Underwater LF wave propagation study for positioning

In 1998, JAMSTEC started the development project of the first prototype of a long-range cruising AUV (LCAUV) to evaluate fundamental technologies needed to travel through under the ice covered area of the Arctic. In 2005, The LCAUV, Urashima, achieved 317 km continuous cruising powered by a deep sea fuel cell developed in JAMSTEC [1]. We then moved to next stage and have conducted to design the second prototype LCAUV with target range of over 3,000 km. It included improvement of power source, communication system, and positioning system. In 2010 a small high efficiency multi-less (HEML) fuel cell was completed [2] and a long range acoustic communication system achieved 1,000 km communication using time-reversal waves. But we had not developed practical positioning system for under the ice by 2010. In past years the dramatic melting of Arctic ice would be driving extreme weather. This is very serious problem, but it is still poorly understood. Scientists need more research to understand it. We have thus a plan to develop an Arctic research platform that especially performs observations under the ice. Now we are conducting a research of a new positioning method with communication availability before developing the platform or an AUV. The proposed method is based on low frequency electromagnetic waves which can propagate inside of ice and sea water. A prototype to evaluate the method is like GPS repeater. The repeater to be set on the ice receives GPS signal, transmitting radio waves into the sea water via the ice up to several tens meters deep. To realize the system feasibility we started developing underwater antennas and measuring wave propagation in the sea ice and the sea water in 2016.