GB2582058A - Acoustic methods and systems - Google Patents

Abstract

A method of constructing a tranquillity map for a region comprising a plurality of survey locations, using at least one acoustic sensor. Using acoustic signal processing the method calculates the probability of at least one tranquillity score from a plurality of tranquillity scores, wherein said probability is calculated using an overall average level sound, LAT, the average level of sound is corrected as appropriate, LRR, detected from road and rail sources, a first parameter, NAMM, representing the relative proportions of sounds from natural and man-made sources, and a second parameter, PONS, which represents percentage of time only sound produced from natural sources is detected.

Description

Acoustic Method and System

Technical Field

Aspects of the present invention generally relate to acoustic methods and systems and in particular to methods and systems for constructing a tranquillity map using at least one acoustic sensor.

zo Background

Tranquillity generally refers to the degree to which an outdoor space is likely to be considered to be tranquil. Spending time in tranquil spaces is known to have clear benefits to people's health and well-being. The protection and enhancement of tranquillity is therefore an important step for a civilised, healthy society. This applies both in rural environments, where current levels of tranquillity may be high but where the pressures of development may threaten the fragile peace meaning that it could be permanently lost; and in urban environments, where tranquillity may be relatively low but, compared with the surrounding area, a location which feels only "slightly" tranquil may be considered to be a valuable resource.

The Oxford English Dictionary describes tranquillity as: "The quality or state of being tranquil; freedom from disturbance or agitation; serenity, calmness; quietness, peacefulness, and this can relate to states of mind and landscapes." The present disclosure relates to tranquillity of Landscapes and in particular to providing acoustic methods and systems which enable the construction of tranquillity maps in an effective and objective manner.

There are currently strong drivers from the UK government to try to promote, improve and protect tranquil places. However, without a reliable way of assessing tranquillity, the designation of tranquil and quiet areas and their subsequent protection is difficult to achieve and the degree of protection is bound to be inconsistent.

The UK Government's NationaL Planning Policy Framework (NPPF) requires, amongst other is things, that: "Planning poLicies and decisions should also ensure that new deveLopment is appropriate for its location taking into account the likeLy effects (including cumulative effects) of pollution on health, living conditions and the natural environment, as well as the potential sensitivity of the site or the wider area to impacts that could arise from the development. In doing so they should: identify and protect tranquil areas which have remained reLatively undisturbed by noise and are prized for their recreational and amenity value for this reason." Since the pubLication of the NPPF, planning decisions are being made which cite the impact on tranquillity as a reason for refusal, but there is currently no reliabLe acoustic technique to determine how tranquil a place is or what effect any proposed development might have on that tranquillity.

Although methods for the assessment of tranquillity have been proposed in the past, none of the existing methods are sufficiently effective, high enough resolution or robust For these reasons, a reliable, repeatable method of assessment is needed.

It is to these problems, amongst others, that aspects according to the invention attempt to offer a solution.

Summary

According to a first independent aspect of the invention, there is provided a method according to claim 1. In particular, the method is for constructing a tranquillity map for a region, using at least one acoustic sensor, the region comprising a plurality of survey Locations, with a first subset of the plurality of survey locations Located along a perimeter of the region; wherein, for at least one survey Location from the plurality of survey Locations in the region, for a period of time t, the method comprises the steps of: measuring, with the least one acoustic sensor, an overall average Level of sound, [AT, detected at said at least one survey Location; determining an average Level of sound, [KR, from road and rail sources; providing a first parameter, NAMM, representing a relative contribution to the overall average Level of sound, [AT, of natural sources and man-made sources; providing a second parameter, PONS, representing a percentage of said period of time t in which only sound produced from natural sources is detected at said at Least one survey location; providing a plurality of tranquillity scores, wherein each tranquillity score represents a level of tranquillity at said at least one survey location; and calculating a probability of at Least one tranquillity score from said plurality of tranquillity scores, wherein said probability is calculated using the overall average level of sound, [AT, the average level of sound, LRR, detected from road and rail sources, the first parameter, NAMM, and second parameter, PONS.

The acoustic method is referred to as the "Natural Tranquillity Method" and enables an environmental noise specialist to objectively evaluate tranquillity using measured sound Levels and observations. This is due to a combination of providing specific physical locations in the region to locate the acoustic sensors and acoustic processing techniques to determine the overall tranquillity of the region. The combination is considered to be a significant advance in acoustic science.

It provides an evidence based, repeatable technique for the assessment and mapping of tranquillity on a Local Level. This enables planning decision makers to establish the baseline tranquillity of a location and to see what change in tranquillity would arise as a result of a development proposal. The method can thus be an important tool to assist with the UK Government's National Planning Policy.

By 'a perimeter' we refer to a region boundary and the first subset of locations is preferably as close as physically practical to the boundary. For example, this may be near a fence or edge of a park. Preferably, the steps a) to f) are carried out for at least one location in the first subset It will be appreciated that in many situations, the map will need to extend beyond the boundary of the site of interest to understand the tranquillity score in the surrounding areas. Accordingly, a further subset of survey locations may be provided outside the perimeter of the region.

