Underwater low-frequency sound triggered by submarine earthquakes (5 to 20Hz) can travel great distances in the oceans, and it can be detected at thousands of kilometers from the epicenter. As a variety of geological and physical oceanographic features can cause horizontal refraction, reflection, and diffraction, 3D underwater sound models are required for accurately predicting global scale...
On 9 April 2019, flight control of the Japanese Air Self-Defense Forces lost contact with a F-35 fighter plane deployed on a training exercise off-coast northern Honshu, Japan. Floating debris recovered during the initial phase of the search and rescue mission suggests that the plane may have crashed, its last known position being communicated as approximately 135 km east of Misawa Airbase,...
The end-to-end calibration from the hydrophone ceramic element input to the digitizer output of CTBT IMS Hydroacoustic (HA) hydrophone stations is measured in a laboratory environment before deployment. After the hydrophones are deployed permanently with the Underwater System (UWS) hydrophone triplets, the response of the digitizer component can be measured by activating remotely a relay which...
When considering acoustic events of impulsive nature in the ocean that generate shock waves as detonation of explosive charges (especially those close to free surface or seabed), air-guns, electric shocks or collapses of metallic objects or glassware, we should be especially careful verifying the conditions of validity of equations used in the range of distances, depths and frequencies of...
The CEA/DAM has developed the DTK (Dase ToolKit) suite of software dedicated to array processing, which is available in the NDC-in-a-Box package delivered by the PTS since 2016. Originally designed for processing infrasound and seismic data, the software package has evolved during the past two years, with significant efforts carried out to extend the existing functionalities to hydroacoustic...
The concept of a modular alternative for the current linear hydroacoustic triplet design has been the focus of significant development by the University of Washington Applied Physics Laboratory (APL-UW) in recent years. A number of options have been studied from the perspective of two key criteria: the desirability of maintaining the existing highly effective linear deployment method, and the...
The existing infrastructure of the six Hydroacoustic Systems spans remote locations of the world. The first of these systems at Diego Garcia is reaching its 20 year life and consideration to the maintenance and replacement of the systems is ongoing. This presentation will discuss opportunities to incorporate advancements in active junction box design, facilitating the inclusion of wet-mate...
Real-time monitoring and early detection of undersea volcanic activity are indispensable in relation to disaster reduction, however it remains difficult to implement continuous in-situ observation of undersea volcanoes due to their difficult accessibility compared to above-surface volcanoes. International Monitoring System (IMS) hydroacoustic stations, which are equipped with triplets of...
Marine seismic surveys make use of a ship-towed air-gun array. The compressed-air shots fired into the water generate impulsive sound wave fronts whose reflections are recorded to map the oceanic crust. These intense sounds cause depletion of the local zooplankton [1], and can impact the detection capability of the CTBTO hydroacoustic stations and their automated processing [2]. It is...
Each of the six IMS HA hydrophone stations consists of two triplets (one north and one south triplet), except for HA01 Cape Leeuwin (Australia) which has only one triplet. The hydrophone triplets are designed for a minimum 20 year-life, with no scheduled maintenance required. In the current robust design, triplet nodes and components are linearly interconnected in such a way that the repair of...
Activities of Monowai Volcanic centre have been observed as seismic waves recorded at Rarotonga station (RAR), as well as hydroacoustic waves recorded at Ascension Island (H10). Beamforming has been performed on the hydroacoustic data to verify the source and study the effect of performing calculations with a best beam. The lag time that is calculated by cross correlating seismic and...
Deployments of real-time offshore observatory stations could contribute to enhancing early signal detection of hydroacoustic, seismic, and tsunami phases and also to improving accuracies for source analyses of the phases. We investigated pressure gauge data recorded at offshore stations in northeast and southwest Japan to develop an estimation method of providing rapid and reliable magnitude...
On 15th November, 2017, the CTBT IMS hydroacoustic stations HA10 (Atlantic Ocean) and HA04 (southern Indian Ocean) detected an unusual impulse-like event whose estimated location was in the vicinity of the last known position of the missing Argentine submarine ARA San Juan (EGU2018-18559, 2018). This detection and localization was further confirmed by a controlled air-dropped depth charge...
Ocean weather can have a dramatic impact on maritime operations, particularly in areas where weather conditions change rapidly and in extreme ways. Several locations where International Monitoring System (IMS) Hydroacoustic (HA) hydrophone stations are located are characterized by such rapid and extreme variability. For this reason, weather conditions have always been monitored carefully...
In Japan, some offshore real-time monitoring systems have been deployed off the coast of the Pacific Ocean including the Nankai Trough Seismogenic zone and the Tohoku Seismogenic zone (i.e., the Japan Trench). DONET and S-NET have been deployed in the Nankai Trough and the Japan Trench, respectively, since the 2010s. Now, new development of next generation real-time monitoring system namely...
