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A study of acoustic descriptors for an Environmental Imapct Assessment: a case study in Curitiba, Brazil.

An analysis was made of acoustic descriptors for the preparation of an Environmental Impact Study. The parameters evaluated were: noise measurement time, the need for triplicate noise measurements, and determination of the grid spacing for noise
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  A study of acoustic descriptors for an Environmental Imapct Assessment: a casestudy in Curitiba, Brazil. Margret Sibylle Engel 1 , Paulo Henrique Trombetta Zannin 2   1 Federal University of Paraná, Post Graduation Program in Water Resources and Environmental Engineering,Curitiba, Brazil. 2 Federal University of Paraná, Laboratory of Environmental and Industrial Acoustics and Acoustic Comfort,Curitiba, Brazil. E-Mail:  Introduction  Noise pollution today is one of the main forms of urbanenvironmental pollution and is responsible for negativeimpacts that are harmful to the environment and the qualityof life of the population [1].The environmental noise assessment is a way to check thenature and the characteristics of noises; to perfom it a set of reliable parameters are needed to take sound measurements,as well as the sound mappings and acoustic predictions.The aim of this paper is to obtain reliable acoustic parameters that will facilitate the findings, interpretation andenable the document production which will be useful indecision making in an attempt to reduce and control highwaynoises in the south of Brazil. The focused parameters werethe following: the sound measurement observation time, theneed to do triplicate sound measurements and the best sizedetermination of the grid in carrying out the sound mapping. Materials and methods   Study area The city of Curitiba is one of the main cities of the south of Brazil, with a population of 1 800 000 inhabitants. The cityis crossed from north to south by a highway which connectsthe southern region to the southeast region, as well as to theother parts of the country. Since 2007 public revitalizing andurbanization works have been carried out along thishighway, transforming it into an important urban avenue,called Green Line. Figure 1: Study area showing the 500 meter distance between thenoise measurement points.   The noise measurements and the noise mapping were takenin a small urbanized section of the Green Line (fig. 1). Twonoise measurement points were picked out, separated by 500meters between them. Equipment In order to collect the noise measurement data for this studyacoustic descriptors B&K 2238, B&K 2250 and B&K 2260and an acoustic calibrator B&K 4310, as well as the NoiseExplorer software 7815 were used. The noise mapping was performed with the software B&K Predictor 7810, version6.2. Noise measurement observation time The generally recommended noise measurement observationtime varies between 10  ±  15 minutes [2]. For this studymeasurements were taken with three different durations: 10minutes, 15 minutes and 30 minutes. The noisemeasurements took place separately, always using the sameequipment. Along with the noise measurements the number of the passing vehicles was counted in order to characterizethe intensity of the traffic flow at the moment of eachmeasurement. This information was one of the utilized parameters for the noise mapping calibration. Verifying the necessity of doing soundmeasurement triplicates In order to verify if the sound measurement data were reallyconstant triplicate measurements were taken at the twoselected points for the pilot study. These measurements took  place at distinct days, always at the same time. Linear regressions of these findings were used for eachmeasurement point in order to verify the variation of thetriplicate findings.The urban traffic noise of vehicles generally shows a highdegree of constancy; normally no variations higher than 1dB will take place due to the constant flow of vehicles [2]. The grid size determination for noise mapping European Union Guides [3] suggest that the software user of noise mapping, in selecting the grid size accepts theresponsibility for the map accuracy and does his best in thecalculation, including