, representing a broad range of generations of rolling stock, configurations and operating speeds. The database also provides default data. Noise modellers who wish to model vehicle types that are not already within the database are provided with guidance on how to acquire the data. Such a comprehensive pan-European rail source database has not been available previously and represents a significant improvement in knowledge as well as in the harmonisation of rail noise modelling.
If industry is located next to housing development, noise can become a problem. Unlike roads, where a large number of different vehicles pass by, the noise may be the product of just a few sources. Although these sources may be common to a large variety of industries, their usage (operating speed-maintenance level-operating hours) may differ greatly from company to company. So it is often not enough to have a general knowledge of the source, it is better to measure the source.
Deliverable 14 gives a very large number of measurement possibilities, in order to obtain the sound power levels of machine and areas. If no measurement data are available, the source database SourcedB can be used containing a large variety of noise sources, based on measurements or formulae. This database which contains more than 1 500 entries is available from the DGMR website and has already been downloaded more than 200 times. The noise propagation part is superior to the interim methods because of the possibilities of including meteorological conditions. The method proved to be valid for many meteorological situations. A method is proposed for calculating the Lden and Lnight based on the statistics over a year.
Currently used aircraft noise models, including the interim model, are based on the 'integrated' modelling guideline defined in European Civil Aviation Conference (ECAC) Doc. 29. These models have all noise sources (engine and airframe) and propagation combined into a set of 'noise-power-distance' (NPD) curves for each of the two phases of flight - approach and departure. This method does not allow for taking into account:
- realistic directivity of the aircraft source under various operating conditions;
- temperature gradients and other meteorological effects;
- ground characteristics and shielding by relief.
The IMAGINE model is a source propagation model that takes all these factors into account, enabling much more accurate analysis to be undertaken.
Work performed in IMAGINE has demonstrated the creation of example source data either by measurement or by reverse-engineering of NPD data. For the noise calculations, the aircraft is modelled as a point source with three-dimensional (3D) spectral directivity to account for the different contributions from individual sound sources like fan, engine, jet and aerodynamic effects.
The interim propagation method and most national propagation methods are derived from the ISO 9613-2 standard. This standard provides an empirical model to estimate the propagation effects in a very simplified situation (i.e. a flat terrain with a single screen). When applied to more complex situations, the real geometry has to be 'matched' to this simplified description. How to do this is not part of the ISO standard. Even though some national methods provide rules for the determination of the geometrical parameters, a large degree of freedom is left to the software developers. As a consequence, different implementations based on these common standards often lead to significantly different results, even in moderately complex situations, and differences up to 5 or even 10 dB(A) are not unusual.
With HARMONOISE / IMAGINE methods a harmonised approach is possible through the following steps:
1. The HARMONOISE model relies on explicit geometrical modelling of propagation paths; i.e. it is the complex geometry of the paths that is used as the input to the model. Because the software developers do not need to interpret the geometrical data, this will clearly result in higher reproducibility of the results.
2. The IMAGINE project provides a complete and explicit set of specifications for the geometrical model (i.e. the data) on which the HARMONOISE methods (i.e. the algorithms) operate. Such specifications define the end-user requirements for the collection of data and for the construction of the geometrical model. As much as possible, these requirements are expressed in quantitative terms.
3. Sensitivity analysis of the HARMONOISE / IMAGINE method provides explicit links between the accuracy and the level of detail of input data and the expected accuracy of the results. This also allows for objective rank ordering of the data items to be collected.
As part of the common models and methods as prescribed by the END, the IMAGINE project also looked into common methods for the estimation of populations exposed to noise.
There is no interim method for the measurement of Lden nor is there any international or national method addressing all the relevant parameter related problems resulting from the use of the HARMGNOISE source and meteorological models. Thus, the measurement method developed within IMAGINE introduces many new features compared to available methods. The most important new features are:
- measurements are classified into meteorological classes. The measurement method is harmonised with the IMAGINE calculation methods for road, rail, aircraft and industry noise.
- stratification of measurement according to meteorological conditions.
- measurement uncertainty is dealt with in compliance with the guidelines given in ISO GUM.
- the method is general and can be adapted both to industrial noise and road, rail and air traffic.
- both short term and long term measurements are dealt with correction of measured values to be representative for yearly averages is dealt with the method is flexible, different measurement efforts will yield different measurement uncertainties.
The overall objective of both projects was therefore to provide a model which meets the requirements of a common assessment method and which eventually can be adopted for use for strategic mapping as defined by the Environmental Noise Directive.
