While the Australian Noise Exposure Forecast (ANEF) system helps guide land use planning decisions near airports, it is based on highly complex calculations and is not as useful to describe noise as it is heard. Aircraft noise will also be audible outside ANEF contours from time to time.
In Australia, other maps are used to help local residents understand the "whole of airport" aircraft noise environment. These maps show the distribution of noise around Darwin as it will be heard - i.e. a noise event corresponds to a single over flight - and generally show that noise is concentrated near the airport and below key flight paths.
An Australian Army Black Hawk helicopter from 6th Aviation Regiment conducts a training activity
"Number Above" maps represent the number of times per day aircraft noise reaches a nominated decibel level. For example, Number Above 70 maps show the number of events that exceed 70 decibels during an average day.
Like the ANEF, Number Above maps are based on predictions of average flight activity and weather conditions. The specific flight paths in use and the aircraft type will result in noise being heard outside of the contours, or being different day to day.
The following Number Above maps are available for download:
A Royal Australian Air Force F/A-18A Hornet lands at RAAF Base Tindal
Land outside ANEF contours and Number Above contours will still receive aircraft noise from time to time. Maps showing maximum noise levels can be useful to show aircraft noise that can be heard at some distance from an airport, even if only occasionally.