Relation of SNR thresholds for time delay estimation to available prior information

Signal-to-noise ratio (SNR) thresholds in time delay estimation are discussed. At very low signal-to-noise ratios, mean square estimation errors are dominated by prior information because of the high probability of large errors in an extended search region. At higher SNR values mean square errors are dominated by the measured data unless the lack of prior information is extreme. Barankin bound techniques are used to show that the transition occurs in the range 1<SNR<10. It also shows that these calculations are essentially the same for one or two reflectors. In the later case, reflector separation has only a minor influence on the threshold