Acoustic Monitoring Report, Denali National Park and Preserve, 2010

Withers, Jared; Betchkal, Davyd

Park staff deployed acoustic monitoring systems to nine locations in Denali National Park and Preserve in 2010. The purpose of this monitoring effort was to inventory the ambient acoustic conditions and amount of non-natural sound in Denali National Park as called for in the 2006 Backcountry Management Plan. Data collected included existing ambient sound pressure levels, natural ambient sound pressure levels, percentage of time audible, and loud acoustic event statistics for intrinsic and extrinsic sound sources. Deployed systems were configured to log sound pressure levels every second and continuous mp3 audio recordings, 24 hours per day. These data serve as a permanent record of existing acoustical conditions at these locations for the summer of 2010. Table 1 shows summarized results of 2010 monitoring, including ambient and natural ambient sound statistics in dBA (A-weighted decibels) and average percentage of time audible, number of events per day, and maximum sound pressure level (SPL) for aircraft sound sources, which are the most prominent of extrinsic sounds occurring at these sites. Median ambient (L50) describes the acoustical environment as is, including both natural and extrinsic sounds. Natural ambient (Lnat) estimates what the acoustical environment might sound like without the contribution of extrinsic sounds. This table also shows exceedence metrics L10 and L90, which mark the average maximum and minimum exceedence levels over the monitoring periods. When interpreting sound pressure level data, it should be noted that the decibel scale is logarithmic. As such, a three decibel increase in sound pressure level is a doubling of sound energy. Overall, the acoustic conditions of these 2010 sites varied. The Myrtle site experienced the lowest ambient and natural ambient sound levels, as well as relatively low levels of aircraft activity. Of the flights which occurred at Myrtle during the measurement period, the average maximum sound pressure level for an event was the lowest measured thus far in Denali.

Acoustic Monitoring Report, Denali National Park and Preserve, 2010

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