Michel Berengier

AMBIENT SOUND ASSESSMENT OF URBAN ENVIRONMENTS: FIELD STUDIES IN TWO FRENCH CITIES

This work aims to investigate the appraisal of typical urban soundscapes. The method consists of two simultaneous on-site procedures in various urban situations in two French cities (main thorough fares, pedestrian precincts, playgrounds and market squares). While passers-by were required to express their opinion about soundscapes through questionnaires, we recorded samples of ambient sound environments and calculated acoustic parameters. The cross analysis between survey data and acoustic parameters indicated the sound level is appropriate to the description of main thorough fares, but for similar sound level locations (square, market, or playground) two further perceptive factors were remind. The perceptual spatial dimension was correlated with acoustic indicators as background noise or standard deviation of short LAeq, whereas the temporal dimension revealed differences in the perceptual attitudes of the survey respondents. The results obtained consequently identified the limitation of matching a unique acoustic descriptor with two cognitive representations (a global point of view versus a discrete listening) of the same acoustic phenomenon.

Porous road pavements: Acoustical characterization and propagation effects

Measurements of the acoustical properties of some porous road pavements are presented here and an acoustical method for monitoring the performance of these surfaces is presented. Porous road pavements have been used previously because of their driving qualities and drainage capacities during rainy days (i.e., the elimination of water splash and spray) but they have also been found to reduce traffic noise substantially. Reductions in A-weighted sound levels of 3–5 dB, compared to a dense pavement structure, have been measured. To study further their acoustical performance, measurements over real road surfaces have been carried out and the results compared to theoretical predictions based upon models describing the surface impedance and sound propagation. For the impedance characterization, both a phenomenological and a microstructural model were used. Both approaches introduce a viscous and a thermal dependence to account for the different phenomena inside the porous structure. By incorporating these model...

Sound field modeling in a street canyon with partially diffusely reflecting boundaries by the transport theory

The transport theory, applied to the concept of sound particles, seems to be well adapted to predict the sound propagation in urban areas, including most complex effects, like diffuse scattering by building facades, atmospheric attenuation, scattering by urban objects in streets, etc. In this paper, the transport theory is then applied to the sound field modeling in an empty street canyon with partially diffusely building facades. In this case, the temporal and spatial distribution of sound energy in a street is the solution of a transport equation, with mixed specular-diffuse boundary conditions. Using an asymptotic approach, the transport equation may be reduced to a diffusion equation for the sound energy, where the diffusion coefficient depends only on the building facades properties. Comparisons with experiments show that the diffusion model gives consistent results with experimental data, both for the sound attenuation level and the reverberation time.

Including the Drag Effects of Canopies: Real Case Large-Eddy Simulation Studies

We use the mesoscale meteorological model Meso-NH, taking the drag force of trees into account under stable, unstable and neutral conditions in a real case study. Large-eddy simulations (LES) are carried out for real orography, using a regional forcing model and including the energy and water fluxes between the surface (mostly grass with some hedges of trees) and the atmosphere calculated using a state-of-the-art soil-vegetation-atmosphere-transfer model. The formulation of the drag approach consists of adding drag terms to the momentum equation and subgrid turbulent kinetic energy dissipation, as a function of the foliage density. Its implementation in Meso-NH is validated using Advanced Regional Prediction System simulation results and measurements from Shaw and Schumann (Boundary-Layer Meteorol, 61(1):47–64, 1992). The simulation shows that the Meso-NH model successfully reproduces the flow within and above homogeneous covers. Then, real case studies are used in order to investigate the three different boundary layers in a LES configuration (resolution down to 2 m) over the “Lannemezan 2005” experimental campaign. Thus, we show that the model is able to reproduce realistic flows in these particular cases and confirm that the drag force approach is more efficient than the classical roughness approach in describing the flow in the presence of vegetation at these resolutions.

Outdoor sound propagation modeling in realistic environments: Application of coupled parabolic and atmospheric models

Predicting long-range sound propagation over a nonurban site with complex propagation media requires the knowledge of micrometeorological fields in the lower part of the atmospheric boundary layer, and more precisely its characteristics varying in both space and time with respect to local (“small-scale”) and average (“long-term”) conditions, respectively. Thus in this study, a mean-wind wide-angle parabolic equation (MW-WAPE) code is coupled with a dedicated micrometeorological code (SUBMESO) which simulates wind and temperature fields over moderately complex terrain with high resolution. Its output data are used as input data for the MW-WAPE code, which can also deal with different boundary conditions, such as the introduction of impedance jumps, thin screens or complex topography. Both codes are presented in the present paper. Comparisons between numerical predictions, and experimental data are also presented and discussed. Finally, we present an example of such a coupling method (MW-WAPE/SUBMESO) for t...

