Abstract: A method of tracking an entity by monitoring a signal, the signal tending to vary spatially and be generally time-invariant, the entity moving from a first location within an area to a second location within the area, the method being suitable for use when the location of the source of the signal is unknown, the method comprising providing a plurality of particles for use with a particle filter, each particle being associated with a first particle location, a first particle location being an estimate of the first location of the entity, providing an estimate of the motion of the entity between the first location and the second location, using the estimate of the motion and using the particle filter, for each particle, updating the first particle location for that particle thereby producing an updated particle location, the updated particle location being an estimate of the second location of the entity, for each updated particle, estimating at least one expected signal parameter at the updated particle locati

Abstract: A method for correcting for refraction effects of the earth's atmosphere in an emitter geolocation technique for locating an emitter of electromagnetic waves, by way of a plurality of receivers, includes detecting the times of arrival of electromagnetic waves at the receivers, computing the relative time differences of arrival between the various receivers and estimating therefrom the position of the emitter, and, for correcting, by way of an iterative procedure, the detected times of arrival for path length discrepancies caused by refraction in the earth's atmosphere. The receivers are each mounted on a respective airborne platform, and at least three pairs of the receivers are provided.

Abstract: A method of tracking an entity by monitoring a signal, the signal tending to vary spatially and be generally time-invariant, the entity moving from a first location within an area to a second location within the area, the method being suitable for use when the location of the source of the signal is unknown, the method comprising providing a plurality of particles for use with a particle filter, each particle being associated with a first particle location, a first particle location being an estimate of the first location of the entity, providing an estimate of the motion of the entity between the first location and the second location, using the estimate of the motion and using the particle filter, for each particle, updating the first particle location for that particle thereby producing an updated particle location, the updated particle location being an estimate of the second location of the entity, for each updated particle, estimating at least one expected signal parameter at the updated particle locati

Abstract: A method and means for correcting for refraction effects of the earth's atmosphere in an emitter geolocation technique for locating an emitter of electromagnetic waves by means of a plurality of receivers, including detecting the times of arrival of electromagnetic waves at the receivers, computing the relative time differences of arrival between the various receivers and estimating therefrom the position of the emitter, and for correcting, by means of an iterative procedure, the detected times of arrival for path length discrepancies caused by refraction in the earth's atmosphere. The receivers are each mounted on a respective airborne platform, and at least three pairs of said receivers are provided.