Computer Modeling of Noise Exposure

The Federal Aviation Administration has approved two quantitative models for predicting noise exposure around airports: The Integrated Noise Model (INM) and the Heliport Noise Model (HNM). These models are the responsibility of the FAA's Office of Environment and Energy (AEE-100).

Integrated Noise Model (INM)

The Integrated Noise Model (INM) evaluates aircraft noise impacts in the vicinity of airports. INM has many analytical uses, such as assessing changes in noise impact resulting from new or extended runways or runway configurations, assessing new traffic demand and fleet mix, evaluating revised routing and airspace structures, and assessing alternative flight profiles or modifications to other operational procedures.

INM outputs include noise contours used in land use compatibility studies, noise impacts by aircraft on individual flight tracks, and user-defined point analysis of noise impacts.

The INM has been the FAA's standard tool since 1978 for determining the predicted noise impact in the vicinity of airports. Statutory requirements for INM use are defined in:

The model utilizes flight track information, aircraft fleet mix, standard and user-defined aircraft profiles, and terrain as inputs. It can also process U.S. census population data and flight schedules from the Official Airline Guide (OAG).

The model supports 16 predefined noise metrics that include cumulative sound exposure, maximum sound level, and time-above metrics from both the A-weighted, C-weighted, and the effective perceived noise level families. The user may also create user-defined metrics from these families, a popular example being the ability to create the Australian version of the Noise Exposure Forecast (NEF).

INM produces noise exposure contours that are used for land use compatibility maps. The INM program includes built-in tools for comparing contours and utilities that facilitate easy export to commercial Geographic Information Systems. The model also calculates predicted noise at specific sites such as hospitals, schools, or other sensitive locations. For these grid points the model reports detailed information for the analyst to determine which events contribute most significantly to the noise at that location. Graphic displays include navigational aids from the National Flight Data Center (NFDC) data base, terrain contours, census population and street map data, and airport layouts.

The INM aircraft profile and noise calculation algorithms are based on several guidance documents published by the Society of Automotive Engineers (SAE). These include the SAE-AIR-1845 report titled "Procedure for the Calculation of Airplane Noise in the Vicinity of Airports" as well others that address atmospheric absorption and noise attenuation.

INM is an average-value model and is designed to estimate long-term average effects using average annual input conditions. Because of this, differences between predicted and measured values can occur because certain local acoustical variables are not averaged, or because they may not be explicitly modeled in INM. Examples of detailed local acoustical variables include temperature profiles, wind gradients, humidity effects, ground absorption, individual aircraft directivity patterns and sound diffraction around terrain, buildings, barriers, etc. Differences may also occur due to errors or improper procedures employed during the collection of the measured data.

For more information see the FAA's Technology Division Web site and the following documents:

Integrated Noise Model, Version 3 User's Guide -- Revision 1, June 1992. DOT/FAA/EE/92-02.

Integrated Noise Model, Version 4.11 User's Guide Supplement, December 1993. DOT/FAA/EE/93-03, DOT-VNTSC/FAA/93- 19.

Integrated Noise Model, Version 5.01. 1995. U.S. Dept. Transportation, Federal Aviation Admin.

Update of Aircraft Profile Data for the Integrated Noise Model Computer Program, 3 volumes, March 1992. FAA/EE/91-02, DOT-VNTSC/FAA/91-4.

Heliport Noise Model (HNM)

For more information see the FAA's Technology Division Web site and the following documents:

HNM Heliport Noise Model Version 2.2 User's Guide. John A. Volpe National Transportation Systems Center, Cambridge, MA (1994), 92 pages. DOT/VNTSC-FAA-94-3, DOT/FAA/EE-94/01 (NTIS PB94-151883/XAB).