GEOLOCATION OF HF SIGNALS USING TIME DIFFERENCE OF ARRIVAL METHODS Larisa Lindsay Defence Science and Technology Organisation, PO Box 1500, Edinburgh, SA 5111, Australia, Larisa.Lindsay@DSTO.defence.gov.au The time difference of arrival of a signal at geographically separated receiving sites may be used to geolocate signals of interest. In the HF environment these signals are often subject to strong interference and background noise can be correlated across the sites due to large numbers of weak interferers. For these reasons simple thresholding and cross- correlation methods are inappropriate. A matched filtering approach can avoid these problems but relies on adequate knowledge of the signal type and parameters. A robust method of determining these is desirable. Several signals from November data have been geolocated including a known JORN transmission, an unknown FMCW signal and an unknown wideband parabolic signal.