What about a fully autonomous submersible that surfaces periodically to get its bearings from GPS, upload data, recharge through solar, etc...
It could be programmed with a certain number of goals and priorities and follow the goal with the highest priority given some parameters.
Or, what about using low power radio to communicate relatively short distances to other submersibles scattered upward toward the surface, forming a mesh network that eventually has an endpoint connected to the ship or satellite?
