Who is this article for?

Noise analysts who want to understand how ANOMS detects and classifies noise events.

Access to the ANOMS Noise Analyst Workbench is required.

ANOMS identifies aircraft noise events at Remote Monitoring Terminals (RMTs) using a detection technique called the Floating Threshold, which is more reliable than a fixed detection threshold.

Understanding noise event identification

Noise event identification matches a noise event detected at an RMT to either a flight track or a community source (such as locomotives or heavy traffic).

ANOMS contains sophisticated algorithms for distinguishing the unique characteristics of aircraft noise from other types of noise events. These algorithms have been field tested and proven at many airports over several years, delivering high classification accuracy even at noise monitoring terminals several miles from the airport.

Classification accuracy is essential because the summary values that ANOMS calculates and reports for hourly and daily aircraft and community noise rely directly on each noise event being classified correctly.

Understanding how the Floating Threshold works

The Floating Threshold technique has been evaluated independently and found to significantly improve the identification accuracy of aircraft noise events. It continuously compares the latest 1-second noise value to a running average of existing and recent background noise.

To detect a noise event:

1. When noise levels start to increase over the captured background noise, an event record is triggered.
2. Event characteristic processing functions then decide whether the triggered event should be retained as aircraft noise.
3. These functions filter out potential false triggers such as dog barks or heavy traffic.

Managing wind-induced noise

The Floating Threshold is particularly advantageous when dealing with wind-induced noise. When wind speeds exceed 25 knots, the background noise level rises above a typical fixed threshold setting (for example, 65 dB). On a monitoring terminal that relies on a fixed threshold, this would trigger one very long noise event, and any aircraft noise events occurring during that time would either not be recorded or be obliterated.

Because the Floating Threshold tracks the background level, aircraft events can still be detected above the elevated background.

Viewing noise event records

Noise records for each event are stored in the database and can be viewed in a number of ways, including the Noise Events Browser. See the article Using the Noise Events Browser.