In a dependent aspect, the region further comprises a plurality of identified features inside the perimeter, the method further comprising the step of providing a second subset of the plurality of survey locations in sub-regions of the region which respectively include the is identified features; and carrying out steps a) to 0 for at least one survey location in the second subset By 'features' we mean locations or areas in the region which are likely to significantly impact tranquillity. Figure 12 shows an exemplary site and surroundings with main park features labelled. The park paths are represented by stippled lines and they can also be considered 'features' of the region. Tranquillity scores are thus advantageously calculated for significant locations around the perimeter as well as within the perimeter.

Importantly, this enables surveyors to understand how tranquillity varies around the region, which maybe bounded outside the perimeter by regions of different tranquillity.

In a dependent aspect, there is provided a third subset of the plurality of survey locations at boundaries of contiguous sub-regions from said sub-regions and carrying out steps a) to f) for at least one location in the third subset For example, the boundaries of the contiguous sub-regions may be public paths within a park, as exemplified in Figure 14.

In a dependent aspect, the method further comprises the step of assigning, to each of the plurality of survey locations in the region, a tranquillity score from the plurality of tranquillity scores with the highest calculated probability, and grouping the at least one location in the region having the same assigned tranquillity score. This enables the construction of a tranquillity map.

In a dependent aspect, the method further comprises the step of providing a tranquillity map using the grouped at least one survey locations and assigned tranquillity scores. The tranquillity map is a reliable, objective instrument which may be used in planning permissions.

In some embodiments, the NAMM parameter may be provided from a scale, wherein a Lowermost value (e.g. 1) corresponds to all or virtually all sound coming from man-made sources; and an uppermost value (e.g. 5) corresponds to all or virtually all coming from natural sources. It will be appreciated that NAMM does not have to be an integer, and that the chosen scale is arbitrary. In a dependent aspect, NAMM is determined according to rules tabulated in Table 1 or Table 4.

The PONS parameter is usually represented as a percentage although it can be a fraction for example, or any other value from an arbitrarily chosen scale. In a dependent aspect, at least one of steps c) and d) uses a rule (NP1 to NP9) tabulated in Table 2.

The tranquillity score is a parameter which is also typically provided from a scale, wherein a Lowermost value (e.g. 1) which corresponds to a location deemed to be chaotic, frantic or harsh and an uppermost value (e.g. 8) which corresponds to a location with excellent tranquillity. It will be appreciated that the chosen scale for the tranquillity scores is arbitrary.

In a dependent aspect, the relative probabilities of each possible tranquillity score (scores being as shown in Table 5A) is calculated and the highest value is selected as the most likely score and therefore reported as the predicted tranquillity score. The relative probabilities are calculated as follows: The relative probability, Pi of the tranquillity score 1 (corresponding to the tranquillity score of 1) described as shown in Table 5A below) is always zero: Pi = 0.00; and the relative probability of each other tranquillity score, P, (where n is a value between 2 and 8, corresponding to the tranquillity scores of 2 to 8) as shown in Table 5A) is given by; 30 Pn = Ann + Abn x NAMM + Ann x PONS + Adn X LRR + Ann x Lir Where Ann, Abn, Ann, Adn and An, are five different constants for each value of n, such that there are in total of 35 different constants (five constants per tranquillity score and seven tranquillity scores) in total.

The average level of sound, [RR, from road and rail sources (provided e.g. in decibels) may be determined according to methods known in the art. The [RR may be corrected according to certain rules. It will be appreciated that it could be measured or modelled. In a dependent aspect, the step of determining an average level of sound, [RR, from road and rail sources comprises, adjusting the level of sound, [RR, using at least one rule (RR1 to RR7) tabulated in Table 3.

The overall average level of sound, [AT, (provided e.g. in decibels) typically represents the average level of sound detected, which may be corrected according to certain rules, from all present sources and is measured in decibels. In a dependent aspect, determining the overall average Level of sound, [AT, comprises measuring an A-weighted equivalent, LAGq, sound level.

If sound is detected from rail sources, preferably, the measured A-weighted equivalent, LAeq, is excludes the sound detected from rail sources and the overall average level of sound, [AT, is determined by adding a corrected value of the sound detected from rail sources. This provides a more accurate assessment of tranquillity when rail sources are present If sound is detected from aircraft sources (wherein aircraft noise is detected in the overall average level of sound, [AT), providing the first parameter, NAMM, may comprise estimating a level of sound produced only from natural sources, [NA, and estimating a level of sound produced from man-made sources Lmm, including aircraft noise. Preferably, the method is then repeated for at least one second period of time during which no aircraft noise is detected. Advantageously, the contribution of aircraft to the NAMM and PONS parameters is recoded separately in the separate periods of time and then, at the end of the survey, this is used to accurately assess the overall impact to the site.

