19 th INTERNATIONAL CONGRESS ON ACOUSTICS MADRID, 2-7 SEPTEMBER 2007

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19 th INTERNATIONAL CONGRESS ON ACOUSTICS MADRID, -7 SEPTEMBER 007 IMAGINE proect: urba measuremets of Lde ad Light ad calculatio of the associated ucertaities. PACS: 43.50.

1 19 th INTERNATIONAL CONGRESS ON ACOUSTICS MADRID, -7 SEPTEMBER 007 IMAGINE proect: urba measuremets of Lde ad Light ad calculatio of the associated ucertaities. PACS: rq Paviotti, Marco 1 ; Kephalopoulos, Styliaos 1 ; Joasso, Has 1 Europea Commissio, DG JRC; v. E. Fermi, 1, Ispra, 107, Italy; marco.paviotti@rc.it SP Techical Research Istitute of Swede, Box 857, SE Borås, SWEDEN; has.oasso@sp.se ABSTRACT This article describes the priciples of the ew measuremet method developed withi the IMAGINE Europea proect to determie L de ad L ight, as defied by the Europea Noise Directive 00/49/EC, by direct measuremet of the oise levels. The measuremet method was tested i a real ad complex urba eviromet icludig a maor road, a maor railway lie ad a idustrial site. A descriptio is give for the calculatio of the yearly averaged levels ad the ucertaity estimatio. Cocerig such log term idicators, estimatio of ucertaity is a rather complex task, especially if the yearly L de ad L ight are derived from measuremets performed over a short period of the year. The ucertaities cocer the microphoe positio, the source variatio, the meteorological variatios, the correctio for backgroud oise ad the soud level meter class 1 ucertaity. The example described here is based o a measuremet campaig performed over oe year i the city of Pisa (Italy).The aforemetioed measuremets would be typically applied to support the credibility of oise map calculatios towards the citizes ad to validate calculatios of oise maps i well-defied situatios. INTRODUCTION Followig the requiremets of the Evirometal Noise Directive 00/49/EC (END) [1], oise levels are to be mapped i Europe. The metrics used by this Europea Directive are L de ad L ight : I the END it is stated that L de ad L ight ca be either computed or measured. Therefore, withi the Europea IMAGINE proect [] work has bee performed to produce a protocol to measure these two values, repetative of the average year, as defied i the END. A lot of effort has bee spet to give ot oly a framework for the measuremet of the two idicators L de ad L ight, but also to attribute a overall ucertaity so that, depedig o the method used to perform the measuremet, it could be stated how accurate that value is. A cocrete example is give cocerig the oise measuremets performed of a maor road, however far from the road itself ad i a complex urba eviromet. BASIC PRINCIPLES The method to measure the Europea oise idicators L de ad L ight, makes it possible to separate the assessmet of the source variatio ad its ucertaity o oe had ad the trasfer fuctio betwee the source ad the receiver uder differet propagatio coditios, which depeds o the meteorological parameters, ad its ucertaity o the other had. The geeral equatios described i the END are used to calculate the L de ad L ight durig each combiatio of source ad propagatio coditio. Source ad propagatio are grouped i classes defied by level itervals that are specified by the team performig the measuremet. The choice of the itervals depeds o the variability of the source ad the propagatio coditios as well as o the possibility to have a large or a small amout of samples (geerally L pa ) to use for the evaluatio. Oce a combiatio of these itervals is set, L de ad L ight ca be calculated averagig the levels recorded durig these combiatios. Ucertaities are the associated with the overall log-term oise value obtaied, by itegratig the several separate short-term measuremets ad related ucertaities used to extrapolate the yearly average L de ad L ight. The method developed follows the requiremets of the GUM [3], which states that each sigificat source of error has to be idetified ad corrected for. The basic priciple is that, if the quatity L m is measured, which is a fuctio of the quatities x, the:

