Yasuhisa Ishihara

Development of an oceanographic observation buoy for rough and icy sea conditions

Performing oceanographic measurements from the sea surface to the sea bottom is technically challenging under rough or icy sea conditions. As a measure to deal with rough seas, a new dynamic simulation program was developed and its validity was verified by comparison with the results of actual sea tests. This program can therefore be used as a design tool. To develop countermeasures against icing, we carried out basic tests in a large-scale snow and ice laboratory. Some of these countermeasures were then implemented in real sea tests and were found to be effective under icy conditions. These results indicate that deployment of moored surface buoys in regions of rough and icy sea conditions will soon be practical.

Buoy Platform Development for Observation of Tsunami and Crustal Deformation

We constructed a buoy system for real-time observations of tsunamis and crustal deformation in collaboration with the Japan Agency for Marine-Earth Science and Technology, Tohoku University, and the Japan Aerospace Exploration Agency. The most important characteristics of our system are resistance to the strong sea currents in the large-earthquake rupture zone around Japan (e.g., the Kuroshio maximum speed > 5 knots), and the capability to transmit data in real-time. Our system has four units: (1) a buoy station with a GPS/Acoustic station serving as a central base, (2) a wire-end station (WES) 1,000 m below the sea surface that serves as a staging base, (3) a pressure seafloor unit (PSU) comprising a pressure sensor, and (4) six GPS/Acoustic transponders to measure crustal deformation. The pressure data used to detect tsunamis and the vertical component of crustal deformation are sent to the land station via the wire-end and buoy stations at intervals of 1 h in normal mode and 15 s in tsunami mode. The data measured between the buoy and six transponders are also sent to the land station at 1-week intervals. The Iridium satellite is used for data transmission of all data to land station. The dynamic range for pressure observations is + ∕− 8 m with a fine resolution of 2 mm, and the accuracy of the crustal deformation measurements is less than 1 m. We tuned the system for an observation period of 5 months and carried out a sea trial. The length of the observation period influences the total system due to the weight of the battery. We rearranged the geometry of the total system to new one with heavier weight and a lot of batteries on the buoy considering long period observation and decided upon a slack ratio of 1.6. In addition, it is important for a long observation period to minimize electrical consumption. We used double pulses for acoustic data transmission between the PSU and WES. The time difference between two pulses indicates the observed pressure value. For the PSU, we designed a tsunami mode on the basis of data from the tsunami generated by the 2011 earthquake off Tohoku, which were recorded by cabled network system data and offline bottom pressure data. The results confirmed that a tsunami can be detected even if the first tsunami signals include strong-motion signals. In this case, the tsunami was detected 10–20 s after the first seismic arrival. During sea trials, we successfully tested the tsunami mode we designed. We succeeded real-time observation of pressure and crustal deformation using buoy system in strong sea current speed area for 5 months. However, there are some issues to be resolved at this moment. For acoustic data transmission, 1 ms step difference of the detection of acoustic signals at the WES, wrong detection of the multiple phases are issues to be resolved. We will consider assigned mapping of transmitted data to the time difference of the double pulses and take measures on the PSU and WES. In addition, we consider strategy to reduce slack ratio in the future. For data transmission from the WES to the buoy station, we experienced electrical unhealthy of the wire rope due to damages by the fisheries activities and the torsion brought by rotation of the buoy. We consider the countermeasure to reduce the rotation.

Development of an underwater glider for virtual mooring and its buoyancy engine

This paper describes the present status of the development of the underwater glider for virtual mooring. It will be able to stay in a designated area for more than one year, moving between the sea surface and the seafloor up to 2,100 m in depth, and monitor the sea environment. It will be able to sleep on the seafloor or while drifting in water to extend the monitoring duration. The first sea-test was conducted in March 2012. In 2013, a new small buoyancy engine was developed and then substituted for the existing one. In recent sea-tests, we evaluated its pitching and heading control performance.

Buoyancy engine developed for underwater gliders

A buoyancy engine with a swashplate-type axial piston pump was developed. Its oil extrusion and drawing properties under high hydraulic pressure were evaluated. This buoyancy engine is now installed in an underwater glider that will achieve long-term monitoring of ocean environments up to 2100 m depth in a designated area with lower operational costs. This bidirectionally functioning pump can control the amount of oil in extrusion and draw operations. When drawing oil under high pressure, the hydraulic pump and the electric motor, respectively, act as a hydraulic motor and an electric generator. The generated electric power is absorbed by a damping resistor. The oil-drawing and extrusion properties were measured using a large hyperbaric chamber that is able to produce an almost identical environment to that of actual operations. Results confirmed stable oil extrusion operations up to 21 MPa. Regarding oil-drawing properties, although it was measured only up to 10 MPa in the hyperbaric chamber, it can be inferred that the system can draw the oil and can control the buoyancy precisely up to 21 MPa by replacing the two-way ball valve with an electromagnetic latching solenoid valve.

