Growler noise study supports computer modeling

A $1.9 million study of aircraft noise at two Navy bases is unlikely to satisfy critics.

Last week, the Navy submitted its report to Congress on real-time sound monitoring of aircraft at Naval Air Stations Whidbey Island and Lemoore. The report states that the Navy determined that noise models “operate as intended and provide an accurate prediction of noise exposure levels from aircraft operations for use in impact assessments and long-term land use planning.”

In fact, the study finds that the noise modeling overstates the actual levels of sound.

Anti-noise advocates, however, are skeptical of the study for its lack of independence as well as other perceived shortcomings.

“The Navy concludes that its real-time monitoring validates their modeling. Perhaps,” Bob Wilbur, president of anti-noise group Citizens of Ebey’s Reserve, said in an email. “But they will need to be far more forthcoming.”

The Navy’s Environmental Impact Statement that was completed prior to the addition of 36 additional EA-18G Growler aircraft at NAS Whidbey and a fourfold increase of Growler practice at Outlying Field Coupeville relied on computer modeling of aircraft noise instead of real-world noise monitoring.

Professionals and amateurs who have measured Growler noise near OLF Coupeville, including the Department of the Interior, claimed that the modeling significantly underreported noise levels.

The Navy resisted conducting the monitoring until U.S. Rep. Rick Larsen, a senior member of the House Armed Services Committee, added the noise monitoring at two bases in the Fiscal Year 2020 National Defense Authorization Act.

“I am glad to see the real-time noise monitoring review is complete, but I have asked the Navy to release the technical underlying data and expect to receive the data from the Navy soon,” Larsen said Wednesday. “I cannot make any conclusions on the review without complete data.”

The report doesn’t answer a central question the community has been asking: Just how loud does it get at homes surrounding the small Coupeville airfield?

Most of the report discusses “day-night average sound level,” a metric state and local officials have questioned. It averages sound over time and is used in studies at civilian airlines where the noise is lower but more continuous. Critics said it’s not a fair assessment on Whidbey, where noise is much more sporadic; the result is that spikes in sound are diluted over time.

The report does includes “sound exposure levels” for individual events at two locations on North Whidbey, but not around OLF Coupeville for an unclear reason. The report shows that the computer models predicted single-event noise at higher levels than the actual measurements of single events.

The report states that additional sound exposure level comparisons will be provided in a follow-up technical report.

The report shows “outliers” measured during the study “demonstrate the large variability observed in individual events due to various environmental and operational factors.”

For the study, the Navy collected real-time aircraft sound level and operational data during four discrete seven-day monitoring periods in 2020 and 2021. The sites were both around the Ault Field Base and OLF Coupeville.

The data collected included acoustic recordings at sites around each airfield to capture sound levels during a range of flight operations across a range of seasonal weather conditions, the document states.

The study collected operations data, including logs of air traffic controllers and the monitoring teams, to document the flight activity scheduled and observed during each monitoring period, the report states.

“Although the results of this study indicate that DoD-approved aircraft noise models work as intended, the Navy will continue to refine operational data collection procedures to enhance model accuracy and reliability,” the report concludes.