Search

We are developing an underwater glider for virtual mooring. It can remain in a designated area for several years, moving between the sea surface and the seafloor up to 2,100 m deep, monitoring the sea environment. It can sleep on the seafloor or while drifting in water to extend the monitoring duration. If drifting far away from a designated area, it can glide back to the target point. If it is just at the target point, then one method to maintain its position is to glide spirally. As described herein, we present the spiral gliding tests results. We also evaluate some elements that affect the turning characteristics by simulation and demonstrate that simulation results agree well with experimentally obtained results. Results confirmed that spiral gliding is useful to maintain a position. Moreover, a small misalignment of wings can affect the rotation characteristics.

We have developed a new system for real-time observation of tsunamis and crustal deformation using a seafloor pressure sensor, an array of seafloor transponders and a Precise Point Positioning (PPP ) system on a buoy. The seafloor pressure sensor and the PPP system detect tsunamis, and the pressure sensor and the transponder array measure crustal deformation. The system is designed to be capable of detecting tsunami and vertical crustal deformation of ±8 m with a resolution of less than 5 mm. A noteworthy innovation in our system is its resistance to disturbance by strong ocean currents. Seismogenic zones near Japan lie in areas of strong currents like the Kuroshio, which reaches speeds of approximately 5.5 kt (2.8 m/s) around the Nankai Trough. Our techniques include slack mooring and new acoustic transmission methods using double pulses for sending tsunami data. The slack ratio can be specified for the environment of the deployment location. We can adjust slack ratios, rope lengths, anchor weights and buoy sizes to control the ability of the buoy system to maintain freeboard. The measured pressure data is converted to time difference of a double pulse and this simple method is effective to save battery to transmit data. The time difference of the double pulse has error due to move of the buoy and fluctuation of the seawater environment. We set a wire-end station 1,000 m beneath the buoy to minimize the error. The crustal deformation data is measured by acoustic ranging between the buoy and six transponders on the seafloor. All pressure and crustal deformation data are sent to land station in real-time using iridium communication.

We are now developing a prototype underwater glider for long-term virtual mooring. It can land on the seafloor and remain inactive (sleep) there for a predetermined time to extend its monitoring period. If the seafloor is too deep, then it can sleep while drifting underwater. If it drifts because of the sea current, it will glide back to the designated area and remain there for more than one year. We have conducted a series of sea tests in the initial stage and confirmed its basic functions including landing-sleep, drifting-sleep, and heading control. To extend the maximum descent depth, we are also developing ceramic pressure-tight housings. Because of the high compressive strength of ceramics, we expect to be able to extend the maximum depth of the underwater glider to 6,000 m, which covers more than 98% of the world oceans. As described herein, an outline of the prototype underwater glider and sea test results is presented. An outline of the ceramic pressure-tight housings is also presented.