SUMMARY

The development of predeployed underwater infrastructures to aid in Autonomous Underwater Vehicle (AUV) navigation is of keen interest, with the increased use of AUVs for undersea operations. This work presents a class of passive underwater acoustic markers, termed Acoustic IDentification (AID) tags, which are inexpensive to construct, simple to deploy, and reflect unique, engineered acoustic signatures that can be detected by an AUV instrumented with high-frequency SOund NAvigation and Ranging (SONAR) systems. An AID tag is built of layers of materials with different acoustic properties and thicknesses such that a portion of the acoustic energy from an incident pulse from an AUV, for example, is reflected from each interface between two adjacent layers. In this manner, unique acoustic signatures can be generated, similar to an optical barcode. AID tags can be used therefore as geospatial markers to highlight checkpoints in AUV trajectories, or to mark areas of interest underwater. Numerical simulations of the acoustic signatures of two AID tag design iterations i.e. a horizontally stratified AID tag, and a hemispherically stratified AID tag, were experimentally validated using a sub-scale ultrasound setup. Furthermore, an energy based layer optimization strategy was proposed to maximize the strength of reflected AID tag signatures for different source frequency ranges. Subsequently, the detectability of AID tags in the proximity of strong interference such as a hard seabed or another AID tag was quantified, and the detection range of an AID tag was computed based on the standard SONAR equation. Finally, experimental results of hemispherical AID tags interrogated by high-frequency SONAR were presented to demonstrate AID tag performance in realistic deployment scenarios.