BEARINGS-ONLY TRACKING - A HYBRID COORDINATE SYSTEM APPROACH

In this paper a bearings-only tracking algorithm is described. The algorithm is an extended Kalman filter (EKF) which combines the linear-in-state properties of the Cartesian state variable definition with the linear-in-measurement properties of the modified polar (MP) state variable definition. This hybrid approach employs the Cartesian system for state and state covariance extrapolation and employs the MP system for state and state covariance updating. Accurate state and state covariance extrapolation is achieved without numerical integration. The filter equations of this EKF are, furthermore, derived using a new line-of-sight algebra which yields equations which are nonlinear algebraic rather than transcendental. This new formulation obviates the need for real-time calculation of inverse trigonometric function and allows for the straightforward derivation of the three-dimensional problem. In comparison to previous formulations, this approach allows for easier manipulation of the filter equations and provides for greater insight into bearings-only tracking problem.