According to a second independent aspect of the invention, there is provided a system as set out in independent claim 14. In particular, the region comprises a plurality of survey locations, with a first subset of the plurality of survey Locations Located along a perimeter of the region; the system comprising at least one acoustic sensor for detecting sound, over a period of time t, at at Least one survey Location from the plurality of Locations in the region, and a processor configured to: for said at least one survey location, for said period of time t: measure an overall average Level of sound, [AT, detected at said at least one survey Location; determine an average level of sound, [RR, from road and rail sources; provide a first parameter, NAMM, representing a relative contribution to the overall average Level of sound, [Al, of natural sources and man-made sources; provide a second parameter, PONS, representing a percentage of said period of time t in which only sound produced from natural sources is detected at said at least one survey Location; provide a plurality of tranquillity scores, wherein each tranquillity score represents a Level of tranquillity at said at Least one survey location; and calculate a probability of at Least one tranquillity score from said plurality of tranquillity scores, wherein said probability is calculated using the overall average level of sound, [AT, the average level of sound, [RR, detected from road and rail sources, the first parameter, NAMM, and second parameter, PONS.

Preferred features of either independent aspect of the present invention are provided in the dependent claims.

zo Detailed Description

Aspects of the present invention will now be described, by way of example only, with reference to the accompanying Figures 1 to 14.

The Natural Tranquillity Method involves the collection of acoustic data by sensors Located within a surveyed region, acoustic analysis of this data and production of tranquillity maps for the surveyed region. The acoustic methods and systems are described below in the following five parts: 1 Method parameters; 2 Understanding the site -according to preferred implementations of the invention; 3 Obtaining the necessary data -this is done by positioning acoustic sensors within the site and determining road and rail noise. The system enables the obtaining of reliable, repeatable results.

4 Once obtained, the results will need to be processed and preferably moderated taking into account the knowledge gained during the initial research; and Mapping and reporting -the end goal is to produce a tranquillity map efficiently and effectively. Again, this process needs to be carried out in a reliable, repeatable manner.

1. The Parameters NAMM and PONS NAMM refers to the relative levels of natural and man-made sound, recorded according to

Table 1 of Figure 1.

With reference to parameter 2 in Table 1, it will be understood that "man-made" sounds include noise from items or animals brought to (or near to) the location by people, so would, is for example, include noise from dogs or radios.

PONS is recorded as the percentage of time when you can only hear natural sound. Silence (or absence of man-made and natural sounds, as defined here) is considered a "natural sound" contributing to the PONS value.

When scoring NAMM and PONS, the additional rules set out in Table 2 of Figure 2 are followed to estimate the value over a 12 hour day (from 07:00 to 19:00 hours) for example. Atypical events (which occur when the circumstances found at or near the site are different to those normally found) should be excluded from results altogether.

With reference to Table 2 in Figure 2: *Disregarded means treating it as if it does not exist at all. Other than for rules NP2, NP3 and NP4, road traffic (and rail) noise is effectively considered to be inaudible when assessing NAMM and PONS.

** Continuous means present all or virtually all the time. Even busy roads can have brief lulls in traffic flow occasionally; where these occur, the flow may still be considered continuous if it is audible most of the time.

Road and rail noise -the LRR parameter The assessment of road traffic noise and rail noise is well known in the art, therefore the approach to calculating these levels is not described in detail here.

For road traffic, ideally, levels around a site should be predicted using road traffic flow information (number, type and speed of vehicles) fed into a computer model enabling noise propagation to be calculated taking into consideration local topography, screening, wind conditions, ground and air absorption of sound. This is not a[ways possible in practice, however. When assessing a site it is important to try to assess the contribution of road traffic noise by measurement either to validate the model or because no modelled values are likely to be available. When it is not possible to predict levels by modelling or calculation, the LRR rules in Table 3 of Figure 3 should be followed.

is Rail noise can be predicted by modelling using information about train types and numbers.

In practice, however, specific data about train and carriage/wagon types may be difficult to access/utilise. It is therefore often calcuEated by measuring the Lev& of noise from different train types as the single event level, LAE, at a particular distance, adding up the contribution from each type depending on the number of trains which run in a typical day, then correcting for attenuation with distance and other factors which affect sound propagation, as appropriate to caEculate an average level for the period of interest; in this exampEe, generally, a 12 hour day. The approach to doing this is set out in acoustics textbooks known in the art, therefore is not reproduced here.

In order to obtain a value for LRR for sites where both road and rail noise is present, the road traffic noise (RTN) may be logarithmically added to (the level of rall noise (RN) -6 dB) over a 12 hour day between 07:00 and 19:00 hours using the following formula: LRR = 10 X 1.0gio [10(RTN/10) 1O((RN-6)/10)] Using the LRR parameter for other sound sources The LRR parameter was designed for assessing the contribution of road and rail noise, but it has been also found to be useful for one additional type of sound source. Occasionally, where there is a continuous, distant man-made sound such as a fan or motor which is only noticeable when listening carefully, this should be logarithmically (base 10) added to the LREt parameter without the application of any correction.

The LAT -the corrected overall average sound level The overall average sound level LAT may be derived from the measured LAeq, which may be modified according to certain rules in certain conditions. The LAeq is the A-weighted equivalent sound level expressed with a time reference period. It will be understood that this could be adapted to take account of multiple noise sources, including man-man and natural sources.

