FTV: a sonar for tracking macrozooplankton in three dimensions

A three-dimensional sonar imaging system, Fish TV (FTV), was developed to observe the three-dimensional trajectories of macrozooplankton in situ. Consisting of two arrays of eight transducers, the sonar uses one of the arrays as a projector and the other as a receiver. In this way, a combination of 8 × 8, or 64 beams, is constructed. Spatial resolution is approximately 2° by 2° and the range resolution is 3 cm. The sonar is capable of recording up to five images every second. The data is stored digitally in a three-dimensional matrix which can be postprocessed. Tests performed in the lab with both test targets and freshwater shrimp indicate that the system has the sensitivity and accuracy to track euphausiids in the ocean. The system was deployed at sea on an ROV (Remote Operational Vehicle) and the tracks of euphausiid sized objects were recorded.