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National Park Service
U.S. Department of the Interior

Science Report NPS/SR—2026/438

• Top of Page
• Table of Contents
• List of Figures
• List of Tables

Great Basin National Park: Acoustic Monitoring Report 2015

Ashley R. Pipkin, Erik W. Meyer 

Please cite this publication as:

Pipkin, A.R., and E.W. Meyer. 2026. Great Basin National Park: Acoustic Monitoring Report 2015. Science Report NPS/SR—2026/438. National Park Service, Fort Collins, Colorado. https://doi.org/10.36967/2318205

Abstract

This study was initiated in response to Technical Assistance Request 1097 from Great Basin National Park (GRBA) to collect baseline acoustic data across various park management zones. The request supports the GRBA Foundation Document, which identifies solitude as a fundamental park resource and emphasizes the importance of soundscape monitoring. Therefore, during late summer in 2015, the Natural Sounds and Night Skies Division (NSNSD) gathered acoustical data at three sites in GRBA to provide park managers with information about the acoustical environment, sources of noise, and the existing ambient sound levels within the park. On average, noise was present from 25.8 (Decathon) to 96.6 (Visitor Center) percent of that time across 3 sites. The most common sources of noise were aircraft, motors, and vehicles. The maximum percent time audible of aircraft noise was at Decathon, audible for 25.8% of a 24-hr period. For motor noise at the Visitor Center, the maximum time audible was 62.6% of a 24-hr period, and for vehicle noise at the Visitor Center, the maximum time audible was 38.8% of a 24-hr period. Overall, existing ambient sound levels (L_A50) at sites within GRBA ranged from 25.6 to 32.5 dB during the day and 20.4–39.6 dB at night during the sampling period. Natural ambient sound levels (L_Anat) at sites within GRBA ranged from 24.6 to 26.5 dB during the day and 19.8–35.3 dB at night. The median impact across all sites, defined as the difference in dB between the L_A50 and L_Anat, was 1.4 dB, reducing the listening area by 26.3%. Finally, noise impacts ranged from 0.6 dB at Shingle Creek to 5.5 dB at the Visitor Center.

Acoustic monitoring in Great Basin National Park.

NPS / NATURAL SOUNDS & NIGHT SKIES DIVISION

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Table of Contents

• Abstract

• List of Figures

• List of Tables

• Acknowledgments

• List of Terms

• Executive Summary

• Introduction

  • Soundscape Planning Authorities

  • Focal Park Unit

  • Study Area

• Methods

  • Automatic Monitoring

  • Monitoring Period

  • Calculation of Metrics

• Off-Site Listening and Spectrogram Analysis

  • Listening Center Software Analysis

  • Sound Pressure Level Annotation Tool

• Results

  • Frequency Content

  • Sound Level: Time Above

  • Sound Level: Percentile Levels

  • Event Duration

    • Listening Center Software

    • Sound Pressure Level Annotation Tool

• Conclusions

• Literature Cited

• Appendix A: Site Photos

• Appendix B: Modeled Impact Levels

• Appendix C: Detailed Sound Source Descriptions

• Appendix D: On-Site Listening

• Appendix E: Previous Acoustic Monitoring

• Author Information

• About the National Park Service Science Report Series

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List of Figures

• Figure 1. Study sites in Great Basin National Park, NV, USA.

• Figure 2. Depictions of auditory analysis by trained technicians.

• Figure 3. Day and night percentile sound pressure levels for 33 one-third octave bands at the Visitor Center in summer, 2015.

• Figure 4. Day and night percentile sound pressure levels for 33 one-third octave bands at Shingle Creek in summer, 2015.

• Figure 5. Day and night percentile sound pressure levels for 33 one-third octave bands at Decathon in summer, 2015.

• Figure 6. Hourly percentile sound levels (L_Aeq,1s), in dB re 20 µPa, at the Visitor Center in summer, 2015.

• Figure 7. Hourly percentile sound levels (L_Aeq,1s), in dB re 20 µPa, at Shingle Creek in summer, 2015.

• Figure 8. Hourly percentile sound levels (L_Aeq,1s), in dB re 20 µPa, at Decathon in summer, 2015.

• Figure 9. Hourly time audible for the top noise sources and all noise sources at the Visitor Center in summer, 2015.

• Figure 10. Hourly time audible for the top noise sources and all noise sources at Shingle Creek in summer, 2015.

• Figure 11. Hourly time audible for the top noise sources and all noise sources at Decathon in summer, 2015.

• Figure 12. GRBA010, the Visitor Center sampling site.

• Figure 13. GRBA011, the Shingle Creek sampling site.

• Figure 14. GRBA012, the Decathon sampling site.

• Figure 15. Map of predicted existing acoustic levels in GRBA for an average summer day.

• Figure 16. Map of predicted natural acoustic levels in GRBA for an average summer day.

• Figure 17. Map of predicted impact levels in GRBA for an average summer day.

• Figure 18. Comprehensive sound source description results from off-site listening at the Visitor Center in summer, 2015.

• Figure 19. Comprehensive sound source description results from off-site listening at Shingle Creek in summer, 2015.

• Figure 20. Comprehensive sound source description results from targeted spectrogram annotation analysis at Decathon in summer, 2015.

• Figure 21. GRBA001, Ridge S. of Shingle Creek Acoustic Monitoring Station.

• Figure 22. GRBA002, Baker Ridge above burn pit Acoustic Monitoring Station.

• Figure 23. Location of acoustic monitoring sites at Great Basin National Park where data was collected in 2006.

• Figure 24. Day and night dB levels for 33 one-third octave bands at Ridge S. of Shingle Creek (GRBA001).

• Figure 25. Day and night dB levels for 33 one-third octave bands at Baker Ridge above burn pit (GRBA002).

• Figure 26. Comparison of hourly aircraft audibility and overall noise audibility at GRBA001.

• Figure 27. Comparison of hourly aircraft audibility and overall noise audibility at GRBA002.

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List of Tables

• Table 1. Sound level examples.

• Table 2. Percent time above metrics for acoustic records collected in Great Basin National Park (GRBA) in summer, 2015.

• Table 3. Summary of summer noise sources and sound levels at three Great Basin National Park (GRBA) study sites.

• Table 4. Metadata for acoustical monitoring sites at Great Basin National Park in 2015.

• Table 5. Percent time above metrics for acoustic records collected in Great Basin National Park (GRBA) in summer, 2015.

• Table 6. Summary of sound levels at Great Basin National Park (GRBA) in summer, 2015.

• Table 7. The eight days in 2015 at each site used for off-site listening.

• Table 8. Results from SPLAT analysis for Decathon (n = 17 days).

• Table 9. Two hours of on-site listening at GRBA010, the Visitor Center site on August 11–12, 2015.

• Table 10. Two hours of on-site listening at GRBA011, the Shingle Creek site on August 11–12, 2015.

• Table 11. Two hours of on-site listening at GRBA012, the Decathon site on August 12–13, 2015.

• Table 12. Locations of acoustic recording equipment throughout the park.

• Table 13. Percent time above sound levels, represented in a truncated (T) frequency range and the full measured frequency range, for daytime and nighttime during the monitoring period in 2006.

• Table 14. Exceedance levels for existing conditions in GRBA, in a truncated (T) frequency range and the full measured frequency range, for daytime and nighttime during the monitoring period in 2006.

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Acknowledgments

The authors would like to acknowledge the staff at Great Basin National Park for their support in this fieldwork and logistics, including Ben Roberts, Meg Horner, Julie Long and Jonathan Reynolds who made this work possible. A special thanks is extended to Jacob Job at the listening lab for coordinating students who initially listened to the recordings. We also thank the peer reviewers for recommendations that improved this series of reports; they included Tyra Olstad, Jonathan Reynolds, Meg Horner and Gretchen Baker.

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List of Terms

Acoustic Environment: A combination of all the physical sound resources within a given area. This includes natural sounds and cultural sounds, and non-natural human-caused sounds. The acoustic environment of a park can be divided into two main categories: intrinsic and extrinsic.

Acoustic Resources: Includes both natural sounds like wind, water, and wildlife and cultural and historic sounds like tribal ceremonies, quiet reverence, and battle reenactments.