The main technical objectives of IMAGINE were:
1. to provide practical guidelines for data management and information technology aspects of noise mapping (work package (WP) 1);
2. to provide guidelines and examples for an efficient link between traffic flow management on the one hand and noise mapping and noise action planning on the other hand (WP 2);
3. to provide guidelines and examples of how and when noise measurements can add to the credibility and reliability of assessed noise levels (WP 3);
4. to provide a harmonised, accepted and reliable method for the assessment of environmental noise levels from airports, which links well within the methods for noise propagation description developed in HARMONOISE and - at the same time - has a large acceptance in the field of future users and other stakeholders (WP 4);
5. to provide default databases for the source description of road noise, i.e. vehicle category and road surface type, for a typical fleet of European road traffic, and provide guidelines on how to deal with situations deviating from the default value (WP 5);
6. to provide databases for the source description of rail noise, i.e. vehicle category and track type, for an example sample of the European rail traffic fleet, as well as default data sets, and provide guidelines on how to deal with situations deviating from the typical (WP 6);
7. to provide a harmonised, accepted and reliable method for the assessment of environmental noise levels from industrial sites and plants, which links well within the methods for noise propagation description developed in HARMONOISE, in combination with methods for source description by measurements based on the existing set of standards and guidelines, together with a default database for typical sound production for a limited but representative number of industrial activities (WP 7);
8. to provide for acceptance and easy and quick implementation of the above deliverables and those from the HARMONOISE projects, in order to allow a smooth and harmonised process of noise mapping and noise action planning in all member states (WP 8).
The HARMONOISE propagation method has been extended in IMAGINE for practical use and for the calculation of Lden at the receiver. The points which have been added and improved are:
- use of external GIS data in the noise modelling;
- adaptation of the propagation model to industrial noise sources;
- adaptation of the propagation model to aircraft noise;
- estimation of populations exposed to noise;
- determination of Lden and Lnight as long term averaged quantities;
- pre-processing of meteorological data to calculate the Lden and Lnight.
In the HARMONOISE project, it was shown how noise levels are influenced by meteorological conditions such as wind speed, wind direction and thermal inversion effects. For the determination of long term averaged noise levels by means of measurement or calculations, short term levels, valid under specific meteorological conditions, must be weighted according to their frequency of occurrence. The step by step method to define the occurrence of meteorological conditions is an output of IMAGINE.
The road noise source method represents the noise emission of the average European road vehicle. It is more suitable for noise mapping purposes than currently used methods because:
- it is based on extensive and recent measurement sets from the most important European regions, and therefore is truly representative of the European average heavy duty vehicles (trucks) and powered two-wheelers (mopeds, motorcycles) have received special attention and are now supported with extensive measurement data;
- it provides correction factors to adapt for local variations in road surfaces and vehicle fleet.
With the guidelines given in deliverable 7 (Guidelines for the use of traffic models in noise mapping and noise action planning), more accurate traffic flow data can be produced when using a traffic model. The purpose of the report is to assist authorities and consultants in using traffic models to produce road traffic data for noise mapping and noise action planning. Separate guidelines are given for noise mapping and noise action planning. For noise mapping, a further distinction is made between noise mapping for main roads and agglomerations, and between macroscopic and microscopic traffic models.
In the HARMONOISE / IMAGINE rail model the combined roughness of the wheels and the rails is a key parameter for rolling noise. The inclusion of the combined roughness leads to a major improvement in modelling accuracy, especially because local track roughness can cause rolling noise to vary over a range of up to 20 dB. At present, most national rail noise models include overall rolling noise data (i.e. vehicle and track contributions combined) that have been acquired from pass-by measurements on track that is not excessively rough or corrugated.
In the HARMONOISE / IMAGINE model, rolling noise is split into the vehicle and track contribution. In addition, the rail model takes into account all other potential noise sources, such as traction elements (exhaust, fans, and compressors), braking noise (including brake squeal), curve squeal and aerodynamic noise. The level of detail of these extra sources is significantly greater than is the case with other available mapping models.
This complete separation allows a detailed apportionment of the rolling noise sub-sources and it allows an evaluation of the effects of noise mitigation applied to sub-sources. This is a valuable tool in action planning, and is also useful for identifying whether vehicles or track are the prime emitters of noise, helping with such considerations as track access charging or determining responsibility when levels are exceeded.
