ISARLAB - Inverse Synthetic Aperture Radar Simulation - Defence ...

DSTO-GD-0210the rotational components have a significant effect on the formation of ISAR images,the linear components are not simulated.Induced motion is therefore implemented as rotations applied to the scattererpositions, which are defined in the local coordinate system xyz. These rotationssimulate actual roll, pitch and yaw. They are defined by anticlockwise rotations aboutthe x, y and z-axes respectively, where the sense is determined by looking along theaxes towards the origin. Figure 2 graphically depicts this covention. As rotations onlycommute (approximately) with small angles, the induced rotation is achieved byupdating scatterer positions over small time intervals. The new positions are stored sothey can be updated (again incrementally) at the next iteration. The positions togetherwith the Motion matrix (Eqn 6) are a representation of the target’s current state ofinduced motion.ZYAWLocal CoordinatesXROLLPITCHYFigure 2: Definition of induced motions within the local coordinate system.Induced motion can be specified in two ways. It can be specified crudely by giving theamplitude, period and phase of independent sinusoids that represent roll, pitch andyaw (as shown below) or more realistically it can be specified using pre-calculated andstored sets of roll, pitch and yaw angles that can be read from a file. An example ofpre-calculated values is the result from a detailed ship motion modelling program [4].If the former method is used, the array of parameters describing the induced targetmotion is:10