Amplitude: The relative strength of a sound wave, described in decibels (dB). Amplitude is related to what we commonly call loudness or volume.

ANS Weighting: The Natural Sounds modification to A-weighting eliminates high-frequency sound (leaf rustle, equipment noise, and biologic sounds) allowing for more accurate comparisons of low-frequency ambient sound levels across different land use types (e.g., urban, protected areas; ANSI S3/SC1.100, 2014 [R2020]). This frequency weighting scheme improves ambient sound level measurements in quiet environments.

Audibility: The ability of animals with normal hearing, including humans, to hear a given sound. It can vary depending upon the frequency content and amplitude of sound and by hearing ability of individual animals.

A-weighting: A-weighting is applied to sound levels to account for the sensitivity of the human ear (Harris 1998). To approximate human hearing sensitivity, A-weighting discounts sound below 1 kHz and above 6 kHz.

Day-Night Average Sound Levels (L_dn): Average equivalent sound level over a 24-hour period, with a 10-dB penalty added for sound levels between 10 p.m. and 7 a.m.

Decibel (dB): A unit of sound energy. Sound levels are measured on a logarithmic scale relative to the reference sound pressure for atmospheric sources, 20 µPa. The logarithmic scale is a useful way to express the wide range of sound pressures perceived by the human ear. Every 10 dB increase represents a tenfold increase in energy. Therefore, a 20 dB increase represents a hundredfold increase in energy.

Energy Equivalent Sound Level (L_Aeq): The sound energy level averaged over the measurement period. Generally, it refers to A-weighted 1-second time averaged sound levels measured between 12.5 Hz and 20 kHz. This is a standard measurement collected using the NSNSD acoustic monitoring protocol for sound level meters. Sound levels measured over 1 second intervals are used to calculate summary statistics, specifically percent of the time a sound level of interest is exceeded.

Existing Ambient Sound Level (L_A50): Sound level (L_Aeq,1s) exceeded 50% of the time (50^th percentile) for a specified duration. This level is referred to as the existing ambient sound level and is the preferred metric for chronic conditions, as it is insensitive to infrequent loud events.

Frequency: Related to the pitch of a sound, defined as the number of times per second that the wave of sound repeats itself and expressed in terms of hertz (Hz). Sound levels are often adjusted (“weighted”) to match the hearing abilities of a given animal. In other words, different species of animals and humans are capable of hearing (or not hearing) at different frequencies. Humans with normal hearing can hear sounds between 20 Hz and 20,000 Hz, and as low as 0 dB at 1,000 Hz. Bats, on the other hand, can hear sounds between 20 Hz and 200,000 Hz.

Natural Ambient Sound Level (L_Anat): The natural sound conditions in parks, which would exist in the absence of any human-caused noise sources. L_Anat is the preferred metric to represent baseline or reference conditions.

Noise Free Interval (NFI): The length of time that passes between the end of one noise event and the beginning of the next. Over a longer sampling period, the median NFI can describe how a typical opportunity for solitude has been fragmented by noise.

Percentile Sound Levels (L_A10, L_A50, L_A90): Metrics used to describe A-weighted sound pressure levels (L), in decibels, exceeded 10, 50, and 90 percent of the time, respectively. Put another way, half the time the measured levels of sound are greater than the L_A50 value, while 90 percent of the time the measured levels are higher than the L_A90 value and 10 percent of the time measured levels are higher than the L_A10 value.

Sound Exposure Level (SEL): The total sound energy of the actual sound during a specific time period. SEL is usually expressed using a time period of one second.

Sound Pressure: Minute change in atmospheric pressure due to passage of sound that can be detected by microphones.

Soundscape: The human perception of physical sound resources.

Sound vs. Noise: Sound and noise are often used interchangeably to describe an acoustic source. A common definition of noise is unwanted sound or sounds that interfere with a signal of interest (Harris 1998; Templeton 1997). However, noise is not a purely subjective designation. Any sound that serves no function is noise. Most sounds produced by human transportation and other machinery are unintended and serve no function, therefore are noise regardless of the attitudes of the listener. While there are unintended sounds in nature, like the footfalls of an animal, these sounds provide vital cues for some receivers and are therefore considered sounds to the receiver, yet noise from the perception of the producer.

Time Above: Within a defined period, the percent of the time sound levels (L_Aeq,1s) are above a specified sound level (L_Aeq,1s). Commonly used levels are 35, 45, and 52 dB (L_Aeq,1s).

Time Audible: The amount of time that various sound sources are audible to humans with normal hearing, commonly expressed in percent of day, or percent of daytime hours and nighttime hours. A sound may be above natural ambient sound pressure levels, but still not audible. Similarly, some sounds that are below the natural ambient can be audible. Time Audible is useful because of its simplicity. It is a measure that correlates well with visitor complaints of excessive noise and annoyance. Most noise sources are audible to humans at lower levels than virtually all wildlife species. Therefore, time audible is a protective proxy for wildlife. These data can be collected either by a trained observer (on-site listening) or by making high-quality digital recordings for later playback (off-site listening).

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Executive Summary

This report presents acoustical data gathered by the Natural Sounds and Night Skies Division (NSNSD) at Great Basin National Park (GRBA) during late summer in 2015. Data were collected at three sites to provide park managers with information about the acoustical environment, sources of noise, and the existing ambient sound levels within the park. In these deployments, sound pressure level (SPL) was measured continuously every second by a calibrated sound level meter. Other equipment included an anemometer to collect wind speed and a digital audio recorder collecting continuous recordings to document sound sources.

In this document, “sound pressure level” refers to broadband (12.5 Hz–20,000 Hz), A-weighted, 1-second time averaged sound level (L_Aeq,1s [12.5 − −20, 000 Hz]), and hereafter is referred to as “sound level.” Sound levels are measured on a logarithmic scale relative to the reference sound pressure for atmospheric sources, 20 µPa. The logarithmic scale is a useful way to express the wide range of sound pressures perceived by the human ear. Sound levels are reported in decibels (dB). A-weighting is applied to sound levels to account for the response of the human ear (Harris 1998). To approximate human hearing sensitivity, A-weighting discounts sound below 1 kHz and above 6 kHz. For reference, Table 1 provides examples of sound levels measured in parks compared to sound levels of common sources.

Table 1. Sound level examples.

Park Sound Sources	Common Sound Sources	Sound Level dB A
Volcano crater (HALE)	Human breathing at 3 m	10
Leaves rustling (CANY)	Whispering	20
Crickets at 5 m (ZION)	Residential area at night	40
Conversation at 5 m (WHMI)	Car at 15 m, 30 mph	60
Cruiser motorcycle at 15 m (BLRI)	Curbside of busy street	80
Thunder (ARCH)	Jackhammer at 2 m	100
Military jet at 100 m AGL (YUCH)	Train horn at 1 m	120

^A dB re 20 µPa A-weighted broadband (12.5 Hz–20 kHz), sound level measured over varied measurement durations and at the distances indicated.

Overall, existing ambient sound levels (L_A50) at sites within GRBA ranged from 25.6 to 32.5 dB during the day and 20.4–39.6 dB at night during the sampling period. Table 2 reports the percentage of time that measured levels at the monitoring locations were above four key sound level values. The first value, 35 dB (L_Aeq,1s), is used by the National Park Service (NPS) as an indicator of overall quality of the acoustic environment. Beyond this level, noise begins to negatively affect the visitor experience in an otherwise natural acoustic environment (Betchkal and Hug 2024; Pilcher et al. 2009; Watts et al. 2020). Moreover, sound events as low as 35 dB can adversely affect sleeping humans (Haralabidis et al. 2008). The second value addresses the World Health Organization’s recommendations that noise levels inside bedrooms remain below 45 dB (L_Aeq,1s) (Berglund et al. 1999). As wildlife begin to exhibit signs of disturbance at noise levels as low as 40 dB (Shannon et al. 2016), 45 dB also represents a conservative estimate of negative effects on wildlife. The third value, 52 dB (L_Aeq,1s), is based on the EPA’s analysis of speech interference for an individual speaking in a raised voice to an audience at 10 meters (EPA 1974)—an acoustic level that would affect interpretive presentations in parks. The final value, 60 dB (L_Aeq,1s), marks the point at which normal voice communications at 1 meter begin to be interrupted (EPA 1974); sounds at or exceeding this level would affect conversation between visitors and/or staff.

