Impact of meteorological conditions on noise propagation from freeway corridors
Cross section of Loop 202 site as elevation above sea level. Horizontal distance is measured in feet from the fence on the south side. Positions of instruments are shown as squares for microphones and triangles for sonic anemometers in the November 2006 field campaign. Arrows indicate distances from the center of the nearest travel lane (filled circle) on the West Bound side (WB).
A schematic of the coupled models used to resolve the far-field propagation of traffic noise from a freeway corridor. The filled circles represent monofrequency coherent effective line sources above the centerline of the nearest lane of traffic. A Green’s function method is utilized both to determine virtual source heights and strengths from the sound meter data and also to initialize the sound field along the vertical dashed line at the edge of the pavement. A PE model then marches this input pressure field across the domain, handling each frequency component separately.
Temperature and crosswind (to the freeway) data with fitted theoretical profiles for the three cases. All data points above are given by the SODAR-RASS with lower height information obtained from the sonic anemometers as shown in the legend.
The difference in overall -weighted sound level on October 11, 2006, measured between the sound meter located from the center of the nearest lane of traffic at a height of and the sound meter located from the center of the nearest lane of traffic at a height of . The triangles merely display an indication of the traffic conditions at the time (either free flowing, slow moving or intermediate). A decrease of with a doubling of distance corresponds to what is expected for a line source as in a neutral atmosphere.
(a) Virtual source heights for the three cases obtained by minimizing an error norm based on decibel differences between sound meters. (b) Measured dBA minus the dBA obtained from the Green’s function solution for each virtual line source at the three sound meter locations. Circles show measured minus computed dBA for the meter at location 1, diamonds for the meter at location 2, and crosses for the meter at location 3.
Virtual source strengths for the three cases obtained by minimising an error norm based on dB differences between sound meters.
Case A: -weighted SPL contours without meteorological effects (top) and with meteorological effects (bottom). The effect of atmospheric absorption is not included here. Each contour line represents a change of . The bold contour represents the level.
Case A: Overall -weighted SPL and the SPL of each frequency component at a height of above the ground. The top figure shows the SPL for neutral conditions (bold blue dash-dot line), with meteorological effects but without atmospheric absorption (bold black dashed line) and with both meteorological effects and with atmospheric absorption (bold black solid line and frequency bands). The shaded area in the top figure represents the region where the SPL range exceeds the threshold. The bottom figure shows contours of -weighted SPL with meteorological effects for each frequency component at an altitude of with atmospheric absorption. Each contour line represents a change of .
Same caption as for Fig. 7, but for Case B.
Same caption as for Fig. 8, but for Case B.
Same caption as for Figs. 7 and 9, but for Case C.
Same caption as for Figs. 8 and 10, but for Case C.
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