Denali National Park Acoustic Monitoring Report-2008

Withers, Jared

Park staff deployed five acoustic monitoring systems in Denali National Park in 2008 (see Table 1). The purpose of this monitoring effort was to continue to gather data inventorying the current acoustic conditions and level of aircraft operations as called for in the 2006 Denali Backcountry Management Plan. The collected data included existing ambient, natural ambient, percent time audible, and loud acoustic event statistics for intrinsic and extrinsic sound sources. They also serve as a permanent record of existing acoustical conditions in the summer of 2008. Systems were deployed for thirty days to log one-second sound pressure levels and interval audio recordings. Table 2 shows existing and natural ambient statistics in dBA 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 3 dB increase in sound pressure level is actually a doubling of sound energy. Overall, the acoustic conditions of these 2008 sites varied. The Highpower Creek site was the quietest in both ambient and natural ambient. Very low levels of aircraft activity were observed. The Tokositna Glacier site experienced the greatest natural ambient because of the presence of the sound of water exiting the glacier, but also had the highest amount of aircraft activity.

Denali National Park Acoustic Monitoring Report-2008

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