2017.06.13 WS Agenda C - Laserfiche WebLink

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Figure 1 Ideal circular sound level contours with actual contours Siren Location Sitting In most cases, the ground cover around the siren is not uniform; that is, the nature of ground cover is a function of direction from the siren. At each site, the USGS exact location of the siren was physically marked, noted, and entered onto topographic map. The latitude and longitude for each siren was entered into the Computer Model. Appendix C lists the Siren sites, longitude, and latitude used in the sound model for Ramsey county. Siren Contour Plotting The sound coverage provided by each siren is presented in Appendix A Sound Coverage Maps in the form of sound contours, which are lines of equal sound level surrounding the siren locations. For a picture of the Overall Ramsey County acoustic coverage map, a typical Citywide acoustic coverage map, and a typical single siren acoustic coverage map refer to the Figure 6, Figure 7, and Figure 8 in Appendix A. 81 sound coverage maps were created to show the overall sound coverage when all sirens are sounding at the same time, citywide coverage, and individual siren sound coverage. The acoustic coverage maps are delivered as a separate map book to accompany this report. Siren Acoustic Computer Model Anal ysis Description of Calculations Used The acoustic computer model analysis was done using SoundPlan acoustic modeling software. This software model uses the ISO9613 standard. The model includes the effects of temperature, humidity, barometric pressure, atmospheric absorption, ground absorption, siren height and frequency, terrain, and barriers in the sound path including buildings and trees. When omni-directional sirens are next to each other, the additive effect of the siren’s SPL is included in the calculation. Since the ISO9613-2 standard does not directly address the effects of wind speed and temperature gradients, the excess attenuation due to temperature and wind s peed gradients that cause shadow zones has been included in the analysis.