A target receives two signals of different modes in association with a first location and another two signals in association with a second location. The first two signals are assumed to have been emitted effectively simultaneously from the first location, and the second two signals are assumed to have been emitted effectively simultaneously from the second location. A first distance is calculated in view of a receipt time difference of the first two signals in view of differing rates of propagation assumed between these two signals; a second distance is calculated in view of another receipt time difference of these second two signals in view of differing rates of propagation assumed between each of these other signals. A possible location of the target is then calculated in view of the first distance and its associated first location and the second distance and its associated second location.