2 L = f x ) (Eq. 1) m ( If each quatity x has the stadard ucertaity σ the combied ucertaity is give by: where the sesitivity coefficiet c is give by: ( ) σ ( L m ) = c σ (Eq. ) 1 c f = (Eq. 3) x The measuremet ucertaity to be reported is the combied measuremet ucertaity associated with a chose coverage probability. By covetio, a coverage probability of 95% is usually chose, with a associated coverage factor of. This meas that the reported measuremet ucertaity becomes L m +σ. For evirometal oise measuremets f(x ) is complicated ad it is hardly feasible to formulate exact equatios for the fuctio f. The calculatio of ucertaity correlated to each parameter could be i ay case performed followig the approach suggested by Kephalopoulos et.al. [4] where it is explaied how oise levels could be associated to their corpodig ucertaities. Hece, i the followig, it is ecessary simplificatios to be made. Followig the priciples give i ISO 3745 [5], some importat error sources could be idetified: L = + δ + δ + δ + δ + δ (Eq. 4) true L m slm sou met loc where L true is the true (o errors) value durig the specified coditios for which we wat a measured value, L m is the measured value, δ slm is the error of the measuremet chai (soud level meter i the simplest case), δ sou is the error due to deviatios from the ideal operatig coditios of the source, δ met is the error due to meteorological coditios deviatig from the ideal coditios, δ loc is the error due to the selectio of receiver positio ad δ is the error due to idual oise. Equatio (4) is very simplified ad each source of error is a fuctio of several other sources of error. I priciple Eq. (4) could be applied o ay measuremet lastig from secods to years. I [6] the measuremets are divided ito short ad log-term measuremets. A shortterm measuremet may typically rage betwee 10 miutes ad a few hours whereas a typical log-term measuremet may rage betwee a moth ad a year. I may cases the measuremet ults should be maipulated to extrapolate them to other coditios, e.g., ormalizig to differet traffic flows, ad to use them for calculatig quatities like the L de. Let us cosider the followig specific case. I this L deotes the L pa for coditio, which lasts for p of the total time, whereas L. deotes the total L pa for the overall time iterval. We the get: L1 L L ( p 10 + p p ) L 10lg + = (Eq. 5) 1 10 If L 1,..,L are idepedet the sesitivity coefficiet c 1 is the give by L p 10 l(10) 0,1 p 10 = = 10lg( e) = L1 L L Li / 10 p 10 + p p 10 p 10 1 L c (Eq. 6) i L 19 th INTERNATIONAL CONGRESS ON ACOUSTICS ICA007MADRID

3 As p i = 1 these coefficiets are ot idepedet. Istead we write Eq. (5) i the form For c pi we get = L L L 1 10lg p110 p10... p 110 (1 pi ) 10 i= 1 1 L / 10 L (Eq. 7) L Li c pi = = 10lg( e) Li / 10 (Eq. 8) p p 10 i L i is determied with the stadard ucertaity u Li ad p i with the stadard ucertaity u pi. The stadard ucertaity u of L is the give by i 1 ul + i= 1 i i= 1 pi u = u i (Eq. 9) pi where the letter u istead of σ is used to specify that these ucertaities are estimated ucertaities. EXAMPLE OF UNCERTAINTY CALCULATION Maor road oise source The method developed, is based o the aforemetioed rules for the ucertaity calculatio, ad was tested o a assessmet positio located i a complex urba eviromet. The locatio was about 150 m away from a maor road i which were circulatig more tha three millio vehicles per year. The microphoe at the assessmet poit was placed at 4m height ad m away from the flat façade of a house. At this locatio, several other oise sources were most of the time simultaeously pet (e.g., fa oise of a earby idustrial pla, railway, local road, aircraft, people talkig), havig, whe active, approximately the same istataeous L eq as the specific source uder assessmet. It was therefore ecessary to discrimiate the cotributio of the maor road, ad evaluate the ucertaity of the overall measuremet performed. The oise from the maor road was measured to check the traffic variatios durig the day, the week ad the year. Two methods were used to quatify the traffic alog the maor road: the first by direct coutig ad classificatio of the vehicle pass-bys ad the secod by assessig the L 95 value usig a microphoe placed close to the road. Meteo classes The followig meteorological coditios were measured: wid directio, wid speed, temperature, temperature gradiet, T*, u*, 1/L (iverse Moi-Obuchov legth) gradiet. Based o these measuremets ad also followig the defiitio of meteorological classes relevat for oise propagatio developed i the HARMONOISE proect [7], four meteorological classes repetative of the possible propagatio coditios were established. These classes varyig betwee class M1 for stable meteorological coditios with favourable soud propagatio ad class M4 for very ustable meteorological coditios with ufavourable soud propagatio. It is essetial to uderlie the fact that a assumptio for the meteo classes was made. Havig measured the meteo classes over more tha four moths, ad for oe moth each seaso of the year, the iformatio about this subset of the meteo classes used was assumed to be repetative for the whole give year. To get the ucertaity due to the propagatio coditios, four possible meteorological situatios were distiguished, depedig o the curvature of the soud propagatio. About twety differet L pa,i,source were compared to the corpodig L pa,i,receiver ad, based o these measuremets, the followig meteo ucertaities were derived (Table 1). I the Table 1, class M1 corpods to the more favourable propagatig coditio whereas, class M4 to the ufavourable. Sice the eviromet cosidered i this study was a 19 th INTERNATIONAL CONGRESS ON ACOUSTICS ICA007MADRID 3

