Chorale-AC:
Chorale Acoustic main development

Background Used in battlefield observation, the area-control systems allow an area to be supervised, the acquisition and the transmission of any aerial or ground vehicle motion, such as main battle tank, light vehicles. These systems are often equipped with a treatment module for data fusion. Then the results trigger reaction to destroy a detected, recognized and identified threat. The evaluation of such systems requires having a complex environment allowing the generation of realistic physical signals in the various spectral bands. Projects objectives An efficient and operational acoustic model needs to be implemented in the SE-Workbench (Chorale-AC). It shall fulfill the following requirements: compatibility with realistic 3D scenes, compatibility of the 3D scene with the optronic and electromagnetic sensor, performances on the computation time. Unitary tests shall be performed to validate each functionality of the acoustic model. Finally, a global validation test will be performed. Achievements An acoustic model has been implemented in the SE-Workbench (Chorale-AC) software. Four major achievments have been covered: Geometry model The SE-Workbench is based on the SDM++ format, which is an ASCII format for the representation of 3D databases, and the definition of physical data. SDM++ is compliant with standard geometrical files format such as SEDRIS, VRML or Open FLT. For the needs of acoustic simulation, materials are enhanced with the spectral specific acoustic impedance ZS (in kg.s-1.m-2), or the acoustic resistivity (in kg.s-1.m-2), or a mean foliage thickness (for the vegetation). Acoustic sensor An acoustic sensor is characterized by its directivity, its bandwidth, its position and orientation. According to these features, the acoustic software calculate the incoming acoustic pressure p(f, t) as a function of the frequency f and the date t. Sound sources Sound sources are associated to moving (or not) objects (for instance a vehicle on a road, a helicopter, …) and are positioned with regard to the coordinate system of the objects. A sound source is characterized by its spectrum and its directivity. Simulation software The acoustic simulation software is based on an efficient and powerful ray tracing kernel called SE-RAY-AC. For each acoustic sensor in the 3D scene, SE-RAY-AC calculates the incoming acoustic pressure. "Acoustic" beams are cast from each sound source, in all directions, through an "acoustic system" composed of a set of pixels. The beams are propagated into the 3D scene, interact with polygons, are reflected or diffracted, and, for some of them, are received by a sensor. The acoustic functionalities are now fully operational in the multi sensor simulation CHORALE workshop (SE-Workbench). It is dedicated to physical realistic simulations on very accurate and complex 3D scenes. The general philosophy of the acoustic software is: capability of simulating several acoustic, infrared and electromagnetic sensor technologies with the same Synthetic Environment, availability of an API to built transverse applications, compatibility with the infrared and electromagnetic 3D scenes (same geometry, new physical extensions added to materials) allowing the user to perform data fusion (for example between an infrared sensor and an acoustic sensor). This simulation approach is on all accounts promising. The full 3D computation enables the user to forecast highly complex test cases with immeasurably accurate achievements compared to reality.

Customer The project has been made under the control of DGA/ETBS from the French MoD. The partners of the projects are: OKTAL-SE (leader) Saint-Louis Institute - ISL

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