Acoustic Monitoring Report, Denali National Park and Preserve-2012

Betchkal, Davyd

In 2012, park staff deployed acoustic monitoring systems to 11 locations in Denali National Park and Preserve. 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 ANSI-certified Type 1 sound pressure levels every second and continuous MP3 audio recordings throughout the sampling period. These data serve as a permanent record of existing acoustical conditions at these locations for the summer or winter of 2012. Table i shows summarized results of 2012 monitoring, including ambient and natural ambient sound statistics in dBA (A-weighted decibels,) average percentage of time audible, number of events per day, and the average maximum sound pressure level (SPL) for aircraft sound sources. Aircraft are specifically reported because they are the most prominent extrinsic sounds occurring in Denali’s backcountry. (An extrinsic sound is defined as any sound not forming an essential part of the park purpose.) Median ambient (L50) describes the acoustical environment as measured, including both natural and extrinsic sounds. Natural ambient (Lnat) estimates what the acoustical environment would be without the contribution of extrinsic sounds. Table i also shows exceedence metrics L10 and L90, which mark the 90th and 10th percentiles of sound pressure level, respectively. When interpreting sound pressure level data, it should be noted that the decibel scale is logarithmic. As such, a six decibel increase in sound pressure level is a doubling of sound energy. In 2012, park staff deployed acoustic monitoring systems to 11 locations in Denali National Park and Preserve. 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 ANSI-certified Type 1 sound pressure levels every second and continuous MP3 audio recordings throughout the sampling period. These data serve as a permanent record of existing acoustical conditions at these locations for the summer or winter of 2012. Table i shows summarized results of 2012 monitoring, including ambient and natural ambient sound statistics in dBA (A-weighted decibels,) average percentage of time audible, number of events per day, and the average maximum sound pressure level (SPL) for aircraft sound sources. Aircraft are specifically reported because they are the most prominent extrinsic sounds occurring in Denali’s backcountry. (An extrinsic sound is defined as any sound not forming an essential part of the park purpose.) Median ambient (L50) describes the acoustical environment as measured, including both natural and extrinsic sounds. Natural ambient (Lnat) estimates what the acoustical environment would be without the contribution of extrinsic sounds. Table i also shows exceedence metrics L10 and L90, which mark the 90th and 10th percentiles of sound pressure level, respectively. When interpreting sound pressure level data, it should be noted that the decibel scale is logarithmic. As such, a six decibel increase in sound pressure level is a doubling of sound energy. During the winter months, records from the Hines Creek sampling location were collected to inform an environmental assessment related to plowing the park road to Savage Overlook. Data from the station predicted that noise could be audible for up to 8 miles from the road. A second winter site at Bison Gulch collected baseline data from which to compare conditions upon the restart of the Healy Unit 2 coal-fired power plant, scheduled for 2015.