Table 2. Percent time above metrics for acoustic records collected in Great Basin National Park (GRBA) in summer, 2015. Sound level functional values (in decibels, dB L_Aeq,1s re 20 µPa) are shown as the percent of time ANS-weighted sound levels (20–1,250 Hz) and the full measured frequency range (12.5–20,000 Hz) are above those functional values. Due to damage to the microphone from elk, only three days of data are included in sound pressure level data summaries for Shingle Creek (GRBA011).

Site	Frequency Range (Hz)	Time Above Sound Level (% of Daytime Hours, 07:00–19:00)				Time Above Sound Level (% of Nighttime Hours, 19:00–07:00)
		35 dB	45 dB	52 dB	60 dB	35 dB	45 dB	52 dB	60 dB
GRBA010	Full (12.5–20,000)	33.02	4.27	0.27	0.02	66.63	17.95	0.20	0.00
	ANS (20–1,250)	29.81	2.48	0.12	0.00	7.13	0.41	0.02	0.00
GRBA011	Full (12.5–20,000)	2.89	0.24	0.05	0.00	19.67	5.58	0.01	0.00
	ANS (20–1,250)	1.94	0.16	0.05	0.00	17.65	2.74	0.00	0.00
GRBA012	Full (12.5–20,000)	22.80	2.29	0.19	0.01	0.67	0.02	0.00	0.00
	ANS (20–1,250)	18.46	1.28	0.06	0.00	0.56	0.02	0.00	0.00

Sound levels are often measured over narrow frequency bands (typically in one-third octave bands between 12.5 Hz and 20 kHz) because these smaller bands closely represent how humans distinguish between frequencies of sound. In this study, we examine how often sound levels exceeded key values in two frequency ranges. The top value in each split-cell in Table 2 uses the full frequency range (12.5 Hz–20 kHz) collected, whereas the bottom value focuses on frequencies affected by low frequency noise sources (20–1,250 Hz). This Natural Sounds modification to A-weighting (referred to as A-weighted Natural Sounds (ANS) weighting; ASA/ANSI S3/SC1.100-2014 [R2020]) eliminates high-frequency sound (leaf rustle, equipment noise, and biologic sounds) allowing for more accurate comparisons of low-frequency ambient sound levels across different land use types (e.g., urban, protected areas; ASA/ANSI S3/SC1.100-2014 [R2020]). This frequency weighting scheme improves ambient sound level measurements in quiet environments. For example, in the full frequency range, the 35 dB (L_Aeq,1s) threshold was exceeded at the Visitor Center 33.0% of the time during the day and 66.6% at night. In the 20–1,250 Hz range, the same threshold was exceeded 29.8% of the time during the day and only 7.1% at night. These results suggest that natural sources are primarily responsible for elevated sound levels during nighttime hours at this site. Notably, 60 dB (L_Aeq,1s) was rarely exceeded at any of the sites.

After data collection was complete, trained technicians calculated how often noise sources were audible. See “Methods” section for protocol details, equipment specifications, and metrics calculations. Sound source analysis revealed that noise was audible from about 25.8% of the time at Decathon to 96.6% of the time at the Visitor Center during the sampling period when averaged across all hours of the day (Table 3). The most common noise sources observed during this study were aircraft, motors, and vehicles. Natural sources such as wind, songbirds, and insects were also commonly audible. Natural ambient sound levels (L_Anat) ranged between 24.6 and 26.5 dB during the day and 19.8–35.3 dB at night. Increased natural ambient sound levels during day and night varied by location and were likely caused by diurnal winds and site-specific insect and bird activity.

Table 3. Summary of summer noise sources and sound levels at three Great Basin National Park (GRBA) study sites. Included for each site are mean percent time audible for all human-caused noise, including the top three known noise sources, and existing (L_A50) and natural (L_Anat) ambient sound levels (dB re 20 µPa, A-weighted broadband,12.5 Hz–20 kHz) during the day (0700–1900) and night (1900–0700). The difference between the natural and existing ambient sound levels indicates the deviation from the natural condition. L_Anat is calculated based on sound source identification from audio recordings. Due to damage to the microphone from elk, only three days of data are included in sound pressure level data summaries for Shingle Creek (GRBA011).

Site	Mean Time Audible for Noise (% of 24-Hour Time Period)				Median Existing Ambient (LA50) in dB		Median Natural Ambient (LAnat) in dB
	Noise	Aircraft	Motors	Vehicles	Day	Night	Day	Night
GRBA010	96.6	9.3	62.6	38.8	32.5	39.6	25.8	35.3
GRBA011	26.5	20.7	N/A	1.3	25.6	25.3	24.6	25.1
GRBA012	25.8	25.8	N/A	N/A	28.7	20.4	26.5	19.8

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Introduction

Noise has the potential to affect a visitor’s experience in parks by causing annoyance (Rapoza et al. 2015), reducing the perceived scenic beauty (Weinzimmer et al. 2014) and tranquility (Watts et al. 2020), and by limiting opportunities for solitude or a wilderness experience. Increased sound levels may also have wide-ranging effects on wildlife such as reduced predatory success (Mason et al. 2016), changes in vocal communication, and increased vigilance by keystone species (Shannon et al. 2014). In a review of literature addressing the effects of noise on wildlife published between 1990 and 2013, wildlife responses to noise were observed beginning at about 40 dB (L_Aeq, as a composite of multiple metrics with varying time-averaging). Of the papers reviewed, 20% showed impacts to terrestrial wildlife at or below noise levels of 50 dB (L_Aeq,1s) (Shannon et al. 2016).

A 1998 survey of the American public revealed that 72 percent of respondents thought that providing opportunities to experience natural quiet and the sounds of nature was a very important reason for having national parks, while another 23 percent thought that it was somewhat important (Haas and Wakefield 1998). In another survey specific to park visitors, 91 percent of respondents considered enjoyment of natural quiet and the sounds of nature as compelling reasons for visiting national parks (McDonald et al. 1995). Acoustic monitoring provides a scientific basis for assessing the status of acoustic resources, identifying trends in resource conditions, quantifying impacts from other actions, assessing consistency with park management objectives and standards, and informing management decisions regarding desired future conditions. The National Park Service (NPS) Natural Sounds and Night Skies Division (NSNSD) helps parks manage sounds in a way that protects park resources and the visitor experience. NSNSD addresses acoustic issues raised by Congress, NPS Management Policies, and NPS Director’s Orders. The NSNSD works to protect, maintain, or restore acoustic environments throughout the National Park System. Its goal is to provide coordination, guidance, and a consistent approach to soundscape protection with respect to park resources and visitor use. The program also provides technical assistance to parks in the form of acoustic monitoring, data processing, park planning support, and comparative analyses of acoustic environments.

Soundscape Planning Authorities

The National Park Service Organic Act of 1916 states that the purpose of national parks is “… to conserve the scenery and the natural and historic objects and the wild life therein and to provide for the enjoyment of the same in such manner and by such means as will leave them unimpaired for the enjoyment of future generations.” In addition to the NPS Organic Act, the Redwoods Act of 1978 affirmed that, “the protection, management, and administration of these areas shall be conducted in light of the high value and integrity of the National Park System and shall not be exercised in derogation of the values and purposes for which these various areas have been established, except as may have been or shall be directly and specifically provided by Congress.” NPS Management Policies 2006 (NPS 2006) Chapter 4.9 provides direction for management of natural soundscapes:

The National Park Service will preserve, to the greatest extent possible, the natural soundscapes of parks…

The Service will restore to the natural condition wherever possible those park soundscapes that have become degraded by unnatural sounds (noise) and will protect natural soundscapes from unacceptable impacts.

