The journey of the electronic plastic bottle (2020)

> Duncan and Davies actually cobbled together two generations of electronic bottles. Their first generation of devices, the ones that sailed along the Ganges, had plenty of cell towers to ping along the way, so a SIM card would do. But the researchers also wanted to see how plastic bottles might behave once they get to the ocean. So they outfitted a second generation with GPS. Here they took inspiration from their prior work tracking sea turtles: GPS works great on the open ocean, far away from any cell service. (Their designs are open source, so any plastic researcher can build their own, and even improve upon the system.)

So cellular networks in the earlier system doubled as a localization + communication system. GPS is useful only for localization - I assumed they use satellite for actually communicating with and tracking the bottle?