The LAeg should be measured using a type 1 sound level meter, calibrated, with an appropriate wind shield. All measurements should be taken in a free field location at a height of around 1.5 metres above ground. Meteorological conditions should be suitable for the measurement of environmental sound.

The [AT value used will, in general, be an estimate of the LAeg value which would be measured over a typical 12 hour day at each location. Reliable spot checks will normally be sufficient for this and the value to use for [AT will simply be the measured LAeq, with two exceptions: Exception 1: When train noise is present, this needs to be removed from the measurement and then added back in. When adding its contribution back into the assessment to obtain the effective "with train" [AT value, the corrected train noise must be used rather than the actual train noise. For example, the corrected train noise is the actual train noise minus 6dB: [AT = Measured LAeg (without trains) + (Train level -6).

In this example, the subtraction is arithmetic but the addition of levels is logarithmic (to the base 10).

Exception 2: If the survey Location is within 25 metres of an active playground regularly containing children shouting and screaming, then a 5 dB penalty should be added (arithmetically) to the measured LAsq value to account from the impact of this type of sound. In these circumstances, the following formula is used: LAY = Measured LAeg + 5 dB (arithmetic addition).

If a location has both an active playground and train noise present, then both corrections would need to be applied, with the playground correction being applied first.

Dealing with roads with low vehicle flows and more complex road traffic conditions In rural Locations, there is often less than one vehicle passing every minute and, although this can mean that the values of LRR (and therefore [AT) can be quite high) the tranquillity score is often still reasonably good since, for much of the time, there are no vehicles present. According to rules NP2 and NP3, from Table 2 in Figure 2, if the sound of road traffic is not continuous (not audible for all or virtually all of the day), the NAMM and PONS scores should not be modified. NAM M and PONS only need to be modified to take account of this when vehicle numbers rise to the point where road traffic noise is continuous.

Occasionally, one will encounter a more complex situation where there is a local road with low flows and continuous road noise from further away. In this situation, the value of LRR is quite Likely to be primarily affected by road traffic on the local low-flow road but the continuous sound of traffic on the more distant road(s) would also need to be considered.

To determine whether to correct the NAMM and PONS scores, one must first consider only the distant continuous road traffic noise, ignoring any noise from the Local road.

This approach would be important when considering the potential impact that a new road scheme might have on a rural Location which may currently experience good or excellent tranquillity, and which could result in a noticeable drop in tranquillity as a result of the scheme.

2. Understanding the site Before beginning survey work, it is suggested that three steps be undertaken: 1 Carry out consultation with the Local planning authority and other key stakeholders about the relative importance of tranquillity at the Location, the key features which contribute to this tranquillity and the location and extent of these features.

2 Review and critically evaluate any existing surveys of site users or other relevant data sources. Consider changes that have occurred since the previous surveys.

3 Identify suitable survey locations for the acoustic sensors required to adequately characterise and map the site and surroundings bearing in mind the following: * How tranquil is the area considered to be and how important is this tranquillity? Is it of national, regional or Local significance? Has the location or its surroundings been designated as having a quiet character within a conservation area, Area of Outstanding Natural Beauty, National Park or Local Green Space? * What are the key features or areas of the site / area which are considered to affect tranquillity or which have been identified as being tranquil or sensitive to change and where are these located on or near the site? * What is the spatial extent of the area to be considered? * What are people's expectations when visiting working or living in the Location? (i.e. will they be expecting virtually no man-made sound or will they be expecting some continuous noise, such as that from distant road traffic, to be present?) * If considering the potential impact on tranquillity from a proposed development, what are the other potential health and wellbeing benefits or detriments which might occur as a result of that development? Does the development have the potential to provide a beneficial impact, for example, by encouraging greater use of an existing tranquil space and thus an overall improvement in well-being for more people? Conversely, the development may result in other additional pollutants, such as air pollution or odour which may reduce overall well-being * Which parts of the site are accessible? Which parts of the site do most people use? At many sites there are some areas which are well used and other areas which, whilst open to all, have very few visitors (for example, because they are far from any visitor car park). It is necessary to understand the patterns of use of a site.

3. Obtaining the necessary data -the field survey

Assess and record values of the NTM parameters around the site.

Note details of all noise sources, observations of people's activities and estimates of sound Level contributions from natural sounds (wherever this is possible). Levels of any other sounds which can be estimated should be recorded whilst noting the overaFF measured LAeq, NAMM and PONS parameters. If aircraft, boat or train noise is present at Levels which have the potential to affect the tranquilFity score, then these levels need to be recorded. Road traffic noise will need to be assessed either by collecting data for modelling, such as traffic counts, or by measurement according to the rules above.

Review the site for a period long enough to capture the range of use patterns: this would usuaRy be a minimum of two days. If the site has varied use, try to represent the differences, is e.g., one weekend day and one week-day, or one in school summer holidays and one not.

