Radio location finding

A method (1) for passively locating a radio emission source (2a, 2b) is described. The method includes including receiving radio signal datasets corresponding to each of three of more sensors (3). Each sensor (3) includes at least one radio receiver (4, fig 4). The method also includes receiving or retrieving a physical location corresponding to each sensor (3). The physical locations define a convex hull (5). The method also includes determining whether an emitter signal (8) within a target frequency range is present in any of the radio signal datasets and assigning any radio signal dataset which comprises the emitter signal as a detection dataset. The method also includes, in response to determining three or more detection datasets, calculating a signal location based on arrival times of the emitter signal and the respective physical locations. The method also includes generating a locus of possible positions based on calculating two or more alternative signal locations. Each alternative signal location is calculated by adding synthetic noise to one or more of the detection datasets and repeating the calculations used to calculate the signal location. When the signal location is inside the convex hull, cluster filtering based on circles or spheres is applied. When the signal location is outside the convex hull, cluster filtering is based on ellipses or ellipsoids and on the locus of possible positions. The method also includes outputting one or more estimated radio emission source locations. Each estimated radio emission source location is determined based on a respective cluster of signal locations.