Evaluation of nighttime helicopter noise in an urban neighborhood

Sound level measurements were gathered at two locations within an urban neighborhood close to a helipad. A sound level meter was placed at each location for approximately one week, where data were collected continuously from 10:00 PM to 6:00 AM in fifteen-minute intervals. L90 was measured to establish existing background levels and LAFmax was measured to capture the helicopter noise. Additionally, a sound level trigger was set up to capture details and audio recordings of elevated levels associated with helicopter flights. Due to the lengthy data collection period, care was taken to collect as much data as needed without exceeding the storage capacity of the meter. Based on preliminary data, the trigger was set to capture only events with a minimum sound pressure level and a minimum time duration, ensuring shorter noise events not of interest (barking dogs, passing cars, etc.) were not captured. Audio files for each sound event were used to identify helicopter events, which were confirmed by comparing timestamps with the helicopter flight logs. This case study describes the details of unattended long-term data collection for this application and evaluation of the helicopter noise measurements.