November 5, 2019

KTH Sweden Underwater Sensing Buoy

Professor Jakob Kuttenkeuler and Jari Krützfeldt of the KTH Maritime Robotics Laboratory at the Royal Institute of Technology of Sweden developed the LoTUS (long-term underwater sensing) buoy, a system for collecting oceanographic data from perhaps the most remote place on the planet – the polar region seafloor. Long-term data about the conditions there are vital for understanding complex processes such as ocean currents, melting and refreezing of ice, circulations etc.

In the past, the primary tool for investigating these entities were large ship-based expeditions that were both costly and logistically difficult to conduct. The idea behind the LoTUS system is to offer a small, affordable, lightweight and simple-to-use tool for monitoring conditions on the seafloor.

The LoTUS consists of a spherical polystyrene shell attached to an anchor, known as a bottom lander. The shell can withstand conditions found at depths down to 2000m and contains all the necessary hardware for long-term sampling of temperature, current, conductivity and pressure.

Upon reaching an area of interest, the LoTUS is launched from a ship (with an aircraft launch in the works) and quickly sinks to the seafloor. Data samples are taken every hour or so, and are stored in the LoTUS EEPROM memory which offers a data retention capability of over 100 years. After a pre-set duration, e.g. 1-10 years, the LoTUS buoy will separate from the anchor thanks to electrolytically accelerated corrosion of a steel coil. The LoTUS buoy will then float back up to the water’s surface which will hopefully be ice-free.

At the surface, the LoTUS buoy will be thousands of kilometers away from the closest research team and will likely not be collected by an expedition any time soon. Thus, it will be necessary to send its valuable data back wirelessly. It’s here that the RockBLOCK Mk2’s satellite communications capability comes into play.

As soon as a clear view of the sky is detected by the RockBLOCK, a couple of hundred SBD-messages containing compressed LoTUS data are transmitted up to Iridium. This data is then sent to Rock Seven (now trading as Ground Control) servers which, in turn, push it to an endpoint specified by the research team.

Following the completion of the first part of its mission as a bottom lander, the LoTUS now has a new lease on life as a drifter beacon. For the next few months, it will measure and transmit both buoy GPS positions and surface water temperature, sending data back to researchers in near real-time.

With the help of the newly established Iridium link and the Ground Control API, it will then also be possible to reconfigure the LoTUS buoy’s sampling interval and duration so as to save battery and extend the surface mission further.

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