Track maintenance in covert mission: Passive nonlinear filtering through Cartesian vs Modified Polar EKF

This paper addresses the problem of tracking a non maneuvering target in a maritime surveillance context, under emission constraint. In such a situation, the onboard radar shall be used as few as possible, in order not to be detected. To maintain the tactical situation, it is convenient to take advantage of other non emissive sensors such as ESM. However, we have to jointly face the problem of nonlinear filtering and the lack of observability due to bearing-only measurement. This paper proposes to compare the performances of two algorithms based on Extended Kalman Filter : Cartesian coordinates and Modified Polar coordinates. Simulation results demonstrate that the latter is well adapted to long mission durations where radar is almost not used, while the former gets significantly more inaccurate.