Fabrication, testing, and installation of fluid-filled target spheres for AUTEC´s passive sonar calibration system

The need for calibrated sonar targets is addressed in connection with the development and testing of a set of thin-walled spheres filled with a high-density fluid. Using historical research information as a guide, a set of thin-walled metal spheres was developed and filled with a high-density fluid. The combination of the spherical shape and the acoustic focusing effects of the fluid enhanced the acoustic target strength of the shape so that it was not only stable with temperature but also significantly greater in amplitude. The simple passive nature of the spheres makes them ideal acoustic targets for long-term, unattended deployments