Deployment of an ice buoy at 60 °S in the Southern Ocean

Performing oceanographic measurements from the sea surface to the sea bottom is technically challenging under rough or icy sea conditions. In 2011, we tested measures for protecting a buoy under such severe conditions, by incorporating anti-icing and tolerance to high winds and rough seas. Based on the results, we carried out detailed designs of a suitable buoy system. In January 2012, we succeeded in deploying the buoy in the Southern Ocean off the Adelie Coast at 60°S and 140°E. Some of the meteorological and oceanographic data being gathered by the buoy can now be monitored in real time. In this paper, we describe some details concerning the design of the sensor pole and mooring line, in addition to the data already received from the buoy.

Concept design of satellite communications system for next generation marine observation: Broadband IP network down to underwater

Importance of marine observations and developments has been increasingly recognized as a key to many grand challenges of human beings such as development of mineral resources under seafloor, global climate change, etc. The amount of data obtained by marine devices is increasing because many kinds of data from simple ones like temperature to video image and scanned image of seabed are needed for such applications. In addition, real-time observation is required for secure operation of underwater facilities such as underwater oil wells. It is also required for rapid analysis of scientific data such as complex three-dimensional acoustic geological data. On the other hand, communication net-works for marine observations to carry huge data in real-time has not been realized. This paper describes the initial study result of experimental broadband satellite communication systems for next generation marine observations.

Improvements of oceanic and atmospheric measurements on the TRITON buoy

As it takes about ten years since the current TRITON buoys have started being deployed, the current buoys were rather senescent. It has been necessary to develop new measurement equipments for the TRITON buoy. This study introduced the current situation on the development of meteorological sensor systems, water temperature sensor systems, and underwater non- contact data transmission system, which are developing or have been developed in JAMSTEC in the past three years. New meteorological sensors have already been used as a part of the current TRITON system, and have been transmitted data at the same high quality as from the old systems. New water temperature sensor system and no-contact underwater data transmission system is currently under development; however the results of technical experiments indicate the possible high performance towards better observations.

Criterion of reusability of nylon ropes in the TRITON buoy system

The TRITON (Triangle Trans-Ocean buoy Network), the Japans first basin-scale open sea buoy network, is a series of buoys deployed in the western tropical Pacific Ocean and the eastern tropical Indian Ocean by JAMSTEC. The TRITON buoys are equipped with underwater sensors for measuring water temperature and salinity to a depth of 750 m, current, and other meteorological sensors. These observational data are transmitted in real time by satellite communication. These data are utilized for weather forecasts in the world and improve the skill of numerical models, as well as monitoring and better understanding of ENSO (El Nino-Southern Oscillation) and Asian-Australian monsoon. While there is no place for question about significance of obtained data, a large amount of operational expenses are required. Length of mooring ropes used for each buoy maintained every year is so much as order of km and the total expenses on ropes needs for all buoys is also not so small. None the less JAMSTEC has never used the recovered ropes as a practice, because of a lack of the data about properties of the ropes imposed tons of tension after twice mooring periods for almost two years. On that background we reviewed previous results of ordinarily used ropes and carried out another at-sea-test using used ropes. As a consequence we were able to get some data encourage to reuse mooring ropes

Landing-sleep and drifting-sleep experiments of the underwater glider for long-term observation

For long-term monitoring, the authors are developing a prototype underwater vehicle that can sleep on the seafloor or sleep while drifting underwater. Using these functions, it can carry out long-term monitoring of ocean environments while remaining in a designated area. Recent landing-sleep and drifting-sleep experiments yielded good results. Results of these experiments reported herein demonstrate that the landing motion showed good coincidence with the simulation result.

Basic experiments on measurement of salinity using a heterodyne double-pass interferometer

We propose a new method to measure the salinity of seawater using a heterodyne double-pass interferometer. Results of preliminary experiments show that the effect of the temperature was reduced by about one order of magnitude when compared with Michelson interferometer. The measured phase difference between pure water and 3.50/00 salt water of 182.0 degrees was slightly higher than that of the theoretically expected value of 176.0 degrees. The possible cause of this error is discussed in this paper.