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<br /> <br />temperature lapse sound shadow formation conditions. <br /> <br />For sirens that are within the interior portions of the county, there are several adjacent sirens <br />that will be either sounding downwind or crosswind into a given siren upwind sounding <br />direction. Thus, sound from adjacent sirens will either be enhanced or not affected by the <br />wind, particularly for the Ramsey county siren system, which has a dense siren configuration. <br />The upwind effect is accounted for by placing sirens close enough to the Ramsey county <br />perimeter and close enough to adjacent sirens that will sound in a cross-wind direction such <br />that the expected range shortening does not reduce the coverage area to any area that is <br />populated. <br /> <br /> <br />Siren System Sound Level Compliance Discussion <br /> <br />The FEMA-REP-10 guidelines for ANS acoustic coverage specify a sound pressure level <br />that will generally be greater than 70 dB(C) where population density exceeds 2,000 persons <br />per square mile (ppsm) and 60 dB(C) in other inhabited areas, or the expected siren sound <br />pressure level will generally exceed 10 dB above the average measured summer daytime <br />a mbient levels in areas with less than 2,000 ppsm. <br /> <br /> <br />The design basis for Ramsey County consists of a graphical calculation of sound level as a <br />function of the siren positions on a USGS topographical map. The sound coverage prediction <br />was performed using SoundPlan acoustic modeling software. This software model is based <br />on the ISO9613-2 international standard for determining attenuation of sound during <br />propagation outdoors. The model includes the effects of temperature, humidity, barometric <br />pressure, atmospheric absorption, ground absorption, siren height, frequency, terrain, and <br />documented barriers in the sound path. When omni-directional sirens are next to each other, <br />the additive effect of the siren’s SPL is included in the calculation. <br /> <br />The review of the Acoustic Coverage Map indicates that the warning system generally will <br />provide at least 70 dB(C) of acoustic coverage to all areas populated areas. <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br />