The use of traditional commercial acoustic modems is typically confined to Oil & Gas and military scenarios, as their high power consumption and steep cost make them inaccessible for many other applications, such as aquaculture, diver commu-
nication and low-cost underwater vehicle swarm. While low-cost acoustic modems are gradually entering the market, flexible re-
search platforms like software-defined acoustic modems (SDAMs) remain prohibitively expensive for small research groups and
startup companies, who, on the other hand, often drive innovation and generate new ideas. As a result, the development of these
technologies, which currently find application in a few specialized contexts, remains constrained.
When considering experimentation, what has empowered do-it-yourself practitioners and students approaching circuits and
embedded systems is the availability of user-friendly and affordable prototyping boards like Arduino and Raspberry Pi.
Following this paradigm, we developed the first Raspberry Pi HAT acoustic frontend for underwater acoustic testing and ex-
perimentation, and hence realized the low-cost Subsea software-defined acoustic Modem (SuM). In this paper we present its
evaluation when used with the JANUS waveform at different frequencies bands, in both salt and fresh water. Given that we
succeeded in proving its technological maturity in sea trials, we believe this modem can be both a valuable platform for industrial
applications and a game changer to encourage other research institutes to experiment underwater communications.

Keywords: Underwater acoustic modem,;software defined modem; sea-trial; tests; low-cost underwater modem.