Use of the noise-free interval (NFI) metric to assess the disturbances of airborne vessel noise at Glacier Bay National Park

Abstract

Alaska's Glacier Bay National Park preserves the seventh largest unit of the National Wilderness Preservation System, encompassing 2.6 million acres. Natural acoustic environments are significant to many of the unit's fundamental resources and values. Since 2001, the National Park Service has inventoried acoustic environments of Alaskan parks. One purpose is to document every noise-free interval (NFI) observed. NFI is defined as the time between human-generated noise disturbances. Aggregate properties of NFIs describe fragmentation of acoustic environments by noise. Median NFI estimated at parks in Alaska to date range from < 3 minutes to 16.7 hours, similar to other Arctic sites (0.5 to 13.0 hours, Stinchcomb et al. 2020). For the Glacier Bay Marine Management Plan Environmental Assessment, a geometric NFI model was developed using automatic identification system (AIS) derived vessel tracks. The NFI simulation results, along with NFI data from acoustic monitoring at the park, was then utilized to assess how changes to vessel quotas and vessel management strategies would potentially affect the NFI throughout the park. This paper will discuss the estimation and use of the NFI metric in protected natural areas, along with NFI modeling methods utilized for an environmental assessment at Glacier Bay.