Acoustic Monitoring Report, Denali National Park and Preserve-2007

Withers, Jared

Park staff deployed acoustic monitoring systems to ten locations in Denali National Park and Preserve in 2007. The purpose of this monitoring effort was to inventory the acoustic conditions and level of aircraft operations in as called for in the 2006 Denali Backcountry Management Plan. Data collected included existing ambient sound pressure levels, natural ambient sound pressure levels, percent 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 interval audio recordings once every five minutes, 24 hours per day. These data serve as a permanent record of existing acoustical conditions at these locations for the summer of 2007. Table 1 shows summarized results of 2007 monitoring, including existing 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 extrinsic sound at these sites. Median existing 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 essentially 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 actually a doubling of sound energy. Overall, the acoustic conditions of these 2007 sites varied. The Bear Creek site was the quietest in both ambient and natural ambient sound. Very low levels of aircraft activity were observed at Chitsia Creek. Ambient conditions at the winter monitoring locations were measured to be 7.4 dB quieter than the summer sites, on average.

Acoustic Monitoring Report, Denali National Park and Preserve-2007

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