Experimental evaluation of passive underwater acoustic markers

Abstract

Autonomous Underwater Vehicle (AUV) navigation requires accurate positioning information underwater which is most commonly achieved using active acoustic transponders. Such transponders typically require maintenance, power and are not covert. As an alternative, the concept of using passive underwater acoustic markers with layered media for underwater navigation has been previously explored theoretically and experimentally using flat interfaces [Satish et al., JASA-EL 145(1), EL84–EL89]. In order to design passive acoustic markers with a more isotropic scattered response, acoustic markers with curved symmetry were investigated experimentally using scaled ultrasonic testing of 3-D printed concentric hemispheres. Subsequently, larger acoustic markers using acrylic hemispherical shells are constructed and insonified by conventional high-frequency SONAR, and their acoustic signatures are measured and compared to theoretical responses. Tag design considerations and preliminary results for the scattered response from different acoustic markers are compared for uniqueness of acoustic signature.