Using appropriate management planning, superintendents will identify what levels and types of unnatural sound constitute acceptable impacts on park natural soundscapes. The frequencies, magnitudes, and durations of acceptable levels of unnatural sound will vary throughout a park, being generally greater in developed areas. In and adjacent to parks, the Service will monitor human activities that generate noise that adversely affects park soundscapes [acoustic resources], including noise caused by mechanical or electronic devices. The Service will take action to prevent or minimize all noise that through frequency, magnitude, or duration adversely affects the natural soundscape [acoustic resource] or other park resources or values, or that exceeds levels that have been identified through monitoring as being acceptable to or appropriate for visitor uses at the sites being monitored.

It should be noted that under Management Policies 2006 Chapter 8.2.3, “[t]he natural ambient sound level—that is, the environment of sound that exists in the absence of human-caused noise—is the baseline condition, and the standard against which current conditions in a soundscape [acoustic resource] will be measured and evaluated” (NPS 2006). However, the desired acoustic condition may also depend upon the resources and the values of the park. For instance, “culturally appropriate sounds are important elements of the national park experience in many parks” (NPS 2006). In this case, “the Service will preserve soundscape resources and values of the parks to the greatest extent possible to protect opportunities for appropriate transmission of cultural and historic sounds that are fundamental components of the purposes and values for which the parks were established” (NPS 2006).

Further guidance is provided in Management Policies 2006 §4.1.4 Partnerships, §4.1.5 Restoration of Natural Systems, §8.2 Visitor Use, §8.2.2 Recreational Activities, §8.2.3 Use of Motorized Equipment, and §8.4 Overflights and Aviation Uses (NPS 2006).

Director’s Order 47, “Soundscape Preservation and Noise Management,” was issued in 2000 and builds on the principles set out in Management Policies, directing park management how and when to consider acoustic resources. Through this order, parks are guided to manage noise by identifying noise sources, minimizing noise from park operations, considering the acoustic environment in park planning documents, and promoting park sounds and noise management through communication, education, and outreach.

Focal Park Unit

Great Basin National Park, located in eastern Nevada’s White Pine County, was established in 1986. It encompasses 77,100 acres centered on the rugged Snake Range that rises over 6,000 ft above the basins on either side of it. Wheeler Peak, the park’s highest summit, reaches 13,063 ft. Below ground, Lehman Caves hosts a wonderous array of unique marble cave geology, ecology, and features.

The park’s impressive elevational gradient lends itself to a wide diversity of plant life. Sagebrush grasslands dominate the lower elevations until they mix with a pinyon and juniper forest. Higher up, montane and subalpine forests give way to rocky, alpine habitat. Groves of bristlecone pines, the oldest trees in the world, cover high alpine slopes above 10,000 ft in parts of the park.

The park has a long history of Native habitation recorded in pictographs, artifacts and village sites that date back to at least 1100–1300 B.C.E. In modern times, ranchers and prospectors used the land, but its extreme remoteness prevented significant development on the adjacent lands. As such, Great Basin has some of the darkest night skies in the country and is renowned for the opportunity for visitors to see stars without much detrimental light pollution.

Study Area

This report covers results from an acoustic inventory conducted at three sites over one season in 2015 (Table 4, Figure 1). Sites GRBA010, GRBA011 and GRBA012 were deployed in late summer of 2015. The acoustic environment is a notable and dynamic part of the park so three monitoring sites were set up across the park to capture multiple aspects of its soundscape.

Table 4. Metadata for acoustical monitoring sites at Great Basin National Park in 2015.

Site	Site Name	Dates	Vegetation	Elevation (m)	Latitude	Longitude
GRBA010	Visitor Center (VC)	8/11/2015–8/30/2015	Sagebrush / Pinyon pine	2,076	39.00513	−114.2178
GRBA011	Shingle Creek	8/13/2015–9/17/2015	Montane grassland / Alpine tree line	2,804	39.00370	−114.3463
GRBA012	Decathon	8/12/2015–8/29/2015	Temperate broadleaf / Mixed	2,642	38.82026	−114.2812

Figure 1. Study sites in Great Basin National Park, NV, USA. Click to See A Larger Image for Figure 1

NPS / NATURAL SOUNDS & NIGHT SKIES DIVISION

GRBA010 (Visitor Center) was located near the park’s visitor center to get a sense of the most developed area of the park and assess the impact of unnatural sounds on the acoustic environment. The natural ecosystem near this site is made up of pinyon-juniper woodland and sagebrush habitat (see also Appendix A). At this site, all equipment worked for the duration of the data collection period, 11–30 August.

The Shingle Creek Site, GRBA011, was located on a ridge on the west slope of Wheeler Peak at 2,804 m. At this site, montane shrublands and grasslands give way to subalpine forests and eventually alpine vegetation. Elk are commonly seen at the site, and a herd of 40 elk were counted during deployment at this remote, backcountry monitoring site. Elk at this site destroyed the microphone and reduced the availability of high-quality sound pressure level data to just three days (see also Appendix A).

GRBA012 (Decathon) was located at 2,642 m in the Decathon Canyon on the southern border of the park. This remote backcountry site was in a forest of quaking aspen and white fir along a lightly used trail. Sound level data was recorded here, but due to technical difficulties audio data could not be recorded so not all metrics are present for this field site (see also Appendix A).

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Methods

Automatic Monitoring

A Larson Davis sound level meter (SLM) type 831-A was deployed at three monitoring sites. The SLM is a hardware-based, real-time analyzer which constantly records one-third octave band sound pressure level (SPL) data. This Larson Davis-based site met American National Standards Institute (ANSI) Type 1 standards (ANSI 1968 [R2023], 1983 [R2006], 1992 [R2018]) for accurate survey-grade instrumentation. The sound level meter provided the information needed to calculate metrics described below in “Calculation of Metrics.”

Acoustic monitoring equipment is used by many practitioners to determine noise levels in different environments, both indoors and outdoors. The NPS uses equipment like that used by other practitioners but has developed a unique configuration that stands up to the potentially harsh environment encountered in national parks (NPS 2013). The microphone with environmental shroud was set up on a tripod at 1.5 m above the ground, which approximates the average height of the human ear. The digital audio recorder recorded continuous audio throughout the entire monitoring period (see details below on the acoustic record). An anemometer was attached to a tripod and placed approximately 10 feet from the microphone to capture local wind conditions.

The sampling station consisted of:

• Type 1 sound level meter

• Microphone with environmental shroud

• Preamplifier

• 12 V alkaline battery packs

• Anemometer (wind speed and direction)

• Relative humidity and temperature sensor

• Digital audio recorder (MP3)

The sampling station was designed to collect:

• Flat-weighted, time-averaged sound level (L_Zeq,1s) for each one-third octave frequency band, 12.5–20,000 Hz in dB re 20 µPa [collected by Type 1 sound level meter].

• A-weighted, time-averaged sound level (LAeq,1s[12.5–20000 Hz]) in dB re 20 µPa [collected by Type 1 sound level meter].

• Continuous meteorological data for wind speed [collected by anemometer], relative humidity, and temperature.

• Continuous digital audio recordings collected by Roland R-05 digital audio recorder.

Monitoring Period

It is typical to monitor a minimum of 25 days to capture daily differences within a sampling period that occur at each site within a reasonable margin of error (Betchkal 2017). For this study, the monitoring period ranged from 19 to 38 days. Due to damage to the microphone from elk, only three days of data are included in sound pressure level data summaries for Shingle Creek.

Calculation of Metrics

The status of the acoustical environment can be characterized by sound level (L_A50, L_Anat, L_A90, L_A10, L_Aeq), frequency content, and event durations (determined through off-site listening). NPS uses descriptive figures and metrics to interpret these characteristics.

Two fundamental descriptors are existing ambient (L_A50) and natural ambient (L_Anat) sound levels. These are both examples of percentile levels, where each L_x value refers to the sound level that is exceeded x% of the time. The L_A50 represents the median sound level and is drawn from a full dataset (removing data with wind speed >5 m/s to eliminate error from microphone distortion). The L_A50 is the preferred metric to represent prevailing acoustic conditions. The natural ambient (L_Anat) is an estimate of what the sound levels for a site would be if all human-caused noise sources were removed. L_Anat is the preferred metric to represent baseline or reference conditions.

