Ambiguity function of biosonar cetaceans from HD observations and their automatic classification

Cetaceans use methods based on acoustic signals to perceive the environment (echolocation)[1][2] and communicate due in part to the low visibility in this environment [3]. Studying these acoustic signals enables us to identify and understand these animals better. There are different methods to describe an acoustic signal, one of which involves using transformations to represent signal variations according to time and amplitude modulations [4]. These representations are called time-frequency representations (TFR). However, the TFR method usually used (by short-time Fourier transform) [5] to study cetaceans is not suitable for all types of emitted signals. It is shown here that the Ambiguity Function (AF), is a representation that provides information of transient signals in terms of Doppler and time delay [6]. This representation is used as input for an autoencoder, to analyze the latent space. The results obtained support the hypothesis that there are characteristics within the animal's click that are linked to its behavior and its age/sex. This work opens the door to more advanced analyses such as the ability to monitor populations, differentiate juveniles, males, and females, and improve our knowledge of these cetaceans, which are still little known to the general public.

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[6] Max, J. (1987). Méthodes et techniques de traitement du signal et applications aux mesures physiques. vol. 2: Appareillage, méthodes nouvelles, exemples d’applications. Paris: Masson.