Ebey’s Landing National Historical Reserve Acoustic Monitoring Report Frequently Asked Questions

1.Why does the National Park Service care about sound?

We care about sound because acoustic resources and the acoustic environment are unique and essential national park resources. Whether it’s the rustling of wildlife in the bush or birds singing at dawn, sounds are important to the visitor experience. We call this a park’s soundscape and every park has its own unique soundscape.

We also care about sounds because we have a responsibility to protect animals in national parks and animals need to be able to hear in order to find food, avoid being someone else’s food, establish territory and find mates. Too much noise can disrupt these critical behaviors.

The National Park Service monitors park soundscapes so we can better understand which noises interfere with visitor enjoyment and wildlife and identify ways we can reduce those noises. This supports the agency’s mission to preserve unimpaired the natural and cultural resources and values of the National Park System so our visitors can enjoy them for generations to come.

2. What are the measurements used based on?

NPS takes great care to ensure that our methods for monitoring and analyzing sounds follow the scientific method. The data used in this and other NPS acoustic reports follow established and peer reviewed protocols. These protocols specify things like the type of equipment we use, where we place the equipment, how long we monitor for and even how the data is analyzed and reported.

The National Park Service has collected sound data at 111 park units for a baseline inventory of a variety of sounds that occur in parks, from wildlife to vehicle traffic. We have published sound (acoustic) monitoring reports for many of these units.

3. Why was acoustic monitoring done at Ebey’s Landing National Historical Reserve?

NPS conducted acoustic monitoring at Ebey’s Landing because we are concerned about the impacts that the noise from the U.S. Navy’s EA-18G Growler jets is having on the reserve’s historic rural soundscape.

4. How will the information in this report be used?

The information in this report will be used to establish an acoustic baseline or reference point against which past and future sound levels at the Reserve as well as sounds from specific sources such as airplanes can be measured. The Navy agreed that additional information will be beneficial to their draft Environmental Impact Statement process. Therefore, the information we learn from the acoustic monitoring will allow NPS to make scientifically informed comments on the Navy’s pending draft Environmental Impact Statement, which proposes to increase the number of Growler jets stationed at Naval Air Station Whidbey Island. We will also consult with the Navy on potential effects to historic resources as required by the National Historic Preservation Act. Last, the information in this report will be used to help educate and increase understanding and to inform discussions between the NPS and the Navy to help identify measures that would help address the noise challenges there.

5. Does this report address impacts to human health?

No. It does not evaluate the potential human health impacts. This study gathered baseline data on the acoustic environment, including noise from Growler flights over the reserve. Metrics based on human auditory function were used only as they relate to visitor experience or where they are a reasonable proxy for wildlife response.

6. Where was sound recorded and how were those sites selected?

Ebey’s Landing National Historical Reserve, a unit of the National Park System, shares Whidbey Island with the Naval Air Station Whidbey Island. The reserve is jointly managed by the National Park Service in partnership with Island County, the Town of Coupeville and Washington State Parks. About 85 percent of reserve land is privately owned and includes residential and commercial property.

Outlying Landing Field Coupeville is owned by the Navy and is used to practice field carrier landings. It has been used for this purpose by jet aircraft since 1967. The outlying field is partially within the boundary of the reserve.

Two acoustic sites on National Park Service property were selected. The site selection was based on land use and proximity to military aircraft training activities. The Reuble farmstead (EBLA001) is the base of operations for the reserve. The Ferry House site (EBLA002) was placed further west of Reuble Farmstead closer to Ebey’s Landing, Ebey’s Prairie and the iconic Ferry House. This popular area is a focal point for visitors and a fundamental resource for the reserve.

7. How long and when were data collected?

The systems were deployed from June 19, 2015 to July 20, 2015 and 31 days of data were analyzed. This data included continuous audio recordings and sound pressure level readings with systems that meet the American National Standards Institute type-one standard.

8. Who did the data collection?

The Natural Sounds and Night Skies Division of the National Park Service’s Natural Resource Stewardship and Science Directorate facilitated this data collection. A trained National Park Service technician deployed and retrieved two acoustic monitoring units at the reserve.