4 urba eviromet, free field meteo coditios were ideed ot eve closely related to the local meteo coditios betwee the buildigs ad above these [8]. The ucertaity values calculated cofirmed this hypothesis, sice all values were betwee 1.3 db ad.1 db despite of the fact that i geeral stable meteo coditios (class 1 i this study) should relate to a low ucertaity whereas ustable meteo coditio (class 4 i this study) should relate to a large ucertaity. Table 1. Ucertaities associated to meteo variatio for each meteo class (M1, M, M3, M4). Class M1 M M3 M4 σ met The meteo classes were the averaged durig the period ivestigated. Cosiderig the distributio of the samples (e.g., takig samples every day betwee :00 am ad 3:00 am, after oe moth there were 8 samples distributed betwee M1, M, M3 ad M4), the ucertaity cocerig the determiatio of the meteorological classes distributio could be foud usig the formula of (Eq. ). Operatig coditio classes To extrapolate the oise cotributio of the road, at first a classificatio of the road traffic was performed by moitorig the road traffic over 48h. This obviously itroduced a ucertaity, sice the extrapolatio to the aual average traffic from differet hourly time itervals should be estimated. To partially cope with this, the L 95 level was used as a idicator of the variatio of the road traffic alog the year. I other words, the traffic was moitored usig a microphoe, the the L 95 was used as a rough estimatio of the pece of vehicles. Usig several 15mi samples of the L 95, there was a sufficiet umber of elemets to perform a statistical evaluatio of the traffic coditios durig several momets of the day, durig differet days of the week ad durig differet seasos of the year, which could the be used to determie a σ for the road traffic flow fluctuatios. Five classes of traffic flow durig a sigle day were idetified, ad regarded as A or B durig the day, ad as C, D, E durig the ight. Usig the first techique (direct coutig of vehicles) o iformatio is available o the traffic volumes durig other days tha the oe used for the assessmet, however, coutig vehicles is ecessary to kow which is the expected ucertaity due to the specific types of vehicles durig the specific momet of the short-term measuremet. I other words, if oly oise levels are recorded, there is o iformatio whether or ot these levels are caused by the average vehicle pass bys or by a specific combiatio of acoustically exceptioal vehicles. Therefore, ot oly several levels are to be measured to calculate the oise levels at the assessmet positio, but also the umber of vehicles durig each recorded short-term L pa. For the situatio ivestigated, calculatios were based o 15 mi L pa records. I all differet periods subsequet samples were used to evaluate the ucertaity cosiderig the umber of vehicles each 15 mi, ultig i a selectio of five differet classes (Table ): Table. Ucertaities associated with source variatio for each traffic class. A B C D E σ sou This ucertaity is to be used if the traffic flow is measured directly, or take from local authority statistics, ad the extrapolatio of the L de is performed based o these umbers of vehicles ad traffic distributios. The same procedure was applied to estimate ucertaities comig ot oly from A, B, C, D, E classes for oe sigle day of a week, but also from classes which take ito cosideratio mothly or seasoal variatios by itegratig the differet traffic flows durig the t of the weekdays, Saturdays, Sudays, ad, o a two seaso (summer ad witer time) basis. Oce agai, these could directly be assessed o the basis of the L pa oise levels recorded i each period. I other words, over the weeks the oise measuremets performed (e.g., oe i September 005, oe i December 005, two i February 006, ad oe i Jue 006) to assess the road traffic oise source, the L pa were recorded for each A, B, C, D, E period, each day (therefore, 5 L pa every day). Over such periods the ucertaity is calculated 19 th INTERNATIONAL CONGRESS ON ACOUSTICS ICA007MADRID 4

