Acoustic tomography with an underwater sensor network

Underwater acoustic tomography is a known technique that is traditionally used at large scales to gather temperature and current data about the oceans. Performing acoustic tomography underwater is desirable because it permits information to be derived about the properties of the water between senders and receivers, thus increasing the spatial resolution of the data as compared to only sensing locally at each node. The principals of the technique also apply at much smaller scales (e.g lakes, marinas, bays); however, due to several challenges that must be overcome, acoustic tomography systems have not been developed for small bodies of water. Using an underwater sensor network we have developed a system that can perform underwater acoustic tomography at scales down to 50 meters. Like all sensor networks, underwater sensor networks leverage a network of distributed sensor nodes to perform sensing. In this work we show how to take advantage of such a network to perform acoustic tomography. We discuss the challenges to building such a system and describe the system design and signal processing techniques we have developed to overcome these challenges. Additionally, we present experimental results from a deployment in a marina. The experiments show that our system is capable of measuring water temperature between the nodes using acoustic signals and can deliver 2D temperature maps of the marina.