Extracting speed, heading and turn-rate measurements from extended objects using the EM algorithm

Abstract

In active sonar and radar target tracking, measurements consist of position and often Doppler. Tracking algorithms use these measurements over time to estimate target state comprising position, velocity and turn rate. In most cases there is an underlying assumption in the tracking algorithm that the target is a “point target” (i.e. the target has no physical extent). Another common assumption is that, at most, one measurement per scan originates from the target. For certain combinations of transmitted waveform and target type, the resolution of the waveform is such that the target is “overresolved” (i.e. the error in the measurements is small enough that the spatial characteristics of the target can be measured). For such cases the point target assumption must be replaced with an extended target assumption. This work provides a methodology to exploit the extended nature of the target for the case of a rigid target whose spatial characteristics are fixed with respect to the line of motion. By employing a combination of the expectation maximization (EM) algorithm and allowing more than one measurement per scan to originate from the target, a measurement conversion technique is developed. This technique converts a single scan of rawmeasurements that include position and Doppler into an estimate of target position, velocity, heading and turn rate.