Selected problems of 3-D target tracking

The paper presents selected problems of tracking targets in 3D space, when the only source of measurement data is a primary radar. A radar measures target position in polar coordinates giving three independent readouts - target range to the radar, line of sight azimuth from the north and line of sight elevation (from the Earth surface). Target motion equations for the radar polar coordinates are nonlinear. Most trackers work in their natural Cartesian coordinate system, where motion equations are linear and measurement equations are nonlinear. The necessity for equation linearization, required in Kalman filtering introduces significant errors when measurement nonlinearities are present. These nonlinearities are discussed and modifications of the Kalman filter are proposed to deal with these nonlinearities