Current Issue

Underwater Technology Vol 30 No 3

Spring 2012

A Personal View

Specifying underwater man-made noise – the need for a sound approach

S Robinson

Technical Papers

Technology requirements to investigate the effects of sound on marine wildlife

IL Boyd

Abstract: There is little information about the effects of sound on marine life. In spite of this high uncertainty, several new legal limits to sound levels in the marine environment are being introduced. The present paper summarises the conclusions drawn at a workshop that took a prospective view of the technological developments necessary in order to make significant progress with reducing these uncertainties. These developments would mainly aim to further the understanding of how sound may affect some of the most vulnerable marine species. The most important methods available to examine the effects of sound will involve the development of instruments that measure the received levels of sound at the animal and its behavioural response. The availability of power to operate instruments used in remote sensing is the main factor that limits most aspects of technology capability. Alternatives need to be developed to using sparse data (from a few instruments that are attached to animals or that are widely spaced), and a coordinated approach is required between commercial suppliers and academics to overcome the current constraints, foster innovation and turn new approaches into operational tools. There is also a need to improve the technology used to attach instruments to animals, particularly in the case of small cetaceans. Improved bandwidth for data communication, recovery or retrieval is likely to develop alongside other innovations as a result of improvements in large-scale infrastructure such as satellite systems. There is scope for innovation of sensors to improve the ability to measure behavioural/physiological response variables such as heart and/or respiration rate.

 

Capturing convection in the northwest Mediterranean Sea: using underwater gliders to assess the performance of regional forecast models

BR Loveday, S Swart and D Storkey

Abstract: Ocean models require independent datasets to verify forecast accuracy. Glider data, within an appropriate reference frame, can satisfy this constraint. In the present paper, profiles from the northwest Mediterranean Sea are re-gridded to allow evaluation of modelled deepwater formation episodes. Time-series analysis of temperature, salinity, mixed-layer depth and ocean heat content show that the simulated response to surface flux is consistent with observations and the evolution of convective events is well represented. However, discrepancies in the distributions of the simulated Levantine Intermediate Water (LIW) and western Mediterranean deep water (WMDW) remain. A new ‘sweep’ methodology, developed in the present paper, indicates that the location and duration of the simulated convective events are consistent with that observed, but spatial variability is underrepresented. Variogram analysis ascribes integral scales similar to those observed for the mixed-layer depth, but suggests that simulated scalar fields are too diffuse. The ability to maximise the separation of temporal and spatial variability, inherent in this new methodology, confirms that glider data is suitable for validating high-resolution ocean models.

 

Subsea technologies selection using analytic hierarchy process

S Yasseri

Abstract: One of the primary issues in the offshore oil and gas development is the comparative evaluation of subsea production versus other alternative means. Another issue of importance is assessing the technologies to be used for each concept. The present paper concentrates on such assessments and aims to develop a method for selecting the most appropriate technologies or components for the subsea production systems. Financial viability is the main driver of the concept selection, but the most important decision variables for selection are: technology readiness, reliability and availability, constructability, maintainability, operability and costs. Technology selection requires the combination of these decision variables, as they impact both cost and benefit. The paper provides an integrated analytic framework, using the analytic hierarchy process (AHP) for technology selection that best satisfies all of a decision-maker’s requirements. A survey of all decision influencing factors is presented in the present paper, as well as a case study, a sub-set of which is used to demonstrate the selection process between two subsea trees manufactured by different suppliers. The emphasis is on the practicality and accessibility of AHP.

Technical Briefing

Subsea processing – a holistic approach to marginal field developments

N Abili, O Udofot and F Kara

Abstract: The application of full subsea processing to develop remotely located marginal fields offshore West Africa is an attractive option for breaking the techno-economic barriers which have long hindered the development of these fields. Some of the fields have remained marginal and unproduced over the years, arguably owing to incorrect estimates in recoveries and economics occasioned by erroneous estimates in basic input parameters. Therefore, the right method of application for developing marginal fields must be sought to ensure that both national and international operating companies partake in the development of these fields. The present paper explores the use of full subsea processing (FSP) technology to develop marginal fields economically.

Book Review

Arctic Security in an Age of Climate Change, edited by James Kraska

Reviewed by T Potts

Book Review

The Dance of Sea and Air: How oceans, weather and life link together, by Arnold H Taylor

Reviewed by R Rayner

 

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