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The new multi-beam sonar, Simrad MS70, can transmit over the frequency band 70-120 kHz, and calibration of each individual beam becomes slightly more difficult than for conventional split beam systems. Two new tungsten carbide spheres have been specially designed and manufactured to enable an accurate calibration over the specified frequency band. They are also heavy enough to stabilize the calibration...
Platforms in the North Sea that have reached the end of their commercial life have to be decommissioned in accordance with UK and European Legislation. This paper discusses this process and the challenges involved for the biggest of these structures.
This Paper describes the Extendable Draft Platform (EDP), which has a deeper draft than a conventional drilling semi and a novel construction and deployment method. It then compares the vessel motions behavior of the EDP with a 5th generation drilling semi for a specified high latitude location with a particularly harsh environment including long period swell conditions. Using the motions limits at...
This article presents the formulae and some "rules of thumb" for computing basic performance parameters of synthetic aperture sonar (SAS) systems, with references to relevant literature. Comparisons with traditional side scan sonar (SSS) are given where appropriate. The article then discusses SAS survey patterns and area coverage rate, and presents arguments for and against the addition...
In this paper, we carry out an extensive performance evaluation of multiple access schemes applied to clustered UnderWater Acoustic Sensor Networks (UWASN). Networking underwater sensors poses new and interesting issues with respect to radio environments, as they require to account for unusual channel behaviors, such as large propagation delays, higher energy consumption during transmission as compared...
The NASA-sponsored OceanMotion Web site (http://www.oceanmotion.org) documents humankind's experiences, observations and investigations of ocean surface currents. In addition to the information resources posted on the website, there are also investigations that lead students to explore patterns and relationships through data products (color-coded images, time series graphs and data tables). These...
An AUV (Autonomous Underwater Vehicle) being able to dock without surfacing to a launcher or an underwater station can give us long-time duration. It is important for the AUV to be guided to the dock safely. This paper introduces a test bed platform AUV named ISiMI and her optical terminal guidance system. ISiMI uses the optical terminal guidance system for underwater docking. The guidance system...
Multi-hop underwater acoustic sensor networks constrain the performance of medium access control protocols. The efficiency of the well-known RTS-CTS scheme is degraded due to long propagation delays of such networks. Recently, interest in Aloha variants has surfaced; however, the performance of such protocols within the context of multi-hop networks is not well studied. In this paper, we identify...
Steel structures in the marine environment like Steel Sheet Pile walls at quays and harbors, undergo continuous corrosion subjected to prolong sea water environment. The design of these steel structures currently is been practiced by using respective national annexure in alliance with the Eurocodes. But the correct statistical properties which fit into the semi-probabilistic safety concept of the...
Pulsed, tunable alexandrite lasers in combination with harmonic generators and Raman wavelength shifter form a powerful and versatile tool for lidar (light detection and ranging) remote sensing. Such an integrated laser system can generate any wavelength from ultraviolet to infrared with the necessary beam qualities required for lidar measurement. This paper presents the development of injection seeded...
The present paper describes the current state of the ongoing project of an unmanned aerial vehicle (UAV) intended for surveillance of territorial waters. The UAV will operate from the Portuguese Navy Argos and Centauro class fast patrol boats (FPB), which implies the capability of taking-off and landing in 27 m length, 5.9 m breadth vessels with a small and irregular landing zone at the boat's stern,...
Coastal wind eddies at the 10-40 km scale have been studied over Monterey Bay, California by Archer, Ludwig et al. using shore and buoy anemometers and satellite images. Most frequent in the evening and early morning hours, these, typically cyclonic, eddies are often responsible for fog in the Santa Cruz area. We have previously demonstrated the ability of multifrequency HF radar (4.8 to 21.8 MHz)...
The Kongsfjorden-Krossfjorden system, situated on the northwest coast of Spitsbergen, is connected to the continental shelf slope by a trough, Kongsfjordrenna, that crosses the 50 km wide shelf. Kongsfjorden is the southern arm of this fjord system, and has a maximum depth of 400 m. The fjord system has no typical fjord sill, but Kongsfjordrenna seems to function as a sill of around 270 meters. This...
High data rate communications over underwater acoustic channel is challenging due to time-varying multipath propagation. The orthogonal frequency-division multiplexing (OFDM) is a promising technique for increasing the transmission data rate. However, this requires accurate channel estimation; this can be achieved by using pilot signals superimposed with the data signals. Space-time processing of...
Solar stimulated fluorescence (SSF) signals have been identified as a diagnostic identifier for phytoplankton populations and efforts are underway to relate these signals to algal physiology. However, in coastal waters one must also take into account the effect of algal and non-algal materials on the underwater light field as this could have an impact on fluorescence excitation and propagation to...
The impulse response of shallow water channels that have to be measured during oceanic acoustic tomography experiments consists of many paths with decreasing amplitudes. The estimation of such channels must cope with several problems; in particular, the transmitter transducer strongly distorts the signal. In addition, close paths are generally not resolved at the output of the matched filter. Further...
The project ESONET which is coordinated by IFREMER, France, is a European initiative towards establishing new -and making use of existing- ocean observatories around Europe for observing natural processes that are either very episodic or statistically require long time series. The most important processes are: (1) the episodic release of methane from the seabed affecting climate change, (2) the relationship...
The design and development of the swordfish autonomous surface vehicle (ASV) system is discussed. Swordfish is an ocean capable 4.5 m long catamaran designed for network centric operations (with ocean and air going vehicles and human operators). In the basic configuration, Swordfish is both a survey vehicle and a communications node with gateways for broadband, Wi-Fi and GSM transports and underwater...
Underwater acoustic networks can be quite effective to establish communication links between autonomous underwater vehicles (AUVs) and other vehicles or control units, enabling complex vehicle applications and control scenarios. A communications and control framework to support the use of underwater acoustic networks and sample application scenarios are described for single and multi-AUV operation.
Models that are available for computation of underwater primary production may be classified as available-light models, absorbed-light models, inherent-optical property models or growth models. A systematic comparison of these models reveals that it is simple to transform one type of model into another, and that all these models yield similar results when implemented with comparable parameters. The...
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