Shear Madness: New Ways to measure Ocean Currents from a Glider

Project Rationale
How fast is the seawater flowing, what causes this, how does it vary, and can we predict it? These are the fundamental questions that much of ocean science tries to answer. Traditionally, oceanographers calculate the shear (vertical gradient in horizontal velocity) from ship-based profiles of the temperature and salinity of the water, using what is known as the geostrophic approximation. We then have to make an independent measurement of velocity at a known depth in order to reference this shear, and thus obtain the total geostrophic velocity. For a couple of decades now, we have used ship-based acoustic Doppler current profilers (ADP) to reference the shear. The new challenge is to work out how best to make measurements of currents from long-endurance profiling autonomous underwater vehicles known as gliders. Gliders measure temperature and salinity, so the geostrophic shear can be deduced. From their displacement during a dive, they also provide a dive-average current velocity, which can be used to reference the geostrophic shear. This project will address this challenge by exploring the use of a novel ADP installed in a Seaglider.

Methodology
ADPs have begun to be used on other gliders (e.g. the Spray) to determine the flow field. Through the NERC-funded Bay of Bengal Boundary Layer Experiment (BoBBLE) project, we have recently been awarded funding to purchase a Seaglider with an integrated Nortek 1 MHz ADP. Commissioning trials are scheduled for March 2017 in the Canary Islands, that will compare glider-based ADP measurements with those from more conventional platforms. The student will evaluate the sensor performance and determine the best techniques for exploiting the resulting data set. In 2012 UEA trialled a previous version of the ADP on a Seaglider in the Antarctic. Useful lessons were learnt that will benefit this project. We anticipate that the student will design and undertake a deployment with the ADP-enabled glider in 2017-2018, in conjunction with other funded projects, possibly in the Bay of Bengal.
In parallel, the student will use glider data already obtained by the UEA Glider Science group, applying the dive-average currents to reference geostrophic shear to study shelf-break currents (e.g.) off the Iberian Peninsula and in the Sea of Oman. The science questions to be addressed include quantifying the transport, its variability, and understanding the driving mechanisms.

Training:
The NEXUSS CDT provides state-of-the-art, highly experiential training in the application and development of cutting-edge Smart and Autonomous Observing Systems for the environmental sciences, alongside comprehensive personal and professional development. There will be extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial / government / policy partners. The student will be registered and hosted in the Centre for Ocean and Atmospheric Sciences (COAS) at UEA in Norwich but will spend time based at NOC in Southampton working with MARS engineers to share best practice for glider operations. Specific training will include:
- ocean glider piloting, operation, and data analysis
- oceanography, ocean dynamics, ocean physics
- principles of acoustic Doppler profilers
- principles of dive-average current calculation and optimisation
- computing and processing of large data sets
- seagoing and marine data collection skills
- engineering challenges for sensor integration and development.