The Japan Trench is one of the most unique zones covered dense seismic networks in a wide area. National Research Institute for Earth Science and Disaster Resilience operates 150 seafloor seismic observatories, and Earthquake Research Institute, the University of Tokyo has 6 seismic stations. Each seismometer is linked with optical fiber cables, and the data are transmitted to Japan...
Small underwater events are often detected by the seismometer and hydrophone stations of the International Monitoring System (IMS) and the Global Seismographic Network. In this study, signals from the 15 November 2017 Reviewed Event Bulletin hydroacoustic event in the South Atlantic Ocean that occurred around 550km east of Argentina are analysed along with signals from a nearby depth charge...
This paper describes the results of applying a statistical method for long term and seasonal trend analysis and uncertainty evaluation from deep-ocean noise data. The analysis method uses a flexible discrete model that incorporates terms that capture seasonal variations in the data together with a moving-average statistical model to describe the serial correlation of residual deviations, with...
The oceans are generally not quiet places. Sound sources are ubiquitous and include surface wind including storms, distant and local shipping, seismic surveys, earthquakes, marine mammals and lightning. In the low frequency band (below 125 Hz), sound travels to very long distances. In this paper, we present a modeling approach based upon the efficient Parabolic Equation that can generate the...
The Engineering and Development Section of the International Monitoring System (IMS) Division is responsible for the installation and maintenance of the hydrophone based hydroacoustic stations within the CTBTO’s IMS. All hydroacoustic stations are now installed, certified and providing near real-time hydroacoustic data to the International Data Centre in Vienna, Austria. Five of these stations...
The International Monitoring System (IMS) of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) comprises eleven hydroacoustic stations to monitor the world’s oceans for nuclear explosions. Five of these are T-phase seismometer stations while six use water-column hydrophones cabled to shore providing real-time data to Vienna. The hydroacoustic network is the only of the four CTBT...
Solving propagation in a three-dimensional environment is one of the most challenging problems in computational physics. However, for cases where the environment possesses some kind of symmetry be it rotational or translational, the propagation problem can be simplified considerably. It can be shown that in problems where the environment is translationally invariant, the 3D wave equation can...
The ocean is nearly transparent to acoustic energy at low frequencies, particularly those sampled by the United Nations Comprehensive Nuclear-Test-Ban Treaty Organizations (CTBTO) hydro-acoustic network (sample rate 250 Hz). This phenomenon is specifically what makes global coverage in support of the test-ban successful. Low frequency sound is less well trapped in the global sound channel and...
A three-dimensional (3D) parabolic-equation (PE) model has been created to simulate global scale underwater sound propagation. This 3D PE model utilizes a map project to transfer the surface of the Earth to a Cartesian plane, which enables an efficient solution marching algorithm. This model also incorporates a data-assimilated global ocean model, the HYbrid Coordinate Ocean Model (HYCOM), and...
We develop a method to retrieve phase-velocity in the SOFAR channel between two neighboring IMS hydroacoustic arrays (HA) for the purpose of monitoring deep- ocean temperature variations which are sparsely sampled. Previous studies Wolf et al., 2015; Evers et al., 2017; Sambell et al., 2019) have used an ambient acoustic field cross-correlation approach to resolve lag time as a proxy for...
Myanmar has long coastal areas and need to set up ocean observation systems. Department of Meteorology and Hydrology set up sea level observation stations at along the coastal areas of Myanmar and also monitoring the disaster including the tsunami disaster. Myanmar have been suffered many times of earthquake disasters and four times of tsunami by known the historical data. The purpose of this...
There is a growing interest for a very low frequency sound source in the frequency range below 40 Hz for such applications as Arctic under-ice thermometry, long-range navigation, sub-bottom seismic profiling, and etcetera. A coherent ultra-low frequency sound source is a quieter and more benign to marine mammals than air-guns, used for the oil exploration. Teledyne Marine recently developed...
This paper describes a statistical method for performing long term trend analysis and uncertainty evaluation of the estimated trends from deep-ocean noise data. The measured data used originate several of the hydro-acoustic monitoring stations of the CTBTO and span up to a maximum of 15 years. The analysis method uses a flexible discrete model that incorporates terms that capture seasonal...
Long term ocean acoustic noise data from CTBTO sites at Wake Is., Ascension Is. and Diego Garcia, spanning periods of up to 15 years, have been analyzed through an effort sponsored by the US Office of Naval Research. Data were Fourier Transformed in 10-sec segments to provide noise spectra with a resolution of 0.1 Hz. Low-frequency spectrum level time series data were then examined for two...
