Improved radar revisit time control to observe ballistic missile mode transitions

For systems that can be modeled using multiple models and Markovian switching probabilities, an interacting multiple model (IMM) estimator is a good approach to state estimation and mode detection. For good mode detection, it is desirable to maintain the mode-probability set so that one of the probabilities is near unity. For radar tracking a ballistic missile, the mode probability is dependent on the so-called revisit time defined as the elapsed time between each measurement. It is shown that selecting a revisit time that controls the value of a mode-switching coefficient yields acceptable performance in terms of both the mode probability and tracking error. The potential robustness of the method to tracking conditions is demonstrated through a mid-fidelity, physics-based radar simulation using targets that differ in both type and radar-to-target geometry. The results show that the proposed adaptive-revisit method performs well during boost, boost-to-coast transition, and ballistic coast, as measured by tracking error when compared to both a constant revisit interval and an ad-hoc, altitude-based revisit schedule.