Purchase and Licensing

How much does AAM cost and where can I purchase it? 

The Advanced Acoustic Model (AAM) software is available without charge. AAM can be requested via the Volpe Center’s website at https://www.volpe.dot.gov/AAM.

Is there a trial version of AAM? 

No, there are no trial versions of AAM.

With a site license, can I install AAM on multiple machines in my office?

An AAM site license includes a single seat license, which allows installation of the full AAM application on multiple computers within a single office. An office is defined as a single organizational unit or entity, having a unique function, comprising one or more contiguous rooms in a single location. Installation on additional computers within the office, portable computers while on official travel, or home computers for use on behalf of the office is permitted. 

View the AAM License Agreement. 

General Questions

What is AAM?

The Advanced Acoustic Model (AAM) is a suite of computer programs that predicts far-field noise from fixed-wing aircraft, rotary-wing aircraft, or moving and stationary ground-based operations. It is a simulation model that computes time varying noise levels for each step in a user-defined flight trajectory or vehicle path, or over a distributed quadrilateral area. When computing noise from multiple operations, the results can be combined to create integrated metric contours suitable for use in National Environmental Policy Act (NEPA) analyses.

AAM also includes 1/12 Octave Band source modeling and “pearls on strings” (mixed fidelity simulation mode) features for single event analysis to facilitate eVTOL time varying loudness (TVL) calculations and assessment using varying background sound levels. These advanced features are available in single event analysis modes. 

Who developed AAM?

AAM has its roots in the Rotorcraft Noise Model (RNM), originally sponsored by NASA and further developed under funding from NASA, the U.S. Department of Defense, the Oregon Department of Transportation, and Uber Elevate. The U.S. Department of Transportation’s Volpe National Transportation Systems Center is currently the custodian responsible for technical oversight and distribution of the code. Read more about the history of AAM.

What is the Quarry Noise Model?

The Quarry Noise Model (QNM), developed for the Oregon Department of Transportation, leverages the AAM propagation physics for computing noise from areas surrounding aggregate source sites (rock quarries). QNM has three inter-communicating components: QNM Graphical Information System (GIS) Module, QNM Noise Database, and the AAM Acoustic Engine (AAM executable). The GIS Module represents the graphical user interface for QNM and harnesses both custom and existing tools within ESRI’s ArcGIS to streamline the analysis of quarry noise scenarios. Two types of parameters are included in the noise database: classification parameters, which are used to identify the source, and emission parameters, which characterize the emitted noise. The Acoustic Engine leverages AAM, which has been updated to include the ability to model operations from equipment distributed over a quadrilateral area, calculation of attenuation due to surrounding foliage, and a simplified blast model for prediction of initial blast overpressure. For more information on the Quarry Noise Model, visit https://rosap.ntl.bts.gov/view/dot/40274.

What atmospheric propagation capabilities does AAM have?

Noise propagation from source (vehicle) to receivers accounts for geometric spreading, air absorption, and finite ground impedance. For high-thrust military aircraft, non-linear propagation effects associated with high noise levels may be computed. AAM can optionally account for varying ground terrain or atmospheric gradient effects. AAM includes a curved ray module that can be used to compute the effects of propagation through wind and temperature gradients over uniform terrain. Propagation effects due to foliage are also included in AAM.

How does AAM model noise sources?

AAM uses three-dimensional noise spheres defined for a vehicle moving along a trajectory. A collection of noise spheres may be used to describe the different noise emissions characteristics of the vehicle under different operating conditions. The AAM acoustic source characteristic database lookup procedure allows users to model numerous flight vehicles—such as conventional fixed-wing aircraft, thrust-vectored fixed-wing aircraft, rotorcraft, and tilt-rotor vehicles—as well as ground-based vehicles. Three-dimensional source modeling may include the effect of thrust vectoring, implicit for rotorcraft and present on certain fixed-wing aircraft. 

Noise spheres for several aircraft are supplied with the AAM software distribution, and include the Bell 412 and Bo105 helicopters. Additional noise spheres for other sources may be input by the modeler. Noise spheres may be derived from flight tests, wind tunnel measurements, or theoretical predictions. Additionally, ground-based noise source data for more than 300 vehicles and pieces of construction equipment is included with the Quarry Noise Model.

How are trajectories modeled in AAM?

The user prescribes a trajectory input, including the position, motion of the vehicle, orientation, and operating state. AAM is an acoustic simulation tool and moves the vehicle along this prescribed trajectory in the manner defined, and propagates the sound to receivers, where it may be aggregated. AAM does not include a vehicle performance or kinematics model.

How are terrain elevation and ground cover properties input into AAM?

Terrain elevation data are input into AAM on a binary grid. Surface properties, in the form of flow resistivity, are also input using a grid file. Foliage height data may be defined on a similarly structured binary grid file. The user can create these files using the Quarry Noise Model (QNM) within ArcGIS. The files can also be created using user-provided external means. AAM is distributed with utility codes to translate the elevation, impedance, and foliage binary grids into ASCII versions and vice versa. ArcGIS is commercially available Graphical Information System software from ESRI.

What types of output does AAM provide? 

