Orientation Estimation and Signal Reconstruction of a Directional Sound Source

Francesco Guarato

Publikation: AfhandlingPh.d.-afhandling


Previous works in the literature about one tone or broadband sound sources mainly deal with algorithms and methods developed in order to localize the source and, occasionally, estimate the source bearing angle (with respect to a global reference frame). The problem setting assumes, in these cases, omnidirectional receivers collecting the acoustic signal from the source: analysis of arrival times in the recordings together with microphone positions and source directivity cues allows to get information about source position and bearing.

Moreover, sound sources have been included into sensor systems together with sound receivers for accomplishing investigation of the surrounding environment in order to integrate data from vision systems and in cases where vision is unfeasible. There have been developed sensor systems inspired by real animals trying to reproduce their behaviour, for it is optimized by nature.

The problem of calculating the spectrum of the signal produced by a directional sound source allowing to reconstruct the signal in the far field is developed in this thesis. The method for the reconstruction estimates, as an intermediate step, the orientation of the source and makes use of microphone recordings of the signal at several locations around the source. The reconstruction provides the signal necessary for predicting the same signal in the far field, taking into account microphone positions in the source reference frame and source directivity. Both simulations and experiments in a laboratory environment reveal the method estimates source orientations accurately and provides reconstructions that approximate the true signal.
The method was also applied to bat calls with the purpose of estimating the direction the bat was aiming its beam when performing hunting tasks: the so obtained orientations, one for each call emission, were compared to those calculated through a pre-existing technique based on interpolation of sound-pressure levels at microphone locations.

The application of the method to the bat calls could provide knowledge on bat behaviour that may be useful for a bat-inspired sensor system based on ultrasounds in order to optimize its performances in terms of acoustical features such as orientation and signal emitted when emulating bats' echolocation. Indeed, sensor systems based on ultrasounds have already been developed, but no optimization of their performances achieved when imitating bat's behaviour appears to be developed in the literature.

Hence, the method addressed in this thesis is of value because of itself, as it shows never to be generated before, but it also constitutes an important support for both activities of investigating bats' behaviour and optimizing sensor systems inspired by them in the research fields of biology and robotics respectively.
StatusUdgivet - 28. feb. 2011


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