When did the system officially become operational?
The Department of Aviation officially began storing data in January 1997.

How many noise monitors are there?
There are currently 12 monitors installed in the communities surrounding Midway. Ten portable monitors that can be taken to a specific location on a temporary basis are also available.

What is measured by the system?
All noise sources including aircraft, automobiles, railroad and ambient noise are measured by the noise monitors. Each noise monitor continuously records all noise sources 24 hours a day, 365 days a year.

In addition, the Chicago Department of Aviation and the Federal Aviation Administration (FAA) have entered into an agreement that allows the Department of Aviation Environment Office access to data from the FAA's air traffic control computer (after a five day waiting period for security purposes). This information is used to distinguish aircraft noise events from other noise sources at each monitoring location.

How is the information gathered by the noise monitors used?
Data from the system is useful in many aspects of the airports' noise control efforts, including:

1. Measure actual noise levels, not just computer projections.
2. Identify noise affected areas.
3. Track changes in noise levels over time that may occur around each airport.
4. Identify the source of a particular loud noise event.
5. Monitor compliance with the noise abatement procedures at each airport.
6. Continued evaluation and development of existing and/or additional noise mitigation programs.