5 based o the several i-th day samples (e.g., 9 weekdays implies 9 samples -Mo, Tue, Wed, etc.). Extrapolatio at the receiver by meas of measured trasfer fuctios I the situatio ivestigated, local oises were pet, such as cars passig by the local road, people chattig, birds sigig, besides the pece of three other maor evirometal oise sources (maor railway lie, idustrial source, maor airport). To evaluate the cotributio to the overall oise levels of the road traffic oly, a trasfer fuctio betwee the maor oise source ad the receiver was estimated uder several meteorological classes. Based o the trasfer fuctio it was possible to use oly the oise records (oise levels) whe the oise source uder assessmet (i.e., road traffic) was clearly distiguished from other oise sources. Besides estimatig the trasfer fuctio, a correctio should evertheless be made for the idual oise at the receiver, sice recordig a clearly distiguished oise did ot ecessarily mea havig it more tha 10 db (as typically cosidered i measuremets) louder tha all the other oise sources pet at the same time. What was regarded i other stadards as backgroud oise or extraeous oise or idual oise was all regarded here as idual oise. Residual oise is the oise produced by all sources but the specific source uder assessmet. Residual oise could therefore be cosidered a local oise occasioally produced, aother relevat mai oise source, or a frequet o-evirometal oise source (e.g., people chattig, birds sigig). Sice the short-term periods used i this study were selected durig a time period whe o other oise sources (such as railway, local road, aircraft, people, birds) were pet, i the time period used for the assessmet, the idual oise was limited oly to the fa from the earby idustrial pla. This fa oise was previously measured to be L pa, = 43.5 db ad it was a costat source. Sice the road traffic oise had a L pa o more tha 10dB higher tha the L pa of the fa (=L ), the correctio for idual oise should be used the. Therefore, the followig formula should be used: L' L = 10 log Subsequetly, ucertaity was calculated over the trasfer fuctio for each meteo class, ad the idual oise ucertaity was also cosidered. This latter ucertaity was derived usig the formula L (Eq. 10) c ( L' L ( L' L At the assessmet positio, the average LpA was L = 49.0 db, whereas LpA, = 43.5 db, hece, the sesitivity coefficiet is c L =c = Other specific ucertaities The distace betwee the source ad the receiver was about 50 m, therefore the ucertaity of atmospheric absorptio was also cosidered (although it was expected to be very low) ad assumed to be 0. db. For the soud level meters used (oe at the receiver poit, ad oe at the road side), the ucertaity attributed was u slm =0.5 db for each microphoe. The idual oise at the road was about 30 db(a) lower tha the road traffic oise, therefore o correctio was eeded ad the ucertaity of the idual oise was set u =0 db. Because of the positio m i frot of a façade, the ucertaity was take as u pos =0.5 db as derived from a study, performed i the cotext of the IMAGINE proect, to test the acoustical correctios for reflectios o a façade [9]. Calculatio of the overall ucertaity Basically, the sesitivity coefficiets were calculated usig the formula (Eq. 6), sice the oise levels used were idepedet values. 19 th INTERNATIONAL CONGRESS ON ACOUSTICS ICA007MADRID 5 ) = (Eq. 11) )