9. How were the acoustic data collected and who handles the information?

The data is sent back to the Natural Sounds and Night Skies Division. Trained students at the Colorado State University Listening Lab processed the audio recordings. A soundscape specialist completed the analysis and report. Refer to the methods section on page six of the report for further information.

10. What sound metrics were reported?

Several metrics were used to characterize the duration of and overall sound levels (loudness)
  • The amount of time sound levels were above certain values that relate to human auditory function such as speech and sleep interference, including increases in blood pressure and heart rates in sleeping humans; the recommended maximum noise level inside bedrooms; speech interference for interpretive programs; and speech interruption for normal conversation.
  • The exceedance levels for existing conditions (Lx), where Lx refers to sound levels that are exceeded x% of the time. For example, L50 represents the median sound level. L90 represents the sound level that is exceeded 90% of the time. The average sound level for the monitoring period is the LAeq.
  • The day-night average sound level, which is the average sound level over a 24-hour period, with a 10-dB penalty added for sound levels between 10 p.m. and 7 a.m.
  • The maximum sound pressure level or loudest sound level.

11. What are the relevant acoustical findings from the report?

The detailed findings are listed in the results section of the report. Some of the results are summarized here.

Table 1 in the report and below represents the number of aircraft events for each site and the total time that the military aircraft were audible during the 31-day study period.

Table 1.

Sites Locations Commercial Aircraft Events Military Aircraft Events Total time audible for military aircraft (hh:mm:ss)
EBLA001 Reuble Farmstead 571 417 10:25:23
EBLA002 Ferry House 407 1436 28:55:53
The loudest events were recorded at EBLA001 and are a result of this site’s proximity to the outlying landing field and the field carrier landing practice that occurred during the monitoring period. For example, the quietest 10% of sounds, or the L90 was 32.9 dBA (day) and 30.5 dBA (night) at EBLA001. The highest recorded sound pressure level was 113 dBA during field carrier landing practice of Growlers. The loudest and most frequent aircraft events occurred between 2:00 and 4:00 p.m. and 10:00 p.m. and 12:00 a.m. The quietest and fewest aircraft events occurred between 2:00 and 4:00 a.m. (Figure 10 in the report).

At EBLA002, the maximum sound pressure levels were lower than EBLA001 but there were more military aircraft events. The L90 was 35.5 dBA (day) and 35.7 dBA (night) and 85 dBA was the loudest recorded military aircraft. The most overflight activity was between 9:00 a.m. and midnight. Military overflight activity at EBLA002 was lowest between 1:00 and 8:00 a.m. (Figure 11 in the report).

Spectrograms are plots that display sound level as a function of time and frequency. Since aircraft have a recognizable sound signature, they are visually identifiable on spectrograms. Figure 7, taken from the report, shows the number of military overflight events that occurred over a two hour period of heavy use between 10:00 p.m. and 12 midnight on July 6, 2015. A military jet is identified by the sharp white bars seen across the plot. This spectrogram shows 59 events from military aircraft during the two-hour period. Also visible on this spectrogram is a 15 minute break in jet overflight activity between 10:35 and 10:50 p.m.
Spectogram Image

12. What are the limitations of the data?

The report and our analysis are based on a 31-day monitoring period of data collected at two sites during a single summer season.

13. How does this empirical data compare with the Navy’s studies?

The noise averaging and other noise metrics presented in the report were calculated based on actual recorded sound pressure levels (that included Growler training at OLF Coupeville) recorded during 31 days. The purpose of the study was to establish an acoustic baseline. We did not evaluate the Navy’s studies as part of this study. The Navy has completed several noise studies evaluating acoustic impacts to the reserve using modeled data.

14. Why didn’t the National Park Service use a data model that could be easily compared to the Navy’s data?

The NPS study was done using standard NPS acoustic data collection protocols and measured actual sound levels at two locations. The purpose of the study was to collect existing sound data.

15. Where can I find the acoustic monitoring report?

NPS publishes natural resource technical reports on the Integrated Resource Management Applications portal (irma.nps.gov) so the public will be able to access and view this report here.

Last updated: November 14, 2016

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