What is the difference between modeled versus measured noise?
Generally speaking, modeled noise is calculated using computer software, and measured noise is recorded using a sound level meter.
Modeled aircraft noise is the result of a computerized process that uses a federally-prescribed software program to calculate noise exposure. The current software used for modeling aircraft noise is called the Aviation Environmental Design Tool (AEDT). AEDT uses inputs, such as aircraft type, time of operation, weather, terrain, weight of aircraft, runway use and many more details that contribute to noise output overall. AEDT is able to calculate noise exposure using many different metrics, but the most common metric is the Day-night level (DNL) which applies a 10-decibel penalty for aircraft operations that occur during the nighttime hours of 10 p.m.-7 a.m. to account for the increased sensitivity to noise during "sleeping" hours.
The modeling process is beneficial for calculating aircraft noise exposure because the process is flexible and may be used to calculate aircraft noise exposure for various aircraft operating scenarios, such as current runway use versus future runway use, etc. Additionally, the MAC is obligated to use AEDT modeling results to assess aircraft noise exposure related to actual MSP activity each year. The assessment is used to determine eligibility for its Residential Noise Mitigation Program. Results of the annual calculations are found in the Annual MSP Noise Contour Analysis Report.
Aircraft noise measurements are recorded using noise monitoring equipment placed within areas where aircraft overfly, typically near airports. The MAC installed permanent noise monitoring equipment in 39 locations, called Remote Monitoring Towers (RMTs), surrounding Minneapolis-St. Paul International Airport (MSP). Additionally, the MAC uses portable noise monitoring equipment for special studies.
Each permanent RMT operates continuously and records aircraft and community sounds that occur within a defined listening radius, which typically ranges from 1-2 miles. An aircraft does not have to fly directly over an RMT to be recorded. Each month, the MAC uses customized processing, called MACNOMS, to match aircraft sound events recorded at RMTs with MSP aircraft arrivals and departures. These data are published here: Interactive Reports
Measured aircraft noise events are not used to determine eligibility for the MAC's Residential Noise Mitigation Program.
For more information about mobile noise monitoring studies, click here: Mobile Noise Monitoring