For multiple operation analyses, AAM can provide the following information:

• Noise metric values at points of interest
• Noise values and contours over a grid area
• Ranked noise contributors at points of interest

For single-event or research analyses, AAM can provide the following information:

• Spectral time history information at receiver points
• Noise footprint on a mesh of receivers at a given time for single event metrics
• Integrated noise metrics at a point or a footprint on a mesh of receivers
• Spectral propagation time history details including contributions from physical mechanisms such as absorption, ground and terrain effects, and foliage attenuation

Processing tools provided with AAM also allow for creation of:

• Noise spheres from empirical measurement data in 1/3 or 1/12 octave band data formats
• Acoustic animation videos from single-event simulations in a variety of metrics

What metrics does AAM compute?

The basic computational module calculates single-event and cumulative noise metrics such as maximum A-weighted sound level (Lmax), Sound Exposure Level (SEL) (overall, C , A weighted), Perceived Noise Level (PNL), Tone-Corrected Perceived Noise Level (PNLT), Effective Perceived Noise Level (EPNL), Day-Night Average Sound Level (DNL), Community Noise Equivalent Level (CNEL), Noise Exposure Forecast (NEF), Weighted Equivalent Continuous Perceived Noise Level (WECPNL), and d-Prime audibility. Supplemental computing tools are provided with AAM to compute Time Varying Loudness (TVL) in the presence of ambient noise at points of interest as well as for a grid of receptors. It is also possible to output a detailed spectral time history (commensurate with the sphere fidelity) from which other metrics can be post-processed using user-provided tools.

What features in AAM are used to model sound from eVTOL or Advanced Air Mobility vehicles?

Features were added to AAM to facilitate research related to eVTOL and Advanced Air Mobility aircraft community acoustic acceptance. The Pearls on Strings trajectory feature in AAM allows for mixed fidelity time step analysis to facilitate periodic computation of metrics, including Time Varying Loudness (TVL) for eVTOL vehicles using a 1/12 Octave Band (OB) analysis. 

What is the AAM Pearls on Strings Feature?

The Pearls on Strings trajectory feature in AAM (implemented via a keyword option) allows for mixed fidelity time step analysis to facilitate periodic computation of metrics and is compatible with the 1/12 octave band analysis capability. The variety of eVTOL configurations and their expected complex sound emission properties necessitates the use of the narrowband analyses with 1/12 OB center band frequencies. This capability facilitates research into community acceptability and evaluation of suitable analysis parameters and audibility metrics including Time Varying Loudness (TVL). The 1/12 OBs are modeled as narrow bands in AAM, leveraging and extending the existing functionality of the toolset.

For situations where continuous high frequency time sample rate propagation modeling for an entire trajectory is not likely needed for audibility assessment, the AAM Pearls on Strings analysis mode (PEARLS keyword) was created. It includes hybrid micro and macro time-based modeling in the AAM trajectory. This improves computational efficiency by reducing run time and memory requirements, and permits the calculation of full flight operations using a personal computer.

For more information on using AAM to compute Time Varying Loudness (TVL) for eVTOL vehicles, visit https://rosap.ntl.bts.gov/view/dot/43515.

Is there training on the use of AAM?

Yes. The AAM User’s Guide (to be released soon) includes the following tutorials and examples, and the corresponding sample files are distributed with the AAM software:

• Basic Setup of the AAM environment
• NMPlot Single Event Noise Contour
• ASCII Grid File (.PLT) Single Event Noise Contour
• Detailed Time History at Points of Interest
• Creating a 3D Audibility Animation Video
• Creating Noise Contours Using the Multiple Operations Input Format
• Visualizing Source Data (.NC Files)
• Creating Source Data (.NC Files) from Measured Data
• Creating a One-Third Octave Band .NC File from Text with Bullwink
• Creating Stationary Source Spheres from Measurement Data (DeDopplerizer)
• Foliage Examples
• Time Varying Loudness and 1/12 Octave Band Examples for eVTOL Vehicles

Volpe can also provide tailored training to users for a fee. Please contact us to discuss training options.

How does AAM interface with BaseOps and NoiseMap?

The AAM executable is compatible with the BaseOps tool. The BaseOps graphical user interface (GUI) allows the user to define georeferenced aircraft trajectories (ground tracks and profiles), operating state and environmental conditions for multiple operations at an air installation. Within BaseOps, the user can control via settings and data availability, if a given vehicle is analyzed using NoiseMap or AAM. BaseOps creates an AAM input file, runs the AAM executable, and interprets the AAM output. BaseOps facilitates noise analysis and allowing for the summation and plotting of noise grids from AAM and NoiseMap using NMPlot. BaseOps is available here. 

Can AAM compute echoes or reflected sounds as would occur in urban environments?

AAM only includes reflections from forward propagating rays, as might occur as a bounce on the ground between an elevated source and receiver. It does compute the effects due to shielding by terrain, but does not include the ability to model buildings. One can create a high-resolution terrain file, which approximates buildings and allows for calculation of the shielding effects.

How is non-linear propagation modeled from high-thrust sources?

There are two means for modeling non-linear propagation in AAM. The user can prescribe a high-fidelity waveform as part of the noise sphere and AAM will invoke a Burgers solver, which steepens, ages, and advances the waveform. Companion noise characteristic non-linear data tables can also be externally pre-computed to create non-linear gain lookup tables (as a function of azimuth, elevation angle, distance, temperature, and humidity). These non-linear gain tables are companion files to the noise spheres. AAM then applies these corrections during the noise calculations.