Crosscorrelating the output of two receivers may fail to provide a means to estimate the arrival time difference of the first arriving signals when the crosscorrelation of accompanying multipaths have amplitudes that may be confused with that between the first arrivals. Based on information in two autocorrelation functions, a new method is described for identifying which peak in the cross-correlation function corresponds to the arrival time difference between the first arrivals [J. L. Spiesberger, J. Acoust. Soc. Am. 100, 910--917 (1996)]. The technique relies on (1) a high signal-to-noise ratio following auto and crosscorrelation and (2) time series which have been preprocessed to suppress all signals except those emanating from a single source. The technique works even when (1) the number of multipaths are unknown, (2) the received signal is not visible above the noise, (3) the transmission time is unknown, (4) the transmitted waveform is unknown, and (5) the spatial coordinates of the multipaths are unknown or are impractical to estimate. These techniques may be useful for localizing transient signals.