the time necessary for calculation. Inthis connection, a common practice in noise mapping of large areas is the division of the calculation into two steps:the first one consists in utilizing a gross grid (30m x 30m) tofind the areas of interest. The second one consists in    DAGA 2012 - Darmstadt                          1 1 3      applying a smaller grid resolution (generally 10m x 10m),which is applied in specific areas of interest, such as populated areas. Occasionally smaller grids may be used.In this study, in order to determine the noise mapping grid,maps were developed of the same measurement point. It wasdecided to plot maps with different grids in the region near the measurement point 2 of the study area. The tested gridsof the following sizes: 30m x30m, 20m x 20m, 15m x 15mand 10m x 10m. As the grids are reduced in size thesimulated receivers will increase. Results and discussionResults of the measurement observation time Table 1 shows the results of equivalent sound pressure levelsfor each the tree studied measurement times, as well asstatistical DQDO\VLVVKRZLQJWKHG%YDULDWLRQǻG%EHWZHHQPHDVXUHPHQWVDQGWKHSHUFHQWYDULDWLRQǻ)URPWKHVH results it can be concluded that after measurement durationof 15 minutes or more, there is a greater constancy in thenoise measurement results. Table 1 : Sound measurement results according to measurementobservation time and variations in dB and %. Point 1 Parameter L Aeq   ǻG%   ǻ  10 min. 73 - -15 min. 71 -2 -2,7430 min. 74 +1 +1,37Point 2 Parameter L Aeq   ǻG%   ǻ  10 min. 73 - -15 min. 72 -1 -1,3730 min. 72 -1 -1,37 Results of the verification of the need of doingnoise measurement triplicates The obtained results in the verification of the need of doingnoise measurement triplicates are shown in table 2 bellow. It DOVRVKRZVDYDULDWLRQLQG%ǻG%DQGWKHSHUFHQWYDULDWLRQǻ between the measurements. Table 2: Noise measurement triplicates results, dB and %variation.  Point 1 Parameter L Aeq   ǻG%   ǻ  1 st . triplicate 72,9 - -2 n triplicate 72,7 -0,2 -0,33 r  triplicate 72,2 -0,7 -1,0Point 2 Parameter L Aeq   ǻG%   ǻ  1 st . triplicate 72,8 - -2 n triplicate 71,3 -1,5 -2,13 r  triplicate 70,5 -2,3 -3,2The linear regression coefficients (R  2 ) of the twomeasurement points are near 1.00; in measurement point 1R  2 = 0.94123 and in measurement point 2 R  2 = 0.97. Theseresults show that there is no variation between the triplicateresults and that triplicate measurements are not necessary. Grid size determination for noise mappingresults It was found that maps with greater grids had a smaller accuracy than maps with smaller grids, as in [3]. Maps withsmaller grids have more details, the sound waves depiction,as well as the sound itself decline, have more roundedshapes and shows with greater reliability of the sound behavior according to its propagation path. Figure 2, shows acomparison between four sound maps of the same region,where the tests with the grids were performed.According the grid tests it was found the best grid is grid 10(10m x 10m), as the study area is densely populated. Conclusion Obtaining reliable acoustic parameters for preparingEnvironmental Impact Assessment is of utmost importancefor report elaborations aimed an accurate acoustic diagnosisfor decision making in mitigating actions and environmentalcontrol.These paper succeeded in confirming theories andobservations of specialists in the acoustics areademonstrating the adoption acoustics parameters for theachieving those reports can be standardized independently of the study area. References [1] WHO  ±  WORLD HEALTH ORGANIZATION. 5pVXPp'¶RULHQWDWLRQ'HV'LUHFWLYHV   'H,¶RPV5HODWLYHV$X%UXLW'DQV,¶HQYLURQPHQWDO Genev, 2003.[2] Hansen, C. H. Noise control: from concept toapplication. New York, USA: Taylor & Francis, 2005.   [3] European Commission Working Group  ±   assessment of exposure to noise, Good practice guide for strategic noise mapping and the production of associateddata on noise exposure.Version 2, WG-AEN 004.2007;2007.   Figure 2: Map 1 with grid 30 (30m x 30m), map 2 with grid 20(20m x 20m), map 3 with grid 15 (15m x 15m) and map 4 with grid10 (10m x 10m).    DAGA 2012 - Darmstadt                          1 1 4    
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