Detecting Low SNR Tracks With OTHR Using a Refraction Model

Abstract

Over-the-horizon radar is used to detect targets at very long ranges by reflecting of/refracting signals within the ionosphere. Multiple propagation paths exist between the radar and the target, which can result in multiple target-originated measurements in each scan. It is uncertain which path corresponds with each measurement. Due to the necessary low detection threshold for very low signal-to-noise ratio targets, there are also many false alarms. The maximum-likelihood probabilistic multihypothesis tracker, which is a deep track extractor, is generalized to allow multiple propagation paths. A ray-tracing algorithm is used to model the refraction in the ionosphere. Monte Carlo simulation results are presented for three types of targets: a surface target, a constant altitude target, and a constant vertical acceleration target. We also calculate the Cramer–Rao lower bound for these scenarios, and an analysis is done to determine the probability of track detection, $P_{\text{DT}}$ , for specified probabilities of false track $P_{\text{FT}}$ .