NMPB-Routes-2008: The Revision of the French Method for Road Traffic Noise Prediction

The revision of the French method for road traffic noise prediction (NMPB-Routes-2008) is now published. The major principles of NMPB-Routes-2008 are outlined. The most important modifications regarding the source are the reduction of its height and the introduction of two different spectra. In this complete revision, the main change is the replacement of the ISO 9613-2-based ground attenuation formula in downward-refraction conditions by the formula for ground attenuation in homogeneous conditions of NMPB-Routes-1996 with corrected heights in order to take into account the mean curvature of rays (refraction) and its scattering (turbulence). NMPB-Routes-2008 adds an attenuation term for an occasional cutting embankment. Regarding diffraction the dif formula is now more suitable for low height barriers. The validation of NMPB-Routes-2008 with respect to experiment is presented. It is based on measurement campaigns on 6 sites with complex geometries and shows that the predicted noise levels obtained from NMPB-Routes-2008 are significantly closer to experimental results than in the case of the original method. S. Hirzel Verlag.

Geostatistical modeling of sound propagation: Principles and a field application experiment

The assessment of noise sources for environmental purposes requires reliable methods for mapping. Numerical models are well adapted for sophisticated simulations and sensitivity analyses; however, real-time mapping of large frequency bands must be based on fast and acceptable computations and honor in situ measurements. In this paper, a real-time mapping procedure of noise exposure is proposed. The procedure is based on geostatistical modeling of spatial variations and applied to a case study taken from an experimental campaign, where a point source was placed on a flat meadow. An analytical approximation of the acoustic field was first computed with the Embleton model. The difference between this approximation and the actual measurements (L(eq15 min) 1/3-octave bands samples from 19 microphones spread over the meadow) showed spatial structure, which has been modeled with a variogram. Finally, the geostatistical technique of kriging with external drift provided an optimal interpolation of the acoustic field data while encapsulating the first approximation from the Embleton model. Systematic geostatistical inference and real-time mapping with the proposed procedure can be envisaged in simple cases.

Traffic noise prediction with the parabolic equation method: Validation of a split-step Padé approach in complex environments

This study deals with sound propagation in typical traffic noise conditions. The numerical results are obtained through the split-step Padé method and the discrete random Fourier modes technique. These are first evaluated qualitatively, by color contour maps showing noise propagation, diffraction by an impedance discontinuity or a screen edge, and scattering by atmospheric turbulence. Next, our numerical results are quantitatively validated by comparison with analytical models and other parabolic equation models. For all the atmospheric conditions and geometrical configurations available in literature, the agreement between the different methods is very good, except for some cases involving the atmospheric turbulence. However, in those particular cases, the split-step Padé results are shown to be more consistent with physical theory. Finally, our method seems to be very powerful and reliable for traffic noise prediction.

State-of-the-Art Prediction and Control of Road Traffic Noise in France

Because traffic noise is considered by the French population as the primary environmental nuisance, prediction of road traffic noise and development of efficient noise control techniques is very important. The first step is to analyze the source, the main part of which is due to the contact between tires and the road pavement. Many efforts have been devoted to the assessment of a reliable measurement method, and a classification of road pavements in relation to noise has been established for some years. To abate road traffic noise, special attention has been paid to low-noise pavements. Thus, the modeling of the absorption properties of porous asphalts has been particularly studied in the past 10 years. The second step is to understand the physics of sound propagation outdoors, especially the meteorological effects on the propagation of road traffic noise. Both theoretical and experimental approaches have been undertaken. Finally, the effect of road noise barriers of any shape on the propagation of road noise and their interaction with porous road surfaces have been investigated by using numerical models.

Sound propagation above a porous road surface with extended reaction by boundary element method.

Acoustic impedance of an absorbing interface is easily introduced in boundary element codes provided that a local reaction is assumed. But this assumption is not valid in the case of porous road surface. A two-domain approach was developed for the prediction of sound propagation above a porous layer that takes into account the sound propagation inside the porous material. The porous material is modeled by a homogeneous dissipative fluid medium. An alternative to this time consuming two-domain approach is proposed by using the grazing incidence approximate impedance in the traditional single-domain boundary element method (BEM). It can be checked that this value is numerically consistent with the surface impedance calculated at the interface from the pressure and surface velocity solutions of the two-domain approach. The single-domain BEM introducing this grazing incidence impedance is compared in terms of sound attenuation with analytical solutions and two-domain BEM. The comparison is also performed with the single-domain BEM using the normal incidence impedance, and reveals a much better accuracy for the prediction of sound propagation above a porous interface.