A site map should be studied to provide an outline of the extent of the area to be surveyed prior to arriving at the site.

Weather conditions and seasonaFity should be considered. Survey conditions should be suitable for the measurement of sound levels, as set out in other guidance and standards.

Seasonality can also affect way that a site is used and the presence or absence of certain noise sources. Survey work during winter months will often be difficult, since weather conditions are poor; there will usualFy be fewer people present than during the rest of the year and there may be less natural noise from wind in the trees, due to the absence of leaves.

Also, if there is any water flowing, this will tend to produce more noise in winter than during other seasons, so winter conditions may not be typical of the rest of the year. Of course, if the use of the area during winter is a key consideration, then surveying at that time would be appropriate, bearing in mind how the noise may change during other seasons.

Site survey work should generally begin with a familiarisation tour of the site to identify the number and location of survey points needed and to note any relevant features which were not apparent from desk-based research. This will normally be informed by consultations and research undertaken prior to the site visit but changes may need to be made once on site due to Focal conditions. It will be important to note if there are any variations which might exist to noise levels or appearance due to short term events (such as agricultural work or grass mowing) or weather (for exampie, if there are more distant sounds whose propagation may be dependent on the wind direction).

Preferably, the survey team will need to visit each survey location within the site at leas: once, and ideally twice on each survey day for a minimum of fifteen minutes to measure sound levels and make observations of the following: * noise sources (including an estimate of their contribution to the measured I where this is possible); * estimates of the NAMM and PONS values; * estimates of proportions of sound from natural and man-made sources; * any other unusual, non-acoustic factors which have the potential to affect perceived tranquillity, where such factors are not transient; * an estimate of road traffic noise level; and * the measured LAeg for the period.

It may also be helpful to note the number of people encountered at the survey Location (along with some details of their activities, e.g., cycling, walking quietly, playing loudly) dogs barking), as this may aid subsequent interpretation of data.

When atypical noise events occur, which are not representative of this Location, the event should be recorded but the survey repeated when the atypical event has stopped. A passing emergency vehicle sounding its siren may be unusual or it may be on a common route to a nearby hospital. It may be necessary to return to the site on a different day to avoid atypical sources (e.g., road works).

Measuring Rail Noise in practice Whilst it is possible to calculate rail noise by inputting data about the train type, the number of carriages, speed, etc., into a recognised calculation modei to predict train noise around the site, it is often more practical to follow the method outlined below.

Measurements of passing trains should preferably be undertaken separately from the main survey and the LAE from the different types of train assessed at Locations close to the boundary of the site. These values can then be used along with timetable information showing the number of each train type on a typical day to calculate noise Levels from rail alone across the site. This can then be added to road traffic noise levels in the manner described above to provide a value for the LRR parameter for each survey location.

There are two practical ways to separate out rail noise from other sounds at a site. The first is to use a sound level meter which runs continuously but which has a function enabling each source to be coded; the second is to use two sound level meters and when a train or aircraft passes, pause the first meter and measure the event level on the second meter, restarting the first meter once the event is complete and recording the results from each separately.

Whichever way that trains are removed from the measurement, it is important to add their contribution back into the assessment, both to the LRR parameter and to the overall measured value. The corrected measured value is denoted as LAT. When doing this, the corrected rail noise is used rather than the actual rail noise.

LAT = Measured LAeg (without trains) + (Rail level -6) Rail noise is subtracted arithmetically first, then added logarithmically (base 10) to the level from other sounds.

Measuring noise from aircraft and boats in practice When assessing aircraft and boats, the NAMM and PONS scores should be adjusted to account for their presence.

If the site has no audible aircraft or boats or if these sources are present but make no difference to the overall measured level (e.g., in a city centre) then these events can be ignored. However, when ambient sound levels are lower (as is often the case in rural Locations) these sources may be more audible and therefore have more of a potential impact on tranquillity. Boats generally run on a predictable route whereas aircraft will frequently cross the area of interest at different heights, going in different directions and at a range of distances from the site.

A boat on a river or other watercourse will only be likely to influence NAMM values near to that route. Provided that NAMM and PONS scores are determined for a representative period at Locations close to these routes, their contribution will be properly included in unprocessed survey data. However, aircraft noise needs separate consideration due to its wider range of potential levels and spatial spread of impact. Aircraft noise therefore needs to be separated from other sounds in the same way as recommended for train noise. Whichever way is chosen, some post-processing is required to separate out levels from aircraft noise. Once separated, the contributions from aircraft noise can be added back into the assessment. The method for processing data from each of these sound sources is described below.

Adding aircraft noise into the assessment Aircraft noise tends to affect a wide area and so will often affect the whole site or at least a large part of it. Assessment of aircraft noise is influenced by how frequent, predictable and Loud the events are. Some Locations within a site might experience several aircraft in a 15-minute survey period by chance whereas others might not experience any. One cannot, therefore, use the observed NAMM and PONS for each survey Location as this would not provide a reliable picture of the impact of aircraft over the site over a day. At larger sites, is therefore, it is necessary to record the contribution from aircraft to the NAMM and PONS separately and then, at the end of the survey, add their impact back in for the site as a whole. Sometimes, high altitude aircraft will be audible but will not result in a change to the measured level. Where this occurs, the NAMM would remain the same as if there were no aircraft, but the PONS must be reduced to account for their presence.

