On the Accuracy Analysis of Airborne Techniques for Passively Locating Electromagnetic Emitters

Discussion of methods of locating electromagnetic emitters from airborne electronic reconnaissance systems, using passive measurements on the electromagnetic waves of the emitter taken from several locations. Measurements for finding the emitter may be either the direction of arrival at 2 or more locations along the aircraft's flight path for single-aircraft DF (direction-finding) systems, or the relative time of arrival of emitter pulses at the different aircraft locations for 3-aircraft TOA (time-of-arrival) systems. Emitter location accuracy is a function of the accuracy of these indirect measurements of the emitter location and the estimation procedure used to combine the accuracies of various measurements of location and bearing. A general expression is derived for a lower bound to the covariance matrix of the unbiased estimates of emitter location coordinates (and consequently the location CEP), using the Cramer-Rao inequality. Examples illustrate the application of the Cramer-Rao lower bound to the emitter CEP for both DF and TOA systems.