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We introduce a low data rate video compression scheme for underwater acoustic communication. Recently, multi-carrier based underwater acoustic modems have been proposed and tested for data rates of up to tens of kilobits-per-second for about 1–4 kilometers transmission range. Online transmission of video data using these rates requires extreme compression. Herein, we propose pre-encoder and post-decoder...
Owing to the special economic position and environment protection requirements for shallow water, shallow water acoustic communication becomes a hot research area in recent years. The frequency-hopping (FH) technique being considered as one robust and reliable communication plays a vital role in communication system design, because of the characteristics of shallow water channel, e.g., strong multipath,...
This paper proposes a new method for detection of the vortex presence in fluid flow based on an active acoustic system. The experiment that validates the theory was done on a reduced scale facility using ultrasonic transceivers. The main objective was to highlight the effect of a cavitation vortex on an applied wide band signal. In order to accomplish that, the Recurrence Plot Analysis (RPA) was investigated...
In an inverse problem of ocean acoustic current mapping, prior information about the unknown current fields is usually required to better determine model parameters due to finite number of the acoustic rays. An iterative inversion method is applied to tomographic reconstruction of horizontal ocean current field to improve the estimate of current fields while prior information of the current distribution...
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...
Underwater acoustic measurements are made to provide validation and qualification for a wide range of applications and developments in the off-shore industry, oceanography, defense, fisheries, and geophysics. However, measurements are only meaningful if they are performed in a technically sound manner and if they can be related to common standards of measurement. In this paper, a summary is given...
Floating breakwaters are commonly used for wave protection of onshore and offshore facilities in the last decade. The majority of the floating breakwaters developed in the past are solid-type structures that have fixed drafts and may be highly reflective to the incoming waves. In this study, the H-type floating breakwater is proposed to serve as a wave attenuator instead of a wave reflector. The buoyancy...
In this paper, we describe and demonstrate for the first time in the literature a light-weight joint underwater acoustic channel estimation and data detection (JOCEDD) procedure. The procedure generates iteratively channel estimates and data decisions with guaranteed convergence. No pilot signaling is required (blind/unsupervised scheme), except for one-shot overall data frame sign/phase ambiguity...
Human listeners are capable of segregating and recognizing the class of signal better than machine recognizer in complex noisy conditions. In this paper, we proposed a novel approach for underwater target recognition applying auditory slow feature analysis (ASFA) based on gammatone (GT) filter and slow feature analysis. Our experimental evaluations show that the ASFA feature was proved to be considerably...
The significantly slower propagation speed of acoustic signals, in contrast to RF signals, make the protocol design differ from RF wireless networks. This paper presents an efficient link scheduling method applied to underwater acoustic networks based on TDMA by analyzing the four conflict model in wireless network, and puts forward a conflict description method based on correlation matrix. The proposed...
The intensive cultures have expanded rapidly due to their good productivity. However, the sustainability of intensive shrimp culture is increasingly being questioned. Many problems like disease due to virus, excessive nutrient enrichment, and hypoxic condition around the bottom soil are reported in the intensive culture ponds. In order to solve such problems, the water quality of the culture pond...
Owing to huge amount of kinematic energy, ocean current has the potential to be a base power source. However, ocean current power plant has to be submerged in the sea, making it difficult to maintain; therefore it must have high durability and reliability for long-term operation towards utilization. Equipment design approach considers various loads which occur during normal operation of the plant...
In this paper we propose covariance analysis as a metric for reinforcement learning to improve the robustness of a learned policy. The local optima found during the exploration are analyzed in terms of the total cumulative reward and the local behavior of the system in the neighborhood of the optima. The analysis is performed in the solution space to select a policy that exhibits robustness in uncertain...
The main objective of this research is to enhance the sensitivity of ultrasonic detector device to be applied in the object detection and image acquisition of longer distance. In this experiment, MEMs process technology and sacrificial layer technology are used to prepare micro-bridge structure so as to reinforce the ultrasonic signal sensitivity of PZT thin film device. In this research, Al is adopted...
This paper compares the differences of powersystem stability before and after an offshore wind farm is connected to Taiwan Power System. A commercial power-system simulation software of DIgSILENT is properly utilized to establish the system model of simplified Taiwan Power System connected with the studied offshore wind farm. The operating points, eigenvalues, and time-domain simulations of the studied...
This paper presents the transient simulation results of an offshore wind farm connected to Taiwan Power System using a commercial power-system simulation software of PSS/E. A three-phase short-circuit fault is suddenly applied to one of the six feeders of the studied system. The simulated transient voltage variations, power fluctuations, and frequency deviations can be employed as an operation reference...
In the shallow water environment, detecting and classifying buried objects is a challenging problem with high operational importance. Acoustical wave becomes an important tool in the detection of objects in underwater systems due to its effectiveness of propagation in the water. Later on, the acoustic scattered field modal for fluid-loaded and thin spherical shell have been determined by the shell's...
Considering the scattering and absorption caused by seawater molecules and suspended particles, the characteristics of blue-green laser in seawater are described. Then a transmission model of blue-green laser in shallow seawater is established and the relations of the attenuation of received power and the requisite transmission power to the transmission distance are summed up. Results of the simulation...
Estimation of bottom profile is one of the important geo-acoustic reversal problems in underwater acoustics that gives an idea about depth and structure of the sub-bottom layers of the ocean. Estimation of time of arrival (TOA) of bottom and sub-bottom reflections are the key to these estimations. To estimate TOAs from different bottom layers, an active sonar transmits a signal and receive its bottom...
When an object crosses the source-receiver line, a weak acoustic field aberration would be generated. However, it is often overwhelmed by strong direct blast. A lake experiment with a vertical receiver array spanning along water column was designed and conducted, with a 10 kHz pulse. The interested signal was the aberration caused by the forward scattering of a submerged object. The acoustic field...
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