Measurement configuration effects on target observability with bearings-only tracking

A passive sensor cannot measure the range of an emitter, but is restricted to measurements of angle. In the important case of an aircraft platform in horizontal flight, collecting measurements of bearing (i.e. azimuth) over a long enough observation path can provide a two-dimensional location. The accuracy of this location depends on such factors as the observation time, antenna arrangement, and the signal itself. From an operational point of view, one of the important issues for an airborne system tasked with locating ground-based targets is the time required to locate the target to a specified accuracy. The purpose of this paper is to present a framework by which different system configurations can be compared in terms of their location performance as a function of observation time, platform speed and angle measurement technique. It is the last of these that is often of particular interest, as the implementation of a high accuracy DF antenna array can present major technical challenges and the trade-offs between a number of options may need to be investigated. Interferometry is discussed in particular.