LoTUS-mätsonden monterad på CTD:n för test. Foto: Jari Krützfeldt
Most of the measurements done during the Petermann expedition on Oden give scientists either a pictures of the current situation or they enable them to look back into the past, often for several thousand years. But what about future developments, what is happening here when we are leaving?
My master thesis at the KTH Royal Institute of Technology in Stockholm was centred around this question. How can we acquire long-term time series of temperature data in remote polar regions? At the beginning of this year I started with trying to find an answer. The Petermann expedition 2015 gave me the opportunity to test the sensing system that we at the Centre for Naval Architecture at KTH have developed and build, the LoTUS bottom lander system. LoTUS is short for Long Term Underwater Sensing and that is exactly what we want to achieve with this project. But let me explain what that means, and what a bottom lander is.
The LoTUS bottom lander system consists of a positive buoyant, football-sized buoy and an anchor. The buoy is basically a thermometer, which is thrown into the water. It sinks due to the anchor and eventually lands on the sea floor where it is moored. As easy as it gets! However, this thermometer measures temperature for up to 10 years in water depths up to 2000m, it is equipped with satellite communication, GPS, deep-hibernating sleep function and much more technical stuff that is needed to accomplish such a mission.
The buoy stays moored at the sea floor until its timer triggers the electrolytically accelerated corrosion anchor release at a pre-set time. Afterwards the buoy rises to the water surface and sends its data home via satellite. The advantage is that nobody has to come back to collect it!
If the buoy gets trapped underneath ice (which is very likely to happen in this waters), the buoy can wait for several years, checking every month if it is able to transmit its data. When the main task, which is sending the temperature data, is accomplished, the buoy re-configures itself and acts as a GPS beacon afterwards. This is called a ‘drifter’ and what it does is, it floats on the water surface following the currents and sends out its position regularly. That way one can observe the current direction and velocity.
Now, the first LoTUS bottom landers are deployed in the Petermann Fjord and so far everything went well (at this point that means that they sunk 🙂 ). More to hear from them hopefully in the coming weeks and month!