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Obscurant representation improvements in the CHORALE workshop

Download PDF SPIE 2005
CHORALE (simulated Optronic Acoustic Radar battlefield) is used by the French DGA/DET (Directorate for Evaluation of the French Ministry of Defense) to perform multi-sensors simulations. CHORALE enables the user to create virtual and realistic multi spectral 3D scenes, and generate the physical signal received by a sensor, typically an IR sensor. Some assessments concern the study of the duality between a threat (a missile for example) and a target (a battle tank for example) in the battlefield. In these cases, obscurants are special counter measures (clouds), classically used to hide armored vehicles and/or to deceive threatens. To evaluate their efficiency in visible and infrared wavelength, simulations tools, that give a good representation of physical phenomena, are used. The first part of this article describes the elements used to prepare data for the simulation. The second part explains the physical model used in CHORALE for the resolution of the Radiative Transfer Equation when obscurants are set in the scene. Obscurants are modeled by a set of voxels (elementary volume elements). Each voxel contains the spectral absorption and scattering coefficients, phase function coefficient and temperature information. The shape is changing with time to take into account the dynamic evolution of the obscurant. A "photon map" method is used in the ray tracing process to take into account global illumination within the cloud and solve the Radiative Transfer Equation.


Download PDF RADAR 2005
Tools for electromagnetic simulation, such as SPECRAY EM / FERMAT, a jointed development of OKTAL SE company and French ONERA EM research centre, are well adapted to RCS or ISAR image computations down to millimetre wavelength for high realistic targets described using detailed CAD files. Moreover, this type of tool can be efficiently used in order to compute the same RCS of targets but taking into account the close environment, i.e. the clutter of this target, in the same run. Besides, it is possible to use the same type of tool in order to compute a complete reflectivity map of the terrain, including targets, that can be a very nice input of SAR treatment models. The basic problem is the terrain modeling. OKTAL SE company has developed the AGETIM terrain modeling tool, with the support of ANVAR, DGA and CELAR in France. This tool enables to automatically generate a 3D terrain mesh including complete modeling of features like roads, rivers or forests. This "terrain CAD file" is enhanced with physical attributes at polygon or texture level, which enables to perform EM ray tracing computations in order to provide a virtual stimulus to SAR imagery models. This paper intends to present the whole process from geographical data to SAR reflectivity map.