This is the transducer for the AquaModem – an underwater acoustic modem developed for shallow water littoral zones, specifically the lagoon surrounding the island of Moorea (a small island off the coast of Tahiti). The University of California has a research station there dedicated to the study of coral reefs. I spent about a week with several graduate students testing this modem in Summer 2007. This involved going out on a couple of boats, anchoring the transducers on the lagoon floor or on coral bommies (like the one in the picture) at various distances and sending data from one to the other. It’s a tough job, but someone’s gotta do it.