- Title: Time-frequency analysis of the dolphin SONAR beam
- Description: In connection to ongoing research at LTH is has been recently found that dolphins can shape their SONAR beam into two separate peaks, only partially overlapping in space and frequency content instead of the more commonly seen type of beam with just one uniform peak. However, it is not yet understood how the animal generates these two peaks within the beam. One way of finding out more about this is to investigate the spatial origin of different parts of the acoustic beam. This requires a method that accurately traces and compares the azimuth of the sound in different parts of the echolocation beam. To achieve this a very precisely determination of the timing of the onsets of different frequency components in the echolocation signal could be compared to those with the signals sampled at different spatial position across the cross section of the SONAR beam. Such timing information for different frequencies could potentially be obtained through highly resolved time-frequency representations of the signals. However, it is not yet known how well algorithms would work for determining the precise onsets and offsets of signal components of a signal with specific frequency properties. The reassignment technique has been known for some time and is a technique to reassign spectrum values of smoothed spectrograms to the center of gravity. This gives for a single undisturbed chirp signal a perfect localization in time- and frequency. In the case of a sum of shorter chirp-signals (such as the sonar beam signals from dolphins) the technique has drawbacks. To find an optimal reassignment technique for localization and precise onsets and offsets of the signals would be very valuable and directly applicable to a currently very “hot” topic in marine bioacoustics as well as in signal processing.
- Contact: Maria Sandsten
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Last update: 2013-04-11
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