By Bill Beatty

The Interactive Multisensor Analysis Training (IMAT) system is a concept-based instructional tool, designed to promote context-based learning in a multimedia environment. It is primarily used to teach the physics that underlie the conduct of acoustic undersea warfare. It also has optics, magnetics and radar modules.

The IMAT system employs Navy standard physics-based models, Navy standard high-resolution databases and scientific visualization to illustrate complex physical interactions. This unique advancement in modeling/simulation creates a highly visual cause and effect training tool. All of the major variables relative to the interaction of target, sensor and the environment are available for manipulation. By changing one or more variables at a time, the student can observe the impact on the overall outcome. Many IMAT displays allow creation of animations, which illustrate how acoustic and oceanographic phenomenon might vary over a range of these variables. Effectiveness studies of IMAT have shown that IMAT training can be accomplished faster and more effectively, retention is enhanced, and the need for constant refresher training is reduced. The IMAT system is currently being used by air, surface and submarine communities to perform basic through advanced acoustics and oceanography training for both officer and enlisted personnel.

Training of the Navy acoustic analyst has historically focused on the rote memorization of frequency families for specific submarine and surface ship contacts. IMAT allows the instructor to take students to a higher level of understanding tying together aural and visual relationships with what the student may see on a sonar display (Figure 1). IMAT can display 3D graphics of many real world submarines. It can turn the external hull transparent, enabling students to see the internal components of the platform. With the internal components visible, clicking the mouse on an individual component will highlight it and display a textual description. If the acoustic signature for the selected component appears in the sonar display, those features associated with it will be highlighted as well. Conversely, clicking on features of a signature will cause the associated part to be highlighted. The ability to associate signature features with selected components helps the student develop an understanding of how acoustic signatures are generated. By double clicking on a component, it can be magnified and displayed at a high level of detail to better explain its acoustic properties. This allows a better understanding of how complex assemblies work, how these mechanical parts generate signals, and how sources of sound relate to operating modes and speeds of the platform. Sonar displays can be generated from either a real-time acoustic simulator or from actual recordings of in situ data. Additionally, an audio playback feature allows the student to listen to the time-series data represented by the display. A variety of processing options are available to emulate different sonar systems and modes for different communities.

For teaching oceanography (the acoustic undersea environment), IMAT enables students to study visual displays of temperature, salinity and sound speed profiles worldwide during any month of the year (Figure 2). IMAT uses Navy standard databases for bathymetry, temperature, salinity and sound speed profile data. Sound speed profile data can also be input via radio message (JJXX, JJYY or MODAS field messages) or manually input by the operator. These displays can be combined with a tactical display showing a 3D representation of environment. Simply by clicking on a location, the relevant environmental data are retrieved.

Using IMAT, instructors have access to a number of range-dependent Navy standard acoustic and electromagnetic propagation models. All of the acoustic models incorporate interactions with the bottom bathymetry, bottom type and variations in sound speed over range. IMAT displays the results of these models and allows the students to study ray paths and propagation loss. Passive propagation is modeled using the Parbolic Equator (PE), Gaussian Ray Bundle (GRAB) and ASTRAL models. Active Sonar Predictions can use either the Acoustic System Performance Model (ASPM) or the Comprehensive Acoustic Simulation System (CASS). The IMAT active displays can isolate and display the components of the active sonar equation (echo, noise and the components of reverberation). With this detail the student learns how to best modify active sonar settings to maximize ship/sonar system performance in a specific ocean environment.

All of these displays may be combined with the 3D tactical display which provides the student a visualization of the environment along with the predicted propagation loss in that environment (Figure 3). The graphical user interface of the 3D tactical display allows the user to interactively play "what if" games at different locations in the environment and quickly view the results. Directional background noise can also be incorporated into the display showing the impact that directional ambient noise can have on signal excess and therefore detection/ counterdetection.

Instructors can also use IMAT to build tactical scenarios. The 3D tactical display can be populated with objects such as sonobuoy fields, submarines, aircraft, and surface ships. The instructor can then use the scenario to analyze a contact's motion and solve for its range, course and speed by selecting which animated object is the "search" platform and which is the "target" platform. Scenarios can be matched with specific sonar data, thereby providing the instructor with a tool for associating tactical evaluations with the associated acoustic representations (Figure 4).

Generic IMAT research and development has been conducted under the sponsorship of the Office of Naval Research (ONR). The Naval Science Assistance Program has supported field tests and distribution of IMAT to the Fleet. NAVSEA and NAVAIR have sponsored deployment of IMAT to their respective schoolhouses.

IMAT has been a Congressional Special Interest program and is currently a Defense Technology Objective. Last year IMAT was the first recipient of ONR's Bisson Award for Naval Technology Achievement. IMAT has been highlighted by the Naval Studies Board and the OPNAV N84 ASW Assessment as a solution to rebuilding proficiency in ASW.