[The following is from the NIRS website, October 17, 2001.]
The Noise Integrated Routing System (NIRS) is a noise-assessment program designed to provide an analysis of air traffic changes over broad areas. It is intended to work in conjunction with other Air Traffic modeling systems which provide the source of routes, events, and Air Traffic procedures such as altitude restrictions.
The outputs of NIRS include population-impact and change-of-exposure reports and graphics. Population centroids are evaluated as improved or worsened based on their change of exposure. A hierarchy of rules based on FAA guidance and local requirements are then employed to determine if an airspace alternative is likely to be controversial based on noise considerations. Where possible, the system identifies the principal source of the change of exposure. Having identified the route set responsible for an increase, the air traffic planner can begin the evaluation of possible mitigation alternatives.
NIRS applications are organized as projects. A NIRS project contains all of the input files, output files, reports, and graphics necessary to complete the noise analysis.
Prior to the Expanded East Coast Plan (EECP), air traffic proposed actions above 3K ft AGL were considered non-controversial by nature and were categorically excluded (CATEX'd) from further environmental review under the National Environmental Policy Act (NEPA). When the EECP was CATEX'd, populations in the study area strongly reacted. Thus, the action became highly controversial, and Congress mandated that an Environmental Impact Statement (EIS) be completed by the Federal Aviation Administration (FAA). At that time, there was no precedent for analyzing noise effects from aircraft above 3K ft AGL. The FAA chose to model predicted change in noise exposure up to 18K ft AGL to insure that communities with predicted 45 db (decibel) DNL (Day-Night Level) noise footprints were included in the study area. The Enhanced Integrated Noise Model (EINM), a one- time development effort, was used to model and analyze noise affects up to the cut-off altitude (18K ft AGL).
Following the guideline established by the EECP, it was apparant that the development of a wide-area noise model was necessary. The next major airspace study, the Chicago Terminal Airspace Project (CTAP) modeled potential noise effects up to 18K ft AGL. For CTAP, the noise effects were modeled using the prototype Noise Integrated Routing System (NIRS). Released in 1998, NIRS was subsequently approved for quantifying predicted change in noise exposure for the CTAP EIS. NIRS is currently in use on the Potomac Consolidated TRACON (PCT) project and projected as the noise modeling tool of choice for the New York area airspace redesign as well as upcoming airspace projects under the National Airspace Redesign.
Under the direction of Mr. William J. Marx, Manager, FAA Office of Air Traffic Airspace Management (ATA), Air Traffic Environmental Programs Division (ATA-300), and Mr. Jake Plante, Manager, FAA Office of Environment and Energy (AEE), Analysis and Evaluation Branch (AEE-120), the FAA has developed the Noise Integrated Routing System (NIRS) in response to this need.
For more information see the NIRS website.