For a given hour (or other specified time period), L_Anat is calculated to be the sound level exceeded x percent of the time, where x is defined by the equation:

where P_H = percentage of samples containing noise for the hour.

For example, if human-caused sounds are present 30% of the hour, x = 65, and the L_Anat is equal to the L₆₅, or the level exceeded 65% of the time. To summarize and display these data, the median of the hourly L_Anat values for the daytime hours (0700–1900) and the median of the hourly L_Anat values for the nighttime (1900–0700) are displayed in graphical format in the following sections.

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Off-Site Listening and Spectrogram Analysis

Listening Center Software Analysis

Off-site analysis is completed by listening to the audio record while simultaneously viewing its spectrogram representation. Auditory analysis was used to calculate the audibility of sound sources at the Visitor Center and Shingle Creek. Trained technicians at Colorado State University (Figure 2A) listened to 8 days of the audio record. Technicians considered only a subsample of each day representing the first 10 seconds of every two-minute period, resulting in 16 hours of audio data being analyzed per site. Within each subsample every audible sound source was categorized. This allowed the temporal extent of audibility for each source type to be estimated. The total percent time noise was audible was then used to calculate the natural ambient sound level (L_Anat) for each hour (see equation above for more information). For any off-site audio playback listening techniques, Bose Quiet Comfort Noise Canceling headphones were used to minimize limitations imposed by the office acoustical environment.

Figure 2. Depictions of auditory analysis by trained technicians. The top image (A) shows a Colorado State University student identifying sound sources using Listening Center software (NPS). The bottom image (B) is a screen shot of NPS Sound Pressure Level Annotation Tool (SPLAT) software with an annotated propeller aircraft noise event.

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Sound Pressure Level Annotation Tool

Because a full digital audio record was unavailable, sound pressure level data was annotated visually across 17 days of spectrograms at Decathon using the NPS-developed software, Sound Pressure Level Annotation Tool (SPLAT; Figure 2B). Trained technicians used SPLAT to draw bounding boxes at the beginning and end of noise events using visual cues from the sound pressure energy, time, and frequency of a spectrogram. From the drawn bounding boxes, noise event counts (i.e., the number of boxes), and noise duration (i.e., the length of each box) were obtained. In addition, the noise-free interval (NFI) metric was generated. The NFI represents the length of time that passes between the end of one noise event and the beginning of the next. Over a longer sampling period, the median NFI can describe how a typical opportunity for solitude has been fragmented by noise (Poling and Betchkal 2023). Like the Listening Center software, the total percent time noise was audible was then used to calculate the natural ambient sound level (L_Anat) for each hour.

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Results

Frequency Content

To determine the effect that noise has on the acoustic environment, it is useful to examine percentile metrics across a frequency range. High frequency sounds (such as a cricket chirping) and low frequency sounds (such as flowing water) often occur simultaneously, so the frequency spectrum is split into 33 narrower bands, each encompassing one-third of an octave. These narrow bands closely represent how humans distinguish between frequencies of sound. The percentile sound levels for 33 one-third octave band frequencies over the day and night periods are shown in Figures 3–5.

Figure 3. Day and night percentile sound pressure levels for 33 one-third octave bands at the Visitor Center in summer, 2015. For each bar, the bold color indicates the range of existing (L₅₀; upper) and natural (L_nat; lower) sound pressure levels.

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Figure 4. Day and night percentile sound pressure levels for 33 one-third octave bands at Shingle Creek in summer, 2015. For each bar, the bold color indicates the range of existing (L₅₀; upper) and natural (L_nat; lower) sound pressure levels. Due to damage to the microphone from elk, only three days of sound pressure data are included in this analysis.

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Figure 5. Day and night percentile sound pressure levels for 33 one-third octave bands at Decathon in summer, 2015. For each bar, the bold color indicates the range of existing (L₅₀; upper) and natural (L_nat; lower) sound pressure levels.

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Examining the sound energy in each one-third octave band (combined with digital audio recordings) allows acoustic technicians to determine what types of sounds are contributing to the overall sound levels at a site. The grayed areas of Figures 3–5 represent sound levels outside of the typical range of human hearing. The percentile levels (L_x) are also shown for each one-third octave band. They represent the sound levels exceeded x percent of the measurement period. For example, L₉₀ is the sound level that has been exceeded 90% of the time, and only the quietest 10% of the samples can be found below this point. On the other hand, the L₁₀ is the sound level that has been exceeded 10% of the time, and 90% of the measurements were quieter than the L₁₀. The bold portion of the column represents the difference between L₅₀ and L_nat. The height of this bold portion is a measure of the contribution of anthropogenic noise to the existing sound levels at this site. The size of this portion of the column is directly related to the percent time that human-caused sounds are audible. When bold portions of the column do not appear the natural and existing sound levels were either very close to each other or were equal. The typical frequency levels for transportation, conversation, and songbirds are presented on the figure as examples for interpretation of the data. These ranges are estimates and are not vehicle-, species-, or habitat-specific.

Sound Level: Time Above

To understand how acoustic conditions in the park might affect visitors, measured sound levels are compared to sound levels of interest. Specifically, Table 5 reports the percent of time that measured sound levels (L_Aeq,1s) were above four key functional effect levels during the monitoring periods (daytime and nighttime). The top value in each split-cell uses the full frequency range, whereas the bottom values report the percentage of the sample that ANS-weighted sound levels (20–1,250 Hz) were above functional effect thresholds. 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. ANS weighting eliminates high-frequency sound (leaf rustle and biologic sounds) allowing for more accurate comparisons of low-frequency ambient sound levels across different land use types (e.g., urban, protected areas; ANSI S3/SC1.100, 2014 [R2020]). This frequency weighting scheme improves ambient sound level measurements in quiet environments.

Table 5. Percent time above metrics for acoustic records collected in Great Basin National Park (GRBA) in summer, 2015. Sound level functional values (in decibels, dB L_Aeq,1s re 20 µPa) are shown as the percent of time ANS-weighted sound levels (20–1,250 Hz) and the full measured frequency range (12.5–20,000 Hz) are above those functional values. Due to damage to the microphone from elk, only three days of data are included in sound pressure level data summaries for Shingle Creek (GRBA011).

Site	Frequency Range (Hz)	Time Above Sound Level (% of Daytime Hours, 07:00–19:00)				Time Above Sound Level (% of Nighttime Hours, 19:00–07:00)
		35 dB	45 dB	52 dB	60 dB<	35 dB	45 dB	52 dB	60 dB
GRBA010	Full (12.5–20,000)	33.02	4.27	0.27	0.02	66.63	17.95	0.20	0.00
	ANS (20–1,250)	29.81	2.48	0.12	0.00	7.13	0.41	0.02	0.00
GRBA011	Full (12.5–20,000)	2.89	0.24	0.05	0.00	19.67	5.58	0.01	0.00
	ANS (20–1,250)	1.94	0.16	0.05	0.00	17.65	2.74	0.00	0.00
GRBA012	Full (12.5–20,000)	22.80	2.29	0.19	0.01	0.67	0.02	0.00	0.00
	ANS (20–1,250)	18.46	1.28	0.06	0.00	0.56	0.02	0.00	0.00

The first functional effect in Table 5 occurs around 35 dB (L_Aeq,1s), which is designed to address the health effects of sleep interruption. Studies suggest that sound events as low as 35 dB can have adverse effects on blood pressure in sleeping humans (Haralabidis et al. 2008). This 35 dB (L_Aeq,1s) value is used by the NPS as an indicator of overall quality of the acoustic environment. Beyond this level, noise begins to negatively affect the visitor experience in an otherwise natural acoustic environment (Betchkal and Hug 2024; Pilcher et al. 2009; Watts et al. 2020). For application to the present study, the 35 dB (L_Aeq,1s) threshold was exceeded at the Visitor Center 33.0% of the time during the day and 66.6% at night. In the 20–1,250 Hz range, the same threshold was exceeded 29.8% during the day and only 7.1% at night. These results suggest that natural sources are primarily responsible for elevated sound levels during nighttime hours at this site. The second functional effect is expected to occur around 45 dB (L_Aeq,1s). It addresses the World Health Organization’s recommendations that noise levels inside bedrooms remain below 45 dB (L_Aeq,1s) (Berglund et al. 1999). The third functional effect is expected to occur around 52 dB (L_Aeq,1s), based on the EPA’s speech interference threshold for speaking in a raised voice to an audience at 10 meters (EPA 1974). This threshold addresses the effects of sound on interpretive presentations in parks. The final functional effect at 60 dB (L_Aeq,1s), provides a basis for estimating impacts on normal voice communications at 1 meter. Visitors viewing scenic areas in the park regularly conduct such conversations.

