Landing motion control of an underwater glider for ocean floor resources exploration

Ocean floor resources such as sea-floor hydrothermal deposit, methane hydrate and manganese nodule are promising resources for future ocean development. It is becoming apparent by recent research that certain amount of these resources deposit also near Japan. Though several kinds of exploration methods such as seismic exploration, a multi-beam echo sounder and a sub-bottom profiler which are equipped with a survey ship are used for the resource explorations in general, these exploration methods need a large amount of cost and efforts. On the other hand, an autonomous underwater glider which equips an OBEM (Ocean Bottom Electromagnetometer) which has been developed in the author’s laboratory is a hopeful instrument for the ocean floor resources explorations. The autonomous vehicle has an ability to achieve a continuous resource exploration autonomously for a long term. The buoyancy and attitude control mechanism enable the vehicle to move to the next measurement point by gliding. The landing point for the measurement must be precisely controlled by the motion control system because the vehicle measures the slight variation of electromagnet wave on the sea bottom. The performance in a landing stage is essential for the motion control of the vehicle. Here, the motion control system of a weight shift device in the vehicle’s pressure container is developed for a landing stage. The authors attempt to make clear the performance of the controller in this report. Moreover, the characteristics of a buoyancy control device is examined by tank experiments. This unit is used to raise the vehicle to an appropriate height for the next gliding.