However, wherever the contribution from aircraft produces a change in the overall measured NAMM scores also need to be adjusted to take account of this. Table 4below shows the recommended approach for assessing NAMM scores from aircraft, using measured values rather than by observation.

In Table 4, LNA denotes an estimate of the value of LAeq, 12 hours from natural sound only and LIAM denotes an estimate of the value of LAeq,12 hours from man-made sound including aircraft noise (but excluding road and rail, as normal).

Moderation of results It will be appreciated that NAMM and PONS scores will need to be based on the surveyed values to the extent that the surveyed values are typical for the surveyed region. Where conditions at the time of the survey were not typical, the results will need to be moderated taking account of whatever information is available from the background research or which becomes apparent during the survey.

4. Mapping and reporting Once all values of NAMM, PONS, LRR and LAT have been finalised, the approach described above may be used to obtain tranquillity scores for each location (using the scoring system shown in the Table 6 of Figure 6).

The period of interest will generally be the 12 hour day between 07:00 and 19:00 hours although a different period may appropriate in some circumstances, for example if a site is only open for access at certain times.

is For each Location, the tranquillity score to use will be the highest probability of the score which is chosen.

The tranquillity scores now need to be reported.

Any given site will have variations in tranquillity across it. One edge of the site may be near to a road so will feel less tranquil close to that edge; there may be an area of woodland with higher levels of natural sounds which feels more tranquil. Even at wilder sites, roads, picnic areas and car parks can reduce tranquillity in their vicinity. In order to determine whether or not tranquillity should be protected when considering a planning application, it is helpful to understand how existing tranquillity varies around the site in order to properly understand how a development proposal might affect this. For example, if a children's play area were proposed in a woodland location which has a reputation for tranquillity, this may appear at first to be a bad idea. However, if the play area was to be sited immediately adjacent to an existing picnic area, car park and road, it may be that this location is only "just tranquil" and therefore the impact of the play area on tranquillity may be acceptable.

Also, since tranquillity is perceived relative to the area around it, understanding the tranquillity in the surrounding area will also be important.

For these reasons, it is helpful to report tranquillity using a map of the area of interest and its surroundings. Once a tranquillity map has been produced, this can be published for the benefit of those who are wanting to consider the importance of tranquillity at a site. Areas with "excellent tranquillity" will almost certainly be in need of protection, but it may also be important to protect areas with "good tranquillity". In cities for example, spaces with "fairly tranquil" may be important and even "just tranquil" scores may be worthy of protection too, dependent on local circumstances and policy. It is not just the site itself but the tranquillity scores in the area around the site (neighbourhood tranquillity) which determine its importance.

Sometimes the goal may be to improve the tranquillity found at a site. Where this is the aim, predictions of the effects of proposed mitigation and improvement schemes will need to be prepared as rigorously as the reports of a site's current tranquillity and presented accordingly.

Drawings showing how a tranquillity map can be created are provided in Figures 7 to 11. Figure 7 shows an example of a base layer map (of a park on the edge of a town) with main features marked. Figure 8 shows the same map with 37 monitoring locations added. Layers can be created over these base maps showing the tranquillity scores marked for each measurement location. These scores can then be used, along with knowledge of the park's features, to create tranquillity contours (see Figure 9). Finally, clean contour lines can be traced over the rough contours and colour coding can be added. These steps are shown in Figures 10 and 11, respectively.

The potential detrimental or beneficial impact of a scheme on tranquillity can be evaluated by predicting the changes to NAMM, PONS, LRR and LAT values which would result from the proposals and then by mapping the existing tranquillity and the predicted tranquillity with the development in place. For example, it may be that at the site shown in Figure 11, it was proposed to introduce an additional play area near to the South-western corner of the site.

From the map, it can clearly be seen that the South-western corner currently has "good tranquillity" and that this would be adversely affected by such a play area. However, the South-eastern corner is "not quite tranquil" at best to start with so may provide a more suitable site. Modelling the two possibilities would provide an objective comparison of the relative impacts. The Natural Tranquillity Method empowers users to make decisions based on an objective, reliable prediction of the tranquillity that might be experienced.

When reporting on the output from the method, the following information will normally need to be included.

* Background to the study: why it is being carried out, what are the aims? * Details of a relevant information from initial research carried out to understand the site. This should include a summary of the views of stakeholders, relevant local policy and an overview of the site and its main features, details of the extent of the area of interest to be surveyed and an explanation of the reasoning for choosing this area.

* Details of the survey including dates and times, a plan of the site showing survey Locations, weather, equipment used and raw survey data.

* Details of moderation and corrections applied and a table of finalised parameter values and calculated tranquillity scores for each survey Location.

* A commentary on how tranquil the site is, along with its relative importance in the context of its surroundings and stakeholder views.

