The interferometer is the traditional instrument used to find the direction
of an emitter by measuring the phase difference of arrival of its RF emiss
ions. Bearings-only motion analysis indicates that an observer with these d
irection measurements can locate the position of the emitter in a period of
time. A novel passive location method is introduced with phase difference
and phase difference rate measurements with the interferometer mounted on a
moving observer. The accuracy of a passive location system with these meas
urements is analysed. The results show a significantly improved performance
compared with the traditional method.