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40 The group has also been working on acoustic comms and took Janus as the basis of that development. Janus defines the encoding in purely mathematical terms, and although the frequencies and timings were selected with real-world hardware and software implementations in mind, how signals should be encoded or transmitted is not specified, and the implementation is left to the individual developer. For AUV comms, the requirements vary tremendously. Status monitoring or issuing simple mission commands to the vehicle can still be achieved with a low- bandwidth link at tens of bits per second; sending real-time sensor data can be achieved at perhaps 100 bps. Higher bandwidth sensors such as those that profile the ocean currents, or multi-beam echo sounders, generate point-cloud data that needs a kilobit/s connection, while acoustic imaging systems such as sidescan sonar and bottom profilers would push the limits of current acoustic comms technology. So SWiG is looking at a first draft of a system based strongly on Janus but with a new centre frequency and enhancements to the data link and transport layers to reflect the needs of AUVs used by the offshore oil and gas community. The next priority will be to develop an application layer interface, which is likely to be based on an existing open standard. The US defence research agency DARPA is also working on very low frequency signals, between 3 kHz and 30 kHz, that would use the atmospheric corridor between the Earth’s surface and the ionosphere to send low-frequency, low-bandwidth signals around the planet and also work in water to communicate with AUVs around the world.  The agency has a project called A Mechanically Based Antenna that aims to produce a comms tool that would be small and light enough to fit into an AUV. It would generate signals by mechanically moving materials in which strong electric or magnetic fields are stored.  Much of the physics has still to be August/September 2017 | Unmanned Systems Technology Focus | Sonar systems SWiG is looking at a first draft of a system based on Janus but with a new centre frequency and enhancements to reflect the needs of oil/gas AUVs Testing out the Janus acoustic comms technology at the Centre for Maritime Research and Experimentation in the sea off the coast of Italy (Courtesy of NATO)