Patent ID: 8081111

Claim:
A method of locating the source of an unknown signal, characterised in that the method comprises the steps of: i. calculating a differential offset for a signal for each of a plurality of positions within a region in which the transmitter must lie, for each of a series of times m with respect to first and second signal relays and respective first and second receivers, the positions of the signal relays and receivers being known; ii. generating a cross-ambiguity function (CAF) using data corresponding to samples of the unknown signal received at the first and second receivers via the first and second signal relays respectively; iii. estimating the level of noise and values of waveform parameters from the CAF; and iv. using data generated in steps (i), (ii) and (iii) to obtain a measure of the likelihood that the source is located within defined areas within said region; wherein the differential offsets are differential time offsets (DTOs), or differential frequency offsets (DFOs), or both DTOs and DFOs.