* A statement on the degree to which the site may need to be protected because of its tranquillity (with reference to relevant policy).

Assessing proposals for changes which may affect tranquillity Potential impacts on tranquillity can be evaluated by predicting the changes to NAMM, PONS, [RR and [AT which would result from the proposals and producing maps to enable a comparison to be made of existing and predicted tranquillity with the development in place. If a development is being considered, calculations will need to be undertaken using the same approach as is taken when adding the effect of aircraft noise described above but substituting predicted 'with development! enhancement' levels for the 'with aircraft' levels in Table 4. If the proposal would result in a change in natural sounds, the [NA parameter would also need to be adjusted in the same way.

Details of the proposal and an explanation of how this would change the values of NAM M, PONS, LRt and [AT found in each location need to be reported. A comparison of values using Table 4 and the same approach as that for adding the effect of aircraft above can be used to create a 'with development' tranquillity prediction. In these circumstances, the following would need to be reported: * details of the proposed scheme; * description of measures designed to reduce adverse impact on tranquillity or to enhance tranquillity; * details of predicted 'with development' levels of natural sound, man-made sound and overall sound level plus, where appropriate, predicted new road or rail noise Levels; * details of the calculations to show how development would affect the NAM NI, PONS, LRR and [AT values and thus the tranquillity scores. A table showing 'with mitigation / enhancement' values for all parameters and the predicted tranquilLity scores for each location; * tranquillity maps for both the existing situation and the proposed situation (with development or enhancement in place); and * commentary on extent to which the proposals considered would change tranquillity at the site and statement on whether tranquillity would be adequately protected or whether the changes would achieve the enhancement desired.

Any change to tranquillity which would result from a proposed development would need to be considered in context If the area currenty has excellent tranquillity, any reduction would almost certainly be significant. If the area currently has good tranquillity but would change to 'not quite tranquil' (or worse), this is also Likely to be significant However, if the existing area is only 'just tranquil' and changes to 'not quite tranquil', this may not be significant. It is worth noting that some areas within a busy city are predicted to be 'not quite tranquil' using this method but are viewed by visitors as 'an oasis of tranquilLity'.

Other relevant factors which may affect the interpretation of results are: * the proportion of people using the Location who might be affected; * the overall area affected compared to the size of the surrounding tranquil area; * the proximity of other tranquil spaces (particularly in urban areas); and * the existing temporal variability in tranquillity at the site due to changes in Local circumstances or weather conditions.

When reviewing the overall impact of a new development, it is worth considering other health and wellbeing benefits. For exampLe, a deveLopment which wouLd reduce tranquillity in a relatively small area of an otherwise tranquil location, but which enabled increased access to a nature trail, would result in a greater number of people having access to a tranquil space and therefore overalL benefit Using the formulae in Table 5A of Figure 5A, three worked examples are shown below:

Worked examples

1. A location in a country park has noise from distant road traffic and a relatively busy rail line at a distance of 100 metres. It is otherwise quite a natural environment, with birdsong being the dominant sound, a Little wind in the trees and occasionally one or two people passing by talking. The NAMM score is 4, the PONS is 85%, road traffic noise is 40dB, rail noise is 54dB (so the [RR would be 49dB) and the [AT is 51dB.

Using the formulae in example Table 5B, the calculated probabilities would be as shown in Figure 12.

The most likely tranquillity score in this case would therefore be a rating of 6-Fairly tranquil.

2. The Location is in a busy city, with road traffic noise and many people nearby and a busker in the distance. Road traffic noise dominates with a level of 66dB but there is also some noticeable contribution from people, and the overall measured Level is 67dB. Since road traffic is dominant, the NAMM score is 1 and PONS is 0%.

Using the example formulae in Table 5B, the calculated probabilities would be as shown in Figure 13.

The most likely tranquillity score in this case would therefore be a rating of 2 -Busy / noisy.

3. The location is on a river estuary, with sounds from birds calling, waves on the shore and no road or rail audible. There are no man-made sounds other than high altitude aircraft which pass over roughly twice per hour and produce a noise level which is not measureable, although they can be heard. NAMM is 5, PONS is 95%, [RR is 15dB and [AT (which is entirely due to wave and bird sounds) is 52dB.

Using the example formulae in Table 5B, the calculated probabilities would be as shown in Figure 14.

The most Likely tranquillity score in this case would therefore be a rating of 8 -Excellent tranquillity.

Those skilled in the art will be able to make modifications and alternatives in view of the disclosure which are contemplated as falling within the scope of the appended claims. Each feature disclosed or illustrated in the present specification may be incorporated in the invention, whether alone or in any appropriate combination with any other feature disclosed or exemplified herein.