Sound Level: Percentile Levels

To understand the range of acoustic conditions at the park, percentile sound levels are reported (Table 6, Figures 6–8). Shingle Creek and Decathon had similar existing and natural sound levels, suggesting minimal noise impact. The Visitor Center showed the largest difference between L_Anat and L_A50, indicating the greatest noise impact. In Figures 6–8 the A-weighted percentile sound levels (L_A90, L_Anat, L_A50, and L_A10) are shown. The hourly percentile sound levels are calculated from the broadband (12.5 Hz–20 kHz) A-weighted, 1-second time averaged sound levels (L_Aeq,1s) within each hour of the day. For instance, in Figure 8, the L_A50 (median) sound level for Decathon at 8:00 is 23.0 dB. The sound level exceeded 10% of the time (L_A10) for the same hour at this site is 30.3 dB, meaning 90% of the measurement period is quieter. Hours where the L_A50 and the L_Anat differ the most are usually hours with the most human-caused noise, as shown with the Visitor Center (Figure 6). The larger the span of the black bars, the greater the difference of the existing sound level from natural conditions. At the Visitor Center, existing sound levels are closest to natural conditions in the early morning hours but depart from natural conditions for most of the day (Figure 6). In general, higher natural ambient sound levels occurred in the late evening and early morning hours and are largely due to wind, insect and bird activity (Figures 6–8).

Table 6. Summary of sound levels at Great Basin National Park (GRBA) in summer, 2015. Included for each site are the 90^th percentile (L_A10), existing (L_A50), natural (L_Anat) and 10^th percentile (L_A90) ambient sound levels (dB re 20 µPa, A-weighted broadband, 12.5 Hz—20 kHz) during the day (0700–1900) and night (1900–0700).

Site	Time	LA10	LA50	LAnat	LA90
GRBA010	Day	41.6	32.5	25.8	27.9
	Night	43.4	39.6	35.3	36.6
GRBA011	Day	30.9	25.6	24.6	22.7
	Night	30.0	25.3	25.1	24.0
GRBA012	Day	38.0	28.7	26.5	22.8
	Night	25.5	20.4	19.8	17.6

Figure 6. Hourly percentile sound levels (L_Aeq,1s), in dB re 20 µPa, at the Visitor Center in summer, 2015.

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Figure 7. Hourly percentile sound levels (L_Aeq,1s), in dB re 20 µPa, at Shingle Creek in summer, 2015. Due to damage to the microphone from elk, only three days of sound pressure data are included in this analysis.

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Figure 8. Hourly percentile sound levels (L_Aeq,1s), in dB re 20 µPa, at Decathon in summer, 2015.

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Event Duration

Listening Center Software

Through off-site listening analysis, event duration for all audible sounds is calculated and averaged over the listening period. For both sites (GRBA010, GRBA011) with available audio data, mean hourly audibility was obtained for each hour of the day over an 8-day listening period (Table 7; CSU 2026). Hourly audibility is also displayed for all non-natural sources, while also highlighting the top two sources at each site (Figures 9–11; see also Appendix C). For example, at the Visitor Center (GRBA010), noise was audible more than 85% of the time across all hours of the day, and the primary contributor was motors (Figure 9), likely from a nearby HVAC unit. At Shingle Creek (GRBA011), noise was audible under 40% of the time across all except three hours of the day. From 06:00–09:00, aircraft noise peaked and was the main contributing source to the increased audibility of noise (Figure 10).

Table 7. The eight days in 2015 at each site used for off-site listening.

Site	Dates of Off-site Listening
GRBA010	8/12, 8/16, 8/17, 8/20, 8/22, 8/23, 8/27, 8/28
GRBA011	8/16, 8/18, 8/19, 8/20, 8/22, 8/23, 8/26, 8/27

Figure 9. Hourly time audible for the top noise sources and all noise sources at the Visitor Center in summer, 2015.

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Figure 10. Hourly time audible for the top noise sources and all noise sources at Shingle Creek in summer, 2015.

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Figure 11. Hourly time audible for the top noise sources and all noise sources at Decathon in summer, 2015.

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Sound Pressure Level Annotation Tool

Event duration metrics were also obtained from Decathon, but only for aircraft sources. Using the SPLAT technique, mean hourly audibility of noise events were obtained for each hour of the day over a 17-day period and published as a separate dataset (CSU 2026). Jets and prop aircraft accounted for all the aircraft noise events (Figure 11, Table 8). In both day and nighttime hours, both aircraft sources contributed a similar duration of noise, typically lasting around 3:00 minutes (shown in mm:ss in Table 8). The median NFI across all hours of the day was 05:13 mm:ss. The lowest hourly median NFI occurred at 08:00 h (2:25 mm:ss), and the highest hourly median NFI occurred at 03:00 h (57:31 mm:ss).

Table 8. Results from SPLAT analysis for Decathon (n = 17 days).

Sound Source	Day		Night
	Mean Event Counts	Mean Event Length (mm:ss)	Mean Event Counts	Mean Event Length (mm:ss)
Jet	74.5	02:51	42.4	03:20
Prop	4.4	03:11	0.8	03:17

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Conclusions

The purpose of this study was to assess current conditions of the acoustical environment at GRBA. Monitoring results characterizing the existing sound levels are intended to provide the park with baseline information as well as to inform management decisions. SPL data, meteorological conditions, continuous audio, and on-site listening were collected from three different acoustical monitoring site locations that were chosen to assess noise impacts at varying elevations and habitats within the park ranging from the front country near the park’s visitor center to two backcountry sites in differing habitats. Data was analyzed using visual/auditory analysis of spectrograms and summarized using a suite of metrics. Field staff listened while visiting the sites to provide a small sample of on-site listening that could be used to describe the full suite of anthropogenic and natural sounds at the site (Appendix D). The goal of the study was to determine existing ambient sound levels as a baseline condition in Great Basin National Park.

The Visitor Center Acoustic Monitoring Site (GRBA010) was the lowest elevation site of the three. This site had the most active nighttime insect chorus, which is most likely the cause of the higher nighttime acoustic ambient levels. While this front-country site has many audible sources of anthropogenic noise, insects and other natural sounds still dominate the soundscape. The daytime natural ambient level at GRBA010 was 25.8 dBA, while the nighttime natural ambient level was 35.3 dBA. This nearly 10 dBA difference can mostly be attributed to the very active insect chorus, which appears in the high frequencies in Figure 3 and was noted by listeners (see Appendix C). This site is also the epicenter of human activity at the park, with significant visitor presence. Anthropogenic sounds included vehicles, traffic, visitors, and park operations, all likely associated with the Visitor Center location. Additional anthropogenic noises, such as aircraft and rumble strips/cattle guards, were also heard but were not directly tied to Visitor Center operations. Because of human activity at this site, we would expect to see the largest differences between ambient and natural ambient conditions, and that is indeed the case: a 6.7 dBA difference during the daytime and a 4.3 dBA difference at night. We would also expect more anthropogenic noise during the daytime than at night, as human activity is generally concentrated during the day. Overall, this site is typical of a front-country location in a remote natural park setting. While human-caused sounds are common, natural sounds still dominate, and the nighttime insect chorus has a stronger impact on the acoustic environment than any anthropogenic noise. Finally, exceedance metrics show that GRBA010 never exceeded 60 dBA, an important threshold because sound levels above this could interfere with interpretive programming.

