A $ 1.9 million study of aircraft noise at two naval bases is unlikely to please critics.
Last week the Navy presented its report to Congress on real-time noise monitoring of aircraft at Naval Air Stations Whidbey Island and Lemoore. The report states that the Navy has determined that noise models “work as intended, providing accurate predictions of noise exposure from flight operations for use in impact assessments and long-term land-use planning.”
In fact, the study finds that noise modeling overstates actual sound levels.
However, noise abatement proponents are skeptical of the study as it is not independent and other shortcomings are noted.
“The Navy concludes that their real-time monitoring validates their modeling. Maybe, ”said Bob Wilbur, president of the anti-noise group Citizens of Ebey’s Reserve, in an email. “But they have to be much more accommodating.”
The Navy Environmental Impact Statement, which was drawn up prior to the addition of 36 additional EA-18G Growler aircraft at NAS Whidbey and a quadrupling of the growler practice at Outlying Field Coupeville, relied on computer modeling of aircraft noise rather than real-world noise monitoring.
Professionals and amateurs who measured growler noise near OLF Coupeville, including the Home Office, claimed the modeling significantly undervalued noise levels.
The Navy refused to conduct surveillance until U.S. Rep. Rick Larsen, a senior member of the House Armed Services Committee, included noise surveillance at two bases in the National Defense Authorization Act for Fiscal Year 2020.
“I am pleased that the real-time noise monitoring review is complete, but I have asked the Navy to release the underlying technical data and I expect to receive the data from the Navy soon,” said Larsen on Wednesday. “Without complete data, I cannot draw any conclusions about the evaluation.”
The report does not answer a central question from the community: How loud is it in the houses around the small Coupeville airfield?
Most of the report looks at “average day-night sound levels,” a metric state that has been questioned by local officials. It averages the sound over time and is used in studies on civil airlines where the noise is lower but more continuous. Critics said it wasn’t a fair review of Whidbey, where noise is far more sporadic; The result is that peaks of sound are weakened over time.
The report includes “Sound Exposure Levels” for individual events in two locations in North Whidbey, but not near OLF Coupeville for an unclear reason. The report shows that the computer models predict single event sounds at levels higher than actual measurements of single events.
The report states that additional comparisons of sound exposure levels will be provided in a technical follow-up report.
The report shows that “outliers” measured during the study “show the large variability observed in individual events due to various environmental and operational factors”.
For the study, the Navy collected real-time aircraft noise levels and operational data over four discrete seven-day monitoring periods in 2020 and 2021. The sites were both near Ault Field Base and the OLF Coupeville.
The data collected included acoustic recordings at locations around each airfield to capture sound levels during a range of flight operations over a range of seasonal weather conditions, the document says.
The study collected operational data, including logs from air traffic controllers and surveillance teams, to document flight activities planned and observed during each surveillance period, the report said.
“Although the results of this study show that DoD-approved aircraft noise models are performing as intended, the Navy will continue to refine operational data collection procedures to improve the accuracy and reliability of the models,” the report concludes.