Prototype of a linear array on an autonomous surface vehicle for the register of dolphin displacement patterns within a shallow bay

Abstract

A semi-resident population of tursiops has been reported in the south of La Paz bay in Baja California Sur, Mexico, where specific zones for social, feeding and resting behaviors have been detected. Nevertheless, increasing human activities and new constructions are attributed to have shifted the areas of their main activity. Therefore, it becomes important to study displacement patterns of dolphins within the bay and their spatial relationship to maritime traffic and other sources of anthropogenic noise. A prototype of an Autonomous Surface Vehicle (ASV) designed for shallow water bathymetry has been adapted to carry a linear array of hydrophones previously reported for the localization of dolphins from their whistles. Conventional beam-forming algorithms and electrical steering are used to find Direction of Arrival (DOA) of the sound sources. The left-right ambiguity typical of a linear array and front-back lobes for sound sources located at end-fire can be resolved by the trajectory of the ASV. Geo-referenced positions and bearing of the array, provided by the Inertial Measurement Unit of the ASV, along with DOA for various positions allows triangulating and mapping the sound sources. Results from both, controlled experiments using geo-referenced know sources, and field trials within the bay, are presented.