## 3 Full-Scale Measurement in Real Urban Streets for Model Validation
### Estimation of Acoustic Parameters of Building Facades
Therefore, rectangular structures with large plane surfaces (the ratio of the dimension of the surface to the wavelength was larger than 10, 6.8 m for 500 Hz) were considered as planes rather than diffusers when counting the coverage density. Given that the regression equation in Figure 5b was established by the data measured within the range of 0.1 < h/\(\lambda\) < 0.4, there was a frequency limitation of the estimated scattering coefficient. The common heights of diffuse structures in five measured streets varied from 10 to 15 cm. Therefore, the lower limit frequency for the estimated scattering coefficient was 227-340 Hz, which is approximately the lower limit frequency of the 500 Hz octave band. Meanwhile, the upper limit frequency was within the range of 900-1360 Hz, which is approximately the upper limit frequency of the 1000 Hz octave band. Therefore, in the model validation, the corresponding frequency range is analyzed (500 Hz and 1000 Hz octave bands). In this study, building facades in the measured streets are all continuous surfaces with no junctions in the measurement zone. Therefore, the diffraction that needs to be considered is only caused by the irregular structures on the building facades. In fact, the multiple reflections and diffractions by these structures are the major causes of the scattering of the surfaces. The scattering coefficient in this study was estimated by the laboratory-measured data, which contained the influence of diffraction. Therefore, although no diffraction modeling process was applied in IMCRI, the influence of diffraction was considered by the scattering modeling process. Another important acoustic parameter is the absorption coefficient, which may have an influence on the simulation results. As shown in Figure 4, all the building facades were made of glass and concrete, which can be considered as reflective materials in the frequency range of 500-1000 Hz. Measurements and estimations have been carried out for similar materials [38]. The absorption coefficient of the building facades varied from 0.03 to 0.09 in the range of 400-4000 Hz. Therefore, in the calculation model, the range of the absorption coefficient of the building facades was set as 0.05. Given \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Coverage Density**} & \multicolumn{3}{c}{**Estimated Scattering Coefficient**} \\ \cline{2-9}
**Street Name** & **Facade A** & **Facade B** & \multicolumn{3}{c}{**Facade A**} & \multicolumn{3}{c}{**Facade B**} \\ \cline{3-9}  & & & \(\mathbf{S_{r}}\) & \(\mathbf{S_{h}}\) & \(\mathbf{S_{g}}\) & \(\mathbf{S_{r}}\) & \(\mathbf{S_{h}}\) & \(\mathbf{S_{g}}\) \\ \hline Street 1 & 2.00\% & 7.00\% & 0.08 & 0.07 & 0.09 & 0.17 & 0.16 & 0.23 \\ Street 2 & 6.50\% & 15.00\% & 0.16 & 0.15 & 0.22 & 0.30 & 0.28 & 0.42 \\ Street 3 & 7.10\% & 10.60\% & 0.17 & 0.16 & 0.23 & 0.23 & 0.22 & 0.32 \\ Street 4 & 35.00\% & 18.00\% & 0.52 & 0.52 & 0.71 & 0.34 & 0.33 & 0.48 \\ Street 5 & 37.00\% & 54.00\% & 0.53 & 0.54 & 0.73 & 0.58 & 0.64 & 0.74 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Coverage densities and estimated scattering coefficients of building facades on five measured streets. \(\mathbf{S_{r}}\), \(\mathbf{S_{h}}\), and \(\mathbf{S_{g}}\) are the estimated scattering coefficients of the regression curves of groove, hemisphere, and rectangular diffusers, respectively. Figure 5: Effect of size, coverage density, and structure type on the scattering coefficients: (**a**) scattering coefficients of samples with different heights; (**b**) relationship between the coverage density and scattering coefficient for different structures (0.1 < h/\(\lambda\) < 0.4). The solid line, dotted line, and dash–dot line are quadratic regression curves for groove, hemisphere and rectangular diffusers, respectively. that the ground surface in each measured street was very smooth and reflective, a scattering coefficient of 0.02 and an absorption coefficient of 0.02 were used.