The Shingle Creek Acoustic Monitoring Site (GRBA011) is located at the highest elevation of the three sites. On August 19, less than one week into deployment, an elk pulled the windscreen off the microphone. Then, on September 3, the anemometer was knocked over (see Appendix A). These disturbances affected data availability because high winds at this site create artifacts in the sound pressure level data that do not reflect actual ground conditions. As a result, only three days of sound pressure data were included in the final analysis. At this remote site, aircraft—including jets, propeller planes, and helicopters—were the most common sources of noise (Figure 6). Aircraft were heard during more than 25% of each hour between 6:00 and 11:00 (Figure 11). This pattern is similar to what was documented in 2006 (see Appendix E) and coincides with the dawn chorus, the most vocally active time for birds. Elk were also relatively common at this site and were heard throughout a typical day during the sampling period. Insects were present as well, but unlike the lower-elevation Visitor Center site, they did not produce a strong nighttime signal and were more common during the day. Highway 93 is visible from this site, but it is far away; only occasional loud cars were heard, usually in the quiet morning hours. Overall, this site had abundant natural sounds. Anthropogenic noise had less impact here than at the Visitor Center, adding 1.0 dBA during the day and 0.2 dBA at night to the ambient acoustic environment (Table 6). While an increase of 1.0 dBA may seem small, it can reduce wildlife listening areas by 21%. Natural sounds dominate, but noise—mostly from aircraft—is still common.

The Decathon Acoustic Monitoring Site (GRBA012) provided a complete sound pressure level (SPL) record; however, no audio was collected because the recorder was not functioning. The daytime natural ambient level at GRBA012 was 26.5 dBA, while the nighttime natural ambient level was 19.8 dBA. The 7 dBA difference can largely be attributed to diel wind patterns, which are stronger during the day and diminish in the evening. This site is in a remote area near designated wilderness. In the absence of audio files, off-site analysis relied on spectrogram annotation, which focused exclusively on aircraft events. On average, 79 aircraft events occurred during daytime hours and 43 at night, each lasting approximately three minutes. Due primarily to aircraft activity, anthropogenic noise increased ambient levels by 2.2 dBA during the day and 0.6 dBA at night. Despite these impacts, someone in this area of the park could generally expect to experience a noise-free interval for an average of about five minutes between the end of one noise event and the beginning of the next. On-site analysis indicates that this location is characterized by a mostly quiet acoustic environment, punctuated by frequent aircraft sounds.

This report is a summary of the acoustic environment that provides information about the conditions in the park including the natural sounds and the noise that impacts the soundscape. Repeat measurements can be collected to get a broader acoustic picture and if new noise sources are introduced into the environment. This acoustic data can serve as a baseline for sound conditions in the park.

The information presented in this report will be used to inform park managers and planners, and it will also serve as a permanent record of what the park sounded like in the summer of 2015. Sound level data as well as continuous digital audio recordings will be archived with the Natural Sounds and Night Skies Division office in Fort Collins, Colorado.

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Literature Cited

• American National Standards Institute (ANSI). 1968. Audiometer Standard 3.6. American National Standards Institute, New York, NY. ANSI/ASA S3.6-2018 (R2023).
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• Berglund, B., T. Lindvall, and D.H. Schwela, editors. 1999. Guidelines for community noise. World Health Organization, Geneva, Switzerland.
• Betchkal, D. 2017. Revisiting sample length determination from Iyer 2005. Unpublished NPS white paper, Natural Sounds and Night Skies Division, National Park Service, Fort Collins, CO.
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Appendix A: Site Photos

Photos of the three sites where sampling took place during this study are shown in Figures 12–14.

Figure 12. GRBA010, the Visitor Center sampling site.

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Figure 13. GRBA011, the Shingle Creek sampling site. The top image (A) shows this site at deployment, and the bottom image (B) shows the station after the windscreen was eaten by an elk and the anemometer was knocked over by an elk on a separate visit.

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Figure 14. GRBA012, the Decathon sampling site.

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Appendix B: Modeled Impact Levels

NSNSD developed a geospatial sound model (Mennitt et al. 2013, NPS 2021) that predicts the median sound level using measurements made at hundreds of national park sites as well as 109 explanatory variables such as location, climate, land cover, hydrology, wind speed, and proximity to noise sources such as roads, railroads, and airports. The resulting model can predict sound levels anywhere in the contiguous United States and estimate how much lower these sound levels would be in the absence of human activities. Each pixel in the graphic shown in Figures 15–17 represents 270 m and represents the acoustic conditions on a typical summer day.

Figure 15. Map of predicted existing acoustic levels in GRBA for an average summer day. Click to See A Larger Image for Figure 15

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Figure 16. Map of predicted natural acoustic levels in GRBA for an average summer day. Click to See A Larger Image for Figure 16

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Figure 17. Map of predicted impact levels in GRBA for an average summer day. Click to See A Larger Image for Figure 17

NPS / NATURAL SOUNDS & NIGHT SKIES DIVISION .

Within GRBA, the modeled median sound level (L_{A50, existing}) was 30.7 dB (Figure 15) and natural sound level (L_{A50, natural}) was 28.3 dB (Figure 16). The modeled difference between the existing and predicted natural sound level (L_50impact) at GRBA is shown in Figure 17 and provides a measure of how much anthropogenic noise is increasing the existing sound level above the natural sound level on an average summer day in the park. Across GRBA the mean modeled sound level impact is 2.5 dB (ranging from 1 dB in the least impacted areas to 5.7 dB in the most impacted areas).

For translating sound level impacts into functional effects (for human visitors and resident wildlife), an increase in background sound level of 3 dB produces an approximate decrease in listening area of 50%. In other words, by raising the sound level at GRBA by just 3 dB, the ability of listeners to hear the sounds around them is effectively cut in half. Furthermore, an increase of 7 dB leads to an approximate decrease in listening area of 80%. An increase of 2.5 dB would reduce the listening area for wildlife and visitors by 44%. For example, if a predator can hear a potential prey animal in an area of 100 square feet in a setting with natural ambient sounds, that animal’s ability to hear would be reduced to 56 square feet if the sound levels were increased by the modeled average impact of 2.5 dB.

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Appendix C: Detailed Sound Source Descriptions

Sound source description results are displayed in Figures 18–20.

Figure 18. Comprehensive sound source description results from off-site listening at the Visitor Center in summer, 2015. Click to See A Larger Image for Figure 18

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Figure 19. Comprehensive sound source description results from off-site listening at Shingle Creek in summer, 2015. Click to See A Larger Image for Figure 19

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Figure 20. Comprehensive sound source description results from targeted spectrogram annotation analysis at Decathon in summer, 2015. Click to See A Larger Image for Figure 20

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Appendix D: On-Site Listening

While the sound level provides information about how loud or quiet the acoustic environment is at a given time, we need .mp3 recordings or on-site listening sessions to know what or who is making the sound. On-site listening is the practice of placing an observer near the acoustic monitoring station with a handheld personal digital assistant (PDA; or in this case, an Apple iPod Touch device). The observer listens for a designated period (in this case, two hours) and identifies all sound sources and their durations. On-site listening takes full advantage of human binaural hearing capabilities and closely matches the experience of most park visitors. Logistic constraints prevent comprehensive sampling by this technique, but selective samples of on-site listening provide a basis for relating the results of off-site listening to the probable auditory perception of events by park visitors and wildlife. On-site listening sessions are also excellent screening tools for parks initiating acoustic environment studies. They produce an inventory of sound sources, require little equipment or training, and can help educate park staff and volunteers.

Thus, two periods of on-site listening were conducted at the three sites, to discern the type, timing, and duration during sound-level data collection. As recommended by NSNSD protocol (Betchkal 2017), these sessions lasted for one hour each. Staff recorded the beginning and ending times of all audible sound sources using custom-designed software. These on-site listening sessions provided the basis for the calculation of metrics including the time between noise events (average noise free intervall [NFI]), percent time each sound source was audible, and maximum, minimum, and mean length (in seconds) of sound source events.

Tables 9–11 display the results of on-site listening sessions at GRBA. Each audible sound source is listed in the first column. Percent time audible, or PA, is shown in the second column. The third column, Max Event, reports the maximum event length among the sessions for each sound source. Likewise, Mean Event and Min Event columns report the mean and minimum length of events, respectively. Std Dev reports the standard deviation among event lengths, and the Events column reports the audible discrete occurrences of each sound source. The last row in the table, noise free interval (NFI), is a metric which describes the length of time between extrinsic or human-caused events (when only natural sounds were audible). The NFI row and the Max Event, Mean Event, Min Event, and Std Dev columns are reported in seconds. These on-site listening tables reveal the sounds heard in-situ at the location where the acoustic monitoring stations sat for the entirety of the monitoring period.

