Haleakalā National Park: Acoustic monitoring report

Job, Jacob; Pipkin, Ashley; Beeco, J.

In 2013, the Natural Sounds and Night Skies Division (NSNSD) received a request to collect baseline acoustical data at Haleakalā National Park (HALE). Between September and November 2013, one acoustical monitoring system was deployed for approximately 58 days within the park boundary. The goal of the study was to establish a baseline soundscape inventory of the newly acquired Nu’u unit, as well as inform possible air tour management at HALE. This inventory will be used to establish indicators and thresholds of soundscape quality that will support the park and NSNSD in developing a comprehensive approach to protecting the acoustic environment through soundscape management planning. Results of this study will help the park evaluate the exposure of this area to overflight noise, as well as provide a baseline understanding of the acoustical environment for use in potential future comparative studies. Previous studies at HALE related to noise from overflights, including two ambient measurement studies, social science research, and an ethnographic study, are summarized in Lynch 2012. For the purposes of this document, we will refer to “noise” as any human-caused sound that masks or degrades natural sounds (Lynch et al. 2011). Ambient sound pressure level (SPL) was measured continuously every second over the 58 day monitoring period by a calibrated, Type 1, Larson Davis 831 sound level meter. Trained technicians calculated percent time audible metrics after monitoring was complete. See Methods section for protocol details, equipment specifications, and metric calculations. Median existing (L50) and natural ambient (Lnat) metrics are also reported for daytime (0700–1900 hours) and nighttime (1900-0700 hours). Prominent noise sources in the Nu’u unit included aircraft and a non-natural unknown low frequency rumble that the listening lab technician thought was most likely nearby farm equipment. Table 1 displays percent time audible values for each of these noise sources during the monitoring period, as well as ambient sound levels. In determining the current conditions of an acoustical environment, it is informative to examine how often SPLs exceed certain values. Table 2 reports the percent of time that measured levels at HALE004 were above four key values. The first value, 35 dBA, is designed to address the health effects of sleep interruption. Recent studies suggest that sound events as low as 35 dB can have adverse effects on blood pressure while sleeping (Haralabidis et al. 2008). This is also the desired background sound level in classrooms (ANSI S12.60-2002). The second value addresses the World Health Organization’s recommendations that noise levels inside bedrooms remain below 45 dBA (Berglund et al. 1999). The third value, 52 dBA, is based on the EPA’s speech interference level for speaking in a raised voice to an audience at 10 meters (EPA 1974). This value addresses the effects of sound on interpretive presentations in parks. The final value, 60 dBA, provides a basis for estimating speech interference on normal voice communications at 1 meter. Visitors viewing scenic areas in the park would likely be conducting such conversations. The top value in each split-cell focuses on frequencies affected by low frequency noise sources (20-1250 Hz), whereas the bottom values use the full frequency range (12.5-20,000 Hz) collected. Most motorized human-caused noise is confined to the truncated, lower-frequency range, while many natural sounds, including insects and birds, are higher in pitch. Therefore, the truncated range (20-1250 Hz) is more appropriate for identifying impacts from anthropogenic noise in parks (Acoustical Society of America 2014).

Haleakalā National Park: Acoustic monitoring report

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