6 Subsequetly, the formula (Eq. 7) should be applied iteratively: the first time, while averagig over the day, eveig ad ight, the while averagig for the day of the week, the while averagig for the seasos ad fially while calculatig the L de usig the three periods (day, eveig, ight). It should be oted that u sou ad u met are the icluded i the calculatio of u de. For the measuremet campaig i this study, this was foud to be 0.7 db (u de is ot the overall ucertaity). Oce all the ucertaities were calculated, for this specific situatio, the overall ucertaity was: de pos slm1 slm atm u = u + c u + u + u + u + u (Eq. 1) ad, after substitutig with the values, we get u = 1. db. CONCLUSIONS I the pet article the method developed for the testig of the protocol cocerig the measuremet of L de ad L ight followig the requiremets of the END was peted, i the case of road oise source measuremets. Specifically, it was show how it is possible to measure the required values i complex situatios, obtaiig both the required oise levels ad the associated ucertaities. Oce this accomplished, the ults are satisfactory for commuicatig them to the populatio exposed as well as to the policy makers who eed to implemet oise reducig measu where appropriate. I the past the measuremets performed were ofte either icludig extraeous oise sources, or oly oe source, however this measuremet was repetative oly of a partial period of the year. The techique described here esu that log term oise values for a selected specific source could be obtaied i ay complex situatio which icludes periodical variatios ad coexistece of other oise sources, together with a statistically robust evaluatio of the ucertaity associated to the value calculated. I the past, ofte complais were arisig from the cosideratio that the measuremet performed was ot ecessarily repetative of a log term period close to the true yearly average. Adoptig i a iteratioal oise measuremet stadard which might be similar to the oe described by Joasso [6], the priciple of deliverig a ucertaity associated to ay measuremet performed to evaluate the L de ad L ight idicators, ca be clearly cosidered as a improvemet, sice this way is always possible, e.g. to state that a certai L de ad L ight is with 95% cofidece ot more tha the give L de +u ad L ight +u values. Also, i view of the oise mappig of the maor Europea cities, it will be possible to demostrate to the populatio as well as to the local authorities that the computed oise levels are a correct estimatio of the real value of L de ad L ight, by performig ust a few measuremets over short time periods i urba areas. Further implemetatio of these priciples i future oise measuremets will cotribute to the extesive testig ad evetual fial acceptace of these procedu by the iteratioal oise measuremet stadards. Refereces: [1] Directive 00/49/EC relatig to the assessmet ad maagemet of evirometal oise, 00 [] IMAGINE proect, "Improved Methods for the Assessmet of the Geeric Impact of Noise i the Eviromet", ( Cotract Number: SSPI-CT IMAGINE [3] ISO, Guide for the expsio of ucertaity i measuremet (GUM) [4] S. Kephalopoulos, M. Paviotti, D. Kauss ad M. Béregier, Ucertaities i Log-Term Road Noise Moitorig Icludig Meteorological Variatios, Noise Cotrol Eg. J. 55 (1), , 007. [5] EN ISO 3745 Acoustics - Determiatio of soud power levels of oise sources usig soud psure Precisio methods for aechoic ad hemi-aechoic rooms, 003 [6] H. Joasso, Determiatio of L de ad L ight usig measuremets, report delivered to IMAGINE proect (IMA SP10), 007 [7] D. Heima, O a meteorological classificatio for log term oise calculatios, report delivered to HARMONOISE proect (HAR5MO-0073-DLR01), 00. [8] M.V. Rotach, R. Vogt, C. Berhofer, E. Batchvarova, A. Christe, A. Clappier, B. Fedderse, S.-E. Gryig, G. Martucci, H. Meyer, V. Mitev, T.R. Oke, E. Parlow, H. Richer, M. Roth, Y.-A. Roulet, D. Ruffieux, J. A. Salmod, M. Schatyma, J.A. Voogt, BUBBLE a Urba Boudary Layer meteorology proect, Theor. Appl. Climatology 81, 31-61, 005 [9] G. Memoli, M. Paviotti, S. Kephalopoulos, G. Licitra, Effect o measured oise levels of the microphoe positio i frot of a façade, Iteroise006, Hoolulu (USA), 3-6 December th INTERNATIONAL CONGRESS ON ACOUSTICS ICA007MADRID 6

Expected mean in an environmental noise measurement and its related uncertainty

Expected mean in an environmental noise measurement and its related uncertainty Expected mea i a evirometal oise measuremet ad its related ucertaity M. Paviotti ad S. Kephalopoulos Europea Commissio, via e. fermi,, 00 Ispra, Italy marco.paviotti@jrc.it 85 I the cotext of the implemetatio