Multi-modal communications in underwater sensor networks using depth adjustment.

Acoustic communication typically dominates the power usage in underwater sensor networks. As networks underwater have very limited recharging capabilities, this challenges the network's ability to communicate collected data. To balance these conflicting needs, we utilize a sensor network platform with underwater acoustic communication, surface level radio communication, and a depth adjustment system to switch between them. Nodes determine if they should surface to communicate by approximating the network energy usage and data latency given the data transmission size. For a given path, we develop and examine a set of algorithms to select the nodes to rise to communicate the data via radio across the network while taking energy usage into account. We perform a preliminary analysis of the methods and show that for typical networks greedy approaches are nearly as good as centralized approaches, yet require minimal communication overhead and only local information.