Table 9. Two hours of on-site listening at GRBA010, the Visitor Center site on August 11–12, 2015.

Sound Source Description	PA (%)	Max Event (s)	Mean Event (s)	Min Event (s)	SD (s)	Event Count
Jet	13.2	100	55.8	1	30.5	17
Vehicle	79.6	1110	163.8	4	222.7	35
Vehicle Alarm	0.1	3	2.0	1	1.4	2
Vehicle Door	3.7	62	5.4	1	9.5	49
Truck	4.2	95	24.9	1	26.1	12
Motor	1.8	119	43.0	1	65.9	3
Trash Lid	0.1	5	5.0	5	–	1
People	3.5	37	15.0	1	10.7	17
Talking	13.5	189	28.6	1	37	34
Walking	4.0	65	31.9	12	19.4	9
Portable Audio	1.7	66	59.5	53	9.2	2
Domestic Animal	5.2	156	47.1	2	53.8	8
Construction	0.2	17	17.0	17	–	1
Human, Unknown	3.2	81	14.3	1	19.9	16
Wind A	25.3	292	67.4	7	76.4	27
Thunder A	1.4	28	19.6	9	7.2	5
Bird A	89.2	1659	142.8	3	267.2	45
Insect A	21.6	82	16.4	1	17.9	95
Animal A	0.1	3	2.5	2	0.7	2
Total Non-natural	92.0	–	–	–	–	–
Noise-Free Interval	–	156	18.2	1	31.5	32

^A Natural sound source, also shown shaded in gray.

Table 10. Two hours of on-site listening at GRBA011, the Shingle Creek site on August 11–12, 2015.

Sound Source Description	PA (%)	Max Event (s)	Mean Event (s)	Min Event (s)	SD (s)	Event Count
Jet	24.2	193	69.8	7	48.0	25
Wind A	71.8	3407	147.8	5	568.9	35
Bird A	34.2	338	30.8	2	44.8	80
Insect A	27.5	407	35.4	1	74.0	56
Animal A	4.9	57	8.7	2	8.9	41
Natural, Unknown A	0.5	33	12.0	1	18.2	3
Total Non-natural	24.2	–	–	–	–	–
Noise-Free Interval	–	1124	194.9	1	238.1	28

^A Natural sound source, also shown shaded in gray.

Table 11. Two hours of on-site listening at GRBA012, the Decathon site on August 12–13, 2015.

Sound Source Description	PA (%)	Max Event (s)	Mean Event (s)	Min Event (s)	SD (s)	Event Count
Jet	36.2	244	65.2	2	65.0	40
Propeller	1.1	81	41.0	1	56.6	2
Human, Unknown	1.0	51	36.0	21	21.2	2
Wind A	88.5	1540	276.9	1	385.7	23
Mammal A	13.7	387	98.6	2	117.3	10
Bird A	51.3	266	42.9	2	49.4	86
Insect A	44.8	193	24.5	1	34.3	132
Animal A	1.0	69	35.5	2	47.4	2
Natural, Other A	0.9	37	5.9	1	10.5	11
Natural, Unknown A	0.1	6	4.0	2	2.8	2
Total Non-natural	37.9	–	–	–	–	–
Noise-Free Interval	–	729	101.6	1	148.3	44

^A Natural sound source, also shown shaded in gray.

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Appendix E: Previous Acoustic Monitoring

In 2006 two acoustic units were placed in GRBA. Metrics are reported here to supplement the 2015 data described in this report. The data were put into a format in this appendix that is comparable to the 2015 data in this report. GRBA001 is in a similar location to GRBA011.

A different methodology was used to analyze the acoustic recordings from this 2006 data set. Trained technicians analyzed 8 days of data collected from the sound pressure level meter and MP3 recorder deployed at each site. From the SPL data, spectrograms were created with the accompanying recorded audio. Spectrograms are plots that display sound level as a function of time and frequency. The only anthropogenic noise sources that went into the calculation of L_nat were aircraft. Since aircraft have a recognizable sound signature, they are visually identifiable on spectrograms. Individual events can be isolated and analyzed. For every noise event the user can record beginning and end times. This dataset also included continuous audio that can be played for events with questionable sound signatures. This method uses a platform created for sound pressure level annotation referred to as SPLAT by NSNSD. SPLAT analysis is suitable for back country sites like GRBA001 and GRBA002.

Site Description

The locations of the acoustic recording equipment at the sites sampled in 2006 is given in Table 12 and Figures 21–23.

Table 12. Locations of acoustic recording equipment throughout the park. GRBA011 was near GRBA001.

Site	Site Name	Dates	Elevation	Latitude	Longitude
GRBA001	Ridge S. of Shingle Creek	2006	2,768 m	39.005126	−114.217827
GRBA002	Baker Ridge above burn pit	2006	2,109 m	39.003700	−114.346320

Figure 21. GRBA001, Ridge S. of Shingle Creek Acoustic Monitoring Station.

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Figure 22. GRBA002, Baker Ridge above burn pit Acoustic Monitoring Station

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Figure 23. Location of acoustic monitoring sites at Great Basin National Park where data was collected in 2006.

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Results from 2006 Data

The results of the 2006 acoustic monitoring program include day and night sound levels (Figures 24 and 25), percent time above sound levels (Table 13), exceedance levels for existing conditions (Table 14), and hourly comparisons of aircraft and overall noise audibility (Figures 26 and 27) at two sites in GRBA.

Figure 24. Day and night dB levels for 33 one-third octave bands at Ridge S. of Shingle Creek (GRBA001).

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Figure 25. Day and night dB levels for 33 one-third octave bands at Baker Ridge above burn pit (GRBA002).

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Table 13. Percent time above sound levels, represented in a truncated (T) frequency range and the full measured frequency range, for daytime and nighttime during the monitoring period in 2006.

Site	Frequency (Hz)	% Time Above Sound Level: 0700 to 1900 (DAY)				% Time Above Sound Level: 1900 to 0700 (NIGHT)
		35dBA	45dBA	52dBA	60dBA	35dBA	45dBA	52dBA	60dBA
GRBA001	20–1250 (T)	60.70	14.24	1.07	0.01	24.01	1.72	0.04	0.00
	12.5–20,000	64.10	21.05	4.08	0.19	27.28	3.18	0.36	0.00
GRBA002	20–1250 (T)	16.03	0.85	0.08	0.00	16.10	0.86	0.01	0.00
	12.5–20,000	17.36	1.42	0.15	0.01	16.96	1.45	0.06	0.00

Table 14. Exceedance levels for existing conditions in GRBA, in a truncated (T) frequency range and the full measured frequency range, for daytime and nighttime during the monitoring period in 2006.

Site	Frequency (Hz)	Exceedance levels (dBA): 0700 to 1900 (DAY)				Exceedance levels (dBA): 1900 to 0700 (NIGHT)
		L90	L50	Lnat	L10	L90	L50	Lnat	L10
GBRA001	20–1250 (T)	28.9	36.9	33.9	44.6	28.5	31.3	30.5	28.5
	12.5–20,000	29.7	37.6	34.5	46.1	29.1	31.9	31.1	37.3
GRBA002	20–1250 (T)	21.3	24.9	27.3	35.5	25.1	27.5	26.8	30.3
	12.5–20,000	2.9	28	25.7	36.1	26.1	28.2	27.6	30.7

Figure 26. Comparison of hourly aircraft audibility and overall noise audibility at GRBA001.

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Figure 27. Comparison of hourly aircraft audibility and overall noise audibility at GRBA002.

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Author Information

Ashley R. Pipkin

Erik W. Meyer https://orcid.org/0000-0003-2128-3532

National Park Service
Natural Sounds and Night Skies Division
1201 Oakridge Dr., Ste. 200
Fort Collins, CO 80525

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