September 2003

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Newsletter Home Page

Link Fellowship Awardees for 2003

Inside this Issue


The First Annual Link Fellowship Newsletter, Lee Lynd

Link Foundation 50th Anniversary Celebration, David Gouldin


Energy (2003-2005)

Simulation and Training (2003-2004)

Ocean Engineering (2003-2004)

Fellowships awarded annually since 1963.
Program Manager, George Maul, Administrator

Cristina D S Tollefsen
Department/University: Department of Physics and Physical Oceanography, Memorial University of Newfoundland
Advisor: Dr. L. Zedel
Email Address:

Title: Evaluation of a Doppler Sonar for Fisheries Applications

Fisheries managers are increasingly relying on acoustic surveys to obtain reliable biomass estimates for species of interest. In a typical acoustic survey, a sonar is mounted on a ship which follows a prescribed route, and the results are analyzed to estimate the fish population. However, the finite time required for the survey can limit the quality of the survey data.

An acoustic Doppler current profiler (ADCP) is a sonar capable of measuring position and velocity of targets. ADCPs are normally used for ocean current measurements, but with some modifications, they can provide fish swimming speed and position information. In contrast to conventional fisheries sonar systems, ADCPs are typically deployed at fixed locations for extended periods of time, which has the potential to both improve temporal coverage and reduce the costs associated with fisheries surveys.

I will investigate several questions which have arisen during preliminary measurements made with a prototype sonar system specifically designed for fisheries monitoring. Through laboratory and field trials, I will develop suitable signal processing methods and estimate limitations on accuracy. An evaluation of the tradeoffs among various sources of uncertainty will result in the proposal of a sonar system configuration optimized for fisheries applications.

Laura Lapham
Department/University: Graduate student, University of North Carolina - Chapel Hill, Department of Marine Sciences
Advisor: Dr. Christopher S. Martens
Email Address:

Title: Development of in situ probes for sampling sediment pore waters surrounding gas hydrates

Gas hydrates are ice-like solids that form in the presence of saturated methane concentrations under high pressures and low temperatures found in continental shelf sediments and permafrost. Hydrates are important to understand because of their potential roles in stabilizing continental slope sediments, providing new energy resources and controlling global climate change. The goal of this project is to determine the in situ conditions under which hydrates form and dissociate by measuring vertical and horizontal chemical gradients in gas and dissolved ion concentrations in undecompressed pore water fluids from sediments near hydrate mounds. The Gulf of Mexico exposed hydrate sites provide a natural laboratory for studying hydrate formation and decomposition. I will construct, test, and deploy two novel probe instruments in methane-rich Gulf of Mexico sediments near hydrate mounds to achieve this goal. Deployment of these two new in situ probes should provide in situ dissolved gas and salt concentration data critical for understanding the processes and environmental conditions controlling gas hydrate occurrences in Gulf of Mexico sediments.