Detection and Classification of MARINE MAMMALS Using an LFAS System

World wide a concern is emerging about the influence of man-made sound in the sea on marine life, and particularly about high power active sonars systems. Most concern lies with marine mammals, which fully depend on sound in their natural behaviour (foraging, navigation and communication). One of the sonars under debate is the Low Frequency Active Sonar (LFAS). This type of system is designed for long range detection of submarines. It consists of a powerful source and a towed array receiver. Incidents with marine mammals could be avoided if the receiver that is dedicated to detection of submarine echoes, is equipped with Detection, Classification and Localisation capabilities for marine mammals as well. In this paper the development of a prototype transient detector and classifier for the TNO-FEL LFAS array (named CAPTAS) is described. A broadband beamformer is developed that creates 8 beams (sectors) that are equally wide over the whole frequency band. A multi-bearn LOFAR display is presented. On the normalised data a Page's test detector is applied that is "optimum" for signals with unknown duration. Detected transients are sent to a classifier that tries to discriminate between biological and man-made or natural transients. Time-frequency analysis is performed and in the resulting time-frequency plot structures are determined by means of cluster analysis after which the sound is classified. Detection results of the prototype are very good, the Classification module is under development and the Localisation module is part of future research. Part of this research is sponsored by the Royal NetherLands Navy (RNLN).Original Abstract: L'impact des sons d'origine artificielle sur l'ecosysteme sous-marin souleve un interet mondial croissant. Plus particulierement, cet interet se porte sur l'impact des systemes sonar actifs a forte puissance sur les mammiferes marins, dont le comportement est entierement base sur 1'utilisation du son (aussi bien pour s'alimenter, s'orienter ou comrnuniquer). Un des systemes sonar concernes est le Sonar Actif a Basses Frequences (LFAS). Ce type de systeme est concu pour la detection longue distance de sous-marins. II consiste generalement d'une source puissante et d'une antenne de reception remorquee. Les accidents causes par 1' interaction de ces systemes sur les mammiferes marins pourraient etre evites si l'antenne receptrice dediee a la detection d'echos de sous marins etait munie de capacites de Detection, Classification, et