Frequency agility and fusion for tracking targets in the presence of multipath propagation

The problems induced by over-the-water multipath effects in the tracking of low elevation targets is addressed through the use of two fixed radar frequencies. Since the multipath propagation depends on radar frequency and the acute elevation errors are often localized to intervals along the sensor-to-target range coordinate, fusion of dual frequency tracks is proposed for tracking low elevation targets. Two tracks are formed with elevation measurements obtained at two different waveform frequencies. The interacting multiple model (IMM) algorithm is used to estimate the target state for each waveform frequency. A “multipath effect present” mode and a “multipath effect absent” mode are included in the IMM algorithm so that the output error covariance will reflect the degradation in the accuracy of state estimates when multipath propagation is present. The state estimates of the two IMM algorithms are then used as track fusion algorithms to form an output state estimate. The results of extensive simulation studies of the tracking technique are given