Time-Frequency Processing of Bat Sonar Signals

It is known that time-frequency distributions can be used for the demodulation of bat sonar signals and, in some cases, for detection-estimation tasks via a 2-D correlation process. In this paper, we formalize the intuitive notion of correlation of time-frequency structures in the simplified case of AM + FM signals. This results in a general time-frequency receiver structure depending only on a time-frequency smoothing function. According to the choice of this smoothing, it is shown that the receiver can vary continuously from a semi-coherent (matched filter and envelope detector) to a non-coherent (energetic) one. This suggests that both can be viewed as limiting cases of a unique time-frequency processing. The proposed approach is illustrated on the detection of echoes (over water) of signals emitted by Myotis daubentoni and recorded in the field.

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