The source term database and associated procedures for acquiring and storing data provide a standardised and efficient method both for accessing appropriate data and for adding new data. In its delivered form it holds example data from France, the Netherlands, Sweden, Hungary and the United Kingdom, representing a broad range of generations of rolling stock, configurations and operating speeds. The database also provides default data. Noise modellers who wish to model vehicle types that are not already within the database are provided with guidance on how to acquire the data. Such a comprehensive pan-European rail source database has not been available previously and represents a significant improvement in knowledge as well as in the harmonisation of rail noise modelling.
If industry is located next to housing development, noise can become a problem. Unlike roads, where a large number of different vehicles pass by, the noise may be the product of just a few sources. Although these sources may be common to a large variety of industries, their usage (operating speed-maintenance level-operating hours) may differ greatly from company to company. So it is often not enough to have a general knowledge of the source, it is better to measure the source.
Deliverable 14 gives a very large number of measurement possibilities, in order to obtain the sound power levels of machine and areas. If no measurement data are available, the source database SourcedB can be used containing a large variety of noise sources, based on measurements or formulae. This database which contains more than 1 500 entries is available from the DGMR website and has already been downloaded more than 200 times. The noise propagation part is superior to the interim methods because of the possibilities of including meteorological conditions. The method proved to be valid for many meteorological situations. A method is proposed for calculating the Lden and Lnight based on the statistics over a year.
Currently used aircraft noise models, including the interim model, are based on the 'integrated' modelling guideline defined in European Civil Aviation Conference (ECAC) Doc. 29. These models have all noise sources (engine and airframe) and propagation combined into a set of 'noise-power-distance' (NPD) curves for each of the two phases of flight - approach and departure. This method does not allow for taking into account:
- realistic directivity of the aircraft source under various operating conditions;
- temperature gradients and other meteorological effects;
- ground characteristics and shielding by relief.
The IMAGINE model is a source propagation model that takes all these factors into account, enabling much more accurate analysis to be undertaken.
Work performed in IMAGINE has demonstrated the creation of example source data either by measurement or by reverse-engineering of NPD data. For the noise calculations, the aircraft is modelled as a point source with three-dimensional (3D) spectral directivity to account for the different contributions from individual sound sources like fan, engine, jet and aerodynamic effects.
The interim propagation method and most national propagation methods are derived from the ISO 9613-2 standard. This standard provides an empirical model to estimate the propagation effects in a very simplified situation (i.e. a flat terrain with a single screen). When applied to more complex situations, the real geometry has to be 'matched' to this simplified description. How to do this is not part of the ISO standard. Even though some national methods provide rules for the determination of the geometrical parameters, a large degree of freedom is left to the software developers. As a consequence, different implementations based on these common standards often lead to significantly different results, even in moderately complex situations, and differences up to 5 or even 10 dB(A) are not unusual.
With HARMONOISE / IMAGINE methods a harmonised approach is possible through the following steps:
1. The HARMONOISE model relies on explicit geometrical modelling of propagation paths; i.e. it is the complex geometry of the paths that is used as the input to the model. Because the software developers do not need to interpret the geometrical data, this will clearly result in higher reproducibility of the results.
2. The IMAGINE project provides a complete and explicit set of specifications for the geometrical model (i.e. the data) on which the HARMONOISE methods (i.e. the algorithms) operate. Such specifications define the end-user requirements for the collection of data and for the construction of the geometrical model. As much as possible, these requirements are expressed in quantitative terms.
3. Sensitivity analysis of the HARMONOISE / IMAGINE method provides explicit links between the accuracy and the level of detail of input data and the expected accuracy of the results. This also allows for objective rank ordering of the data items to be collected.
As part of the common models and methods as prescribed by the END, the IMAGINE project also looked into common methods for the estimation of populations exposed to noise.
There is no interim method for the measurement of Lden nor is there any international or national method addressing all the relevant parameter related problems resulting from the use of the HARMGNOISE source and meteorological models. Thus, the measurement method developed within IMAGINE introduces many new features compared to available methods. The most important new features are:
- measurements are classified into meteorological classes. The measurement method is harmonised with the IMAGINE calculation methods for road, rail, aircraft and industry noise.
- stratification of measurement according to meteorological conditions.
- measurement uncertainty is dealt with in compliance with the guidelines given in ISO GUM.
- the method is general and can be adapted both to industrial noise and road, rail and air traffic.
- both short term and long term measurements are dealt with correction of measured values to be representative for yearly averages is dealt with the method is flexible, different measurement efforts will yield different measurement uncertainties.