Time-of-arrival (TOA) method and time-difference-of-arrival (TDOA) method. (a) The TOA method uses the time difference between the time of emission and the time of arrival to obtain parametric equations of a circle, and the location of the source is the point of intersection. (b) The TDOA method uses the time difference between each pair of receivers to obtain parametric equations of a hyperbola, and the point of intersection of the hyperbolas is the location of the source. The uncertainty of a single measurement, shown by the thickness of a path, is governed by the cadence of the instrument. Spacecraft configuration determines how these areas overlap. If the overlapping is perpendicular, the area of uncertainty is minimised. If the overlapping is tangential, the area of uncertainty is maximised.