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In this research, the automatically analyzation method which detect acoustic events such as fin whale calls and its locations is embedded in cable observatory system. This system has detection method about fin whale calls using spectrogram correlation, and the localization of fin whale calls using two hydrophones and a three-axis seismometer. This observation at off Kushiro-Tokachi has been continuously...
We have developed an automated cable-laying system that is operated with a remotely operated vehicle (ROV) and can automatically dispense a thin optical-fiber submarine cable at a rate that keeps pace with the ROV's ground speed. The use of an ROV allows to install a thin optical-fiber submarine cable on the deep seafloor accurately and safely. The ROV-based automated cable-laying system is being...
Many animals in the ocean produce sounds for mating choice, territorial defending, group cohesion and echolocation. Sound travels much longer distance in the water comparing with light that makes the acoustic waves efficient for long distance communication and sensing. The species or family specific sounds can be used to identify not only the presence of animals but also counting the number and density...
NEC is participating in the development of the next-generation marine resource investigation technology “The development of the cable type observation system” which is one of the development items in the SIP project. Under the technical guidance of JAMSTEC, NEC developed DONET system which has NODE equipment. Special feature of NODE system is ocean bottom observation equipment mobility, expandability...
DONET (Dense Oceanfloor Network System for Earthquakes and Tsunamis) is a cabled observation system for long-term and real time monitoring using precision sensors on the seafloor. The development and the manufacturing of DONET2 system were commenced in 2013, and the construction was completed on schedule in 2016. In this paper, the DONET2 system and its installation technologies are introduced.
Real-time borehole observation system for seismogenic zone monitoring called long-term borehole monitoring system (LTBMS) was developed to give better access to the seismogenic faults nucleating earthquakes while avoiding observational effects of dampening by shallow soft sediment and oceanographic noise commonly experienced in the seafloor observation. Installation of the LTBMS has been conducted...
As part of the Next-Generation Technology for Ocean Resources Exploration project in the Cross-ministerial Strategic Innovation Promotion Program (SIP) of the Japanese government, Japan Agency for Marine-Earth Science and Technology (JAMSTEC) is promoting the development of the cabled seafloor observatory system which allows long-term monitoring of hydrothermal vents and ecological changes. Exploring...
We assessed a quartz pressure sensor characteristics assuming an ocean bottom and borehole environment in the laboratory. Accuracy evaluations of the hydraulic pressure sensors with a scale of 1 hPa are required for obtaining small pressure change related to crustal deformations on the seafloor. However, quantitative assessments to understand pressure sensor characteristics are not performed yet....
Studies about ambient noise have been investigated on the North Pacific, the Atlantic oceans and so on. It has been clarified that the increasing ship traffic correlated with an overall increase of the ambient noise level. However, the ambient noise level has not been well measured and analyzed in Japan's coast. Recently, DONET (Dense Oceanfloor Network System for Earthquakes and Tsunamis) was constructed...
A previous research reported that the cable system off Kushiro-Tokachi was detected low frequency calls of fin whales. In this research, as an application using cable observatories about “development of remote species identification technologies for marine organisms”, we developed a real-time processing system for underwater acoustic signal with cable observatory. This paper reports the results of...
Utilizing a variety of substances which exist in seafloor as resources has a possibility to influence on the environment. The practical use of seafloor resources needs a development of environmental impact prediction method and a development of framework to carry out the continuous environmental impact assessment. A submarine cabled observatory is plant to deploy to hydrothermal activity area in submarine...
We have installed the Dense Oceanfloor Network System for Earthquakes and Tsunamis (DONET) that includes 20 observatories at Kumanonada (called DONET1) for the purpose of monitoring the seismogenic zone around the Nankai Trough. During the construction of DONET1, a remotely operated vehicle (ROV) was successfully used to lay the optical-fiber submarine cables that connect the observatories with the...
DONET, i.e., the dense ocean-floor network system for earthquakes and tsunamis has started its operation in the Nankai Trough, SW Japan in the early of 2010. DONET in 20 observatories consists of various geophysical sensors such as broadband seismometer, seismic accelerometer, tsunami meter, and so on. The present study focuses on pressure sensors being used as tsunami meters measuring hydraulic pressure...
The seismometer used in Dense Oceanfloor Network system for Earthquakes and Tsunamis (DONET), is buried under the seabed to suppress the background noise [1]. To make a hole for burying the seismometer, a new caisson installation technique using hydraulic vibration hammer is developed. This paper describes the detail of the hammer, a field test, and a trial test in deep sea.
Feasibility of monitoring seismic velocity structure using seismic noise observed in the seafloor is demonstrated through two different types of waves, infragravity wave in 0.005 – 0.02 Hz and microseisms in 0.1 – 3 Hz. The examples of seismic velocity measurement using these waves are shown by observation data obtained by seafloor observatories deployed in the Nankai Trough south of Japan seafloor.
We developed a new cabled OBS (Ocean Bottom Seismometer). The OBS was designed to achieve time synchronized seismic vertical array acquisition with borehole seismometers by being deployed on the seafloor and connected to borehole observatory network system. The OBS comprises 3-component geophone unit, telemetry unit and battery unit installed in each pressure housing. We used 4.5 Hz type geophone...
In seafloor seismic observation, the seismometer is usually installed on the seafloor. The data obtained from the seismometer installed on the seafloor is influenced by background noise. Therefore, in seafloor observation, it is necessary to install seismometer with consideration of influence depending on installation environment for observation with high accuracy. We investigated that whether the...
DONET (Dense Ocean-floor Observatory Network for Earthquakes and Tsunamis) is a submarine cabled real-time seafloor surveillance infrastructure for earthquake activity at assumed focus region of mega-thrust earthquake around Japan. The original system DONET1 was constructed in To-Nankai earthquake focus region and twenty seafloor observatories are working in operation beginning in 2011 to contribute...
We report performance characteristics of borehole seismometers installed in the C0002G observatory located at the Nankai Trough seismogenic zone, Japan. We conducted initial data processing including 1) Power spectral density analysis calculated from short-term records. 2) Running spectrum analysis using continuous long-term data. 3) Estimation of sensor orientation for borehole seismometers. We then...
DONET (Dense Ocean-floor Network system for Earthquakes and Tsunamis) is a submarine cabled real-time observation network for earthquakes and tsunamis monitoring around the Nankai trough, southwestern Japan. The scheduled twenty observatories have operated since August 2011. Various sensors such as a broadband seismometer, a pressure gauge, a hydrophone, etc. are equipped with each observatory, because...
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