Sound is Down in 2020Posted on October 28, 2020
The Metropolitan Airports Commission (MAC) owns and operates a permanent system of 39 sound measurement sites around Minneapolis-Saint Paul International Airport (MSP). Aircraft and community sounds are collected, with a goal to capture as much aircraft sound as possible from airplanes flying to and from MSP. The levels from these measurement sites show the Minneapolis-St. Paul area had a quiet spring and summer.
The chart below shows a weekly system-average sound level in a metric called the Equivalent Level (LAeq ). The LAeq is the continuous sound level equivalent of the average sound energy for a period of time. The LAeq takes into account all sounds regardless of the source, including sounds from aircraft, environment (i.e. wind, thunder, wildlife), and community (i.e. road traffic, sirens, construction activity, trains).
In May, we provided information on the sound data collected and evaluated by MAC staff and discussed how changes in aircraft and community activity resulted in about a 4 decibel (dB) reduction in LAeq in April 2020 compared to a 4-year average (article available here). Higher LAeq values during week 16 and week 27 are due to severe weather week tornado siren drills and Fourth of July fireworks (also evident in the 4-year average), respectively.
The chart above compares 2020 sound data through September to a 4-year average (2016 through 2019). The comparison reveals that during the first months of 2020, LAeq levels were similar to average levels. From weeks 13 through 40 (April through September) there was a reduction of about 3 dB. While 3 dB may not sound like much, an increase or decrease of 3 dB represents a doubling or halving of sound energy due to the logarithmic nature of the dB scale.
This decrease in sound energy is most likely attributed to a decrease in aircraft activity and community sources such as vehicle traffic and other community activity near sound measurement sites. These quieter conditions are not typical and are expected to return to previous levels as aircraft and community activity returns to normal.
More information about sound monitoring is available at: https://macnoise.com/faq/what-sound-monitoring.