Using underwater ambient sound to localize swarms of underwater vehicles

We have recently completed a project to create a swarm of 20 miniature, 1.5 liter vehicles that can be deployed autonomously to track underwater currents. The results of several afternoons of experiments, where the vehicles were kept at depth, indicate the passage of several internal waves, illustrating their utility. However, a time consuming and complicated aspect of their deployment is the installation of a surface array with tightly controlled GPS and time signals that is then used for localization. If some way could be found to use ambient noise to judge inter-float distances, the general deployment scheme would be greatly simplified. As one candidate, ambient noise correlation may provide an accurate way to judge inter-float distances obviating the necessity of deploying the surface array. In this abstract, promising preliminary results are reported.