Claims (14)

1. Claims 1. A method of constructing a tranquillity map for a region, using at least one acoustic sensor, the region comprising a plurality of survey locations, with a first subset of the plurality of survey locations Located along a perimeter of the region; wherein, for at least one survey location from the plurality of survey Locations in the region, for a period of time t, the method comprises the steps of: a) measuring, with the least one acoustic sensor, an overall average Level of sound, [AT, detected at said at least one survey Location; b) determining an average level of sound, [KR, from road and rail sources; c) providing a first parameter, NAMM, representing a relative contribution to the overall average Level of sound, [AT, of natural sources and man-made sources and making an assessment of the value of that parameter; is d) providing a second parameter, PONS, representing a percentage of said period of time t in which only sound produced from natural sources is detected at said at least one survey Location and making an assessment of the value of that parameter; e) providing a plurality of tranquillity scores, wherein each tranquillity score represents a level of tranquillity at said at least one survey location; and 0 calculating a relative probability of each tranquillity score from said plurality of tranquillity scores, wherein said probability is calculated using the overall average level of sound, [AT, the average level of sound, [KR, detected from road and rail sources, the value of the first parameter, NAMM, and the value of the second parameter, PONS; and selecting the score with the highest probability of occurring for each Location as the tranquillity score for that location, Wherein, the relative probability, Pi corresponding to the tranquillity score of 1 P1 = 0.00; and the probability of each other tranquillity score, Pn is given by; Pn = Aan + Abn x NAMM + Acn x PONS + Adn X [RR Aen X LAT wherein A., Abn, A., A. and Aen are constants.
2. 2. A method according to claim 1, wherein steps a) to f) are carried out for at least one location in the first subset.
3. 3. A method according to claim 1 or claim 2, wherein the region further comprises a plurality of identified features inside the perimeter, the method further comprising the step of providing a second subset of the plurality of survey Locations in sub-regions of the region which respectively include the identified features; and carrying out steps a) to f) for at least one survey location in the second subset.
4. 4. A method according to claim 3, further comprising the step of providing a third subset of the plurality of survey locations at boundaries of contiguous sub-regions from said sub-regions and carrying out steps a) to f) for at Least one Location in the third subset.
5. 5. A method according to any preceding claim, further comprising the step of assigning, to each of the plurality of survey locations in the region, a tranquillity score from the plurality of tranquillity scores with the highest calculated probability, and grouping the at least one Location in the region having the same assigned tranquillity score. 6. 7. 8. 9.
6. A method according to claim 5, further comprising the step of providing a tranquillity map using the grouped at Least one survey locations and assigned tranquillity scores.
7. A method according to any preceding claim, wherein determining the overall average level of sound, [AT, comprises measuring an A-weighted equivalent, Leg, sound level.
8. A method according to any preceding claim, wherein, if sound is detected from rail sources, the measured A-weighted equivalent, LAeq, excludes the sound detected from rail sources and the overall average Level of sound, [AT, is determined by adding a corrected value of the sound detected from rail sources.
9. A method according to any preceding claim, wherein aircraft noise is detected in the overall average level of sound, [AT, and wherein providing the first parameter, NAMM, comprises estimating a Level of sound produced only from natural sources, [NA, and estimating a Level of sound produced from man-made sources Wm, including aircraft noise.
10. 10. A method according to any preceding claim, wherein a first parameter, NAMM, is provided according to rules tabulated in Table 1 or Table 4.
11. 11. A method according to any preceding claim, wherein at least one of steps c) and d) uses a rule (NP1 to NP9) tabulated in Table 2.
12. 12. A method according to any preceding claim, wherein the step of determining an average level of sound, LRR, from road and rail sources comprises, adjusting the Level of sound, LRR, using at Least one rule (RR1 to RR7) tabulated in Table 3.
13. 13. A method according to any preceding claim, wherein the probability of each tranquillity score is calculated using at least one formula tabulated in Table 5A or 5B.
14. 14. A system for constructing a tranquillity map for a region, the region comprising a plurality of survey locations, with a first subset of the plurality of survey locations Located along a perimeter of the region; the system comprising at least one acoustic sensor for detecting sound, over a period of time t, at at least one survey location from the plurality of Locations in the region, and a processor configured to: for said at least one survey location, for said period of time t: measure an overall average Level of sound, [AT, detected at said at Least one survey Location; determine an average level of sound, LRR, from road and rail sources; provide a first parameter, NAMM, representing a relative contribution to the overall average Level of sound, LAT, of natural sources and man-made sources; provide a second parameter, PONS, representing a percentage of said period of time t in which only sound produced from natural sources is detected at said at Least one survey Location; provide a plurality of tranquillity scores, wherein each tranquillity score represents a level of tranquillity at said at least one survey location; and calculate a probability of each tranquillity score from said plurality of tranquillity scores, wherein said probability is calculated using the overall average Level of sound, LAT, the average level of sound, LRR, detected from road and rail sources, the first parameter, NAMM, and second parameter, PONS and select the score with the highest probability to represent the score for each location, Wherein, the relative probability, PL of the tranquillity score 1 (corresponding to the tranquillity score of 1, described as shown in Table SA below) is always zero: P1 = 0.00; and the probability of each other tranquillity score, Pr, is given by; Pn = Aan + Abn x NAM M + Ann x PONS + Adn X LRR Aen X LAT wherein Aan, Abn, A., Adn and ken are constants.