• Sound level decreases by 6 dB per doubling of distance • Additional losses due to atmospheric absorption Ground Effect: • Sound levels are lower when reflected off of soft ground vs. hard ground Sound Propagation Refraction due to Temperature: • Gradients in temperature cause the bending of sound paths • Sound bends upward during a temperature lapse (cool air over warm) • Sound bends downward during a temperature inversion (warm air over cool) Sound Propagation Refraction due to Wind: • Gradients in wind speed cause the bending of sound paths • Sound bends upward causing sound shadows in the upwind direction • Sound bends downward increasing sound levels in the downwind direction • Differences between upwind and downwind directions can be 20 dB Scope of Services ✓Ground Noise Data Research • Meet with StART • Identify ground noise sources and locations • Identify atmospheric conditions that may increase ground noise • Noise Monitoring (in progress – data acquisition complete) • Obtain and analyze data from permanent monitors • Collect and analyze additional temporary noise monitoring data • Identify Mitigation Options • Present findings on ground noise sources and levels and solicit input on mitigation measures • May include changes in aircraft operating procedures or utilization of new or existing structures to reduce community noise exposure • Report Project Results Noise Measurement Locations • Site 1: Northeast • Taxiing/queueing • Start-of-takeoff roll • Engine run-ups • Site 2: East • Terminal din • Auxiliary Power Units (APU) and taxi •…Open full document
Notes
A progress update presentation on a ground noise study conducted at Seattle-Tacoma International Airport (SEA) in October 2021. The document covers acoustic terminology including sound measurement metrics, sound propagation principles, scope of work, noise monitoring procedures, and next steps for the ongoing study.