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Communication security is a critical and increasingly challenging issue in wireless networks. Signals have the risk of being intercepted in traditional wireless communication because of the wireless propagation characteristics. There is also the same problem for ship satellite communication. The direct antenna modulation (DAM) is a promising secure communication technique, which scrambles signals...
Ultra-Short BaseLine (USBL) positioning systems born as a technology for underwater target tracking from a vessel. Despite they are commonly and efficiently used for this purpose, the recent literature about navigation of Autonomous Underwater Vehicles (AUVs) demonstrates that they can represent a valuable support for these systems. Measurements of the AUV position can be exploited as observations...
In this paper, we continue the discussion about of fast numerical simulation of tsunami wave propagation. In case of seismic event offshore Japan, tsunami approaches the nearest shore in approximately 20 minutes. As the calculation of tsunami wave propagation normally serves as a part of any warning system, speeding up this software results in overall better performance for tsunami warning. Implementation...
In this work we describe an experimental investigation into wideband channel models for acoustic wave propagation in rigid and elastic pipelines operating over the 1∼50 kHz frequency band. We provide frequency domain transfer function measurements for both rigid and elastic pipes, from which time domain responses of the pipeline channel can be calculated. Narrowband impulse responses are studied to...
In this paper, a grid-based matching multiple sources localization (MUSOL) method is proposed and a spatial spectrum about multiple sources positions is obtained. The spatial spectrum obtained by MUSOL can provide a visualization results about the possible region of the multiple sources positions only if the AOA measurements have the right data association. This property permit the MUSOL not to perform...
For a better understanding of the air-sea interactions that occur during typhoons and improved accuracy in typhoon forecasting, the Institute of Oceanography at the National Taiwan University has developed a buoy that can measure meteorological and hydrographic conditions, and transmit the high-precision data in near real-time. The buoy captures various types of meteorological data, including air...
The present research in underwater robotics aims to increase the autonomy of manipulation operations in fields such as archaeology or biology, that cannot afford costly underwater interventions using traditional Remote Operated Vehicles (ROV). This paper describes a work towards the long term goal of autonomous underwater manipulation. Autonomous grasping, with limited sensors and water conditions...
Increasing demand on marine resources is driving the need to more efficiently and effectively enable multiple uses of marine space by different sectors and interests. This raises governance challenges particularly because traditional management practice primarily has been sector and issue-specific. Conceptually, marine spatial planning (MSP) provides an integrated framework that could be a viable...
Laser-induced breakdown spectroscopy (LIBS) is a form of chemical analysis that can determine the elemental composition of targets. LIBS has been used for underwater exploration, at over 1000 m depth in active vent fields, and it can potentially form the basis of an efficient screening method prior to detailed sampling or boring surveys. In this study, a method for in-situ chemical classification...
Photocatalytic technology using TiO2 is one of the emerging approaches for water treatment, especially as a final step to remove complex organics such as pesticides, hormones or humic acids. Titanium dioxide (TiO2) is a semiconductor material with strong UV absorption band and exhibits strong photocatalytic activity. The photocatalytic activity of TiO2 powders have been extensively studied, using...
Long period fiber gratings (LPFGs) were over coated with iron (Fe) and subjected to oxidation in air and in solutions of water containing different sodium chloride (NaCl) concentrations. The formation of iron oxides and hydroxides was monitored in real time by following the features of the gratings attenuation band. Preliminary results show that Fe coated LPFGs can be used as sensors for early warning...
The optimal detector based on matched-field processing with a large-aperture vertical linear array (VLA) suffers from the so called “snapshot deficient problem”, which leads to an inaccurate estimate of the noise covariance matrix and hence a degraded detection performance. In this paper, to improve the detection performance with deficient snapshots, a two-step sub-array detector (SAD) is proposed...
The General Bathymetric Chart of the Oceans (GEBCO, http://www.gebco.net/) training of a new generation of hydrographers and scientists in ocean mapping has been funded by the Nippon Foundation, based in Tokyo, Japan, since 2004. The Nippon Foundation is a private, non-profit foundation, whose overall objectives include social innovation, assistance for humanitarian activities and global ocean management...
This work describes the development and characterization of a wide beam and wideband ultrasonic transducer, designed as an emitter for underwater communications up to 1.5 MHz. The active element being used is composed of two layers of 110 μm PVDF (Polyvinylidene fluoride) film, with NiCu electrodes. The transducer has a semicircular shape with a diameter of 15 cm. Pool trials show a transmitting voltage...
Propulsive performance of harmonically heaving and pitching foil is degraded by a breakdown in the angle of attack profile. In this paper, we build up a two-degree freedom harmonic motion in both heave and pitch motion as the baseline, and compare directly the performance obtained with specific angle of attack profiles and three-degree freedom harmonic motion. We set these profiles are: a square,...
Field optical measurement results show that a classification study of inshore water is necessary. Typical dehazing methods rely on a dark channel model using global rough estimates of back-scattering, that performs poorly on inshore underwater image restoration. This paper introduces a restoration approach to the problem that focuses on inshore water body optical properties. The method introduces...
This paper deals with accurate navigation for underwater remotely operated vehicles. A feasibility study for a multi-pressure device to be mounted on an ROV is presented. The device can provide accurate estimates of a ROV orientation and angular speed. It is based on the well-known total pressure principle, also used in a Pitot tube, and allows reconstruction of static and dynamic pressures, which...
This paper proposes a superdirective beamforming method for dual concentric circular hydrophone arrays based on the previously established eigenbeam decomposition and synthesis model. The optimal solutions of superdirectivity, including the optimal beampattern, the global directivity factor, and the total sensitivity function, are all decomposed into corresponding sub-solutions termed eigenbeams,...
The Autonomous Underwater Vehicle (AUV) will suffer severe impact load during the water entry, sometime this load may cause structural failure of AUV. In order to decrease the impact load level, a design and cushioning properties analysis of mitigator for AUV is presented in this paper. Numerical simulations based on Arbitrary Lagrangian-Eulerian (ALE) method are carried out so as to study the mitigation...
Autonomous underwater vehicles (AUVs) are used to execute an increasingly challenging set of missions in commercial, environmental and defense industries. The resources available to the AUV in service of these missions are typically a limited power supply and onboard sensing of its local environment. Optimal path planning is needed to maximize the chances that these AUVs will successfully complete...
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