Microdrifters for Ocean Currents

Surface currents in the ocean are measured well over broad scales, by satellite altimetry and sporadic ocean drifters. However, these measurement methods do not resolve smaller scale processes including submesoscale eddies, filaments, and higher time varying processes like surface wind-driven events under variable forcing. One oceanographic case where these small scale processes are likely to be critical is in shelf-edge exchange. Over the UK shelf edge, continental shelf-deep water exchange processes are important for replenishing surface nutrients to fuel biological productivity. Around Greenland, shelf waters are very fresh, due to recent ice melt from the Greenland Ice Sheet and Arctic, and the cross-shelf exchange of these freshwaters can influence or even shutdown deep convection and the overturning circulation. At the shelf, there is often a boundary current following the slope which presents a barrier to cross-shelf exchange, except under the influence of surface wind-driven processes or until the boundary current becomes unstable and sheds eddies. These processes are opaque to coarse satellite measurements, and cannot be resolved by sparsely distributed individual drifters.

Traditional ocean drifters float near the surface of the oceans, following the currents. They regularly determine their position from GPS satellites, and transmit their position and other measured quantities (temperature, conductivity) via satellite communications. These drifters are about the size of a beach-ball, weigh 20 kg, and cost > £1000/unit. To investigate time-varying smaller scale processes, 100s of drifters would be needed, representing an enormous cost. We propose the development of micro-drifters – the size of a tennis ball, < 500 g and O(£200/unit) – to enable process-based oceanographic studies requiring large numbers of drifters.

This PhD studentship would develop a micro-drifter that will follow surface currents while tracking its position, and measuring basic oceanographic properties (e.g., temperature) every few hours. The novelty of the drifter is that it will be small and compatible with aerial deployment, and low cost for deployment in large numbers.

The drifter design will involve low power circuits and components, a robust antenna, and outer protective case that is waterproof and potentially robust to sea ice. Production design will be optimized for low cost, long endurance and durability. This design may be based on a technology proven in glacial environments (Bagshaw et al., 2014), using a very low power microchip processor, but fully re-designed for deployment in oceans and using satellite-based communication (Carlson et al., 2017). These drifters will be useful for oceanographic applications (both biological and physical), but also for oil spill response or a better understanding debris trajectories at the ocean’s surface.

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 at University of Southampton, and hosted at University of Southampton /National Oceanography Centre. Specific training will include:

The student will work in collaboration with scientists, technologists and the industry partner. They will gain experience in the design of platforms for Earth observation. Training will be provided in electronics design for marine applications, materials engineering for the marine environment, and numeric data analysis for scoping out a possible real-world deployment of ocean drifters. Initial testing will be carried out off the pontoon at the National Oceanography Centre Southampton, with further tests anticipated aboard the University of Southampton vessel (R/V Callista). Additional funding will be sought to support in situ deployments of drifters in more remote locations.