Tracking the Slipper Lobster Using Acoustic Tagging: Testbed Description

The technique of underwater acoustic localization (UAL) is widely used to track submerged targets. In the present study, we consider UAL in the specific application of locating the Mediterranean slipper lobster, Scyllarides latus (S. latus), for the aim of continuous and long-term investigation of its movement patterns. Since visual inspections only offer a snapshot to the life of these nocturnal crustaceans, we used underwater acoustic tags and deployed the first testbed to track a community of S. latus through UAL. The testbed included 19 acoustically tagged S. latus, as well as a sensor network of four receivers that record the time-of-arrival of detected tag's emissions. The testbed operated for six months, and the data collected were analyzed offline. In this paper, we describe the design details of our testbed. We discuss the considerations in choosing both the type of acoustic tags and the structure of the testbed. We also present our algorithm to time synchronize the receivers, and the localization procedure. Our preliminary results show that, for this long-term deployment, the widely used model of clock offset for the receivers is too simplified, and that time synchronization must consider also the clock's skew. We also show that the tagged lobsters are mostly detected by fewer than three receivers, thereby making localization using traditional trilateration methods highly challenging. Finally, preliminary results for the localization of the tagged lobsters in the deployment area are presented.